Exploring the relationship between novel Coronavirus pneumonia and Parkinson’s disease

The hypothesis is that there is 0a relationship between Parkinson’s disease and coronavirus disease 2019 (COVID-19). By summarizing the pathogenesis of Parkinson’s disease and COVID-19 and the impact of COVID-19 on the central nervous system, the relationship between Parkinson’s disease and COVID-19 was analyzed, including whether Parkinson’s disease is a predisposition factor for COVID-19 and whether COVID-19 causes the occurrence of Parkinson’s disease. Discuss the impact of COVID-19 on patients with Parkinson’s disease, including symptoms and life impact. To summarize the principles, goals and methods of home rehabilitation for Parkinson’s disease patients during COVID-19. Through the analysis of this paper, it is believed that COVID-19 may cause Parkinson’s disease. Parkinson’s disease has the condition of susceptibility to COVID-19, but this conclusion is still controversial.     

Amelioration of pathologic α-synuclein-induced Parkinson’s disease by irisin

Physical activity provides clinical benefit in Parkinson’s disease (PD). Irisin is an exercise-induced polypeptide secreted by skeletal muscle that crosses the blood–brain barrier and mediates certain effects of exercise. Here, we show that irisin prevents pathologic α-synuclein (α-syn)-induced neurodegeneration in the α-syn preformed fibril (PFF) mouse model of sporadic PD. Intravenous delivery of irisin via viral vectors following the stereotaxic intrastriatal injection of α-syn PFF cause a reduction in the formation of pathologic α-syn and prevented the loss of dopamine neurons and lowering of striatal dopamine. Irisin also substantially reduced the α-syn PFF-induced motor deficits as assessed behaviorally by the pole and grip strength test. Recombinant sustained irisin treatment of primary cortical neurons attenuated α-syn PFF toxicity by reducing the formation of phosphorylated serine 129 of α-syn and neuronal cell death. Tandem mass spectrometry and biochemical analysis revealed that irisin reduced pathologic α-syn by enhancing endolysosomal degradation of pathologic α-syn. Our findings highlight the potential for therapeutic disease modification of irisin in PD.

Parkinson’s disease (PD) is a chronic neurodegenerative disorder characterized by progressive worsening of motor symptoms, including bradykinesia, resting tremor, and rigidity (1, 2). Nonmotor symptoms often precede and accompany the motor symptoms and include autonomic dysfunction and neuropsychiatric sequelae (3). The most notable loss of neurons occurs in the dopaminergic neurons of the substantia nigra pars compacta (SNpc), although neuronal loss also occurs in the locus coeruleus, dorsal raphe nucleus, the dorsal motor nucleus of the vagus, and nucleus basalis of Meynert (4). In addition to neuronal loss, there is accumulation of misfolded pathologic α-synuclein that drives the pathogenesis of PD, including the neuronal dysfunction and the ultimate of neuronal degeneration (5, 6). Current treatments for PD include the replacement of dopamine (DA) via L-DOPA, DA agonists, and other agents to treat the nonmotor symptoms. As the disease progresses, deep brain stimulation and other neurosurgical approaches can be used to treat the side effects of DA replacement therapy. Importantly, these treatments only address the symptomology, and over time there is a progressive decline in normal function. Moreover, there are no treatments that slow the progression or inhibit the underlying drivers of PD pathogenesis. As such, treatments that result in durable arrest of PD symptoms are urgently needed.Irisin is a small polypeptide that is secreted by skeletal muscle and other tissues into the blood of mice and humans (7, 8). The amino acid sequence is conserved 100% between mice and humans, suggesting a critical, conserved function. Importantly, the expression of irisin and its precursor protein FNDC5 is increased in muscle in response to many forms of exercise, both in rodents and in humans. Irisin levels increase in the blood of humans with exercise training, as determined by tandem mass spectrometry (8). In adipose cells, osteocytes, osteoclasts, and astrocytes integrin αV/β5 is the major functioning receptor for irisin (9, 10).Physical activity can prevent and ameliorate the symptoms of multiple forms of neurodegeneration, including Alzheimer’s disease (AD) and PD (11–14). Since irisin carries some of the benefits of exercise to adipose tissues, we and others have begun to study the effects of irisin in various models of neurodegeneration. In the earliest study, we showed that elevated expression of FNDC5 in the liver via the use of adenoviral vectors, and presumptive elevations of irisin in the blood, stimulated an “exercise-like” program of gene expression in the hippocampus (15). Moreover, the expression of FNDC5 with these same viral vectors rescued memory deficits in a mouse model of AD (16). Most recently, irisin itself was shown to be the active moiety regulating cognitive function in four separate mouse models. Importantly, elevation of the blood levels of the mature, cleaved irisin using adeno-associated virus (AAV) was sufficient to improve cognitive function and reduce neuroinflammation in two distinct models of AD (9). Furthermore, irisin itself crossed the blood–brain barrier (BBB), at least when the protein was produced from the liver with these AAV vectors.In the current study, we examine the effects of irisin on the pathophysiology of PD, using the α-synuclein preformed fibril (α-syn PFF) seeding model in vitro and in vivo. Pathologic α-syn is thought to spread “prion-like” in the brains of PD patients and certain other neurological disorders, where they cause neuronal death and dysfunction. We show here that irisin has powerful effects in preventing both the accumulation of pathologic α-syn and neuronal cell death in primary cell culture. Furthermore, elevation of blood irisin levels in mice normalizes the histological manifestations in the SNpc and the PD-like symptomology involving movement and grip strength induced by intrastriatal injection of α-syn PFF. Together, these data suggest the potential therapeutic value of irisin in PD and other neurodegenerative states that involve α-syn.     

Nanobodies as allosteric modulators of Parkinson’s disease–associated LRRK2

Mutations in the gene coding for leucine-rich repeat kinase 2 (LRRK2) are a leading cause of the inherited form of Parkinson’s disease (PD), while LRRK2 overactivation is also associated with the more common idiopathic form of PD. LRRK2 is a large multidomain protein, including a GTPase as well as a Ser/Thr protein kinase domain. Common, disease-causing mutations increase LRRK2 kinase activity, presenting LRRK2 as an attractive target for drug discovery. Currently, drug development has mainly focused on ATP-competitive kinase inhibitors. Here, we report the identification and characterization of a variety of nanobodies that bind to different LRRK2 domains and inhibit or activate LRRK2 in cells and in in vitro. Importantly, nanobodies were identified that inhibit LRRK2 kinase activity while binding to a site that is topographically distinct from the active site and thus act through an allosteric inhibitory mechanism that does not involve binding to the ATP pocket or even to the kinase domain. Moreover, while certain nanobodies completely inhibit the LRRK2 kinase activity, we also identified nanobodies that specifically inhibit the phosphorylation of Rab protein substrates. Finally, in contrast to current type I kinase inhibitors, the studied kinase-inhibitory nanobodies did not induce LRRK2 microtubule association. These comprehensively characterized nanobodies represent versatile tools to study the LRRK2 function and mechanism and can pave the way toward novel diagnostic and therapeutic strategies for PD.

Parkinson’s disease (PD) is a common and devastating neurodegenerative movement disorder affecting around 2% of the global population (1). The disease is characterized by degeneration of dopaminergic neurons, which leads to the typical symptoms, including resting tremor, bradykinesia, and postural instability. Although treatments to alleviate these symptoms have been available for a long time, there is still no cure. A very promising strategy that is currently being intensively pursued is the targeting of the protein leucine-rich repeat kinase 2 (LRRK2). Mutations in LRRK2 are among the most common causes of familial PD (2), while an increased LRRK2 activity has also been associated with the more frequent idiopathic form of PD (3, 4). Moreover, LRRK2 mutations and/or overexpression have also been linked to a number of chronic inflammatory conditions, including Crohn’s disease (5, 6).LRRK2 is a large multidomain protein belonging to the ROCO family (Fig. 1A) that bears a rather unique combination of two catalytic activities: GTPase activity mediated by the Roc domain and Ser/Thr protein kinase activity (7). Recently, several Rab GTPases were identified as the physiological substrates of LRRK2 kinase activity (8, 9), while LRRK2 is also known to autophosphorylate (10). Although the details of the regulatory mechanism of LRRK2 are not yet completely understood, we previously showed, using a more simple LRRK2 homolog from the bacterium Chlorobium tepidum (CtRoco), that the RocCOR supradomain undergoes a dimer–monomer cycle concomitant with GTP binding and hydrolysis (11). This is in line with findings for LRRK2 in cells, which show that the protein predominantly occurs as a monomer with low-kinase activity in the cytosol and as a dimer with high-kinase activity at the membrane (12, 13). These results point toward a complex interplay between the GTPase and kinase domains of LRRK2, regulated by large-scale, conformational changes.Open in a separate windowFig. 1.Identification of LRRK2-targeting Nbs. (A) Domain arrangement of LRRK2, with important PD mutations indicated. Two LRRK2 kinase activities relevant to this study are also indicated: phosphorylation of Rab proteins and autophosphorylation at position S1292. (B) Funnel approach used in this study to identify and characterize LRRK2-binding and modulating Nbs. The 10 Nbs that are characterized in detail are categorized into five functional groups: group1, inhibit all LRRK2 kinase activities (dark green); group 2, specifically inhibit LRRK2 Rab phosphorylation (light green); group 3, activate LRRK2 kinase (red); group 4, inhibit LRRK2 activity in cells (orange); and group 5, no effect on LRRK2 activity (black). (C) Sequences of the CDR3 regions of the 10 Nbs that were analyzed in detail. Nb36 and Nb38 belong to the same CDR3 sequence family. (D, Lower) Domain mapping of the purified Nbs using ELISA on either FL-LRRK2, the RocCOR, Roc, COR-B, or K-WD40 constructs. The Nbs that only show binding to FL-LRRK2 were additionally tested for binding on the RCKW and ARM domain constructs (SI Appendix, Fig. S3). Each ELISA signal is the average of three experiments. (Upper) The results of both of these domain-mapping experiments are schematically shown.The most prevalent PD mutations in LRRK2 are clustered within the catalytic RocCOR and kinase domains (Fig. 1A), and several PD mutations lead to a decrease in GTPase and/or an increase in kinase activity (14, 15). Most notably, autophosphorylation of serine-1292 (16) and Rab protein phosphorylation (8) are increased by pathogenic LRRK2 variants and particularly by the most common G2019S mutation. These findings support the idea that LRRK2 mutations cause PD through a gain‐of‐function mechanism, and inhibition of LRRK2 kinase activity is therefore considered to be a particularly promising strategy for the treatment of PD (17, 18). However, preclinical studies have indicated that long‐term inhibition of LRRK2 with ATP-competitive inhibitors might potentially be associated with toxic side effects, including kidney abnormalities in rodents and an accumulation of lamellar bodies in type II pneumocytes in the nonhuman primate lung (19–21). Targeting the multiple enzymatic functions and regulatory mechanisms of LRRK2 in an alternative way, using compounds that bind outside the ATP-binding pocket, could form a very attractive strategy complementing the currently explored approaches (22). One way to modulate the dynamics, regulation, and activity of proteins is via the use of nanobodies (Nbs), the small and stable single-domain fragments derived from camelid heavy chain–only antibodies (23). Accordingly, we recently reported the identification of Nbs that allosterically activate the GTPase activity of a bacterial LRRK2 homolog by interfering with the protein’s monomer–dimer cycle (24).Here, we report the identification and in vitro and in-cell characterization of a wide range of Nbs acting as modulators of human LRRK2 kinase activity. Some of these Nbs bind to sites that are topographically distinct from the active site and thus act via a completely different mode-of-action compared to the currently available, ATP-competitive kinase inhibitors.     

Cell type-specific lipid storage changes in Parkinson’s disease patient brains are recapitulated by experimental glycolipid disturbance

Neurons are dependent on proper trafficking of lipids to neighboring glia for lipid exchange and disposal of potentially lipotoxic metabolites, producing distinct lipid distribution profiles among various cell types of the central nervous system. Little is known of the cellular distribution of neutral lipids in the substantia nigra (SN) of Parkinson’s disease (PD) patients and its relationship to inflammatory signaling. This study aimed to determine human PD SN neutral lipid content and distribution in dopaminergic neurons, astrocytes, and microglia relative to age-matched healthy subject controls. The results show that while total neutral lipid content was unchanged relative to age-matched controls, the levels of whole SN triglycerides were correlated with inflammation-attenuating glycoprotein non-metastatic melanoma protein B (GPNMB) signaling in human PD SN. Histological localization of neutral lipids using a fluorescent probe (BODIPY) revealed that dopaminergic neurons and midbrain microglia significantly accumulated intracellular lipids in PD SN, while adjacent astrocytes had a reduced lipid load overall. This pattern was recapitulated by experimental in vivo inhibition of glucocerebrosidase activity in mice. Agents or therapies that restore lipid homeostasis among neurons, astrocytes, and microglia could potentially correct PD pathogenesis and disease progression.

Both neurons and glia depend on tight regulation and exchange of lipids for proper function. Typically through lipid transport mechanisms (1, 2), the continuous exchange of lipids is essential for maintaining physiological function as brain lipid content, transport, and distribution are complex and critical aspects of neuropathology. Recently, both clinical findings and experimental studies have implicated lipid storage and trafficking in the pathogenesis of Parkinson’s disease (PD) and related disorders (3, 4). Reduced function of lysosomal hydrolases that are associated with lysosomal storage disorders increases the risk for PD and results in brain pathology similar to that seen in most sporadic and genetic forms of the disease (5–11).One of the strongest genetic risk factors for PD is heterozygous loss-of-function mutations in GBA1, encoding the lysosomal hydrolase glucocerebrosidase (GCase) (12–14), a deficiency that causes systemic accumulation of its glycolipid substrate glucosylceramide (GlcCer). GCase activity is reduced with aging of both the human and murine brain (6, 15), and age is the overall greatest risk factor for developing PD (16). In contrast, the more severe loss of GCase activity in homozygous GBA1 mutant carriers causes the lysosomal storage disease Gaucher disease (GD) (17). Conduritol beta epoxide (CBE), an irreversible inhibitor of GCase, causes widespread accumulation of GlcCer and related glycosphingolipids in mice. In this model, there is marked increase of high molecular weight alpha-synuclein (aSYN) and deposition of proteinase K-resistant aSYN resembling that seen in PD (18–20). aSYN is a constituent of the classical Lewy bodies and Lewy neurites (21) found in surviving dopaminergic neurons in postmortem PD materials as a standard pathological criterion for PD (22). aSYN has a lipid-binding domain, and aSYN protein–lipid interactions are potentially perturbed in PD (reviewed in refs. 17, 23, 24). We recently demonstrated that excessive aSYN can deposit into lipid compartments, and that this process is reversible under increased lysosomal β-hexosaminidase expression (25).Several in vitro physiological studies have demonstrated that a reduction in neuronal neutral lipid storage or knockdown of fatty acid desaturases protects cultured neurons from degeneration (26–28). However, as neurons exhibit limited capacity to synthesize, metabolize, and transport lipid species under physiological conditions (29), other resident cells of the substantia nigra (SN), such as glial cells, are required to maintain lipid homeostasis in the brain. Astrocyte health and lipid exchange function—and microglial activation—are potentially central to PD pathogenesis and other age-dependent neurodegenerative diseases (30–33). Brain resident microglia can accumulate and generate lipids, which may propagate inflammatory processes through, for example, TREM2 binding of apolipoproteins (34–38). Proinflammatory cytokines present in chronic conditions are attenuated by the binding of glycoprotein nonmetastatic melanoma protein B (GPNMB) to the CD44 receptor on astrocytes (39). In GD patient serum, GPNMB level is significantly correlated with disease severity (40), and GPNMB is increased in human PD SN and following CBE-induced glycolipid accumulation in mice (41).There are surprisingly little data on lipid distribution patterns in PD-affected cell types given the relevance of lipid homeostasis, aSYN–lipid interactions, and lipidopathy-associated inflammatory signatures as they relate to PD (17, 41). In this study, we measured the differences in total lipid content and cellular distribution between PD and healthy subject (HS) SN and compared them with a lipid-associated neuroinflammatory signal, GPNMB. To quantify cell type-specific intracellular lipid content, colocalization analysis was performed on human postmortem SN sections that were costained for neutral lipids and markers of dopaminergic neurons, astrocytes, and microglia. Compared with HS SN, the lipid content of PD dopaminergic neurons and microglia was significantly higher, and that of astrocytes was significantly lower. To understand a possible mechanistic reason for this lipid distribution pattern, we used an in vivo mouse model of glycolipid dysregulation and attendant aSYN accumulation through GCase inhibition by CBE. This in vivo model recapitulated the lipid distribution pattern that we observed in human PD SN. Based on these data, we propose that PD is characterized by a unique neutral lipid distribution signature in neurons, astrocytes, and microglia that can be recapitulated experimentally by glycolipid dysregulation.     

Therapeutic functions of astrocytes to treat α-synuclein pathology in Parkinson’s disease

Intraneuronal inclusions of misfolded α-synuclein (α-syn) and prion-like spread of the pathologic α-syn contribute to progressive neuronal death in Parkinson’s disease (PD). Despite the pathologic significance, no efficient therapeutic intervention targeting α-synucleinopathy has been developed. In this study, we provide evidence that astrocytes, especially those cultured from the ventral midbrain (VM), show therapeutic potential to alleviate α-syn pathology in multiple in vitro and in vivo α-synucleinopathic models. Regulation of neuronal α-syn proteostasis underlies the therapeutic function of astrocytes. Specifically, VM-derived astrocytes inhibited neuronal α-syn aggregation and transmission in a paracrine manner by correcting not only intraneuronal oxidative and mitochondrial stresses but also extracellular inflammatory environments, in which α-syn proteins are prone to pathologic misfolding. The astrocyte-derived paracrine factors also promoted disassembly of extracellular α-syn aggregates. In addition to the aggregated form of α-syn, VM astrocytes reduced total α-syn protein loads both by actively scavenging extracellular α-syn fibrils and by a paracrine stimulation of neuronal autophagic clearance of α-syn. Transplantation of VM astrocytes into the midbrain of PD model mice alleviated α-syn pathology and protected the midbrain dopamine neurons from neurodegeneration. We further showed that cografting of VM astrocytes could be exploited in stem cell–based therapy for PD, in which host-to-graft transmission of α-syn pathology remains a critical concern for long-term cell therapeutic effects.

Parkinson’s disease (PD) is a prevalent neurodegenerative disorder with movement symptoms characterized by progressive loss of dopaminergic (DA) neurons in the substantia nigra (SN) pars compacta of the midbrain with the concomitant loss of nigrostriatal DA neurotransmission. A pathologic hallmark of PD is intraneuronal inclusion of α-synuclein (α-syn) aggregates, called Lewy bodies and Lewy neurites. The α-syn aggregates cause various cellular dysfunctions including mitochondrial impairment, defective endoplasmic reticulum (ER) function, autolysosomal pathways, and synaptic and nuclear dysfunctions (1, 2). Aggregated α-syn is released from neuronal cells and acts as a ligand for patterned recognition receptors, which activate inflammatory responses in glial cells (3, 4). Furthermore, the pathologic protein aggregates undergo neuron-to-neuron transmission in a prion-like fashion (reviewed in ref. 5). The α-syn propagation and neuroinflammation are closely related to disease progression and clinical severity (6).Given its pathologic significance, the α-syn proteinopathy is a major research focus to develop disease-modifying therapies for PD and other synucleinopathic disorders such as Lewy body dementia, multiple system atrophy, and certain forms of Alzheimer’s disease. However, no therapeutic intervention to effectively eliminate the pathologic α-syn has been developed to date. In addition to the diseased conditions, the aggregated species of α-syn are also accumulated in the midbrain SN during normal aging, but not in young brain tissues (7), suggesting the existence of homeostatic regulation to prevent and resolve α-syn aggregation in young and healthy brains. This suggests homeostatic functions may be useful in developing therapeutic tools. In this regard, astrocytes are a prime cell type to be studied for therapeutic applications, as this glia cell type has multiple functions related to maintaining brain homeostasis, including those for correct functioning of neurons and protecting neuronal cells from pathologic insults (reviewed in ref. 8). Recent studies have shown the capacity of astrocytes to efficiently take up and degrade α-syn (9–12). Due to the astrocyte scavenging effect, α-syn inclusions are usually not detected in astrocytes of PD patients except in advanced stages of the disease (13–18). In addition, in contrast to efficient transmission of neuronal α-syn proteins into astrocytes, α-syn transfer from astrocytes to neuronal cells is inefficient (11), collectively suggesting a role for astrocytes in scavenging α-syn rather than in spreading it. The role of homeostatic astrocytes in α-syn pathology, however, remains to be unraveled.In this study, we showed that astrocytes, especially those cultured from the ventral midbrain (VM), the brain region primarily affected in PD, substantially alleviate neuronal α-syn pathology by regulating a series of the proteostasis procedures associated with formation, transmission, disaggregation, and clearance of toxic α-syn aggregates. Upon transplantation, VM-type astrocytes efficiently eliminated pathologic α-syn accumulation and α-syn–induced DA neuron degeneration in the midbrain of PD model mice. We further show that host-to-graft propagation of toxic α-syn, reported as a critical concern in the cell-based therapeutic approach for PD (19, 20), was greatly prevented by cografting the cultured astrocytes. Based on these findings, the therapeutic actions of astrocytes are proposed for use in relieving α-syn–mediated neuronal toxicity and in setting up a desirable cell-based therapy free from host-to-graft α-syn propagation in PD.     

PI3K polymorphism in patients with sporadic Parkinson’s disease

Parkinson’s disease (PD) is a common irreversible neurodegenerative disease associated with cognitive impairment. To investigate the serum level of phosphatidylinositol-3-kinase (PI3K) and the distribution of the genotypes and alleles of 3 PI3K single-nucleotide polymorphisms (RS37,30,087, RS37,30,088, and RS37,30,089) in PD patients with different clinical characteristics. A total of 54 PD patients and 50 healthy individuals were recruited. The serum PI3K level was measured using the enzyme-linked immunosorbent assay. The severity of PD was assessed using the modified Hoehn-Yahr scale. The cognitive function of PD patients was evaluated using the Mini-Mental State Examination scale and the Montreal Cognitive Assessment. The distribution of the alleles and genotypes of PI3K single-nucleotide polymorphisms (SNPs) was calculated using the Hardy-Weinberg equilibrium. PD patients showed a significantly higher serum level of PI3K compared to healthy individuals. Increased serum PI3K level was observed in PD patients with more severe disease, longer disease duration, and impaired cognitive function. Additionally, no significant differences were observed in the distributions of the genotypes and alleles of 3 PI3K SNPs between PD patients with normal cognitive function and those with cognitive impairment. PD patients with different levels of disease severity, disease duration, and cognitive function had significantly different serum levels of PI3K. However, the PI3K SNPs in patients with normal cognitive function were not significantly different from those in patients with cognitive impairment. These findings contribute to a better understanding of the roles of PI3K and SNPs of the PI3K gene in PD.     

A deep eutectic-based,self-emulsifying subcutaneous depot system for apomorphine therapy in Parkinson’s disease

Apomorphine, a dopamine agonist, is a highly effective therapeutic to prevent intermittent off episodes in advanced Parkinson’s disease. However, its short systemic half-life necessitates three injections per day. Such a frequent dosing regimen imposes a significant compliance challenge, especially given the nature of the disease. Here, we report a deep eutectic-based formulation that slows the release of apomorphine after subcutaneous injection and extends its pharmacokinetics to convert the current three-injections-a-day therapy into an every-other-day therapy. The formulation comprises a homogeneous mixture of a deep eutectic solvent choline-geranate, a cosolvent n-methyl-pyrrolidone, a stabilizer polyethylene glycol, and water, which spontaneously emulsifies into a microemulsion upon injection in the subcutaneous space, thereby entrapping apomorphine and significantly slowing its release. Ex vivo studies with gels and rat skin demonstrate this self-emulsification process as the mechanism of action for sustained release. In vivo pharmacokinetics studies in rats and pigs further confirmed the extended release and improvement over the clinical comparator Apokyn. In vivo pharmacokinetics, supported by a pharmacokinetic simulation, demonstrate that the deep eutectic formulation reported here allows the maintenance of the therapeutic drug concentration in plasma in humans with a dosing regimen of approximately three injections per week compared to the current clinical practice of three injections per day.

Parkinson’s disease (PD), the second most common neurodegenerative disease, is characterized by dopamine deficiency arising from the progressive loss of dopaminergic neurons in the pars compacta of the substantia nigra. Multiple motor as well as nonmotor symptoms, such as rigidity, tremor, bradykinesia, and cognitive dysfunction, are associated with PD (1). While a number of disease-modifying therapies to treat PD are currently in clinical trials (2, 3), the approved therapies comprise only those that treat the symptoms. Among them, apomorphine (APO) is a leading drug given to patients to alleviate short intermittent periods of motor complications like dyskinesia, which often develop in advanced PD after long-term prior treatment with oral levodopa (4). APO has poor oral bioavailability and high first pass metabolism, thus leaving subcutaneous injections as the only viable administration mode (Apokyn). However, the short half-life (69.7 ± 25.8 min) of APO in the systemic circulation necessitates frequent injections of Apokyn, namely, three times a day, at the onset of individual off episodes (5). This poses a significant challenge with patient compliance in terms of pain, infection, emetic side effects, inaccurate dosing, lack of manual dexterity, or even inability to self-inject (6–9).Two notable strategies have been evaluated in clinical trials to mitigate the shortcomings of frequent subcutaneous APO injections. Kynmobi, a Food and Drug Administration (FDA)-approved sublingual film containing APO, allows rapid absorption of the drug via buccal administration (10, 11). It consists of two layers, as follows: one labeled as a buffer layer that neutralizes acid generation following drug absorption and another as an active layer that contains APO to allow rapid drug diffusion and absorption. However, it lacks a mechanism for sustained release and thus still requires repeated on-demand administration and induces fluctuations in blood concentrations. The continuous subcutaneous infusion of APO has also been explored as an alternative. The subcutaneous pump continuously injects Apokyn from a prefilled syringe and aims to maintain therapeutic concentrations of APO in systemic circulation and has shown a shortened duration of total daily off episodes in clinical trials. However, this approach is hindered by the complexity of use and local site reactions (12–14). Furthermore, this product recently received Refusal to File from the FDA. Many other preclinical and clinical formulations of APO have attempted to achieve noninvasive administration and prolonged pharmacokinetics (15, 16), for example, prodrug modification for oral delivery (17) or encapsulation in microemulsion for transdermal delivery (18); however, the utility of these approaches is limited by low bioavailability compared to subcutaneous injections. Thus, the development of a safe and simple sustained release formulation of APO remains an unmet clinical need.From a scientific perspective, APO represents one of the most challenging drugs to formulate; it has limited water solubility, is highly susceptible to oxidation, exhibits short plasma half-life (5, 19), and has a tight therapeutic window with a minimum effective concentration (MEC) of 4 ng/mL and a maximum tolerated concentration (MTC) of 10 ng/mL in humans. The use of a large number of sustained release technologies, including microspheres (20, 21), depots (11), liposomes (22), and polymeric as well as solid lipid nanoparticles (23, 24) among others, has been attempted with APO. However, the multiple physicochemical, biological, and clinical constraints have posed a hurdle in delivering APO in a safe and sufficiently sustained manner. Consequently, no long-acting formulation of APO is currently available.Here, we report a strategy for achieving an extended release of APO based simultaneously on the differential miscibility of a deep eutectic solvent, namely, choline and geranic acid (CAGE_1:2) in two solvents, water and n-methyl pyrrolidone (NMP), as well as the differential solubility of APO in each of these three solvents. We designed the formulation to be a homogenous, stable solution of APO in a three-component system (CAGE_1:2/NMP/water). However, upon subcutaneous injection, NMP rapidly diffuses away, and the formulation self-emulsifies into a dispersion of CAGE_1:2 in water while trapping APO in it, thereby achieving sustained release (Fig. 1). This design increased the timescale of APO pharmacokinetics, converting the current clinical standard of three-times-a-day formulation into an every-other-day formulation. While achieving this goal, we satisfied three essential constraints including the following: increased solubility of APO from 10 mg/mL in Apokyn to 30 mg/mL to support long-lasting delivery from a single dose; stability of APO against oxidation; and the use of all components, other than CAGE_1:2, at concentrations already listed in other FDA-approved subcutaneous products, thus facilitating the potential for translation of this strategy. We refer to this formulation as self-emulsifying, APO-releasing therapeutic (SEAPORT). We report the design strategy, ex vivo assessment, in vivo pharmacokinetics in rats, safety in rats, and in vivo pharmacokinetics in pigs.Open in a separate windowFig. 1.Schematic diagram of SEAPORT principle. APO, PEG3350, and SMB are solubilized in a CAGE_1:2/NMP/water (10:42.7:47.3% vol/vol) mixture in SEAPORT, and then upon subcutaneous injection, water-miscible NMP diffuses away quickly and the remaining CAGE_1:2 emulsifies with APO to form a depot, allowing the sustained release of the drug.     

Cascading from SARS-CoV-2 to Parkinson’s Disease through Protein-Protein Interactions

Extensive extrapulmonary damages in a dozen of organs/systems, including the central nervous system (CNS), are reported in patients of the coronavirus disease 2019 (COVID-19). Three cases of Parkinson’s disease (PD) have been reported as a direct consequence of COVID-19. In spite of the scarce data for establishing a definitive link between COVID-19 and PD, some hypotheses have been proposed to explain the cases reported. They, however, do not fit well with the clinical findings reported for COVID-19 patients, in general, and for the PD cases reported, in particular. Given the importance of this potential connection, we present here a molecular-level mechanistic hypothesis that explains well these findings and will serve to explore the potential CNS damage in COVID-19 patients. The model explaining the cascade effects from COVID-19 to CNS is developed by using bioinformatic tools. It includes the post-translational modification of host proteins in the lungs by viral proteins, the transport of modified host proteins via exosomes out the lungs, and the disruption of protein-protein interaction in the CNS by these modified host proteins. Our hypothesis is supported by finding 44 proteins significantly expressed in the CNS which are associated with PD and whose interactions can be perturbed by 24 host proteins significantly expressed in the lungs. These 24 perturbators are found to interact with viral proteins and to form part of the cargoes of exosomes in human tissues. The joint set of perturbators and PD-vulnerable proteins form a tightly connected network with significantly more connections than expected by selecting a random cluster of proteins of similar size from the human proteome. The molecular-level mechanistic hypothesis presented here provides several routes for the cascading of effects from the lungs of COVID-19 patients to PD. In particular, the disruption of autophagy/ubiquitination processes appears as an important mechanism that triggers the generation of large amounts of exosomes containing perturbators in their cargo, which would insult several PD-vulnerable proteins, potentially triggering Parkinsonism in COVID-19 patients.     

Systematic review of the application of virtual reality to improve balance,gait and motor function in patients with Parkinson’s disease

Background:Virtual reality (VR) is an advanced technique used in physical rehabilitation of neurological disorders, however the effects of VR on balance, gait, and motor function in people with Parkinson’s (PD) are still debated. Therefore, the systematic review aimed to determine the role of VR on motor function, balance and gait in PD patients.Methods:A comprehensive search to identify similar randomised controlled trials was conducted targeting 5 databases including Web of Science, PubMed, CINHAL, Cochrane Library, and Physiotherapy Evidence Database. A total of 25 studies were found eligible for this systematic review, and the methodological assessment of the quality rating of the studies was accomplished using the physiotherapy evidence database scale by 2 authors.Results:Out of the 25 included studies, 14 studies reported on balance as the primary outcome, 9 studies were conducted to assess motor function, and 12 assessed gait as the primary outcome. Most studies used the Unified Parkinson disease rating scale UPDRS (part-III) for evaluating motor function and the Berg Balance Scale as primary outcome measure for assessing balance. A total of 24 trials were conducted in clinical settings, and only 1 study was home-based VR trainings. Out of 9 studies on motor function, 6 reported equal improvement of motor function as compared to other groups. In addition, VR groups also revealed superior results in improving static balance among patient with PD.Conclusion:This systemic review found that the use of VR resulted in substantial improvements in balance, gait, and motor skills in patients with PD when compared to traditional physical therapy exercises or in combination with treatments other than physical therapy. Moreover, VR can be used as a supportive method for physical rehabilitation in patients of PD. However, the majority of published studies were of fair and good quality, suggesting a demand for high quality research in this area.     

Establishing a rabbit model of perianal fistulizing Crohn’s disease

BACKGROUNDCrohn''s disease (CD) is a chronic nonspecific intestinal inflammatory disease. The aetiology and pathogenesis of CD are still unclear. Anal fistula is the main complication of CD and is a difficult problem to solve at present. The main limitation of developing new therapies is bound up with the short of preclinical security and effectiveness data. Therefore, an ideal animal model is needed to establish persistent anal fistula and an inflamed rectal mucosa.AIMTo improve the induction method of colitis and establish a reliable and reproducible perianal fistulizing Crohn’s disease animal model to evaluate new treatment strategies.METHODSTwenty male New Zealand rabbits underwent rectal enema with different doses of 2,4,6-trinitrobenzene sulfonic acid to induce proctitis. Group A was treated with an improved equal interval small dose increasing method. The dosage of group B was constant. Seven days later, the rabbits underwent surgical creation of a transsphincteric fistula. Then, three rabbits were randomly selected from each group every 7 d to remove the seton from the fistula. The rabbits were examined by endoscopy every 7 days, and biopsy forceps were used to obtain tissue samples from the obvious colon lesions for histological analysis. The disease activity index (DAI), colonoscopy and histological scores were recorded. Perianal endoscopic ultrasonography (EUS) was used to evaluate the healing of fistulas.RESULTSExcept for the DAI score, the colonoscopy and histological scores in group A were significantly higher than those in group B (P < 0.05). In the ideal model rabbit group, on the 7^th day after the removal of the seton, all animals had persistent lumens on EUS imaging, showing continuous full-thickness high signals. Histological inspection of the fistula showed acute and chronic inflammation, fibrosis, epithelialization and peripheral proctitis of the adjoining rectum.CONCLUSIONThe improved method of CD colitis induction successfully established a rabbit perianal fistula CD preclinical model, which was confirmed by endoscopy and pathology.     

The NLRP3 inflammasome inhibitor OLT1177 rescues cognitive impairment in a mouse model of Alzheimer’s disease

Numerous studies demonstrate that neuroinflammation is a key player in the progression of Alzheimer’s disease (AD). Interleukin (IL)-1β is a main inducer of inflammation and therefore a prime target for therapeutic options. The inactive IL-1β precursor requires processing by the the nucleotide-binding oligomerization domain-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome into a mature and active form. Studies have shown that IL-1β is up-regulated in brains of patients with AD, and that genetic inactivation of the NLRP3 inflammasome improves behavioral tests and synaptic plasticity phenotypes in a murine model of the disease. In the present study, we analyzed the effect of pharmacological inhibition of the NLRP3 inflammasome using dapansutrile (OLT1177), an oral NLRP3-specific inhibitor that is safe in humans. Six-month-old WT and APP/PS1 mice were fed with standard mouse chow or OLT1177-enriched chow for 3 mo. The Morris water maze test revealed an impaired learning and memory ability of 9-mo-old APP/PS1 mice (P = 0.001), which was completely rescued by OLT1177 fed to mice (P = 0.008 to untreated APP/PS1). Furthermore, our findings revealed that 3 mo of OLT1177 diet can rescue synaptic plasticity in this mouse model of AD (P = 0.007 to untreated APP/PS1). In addition, microglia were less activated (P = 0.07) and the number of plaques was reduced in the cortex (P = 0.03) following NLRP3 inhibition with OLT1177 administration. We also observed an OLT1177 dose-dependent normalization of plasma metabolic markers of AD to those of WT mice. This study suggests the therapeutic potential of treating neuroinflammation with an oral inhibitor of the NLRP3 inflammasome.

Alzheimer’s disease (AD) and other related neurodegenerative diseases leading to dementia represent an enormous burden for the society and health economies. AD patients suffer progressive cognitive and functional deficits often for many years, which result in a heavy burden to patients, families, and the public health system. In fact, in 2015 an estimated 46.8 million people worldwide were living with dementia, which could extend to 131.5 million by 2050 (1). Rising prevalence and mortality rates in combination with a lack of effective treatments lead to enormous costs to society. Research on AD in the last decades has focused on the pathological hallmarks and cellular deposits of amyloid-β (Aβ) peptides and neurofibrils (2). Recently, there has been increased evidence supporting a central role of the immune system in the progression or even the origin of the disease (3–5). In this respect, it is noteworthy that it has been known since 1989 that levels of interleukin (IL)-1β, one of the main mediators of innate immune response, are elevated in brains of patients with AD and can be associated with the progression and onset of AD (6–11). Additionally, it was shown that the nucleotide-binding oligomerization domain-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome (12, 13), a multisubunit complex important for the maturation of IL-1β, is activated by Aβ peptides, leading to an overproduction of IL-1β, neuroinflammation, and cognitive impairment (14, 15). Inhibition of the NLRP3 inflammasome and the subsequent reduced IL-1β production can be linked to a change in the phenotype of microglia, the innate immune cells in the brain. Heneka et al. (16) pointed out the important role of the NLRP3 inflammasome/caspase-1 axis in AD pathogenesis by demonstrating significant improvements (e.g., in cognition) in APP/PS1 mice (a mouse model for AD) when crossed with NLRP3^−/− animals. The APP/PS1 mice express a human amyloid precursor protein (APP) and human presenilin-1 (PS1), leading to the accumulation of Aβ peptides, neuroinflammation, and cognitive impairment (17).OLT1177 (rINN: dapansutrile) is a new chemical entity small molecule that specifically targets the NLRP3 inflammasome and prevents the activation of caspase-1 and the maturation and release of IL-1β (18). OLT1177 has been shown to be well tolerated in animals and humans (18) and is currently in phase 2 clinical studies for the treatment of inflammatory conditions, such as osteoarthritis (topical gel dosage form) and inflammatory diseases, such as acute gout flare (oral capsule dosage form), among other diseases (19).In this study, we used the APP/PS1 mouse model of AD to investigate the effects of OLT1177 as an acute, oral pharmacological intervention (17). Six-month-old WT and APP/PS1ΔE9 mice consumed ad libitum OLT1177 in feed pellets (∼0, 500, or 1,000 mg/kg/d based on feed concentrations of 0, 3.75 or 7.5 g of OLT1177 per kilogram of feed; hereafter referred to as 3.75 or 7.5 g/kg OLT1177) for the treatment duration of 3 mo. APP/PS1 mice treated with OLT1177 showed rescue effects in various assessments, ranging from improved cognitive function to overall reduction in proinflammatory cytokines in the brain, suggesting the potential benefits of pharmaceutically blocking NLRP3 signaling in AD.     

The Parkinson’s disease-associated gene ITPKB protects against α-synuclein aggregation by regulating ER-to-mitochondria calcium release

Inositol-1,4,5-triphosphate (IP₃) kinase B (ITPKB) is a ubiquitously expressed lipid kinase that inactivates IP₃, a secondary messenger that stimulates calcium release from the endoplasmic reticulum (ER). Genome-wide association studies have identified common variants in the ITPKB gene locus associated with reduced risk of sporadic Parkinson’s disease (PD). Here, we investigate whether ITPKB activity or expression level impacts PD phenotypes in cellular and animal models. In primary neurons, knockdown or pharmacological inhibition of ITPKB increased levels of phosphorylated, insoluble α-synuclein pathology following treatment with α-synuclein preformed fibrils (PFFs). Conversely, ITPKB overexpression reduced PFF-induced α-synuclein aggregation. We also demonstrate that ITPKB inhibition or knockdown increases intracellular calcium levels in neurons, leading to an accumulation of calcium in mitochondria that increases respiration and inhibits the initiation of autophagy, suggesting that ITPKB regulates α-synuclein pathology by inhibiting ER-to-mitochondria calcium transport. Furthermore, the effects of ITPKB on mitochondrial calcium and respiration were prevented by pretreatment with pharmacological inhibitors of the mitochondrial calcium uniporter complex, which was also sufficient to reduce α-synuclein pathology in PFF-treated neurons. Taken together, these results identify ITPKB as a negative regulator of α-synuclein aggregation and highlight modulation of ER-to-mitochondria calcium flux as a therapeutic strategy for the treatment of sporadic PD.

Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterized by a variety of motor symptoms (including unbalanced gait, resting tremor, and bradykinesia) that are accompanied by psychosis and dementia at later stages of disease. The onset of motor symptoms is largely caused by the selective loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and the corresponding depletion of dopamine innervation in the striatum. Although the cause of neuron loss is unknown, the hallmark pathological feature of PD is the presence of intraneuronal inclusions composed of misfolded and fibrillar α-synuclein (α-syn) in the neurites and soma, termed Lewy neurites and Lewy bodies, respectively (1). Protein-coding single-nucleotide polymorphisms (SNPs), duplications, and triplications in the gene encoding α-syn (SNCA) all cause early-onset, familial forms of PD and result in accelerated aggregation of α-syn protein into insoluble, fibrillar aggregates (1, 2). Recent evidence suggests that these aggregates can spread from cell to cell, leading to the propagation of pathology to neuroanatomically connected brain regions (3, 4). Therefore, therapeutic approaches that reduce the aggregation or spreading of pathological α-syn species represent potential disease-modifying therapies for PD.In addition to SNCA, mutations in several other genes have been identified that cause rare, familial forms of PD. These genes are primarily involved in the autophagic clearance of intracellular aggregates or damaged organelles, especially mitochondria (5–8). Genome-wide association studies (GWAS) have also identified common SNPs in several genes related to endolysosomal function, such as GBA and LRRK2, that are associated with increased risk of PD (8–11). GBA and LRRK2 mutations have been shown to affect lysosomal and mitochondrial phenotypes (12–14), which contribute to the accumulation of PD-like neuropathology in mouse models, primary neurons, and human iPSC-derived cells (15–18). These findings highlight the role of the lysosomal and mitochondria quality control pathways in PD and demonstrate that perturbations in these pathways are sufficient to increase α-syn aggregation. Despite this, the etiology of sporadic PD is not fully understood, and the specific genes and pathways that are tractable for therapeutic modulation remain elusive. Therefore, the discovery of new genes associated with sporadic PD may be critical for both understanding disease pathogenesis and identifying novel therapeutic approaches.Recently, Chang et al. conducted a GWAS analysis that identified 17 novel gene loci significantly associated with sporadic PD in a European population including more than 26,000 patients across three independent cohorts (19). The lead GWAS SNP in the novel 1q42 locus was rs4653767. This is an intronic SNP in the gene encoding inositol-1,4,5-triphosphate kinase B (ITPKB) and produces a thymine-to-cytosine nucleotide substitution that is protective against developing PD (odds ratio [OR] = 0.92, P = 2.4 × 10⁻¹⁰). A follow up meta-analysis study of 37,688 PD patients, which included the discovery cohort, and 18,618 proxy cases strengthened the GWAS finding at this locus (OR = 0.92, P = 1.4 × 10⁻¹⁵). Furthermore, this locus was still significant when the analysis was performed on only the new independent cases and proxy cases (OR = 0.92, P = 2.8 × 10⁻⁵) (20). The rs4653767-C allele is present in similar frequencies across populations (27% in non-Finnish European and 29% in East Asian populations) and was found to have the same direction of effect (OR = 0.87, P = 0.016) in a targeted replication study of the European PD loci in an East Asian cohort (21). ITPKB is also highly expressed in several brain regions related to PD, including the SNpc, striatum, and cerebral cortex (22).ITPKB is one of three ubiquitously expressed kinases known to phosphorylate inositol-1,4,5-triphosphate (IP₃), an intracellular messenger produced from phosphatidylinositol-4,5-bisphosphate by phospholipase C (23, 24). IP₃ binds to IP₃ receptors (IP₃Rs) in the endoplasmic reticulum (ER) to stimulate the release of calcium ions from the ER into the cytosol to mediate various downstream signaling pathways. IP₃ kinases (ITPKA, ITPKB, and ITPKC) add a fourth phosphate group to IP₃ producing inositol-1,3,4,5-tetrakisphosphate (IP₄), which has no activity on IP₃Rs. Thus, IP₃ kinases negatively regulate IP₃-mediated calcium release from the ER. While the role of this pathway in peripheral cell types under normal physiological conditions is well understood (25, 26), whether ITPKB is involved in the pathogenesis of PD is unknown. Here, we investigate whether the modulation of ITPKB expression or kinase activity impacts the accumulation of α-syn pathology in cellular models of PD.     

A TNF receptor 2 agonist ameliorates neuropathology and improves cognition in an Alzheimer’s disease mouse model

Tumor necrosis factor-α (TNF-α) is a pleiotropic, proinflammatory cytokine related to different neurodegenerative diseases, including Alzheimer’s disease (AD). Although the linkage between increased TNF-α levels and AD is widely recognized, TNF-α–neutralizing therapies have failed to treat AD. Previous research has associated this with the antithetic functions of the two TNF receptors, TNF receptor 1, associated with inflammation and apoptosis, and TNF receptor 2 (TNFR2), associated with neuroprotection. In our study, we investigated the effects of specifically stimulating TNFR2 with a TNFR2 agonist (NewStar2) in a transgenic Aβ-overexpressing mouse model of AD by administering NewStar2 in two different ways: centrally, via implantation of osmotic pumps, or systemically by intraperitoneal injections. We found that both centrally and systemically administered NewStar2 resulted in a drastic reduction in amyloid β deposition and β-secretase 1 expression levels. Moreover, activation of TNFR2 increased microglial and astrocytic activation and promoted the uptake and degradation of Aβ. Finally, cognitive functions were also improved after NewStar2 treatment. Our results demonstrate that activation of TNFR2 mitigates Aβ-induced cognitive deficits and neuropathology in an AD mouse model and indicates that TNFR2 stimulation might be a potential treatment for AD.

Tumor necrosis factor-α (TNF-α) is a master proinflammatory cytokine involved in the regulation of innate and adaptive immunity (1). TNF-α plays a crucial role in various autoimmune and neurological disorders, including Alzheimer’s disease (AD) (2, 3). TNF-α–neutralizing therapeutics have been approved for the treatment of different inflammatory and autoimmune diseases, like rheumatoid arthritis or plaque psoriasis (4). However, the treatment of neurological disorders with TNF-α–neutralizing drugs led to inconclusive or even detrimental results (5–8). The latter could be explained, at least partly, by the different functions of the two receptors of TNF: on the one hand, stimulation of cytotoxic and strongly inflammatory pathways by TNF receptor 1 (TNFR1) in response to soluble TNF (sTNF) or membrane TNF (mTNF) or, on the other hand, activation of TNF receptor 2 (TNFR2) by mTNF eliciting pro- and antiinflammatory effects but also neuroprotective functions and tissue regeneration (9, 10).As a consequence, several studies aimed at selective targeting of TNFR1 or TNFR2, instead of completely inhibiting TNF-α. First, targeting TNFR1 by using specific TNFR1 antagonists or sTNF inhibitors resulted in amelioration of inflammation and apoptosis in various in vivo neurodegenerative disease models, such as models of multiple sclerosis (11, 12), Parkinson’s disease (13), and AD (14, 15). Second, targeting TNFR2 by specific TNFR2 agonists exerted an enhancement in neuroregeneration and tissue homeostasis in vitro (16) as well as in in vivo models (17). Therefore, specific targeting of TNFR1 and/or TNFR2 offers a promising new therapeutic avenue.However, clinical and preclinical studies on the effect of specific therapeutic targeting of TNFR2 in AD are lacking. It is acknowledged that during AD, the deposition of Aβ plaques, one of the main hallmarks of AD pathogenesis, occurs as a consequence of an imbalance between Aβ production and clearance (18). The β-secretase 1 (BACE-1) is mainly responsible for the production of toxic Aβ peptides, whereas uptake and degradation of these peptides are achieved by glial cells in the central nervous system (CNS), such as microglia and astrocytes (19, 20). Microglia are the resident macrophages of the CNS and their function is to constantly survey their environment and react to any detected insult, such as tissue damage or pathogen infection (21). Microglia are also involved in tissue repair and maintaining brain homeostasis. Moreover, microglia have been found to be essential for Aβ clearance in AD mouse models (20). It has been reported that in the context of AD, BACE-1 expression is increased, and the presence of Aβ plaques impairs the phagocytic activity of microglia (22, 23). These events could lead to an overproduction of Aβ accompanied by reduced Aβ clearance, which may partly lead to the observed pathogenesis of AD.Previous studies have proven that TNFR2 activation is neuroprotective in different disease models; however, it remains to be established whether TNFR2 stimulation has a protective effect against Aβ-mediated neuropathology and amyloid deposition and if this could improve cognitive functions. Therefore, in this study, we tested the hypothesis that selective stimulation of TNFR2 is able to abrogate Aβ-associated neuropathology and cognitive impairments.     

NAD+ supplementation reduces neuroinflammation and cell senescence in a transgenic mouse model of Alzheimer’s disease via cGAS–STING

Alzheimer''s disease (AD) is a progressive and fatal neurodegenerative disorder. Impaired neuronal bioenergetics and neuroinflammation are thought to play key roles in the progression of AD, but their interplay is not clear. Nicotinamide adenine dinucleotide (NAD⁺) is an important metabolite in all human cells in which it is pivotal for multiple processes including DNA repair and mitophagy, both of which are impaired in AD neurons. Here, we report that levels of NAD⁺ are reduced and markers of inflammation increased in the brains of APP/PS1 mutant transgenic mice with beta-amyloid pathology. Treatment of APP/PS1 mutant mice with the NAD⁺ precursor nicotinamide riboside (NR) for 5 mo increased brain NAD⁺ levels, reduced expression of proinflammatory cytokines, and decreased activation of microglia and astrocytes. NR treatment also reduced NLRP3 inflammasome expression, DNA damage, apoptosis, and cellular senescence in the AD mouse brains. Activation of cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING) are associated with DNA damage and senescence. cGAS–STING elevation was observed in the AD mice and normalized by NR treatment. Cell culture experiments using microglia suggested that the beneficial effects of NR are, in part, through a cGAS–STING-dependent pathway. Levels of ectopic (cytoplasmic) DNA were increased in APP/PS1 mutant mice and human AD fibroblasts and down-regulated by NR. NR treatment induced mitophagy and improved cognitive and synaptic functions in APP/PS1 mutant mice. Our findings suggest a role for NAD⁺ depletion-mediated activation of cGAS–STING in neuroinflammation and cellular senescence in AD.

Alzheimer’s disease (AD) is the most feared neurodegenerative disease and is characterized by progressive cognitive impairment associated with extensive accumulation of amyloid β-peptide (Aβ) plaques and tau neurofibrillary tangles in vulnerable brain regions (1, 2). There are no available treatments. Neuroinflammation, mitochondrial dysfunction, and cellular senescence have been recognized as key drivers of AD (3–6). Microglia are the primary innate immune cells in the brain. Although accumulating evidence challenges the simplified M1-M2 phenotypes of microglia, the classification is still widely in use as microglia can be protective (M2) and detrimental (M1) under different circumstances (7, 8). The detrimental microglia are activated by Aβ and produce interleukin (IL)-1β, TNF-α, and other proinflammatory molecules. The protective microglia secrete the anti-inflammatory cytokines IL-4 and IL-10 (8).The inflammatory response is one of the hallmarks of cellular senescence (9). The senescence-associated secretory phenotype (SASP) includes cessation of cell division and the production of proinflammatory cytokines (10). The SASP is highly correlated with neuroinflammation and has been documented in the brains of AD mouse models (11). During normal aging, the number of senescent cells in tissues increases significantly (10), and evidence suggests that microglia, astrocytes, and oligodendrocyte progenitor cells can become senescent in AD (5, 11, 12). Moreover, senolytic treatments can preserve cognitive function in AD mice (11). However, the mechanisms that result in neuroinflammation and cell senescence in AD remain unclear.Nicotinamide adenine dinucleotide (NAD⁺) plays a central role in cellular metabolism and is also critical for maintaining mitochondrial homeostasis and genome integrity (13). Emerging evidence has identified lower levels of NAD⁺ in affected tissues in many neurodegenerative diseases, including AD (13–16). Supplementation with the NAD⁺ precursor nicotinamide riboside (NR) efficiently increases NAD⁺ and can have beneficial effects on many AD features in mouse models (14). The cyclic GMP-AMP synthase (cGAS)–STING (stimulator of interferon genes) DNA-sensing pathway detects the presence of cytosolic DNA and triggers expression of inflammatory genes that lead to senescence or to the activation of defense mechanisms (17–20). Here, we explore the mechanisms by which NAD⁺ supplementation reduces neuroinflammation and cell senescence in AD. Our results suggest that the cGAS–STING pathway is a therapeutic target for AD.