Neuroprotective effects of carbenoxolone against amyloid-beta 1–42 oligomer-induced neuroinflammation and cognitive decline in rats

The aggregation of Aβ plays a major role in the progression of Alzheimer’s disease (AD) and induces neuroinflammation, neurodegeneration and cognitive decline. Recent studies have shown that the soluble aggregates of Aβ are the major culprits in the development of these aberrations inside the brain. In this study, we investigated the neuroprotective potential of carbenoxolone (Cbx), which has been found to possess anti-inflammatory and nootropic properties.Male SD rats (250−300 g) were divided into the four groups (n = 8 per group): (1) sham control rats injected with vehicles, (2) Aβ 1–42 group rats injected i.c.v. with Aβ 42 oligomers (10 μl/rat), (3) Aβ 1–42+Cbx group rats injected i.c.v. with Aβ 42 oligomers (10 μl/rat) and i.p. with carbenoxolone disodium (20 mg/kg body weight) for six-weeks and (4) Cbx group rats injected i.p. with carbenoxolone disodium (20 mg/kg body weight) for six-weeks.Progressive learning and memory deficits were seen through a battery of behavioral tests and a significant increase in the expressions of GFAP and Iba-1 was observed which resulted in the release of pro-inflammatory cytokines post Aβ oligomer injection. The levels of BDNF, Bcl-2 and pCREB were decreased while Bax, caspase-3, caspase-9 and cytochrome c levels were induced. Also, neurotransmitter levels were altered and neuronal damage was observed through histopathological studies. After Cbx supplementation, the expressions of GFAP, IBA-1, pro-inflammatory cytokines, iNOS, nNOS and nitric oxide levels were normalized. The expression levels of pro-apoptotic markers were decreased and neurotrophin levels were restored. Also, neurotransmitter levels and neuronal profile were improved and progressive improvements in behavioural performance were observed.Our results demonstrated that Cbx might have prevented the Aβ induced neurodegeneration and cognitive decline by inhibiting the neuroinflammation and inducing BDNF/CREB signalling. These findings suggest that Cbx can be explored as a potential therapeutic agent against the progression of AD.     

Strain differences in the extent of brain injury in mice after tetramethylenedisulfotetramine-induced status epilepticus

Acute intoxication with tetramethylenedisulfotetramine (TETS) can trigger status epilepticus (SE) in humans. Survivors often exhibit long-term neurological effects, including electrographic abnormalities and cognitive deficits, but the pathogenic mechanisms linking the acute toxic effects of TETS to chronic outcomes are not known. Here, we use advanced in vivo imaging techniques to longitudinally monitor the neuropathological consequences of TETS-induced SE in two different mouse strains. Adult male NIH Swiss and C57BL/6J mice were injected with riluzole (10 mg/kg, i.p.), followed 10 min later by an acute dose of TETS (0.2 mg/kg in NIH Swiss; 0.3 mg/kg, i.p. in C57BL/6J) or an equal volume of vehicle (10% DMSO in 0.9% sterile saline). Different TETS doses were administered to trigger comparable seizure behavior between strains. Seizure behavior began within minutes of TETS exposure and rapidly progressed to SE that was terminated after 40 min by administration of midazolam (1.8 mg/kg, i.m.). The brains of vehicle and TETS-exposed mice were imaged using in vivo magnetic resonance (MR) and translocator protein (TSPO) positron emission tomography (PET) at 1, 3, 7, and 14 days post-exposure to monitor brain injury and neuroinflammation, respectively. When the brain scans of TETS mice were compared to those of vehicle controls, subtle and transient neuropathology was observed in both mouse strains, but more extensive and persistent TETS-induced neuropathology was observed in C57BL/6J mice. In addition, one NIH Swiss TETS mouse that did not respond to the midazolam therapy, but remained in SE for more than 2 h, displayed robust neuropathology as determined by in vivo imaging and confirmed by FluoroJade C staining and IBA-1 immunohistochemistry as readouts of neurodegeneration and neuroinflammation, respectively. These findings demonstrate that the extent of injury observed in the mouse brain after TETS-induced SE varied according to strain, dose of TETS and/or the duration of SE. These observations suggest that TETS-intoxicated humans who do not respond to antiseizure medication are at increased risk for brain injury.     

Brain immune cells characterization in UCMS exposed P2X7 knock-out mouse

BackgroundSeveral lines of evidence suggest that neuroinflammation might be a key neurobiological mechanism of depression. In particular, the P2X7 receptor (P2X7R), an ATP-gated ion channel involved in activation of the pro-inflammatory interleukin IL-1β, has been shown to be a potential new pharmacological target in depression. The aim of this study was to explore the impact of unpredictable chronic mild stress (UCMS) on behavioural changes, hippocampal neurogenesis, and cellular characterisation of brain immune cells, in P2X7R Knock-Out (KO) mice.MethodsP2X7R KO and wild-type (WT) mice were subjected to a 6-week UCMS protocol and received a conventional oral antidepressant (15 mg.kg⁻¹ fluoxetine) or water per os. The mice then underwent behavioural tests consisting of the tail suspension test (TST), the elevated plus maze (EPM) test, the open field test, the splash test and the nest building test (week 7). Doublecortin immunostaining (DCX) of brain slices was used to assess neurogenesis in the dentate gyrus. Iba1 and TMEM119 immunostaining was used to characterise brain immune cells, Iba1 as a macrophage marker (including microglial cells) and TMEM119 as a potential specific resident microglial cells marker.ResultsAfter a 6-week UCMS exposure, P2X7R KO mice exhibited less deterioration of their coat state, spent a significantly smaller amount of time immobile in the TST and spent a larger amount of time in the open arms of the EPM. As expected, adult ventral hippocampal neurogenesis was significantly decreased by UCMS in WT mice, while P2X7R KO mice maintained ventral hippocampal neurogenesis at similar levels in both control and UCMS conditions. In stress-related brain regions, P2X7R KO mice also exhibited less recruitment of Iba1+/TMEM119+ and Iba1+/TMEM119- cells in the brain. The ratio between these two staining patterns revealed that brain immune cells were mostly composed of Iba1+/TMEM119+ cells (87 to 99%), and this ratio was affected neither by P2X7R genetic depletion nor by antidepressant treatment.DiscussionBehavioural patterns, neurogenesis levels and density of brain immune cells in P2X7R KO mice after exposure to UCMS significantly differed from control conditions. Brain immune cells were mostly increased in brain regions known to be sensitive to UCMS exposure in WT but not in P2X7R KO mice. Considering Iba1+/TMEM119– staining might characterize peripheral immune cells, the ratio between Iba1+/TMEM119+ cells and IBA1+/TMEM119- cells, suggests that the rate of peripheral immune cells recruitment may not be modified neither by P2X7R gene expression nor by antidepressant treatment.     

Activation of liver X receptors prevents emotional and cognitive dysfunction by suppressing microglial M1-polarization and restoring synaptic plasticity in the hippocampus of mice

Depression is a long-lasting and persistent mood disorder in which the regulatory mechanisms of neuroinflammation are thought to play a contributing role to the physiopathology of the condition. Previous studies have shown that liver X receptors (LXRs) can regulate the activation of microglia and neuroinflammation. However, the role of LXRs in depression remains to be fully understood. In this study, we hypothesized that stress impairs the function of LXRs and that the LXRs agonist GW3965 plays a potential anti-depressive role by inhibiting neuroinflammation. The anti-depressive effects of GW3965 were evaluated in both chronic unpredictable mild stress (CUMS) and lipopolysaccharide (LPS) models. The LXRs antagonist GSK2033 was also employed to block LXRs. Behavioural tests were performed to measure depression-like phenotypes and learning abilities. Electrophysiological recordings and Golgi staining were used to measure the plasticity of the dentate gyrus synapse. The expression of synapse and neuroinflammation related proteins were evaluated by Western blotting and immunofluorescence. The activation of LXRs by GW3965 prevented emotional and cognitive deficits induced by either CUMS or LPS. GW3965 prevented the decreased level of LXR-β induced by CUMS. The activation of LXRs significantly improved the impairment of synaptic plasticity, prevented the up-regulation of inflammatory factors and inhibited NF-κB phosphorylation and microglial M1-polarization in both models. The antidepressive-like effects of GW3965 were blocked by GSK2033 in the CUMS and LPS models. Our data suggest that inhibition of the LXRs signalling pathway may be a key driver in the pathogenesis of neuroinflammation during depression and that LXRs agonists have a high potential in the treatment of depression.     

GSK3β is involved in promoting Alzheimer’s disease pathologies following chronic systemic exposure to Porphyromonas gingivalis lipopolysaccharide in amyloid precursor proteinNL-F/NL-F knock-in mice

In line with the strong association between periodontitis and Alzheimer’s disease (AD) clinically, preclinical studies have shown that systemic exposure to Porphyromonas gingivalis (Pg) initiates AD pathologies. However, the involvement of periodontitis in promoting AD pathologies is unclear. In the present study, we provided evidence that chronic systemic exposure to lipopolysaccharide derived from Pg (PgLPS, 1 mg/kg, daily, intraperitoneally) prompted neuroinflammation and tau hyperphosphorylation in 10-month-old of amyloid precursor protein (APP) knock-in mice, a model of AD, carrying the Swedish and Beyreuther/Iberian mutation (APP^NL-F/NL-F). The learning and memory function were assessed using the passive avoidance test. The production of APP, Amyloid (A)β_1-42, cytokines, synaptic proteins and the activation of glycogen synthase kinase (GSK)-3β as well as phosphorylation of tau were analyzed by immunohistochemistry, Western blotting or an enzyme-linked immunosorbent assay (ELISA) in the cortex of APP^NL-F/NL-F mice. We found that systemic exposure of PgLPS for three consecutive weeks induced learning and memory deficits with significantly reduced postsynaptic density protein (PSD95). Increased hyperphosphorylation of tau in multiple residues, including Ser202, Thr231 and Ser396, but not the accumulation of Aβ_1-42 was detected in the neurons of APP^NL-F/NL-F mice. Furthermore, PgLPS increased the GSK3β activity by reducing its phosphorylation of the serine residue at position 9 (Ser9) and promoted neuroinflammation by increasing the expression of interleukin-1β (IL-1β) and tumor necrosis factor (TNF-α) while decreasing that of interleukin-10 (IL-10) and transforming growth factor (TGFβ) in the cortex of APP^NL-F/NL-F mice. Moreover, the PgLPS-increased GSK3β activity was detected in both microglia and neurons, while the PgLPS-increased TNF-α expression was mainly detected in the microglia in the cortex of APP^NL-F/NL-F mice. In in vitro studies, PgLPS (1 µg/ml) stimulation increased the mRNA and protein level of TNF-α in MG6 microglia, which were significantly inhibited by the GSK3β-specific inhibitor TWS119. In contrast, the tau hyperphosphorylation and activation of GSK3β in N2a neurons were enhanced after treatment with conditioned medium from PgLPS-stimulated microglia, which was attenuated after pre-treatment with TNF-α inhibitor. Taken together, these findings indicate that GSK3β is involved in prompting microglia (TNF-α)-dependent tau hyperphosphorylation in neurons, resulting in learning and memory deficits in APP^NL-F/NL-F mice without changes in the Aβ expression during chronic systemic exposure to PgLPS. We propose that dampening GSK3β activation may help delay the periodontitis-promoted pathological progression of AD.     

Immune treatments for alcohol use disorder: A translational framework

While the immune system is essential for survival, an excessive or prolonged inflammatory response, such as that resulting from sustained heavy alcohol use, can damage the host and contribute to psychiatric disorders. A growing body of literature indicates that the immune system plays a critical role in the development and maintenance of alcohol use disorder (AUD). As such, there is enthusiasm for treatments that can restore healthy levels of inflammation as a mechanism to reduce drinking and promote recovery. In this qualitative literature review, we provide a conceptual rationale for immune therapies and discuss progress in medications development for AUD focused on the immune system as a treatment target. This review is organized into sections based on primary signaling pathways targeted by the candidate therapies, namely: (a) toll-like receptors, (b) phosphodiesterase inhibitors, (c) peroxisome proliferator-activated receptors, (d) microglia and astrocytes, (e) other immune pharmacotherapies, and (f) behavioral therapies. As relevant within each section, we examine the basic biological mechanisms of each class of therapy and evaluate preclinical research testing the role of the therapy on mitigating alcohol-related behaviors in animal models. To the extent available, translational findings are reviewed with discussion of completed and ongoing randomized clinical trials and their findings to date. An applied and clinically focused approach is taken to identify the potential clinical applications of the various treatments reviewed. We conclude by delineating the most promising candidate treatments and discussing future directions by considering opportunities for immune treatment development and personalized medicine for AUD.     

Dietary DHA prevents cognitive impairment and inflammatory gene expression in aged male rats fed a diet enriched with refined carbohydrates

The consumption of a processed foods diet (PD) enriched with refined carbohydrates, saturated fats, and lack of fiber has increased in recent decades and likely contributed to increased incidence of chronic disease and weight gain in humans. These diets have also been shown to negatively impact brain health and cognitive function in rodents, non-human primates, and humans, potentially through neuroimmune-related mechanisms. However, mechanisms by which PD impacts the aged brain are unknown. This gap in knowledge is critical, considering the aged brain has a heightened state of baseline inflammation, making it more susceptible to secondary challenges. Here, we showed that consumption of a PD, enriched with refined carbohydrate sources, for 28 days impaired hippocampal- and amygdalar-dependent memory function in aged (24 months), but not young (3 months) F344 × BN rats. These memory deficits were accompanied by increased expression of inflammatory genes, such as IL-1β, CD11b, MHC class II, CD86, NLRP3, and complement component 3, in the hippocampus and amygdala of aged rats. Importantly, we also showed that when the same PD is supplemented with the omega-3 polyunsaturated fatty acid DHA, these memory deficits and inflammatory gene expression changes were ameliorated in aged rats, thus providing the first evidence that DHA supplementation can protect against memory deficits and inflammatory gene expression in aged rats fed a processed foods diet. Lastly, we showed that while PD consumption increased weight gain in both young and aged rats, this effect was exaggerated in aged rats. Aging was also associated with significant alterations in hypothalamic gene expression, with no impact by DHA on weight gain or hypothalamic gene expression. Together, our data provide novel insights regarding diet-brain interactions by showing that PD consumption impairs cognitive function likely through a neuroimmune mechanism and that dietary DHA can ameliorate this phenomenon.     

Novel microglia-mediated mechanisms underlying synaptic loss and cognitive impairment after traumatic brain injury

Traumatic brain injury (TBI) is one of the leading causes of long-term neurological disability in the world. Currently, there are no therapeutics for treating the deleterious consequences of brain trauma; this is in part due to a lack of complete understanding of cellular processes that underlie TBI-related pathologies. Following TBI, microglia, the brain resident immune cells, turn into a “reactive” state characterized by the production of inflammatory mediators that contribute to the development of cognitive deficits. Utilizing multimodal, state-of-the-art techniques that widely span from ultrastructural analysis to optogenetic interrogation of circuit function, we investigated the reactive microglia phenotype one week after injury when learning and memory deficits are also measured. Microglia displayed increased: (i) phagocytic activity in vivo, (ii) synaptic engulfment, (iii) increased neuronal contact, including with dendrites and somata (termed ‘satellite microglia’). Functionally, satellite microglia might impact somatic inhibition as demonstrated by the associated reduction in inhibitory synaptic drive. Cumulatively, here we demonstrate novel microglia-mediated mechanisms that may contribute to synaptic loss and cognitive impairment after traumatic brain injury.     

Toll-like receptor 3 differently modulates inflammation in progressive or benign multiple sclerosis

TLR-dependent signal transduction pathways were analyzed in patients with a diagnosis of either relapsing–remitting (RRMS), secondary progressive (PMS) or benign (BMS) MS and healthy controls (HC). Prototypical TLR molecules expressed either on the cell surface (TLR4) or intracellularly (TLR3) were stimulated with specific antigens (LPS and poly I:C, respectively). Expression of factors involved in TLR signaling cascades, production of downstream immune mediators and TLR expression were evaluated. Results showed that, whereas LPS-stimulation of TLR4 had a marginal effect on cell activation, poly I:C-stimulated TLR3 expression on immune cells was significantly increased in PMS and BMS compared to HC. This was associated with a higher responsiveness to poly I:C that resulted in the activation of the TLR3-mediated pathway and the production of inflammatory cytokines in PMS and, in contrast, in the up-regulation of a peculiar mosaic of inflammation-dampening genes in BMS. Results herein might explain different MS disease phenotypes.