Nuclear TAR DNA-binding protein 43 A new target for amyotrophic lateral sclerosis treatment

Abnormal TAR DNA-binding protein 43 （TDP-43） inclusion bodies can be detected in the degen- erative neurons of amyotrophic lateral sclerosis. In this study, we induced chronic oxidative stress injury by applying malonate to cultured mouse cortical motor neurons. In the later stages of the malonate insult, TDP-43 expression reduced in the nuclei and transferred to the cytoplasm. This was accompanied by neuronal death, mimicking the pathological changes in TDP-43 that are seen in patients with amyotrophic lateral sclerosis. Interestingly, in the early stages of the response to malonate treatment, nuclear TDP-43 expression increased, and neurons remained relatively intact, without inclusion bodies or fragmentation. Therefore, we hypothesized that the increase of nuclear TDP-43 expression might be a pro-survival factor against oxidative stress injury. This hypothesis was confirmed by an in vitro transgenic experiment, in which overexpression of wild type mouse TDP-43 in cultured cortical motor neurons significantly reduced malonate-induced neuronal death. Our findings suggest that the loss of function of TDP-43 is an important cause of neuronal degen- eration, and upregulation of nuclear TDP-43 expression might be neuroprotective in amyotrophic lateral sclerosis.     

RNA quality control and protein aggregates in amyotrophic lateral sclerosis: A review

Amyotrophic lateral sclerosis (ALS) is the most common motor neuron disease in adults. The biologic basis of ALS remains unknown. However, ALS research has taken a dramatic turn over the past 4 years. Ground breaking discoveries of mutations of genes that encode RNA processing proteins, and demonstration that abnormal aggregates of these and other proteins precede motor neuron loss in familial and sporadic ALS, have initiated a paradigm shift in understanding the pathogenic mechanisms of ALS. Curiously, some of these RNA binding proteins have prion‐like domains, with a propensity to self‐aggregation. The emerging hypothesis that a focal cascade of toxic protein aggregates, and their consequent non–cell‐autonomous spread to neighborhood groups of neurons, fits the classical temporo‐spatial progression of ALS. This article reviews the current research efforts toward understanding the role of RNA‐processing regulation and protein aggregates in ALS. Muscle Nerve 47:330‐338, 2013     

Neuropathology of the hippocampus in FTLD‐Tau with Pick bodies: a study of the BrainNet Europe Consortium

G. G. Kovacs, A. J. M. Rozemuller, J. C. van Swieten, E. Gelpi, K. Majtenyi, S. Al‐Sarraj, C. Troakes, I. Bódi, A. King, T. Hortobágyi, M. M. Esiri, O. Ansorge, G. Giaccone, I. Ferrer, T. Arzberger, N. Bogdanovic, T. Nilsson, I. Leisser, I. Alafuzoff, J. W. Ironside, H. Kretzschmar and H. Budka (2013) Neuropathology and Applied Neurobiology 39, 166–178 Neuropathology of the hippocampus in FTLD‐Tau with Pick bodies: a study of the BrainNet Europe Consortium Aims: Frontotemporal lobar degeneration with Pick bodies (Pick's disease) is characterized by the presence of tau immunoreactive spherical structures in the cytoplasm of neurones. In view of confusion about the molecular pathology of Pick's disease, we aimed to evaluate the spectrum of tau pathology and concomitant neurodegeneration‐associated protein depositions in the characteristically affected hippocampus. Methods: We evaluated immunoreactivity (IR) for tau (AT8, 3R, 4R), α‐synuclein, TDP43, p62, and ubiquitin in the hippocampus, entorhinal and temporal cortex in 66 archival cases diagnosed neuropathologically as Pick's disease. Results: Mean age at death was 68.2 years (range 49–96). Fifty‐two (79%) brains showed 3R immunoreactive spherical inclusions in the granule cells of the dentate gyrus. These typical cases presented mainly with the behavioural variant of frontotemporal dementia, followed by progressive aphasia, mixed syndromes or early memory disturbance. α‐Synuclein IR was seen only in occasional spherical tau‐positive inclusions, TDP‐43 IR was absent, and 4R IR was present only as neurofibrillary tangles in pyramidal neurones. Aβ IR was observed in 16 cases; however, the overall level of Alzheimer's disease‐related alterations was mainly low or intermediate (n = 3). Furthermore, we identified six cases with unclassifiable tauopathy. Conclusions: (i) Pick's disease may occur also in elderly patients and is characterized by a relatively uniform pathology with 3R tau inclusions particularly in the granule cells of dentate gyrus; (ii) even minor deviation from these morphological criteria suggests a different disorder; and (iii) immunohistological revision of archival cases expands the spectrum of tauopathies that require further classification.     

New routes in frontotemporal dementia drug discovery

Introduction: Research into the pathogenic mechanisms behind frontotemporal dementia (FTD) has yielded several new targets for therapeutic intervention; such targets include specific new pathways uncovered by mutations as well as targets involving the modulation, formation and degradation of protein aggregates.

Areas covered: Herein, the authors outline the principal molecular causes underlying FTD to date and the research that has been performed in these areas with respect to an eventual corrective strategy.

Expert opinion: While it is worthwhile targeting pathways affected by specific mutations with a causative loss of function linked to FTD, research still has to contend with issues including the remaining presence of protein aggregates or that treatments are rarely universally applicable. Aiming to recover function in a downstream target caused by the protein aggregates will likely be insufficient due to the large cascade of events affected. It is our belief that the clearance of these aggregates and the inhibition of protein misfolding are more appropriate and direct routes to an eventual therapy.     

Connexin 43 Is Necessary for Murine Tendon Enthesis Formation and Response to Loading

The enthesis is a mineralized fibrocartilage transition that attaches tendon to bone and is vital for musculoskeletal function. Despite recent studies demonstrating the necessity of muscle loading for enthesis formation, the mechanisms that regulate enthesis formation and mechanoresponsiveness remain unclear. Therefore, the current study investigated the role of the gap junction protein connexin 43 in these processes by deleting Gja1 (the Cx43 gene) in the tendon and enthesis. Compared with their wild-type (WT) counterparts, mice lacking Cx43 showed disrupted entheseal cell alignment, reduced mineralized fibrocartilage, and impaired biomechanical properties of the supraspinatus tendon entheses during postnatal development. Cx43-deficient mice also exhibited reduced ability to complete a treadmill running protocol but no apparent deficits in daily activity, metabolic indexes, shoulder muscle size, grip strength, and major trabecular bone properties of the adjacent humeral head. To examine enthesis mechanoresponsiveness, young adult mice were subjected to modest treadmill exercise. Gja1 deficiency in the tendon and enthesis reduced entheseal anabolic responses to treadmill exercise: WT mice had increased expression of Sox9, Ihh, and Gli1 and increased Brdu incorporation, whereas Cx43-deficient mice showed no changes or decreased levels with exercise. Collectively, the results demonstrated an essential role for Cx43 in postnatal tendon enthesis formation, function, and response to loading; results further provided evidence implicating a link between Cx43 function and the hedgehog signaling pathway. © 2020 American Society for Bone and Mineral Research.     

Connexin 43 upregulation in burns promotes burn conversion through spread of apoptotic death signals

BackgroundBurn wounds continue to worsen after initial injury in a process known as burn conversion, which lasts about 3–5 days. It causes burn wounds to enlarge and deepen, leading to greater morbidity. Apoptosis is one of the factors contributing to the conversion of the zone of stasis into the zone of coagulation. Suppression of apoptosis has been associated with reducing burn conversion. Connexin 43 (Cx43) gap junctions facilitate the spread of apoptotic signals from dying cells to healthy neighbouring cells in injured tissues through the bystander effect.ObjectivesThe study is to understand the role of Cx43 in burn conversion.MethodsIn our study, 15 burn tissue samples were arranged into three groups as early (beginning of burn conversion), intermediate (extensive burn conversion) and late (established burn conversion) burns.ResultsWe found a striking increase in the amount of Cx43 protein expressed in the dermal fibroblasts (identified with heat shock protein 47 (HSP47) staining) in the zone of stasis in early and intermediate burns. These dermal fibroblasts also express high levels of cleaved-Caspase 3 indicating on-going apoptosis.ConclusionsOur findings suggest that elevation of Cx43 may play an active role in burn conversion spreading apoptosis in the early and intermediate burn wound.     

Thapsigargin Is a Broad-Spectrum Inhibitor of Major Human Respiratory Viruses: Coronavirus,Respiratory Syncytial Virus and Influenza A Virus

The long-term control strategy of SARS-CoV-2 and other major respiratory viruses needs to include antivirals to treat acute infections, in addition to the judicious use of effective vaccines. Whilst COVID-19 vaccines are being rolled out for mass vaccination, the modest number of antivirals in use or development for any disease bears testament to the challenges of antiviral development. We recently showed that non-cytotoxic levels of thapsigargin (TG), an inhibitor of the sarcoplasmic/endoplasmic reticulum (ER) Ca²⁺ ATPase pump, induces a potent host innate immune antiviral response that blocks influenza A virus replication. Here we show that TG is also highly effective in blocking the replication of respiratory syncytial virus (RSV), common cold coronavirus OC43, SARS-CoV-2 and influenza A virus in immortalized or primary human cells. TG’s antiviral performance was significantly better than remdesivir and ribavirin in their respective inhibition of OC43 and RSV. Notably, TG was just as inhibitory to coronaviruses (OC43 and SARS-CoV-2) and influenza viruses (USSR H1N1 and pdm 2009 H1N1) in separate infections as in co-infections. Post-infection oral gavage of acid-stable TG protected mice against a lethal influenza virus challenge. Together with its ability to inhibit the different viruses before or during active infection, and with an antiviral duration of at least 48 h post-TG exposure, we propose that TG (or its derivatives) is a promising broad-spectrum inhibitor against SARS-CoV-2, OC43, RSV and influenza virus.     

Alterations of Ca-responsive proteins within cholinergic neurons in aging and Alzheimer's disease

The molecular basis of selective neuronal vulnerability in Alzheimer's disease (AD) remains poorly understood. Using basal forebrain cholinergic neurons (BFCNs) as a model and immunohistochemistry, we have demonstrated significant age-related loss of the calcium-binding protein calbindin-D_28K (CB) from BFCN, which was associated with tangle formation and degeneration in AD. Here, we determined alterations in RNA and protein for CB and the Ca²⁺-responsive proteins Ca²⁺/calmodulin-dependent protein kinase I (CaMKI), growth-associated protein-43 (GAP43), and calpain in the BF. We observed progressive downregulation of CB and CaMKI RNA in laser-captured BFCN in the normal-aged-AD continuum. We also detected progressive loss of CB, CaMKIδ, and GAP43 proteins in BF homogenates in aging and AD. Activated μ-calpain, a calcium-sensitive protease that degrades CaMKI and GAP43, was significantly increased in the normal aged BF and was 10 times higher in AD BF. Overactivation of μ-calpain was confirmed using proteolytic fragments of its substrate spectrin. Substantial age- and AD-related alterations in Ca²⁺-sensing proteins most likely contribute to selective vulnerability of BFCN to degeneration in AD.