Loss of MyD88 alters neuroinflammatory response and attenuates early Purkinje cell loss in a spinocerebellar ataxia type 6 mouse model

Dynamic molecular network analysis of iPSC-Purkinje cells differentiation delineates roles of ISG15 in SCA1 at the earliest stage

Better understanding of the earliest molecular pathologies of all neurodegenerative diseases is expected to improve human therapeutics. We investigated the earliest molecular pathology of spinocerebellar ataxia type 1 (SCA1), a rare familial neurodegenerative disease that primarily induces death and dysfunction of cerebellum Purkinje cells. Extensive prior studies have identified involvement of transcription or RNA-splicing factors in the molecular pathology of SCA1. However, the regulatory network of SCA1 pathology, especially central regulators of the earliest developmental stages and inflammatory events, remains incompletely understood. Here, we elucidated the earliest developmental pathology of SCA1 using originally developed dynamic molecular network analyses of sequentially acquired RNA-seq data during differentiation of SCA1 patient-derived induced pluripotent stem cells (iPSCs) to Purkinje cells. Dynamic molecular network analysis implicated histone genes and cytokine-relevant immune response genes at the earliest stages of development, and revealed relevance of ISG15 to the following degradation and accumulation of mutant ataxin-1 in Purkinje cells of SCA1 model mice and human patients.

Motor deficits are associated with increased glial cell activation in the hypothalamus and cerebellum of young rats subjected to cerebral palsy

Cerebral palsy (CP) is a syndrome characterized by a wide range of sensory and motor damage, associated with behavioral and cognitive deficits. The aim of the present study was to investigate the potential of a model of CP using a combination of perinatal anoxia and sensorimotor restriction of hind paws to replicate motor, behavioral and neural deficits. A total of 30 of male Wistar rats were divided into Control (C, n = 15), and CP (CP, n = 15) groups. The potential of the CP model was assessed by evaluating food intake, the behavioral satiety sequence, performance on the CatWalk and parallel bars, muscle strength, and locomotor activity. The weight of the encephalon, soleus, and extensor digitorum longus (EDL) muscles, and the activation of glial cells (microglia and astrocytes) were also measured. The CP animals showed delayed satiety, impaired locomotion on the CatWalk and open field test, reduced muscle strength, and reduced motor coordination. CP also reduced the weight of the soleus and muscles, brain weight, liver weight, and quantity of fat in various parts of the body. There was also found to be an increase in astrocyte and microglia activation in the cerebellum and hypothalamus (arcuate nucleus, ARC) of animals subjected to CP.

Proinflammatory activation of microglia in the cerebellum hyperexcites Purkinje cells to trigger ataxia

Specific medications to combat cerebellar ataxias, a group of debilitating movement disorders characterized by difficulty with walking, balance and coordination, are still lacking. Notably, cerebellar microglial activation appears to be a common feature in different types of ataxic patients and rodent models. However, direct evidence that cerebellar microglial activation in vivo is sufficient to induce ataxia is still lacking. Here, by employing chemogenetic approaches to manipulate cerebellar microglia selectively and directly, we found that specific chemogenetic activation of microglia in the cerebellar vermis directly leads to ataxia symptoms in wild-type mice and aggravated ataxic motor deficits in 3-acetylpyridine (3-AP) mice, a classic mouse model of cerebellar ataxia. Mechanistically, cerebellar microglial proinflammatory activation induced by either chemogenetic M3D(Gq) stimulation or 3-AP modeling hyperexcites Purkinje cells (PCs), which consequently triggers ataxia. Blockade of microglia-derived TNF-α, one of the most important proinflammatory cytokines, attenuates the hyperactivity of PCs driven by microglia. Moreover, chemogenetic inhibition of cerebellar microglial activation or suppression of cerebellar microglial activation by PLX3397 and minocycline reduces the production of proinflammatory cytokines, including TNF-α, to effectively restore the overactivation of PCs and alleviate motor deficits in 3-AP mice. These results suggest that cerebellar microglial activation may aggravate the neuroinflammatory response and subsequently induce dysfunction of PCs, which in turn triggers ataxic motor deficits. Our findings thus reveal a causal relationship between proinflammatory activation of cerebellar microglia and ataxic motor symptoms, which may offer novel evidence for therapeutic intervention for cerebellar ataxias by targeting microglia and microglia-derived inflammatory mediators.

Peripheral Inflammation Links with the Severity of Clinical Phenotype in Spinocerebellar Ataxia 2

BACKGROUND

The role of peripheral inflammation in spinocerebellar ataxia type 2 (SCA2) is unknown.

OBJECTIVE

The objective of this study was to identify peripheral inflammation biomarkers and their relationship with the clinical and molecular features.

METHODS

Blood cell count-derived inflammatory indices were measured in 39 SCA2 subjects and their matched controls. Clinical scores of ataxia, nonataxia, and cognitive dysfunction were assessed.

RESULTS

The neutrophil-to-lymphocyte ratio (NLR), the platelet-to-lymphocyte ratio (PLR), the Systemic Inflammation Index (SII), and the Aggregate Index of Systemic Inflammation (AISI) were significantly increased in SCA2 subjects compared with controls. The increases in PLR, SII, and AISI were even observed in preclinical carriers. NLR, PLR, and SII were correlated with the Scale for the Assessment and Rating of Ataxia speech item score rather than with the total score. The NLR and SII were correlated with the nonataxia and the cognitive scores.

CONCLUSIONS

Peripheral inflammatory indices are biomarkers in SCA2, which may help to design future immunomodulatory trials and advance our understanding of the disease. © 2023 International Parkinson and Movement Disorder Society.

Mesenchymal Stem Cell Transplantation Ameliorates Ara-C-Induced Motor Deficits in a Mouse Model of Cerebellar Ataxia

This study investigated the therapeutic effects of transplanting human mesenchymal stem cells (hMSCs) into wild-type mice that were intraperitoneally administered cytosine arabinoside (Ara-C) to develop cerebellar ataxia (CA) during the first three postnatal days. hMSCs were intrathecally injected into 10-week-old mice once or thrice at 4-week intervals. Compared to the nontreated mice, the hMSC-treated mice showed improved motor and balance coordination, as measured using the rotarod, open-field, and ataxic scoring assessments, and increased protein levels in Purkinje and cerebellar granule cells, as measured using calbindin and NeuN protein markers. Multiple hMSC injections preserved Ara-C-induced cerebellar neuronal loss and improved cerebellar weight. Furthermore, the hMSC implantation significantly elevated the levels of neurotrophic factors, including brain-derived and glial cell line-derived neurotrophic factors, and suppressed TNF-α-, IL-1β-, and iNOS-mediated proinflammatory responses. Collectively, our results demonstrate that hMSCs exhibit therapeutic potential for Ara-C-induced CA by protecting neurons through the stimulation of neurotrophic factors and inhibition of cerebellar inflammatory responses, which can improve motor behavior and alleviate ataxia-related neuropathology. In summary, this study suggests that hMSC administration, particularly multiple treatments, can effectively treat ataxia-related symptoms with cerebellar toxicity.

Immunology and microbiome: Implications for motor systems

Immune-inflammatory mechanisms seem to play a relevant role in neurodegenerative disorders affecting motor systems, particularly Parkinson's disease, where activity changes in inflammatory cells and evidence of neuroinflammation in experimental models and patients is available. Amyotrophic lateral sclerosis is also characterized by neuroinflammatory changes that involve primarily glial cells, both microglia and astrocytes, as well as systemic immune dysregulation associated with more rapid progression. Similarly, the exploration of gut dysbiosis in these two prototypical neurodegenerative motor disorders is advancing rapidly. Altered composition of gut microbial constituents and related metabolic and putative functional pathways is supporting a pathophysiological link that is currently explored in preclinical, germ-free animal models. Less compelling, but still intriguing, evidence suggests that motor neurodevelopmental disorders, e.g., Tourette syndrome, are associated with abnormal trajectories of maturation that include also immune system development. Microglia has a key role also in these disorders, and new therapeutic avenues aiming at its modulation are exciting prospects. Preclinical and clinical research on the role of gut dysbiosis in Tourette syndrome and related behavioral disorders is still in its infancy, but early findings support the rationale to delve deeper into its contribution to neural and immune maturation abnormalities in its spectrum.

A Breakdown of Immune Tolerance in the Cerebellum

Cerebellar dysfunction can be associated with ataxia, dysarthria, dysmetria, nystagmus and cognitive deficits. While cerebellar dysfunction can be caused by vascular, traumatic, metabolic, genetic, inflammatory, infectious, and neoplastic events, the cerebellum is also a frequent target of autoimmune attacks. The underlying cause for this vulnerability is unclear, but it may be a result of region-specific differences in blood–brain barrier permeability, the high concentration of neurons in the cerebellum and the presence of autoantigens on Purkinje cells. An autoimmune response targeting the cerebellum—or any structure in the CNS—is typically accompanied by an influx of peripheral immune cells to the brain. Under healthy conditions, the brain is protected from the periphery by the blood–brain barrier, blood–CSF barrier, and blood–leptomeningeal barrier. Entry of immune cells to the brain for immune surveillance occurs only at the blood-CSF barrier and is strictly controlled. A breakdown in the barrier permeability allows peripheral immune cells uncontrolled access to the CNS. Often—particularly in infectious diseases—the autoimmune response develops because of molecular mimicry between the trigger and a host protein. In this review, we discuss the immune surveillance of the CNS in health and disease and also discuss specific examples of autoimmunity affecting the cerebellum.

Quantitative proteomic analysis after neuroprotective MyD88 inhibition in the retinal degeneration 10 mouse

Progressive photoreceptor death occurs in blinding diseases such as retinitis pigmentosa. Myeloid differentiation primary response protein 88 (MyD88) is a central adaptor protein for innate immune system Toll-like receptors (TLR) and induces cytokine secretion during retinal disease. We recently demonstrated that inhibiting MyD88 in mouse models of retinal degeneration led to increased photoreceptor survival, which was associated with altered cytokines and increased neuroprotective microglia. However, the identity of additional molecular changes associated with MyD88 inhibitor-induced neuroprotection is not known. In this study, we used isobaric tags for relative and absolute quantification (iTRAQ) labelling followed by LC-MS/MS for quantitative proteomic analysis on the rd10 mouse model of retinal degeneration to identify protein pathways changed by MyD88 inhibition. Quantitative proteomics using iTRAQ LC-MS/MS is a high-throughput method ideal for providing insight into molecular pathways during disease and experimental treatments. Forty-two proteins were differentially expressed in retinas from mice treated with MyD88 inhibitor compared with control. Notably, increased expression of multiple crystallins and chaperones that respond to cellular stress and have anti-apoptotic properties was identified in the MyD88-inhibited mice. These data suggest that inhibiting MyD88 enhances chaperone-mediated retinal protection pathways. Therefore, this study provides insight into molecular events contributing to photoreceptor protection from modulating inflammation.

Consensus Paper: Strengths and Weaknesses of Animal Models of Spinocerebellar Ataxias and Their Clinical Implications

Spinocerebellar ataxias (SCAs) represent a large group of hereditary degenerative diseases of the nervous system, in particular the cerebellum, and other systems that manifest with a variety of progressive motor, cognitive, and behavioral deficits with the leading symptom of cerebellar ataxia. SCAs often lead to severe impairments of the patient's functioning, quality of life, and life expectancy. For SCAs, there are no proven effective pharmacotherapies that improve the symptoms or substantially delay disease progress, i.e., disease-modifying therapies. To study SCA pathogenesis and potential therapies, animal models have been widely used and are an essential part of pre-clinical research. They mainly include mice, but also other vertebrates and invertebrates. Each animal model has its strengths and weaknesses arising from model animal species, type of genetic manipulation, and similarity to human diseases. The types of murine and non-murine models of SCAs, their contribution to the investigation of SCA pathogenesis, pathological phenotype, and therapeutic approaches including their advantages and disadvantages are reviewed in this paper. There is a consensus among the panel of experts that (1) animal models represent valuable tools to improve our understanding of SCAs and discover and assess novel therapies for this group of neurological disorders characterized by diverse mechanisms and differential degenerative progressions, (2) thorough phenotypic assessment of individual animal models is required for studies addressing therapeutic approaches, (3) comparative studies are needed to bring pre-clinical research closer to clinical trials, and (4) mouse models complement cellular and invertebrate models which remain limited in terms of clinical translation for complex neurological disorders such as SCAs.

Juvenile Huntington's Disease and Other PolyQ Diseases, Update on Neurodevelopmental Character and Comparative Bioinformatic Review of Transcriptomic and Proteomic Data

Polyglutamine (PolyQ) diseases are neurodegenerative disorders caused by the CAG repeat expansion mutation in affected genes resulting in toxic proteins containing a long chain of glutamines. There are nine PolyQ diseases: Huntington’s disease (HD), spinocerebellar ataxias (types 1, 2, 3, 6, 7, and 17), dentatorubral-pallidoluysian atrophy (DRPLA), and spinal bulbar muscular atrophy (SBMA). In general, longer CAG expansions and longer glutamine tracts lead to earlier disease presentations in PolyQ patients. Rarely, cases of extremely long expansions are identified for PolyQ diseases, and they consistently lead to juvenile or sometimes very severe infantile-onset polyQ syndromes. In apparent contrast to the very long CAG tracts, shorter CAGs and PolyQs in proteins seems to be the evolutionary factor enhancing human cognition. Therefore, polyQ tracts in proteins can be modifiers of brain development and disease drivers, which contribute neurodevelopmental phenotypes in juvenile- and adult-onset PolyQ diseases. Therefore we performed a bioinformatics review of published RNAseq polyQ expression data resulting from the presence of polyQ genes in search of neurodevelopmental expression patterns and comparison between diseases. The expression data were collected from cell types reflecting stages of development such as iPSC, neuronal stem cell, neurons, but also the adult patients and models for PolyQ disease. In addition, we extended our bioinformatic transcriptomic analysis by proteomics data. We identified a group of 13 commonly downregulated genes and proteins in HD mouse models. Our comparative bioinformatic review highlighted several (neuro)developmental pathways and genes identified within PolyQ diseases and mouse models responsible for neural growth, synaptogenesis, and synaptic plasticity.

Therapeutic Effects of Human Mesenchymal Stem Cells in a Mouse Model of Cerebellar Ataxia with Neuroinflammation

Cerebellar ataxias (CAs) are neurological diseases characterized by loss of muscle coordination that is a result of damage and inflammation to the cerebellum. Despite considerable efforts in basic and clinical research, most CAs are currently incurable. In this study, we evaluated the therapeutic potential of human mesenchymal stem cells (hMSCs) against CAs associated with neuroinflammation. We observed that hMSC treatment significantly inhibited the symptoms of ataxia in lipopolysaccharide (LPS)-induced inflammatory CA (ICA) mice, which were recently reported as a potential animal model of ICA, through the anti-inflammatory effect of hMSC-derived TNFα-stimulated gene-6 (TSG-6), the protection of Purkinje cells by inhibition of apoptosis, and the modulatory effect for microglial M2 polarization. Thus, our results suggest that hMSC treatment may be an effective therapeutic approach for preventing or improving ataxia symptoms.

Pathomechanism characterization and potential therapeutics identification for SCA3 targeting neuroinflammation

Polyglutamine (polyQ)-mediated spinocerebellar ataxias (SCA) are caused by mutant genes with expanded CAG repeats encoding polyQ tracts. The misfolding and aggregation of polyQ proteins result in increased reactive oxygen species (ROS) and cellular toxicity. Inflammation is a common manifestation of oxidative stress and inflammatory process further reduces cellular antioxidant capacity. Increase of activated microglia in the pons of SCA type 3 (SCA3) patients suggests the involvement of neuroinflammation in the disease pathogenesis. In this study, we evaluated the anti-inflammatory potentials of indole compound NC009-1, 4-aminophenol-arachidonic acid derivative AM404, quinoline compound VB-037 and chalcone-coumarin derivative LM-031 using human HMC3 microglia and SCA3 ATXN3/Q₇₅-GFP SH-SY5Y cells. The four tested compounds displayed anti-inflammatory activity by suppressing NO, IL-1β, TNF-α and IL-6 production and CD68 expression of IFN-γ-activated HMC3 microglia. In retinoic acid-differentiated ATXN3/Q₇₅-GFP SH-SY5Y cells inflamed with IFN-γ-primed HMC3 conditioned medium, treatment with the tested compounds mitigated the increased caspase 1 activity and lactate dehydrogenase release, reduced polyQ aggregation and ROS and/or promoted neurite outgrowth. Examination of IL-1β- and TNF-α-mediated signaling pathways revealed that the tested compounds decreased IκBα/P65, JNK/JUN and/or P38/STAT1 signaling. The study results suggest the potential of NC009-1, AM404, VB-037 and LM-031 in treating SCA3 and probable other polyQ diseases.

Lipopolysaccharide administration for a mouse model of cerebellar ataxia with neuroinflammation

Most cerebellar ataxias (CAs) are incurable neurological disorders, resulting in a lack of voluntary control by inflamed or damaged cerebellum. Although CA can be either directly or indirectly related to cerebellar inflammation, there is no suitable animal model of CA with neuroinflammation. In this study, we evaluated the utility of an intracerebellar injection of lipopolysaccharide (LPS) to generate an animal model of inflammatory CA. We observed that LPS administration induced the expression of pro-inflammatory molecules following activation of glial cells. In addition, the administration of LPS resulted in apoptotic Purkinje cell death and induced abnormal locomotor activities, such as impaired motor coordination and abnormal hindlimb clasping posture. Our results suggest that intracerebellar LPS administration in experimental animals may be useful for studying the inflammatory component of CA.

Gene Deregulation and Underlying Mechanisms in Spinocerebellar Ataxias With Polyglutamine Expansion

Polyglutamine spinocerebellar ataxias (polyQ SCAs) include SCA1, SCA2, SCA3, SCA6, SCA7, and SCA17 and constitute a group of adult onset neurodegenerative disorders caused by the expansion of a CAG repeat sequence located within the coding region of specific genes, which translates into polyglutamine tract in the corresponding proteins. PolyQ SCAs are characterized by degeneration of the cerebellum and its associated structures and lead to progressive ataxia and other diverse symptoms. In recent years, gene and epigenetic deregulations have been shown to play a critical role in the pathogenesis of polyQ SCAs. Here, we provide an overview of the functions of wild type and pathogenic polyQ SCA proteins in gene regulation, describe the extent and nature of gene expression changes and their pathological consequences in diseases, and discuss potential avenues to further investigate converging and distinct disease pathways and to develop therapeutic strategies.

Cerebellar Astrocytes: Much More Than Passive Bystanders In Ataxia Pathophysiology

Ataxia is a neurodegenerative syndrome, which can emerge as a major element of a disease or represent a symptom of more complex multisystemic disorders. It comprises several forms with a highly variegated etiology, mainly united by motor, balance, and speech impairments and, at the tissue level, by cerebellar atrophy and Purkinje cells degeneration. For this reason, the contribution of astrocytes to this disease has been largely overlooked in the past. Nevertheless, in the last few decades, growing evidences are pointing to cerebellar astrocytes as crucial players not only in the progression but also in the onset of distinct forms of ataxia. Although the current knowledge on this topic is very fragmentary and ataxia type-specific, the present review will attempt to provide a comprehensive view of astrocytes’ involvement across the distinct forms of this pathology. Here, it will be highlighted how, through consecutive stage-specific mechanisms, astrocytes can lead to non-cell autonomous neurodegeneration and, consequently, to the behavioral impairments typical of this disease. In light of that, treating astrocytes to heal neurons will be discussed as a potential complementary therapeutic approach for ataxic patients, a crucial point provided the absence of conclusive treatments for this disease.

Increased Neuroprotective Microglia and Photoreceptor Survival in the Retina from a Peptide Inhibitor of Myeloid Differentiation Factor 88 (MyD88)

Myeloid differentiation factor 88 (MyD88) is an adaptor protein for the Toll-like receptor (TLR) and interleukin 1 receptor (IL-1R) families of innate immunity receptors that mediate inflammatory responses to cellular injury. TLR/IL1R/MyD88 signaling is known to contribute to retinal degeneration, although how MyD88 regulates neuronal survival, and the effect of MyD88 on the inflammatory environment in the retina, is mostly unknown. In this study, we tested the hypothesis that blocking MyD88-mediated signaling early in retinal degeneration promotes transition of microglia towards a neuroprotective anti-inflammatory phenotype, resulting in enhanced photoreceptor survival. We also tested whether systemic delivery of a pharmacologic MyD88 inhibitor has therapeutic potential. The rd10 mouse model of retinal degeneration was injected intraperitoneally with increasing doses of a MyD88 blocking peptide or control peptide early in degeneration, and inflammatory responses and photoreceptor survival were measured at specific time points using flow cytometry, cytokine profiling, and electroretinograms. Our results demonstrated that rd10 mice injected with a low dose of MyD88 inhibitor peptide showed increased rod photoreceptor function and reduced apoptosis compared with control peptide and uninjected mice. MyD88 inhibition also resulted in fewer microglia/macrophage cells in the photoreceptor layer whereas total peripheral and retinal macrophage were not changed. Furthermore, increased number of cells expressing the Arg1 marker of neuroprotective microglia in the photoreceptor layer and higher MCP-1 and anti-inflammatory cytokine IL-27 were associated with photoreceptor survival. Therefore, these data suggest that the MyD88 inhibitor modified the retina environment to become less inflammatory, leading to improved photoreceptor function and survival.

Non-self mutation: double-stranded RNA elicits antiviral pathogenic response in a Drosophila model of expanded CAG repeat neurodegenerative diseases

Inflammation is activated prior to symptoms in neurodegenerative diseases, providing a plausible pathogenic mechanism. Indeed, genetic and pharmacological ablation studies in animal models of several neurodegenerative diseases demonstrate that inflammation is required for pathology. However, while there is growing evidence that inflammation-mediated pathology may be the common mechanism underlying neurodegenerative diseases, including those due to dominantly inherited expanded repeats, the proximal causal agent is unknown. Expanded CAG.CUG repeat double-stranded RNA causes inflammation-mediated pathology when expressed in Drosophila. Repeat dsRNA is recognized by Dicer-2 as a foreign or ‘non-self’ molecule triggering both antiviral RNA and RNAi pathways. Neither of the RNAi pathway cofactors R2D2 nor loquacious are necessary, indicating antiviral RNA activation. RNA modification enables avoidance of recognition as ‘non-self’ by the innate inflammatory surveillance system. Human ADAR1 edits RNA conferring ‘self’ status and when co-expressed with expanded CAG.CUG dsRNA in Drosophila the pathology is lost. Cricket Paralysis Virus protein CrPV-1A is a known antagonist of Argonaute-2 in Drosophila antiviral defense. CrPV-1A co-expression also rescues pathogenesis, confirming anti-viral-RNA response. Repeat expansion mutation therefore confers ‘non-self’ recognition of endogenous RNA, thereby providing a proximal, autoinflammatory trigger for expanded repeat neurodegenerative diseases.

Role of Microglia in Ataxias

Microglia, the resident macrophages of the central nervous system, critically influence neural function during development and in adulthood. Microglia are also profoundly sensitive to insults to the brain to which they respond with process of activation that includes spectrum of changes in morphology, function, and gene expression. Ataxias are a class of neurodegenerative diseases characterized by motor discoordination and predominant cerebellar involvement. In case of inherited forms of ataxia, mutant proteins are expressed throughout the brain and it is unclear why cerebellum is particularly vulnerable. Recent studies demonstrated that cerebellar microglia have a uniquely hyper-vigilant immune phenotype compared to microglia from other brain regions. These findings may indicate that microglia actively contribute to cerebellar vulnerability in ataxias. Here we review current knowledge about cerebellar microglia, their activation, and their role in the pathogenesis of ataxias. In addition, we briefly review advantages and disadvantages of several experimental approaches available to study microglia.

Inhibition of MyD88 Signaling Skews Microglia/Macrophage Polarization and Attenuates Neuronal Apoptosis in the Hippocampus After Status Epilepticus in Mice

Inflammation is implicated in epileptogenesis. Activated microglia and macrophages (MG/MΦ) are found in the brains of patients with epilepsy-related diseases and animal models of epilepsy. It is not yet known how the MG/MΦ activation phenotype affects pathological changes in the brain after a single seizure. In this study, we had 2 main purposes: first, to characterize post-status epilepticus (SE) inflammation by tracking MG/MΦ polarization, and, second, to explore the role of an innate immune receptor adaptor protein, namely, myeloid differentiation primary response gene 88 (MyD88), in the induction of SE in a mouse model. A lithium-pilocarpine model of seizure conditions was generated in C57BL/6 mice. The intensity and distribution of MG/MΦ polarization were tracked by fluorescent immunohistochemistry and Western blotting for the polarization markers inducible nitrogen oxygenized synthase, arginase-1, CD163, and mannose receptor. We observed steadily increasing M1 MG/MΦ along with MyD88 signal upregulation after SE in the hippocampi of mice, whereas the M2 marker arginase-1 was localized mainly in astrocytes rather than in MG/MΦ. Inhibition or gene knockout of MyD88 reduced M1 MG/MΦ and gliosis although increasing M2 MG/MΦ in the hippocampi of SE mice. MyD88 inhibition also augmented glutamate transporter 1 expression and reduced N-methyl-D-aspartate receptor NR1 subunit expression in the hippocampus to protect pyramidal neurons from apoptosis. These data suggest that MG/MΦ polarization after SE impacts the pathological outcome of the hippocampus via MyD88 signaling and point to MyD88 as a potential neuroprotective target for epilepsy therapy.

Neurodegenerative diseases have genetic hallmarks of autoinflammatory disease

The notion that one common pathogenic pathway could account for the various clinically distinguishable, typically late-onset neurodegenerative diseases might appear unlikely given the plethora of diverse primary causes of neurodegeneration. On the contrary, an autoinflammatory pathogenic mechanism allows diverse genetic and environmental factors to converge into a common chain of causality. Inflammation has long been known to correlate with neurodegeneration. Until recently this relationship was seen as one of consequence rather than cause-with inflammatory cells and events acting to 'clean up the mess' after neurological injury. This explanation is demonstrably inadequate and it is now clear that inflammation is at the very least, rate-limiting for neurodegeneration (and more likely, a principal underlying cause in most if not all neurodegenerative diseases), protective in its initial acute phase, but pernicious in its latter chronic phase.

Early alteration of epigenetic-related transcription in Huntington's disease mouse models

Transcriptional dysregulation in Huntington’s disease (HD) affects the expression of genes involved in survival and neuronal functions throughout the progression of the pathology. In recent years, extensive research has focused on epigenetic and chromatin-modifying factors as a causative explanation for such dysregulation, offering attractive targets for pharmacological therapies. In this work, we extensively examined the gene expression profiles in the cortex, striatum, hippocampus and cerebellum of juvenile R6/1 and N171-82Q mice, models of rapidly progressive HD, to retrieve the early transcriptional signatures associated with this pathology. These profiles were largely consistent across HD datasets, contained tissular and neuronal-specific genes and showed significant correspondence with the transcriptional changes in mouse strains deficient for epigenetic regulatory genes. The most prominent cases were the conditional knockout of the lysine acetyltransferase CBP in post-mitotic forebrain neurons, the double knockout of the histone methyltransferases Ezh1 and Ezh2, components of the polycomb repressor complex 2 (PRC2), and the conditional mutants of the histone methyltransferases G9a (Ehmt2) and GLP (Ehmt1). Based on these observations, we propose that the neuronal epigenetic status is compromised in the prodromal stages of HD, leading to an altered transcriptional programme that is prominently involved in neuronal identity.

Paradigm for disease deconvolution in rare neurodegenerative disorders in Indian population: insights from studies in cerebellar ataxias

Cerebellar ataxias are a group of rare progressive neurodegenerative disorders with an average prevalence ranges from 4.8 to 13.8 in 100,000 individuals. The inherited disorders affect multiple members of the families, or a community that is endogamous or consanguineous. Presence of more than 3000 mutations in different genes with overlapping clinical symptoms, genetic anticipation and pleiotropy, as well as incomplete penetrance and variable expressivity due to modifiers pose challenges in genotype-phenotype correlation. Development of a diagnostic algorithm could reduce the time as well as cost in clinicogenetic diagnostics and also help in reducing the economic and social burden of the disease. In a unique research collaboration spanning over 20 years, we have been able to develop a paradigm for studying cerebellar ataxias in the Indian population which would also be relevant in other rare diseases. This has involved clinical and genetic analysis of thousands of families from diverse Indian populations. The extensive resource on ataxia has led to the development of a clinicogenetic algorithm for cost-effective screening of ataxia and a unique ataxia clinic in the tertiary referral centre in All India Institute of Medical Sciences. Utilizing a population polymorphism scanning approach, we have been able to dissect the mechanisms of repeat instability and expansion in many ataxias, and also identify founders, and trace the mutational histories in the Indian population. This provides information for genetic testing of at-risk as well as protected individuals and populations. To dissect uncharacterized cases which comprises more than 50% of the cases, we have explored the potential of next-generation sequencing technologies coupled with the extensive resource of baseline data generated in-house and other public domains. We have also developed a repository of patient-derived peripheral blood mononuclear cells, lymphoblastoid cell lines and neuronal lineages (derived from iPSCs) for ascribing functionality to novel genes/mutations. Through integrating these technologies, novel genes have been identified that has broadened the diagnostic panel, increased the diagnostic yield to over 75%, helped in ascribing pathogenicity to novel mutations and enabled understanding of disease mechanisms. It has also provided a platform for testing novel molecules for amelioration of pathophysiological phenotypes. This review through a perspective on CAs suggests a generic paradigm fromdiagnostics to therapeutic interventions for rare disorders in the context of heterogeneous Indian populations.

Alternative splicing in the C-terminal tail of Cav2.1 is essential for preventing a neurological disease in mice

Alternative splicing (AS) that occurs at the final coding exon (exon 47) of the Cav2.1 voltage-gated calcium channel (VGCC) gene produces two major isoforms in the brain, MPI and MPc. These isoforms differ in their splice acceptor sites; human MPI is translated into a polyglutamine tract associated with spinocerebellar ataxia type 6 (SCA6), whereas MPc splices to an immediate stop codon, resulting in a shorter cytoplasmic tail. To gain insight into the functional role of the AS in vivo and whether modulating the splice patterns at this locus can be a potential therapeutic strategy for SCA6, here we created knockin mice that exclusively express MPc by inserting the splice-site mutation. The resultant Cacna1aCtmKO/CtmKO mice developed non-progressive neurological phenotypes, featuring early-onset ataxia and absence seizure without significant alterations in the basic properties of the channel. Interactions of Cav2.1 with Cavβ4 and Rimbp2 were significantly reduced while those with GABAB2 were enhanced in the cerebellum of Cacna1aCtmKO/CtmKO mice. Treatment with the GABAB antagonist CGP35348 partially rescued the motor impairments seen in Cacna1aCtmKO/CtmKO mice. These results suggest that the carboxyl-terminal domain of Cav2.1 is not essential for maintaining the basic properties of the channel in the cerebellar Purkinje neurons but is involved in multiple interactions of Cav2.1 with other proteins, and plays an essential role in preventing a complex neurological disease.

Early strong intrathecal inflammation in cerebellar type multiple system atrophy by cerebrospinal fluid cytokine/chemokine profiles: a case control study

BACKGROUND

The pathology of multiple system atrophy cerebellar-type (MSA-C) includes glial inflammation; however, cerebrospinal fluid (CSF) inflammatory cytokine profiles have not been investigated. In this study, we determined CSF cytokine/chemokine/growth factor profiles in MSA-C and compared them with those in hereditary spinocerebellar ataxia (SCA).

METHODS

We collected clinical data and CSF from 20 MSA-C patients, 12 hereditary SCA patients, and 15 patients with other non-inflammatory neurological diseases (OND), and measured 27 cytokines/chemokines/growth factors using a multiplexed fluorescent bead-based immunoassay. The size of each part of the hindbrain and hot cross bun sign (HCBS) in the pons was studied by magnetic resonance imaging.

RESULTS

Granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-6, IL-7, IL-12, and IL-13 levels were significantly higher in MSA-C and SCA compared with OND. In MSA-C, IL-5, IL-6, IL-9, IL-12, IL-13, platelet-derived growth factor-bb, macrophage inflammatory protein (MIP)-1α, and GM-CSF levels positively correlated with anteroposterior diameters of the pontine base, vermis, or medulla oblongata. By contrast, in SCA patients, IL-12 and MIP-1α showed significant negative correlations with anteroposterior diameters of the pontine base, and unlike MSA-C, there was no cytokine with a positive correlation in SCA. IL-6 was significantly higher in MSA-C patients with the lowest grade of HCBS compared with those with the highest grade. Macrophage chemoattractant protein-1 (MCP-1) had a significant negative correlation with disease duration only in MSA-C patients. Tumor necrosis factor-alpha, IL-2, IL-15, IL-4, IL-5, IL-10, and IL-8 were all significantly lower in MSA-C and SCA compared with OND, while IL-1ra, an anti-inflammatory cytokine, was elevated only in MSA-C. IL-1β and IL-8 had positive correlations with Unified Multiple System Atrophy Rating Scale part 1 and 2, respectively, in MSA-C.

CONCLUSIONS

Although CSF cytokine/chemokine/growth factor profiles were similar between MSA-C and SCA, pro-inflammatory cytokines, such as IL-6, GM-CSF, and MCP-1, correlated with the disease stage in a way higher at the beginning only in MSA-C, reflecting early stronger intrathecal inflammation.

Transient IKK2 activation in astrocytes initiates selective non-cell-autonomous neurodegeneration

BACKGROUND

Neuroinflammation is associated with a wide range of neurodegenerative disorders, however the specific contribution to individual disease pathogenesis and selective neuronal cell death is not well understood. Inflammatory cerebellar ataxias are neurodegenerative diseases occurring in various autoimmune/inflammatory conditions, e.g. paraneoplastic syndromes. However, how inflammatory insults can cause selective cerebellar neurodegeneration in the context of these diseases remains open, and appropriate animal models are lacking. A key regulator of neuroinflammatory processes is the NF-κB signalling pathway, which is activated by the IκB kinase 2 (IKK2) in response to various pathological conditions. Importantly, its activation is sufficient to initiate neuroinflammation on its own.

METHODS

To investigate the contribution of IKK/NF-κB-mediated neuroinflammation to neurodegeneration, we established conditional mouse models of cerebellar neuroinflammation, which depend either on the tetracycline-regulated expression of IKK2 in astrocytes or Cre-recombination based IKK2 activation in Bergmann glia.

RESULTS

We demonstrate that IKK2 activation for a limited time interval in astrocytes is sufficient to induce neuroinflammation, astrogliosis and loss of Purkinje neurons, resembling the pathogenesis of inflammatory cerebellar ataxias. We identified IKK2-driven irreversible dysfunction of Bergmann glia as critical pathogenic event resulting in Purkinje cell loss. This was independent of Lipocalin 2, an acute phase protein secreted by reactive astrocytes and well known to mediate neurotoxicity. Instead, downregulation of the glutamate transporters EAAT1 and EAAT2 and ultrastructural alterations suggest an excitotoxic mechanism of Purkinje cell degeneration.

CONCLUSIONS

Our results suggest a novel pathogenic mechanism how diverse inflammatory insults can cause inflammation/autoimmune-associated cerebellar ataxias. Disease-mediated elevation of danger signals like TLR ligands and inflammatory cytokines in the cerebellum activates IKK2/NF-κB signalling in astrocytes, which as a consequence triggers astrogliosis-like activation of Bergmann glia and subsequent non-cell-autonomous Purkinje cell degeneration. Notably, the identified hit and run mechanism indicates only an early window for therapeutic interventions.

The Enemy within: Innate Surveillance-Mediated Cell Death, the Common Mechanism of Neurodegenerative Disease

Neurodegenerative diseases comprise an array of progressive neurological disorders all characterized by the selective death of neurons in the central nervous system. Although, rare (familial) and common (sporadic) forms can occur for the same disease, it is unclear whether this reflects several distinct pathogenic pathways or the convergence of different causes into a common form of nerve cell death. Remarkably, neurodegenerative diseases are increasingly found to be accompanied by activation of the innate immune surveillance system normally associated with pathogen recognition and response. Innate surveillance is the cell's quality control system for the purpose of detecting such danger signals and responding in an appropriate manner. Innate surveillance is an "intelligent system," in that the manner of response is relevant to the magnitude and duration of the threat. If possible, the threat is dealt with within the cell in which it is detected, by degrading the danger signal(s) and restoring homeostasis. If this is not successful then an inflammatory response is instigated that is aimed at restricting the spread of the threat by elevating degradative pathways, sensitizing neighboring cells, and recruiting specialized cell types to the site. If the danger signal persists, then the ultimate response can include not only the programmed cell death of the original cell, but the contents of this dead cell can also bring about the death of adjacent sensitized cells. These responses are clearly aimed at destroying the ability of the detected pathogen to propagate and spread. Innate surveillance comprises intracellular, extracellular, non-cell autonomous and systemic processes. Recent studies have revealed how multiple steps in these processes involve proteins that, through their mutation, have been linked to many familial forms of neurodegenerative disease. This suggests that individuals harboring these mutations may have an amplified response to innate-mediated damage in neural tissues, and renders innate surveillance mediated cell death a plausible common pathogenic pathway responsible for neurodegenerative diseases, in both familial and sporadic forms. Here we have assembled evidence in favor of the hypothesis that neurodegenerative disease is the cumulative result of chronic activation of the innate surveillance pathway, triggered by endogenous or environmental danger or damage associated molecular patterns in a progressively expanding cascade of inflammation, tissue damage and cell death.