Prevention of axonal injury using calpain inhibitor in chronic progressive experimental autoimmune encephalomyelitis

Altered Expression of Ion Channels in White Matter Lesions of Progressive Multiple Sclerosis: What Do We Know About Their Function?

Despite significant advances in our understanding of the pathophysiology of multiple sclerosis (MS), knowledge about contribution of individual ion channels to axonal impairment and remyelination failure in progressive MS remains incomplete. Ion channel families play a fundamental role in maintaining white matter (WM) integrity and in regulating WM activities in axons, interstitial neurons, glia, and vascular cells. Recently, transcriptomic studies have considerably increased insight into the gene expression changes that occur in diverse WM lesions and the gene expression fingerprint of specific WM cells associated with secondary progressive MS. Here, we review the ion channel genes encoding K⁺, Ca²⁺, Na⁺, and Cl^- channels; ryanodine receptors; TRP channels; and others that are significantly and uniquely dysregulated in active, chronic active, inactive, remyelinating WM lesions, and normal-appearing WM of secondary progressive MS brain, based on recently published bulk and single-nuclei RNA-sequencing datasets. We discuss the current state of knowledge about the corresponding ion channels and their implication in the MS brain or in experimental models of MS. This comprehensive review suggests that the intense upregulation of voltage-gated Na⁺ channel genes in WM lesions with ongoing tissue damage may reflect the imbalance of Na⁺ homeostasis that is observed in progressive MS brain, while the upregulation of a large number of voltage-gated K⁺ channel genes may be linked to a protective response to limit neuronal excitability. In addition, the altered chloride homeostasis, revealed by the significant downregulation of voltage-gated Cl^- channels in MS lesions, may contribute to an altered inhibitory neurotransmission and increased excitability.

Neuron-Oligodendrocyte Interactions in the Structure and Integrity of Axons

The myelination of axons by oligodendrocytes is a highly complex cell-to-cell interaction. Oligodendrocytes and axons have a reciprocal signaling relationship in which oligodendrocytes receive cues from axons that direct their myelination, and oligodendrocytes subsequently shape axonal structure and conduction. Oligodendrocytes are necessary for the maturation of excitatory domains on the axon including nodes of Ranvier, help buffer potassium, and support neuronal energy metabolism. Disruption of the oligodendrocyte-axon unit in traumatic injuries, Alzheimer's disease and demyelinating diseases such as multiple sclerosis results in axonal dysfunction and can culminate in neurodegeneration. In this review, we discuss the mechanisms by which demyelination and loss of oligodendrocytes compromise axons. We highlight the intra-axonal cascades initiated by demyelination that can result in irreversible axonal damage. Both the restoration of oligodendrocyte myelination or neuroprotective therapies targeting these intra-axonal cascades are likely to have therapeutic potential in disorders in which oligodendrocyte support of axons is disrupted.

The Role of Calpain and Proteasomes in the Degradation of Carbonylated Neuronal Cytoskeletal Proteins in Acute Experimental Autoimmune Encephalomyelitis

The present study was designed to investigate the role of calpain and the proteasome in the removal of oxidized neuronal cytoskeletal proteins in myelin basic protein-induced experimental autoimmune encephalomyelitis (EAE). To this end, EAE rats received a single intrathecal injection of calpeptin or epoxomicin at the first sign of clinical disease. Forty-eight hours later, animals were sacrificed and lumbar spinal cord segments were dissected and used for biochemical analyses. The results show that calpain and proteasome activity is specifically, but partially, inhibited with calpeptin and epoxomicin, respectively. Calpain inhibition causes an increase in total protein carbonylation and in the amount of neurofilament proteins (NFPs), β-tubulin and β-actin that were spared from degradation, but no changes are seen in the oxidation of any of three NFPs. By contrast, proteasome inhibition has no effect on total protein carbonylation or cytoskeletal protein degradation but increases the amount of oxidized NFH and NFM. These results suggest that while the proteasome may contribute to removal of oxidized NFPs, calpain is the main protease involved in degradation of neuronal cytoskeleton and does not preferentially targets oxidized NFPs species in acute EAE. Different results were obtained in a cell-free system, where calpain inhibition rises the amount of oxidized NFH, and proteasome inhibition fails to change the oxidation state of the NFPs. The later finding suggests that the preferential degradation of oxidized NFH and NFM in vivo by the proteasome occurs via the 26S and not the 20S particle.

Stem Cells as Potential Targets of Polyphenols in Multiple Sclerosis and Alzheimer's Disease

Alzheimer's disease (AD) and multiple sclerosis are major neurodegenerative diseases, which are characterized by the accumulation of abnormal pathogenic proteins due to oxidative stress, mitochondrial dysfunction, impaired autophagy, and pathogens, leading to neurodegeneration and behavioral deficits. Herein, we reviewed the utility of plant polyphenols in regulating proliferation and differentiation of stem cells for inducing brain self-repair in AD and multiple sclerosis. Firstly, we discussed the genetic, physiological, and environmental factors involved in the pathophysiology of both the disorders. Next, we reviewed various stem cell therapies available and how they have proved useful in animal models of AD and multiple sclerosis. Lastly, we discussed how polyphenols utilize the potential of stem cells, either complementing their therapeutic effects or stimulating endogenous and exogenous neurogenesis, against these diseases. We suggest that polyphenols could be a potential candidate for stem cell therapy against neurodegenerative disorders.

Regulation and dysregulation of axon infrastructure by myelinating glia

Pan and Chan discuss the role of myelinating glia in axonal development and the impact of demyelination on axon degeneration.

Axon loss and neurodegeneration constitute clinically debilitating sequelae in demyelinating diseases such as multiple sclerosis, but the underlying mechanisms of secondary degeneration are not well understood. Myelinating glia play a fundamental role in promoting the maturation of the axon cytoskeleton, regulating axon trafficking parameters, and imposing architectural rearrangements such as the nodes of Ranvier and their associated molecular domains. In the setting of demyelination, these changes may be reversed or persist as maladaptive features, leading to axon degeneration. In this review, we consider recent insights into axon–glial interactions during development and disease to propose that disruption of the cytoskeleton, nodal architecture, and other components of axon infrastructure is a potential mediator of pathophysiological damage after demyelination.

Alterations of Caspr2 and Nav1.6 on myelinated axon damage in a rat model of chronic cerebral hypoperfusion

Myelinated axons require the correct localization of key proteins that are essential for nerve conduction and cognitive function. Little is known regarding the altered expression of contactin-associated protein 2 (Caspr2) at the juxtaparanodal regions and Nav1.6 at the node of Ranvier in response to chronic cerebral hypoperfusion (CCH). The aim of the present study was to examine the alterations in the key protein of myelinated axons and the potential mechanisms that may follow CCH. We established a rat model of CCH by controllable partial narrowing of bilateral common carotid arteries. Then, we detected cerebral blood flow (CBF) after surgery. We also evaluated motor-evoked potentials (MEPs), assessed the Morris water maze test, analyzed Caspr2 expression through immunohistochemistry and Nav1.6 protein expression through western blot analysis at 2, 4 and 12 weeks. The results revealed that the mean CBF value was significantly decreased to 33.90±5.48%. The MEP latencies and the escaping latencies were significantly prolonged. There was also an elongation of the first time passing of the hidden platform with a reduction of crossing platform times in spatial probing. Furthermore, the Caspr2 immunoreactivity demonstrated that the Caspr2 level was significantly downregulated with abnormal locations in the corpus callosum. The western blot analysis of Nav1.6 protein revealed that the level was reduced significantly over time. The results demonstrate that CCH leads to central conductive function loss, cognitive function damage and alterations in the key protein of myelinated axons, which may provide a molecular basis and key link for white matter damage.

Calpain research for drug discovery: challenges and potential

Calpains are a family of proteases that were scientifically recognized earlier than proteasomes and caspases, but remain enigmatic. However, they are known to participate in a multitude of physiological and pathological processes, performing 'limited proteolysis' whereby they do not destroy but rather modulate the functions of their substrates. Calpains are therefore referred to as 'modulator proteases'. Multidisciplinary research on calpains has begun to elucidate their involvement in pathophysiological mechanisms. Therapeutic strategies targeting malfunctions of calpains have been developed, driven primarily by improvements in the specificity and bioavailability of calpain inhibitors. Here, we review the calpain superfamily and calpain-related disorders, and discuss emerging calpain-targeted therapeutic strategies.

Further understanding of the immunopathology of multiple sclerosis: impact on future treatments

INTRODUCTION

The understanding of the immunopathogenesis of multiple sclerosis (MS) has expanded with more research into T-cell subtypes, cytokine contributors, B-cell participation, mitochondrial dysfunction, and more. Treatment options have rapidly expanded with three relatively recent oral therapy alternatives entering the arena.

AREAS COVERED

In the following review, we discuss current mechanisms of immune dysregulation in MS, how they relate to current treatments, and the impact these findings will have on the future of therapy. Expert commentary: The efficacy of these medications and understanding their mechanisms of actions validates the immunopathogenic mechanisms thought to underlie MS. Further research has exposed new targets, while new promising therapies have shed light on new aspects into the pathophysiology of MS.

Axonal degeneration in multiple sclerosis: can we predict and prevent permanent disability?

Axonal degeneration is a major determinant of permanent neurological impairment during multiple sclerosis (MS). Due to the variable course of clinical disease and the heterogeneity of MS lesions, the mechanisms governing axonal degeneration may differ between disease stages. While the etiology of MS remains elusive, there now exist potential prognostic biomarkers that can predict the conversion to clinically definite MS. Specialized imaging techniques identifying axonal injury and drop-out are becoming established in clinical practice as a predictive measure of MS progression, such as optical coherence tomography (OCT) or diffusion tensor imaging (DTI). However, these imaging techniques are still being debated as predictive biomarkers since controversy surrounds their lesion-specific association with expanded disability status scale (EDSS). A more promising diagnostic measure of axonal degeneration has been argued for the detection of reduced N-acetyl aspartate (NAA) and Creatine ratios via magnetic resonance spectroscopic (MRS) imaging, but again fail with its specificity for predicting actual axonal degeneration. Greater accuracy of predictive biomarkers is therefore warranted and may include CSF neurofilament light chain (NF-L) and neurofilament heavy chain (NF-H) levels, for progressive MS. Furthermore, defining the molecular mechanisms that occur during the neurodegenerative changes in the various subgroups of MS may in fact prove vital for the future development of efficacious neuroprotective therapies. The clinical translation of a combined Na⁺ and Ca²⁺ channel blocker may lead to the establishment of a bona fide neuroprotective agent for the treatment of progressive MS. However, more specific therapeutic targets to limit axonal damage in MS need investigation and may include such integral axonal proteins such as the collapsin response mediator protein-2 (CRMP-2), a molecule which upon post-translational modification may propagate axonal degeneration in MS. In this review, we discuss the current clinical determinants of axonal damage in MS and consider the cellular and molecular mechanisms that may initiate these neurodegenerative changes. In particular we highlight the therapeutic candidates that may formulate novel therapeutic strategies to limit axonal degeneration and EDSS during progressive MS.

Acquired channelopathies as contributors to development and progression of multiple sclerosis

Multiple sclerosis (MS), the most frequent inflammatory disease of the central nervous system (CNS), affects about two and a half million individuals worldwide and causes major burdens to the patients, which develop the disease usually at the age of 20 to 40. MS is likely referable to a breakdown of immune cell tolerance to CNS self-antigens resulting in focal immune cell infiltration, activation of microglia and astrocytes, demyelination and axonal and neuronal loss. Here we discuss how altered expression patterns and dysregulated functions of ion channels contribute on a molecular level to nearly all pathophysiological steps of the disease. In particular the detrimental redistribution of ion channels along axons, as well as neuronal excitotoxicity with regard to imbalanced glutamate homeostasis during chronic CNS inflammation will be discussed in detail. Together, we describe which ion channels in the immune and nervous system commend as attractive future drugable targets in MS treatment.

Mechanisms of neurodegeneration and axonal dysfunction in multiple sclerosis

Multiple sclerosis (MS) is the most frequent chronic inflammatory disease of the CNS, and imposes major burdens on young lives. Great progress has been made in understanding and moderating the acute inflammatory components of MS, but the pathophysiological mechanisms of the concomitant neurodegeneration--which causes irreversible disability--are still not understood. Chronic inflammatory processes that continuously disturb neuroaxonal homeostasis drive neurodegeneration, so the clinical outcome probably depends on the balance of stressor load (inflammation) and any remaining capacity for neuronal self-protection. Hence, suitable drugs that promote the latter state are sorely needed. With the aim of identifying potential novel therapeutic targets in MS, we review research on the pathological mechanisms of neuroaxonal dysfunction and injury, such as altered ion channel activity, and the endogenous neuroprotective pathways that counteract oxidative stress and mitochondrial dysfunction. We focus on mechanisms inherent to neurons and their axons, which are separable from those acting on inflammatory responses and might, therefore, represent bona fide neuroprotective drug targets with the capability to halt MS progression.

Effects of a novel orally administered calpain inhibitor SNJ-1945 on immunomodulation and neurodegeneration in a murine model of multiple sclerosis

Multiple sclerosis (MS) pathology is marked by the massive infiltration of myelin-specific T cells into the CNS. Hallmarks of T helper (Th) cells during active disease are pro-inflammatory Th1/Th17 cells that predominate over immunoregulatory Th2/Treg cells. Neurodegeneration, a major factor in progressive MS, is often overlooked when considering drug prescription. Here, we show that oral dosing with SNJ-1945, a novel water-soluble calpain inhibitor, reduces experimental autoimmune encephalomyelitis clinical scores in vivo and has a two pronged effect via anti-inflammation and protection against neurodegeneration. We also show that SNJ-1945 treatment down-regulates Th1/Th17 inflammatory responses, and promotes regulatory T cells (Tregs) and myeloid-derived suppressor cells in vivo, which are known to have the capacity to suppress helper as well as cytotoxic T cell functions. Through analysis of spinal cord samples, we show a reduction in calpain expression, decreased infiltration of inflammatory cells, and signs of inhibition of neurodegeneration. We also show a marked reduction in neuronal cell death in spinal cord (SC) sections. These results suggest that calpain inhibition attenuates experimental autoimmune encephalomyelitis pathology by reducing both inflammation and neurodegeneration, and could be used in clinical settings to augment the efficacy of standard immunomodulatory agents used to treat MS. Multiple sclerosis (MS) pathology is marked by inflammation and infiltration of myelin-specific T cells into the central nervous system. Inflammation leads to neurodegeneration in progressive MS which also leads to epitope spreading, feedback looping to more inflammation. Calpain can play a role in both arms of the disease. Here, oral dosing with SNJ-1945, a novel water-soluble calpain inhibitor, reduces experimental autoimmune encephalomyelitis clinical scores in vivo and has a two-pronged effect via anti-inflammation and protection against neurodegeneration.

Neuroprotection in multiple sclerosis: a therapeutic approach

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system that is pathologically characterized by inflammatory demyelination and neurodegeneration. Axonal damage, along with neuronal loss, occurs from disease onset and may lead to progressive and permanent disability. In contrast with the inflammatory pathways, the molecular mechanisms leading to MS neurodegeneration remain largely elusive. With improved understanding of these mechanisms, new potential therapeutic targets for neuroprotection have emerged. We review the current understanding of neurodegenerative processes at play in MS and discuss potential outcome measures and targets for neuroprotection trials.

Myelin recovery in multiple sclerosis: the challenge of remyelination

Multiple sclerosis (MS) is the most common demyelinating and an autoimmune disease of the central nervous system characterized by immune-mediated myelin and axonal damage, and chronic axonal loss attributable to the absence of myelin sheaths. T cell subsets (Th1, Th2, Th17, CD8⁺, NKT, CD4⁺CD25⁺ T regulatory cells) and B cells are involved in this disorder, thus new MS therapies seek damage prevention by resetting multiple components of the immune system. The currently approved therapies are immunoregulatory and reduce the number and rate of lesion formation but are only partially effective. This review summarizes current understanding of the processes at issue: myelination, demyelination and remyelination—with emphasis upon myelin composition/architecture and oligodendrocyte maturation and differentiation. The translational options target oligodendrocyte protection and myelin repair in animal models and assess their relevance in human. Remyelination may be enhanced by signals that promote myelin formation and repair. The crucial question of why remyelination fails is approached is several ways by examining the role in remyelination of available MS medications and avenues being actively pursued to promote remyelination including: (i) cytokine-based immune-intervention (targeting calpain inhibition), (ii) antigen-based immunomodulation (targeting glycolipid-reactive iNKT cells and sphingoid mediated inflammation) and (iii) recombinant monoclonal antibodies-induced remyelination.

Oligodendroglia and neurotrophic factors in neurodegeneration

Myelination by oligodendroglial cells (OLs) enables the propagation of action potentials along neuronal axons, which is essential for rapid information flow in the central nervous system. Besides saltatory conduction, the myelin sheath also protects axons against inflammatory and oxidative insults. Loss of myelin results in axonal damage and ultimately neuronal loss in demyelinating disorders. However, accumulating evidence indicates that OLs also provide support to neurons via mechanisms beyond the insulating function of myelin. More importantly, an increasing volume of reports indicates defects of OLs in numerous neurodegenerative diseases, sometimes even preceding neuronal loss in pre-symptomatic episodes, suggesting that OL pathology may be an important mechanism contributing to the initiation and/or progression of neurodegeneration. This review focuses on the emerging picture of neuronal support by OLs in the pathogenesis of neurodegenerative disorders through diverse molecular and cellular mechanisms, including direct neuron-myelin interaction, metabolic support by OLs, and neurotrophic factors produced by and/or acting on OLs.

Immunization with a peptide of Semliki Forest virus promotes remyelination in experimental autoimmune encephalomyelitis

Remyelination is one of the elusive topics in treatment of multiple sclerosis (MS). Our previous studies have shown that Semliki Forest virus (SFV)-infected δ-knock-out (KO) mice did not exhibit the extensive remyelination, seen in wild type (WT) B6 mice, after viral clearance and demyelination. The Remyelination in SFV-infected WT mice started on day 15 and was completed by day 35 post-infection (pi), whereas the KO mice remained partially demyelinated through day 42 pi. Treatment with E2 peptide2 in incomplete Freund's adjuvant (IFA), resulted in higher antibody production and earlier remyelination in SFV-infected KO (day 28 pi), than WT mice. This finding suggested that anti-E2 peptide2 antibody could play a part in remyelination. In the current study, the effect of E2 peptide2 treatment was evaluated in the experimental autoimmune encephalomyelitis (EAE) model. Mice with established EAE were treated with E2 peptide2 in IFA to develop antibody. Treated EAE mice made significantly higher anti-E2 peptide2 antibody than untreated EAE group. Average clinical disease scores were significantly lower in peptide treated compared to untreated EAE mice. Furthermore, histopathological and immunohistochemical studies demonstrated increased remyelinating areas and higher number of activated oligodendrocytes and astrocytes, in treated compared to untreated EAE groups. Moreover, the anti-E2 peptide2 antibody showed higher binding to the myelinated areas of treated than untreated EAE mice. We conclude that treatment with, or antibody to, SFV E2 peptide2 triggers some mechanism that promotes remyelination.

Calpastatin overexpression limits calpain-mediated proteolysis and behavioral deficits following traumatic brain injury

Traumatic brain injury (TBI) results in abrupt, initial cell damage leading to delayed neuronal death. The calcium-activated proteases, calpains, are known to contribute to this secondary neurodegenerative cascade. Although the specific inhibitor of calpains, calpastatin, is present within neurons, normal levels of calpastatin are unable to fully prevent the damaging proteolytic activity of calpains after injury. In this study, increased calpastatin expression was achieved using transgenic mice that overexpress the human calpastatin (hCAST) construct under control of a calcium-calmodulin-dependent kinase II α promoter. Naïve hCAST transgenic mice exhibited enhanced neuronal calpastatin expression and significantly reduced protease activity. Acute calpain-mediated spectrin proteolysis in the cortex and hippocampus induced by controlled cortical impact brain injury was significantly attenuated in calpastatin overexpressing mice. Aspects of posttraumatic motor and cognitive behavioral deficits were also lessened in hCAST transgenic mice compared to their wildtype littermates. However, volumetric analyses of neocortical contusion revealed no histological neuroprotection at either acute or long-term time points. Partial hippocampal neuroprotection observed at a moderate injury severity was lost after severe TBI. This study underscores the effectiveness of calpastatin overexpression in reducing calpain-mediated proteolysis and behavioral impairment after TBI, supporting the therapeutic potential for calpain inhibition. In addition, the reduction in spectrin proteolysis without accompanied neocortical neuroprotection suggests the involvement of other factors that are critical for neuronal survival after contusion brain injury.

A novel calpain inhibitor for treatment of transient retinal ischemia in the rat

After an acute ischemia/reperfusion of the rat retina, the activation of cytotoxic proteases, including calpain, results in necrosis and apoptosis of retinal ganglion cells resulting in their degeneration. Using a systemically administered calpain inhibitor that crosses the blood-retinal barrier would provide for novel systemic intervention that protects the retina from acute injury and loss of function. Herein, we study a novel calpain peptide inhibitor, cysteic-leucyl-argininal (CYLA), in an in-vivo rat model of retinal ischemia to determine functional protection using electroretinography. The CYLA prodrug was administered intraperitoneally before and/or after ischemia-reperfusion at concentrations of 20-40 mg/kg. We found that administering 20 mg/kg of CYLA only after ischemia provides significant preservation of retinal function.

Animal models of multiple sclerosis--potentials and limitations

Experimental autoimmune encephalomyelitis (EAE) is still the most widely accepted animal model of multiple sclerosis (MS). Different types of EAE have been developed in order to investigate pathogenetic, clinical and therapeutic aspects of the heterogenic human disease. Generally, investigations in EAE are more suitable for the analysis of immunogenetic elements (major histocompatibility complex restriction and candidate risk genes) and for the study of histopathological features (inflammation, demyelination and degeneration) of the disease than for screening of new treatments. Recent studies in new EAE models, especially in transgenic ones, have in connection with new analytical techniques such as microarray assays provided a deeper insight into the pathogenic cellular and molecular mechanisms of EAE and potentially of MS. For example, it was possible to better delineate the role of soluble pro-inflammatory (tumor necrosis factor-α, interferon-γ and interleukins 1, 12 and 23), anti-inflammatory (transforming growth factor-β and interleukins 4, 10, 27 and 35) and neurotrophic factors (ciliary neurotrophic factor and brain-derived neurotrophic factor). Also, the regulatory and effector functions of distinct immune cell subpopulations such as CD4+ Th1, Th2, Th3 and Th17 cells, CD4+FoxP3+ Treg cells, CD8+ Tc1 and Tc2, B cells and γδ+ T cells have been disclosed in more detail. The new insights may help to identify novel targets for the treatment of MS. However, translation of the experimental results into the clinical practice requires prudence and great caution.

Peptidyl alpha-ketoamides with nucleobases, methylpiperazine, and dimethylaminoalkyl substituents as calpain inhibitors

A series of peptidyl alpha-ketoamides with the general structure Cbz-L-Leu-D,L-AA-CONH-R were synthesized and evaluated as inhibitors for the cysteine proteases calpain I, calpain II, and cathepsin B. Nucleobases, methylpiperazine, and dimethylaminoalkyl groups were incorporated into the primed region of the inhibitors to generate compounds that potentially cross the blood-brain barrier. Two of these compounds (Cbz-Leu-D,L-Abu-CONH-(CH(2))(3)-adenin-9-yl and Cbz-Leu-D,L-Abu-CONH-(CH(2))(3)-(4-methylpiperazin-1-yl) have been shown to have useful concentrations in the brain in animals. The best inhibitor for calpain I was Cbz-Leu-D,L-Abu-CONH-(CH(2))(3)-2-methoxyadenin-9-yl (K(i) = 23 nM), and the best inhibitor for calpain II was Cbz-Leu-D,L-Phe-CONH-(CH(2))(3)-adenin-9-yl (K(i) = 68 nM). On the basis of the crystal structure obtained with heterocyclic peptidyl alpha-ketoamides, we have improved inhibitor potency by introducing a small hydrophobic group on the adenine ring. These inhibitors have good potential to be used in the treatment of neurodegenerative diseases.

New drug therapies for multiple sclerosis

PURPOSE OF REVIEW

Multiple sclerosis (MS) is an autoimmune and inflammatory disease of the central nervous system (CNS) that causes neurological disability in young adults and that to date has no cure. Until now, expensive and only partially efficacious therapies have become available. For this reason, researchers, clinicians and pharmaceutical companies are currently investigating new drugs for the treatment of MS. Here, we review the most recent data on drug candidates for MS.

RECENT FINDINGS

In the preclinical phase, such drug candidates have shown a beneficial effect on the onset of experimental autoimmune encephalomyelitis (microtubule-stabilizing drugs, MS14, Lithium, GEMSP...), a decrease in CNS cell infiltrates (recombinant T cell receptor ligand, lovastatin-rolipram, ribavirin, GEMSP...), prevention of demyelination (lovastatin-rolipram, calpain inhibitor, lithium...); and a reduction of axonal loss (phenytoin, lovastatin-rolipram, calpain inhibitor). In clinical trials, drug candidates against MS have shown safety (rituximab, ustekinumab, intravenous immunoglobulin, laquinimod, BHT-3009, fumarate, chaperonin 10, GEMSP...), an improvement of gadolinium-enhanced lesions (protiramer, fingolimod, laquinimod, BHT-3009, fumarate, daclizumab...), and an improvement of the relapse rate (fingolimod, fumarate...).

SUMMARY

Future research into MS should focus on a combination of therapies and on the development of drugs directed against the remitting and progressive phases of the disease. In this sense, MS is a very complex multifactorial disease that requires treatment able to cover all the aspects of MS and not only the anti-inflammatory aspect.

Role of plasma membrane calcium ATPase 2 in spinal cord pathology

A number of studies have indicated that plasma membrane calcium ATPases (PMCAs) are expressed in the brain and spinal cord and could play important roles not only in the maintenance of cellular calcium homeostasis but also in the survival and function of central nervous system cells under pathological conditions. The different regional and cellular distributions of the various PMCA isoforms and splice variants in the nervous system and the diverse phenotypes of PMCA knockout mice support the notion that each isoform might play a distinct role. Especially in the spinal cord, the survival of neurons and, in particular, motor neurons could be dependent on PMCA2. This is indicated by the knockdown of PMCA2 in pure spinal cord neuronal cultures that leads to cell death via a decrease in collapsing response mediator protein 1 levels. Moreover, the progressive decline in the number of motor neurons in PMCA2-null mice and heterozygous mice further supports this notion. Therefore, the reported reduction in PMCA2 mRNA and protein levels in the inflamed spinal cord of mice affected by experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, and after spinal cord contusion injury, suggests that changes in PMCA2 expression could be a cause of neuronal pathology and death during inflammation and injury. Glutamate excitotoxicity mediated via kainate receptors has been implicated in the neuropathology of both EAE and spinal cord injury, and has been identified as a trigger that reduces PMCA2 levels in pure spinal cord neuronal cultures through degradation of the pump by calpain without affecting PMCA2 transcript levels. It remains to be determined which other stimuli modulate PMCA2 mRNA expression in the aforementioned pathological conditions of the spinal cord.

Reduced expression of plasma membrane calcium ATPase 2 and collapsin response mediator protein 1 promotes death of spinal cord neurons

The mechanisms underlying neuronal pathology and death in the spinal cord (SC) during inflammation remain elusive. We previously showed the important role of plasma membrane calcium ATPases (PMCAs) in the survival of SC neurons, in vitro. We also postulated that a decrease in PMCA2 expression could cause neuronal death during experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. The current studies were undertaken to define the specific contribution of PMCA2 to degeneration of SC neurons, the effectors downstream to PMCA2 mediating neuronal death and the triggers that reduce PMCA2 expression. We report that knockdown of PMCA2 in SC neurons decreases collapsin response mediator protein 1 (CRMP1) levels. This is followed by cell death. Silencing of CRMP1 expression also leads to neuronal loss. Kainic acid reduces both PMCA2 and CRMP1 levels and induces neuronal death. Administration of an alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA)/kainate receptor antagonist, at onset or peak of EAE, restores the decreased PMCA2 and CRMP1 levels to control values and ameliorates clinical deficits. Thus, our data link the reduction in PMCA2 expression with perturbations in the expression of CRMP1 and the ensuing death of SC neurons. This represents an additional mechanism underlying AMPA/kainate receptor-mediated excitotoxicity with relevance to neurodegeneration in EAE.

Neuroprotection in multiple sclerosis: a therapeutic challenge for the next decade

Multiple sclerosis (MS) is the commonest cause of progressive neurological disability amongst young, Caucasian adults. MS is considered to be an auto-immune disease that results from an attack against myelin, the layer which surrounds axons. The pathophysiology of MS is complex, with both demyelination and axonal degeneration contributing to what is essentially an inflammatory neurodegenerative disease. Axonal loss is increasingly being accepted as the histopathological correlate of neurological disability. Currently, the underpinnings of neurodegeneration in MS, and how to promote neuroprotection are only partly understood. No established treatments that directly reduce nervous system damage or enhance its repair are currently available. Moreover, the ability of currently available immunomodulatory therapies used to treat MS, such as interferon-beta, to prevent long-term disability is uncertain. Results from short-term randomized-controlled trials suggest a partial benefit with regards to disability outcomes, but this is yet to be established in long-term studies. Novel neuroprotective agents have been identified in preclinical studies but their development is being hampered by the absence of appropriate clinical platforms to test them. In this article, we will discuss some of the principal therapeutic candidates that could provide neuroprotection in MS and emerging methodologies by which to test them.

Inhibition of calpain attenuates encephalitogenicity of MBP-specific T cells

Multiple sclerosis (MS) is a T-cell mediated autoimmune disease of the CNS, possessing both immune and neurodegenerative events that lead to disability. Adoptive transfer (AT) of myelin basic protein (MBP)-specific T cells into naïve female SJL/J mice results in a relapsing-remitting (RR) form of experimental autoimmune encephalomyelitis (EAE). Blocking the mechanisms by which MBP-specific T cells are activated before AT may help characterize the immune arm of MS and offer novel targets for therapy. One such target is calpain, which is involved in activation of T cells, migration of immune cells into the CNS, degradation of axonal and myelin proteins, and neuronal apoptosis. Thus, the hypothesis that inhibiting calpain in MBP-specific T cells would diminish their encephalitogenicity in RR-EAE mice was tested. Incubating MBP-specific T cells with the calpain inhibitor SJA6017 before AT markedly suppressed the ability of these T cells to induce clinical symptoms of RR-EAE. These reductions correlated with decreases in demyelination, inflammation, axonal damage, and loss of oligodendrocytes and neurons. Also, calpain : calpastatin ratio, production of truncated Bid, and Bax : Bcl-2 ratio, and activities of calpain and caspases, and internucleosomal DNA fragmentation were attenuated. Thus, these data suggest calpain as a promising target for treating EAE and MS.

Animal models of multiple sclerosis for the development and validation of novel therapies - potential and limitations

Various types of experimental autoimmune encephalomyelitis (EAE) reflect some of the pathogenetic, clinical, and therapeutic features of the different forms of multiple sclerosis (MS), thereby, providing some, albeit limited, insight into the molecular and cellular basis of the human disease. Specific questions of MS therapy including the search for new therapeutic targets and strategies and their validation require investigations in different available EAE models. A survey is given of experimental therapeutic approaches that are currently under study with the most promising examples of monoclonal antibodies, gene therapy, stem cell transplantation and orally applied small molecular weight disease-modifying drugs. Reasons for therapy failure and adverse side-effects of some experimental trials are discussed. Precaution is advised, if results of new experimental approaches are translated into clinical practice.