Short-term treatment with interferon-alpha/beta promotes remyelination, whereas long-term treatment aggravates demyelination in a murine model of multiple sclerosis

The roles of microglia and astrocytes in phagocytosis and myelination: Insights from the cuprizone model of multiple sclerosis

In human demyelinating diseases such as multiple sclerosis (MS), an imbalance between demyelination and remyelination can trigger progressive degenerative processes. The clearance of myelin debris (phagocytosis) from the site of demyelination by microglia is critically important to achieve adequate remyelination and to slow the progression of the disease. However, how microglia phagocytose the myelin debris, and why clearance is impaired in MS, is not fully known; likewise, the role of the microglia in remyelination remains unclear. Recent studies using cuprizone (CPZ) as an animal model of central nervous system demyelination revealed that the up‐regulation of signaling proteins in microglia facilitates effective phagocytosis of myelin debris. Moreover, during demyelination, protective mediators are released from activated microglia, resulting in the acceleration of remyelination in the CPZ model. In contrast, inadequate microglial activation or recruitment to the site of demyelination, and the production of toxic mediators, impairs remyelination resulting in progressive demyelination. In addition to the microglia‐mediated phagocytosis, astrocytes play an important role in the phagocytic process by recruiting microglia to the site of demyelination and producing regenerative mediators. The current review is an update of these emerging findings from the CPZ animal model, discussing the roles of microglia and astrocytes in phagocytosis and myelination.

Fingolimod after a first unilateral episode of acute optic neuritis (MOVING) - preliminary results from a randomized, rater-blind, active-controlled, phase 2 trial

Background

Neuroprotection and promotion of remyelination represent important therapeutic gaps in multiple sclerosis (MS). Acute optic neuritis (ON) is a frequent MS manifestation. Based on the presence and properties of sphingosine-1-phosphate receptors (S1PR) on astrocytes and oligodendrocytes, we hypothesized that remyelination can be enhanced by treatment with fingolimod, a S1PR modulator currently licensed for relapsing-remitting MS.

Methods

MOVING was an investigator-driven, rater-blind, randomized clinical trial. Patients with acute unilateral ON, occurring as a clinically isolated syndrome or MS relapse, were randomized to 6 months of treatment with 0.5 mg oral fingolimod or subcutaneous IFN-β 1b 250 μg every other day. The change in multifocal visual evoked potential (mfVEP) latency of the qualifying eye was examined as the primary (month 6 vs. baseline) and secondary (months 3, 6 and 12 vs. baseline) outcome. In addition, full field visual evoked potentials, visual acuity, optical coherence tomography as well as clinical relapses and measures of disability, cerebral MRI, and self-reported visual quality of life were obtained for follow-up. The study was halted due to insufficient recruitment (n = 15), and available results are reported.

Results

Per protocol analysis of the primary endpoint revealed a significantly larger reduction of mfVEP latency at 6 months compared to baseline with fingolimod treatment (n = 5; median decrease, 15.7 ms) than with IFN-β 1b treatment (n = 4; median increase, 8.15 ms) (p <  0.001 for interaction). Statistical significance was maintained in the secondary endpoint analysis. Descriptive results are reported for other endpoints.

Conclusion

Preliminary results of the MOVING trial argue in support of a beneficial effect of fingolimod on optic nerve remyelination when compared to IFN-β treatment. Interpretation is limited by the small number of complete observations, an unexpected deterioration of the control group and a difference in baseline mfVEP latencies. The findings need to be confirmed in larger studies.

Trial registration

The trial was registered as EUDRA-CT 2011–004787-30 on October 26, 2012 and as NCT01647880 on July 24, 2012.

Tumor-suppressive effect of S-adenosylmethionine supplementation in a murine model of inflammation-mediated hepatocarcinogenesis is dependent on treatment longevity

Chronic inflammation precedes the majority of hepatocellular carcinoma (HCC) cases. We investigated the chemopreventive potential of S-adenosylmethionine (SAM), an essential donor for all methylation reactions in the cell, at the late precancerous stage of HCC development using the Mdr2-knockout (Mdr2-KO, Abcb4^−/−) mice, a model of inflammation-mediated hepatocarcinogenesis. Previously, we revealed down-regulation of the genes regulating SAM metabolism in the liver of these mice at the precancerous stages. Now, we have supplied Mdr2-KO mice at the late precancerous stage with SAM during either a short-term (17 days) or a long-term (51 days) period and explored the effects of such supplementation on tumor development, DNA methylation and gene expression in the liver. The short-term SAM supplementation significantly decreased the number of small tumor nodules, proliferating hepatocytes and the total DNA methylation level, while it increased expression of the tumor suppressor proteins Mat1a and p21. Surprisingly, the long-term SAM supplementation did not affect tumor growth and hepatocyte proliferation, while it increased the total liver DNA methylation. Our results demonstrate that the short-term SAM supplementation in the Mdr2-KO mice inhibited liver tumor development potentially by increasing multiple tumor suppressor mechanisms resulting in cell cycle arrest. The long-term SAM supplementation resulted in a bypass of the cell cycle arrest in this HCC model by a yet unknown mechanism.

Multiple sclerosis: experimental models and reality

One of the most frequent statements, provided in different variations in the introduction of experimental studies on multiple sclerosis (MS), is that "Multiple sclerosis is a demyelinating autoimmune disease and experimental autoimmune encephalomyelitis (EAE) is a suitable model to study its pathogenesis". However, so far, no single experimental model covers the entire spectrum of the clinical, pathological, or immunological features of the disease. Many different models are available, which proved to be highly useful for studying different aspects of inflammation, demyelination, remyelination, and neurodegeneration in the central nervous system. However, the relevance of results from such models for MS pathogenesis has to be critically validated. Current EAE models are mainly based on inflammation, induced by auto-reactive CD4+ T-cells, and these models reflect important aspects of MS. However, pathological data and results from clinical trials in MS indicate that CD8+ T-cells and B-lymphocytes may play an important role in propagating inflammation and tissue damage in established MS. Viral models may reflect key features of MS-like inflammatory demyelination, but are difficult to use due to their very complex pathogenesis, involving direct virus-induced and immune-mediated mechanisms. Furthermore, evidence for a role of viruses in MS pathogenesis is indirect and limited, and an MS-specific virus infection has not been identified so far. Toxic models are highly useful to unravel mechanisms of de- and remyelination, but do not reflect other important aspects of MS pathology and pathogenesis. For all these reasons, it is important to select the right experimental model to answer specific questions in MS research.

PDE7 inhibitor TC3.6 ameliorates symptomatology in a model of primary progressive multiple sclerosis

BACKGROUND AND PURPOSE

cAMP plays an important role in the transduction of signalling pathways involved in neuroprotection and immune regulation. Control of the levels of this nucleotide by inhibition of cAMP-specific PDEs such as PDE7 may affect the pathological processes of neuroinflammatory diseases like multiple sclerosis (MS). In the present study, we evaluated the therapeutic potential of the selective PDE7 inhibitor, TC3.6, in a model of primary progressive multiple sclerosis (PPMS), a rare and severe variant of MS.

EXPERIMENTAL APPROACH

Theiler's murine encephalomyelitis virus-induced demyelinated disease (TMEV-IDD) is one of the models used to validate the therapeutic efficacy of new drugs in MS. As recent studies have analysed the effect of PDE7 inhibitors in the EAE model of MS, here the TMEV-IDD model was used to test their efficacy in a progressive variant of MS. Mice were subjected to two protocols of TC3.6 administration: on the pre-symptomatic phase and once the disease was established.

KEY RESULTS

Treatment with TC3.6 ameliorated the disease course and improved motor deficits of infected mice. This was associated with down-regulation of microglial activation and reduced cellular infiltrates. Decreased expression of pro-inflammatory mediators such as COX-2 and the cytokines, IL-1β, TNF-α, IFN-γ and IL-6 in the spinal cord of TMEV-infected mice was also observed after TC3.6 administration.

CONCLUSION

These findings support the importance of PDE7 inhibitors, and specifically TC3.6, as a novel class of agents with therapeutic potential for PPMS. Preclinical studies are needed to determine whether their effects translate into durable clinical benefits.

Effect of treatment with interferon beta-1a on changes in voxel-wise magnetization transfer ratio in normal appearing brain tissue and lesions of patients with relapsing-remitting multiple sclerosis: a 24-week, controlled pilot study

Background

This pilot study investigated changes in remyelinating and demyelinating activity in normal appearing brain tissue (NABT) and lesions, by using voxel-wise magnetization transfer ratio (VW-MTR), in patients with relapsing–remitting multiple sclerosis (RRMS) receiving interferon beta-1a 44 mcg subcutaneously (IFN β-1a SC) three times weekly versus healthy controls (HCs) (NCT01085318).

Methods

Increasing (suggestive of remyelination) and decreasing (suggestive of demyelination) VW-MTR changes in NABT and in T2, T1 and gadolinium (Gd)-enhancing lesion volume were measured over 24 weeks in 23 patients treated with IFN β-1a SC and in 15 HCs (where applicable). VW-MTR changes were tested using the Wilcoxon signed–rank or Wilcoxon rank–sum test.

Results

A trend for greater volume of NABT with increasing VW-MTR at 24 weeks was observed for patients versus HCs (median [range] 1206 [0–15278]; 342 [0–951] mm³; p = 0.061). NABT volume with increasing VW-MTR at 12 weeks was significantly greater in patients than in HCs (852 [6–11577]; 360 [0–1755] mm³; p = 0.028). Similar findings were detected for lesion volumes. Two patients with notably high numbers of Gd-enhancing lesions at baseline had a markedly greater volume of tissue with increasing VW-MTR compared with other patients. Volume of NABT tissue with decreasing VW-MTR was significantly greater in patients versus HCs at 24 weeks (942 [0–6141]; 297 [0–852] mm³; p<0.001).

Conclusions

The significant change in NABT volume with increasing VW-MTR at 12 weeks suggests that active remyelination in patients with RRMS may occur during treatment with IFN β-1a SC. Findings from two patients with the highest number of Gd-enhancing lesions at baseline suggest that extensive remyelination in NABT may occur in patients with high disease activity. Tissue volume with decreasing VW-MTR was greater in patients than in HCs, despite treatment, validating the sensitivity of this technique for detecting MS disease activity.

Trial Registration

ClinicalTrials.gov NCT01085318.

Impact of Theiler's virus infection on hippocampal neuronal progenitor cells: differential effects in two mouse strains

AIMS

Disease-associated alterations in hippocampal neurogenesis are discussed as an important factor contributing to long-term consequences of central nervous system diseases. Therefore, the study aimed to determine the impact of Theiler's murine encephalomyelitis virus infection on hippocampal cell proliferation, neuronal progenitor cells and neurogenesis as well as the influence of microglia on respective disease-associated alterations.

METHODS

The impact of the infection was evaluated in two mouse strains which differ in the disease course, with an acute polioencephalitis followed by virus elimination in C57BL/6 mice and a chronic demyelinating disease in SJL/J mice.

RESULTS

Infection with the low neurovirulent BeAn strain did not exert significant acute effects regardless of the mouse strain. In the chronic phase, the number of neuronal progenitor cells and early postmitotic neurones was significantly reduced in infected SJL/J mice, whereas no long-term alterations were observed in C57BL/6 mice. A contrasting course of microglia activation was observed in the two mouse strains, with an early increase in the number of activated microglia cells in SJL/J mice and a delayed increase in C57BL/6 mice. Quantitative analysis did not confirm a correlation between the number of activated microglia and the number of neuronal progenitor cells and early postmitotic neurones. However, flow cytometric analyses revealed alterations in the functional state of microglial cells which might have affected the generation of neuronal progenitor cells.

CONCLUSIONS

Theiler's murine encephalomyelitis virus infection can exert delayed effects on the hippocampal neuronal progenitor population with long-term alterations evident 3 months following infection. These alterations proved to depend on strain susceptibility and might contribute to detrimental consequences of virus encephalitis such as cognitive impairment.

Viral models of multiple sclerosis: neurodegeneration and demyelination in mice infected with Theiler's virus

Multiple sclerosis (MS) is a complex inflammatory disease of unknown etiology that affects the central nervous system (CNS) white matter, and for which no effective cure exists. Indeed, whether the primary event in MS pathology affects myelin or axons of the CNS remains unclear. Animal models are necessary to identify the immunopathological mechanisms involved in MS and to develop novel therapeutic and reparative approaches. Specifically, viral models of chronic demyelination and axonal damage have been used to study the contribution of viruses in human MS, and they have led to important breakthroughs in our understanding of MS pathology. The Theiler's murine encephalomyelitis virus (TMEV) model is one of the most commonly used MS models, although other viral models are also used, including neurotropic strains of mouse hepatitis virus (MHV) that induce chronic inflammatory demyelination with similar histological features to those observed in MS. This review will discuss the immunopathological mechanisms involved in TMEV-induced demyelinating disease (TMEV-IDD). The TMEV model reproduces a chronic progressive disease due to the persistence of the virus for the entire lifespan in susceptible mice. The evolution and significance of the axonal damage and neuroinflammation, the importance of epitope spread from viral to myelin epitopes, the presence of abortive remyelination and the existence of a brain pathology in addition to the classical spinal cord demyelination, are some of the findings that will be discussed in the context of this TMEV-IDD model. Despite their limitations, viral models remain an important tool to study the etiology of MS, and to understand the clinical and pathological variability associated with this disease.

Type I interferon signals control Theiler's virus infection site, cellular infiltration and T cell stimulation in the CNS

Theiler's murine encephalomyelitis virus (TMEV) establishes a persistent infection in the central nervous system (CNS). To examine the role of type I interferon (IFN-I)-mediated signals in TMEV infection, mice lacking a subunit of the type I IFN receptor (IFN-IR KO mice) were utilized. In contrast to wild type mice, IFN-IR KO mice developed rapid fatal encephalitis accompanied with greater viral load and infiltration of immune cells to the CNS. The proportion of virus-specific CD4(+) and CD8(+) T cell responses in the CNS was significantly lower in IFN-IR KO mice during the early stage of infection. Levels of IFN-γ and IL-17 produced by isolated primed CD4(+) T cells in response to DCs from TMEV-infected IFN-IR KO mice were also lower than those stimulated by DCs from TMEV-infected wild type control mice. The less efficient stimulation of virus-specific T cells by virus-infected antigen-presenting cells is attributable in part to the low level expression of activation markers on TMEV-infected cells from IFN-IR KO mice. However, due to high levels of cellular infiltration and viral loads in the CNS, the overall numbers of virus-specific T cells are higher in IFN-IR KO mice during the later stage of viral infection. These results suggest that IFN-I-mediated signals play important roles in controlling cellular infiltration to the CNS and shaping local T cell immune responses.

Different strains of Theiler's murine encephalomyelitis virus antagonize different sites in the type I interferon pathway

The DA strain of Theiler's murine encephalomyelitis virus (TMEV), a member of the Cardiovirus genus of the family Picornaviridae, causes persistent infection in susceptible mice, associated with restricted expression of viral proteins, and induces a demyelinating disease of the central nervous system. DA-induced demyelinating disease serves as a model of human multiple sclerosis because of similarities in pathology and because host immune responses contribute to pathogenesis in both disorders. In contrast, the GDVII strain of TMEV causes acute lethal encephalitis with no virus persistence. Cardiovirus L is a multifunctional protein that blocks beta interferon (IFN-beta) gene transcription. We show that both DA L and GDVII L disrupt IFN-beta gene transcription induction by IFN regulatory factor 3 (IRF-3) but do so at different points in the signaling pathway. DA L blocks IFN-beta gene transcription downstream of mitochondrial antiviral signaling protein (MAVS) but upstream of IRF-3 activation, while GDVII L acts downstream of IRF-3 activation. Both DA L and GDVII L block IFN-beta gene transcription in infected mice; however, IFN-beta mRNA is expressed at low levels in the central nervous systems of mice persistently infected with DA. The particular level of IFN-beta mRNA expression set by DA L as well as other factors in the IRF-3 pathway may play a role in virus persistence, inflammation, and the restricted expression of viral proteins during the late stage of demyelinating disease.

Type I interferon receptor signalling is induced during demyelination while its function for myelin damage and repair is redundant

The type I interferons, interferon-beta and alpha (IFN-beta, IFN-alpha), are widely used for the treatment of autoimmune demyelination in the central nervous system (CNS). Their effects on de- and remyelination through the broadly expressed type I IFN receptor (IFNAR), however, are highly speculative. In order to elucidate the role of endogenous type I interferons for myelin damage and recovery we induced toxic demyelination in the absence of IFNAR1. We demonstrate that IFNAR signalling was induced during acute demyelination since the cytokine IFN-beta as well as the IFN-dependent genes IRF7, ISG15 and UBP43 were strongly upregulated. Myelin damage, astrocytic and microglia response, however, were not significantly reduced in the absence of IFNAR1. Furthermore, motor skills of IFNAR1-deficient animals during non-immune demyelination were unaltered. Finally, myelin recovery was found to be independent from endogenous IFNAR signalling, indicating a redundant role of this receptor for non-inflammatory myelin damage and repair.

Modulation of viral replication in macrophages persistently infected with the DA strain of Theiler's murine encephalomyelitis virus

Background

Demyelinating strains of Theiler's murine encephalomyelitis virus (TMEV) such as the DA strain are the causative agents of a persistent infection that induce a multiple sclerosis-like disease in the central nervous system of susceptible mice. Viral persistence, mainly associated with macrophages, is considered to be an important disease determinant that leads to chronic inflammation, demyelination and autoimmunity. In a previous study, we described the establishment of a persistent DA infection in RAW macrophages, which were therefore named DRAW.

Results

In the present study we explored the potential of diverse compounds to modulate viral persistence in these DRAW cells. Hemin was found to increase viral yields and to induce cell lysis. Enviroxime and neutralizing anti-TMEV monoclonal antibody were shown to decrease viral yields, whereas interferon-α and interferon-γ completely cleared the persistent infection. We also compared the cytokine pattern secreted by uninfected RAW, DRAW and interferon-cured DRAW macrophages using a cytokine protein array. The chemokine RANTES was markedly upregulated in DRAW cells and restored to a normal expression level after abrogation of the persistent infection with interferon-α or interferon-γ. On the other hand, the chemokine MCP-1 was upregulated in the interferon-cured DRAW cells.

Conclusion

We have identified several compounds that modulate viral replication in an in vitro model system for TMEV persistence. These compounds now await further testing in an in vivo setting to address fundamental questions regarding persistent viral infection and immunopathogenesis.

Lack of interferon-beta leads to accelerated remyelination in a toxic model of central nervous system demyelination

Interferon-beta (IFN-beta) is a pleiotropic cytokine that is known to modulate the immune response in multiple sclerosis (MS), an inflammatory demyelinating disease of the central nervous system (CNS). Spontaneous remyelination and repair mechanisms in MS are mostly insufficient and contribute to clinical disability. Here, we investigated whether IFN-beta has a potential in modifying the extent of de- and remyelination in a toxic model of CNS demyelination induced by the copper chelator cuprizone. IFN-beta deficient (k/o) mice showed an accelerated spontaneous remyelination. However, the amount of remyelination after 6 weeks did not differ between the two groups. Demyelination in IFN-beta k/o mice was paralleled by a diminished astrocytic and microglia response as compared with wildtype controls, whereas the accelerated remyelination was paralleled by an increased number of oligodendrocyte precursor cells (OPC) within the demyelinated lesion at the beginning of the remyelination phase. We hypothesize that the absence of IFN-beta leads to more efficient recruitment and proliferation of OPC already during demyelination, thus allowing early remyelination. These results demonstrate that IFN-beta is able to alter remyelination in the absence of an immune-mediated demyelination.

eIF2B and oligodendrocyte survival: where nature and nurture meet in bipolar disorder and schizophrenia?

Bipolar disorder and schizophrenia share common chromosomal susceptibility loci and many risk-promoting genes. Oligodendrocyte cell loss and hypomyelination are common to both diseases. A number of environmental risk factors including famine, viral infection, and prenatal or childhood stress may also predispose to schizophrenia or bipolar disorder. In cells, related stressors (starvation, viruses, cytokines, oxidative, and endoplasmic reticulum stress) activate a series of eIF2-alpha kinases, which arrest protein synthesis via the eventual inhibition, by phosphorylated eIF2-alpha, of the translation initiation factor eIF2B. Growth factors increase protein synthesis via eIF2B activation and counterbalance this system. The control of protein synthesis by eIF2-alpha kinases is also engaged by long-term potentiation and repressed by long-term depression, mediated by N-methyl-D-aspartate (NMDA) and metabotropic glutamate receptors. Many genes reportedly associated with both schizophrenia and bipolar disorder code for proteins within or associated with this network. These include NMDA (GRIN1, GRIN2A, GRIN2B) and metabotropic (GRM3, GRM4) glutamate receptors, growth factors (BDNF, NRG1), and many of their downstream signaling components or accomplices (AKT1, DAO, DAOA, DISC1, DTNBP1, DPYSL2, IMPA2, NCAM1, NOS1, NOS1AP, PIK3C3, PIP5K2A, PDLIM5, RGS4, YWHAH). They also include multiple gene products related to the control of the stress-responsive eIF2-alpha kinases (IL1B, IL1RN, MTHFR, TNF, ND4, NDUFV2, XBP1). Oligodendrocytes are particularly sensitive to defects in the eIF2B complex, mutations in which are responsible for vanishing white matter disease. The convergence of natural and genetic risk factors on this area in bipolar disorder and schizophrenia may help to explain the apparent vulnerability of this cell type in these conditions. This convergence may also help to reconcile certain arguments related to the importance of nature and nurture in the etiology of these psychiatric disorders. Both may affect common stress-related signaling pathways that dictate oligodendrocyte viability and synaptic plasticity.

Reduced expression of IL-12 p35 by SJL/J macrophages responding to Theiler's virus infection is associated with constitutive activation of IRF-3

Macrophages responding to viral infections may contribute to autoimmune demyelinating diseases (ADD). Macrophages from ADD-susceptible SJL/J mice responding to Theiler's Virus (TMEV) infection, the TLR7 agonist loxoribine, or the TLR4 agonist-LPS expressed less IL-12 p35 but more IL-12/23 p40 and IFN-beta than macrophages from ADD-resistant B10.S mice. While expression of IRF-1 and -7 was similar between B10.S and SJL/J TMEV-infected macrophages, SJL/J but not B10.S macrophages exhibited constitutively active IRF-3. In contrast to overexpressed IRF-1, IRF-5, and IRF-7, which stimulated p35 promoter reporter activity, overexpressed IRF-3 repressed p35 promoter activity in response to TMEV infection, loxoribine, IFN-gamma/LPS, but not IFN-gamma alone. IRF-3 lessened but did not eliminate IRF-1-stimulated p35 promoter activity. Repression by IRF-3 required bp -172 to -122 of the p35 promoter. The data suggest that pre-activated IRF-3 is a major factor in the differences in IL-12 production between B10.S and SJL/J macrophages responding to TMEV.

Effects of interferon-beta on oligodendroglial cells

The effect of interferon-beta (IFN-beta) for the treatment of multiple sclerosis (MS) is thought to be mediated by the modulation of immune cells. In addition, it has been shown that glial cells may be influenced by IFN-beta and a role during remyelination has been suggested. However, the mechanism is not yet clear and there are conflicting data. We have therefore systematically investigated proliferation, differentiation, toxicity, and cytoprotection of IFN-beta on oligodendroglia, both as a direct effect and mediated indirectly via other glial cells. Differentiation of oligodendrocyte progenitor cells (OPC) was significantly (p<0.01) inhibited by IFN-beta only when cultured in the presence with astrocytes and microglia. Proliferation was not changed, neither was IFN-beta toxic. There was no cytoprotective effect of IFN-beta on oligodendroglia injury induced by H2O2, NO, complement, or glutamate. Similarly, there was no cytoprotective effect mediated via treatment of astrocytes with IFN-beta. These data demonstrate that IFN-beta is neither toxic nor cytoprotective for oligodendrocytes. In summary, the only effect of IFN-beta was the inhibition of differentiation of OPC mediated indirectly via other glial cells. In vivo experiments will show how this effect may influence remyelination.

Self-assembly of sensory neurons into ganglia-like microtissues

Unraveling intra- and inter-cellular signaling networks managing cell-fate control, coordinating complex differentiation regulatory circuits and shaping tissues and organs in living systems remain major challenges in the post-genomic era. Resting on the laurels of past-century monolayer culture technologies, the cell culture community has only recently begun to appreciate the potential of three-dimensional mammalian cell culture systems to reveal the full scope of mechanisms orchestrating the tissue-like cell quorum in space and time. Capitalizing on gravity-enforced self-assembly of monodispersed primary embryonic mouse cells in hanging drops, we designed and characterized a three-dimensional cell culture model for ganglion-like structures. Within 24h, a mixture of mouse embryonic fibroblasts (MEF) and cells, derived from the dorsal root ganglion (DRG) (sensory neurons and Schwann cells) grown in hanging drops, assembled to coherent spherical microtissues characterized by a MEF feeder core and a peripheral layer of DRG-derived cells. In a time-dependent manner, sensory neurons formed a polar ganglion-like cap structure, which coordinated guided axonal outgrowth and innervation of the distal pole of the MEF feeder spheroid. Schwann cells, present in embryonic DRG isolates, tended to align along axonal structures and myelinate them in an in vivo-like manner. Whenever cultivation exceeded 10 days, DRG:MEF-based microtissues disintegrated due to an as yet unknown mechanism. Using a transgenic MEF feeder spheroid, engineered for gaseous acetaldehyde-inducible interferon-beta (ifn-beta) production by cotransduction of retro-/ lenti-viral particles, a short 6-h ifn-beta induction was sufficient to rescue the integrity of DRG:MEF spheroids and enable long-term cultivation of these microtissues. In hanging drops, such microtissues fused to higher-order macrotissue-like structures, which may pave the way for sophisticated bottom-up tissue engineering strategies. DRG:MEF-based artificial micro- and macrotissue design demonstrated accurate key morphological aspects of ganglions and exemplified the potential of self-assembled scaffold-free multicellular micro-/macrotissues to provide new insight into organogenesis.

Spontaneous remyelination following prolonged inhibition of alpha4 integrin in chronic EAE

Inhibition of alpha(4)beta(1) integrin blocks immune cell influx into the CNS providing benefit to patients with multiple sclerosis and in animal model systems. We have used this mechanism to examine whether the presence of inflammatory cells suppresses spontaneous myelin repair in experimental autoimmune encephalomyelitis. We observed (1) 87% of plaques showed remyelination after 40 days of treatment; (2) myelin repair occurred in half of the total lesion area; (3) half of the animals regained motor function. There was no significant repair or gain of motor function in vehicle-treated animals. Therefore, prolonged inhibition of CNS inflammation, in the absence of targeted myelin repair, facilitates mechanisms of spontaneous remyelination.

Remyelinating and neuroprotective treatments in multiple sclerosis

Multiple sclerosis (MS) is the most common cause of neurological disability in young adults. The pathological hallmark is multifocal demyelination and inflammation in the CNS. In addition, there is also a variable extent of axonal damage. Remyelination has been seen in up to 70% of lesions but repair is generally incomplete. The demonstration of neuropathological heterogeneity of MS lesions suggests different pathophysiological subtypes and it is therefore unlikely that there is a uniform cause of incomplete remyelination in MS. In recent years, a great body of knowledge has accumulated in order to better understand the regulatory mechanisms of remyelination. This has led to a number of approaches to promote repair mechanisms, most of which have been successful in animal experiments. Unfortunately, the translation of these experimental data into clinical treatments has proven difficult. More information on the pathogenesis of MS, the reason why repair mechanisms fail in MS and a better understanding of the regulation of remyelination are required. This will ultimately lead to a specific treatment tailored for the individual patient and will probably involve a combination of immunomodulation, remyelination and neuroprotection.

Experimental Models of Virus-Induced Demyelination

This chapter reviews two of the most widely studied animal models of virus-induced demyelinating disease. These are Theiler's murine encephalomyelitis virus and murine hepatitis virus. Both viruses produce acute inflammatory encephalitis that is followed by chronic central-nervous-system (CNS) demyelinating disease. The clinical and pathologic correlates of virus-induced demyelination are largely immune mediated. Furthermore, several pathologic mechanisms have been proposed to explain the development of myelin damage and neurologic deficits, and each of the proposed mechanisms may play a role in disease progression depending on the genetic constitution of the infected animal. The induction of demyelinating disease by virus may be directly relevant to human MS. Several viruses are known to cause demyelination in humans and viral infection is an epidemiologic factor that is consistently associated with clinical exacerbation of MS. It is suggested that viral infection may be a cause of MS, although no specific virus has been identified as a causative agent.

Remyelinating strategies for the treatment of multiple sclerosis

Demyelination is the pathological hallmark of multiple sclerosis (MS) lesions. The concept of remyelination has gained acceptance in recent years, but naturally occurring remyelination is incomplete. To improve repair processes, a number of strategies have been explored experimentally and clinical trials are being carried out. In principle, remyelination can be achieved by either promoting endogenous repair mechanisms or by providing an exogenous source of myelinating cells via transplantation. Both approaches have been successful in animal models of demyelination. Besides, many studies have elucidated principal mechanisms of oligodendrocyte biology and remyelination in the central nervous system (CNS). This progress in knowledge also allowed for more specific interventions. First clinical trials to enhance endogenous remyelination have been performed, unfortunately with disappointingly negative results. This illustrates that experimental data cannot be easily transferred to human disease, and more detailed knowledge on the regulatory mechanisms of remyelination in MS is required. Recently, the first MS patient received a transplant of autologous Schwann cells. Many other cell types are being studied experimentally, including stem cells. Despite the ethical problems associated with an embryonic cell source, new developments in stem cell biology indicate that adult stem cells or bone marrow-derived cells may substitute for embryonic cells in the future. In this review, we describe the current views on oligodendrocyte biology, myelination and remyelination, and focus on recent developments leading to reconstructing, remyelinating strategies in MS.