A null mutation within the ciliary neurotrophic factor (CNTF)-gene: implications for susceptibility and disease severity in patients with multiple sclerosis

Aggressive multiple sclerosis (1): Towards a definition of the phenotype

While the major phenotypes of multiple sclerosis (MS) and relapsing-remitting, primary and secondary progressive MS have been well characterized, a subgroup of patients with an active, aggressive disease course and rapid disability accumulation remains difficult to define and there is no consensus about their management and treatment. The current lack of an accepted definition and treatment guidelines for aggressive MS triggered a 2018 focused workshop of the European Committee for Treatment and Research in Multiple Sclerosis (ECTRIMS) on aggressive MS. The aim of the workshop was to discuss approaches on how to describe and define the disease phenotype and its treatments. Unfortunately, it was not possible to come to consensus on a definition because of unavailable data correlating severe disease with imaging and molecular biomarkers. However, the workshop highlighted the need for future research needed to define this disease subtype while also focusing on its treatment and management. Here, we review previous attempts to define aggressive MS and present characteristics that might, with additional research, eventually help characterize it. A companion paper summarizes data regarding treatment and management.

Effects of Neurotrophic Factors in Glial Cells in the Central Nervous System: Expression and Properties in Neurodegeneration and Injury

Astrocytes, oligodendrocytes, and microglia are abundant cell types found in the central nervous system and have been shown to play crucial roles in regulating both normal and disease states. An increasing amount of evidence points to the critical importance of glia in mediating neurodegeneration in Alzheimer’s and Parkinson’s diseases (AD, PD), and in ischemic stroke, where microglia are involved in initial tissue clearance, and astrocytes in the subsequent formation of a glial scar. The importance of these cells for neuronal survival has previously been studied in co-culture experiments and the search for neurotrophic factors (NTFs) initiated after finding that the addition of conditioned media from astrocyte cultures could support the survival of primary neurons in vitro. This led to the discovery of the potent dopamine neurotrophic factor, glial cell line-derived neurotrophic factor (GDNF). In this review, we focus on the relationship between glia and NTFs including neurotrophins, GDNF-family ligands, CNTF family, and CDNF/MANF-family proteins. We describe their expression in astrocytes, oligodendrocytes and their precursors (NG2-positive cells, OPCs), and microglia during development and in the adult brain. Furthermore, we review existing data on the glial phenotypes of NTF knockout mice and follow NTF expression patterns and their effects on glia in disease models such as AD, PD, stroke, and retinal degeneration.

The role of growth factors as a therapeutic approach to demyelinating disease

A variety of growth factors are being explored as therapeutic agents relevant to the axonal and oligodendroglial deficits that occur as a result of demyelinating lesions such as are evident in Multiple Sclerosis (MS). This review focuses on five such proteins that are present in the lesion site and impact oligodendrocyte regeneration. It then presents approaches that are being exploited to manipulate the lesion environment affiliated with multiple neurodegenerative diseases and suggests that the utility of these approaches can extend to demyelination. Challenges are to further understand the roles of specific growth factors on a cellular and tissue level. Emerging technologies can then be employed to optimize the use of growth factors to ameliorate the deficits associated with demyelinating degenerative diseases.

How factors secreted from astrocytes impact myelin repair

Over a century ago, hypertrophy of astrocytes was noted as a pathology of multiple sclerosis (MS) and was hypothesized to play an important role in this disease, yet the contribution of astrocytes has been largely underemphasized in the pathophysiology of CNS demyelination. Astrocytes perform many homeostatic functions within the developing and adult CNS, including enhancing formation and maintenance of the blood-brain barrier, moderating neuronal connections through the tripartite synapse, and perhaps even offering intercellular communication independently of neurons. Although there is a significant body of literature characterizing different types of MS lesions, the inflammatory demyelination in an active MS lesion is accompanied by the presence of macrophages, lymphocytes, and large reactive astrocytes. The astrocyte has long been viewed as a cell that promotes inflammation and demyelination, while also forming the glial scar, thus hindering remyelination and axon growth. Renewed interest in the astrocyte has been brought about by recent studies demonstrating that astrocytes can also function as cellular mediators of CNS myelination by promoting oligodendrocyte progenitor migration, proliferation, and differentiation. Thus, refining our knowledge of astrocytic functions in the regulation of CNS myelination may help us to better understand why remyelination fails in MS.

The balance of pro-inflammatory and trophic factors in multiple sclerosis patients: effects of acute relapse and immunomodulatory treatment

Background: In multiple sclerosis inflammation is primarily injurious to the central nervous system, but its therapeutic suppression might inhibit repair-promoting factors.

Objectives: We aimed at better describing the complexity of biological effects during an acute relapse and analysed the effects of intervention with high-dose i.v. glucocorticoids and immunomodulatory treatment with interferon-beta (IFNβ).

Methods: We studied the intracellular expression levels of the pro-inflammatory mediators tumour necrosis factor alpha (TNFα) and inducible nitric oxide synthase (iNOS) together with the neurotrophins ciliary neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF) in freshly isolated peripheral blood mononuclear cells of multiple sclerosis patients during an acute relapse, after intervention with i.v. methylprednisolone and at baseline, using a highly quantitative flow-cytometric approach.

Results: We demonstrated the expression of CNTF in human leucocytes. We showed that CNTF levels differed in acutely relapsing multiple sclerosis patients compared with controls and increased after corticosteroid treatment. CNTF can counteract the toxicity of TNFα towards oligodendrocytes and we found TNFα increased during acute relapses. Following corticosteroids, neither TNFα nor iNOS expression was reduced. Levels of BDNF were not affected by glucocorticoids, but increased during IFNβ therapy. However, IFNβ also increased the expression of iNOS and major histocompatibility complex class I (MHC-I), underlining its immunomodulatory potential.

Conclusions: Multiple sclerosis patients might benefit from reparative, and not solely from anti-inflammatory, effects of glucocorticoids. Interactive effects of glucocorticoid- and IFNβ-treatment need to be considered to improve neuroprotection and remyelination resulting from immunomodulatory treatment.

Mechanisms of neuronal dysfunction and degeneration in multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system. Due to its high prevalence, MS is the leading cause of non-traumatic neurological disability in young adults in the United States and Europe. The clinical disease course is variable and starts with reversible episodes of neurological disability in the third or fourth decade of life. This transforms into a disease of continuous and irreversible neurological decline by the sixth or seventh decade. Available therapies for MS patients have little benefit for patients who enter this irreversible phase of the disease. It is well established that irreversible loss of axons and neurons are the major cause of the irreversible and progressive neurological decline that most MS patients endure. This review discusses the etiology, mechanisms and progress made in determining the cause of axonal and neuronal loss in MS.

The neuropoietic cytokine family in development, plasticity, disease and injury

Neuropoietic cytokines are well known for their role in the control of neuronal, glial and immune responses to injury or disease. Since this discovery, it has emerged that several of these proteins are also involved in nervous system development, in particular in the regulation of neurogenesis and stem cell fate. Recent data indicate that these proteins have yet more functions, as key modulators of synaptic plasticity and of various behaviours. In addition, neuropoietic cytokines might be a factor in the aetiology of psychiatric disorders.

Continued administration of ciliary neurotrophic factor protects mice from inflammatory pathology in experimental autoimmune encephalomyelitis

Multiple sclerosis is an inflammatory disease of the central nervous system that leads to loss of myelin and oligodendrocytes and damage to axons. We show that daily administration (days 8 to 24) of murine ciliary neurotrophic factor (CNTF), a neurotrophic factor that has been described as a survival and differentiation factor for neurons and oligodendrocytes, significantly ameliorates the clinical course of a mouse model of multiple sclerosis. In the acute phase of experimental autoimmune encephalomyelitis induced by myelin oligodendrocyte glycoprotein peptide 35-55, treatment with CNTF did not change the peripheral immune response but did reduce the number of perivascular infiltrates and T cells and the level of diffuse microglial activation in spinal cord. Blood brain barrier permeability was significantly reduced in CNTF-treated animals. Beneficial effects of CNTF did not persist after it was withdrawn. After cessation of CNTF treatment, inflammation and symptoms returned to control levels. However, slight but significantly higher numbers of oligodendrocytes, NG2-positive cells, axons, and neurons were observed in mice that had been treated with high concentrations of CNTF. Our results show that CNTF inhibits inflammation in the spinal cord, resulting in amelioration of the clinical course of experimental autoimmune encephalomyelitis during time of treatment.

No association of leukemia inhibitory factor (LIF) DNA polymorphisms with multiple sclerosis

Neuropoietins such as leukemia inhibitory factor (LIF) have been shown to ameliorate experimental autoimmune encephalomyelitis (EAE) and promote oligodendrocyte survival in vivo. We tested whether two previously described LIF polymorphisms are associated with MS by genotyping these single nucleotide polymorphisms (SNPs) in a group of MS patients (n=110), rheumatoid arthritis (RA) patients (n=120) and healthy controls (HC, n=109). Similar allele and genotype frequencies for both SNPs were found for all study groups. Furthermore, no associations with MS type or HLA-DR2 expression could be found. In summary, no association was found between the studied LIF DNA polymorphisms and the prevalence of MS indicating that these polymorphisms are not involved in determining disease susceptibility.

Mechanisms of axonal degeneration in EAE—lessons from CNTF and MHC I knockout mice

The major pathological hallmarks of multiple sclerosis (MS) comprise inflammation, demyelination with associated gliosis and axonal damage, which most likely correlates with persisting disability. Axonal damage can occur by several mechanisms. This article focuses on myelin disintegration and direct immune attack on axons by CD8-positive T-cells as two possible scenarios for axonal injury. As protoypic models, we investigated experimental autoimmune encephalomyelitis (EAE) in ciliary neurotrophic factor gene knockout mice (CNTF-/- mice) with severe myelin pathology and EAE in beta-2 microglobulin gene knockout mice (beta2m-/- mice) lacking CD8-positive T-cells. The results from these studies indicate that the trigger attack for axonal injury even in a well-defined experimental design can be multi-faceted. No single factor seems to be absolutely necessary for the initiation of the process, but they rather act in concert and orchestrate tissue destruction, inflammation and regeneration. Some mechanisms of primary or secondary axonal damage may be shared between inflammatory and degenerative diseases of the nervous system, thereby establishing a link which might be of importance for future therapeutic strategies.

CNTF, a pleiotropic cytokine: emphasis on its myotrophic role

Ciliary neurotrophic factor (CNTF) is a cytokine whose neurotrophic and differentiating effects over cells in the central nervous system (CNS) have been clearly demonstrated. This article summarizes the general characteristics of CNTF, its receptor and the signaling pathway that it activates and focuses on its effects over skeletal muscle, one of its major target tissues outside the central nervous system. The evidence for the existence of other molecules that signal through the same complex as CNTF is also reviewed.

Ciliary neurotrophic factor (CNTF) genotype and body composition

Exogenous ciliary neurotrophic factor (CNTF) administration causes significant weight loss in both humans and animal models, but the effects of endogenous CNTF and the CNTF null allele on body composition are not fully understood. A recent study in a European cohort demonstrated a significantly higher body weight and body mass index (BMI) in older males homozygous for the CNTF null allele (A/A genotype). We sought to replicate these findings in three cohorts: the Baltimore Longitudinal Study on Aging (BLSA) consisting of 422 adult men and women (19-90 years); the Study of Osteoporotic Risk in Men (STORM) consisting of 333 older men (50-84 years); and a third sample obtained by combining older males aged 59-73 years from the BLSA and STORM cohorts (n=286). In contrast to the European study, we were unable to detect a significant association between CNTF genotype and body weight in the BLSA (P=0.49), the STORM (P=0.28), or the combined samples (P=0.72). There was also no significant association observed between CNTF genotype and BMI in the BLSA (P=0.59), the STORM (P=0.34) or the combined (P=0.56) samples. In addition, we were unable to detect a significant association between CNTF genotype and total body fat (P=0.95) or fat-free mass (P=0.86) in the BLSA cohort. Our results do not support an effect of the CNTF null allele on body composition, contrary to previous findings.