Daniel Chesik

Insulin-like growth factor system regulates oligodendroglial cell behavior : Therapeutic potential in CNS

Amongst the many soluble extracellular factors stimulating intracellular signal transduction pathways and driving cellular processes such as proliferation, differentiation and survival, insulin-like growth factors (IGFs) stand out as indispensable factors for proper oligodendrocyte differentiation and accompanying myelin production. Owing to its potent myelinogenic capacity and its neuroprotective properties, IGFs hold therapeutic potential in demyelinating and neurodengenerative diseases. However, the IGF system is comprised of a complex molecular network involving regulatory binding proteins, proteases, cell surface and extracellular matrix components which orchestrate IGF-specific functions. Thus, the complexity by which these factors are tightly regulated makes a simplistic therapeutic approach towards treating demyelinating conditions unfeasible. In the present review, we address these issues and consider current therapeutic prospects of oligodendrocyte-targeted IGF-based therapies.

The Insulin‐like Growth Factor System in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic disorder of the central nervous system characterized by inflammation, demyelination, and axonal degeneration. Present therapeutic strategies for MS reduce inflammation and its destructive consequences, but are not effective in the progressive phase of the disease. There is a need for neuroprotective and restorative therapies in MS. Insulin-like growth factor-1 (IGF-1) is of considerable interest because it is not only a potent neuroprotective trophic factor but also a survival factor for cells of the oligodendrocyte lineage and possesses a potent myelinogenic capacity. However, the IGF system is complex and includes not only IGF-1 and IGF-2 and their receptors but also modulating IGF-binding proteins (IGFBPs), of which six have been identified. This chapter provides an overview of the role of the IGF system in the pathophysiology of MS, relevant findings in preclinical models, and discusses the possible use of IGF-1 as a therapeutic agent for MS.

Bone marrow stromal cell interaction reduces Syndecan-1 expression and induces kinomic changes in myeloma cells

CD138 (Syndecan 1) is a heparan sulfate proteoglycan that concentrates heparan sulfate-binding growth factors on the surface of normal and malignant plasma cells (multiple myeloma, MMC). Recent studies have shown the presence of a CD138-negative fraction of MMC within myelomatous bone marrow (BM). We employed kinome array technology to characterize this fraction at a molecular level, using a myeloma cell line model. Compared to CD138-positive cells, CD138-negative MMC showed (i) a reduced activity of kinases involved in cell cycle progression, in agreement with a decreased labeling index and (ii) reduced Rho signaling to F-actin. Interestingly, CD138 mRNA and protein expression was reduced upon interaction of MM cells with stromal cell lines and primary mesenchymal cultures, which was accompanied by the acquisition of an increased Bcl6/Blimp1 ratio. Co-culture induced an increased activity of kinases involved in adhesion and a decreased S-phase transition in both CD138-positive and -negative fractions. In addition, CD138-negative MMC demonstrated an increased STAT3 and ERK1/2 activation compared to CD138+ MMC, in agreement with a lower sensitivity to compound exposure. The presence of a less mature, more resistant CD138-negative myeloma cell fraction within bone marrow microniches might contribute to high incidence of relapse of Myeloma patients.

Progesterone and dexamethasone differentially regulate the IGF-system in glial cells

IGF-1 is an important factor for myelin synthesis and hence possesses therapeutic potential in treating demyelinating disease such as multiple sclerosis. However, IGF-1 poorly crosses the blood-brain barrier. In this study, we investigated the effects of the sex steroid progesterone and the glucocorticoid dexamethasone on regulation of the IGF-system in glial cells. By means of quantitative PCR analysis, we demonstrate that progesterone upregulates IGF-1, the type 1 IGF receptor and IGFBP-2 in primary rat astrocytes and both IGF-1 and IGFBP-6 in OLN-93 oligodendroglial progenitor cells. In contrast, dexamethasone showed a negative effect on expression of IGF-1, the type 1 IGF receptor and the respective IGF binding proteins in both cell types. In oligodendrocytes, the differentiation marker CNPase was positively regulated by progesterone and negatively regulated by dexamethasone. Further, oligodendroglial cell migration was enhanced approximately 4-fold by progesterone. This study implicates progesterone as a positive regulator of IGF-system in glial cells and demonstrates a further biological function of progesterone in oligodendrocyte biology, namely stimulation of progenitor cell migration. Dexamethasone, on the other hand, is a negative regulator of the IGF-system in glial cells.

5HT4 agonists inhibit interferon-γ-induced MHC class II and B7 costimulatory molecules expression on cultured astrocytes

A failure of tight control of MHC class II expression on astrocytes may play a role in the development of autoimmune responses in multiple sclerosis. The 5-HT(4) serotonin receptor agonists cisapride and prucalopride, at concentrations between 10(-10) M and 10(-8) M, reduced interferon-gamma-induced MHC class II immunostaining in cultured astrocytes derived from newborn Wistar rats by approximately 50-60%. The magnitude of MHC class II inhibition by 5-HT(4) agonists was comparable to that of interferon-beta. The alpha(1)-adrenergic receptor agonist phenylephrine was without effect. Cisapride (10(-9) M) also prevented interferon-gamma-induced B7-1 and B7-2 immunostaining. Our results suggest that 5-HT(4) agonists may have therapeutic potential in multiple sclerosis by inhibiting the up-regulation of immune responsiveness of astrocytes in the central nervous system.

Serum levels of insulin-like growth factor-1 and insulin-like growth factor binding protein-3 in relapsing and primary progressive multiple sclerosis

Using radioimmunoassay we measured serum levels of insulin-like growth factor (IGF)-1 and IGF binding protein (IGFBP)-3 in patients with relapsing multiple sclerosis (MS) and a benign course (Expanded Disability Status Scale (EDSS)≤ 3 despite > 10 years disease duration), relapsing MS with cumulative disability leading to an EDSS score > 4 within 10 years of disease duration, primary progressive MS and healthy controls. We found no differences in IGF-1 and IGFBP-3 serum levels, and the IGF-1/IGFBP-3 ratio between the four groups. However, there was a significant correlation (P=0.005) between IGFBP-3 serum levels and both the progression index of disability and the Multiple Sclerosis Severity Score in patients with primary progressive MS.

IGF binding protein alterations on periplaque oligodendrocytes in multiple sclerosis: Implications for remyelination

Why myelin repair greatly fails in multiple sclerosis (MS) is unclear. The insulin-like growth factor (IGF) system plays vital roles in oligodendrocyte development, survival, and myelin synthesis. We used immunohistochemistry to study IGF-I, IGF-I receptors and IGF binding proteins (IGFBPs) 1-6 on oligodendrocytes at the edges of chronic demyelinated plaques and normal appearing white matter of MS, and in cerebral white matter of controls without neurological disease. Oligodendrocytes in all conditions were immunoreactive for IGF-I, IGF-I receptors and IGFBPs-1-5. Oligodendrocytes at the edges of demyelinated plaques displayed enhanced immunoreactivity for IGF-I, IGF-I receptors, IGFBPs-1 and -6. Because increased expression of IGFBPs-1 and -6 has been associated with impaired synthesis of myelin proteins in oligodendrocyte lineage cells, pharmacological approaches to reduce their expression might be useful for promoting remyelination of axons in MS lesions.

Insulin-like growth factor binding protein-1 activates integrin-mediated intracellular signaling and migration in oligodendrocytes

J. Neurochem. (2010) 113, 1319–1330.

Enhanced production and proteolytic degradation of insulin-like growth factor binding protein-2 in proliferating rat astrocytes

Insulin‐like growth factors (IGFs) protect neurons, are important for oligodendrocyte survival and myelin production, and stimulate the proliferation of astrocytes. The effects of IGFs are regulated by a family of IGF binding proteins (IGFBPs). Astrocytes express predominantly IGFBP‐2. In the present study, primary neonatal rat astrocytes were cultivated in a chemically defined medium to initiate a differentiated cell status. After stimulation with fetal calf serum, astrocytes became hypertrophic and increased proliferation. Western blot analysis of cell lysate of proliferating astrocytes displayed an increased expression of IGFBP‐2. This finding was supported by immunocytochemical images. Semiquantitative polymerase chain reaction analysis demonstrated equal mRNA levels in both differentiated and proliferating astrocytes, suggesting that the increase in IGFBP‐2 production in proliferating astrocytes was exerted at the translational level. Concentrated medium of proliferating cells, however, displayed lower levels of IGFBP‐2 than differentiated cells. When recombinant IGFBP‐2 was incubated with culture media, we found degradation in the medium of proliferating cells, but not in medium of differentiated cells. This degradation could be inhibited with protease inhibitors, indicating that lower levels of IGFBP‐2 in the medium of proliferating astrocytes are due to the presence of proteases. Our results suggest that, in proliferating astrocytes, IGFBP‐2 may help target IGFs to IGF‐1 receptors, and IGFBP‐2 proteases may play a role in enhancing the availability of IGFs.

Insulin‐like growth factor binding proteins: regulation in chronic active plaques in multiple sclerosis and functional analysis of glial cells

Studies in experimental allergic encephalomyelitis, an animal model of multiple sclerosis (MS), suggest that astrocyte‐secreted insulin‐like growth factor binding protein‐2 (IGFBP‐2) helps target IGF‐1 to IGF‐1 receptor‐expressing oligodendrocytes and promote remyelination. We examined the presence of IGFBPs 1–6 in astrocytes in normal post‐mortem human brain tissue and lesions of MS by means of immunohistochemistry. Under normal conditions all six IGFBPs were detected. Compared to controls, hypertrophic astrocytes at the borders of chronic active MS lesions displayed increased immunoreactivity for IGFBP‐2 and IGFBP‐4. In vitro studies were performed to analyse the effects of IGFBPs on cellular proliferation of neonatal rat glial cells. Treatment of astrocytes with IGF‐1 and ‐2 enhanced proliferation whereas IGFBP‐2 and ‐4 inhibited cellular growth. Interestingly, combined treatment with IGFBP‐2 and IGF‐1 potentiated effects on cellular proliferation whereas combined treatment with IGFBP‐2 and IGF‐2 inhibited growth. Unlike IGFBP‐2, IGFBP‐4 inhibited proliferation in combined treatment with IGF‐1. In contrast, combined treatment with IGFBP‐2 and IGF‐1 resulted in decreased cell survival of oligodendrocyte precursor cells. Our results suggest that the up‐regulation of IGFBP‐2 in reactive astrocytes in MS lesions may primarily serve to enhance the IGF‐1‐mediated mitogenic stimulus for astrocytes rather than supporting oligodendrocyte survival.