Later stages of multiple sclerosis (MS) are characterized by a reduced number of infiltrative inflammatory cells and an excessive accumulation of extracellular matrix (ECM) components, which leads to tissue fibrosis. The overproduction of ECM is mediated by the effects of the increase in TGF-beta production by reactive astrocytes. However, the intracellular mechanisms by which TGF- beta stimulates the production of ECM are not completely understood. We showed that during the course of experimental allergic encephalomyelitis (EAE), a mouse model of MS, fewer OLG undergo apoptosis in C5- sufficient (C5-s) mice than in C5-deficient (C5-d) mice. Moreover, in chronic EAE, vigorous tissue repair associated with remyelination, axonal preservation, and absence of gliosis are seen in C5-s, but not C5-d mice. The extensive gliosis we observed in C5-d during chronic EAE may be directly related to the up-regulation of TGF- beta. We have identified RGC-32 as a factor that can mediate the TGF- beta -induced production of connective tissue matrix by astrocytes. Our current goal is to assess whether selectively inhibiting RGC-32 can prevent gliosis. Our overall hypothesis is that the complement terminal pathway has beneficial effects, preventing gliosis through modulation of TGF- beta and RGC-32 expression. Understanding the terminal complement pathway protective effects is critical for developing rational interventions to enhance remyelination and prevent gliosis in MS. To accomplish these goals, we have designed experiments to achieve the following three Specific Aims:
In Aim 1, using a genomic approach, we will explore the pathways regulated by the terminal complement components with role in prevention of gliosis and possibly remyelination. We will analyze gene expression profiles in spinal cord samples from C5-d and C5-s mice during EAE. Based on our preliminary data we postulate that an imbalance in insulin-like growth factor binding proteins and TGF- beta levels is responsible for the generation of gliosis and lack of remyelination observed in C5-d mice.
In Aim 2, we will examine whether the TGF- beta profibrotic effects are mediated by RGC-32. It is well known that TGF- beta and its downstream mediators play an essential role in gliosis but the molecular mechanisms governing this process are not well understood and the role of RGC-32 has not been investigated. TGF- beta is known to induce expression of RGC-32. If RGC-32 is involved in mediating the profibrotic effects of TGF- beta then these effects should be inhibited by RGC-32 silencing. The results of these experiments should tell us whether RGC-32 is involved in mediating TGF- beta profibrotic effects. In addition, we will characterize the signaling pathways and transcription factors involved in TGF- beta induced RGC-32 expression.
In Aim 3, we will determine whether the lack of RGC-32 expression can prevent gliosis in mice with chronic EAE. To assess the contribution of RGC-32 to gliosis in C5-d (C5-/-) mice, we will generate mice lacking both C5 and RGC-32 (RGC-32-/- C5-/-). Experiments proposed in this Aim will allow us to determine whether RGC-32 is an appropriate target to inhibit gliosis. Understanding the terminal complement pathway protective effects is critical for developing rational interventions to enhance remyelination and prevent gliosis in MS. Our proposal is novel in that it integrates RGC-32 with the role of C5 in preventing gliosis, allowing us to define a new therapeutic target in MS.
The impact of multiple sclerosis on VA patient care mission continues to be a major concern. Multiple sclerosis is the leading cause of disability in the young adults in USA. New therapies that are effective in promoting remyelination, preventing gliosis and are associated with fewer side effects are needed. As RGC-32 has been implicated in fibrosis and pathogenesis knowledge gained from the proposed studies in a murine model of experimental allergic encephalomyelitis may be useful in developing new and improved therapies to prevent fibrosis and promote remyelination. Since RGC-32 is involved in regulation of extracellular matrix production by astrocytes, inhibition of RGC- 32 expression is a potential therapeutic target to prevent multiple sclerosis development and progression.