ABSTRACT
Extracellular matrix (ECM) deposition in active demyelinating multiple sclerosis (MS) lesions may impede axonal regeneration and can modify immune reactions. Response gene to complement (RGC)-32 plays an important role in the mediation of TGF-ß downstream effects, but its role in gliosis has not been investigated. To gain more insight into the role played by RGC-32 in gliosis, we investigated its involvement in TGF-ß-induced ECM expression and the upregulation of the reactive astrocyte markers α-smooth muscle actin (α-SMA) and nestin. In cultured neonatal rat astrocytes, collagens I, IV, and V, fibronectin, α-SMA, and nestin were significantly induced by TGF-ß stimulation, and RGC-32 silencing resulted in a significant reduction in their expression. Using astrocytes isolated from RGC-32 knock-out (KO) mice, we found that the expression of TGF-ß-induced collagens I, IV, and V, fibronectin, and α-SMA was significantly reduced in RGC-32 KO mice when compared with wild-type (WT) mice. SIS3 inhibition of Smad3 phosphorylation was also associated with a significant reduction in RGC-32 nuclear translocation and TGF-ß-induced collagen I expression. In addition, during experimental autoimmune encephalomyelitis (EAE), RGC-32 KO mouse astrocytes displayed an elongated, bipolar phenotype, resembling immature astrocytes and glial progenitors whereas those from WT mice had a reactive, hypertrophied phenotype. Taken together, our data demonstrate that RGC-32 plays an important role in mediating TGF-ß-induced reactive astrogliosis in EAE. Therefore, RGC-32 may represent a new target for therapeutic intervention in MS.
Subject(s)
Astrocytes/physiology , Encephalomyelitis, Autoimmune, Experimental/metabolism , Gliosis/metabolism , Multiple Sclerosis/metabolism , Nuclear Proteins/metabolism , Actins/metabolism , Animals , Cells, Cultured , Collagen/metabolism , Disease Models, Animal , Extracellular Matrix/metabolism , Female , Fibril-Associated Collagens , Humans , Mice , Mice, Knockout , Nestin/metabolism , Nuclear Proteins/genetics , RNA, Small Interfering/genetics , Rats , Transforming Growth Factor beta/metabolismABSTRACT
Multiple sclerosis (MS) is an inflammatory, demyelinating, and neurodegenerative disease of the central nervous system. The complement system has an established role in the pathogenesis of MS, and evidence suggests that its components can be used as biomarkers of disease-state activity and response to treatment in MS. Plasma C4a levels have been found to be significantly elevated in patients with active relapsing-remitting MS (RRMS), as compared to both controls and patients with stable RRMS. C3 levels are also significantly elevated in the cerebrospinal fluid (CSF) of patients with RRMS, and C3 levels are correlated with clinical disability. Furthermore, increased levels of factor H can predict the transition from relapsing to progressive disease, since factor H levels have been found to increase progressively with disease progression over a 2-year period in patients transitioning from RRMS to secondary progressive (SP) MS. In addition, elevations in C3 are seen in primary progressive (PP) MS. Complement components can also differentiate RRMS from neuromyelitis optica. Response gene to complement (RGC)-32, a novel molecule induced by complement activation, is a possible biomarker of relapse and response to glatiramer acetate (GA) therapy, since RGC-32 mRNA expression is significantly decreased during relapse and increased in responders to GA treatment. The predictive accuracy of RGC-32 as a potential biomarker (by ROC analysis) is 90% for detecting relapses and 85% for detecting a response to GA treatment. Thus, complement components can serve as biomarkers of disease activity to differentiate MS subtypes and to measure response to therapy.
