REGULATION OF CELLULAR BIOENERGETICS IN CNS DEMYELINATING DISEASE

Abstract

Multiple Sclerosis (MS) is a debilitating neurological disease characterized by sclerotic inflammatory demyelination of the white matter tracts in the central nervous system (CNS). There is no “cure” for MS but rather disease modifying treatments that decrease relapse rates and slow disease progression. Due to the lack of insight into the pathogenesis of MS, animal models have been developed to study demyelination in the CNS. Two widely used models of demyelination are experimental autoimmune encephalomyelitis (EAE), and Theiler’s murine encephalomyelitis virus (TMEV). Our studies focused on TMEV mediated demyelination, which was dependent on the expression of the protein tyrosine phosphate SHP-1. SHP-1 is a major negative regulator of cytokine/growth factor signaling and a global deficiency triggers an acute macrophage mediated demyelination in C3H mice. SHP-1 deficient mice are also highly susceptible to systemic inflammation and dysmyelination. Our overall goal was to identify how SHP-1 is mediating susceptibility to inflammatory demyelination. We first demonstrated that SHP-1 deficient oligodendrocytes had increased reactive oxygen species (ROS) production resulting in downregulation of myelin gene expression and oxidation of myelin, a common finding in MS patients. To determine a source of the ROS we investigated how SHP-1 controls metabolic pathways as ROS production is tightly linked to metabolism. To determine how SHP-1 impacts bioenergetics, oligodendrocyte glycolytic and mitochondrial metabolism were quantified using the Seahorse XFe96 analyzer. We determined that SHP-1 enhances oligodendrocyte metabolism, which correlates with its ability to suppress STAT1 activity in oligodendrocytes. We corroborated these results via activation of STAT1 in oligodendrocytes with the proinflammatory cytokine IFN-γ recapitulating the metabolic defects in SHP-1 deficient oligodendrocytes. Based the role of SHP-1 in oligodendrocyte bioenergetics and the importance of macrophage-derived cytokine production during demyelination; we investigated a role for SHP-1 in macrophage bioenergetics. In macrophages, enhanced glycolysis drives activation and proinflammatory cytokine production. TMEV infection specifically induced glycolysis in GM-CSF-derived macrophages lacking SHP-1. This finding may explain why SHP-1 confers susceptibility to macrophage-mediated demyelination after TMEV infection. Overall we demonstrate a novel role for SHP-1 in controlling oligodendrocyte and macrophage bioenergetics that is highly relevant in expanding our understanding of CNS demyelinating disease.