The proton-activated receptor TDAG8 is upregulated in oligodendrocytes during maturation and under acidic conditions

Abstract

Acidosis is one of the hallmarks of demyelinating central nervous system (CNS) lesions in multiple sclerosis (MS). Response to acidic pH is primarily mediated by a family of G protein-coupled proton-sensing receptors: OGR1, GPR4, and TDAG8. These receptors are inactive at alkaline pH, while at acidic pH they are maximally activated. Genome-wide association studies identified a locus within the TDAG8 gene to be associated with several autoimmune diseases including MS. Notably, we here found that TDAG8 expression is upregulated in MS plaques which prompted us to explore the expression and function of TDAG8 in the CNS in human MO3.13 oligodendrocytesin vitroandin vivoin the lipopolysaccharide-induced neuroinflammation model. We found that TDAG8 is upregulated in maturing oligodendrocytes and temporarily under acidic conditions. Acidic pH also induces oligodendrocyte branching, inhibits chemotaxis and affects the expression of oligodendrocyte maturation markers, PDGFRα and MBPin vitro. Even though myelination was not affected in the adult TDAG8-deficient mice, the expression of human and murine TDAG8 was strongly regulated upon inflammationin vivoin the brain andin vitroin lipopolysaccharide and pro-inflammatory cytokine-treated oligodendrocytes. Together these findings point toward a potential role of TDAG8 in oligodendrocyte biology, neuroinflammation and pathophysiology of MS and provide new directions for further scientific enquiry.