The Role of the Ovarian Cancer G -Coupled Receptor (OGR1) in Idiopathic Pulmonary Fibrosis

Abstract

Idiopathic pulmonary fibrosis (IPF) is a disease characterized by irreversible scarring of the lung that is associated with significant mortality and morbidity. The pathophysiology is incompletely understood but it is well-established that fibroblast to myofibroblast differentiation is a key feature of pulmonary fibrosis. Our lab has established that a reduction in extracellular pH is one of several important pathways responsible for the activation of latent TGF-β in the extracellular space. TGF-β activation further decreases extracellular pH and creates a feed-forward mechanism that stimulates myofibroblast differentiation and activation of additional TGF-β. Given the importance of TGF-β and extracellular acidification to the progression of pulmonary fibrosis, we sought to identify novel mechanisms that are involved in pH-dependent fibrotic signaling. The proton sensing G-Protein Coupled family of receptors are activated in acidic environments, but their role in fibrotic signaling has not been studied. Here we report that the Ovarian Cancer G-Protein Coupled Receptor1 (OGR1 or GPR68), a member of the family of proton sensing G-Protein Coupled Receptors, negatively regulates pro-fibrotic signaling.We demonstrate that OGR1 expression is significantly reduced in lung tissue from patients with IPF and TGF-β decreases OGR1 expression. In fibroblasts, a reduction in expression of OGR1 (OGR knockout lung fibroblasts) and knockdown (OGR siRNA), promotes in vitro myofibroblast differentiation. In contrast, OGR1 overexpression inhibits myofibroblast differentiation. Finally, we demonstrate that OGR1 negatively regulates TGF-β stimulation through inhibition of focal adhesion kinase (FAK) phosphorylation. Our results suggest that preserving OGR1 expression may represent a novel therapeutic strategy in pulmonary fibrosis.