New Therapeutic Approach for Intestinal Fibrosis Through Inhibition of pH-Sensing Receptor GPR4

Abstract

Background Patients suffering from inflammatory bowel diseases (IBDs) express increased mucosal levels of pH-sensing receptors compared with non-IBD controls. Acidification leads to angiogenesis and extracellular matrix remodeling. We aimed to determine the expression of pH-sensing G protein-coupled receptor 4 (GPR4) in fibrotic lesions in Crohn’s disease (CD) patients. We further evaluated the effect of deficiency in Gpr4 or its pharmacologic inhibition. Methods Paired samples from fibrotic and nonfibrotic terminal ileum were obtained from CD patients undergoing ileocaecal resection. The effects of Gpr4 deficiency were assessed in the spontaneous Il-10-/- and the chronic dextran sodium sulfate (DSS) murine colitis model. The effects of Gpr4 deficiency and a GPR4 antagonist (39c) were assessed in the heterotopic intestinal transplantation model. Results In human terminal ileum, increased expression of fibrosis markers was accompanied by an increase in GPR4 expression. A positive correlation between the expression of procollagens and GPR4 was observed. In murine disease models, Gpr4 deficiency was associated with a decrease in angiogenesis and fibrogenesis evidenced by decreased vessel length and expression of Edn, Vegfα, and procollagens. The heterotopic animal model for intestinal fibrosis, transplanted with terminal ileum from Gpr4-/- mice, revealed a decrease in mRNA expression of fibrosis markers and a decrease in collagen content and layer thickness compared with grafts from wild type mice. The GPR4 antagonist decreased collagen deposition. The GPR4 expression was also observed in human and murine intestinal fibroblasts. The GPR4 inhibition reduced markers of fibroblast activation stimulated by low pH, notably Acta2 and cTgf. Conclusions Expression of GPR4 positively correlates with the expression of profibrotic genes and collagen. Deficiency of Gpr4 is associated with a decrease in angiogenesis and fibrogenesis. The GPR4 antagonist decreases collagen deposition. Targeting GPR4 with specific inhibitors may constitute a new treatment option for IBD-associated fibrosis.

Physiological relevance of proton-activated GPCRs

“…We will term this here as "OGR1-TDAG8 reciprocity," but it still unknown whether this phenomenon is relevant and whether it occurs in an independent or coordinated manner. In inflammatory bowel disease models, genetic and pharmacological inhibition of GPR4 was also protective and a promising target for therapies aiming at reducing intestinal fibrosis [109,136,137]. Pharmacological inhibition of OGR1 also produced similar protective effects [127].…”

“…Collectively, these studies show an influence of this receptor on multiple downstream effectors and pathways, such as the hippo pathway, MEK/ERK signaling, and activation of SRE and NFAT [99,122,154]. There are no known pharmacological agonists for GPR4, but several antagonists have been developed and successfully applied in vivo [25,82,109,129,137].…”

“…Whether OGR1 also contributes to the vascular response during inflammation has not been addressed to date. However, one should also take into consideration that these receptors also play important roles in other cell types involved in inflammatory processes (and associated events) like epithelial cells, fibroblasts, and smooth muscle cells [77,90,111,137]. For example, OGR1 has been shown to play a role in endoplasmic reticulum stress in an epithelial cell line [77], inhibition of GPR4 in fibroblasts reduces pHdependent transition to myofibroblasts [137], and TDAG8 participates in proliferation and migration of smooth muscle cells with impact in atherosclerosis [11].…”

“…The field is still hampered by the lack of reliable and sufficiently specific antibodies allowing for the exact locali-zation of these receptors or performing studies on their regulation. Proton-activated GPCR reporter mice have been used to partly circumvent this issue [137,147]. 3.…”

Intestinal strictures in Crohn’s disease: a 2021 update

“…Other promising molecules that target fibroblasts or myofibroblasts include GPR4 and miR-155. 25 , 26 GPR4/Gα 12/13 signaling was involved in the initiation of myofibroblast activation, and this effect could be reversed by the inhibition of GPR4. 25 MiR-155 was demonstrated to directly target HMG-box transcription factor 1 and then activate Wnt/β-catenin signaling pathway, leading to intestinal fibrosis [ Figure 2(b) ].…”