GPR4 deficiency alleviates intestinal inflammation in a mouse model of acute experimental colitis

Abstract

GPR4 is a proton-sensing G protein-coupled receptor that can be activated by extracellular acidosis. It has recently been demonstrated that activation of GPR4 by acidosis increases the expression of numerous inflammatory and stress response genes in vascular endothelial cells (ECs) and also augments EC-leukocyte adhesion. Inhibition of GPR4 by siRNA or small molecule inhibitors reduces endothelial cell inflammation. As acidotic tissue microenvironments exist in many types of inflammatory disorders, including inflammatory bowel disease (IBD), we examined the role of GPR4 in intestinal inflammation using a dextran sulfate sodium (DSS)-induced acute colitis mouse model. We observed that GPR4 mRNA expression was increased in mouse and human IBD tissues when compared to control intestinal tissues. To determine the function of GPR4 in intestinal inflammation, wild-type and GPR4-deficient mice were treated with 3% DSS for 7 days to induce acute colitis. Our results showed that the severity of colitis was decreased in GPR4-deficient DSS-treated mice in comparison to wild-type DSS-treated mice. Clinical parameters, macroscopic disease indicators, and histopathological features were less severe in the DSS-treated GPR4-deficient mice than the DSS-treated wild-type mice. Endothelial adhesion molecule expression, leukocyte infiltration, and isolated lymphoid follicle (ILF) formation were reduced in intestinal tissues of DSS-treated GPR4-null mice. Collectively, our results suggest GPR4 provides a pro-inflammatory role in the inflamed gut as the absence of GPR4 ameliorates intestinal inflammation in the acute experimental colitis mouse model.

Pharmacological inhibition of GPR4 remediates intestinal inflammation in a mouse colitis model

“…The pH-sensing GPCRs, including GPR65 (TDAG8), GPR68 (OGR1), and GPR4, have emerged as regulators of intestinal inflammation (de Valliere et al, 2015;Hutter et al, 2018;Lassen et al, 2016;Sanderlin et al, 2017;Wang et al, 2018). Initial studies on the effects of acidic pH-induced activation of GPR65 have provided an anti-inflammatory role for GPR65 in macrophages and other immune cells (Jin et al, 2014;Mogi et al, 2009).…”

“…One such family of GPCRs are the protonsensing GPCRs, which consist of GPR4, GPR65 (TDAG8), and GPR68 (OGR1) (Justus et al, 2013;Justus et al, 2017;Ludwig et al, 2003;Sanderlin et al, 2015). These receptors have been implicated in the modulation of intestinal inflammation (de Valliere et al, 2015;Lassen et al, 2016;Sanderlin et al, 2017;Wang et al, 2018). Studies have shown GPR4 is responsible for acidosis-induced endothelial cell inflammation and can functionally increase leukocyte adhesion with endothelial cells (Chen et al, 2011;Dong et al, 2017;Dong et al, 2013;Tobo et al, 2015).…”

The proton-sensing GPR4 receptor regulates paracellular gap formation and permeability of vascular endothelial cells

“…In order to investigate GPR4 in the ischemia-reperfusion model, we used the [19,20]. GPR4 knockout mice were protected from intestinal inflammation and had reduced adhesion molecule expression in intestinal microvascular endothelial cells when compared to wild-type mice [19].…”

“…For assessment of neutrophilic infiltration into inflammatory exudate, pictures were taken from H&E tissue sections at five random points with a 20x objective. Leukocytes with the distinct polymorphic nuclear morphology were counted in each field of view using ImageJ software in a blind manner as previously described [19]. Pictures were taken using the Zeiss Axio Imager A1 microscope.…”

“…GPR4 has also been shown to potentiate inflammation in vivo. Recent studies found that the genetic deletion of GPR4 in mouse colitis models decreased the expression of endothelial adhesion molecules VCAM-1 and E-Selectin in the intestinal microvasculature which was associated with reduced mucosal leukocyte infiltration and intestinal inflammation [19,20]. Furthermore, GPR4 was shown to increase tissue injury in a renal ischemia-reperfusion mouse model [21].…”