Glucose transporter 2 expression is down regulated following P2X7 activation in enterocytes

Abstract

With the diabetes epidemic affecting the world population, there is an increasing demand for means to regulate glycemia. Dietary glucose is first absorbed by the intestine before entering the blood stream. Thus, the regulation of glucose absorption by intestinal epithelial cells (IECs) could represent a way to regulate glycemia. Among the molecules involved in glycemia homeostasis, extracellular ATP, a paracrine signaling molecule, was reported to induce insulin secretion from pancreatic β cells by activating P2Y and P2X receptors. In rat's jejunum, P2X7 expression was previously immunolocalized to the apex of villi, where it has been suspected to play a role in apoptosis. However, using an antibody recognizing the receptor extracellular domain and thus most of the P2X7 isoforms, we showed that expression of this receptor is apparent in the top two-thirds of villi. These data suggest a different role for this receptor in IECs. Using the non-cancerous IEC-6 cells and differentiated Caco-2 cells, glucose transport was reduced by more than 30% following P2X7 stimulation. This effect on glucose transport was not due to P2X7-induced cell apoptosis, but rather was the consequence of glucose transporter 2 (Glut2)'s internalization. The signaling pathway leading to P2X7-dependent Glut2 internalization involved the calcium-independent activation of phospholipase Cγ1 (PLCγ1), PKCδ, and PKD1. Although the complete mechanism regulating Glut2 internalization following P2X7 activation is not fully understood, modulation of P2X7 receptor activation could represent an interesting approach to regulate intestinal glucose absorption.

A Role of Intestinal Alkaline Phosphatase 3 (Akp3) in Inorganic Phosphate Homeostasis

“…Purine nucleotides are well established extracellular signaling molecules [47]. P2X purinoceptor 7 (P2X7) is a member of the family of ionotropic ATP-gated receptors that localizes at the apical membrane of the epithelial cells of the mouse ileum [43,47]. To examine whether ATP suppresses Npt2b expression, we used the normal rat cell line IEC-6.…”

“…The rat cell line IEC-6 (ATCC, Manassas, VA) was maintained in DMEM (Sigma-Aldrich, St. Louis, MO) supplemented with 10% FBS, as described previously [43,44]. BzATP triethylammonium salt, an activator of the P2X receptors, was obtained from Wako (Tokyo, Japan).…”

C/EBPβ regulates P2X7 receptor expression in response to glucose challenge in intestinal epithelial cells

“…Contrary to the colon, where the function of the P2X7 receptor has been associated with immune and inflammatory phenotypes and the regulation of neuroenteric signaling , the literature concerning the role of this receptor in the small intestine is rather limited. We know from previous studies that the P2X7 receptor is expressed by IECs (Bourzac et al 2013;de Campos et al 2012;Groschel-Stewart et al 1999;Souza et al 2012), and that receptor activation was associated with the induction of apoptosis in response to high ATP concentration, as observed in diseases (Groschel-Stewart et al 1999;Souza et al 2012) and more recently to glucose transport by IECs (Bourzac et al 2013). In addition to its role in IEC glucose transport, there is increasing evidence that the P2X7 receptor is an important element in the regulation of metabolism and glucose homeostasis in particular (Ohtani et al 2011).…”

“…Furthermore, type 2 diabetic patients display resistance to insulin, and thus the retroactive function of this hormone on GLUT2 internalization in IECs may be ineffective, as reported in a model of diabetic mice (Tobin et al 2008). We previously reported that the P2X7 receptor may act as a retroactive controlling sensor by stimulating the internalization of GLUT2 (Bourzac et al 2013). These recent results suggest that expression of the P2X7 receptor by IECs may also be regulated by a variation in glucose concentration.…”

“…However, other studies have suggested that GLUT2 insertion to the apical membrane of enterocytes was required to accommodate the important concentration of luminal glucose in postprandial situations (Chaudhry et al 2012;Ferraris 2001;Leturque et al 2009). In this context, activation of the P2X7 ATP-gated ion channel results in GLUT2 internalization, which significantly reduces glucose absorption and transport by IECs (Bourzac et al 2013). This particular receptor belongs to the P2 family of extracellular nucleotide receptors and has long been associated with cell apoptosis as well as a key element of the NLRP3 inflammasome necessary for IL-1␤ maturation (Cesaro et al 2010;Gulbransen et al 2012).…”