High Glucose Concentration Stimulates NHE-1 Activity in Distal Nephron Cells: the Role of the Mek/Erk1/2/p90^RSKand p38MAPK Signaling Pathways

Abstract

Aims: In models of diabetes, distal nephron cells contribute to glucose uptake and oxidation. How these cells contribute to the use of glucose for the regulation of H⁺ extrusion remains unknown. We used Madin-Darby Canine Kidney (MDCK) cells to investigate the effect of acute or chronic high glucose concentration on the abundance and activity of the Na⁺/H⁺ exchanger (NHE-1). Methods: Using RT-PCR, we also evaluated the mRNA expression for sodium glucose co-transporters SGLT1 and SGLT2. Protein abundance was analyzed using immunoblotting, and intracellular pH (pH_i) recovery was evaluated using microscopy in conjunction with the fluorescent probe BCECF/AM. The Na⁺-dependent pH_i recovery rate was monitored with HOE-694 (50 µM) and/or S3226 (10 µM), specific NHE-1 and NHE-3 inhibitors. Results: MDCK cells did not express the mRNA for SGLT1 or SGLT2 but did express the GLUT2, NHE-1 and NHE-3 proteins. Under control conditions, we observed a greater contribution of NHE-1 to pH_i recovery relative to the other H⁺ transporters. Acute high glucose treatment increased the HOE-694-sensitive pH_i recovery rate and p-Erk1/2 and p90^RSK abundance. These parameters were reduced by PD-98059, a Mek inhibitor (1 µM). Chronic high glucose treatment also increased the HOE-694-sensitive pH_i recovery rate and p-p38MAPK abundance. Both parameters were reduced by SB-203580, a p38MAPK inhibitor (10 µM). Conclusion: These results suggested that extracellular high glucose stimulated NHE-1 acutely and chronically through Mek/Erk1/2/p90^RSK and p38MAPK pathways, respectively.

Nucleosome Positioning and Gene Regulation of the SGLT2 Gene in the Renal Proximal Tubular Epithelial Cells

“…SGLT2 is known to be expressed in PTECs of the human kidney. Some PTEC lines, such as LLC-PK1, KPT2, and MDCK cells, have been used to analyze expression and regulation of the SGLT2 gene in the kidney (Da Costa-Pessoa et al, 2014;Jiang et al, 2014;Zapata-Morales et al, 2014). The human kidney-derived HK-2 cell line, which is available as a human PTEC model (Ryan et al, 1994;Wilmer et al, 2010), has been used to evaluate the regulatory mechanism for the SGLT2 gene in PTECs of the human kidney (Panchapakesan et al, 2013).…”

Endothelial Na+/H+ exchanger NHE1 participates in redox-sensitive leukocyte recruitment triggered by methylglyoxal

“…Mounting evidence suggests that NHE1 participates in the pathogenesis of various complications of diabetes. Recently, high glucose concentrations were demonstrated to stimulate p38 MAPK- and ERK1/2-dependent NHE1 activation in distal nephron cells [ 56 ]. Strikingly, hyperglycemia was shown to induce endothelial dysfunction via Ca 2+ -dependent calpain signaling mediated by the Na + /H + exchanger [ 57 ].…”

Angiotensin II-induced podocyte apoptosis is mediated by endoplasmic reticulum stress/PKC-δ/p38 MAPK pathway activation and trough increased Na+/H+ exchanger isoform 1 activity

“…In turn, p38 MAPK also regulates mechanisms involved in intracellular pH (pHi) control [ 22 ], particularly by phosphorylating the Na + /H + exchanger isoform 1 (NHE1) at serine sites (Ser 726 and Ser 729) [ 23 ]. NHE1 protein is ubiquitously distributed in the plasma membrane and in polarized epithelial cells; its mature form is localized almost exclusively in the basolateral membrane [ 24 ].…”