Restoration of Na+/H+ exchanger NHE3-containing macrocomplexes ameliorates diabetes-associated fluid loss

• Authors: Peijian He, Emory University; Luqing Zhao, Emory University; Lixin Zhu, State University of New York, Buffalo; Edward J. Weinman, University of Maryland; Roberto De Giorgio, University of Bologna; Michael Koval, Emory University; Shanthi Srinivasan, Emory University; Chang-Hyon Yun, Emory University
• Journal Title: Journal of Clinical Investigation
• Volume: Volume 125, Number 9
• Publisher: American Society for Clinical Investigation | 2015-09-01, Pages 3519-3531
• Type of Work: Article | Final Publisher PDF
• Publisher DOI: http://doi.org/10.1172/JCI79552
• Subjects: Health Sciences, Medicine and Surgery; Health Sciences, Pharmacology; Health Sciences, General
• Keywords: Science & Technology; Life Sciences & Biomedicine; Medicine, Research & Experimental; Research & Experimental Medicine; RECEPTOR-BINDING PROTEIN; INTESTINAL ION-TRANSPORT; KINASE-C ISOFORMS; BRUSH-BORDER; LYSOPHOSPHATIDIC ACID; IP3 RECEPTOR; CYTOPLASMIC DOMAIN; REGULATORY PROTEIN; NHE3 TRAFFICKING; EPITHELIAL-CELLS

Abstract

Diarrhea is one of the troublesome complications of diabetes, and the underlying causes of this problem are complex. Here, we investigated whether altered electrolyte transport contributes to diabetic diarrhea. We found that the expression of Na+/H+ exchanger NHE3 and several scaffold proteins, including NHE3 regulatory factors (NHERFs), inositol trisphosphate (IP3) receptor-binding protein released with IP3 (IRBIT), and ezrin, was decreased in the intestinal brush border membrane (BBM) of mice with streptozotocin-induced diabetes. Treatment of diabetic mice with insulin restored intestinal NHE3 activity and fluid absorption. Molecular analysis revealed that NHE3, NHERF1, IRBIT, and ezrin form macrocomplexes, which are perturbed under diabetic conditions, and insulin administration reconstituted these macrocomplexes and restored NHE3 expression in the BBM. Silencing of NHERF1 or IRBIT prevented NHE3 trafficking to the BBM and insulin-dependent NHE3 activation. IRBIT facilitated the interaction of NHE3 with NHERF1 via protein kinase D2-dependent phosphorylation. Insulin stimulated ezrin phosphorylation, which enhanced the interaction of ezrin with NHERF1, IRBIT, and NHE3. Additionally, oral administration of lysophosphatidic acid (LPA) increased NHE3 activity and fluid absorption in diabetic mice via an insulin-independent pathway. Together, these findings indicate the importance of NHE3 in diabetic diarrhea and suggest LPA administration as a potential therapeutic strategy for management of diabetic diarrhea.