Differential Regulation of NHE3 Expression in Type 1 and Type 2 Diabetic Intestine: Impaired Endosomal Regulation of NHE3 Expression in Type 1 Diabetes

Abstract

Chronic diarrhea is a frequent gastrointestinal complication in both type 1 (T1D) and type 2 diabetes (T2D), though the underlying mechanisms differ: T1D is linked to autonomic neuropathy and disrupted transporter regulation, while T2D is often linked to medications and intestinal inflammation. Using streptozotocin-induced mouse models of T1D and T2D, we observed increased luminal fluid in the small intestine of both. Given the role of Na+/H+ exchanger 3 (NHE3) in fluid absorption and its loss in most diarrheal diseases, we examined NHE3 expression across intestinal segments. In T1D, NHE3 protein was significantly reduced in the duodenum and jejunum without changes in mRNA, suggesting post-transcriptional regulation. In contrast, T2D mice exhibited reduced NHE3 protein and mRNA, restricted to the proximal colon. To investigate mechanisms underlying NHE3 loss in T1D, we evaluated endosomal scaffolding proteins involved in NHE3 trafficking. While our previous work showed that the Sorting Nexin-27 (SNX27)-retromer complex does not regulate NHE3 protein stability, we found that SNX17 was significantly decreased in the small intestine of T1D mice but unchanged in T2D. SNX17 knockdown in SK-CO15 cells reduced NHE3 activity and stability. A GST pull-down assay showed that SNX17 interacts with the C-terminus of NHE3. Mutation of the NHE3 distal NPxY motif disrupted this interaction, leading to reduced NHE3 expression and increased degradation. These findings reveal segment-specific and mechanistically distinct causes of diabetic diarrhea in T1D versus T2D, and identify SNX17 loss as a contributor to reduced NHE3 stability and activity in T1D, likely promoting diabetic diarrhea. New and NoteworthyThis study identifies distinct mechanisms of impaired sodium absorption contributing to diabetic diarrhea in type-1 and type-2 diabetes. We identify SNX17 as a novel regulator of NHE3 in the small intestine, showing that SNX17 loss in T1D contributes to post-translational NHE3 destabilization. In contrast, T2D-associated NHE3 downregulation is transcriptional and confined to the colon. These findings reveal disease- and region-specific regulatory pathways that drive impaired fluid absorption in diabetes, with direct implications for the development of targeted therapies. Graphical abstract Schematic overview of differential NHE3 regulation in diabetic diarrhea.In Type 1 Diabetes (T1D), reduced SNX17 expression in the small intestine causes increased degradation of NHE3 and impaired sodium absorption. In Type 2 Diabetes (T2D), SNX17 levels remain unchanged in the small intestine, but NHE3 expression is transcriptionally downregulated in the proximal colon. These distinct mechanisms contribute to segment-specific differential regulation of NHE3 in T1 and T2D diabetes. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=101 SRC="FIGDIR/small/675364v1_ufig1.gif" ALT="Figure 1"> View larger version (37K): org.highwire.dtl.DTLVardef@eabf0aorg.highwire.dtl.DTLVardef@1a46891org.highwire.dtl.DTLVardef@cd2d5corg.highwire.dtl.DTLVardef@5d185b_HPS_FORMAT_FIGEXP M_FIG C_FIG