Endosomal Control of Glucose and Fat Accumulation

The endosomal Na+/H+ exchanger NHE6 (SLC9A6) replaces vesicular H+ with cations, to fine tune the pH of early and recycling endosomes. In humans, where mutations in NHE6 cause the neurodevelopmental disorder Christianson Syndrome, a characteristic co-morbidity is low body weight to the point of emaciation. Similarly, we find that nhe6KO mice on high fat diet gained less weight and accumulated significantly lower fat mass than age-matched wild type controls. Brown and white adipose tissue from knockout mice showed smaller and fewer lipid droplets compared to control. We hypothesized that essential steps in the trafficking and turnover of nutrient transporters and receptors occur within the endo-lysosomal compartments where pH plays a critical role. In 3T3L1 derived adipocytes, NHE6 knockdown hyper-acidified endo-lysosomal compartments and diminished insulin-dependent glucose and fatty acid uptake as evidenced by uptake of radio-isotope tracer, confocal microscope imaging and flow cytometry analysis. Expression of insulin responsive proteins, including Insulin Receptor, Glucose Transporter Isoform 4 (GLUT4) and Lipoprotein Receptor 1 (LRP1), was significantly reduced following silencing of NHE6, affecting Akt phosphorylation and activation of the downstream insulin signaling pathway. In contrast, insulin-insensitive GLUT1 expression was increased in knockdown cells. Expression of GLUT4 and Insulin Receptor was restored by chemical bypass of NHE6 using the Na+/H+ exchanger mimetic monensin or the V-ATPase inhibitor bafilomycin, pointing to pH dysregulation as the underlying defect. We propose that endosomal pH acts as a proteostatic switch that regulates turnover of the insulin responsive compartment. Our observations reveal NHE6 as an important contributor to glucose and fat homeostasis with implications for Christianson Syndrome patients. National Institutes of Health NIGMS R01GM147197 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.