Inverse Regulation of SGK1 and the Mitochondrial Calcium Uniporter Complex in Aortic Smooth Muscle Cells from Mice and Humans with Obesity and Type 2 Diabetes

Abstract

Background: Individuals with a body mass index (BMI) of ≥30 who are affected with obesity have an increased risk of developing type 2 diabetes (T2D) which exacerbates vascular disease and cardiovascular adverse events such as strokes and heart attacks. However, the molecular mechanisms that underlie obesity- and T2D-induced vascular disease are not fully understood. We have shown that serum and glucocorticoid-inducible kinase 1 (SGK1) is up-regulated in vascular smooth muscle cells (VSMC) of mice fed a high fat to induce obesity and hyperglycemia, a main symptom of T2D. Moreover, knocking out SGK1 in VSMC protects against vascular damage by abolishing the mitochondrial dysfunction that typically accompanies obesity and T2D. Vascular protection correlated with elevated levels of the mitochondrial calcium uniporter complex suggesting that our newly discovered SGK1/MCU pathway plays a role in obesity-associated T2D vascular disease development in humans. MCU is a multimeric complex that regulates Ca2+ influx into the mitochondrial matrix and is tightly controlled by different regulatory subunits with varying functions but its regulation in VSMC exposed to obesity and T2D is unknown. Thus, we tested the hypothesis that obesity and T2D exacerbates VSMC dysfunction via a mechanism that involves SGK1-dependent negative regulation of the MCU complex. Methods: We examined regulation of SGK1 and the MCU complex in aortic VSMC from lean and human subjects with obesity and lean and high fat diet-induced obese wildtype (VSMCWT) and VSMC-SGK1 knockout (VSMCKO) mice. To this end, western blot analysis was performed on VSMC total protein extracts from individuals with BMI = 23.5 ± 0.25 (Lean) and BMI = 37.6 ± 7.2 (Obese) with or without T2D and mice fed a 10 kcal% low fat or 45 kcal% high fat diet for eight weeks. Data was analyzed by 2-Way Analysis of Variance. Results: VSMCWT from obese mice showed reduced levels of MCU and its gatekeeping regulatory subunits, MICU1 and MICU2 compared to lean VSMCWT mice. Knocking out SGK1 in VSMC abolished obesity-related downregulation of MCU and its gatekeeper subunits. As observed in obese mice, SGK1 protein was enriched in VSMC from individuals with obesity. Interestingly, T2D potentiated up-regulation of SGK1 independent of BMI classification. In addition, VSMC from persons affected with obesity showed decreased levels of the MICU2 gatekeeping subunit and this decrease was exaggerated in VSMC from obese individuals with T2D. Conclusions: These findings show that obesity enhances SGK1 abundance in VSMC which may promote negative regulation of the MCU complex and that T2D may exacerbate these effects in the vasculature of humans and rodents. Furthermore, the SGK1/MCU novel pathway may play a permissive role in obesity-related VSMC dysfunction and consequent vascular disease. NIH RCMI G12 Grant: 5G12MD007602 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.