Regulation of Renal Cortical PPAR-alpha and Downstream Targets by Sodium Glucose Cotransporter, Type 2 Inhibition (SGLT2i) in High-Fat Fed Mice
Authors: Lee Dexter , Khundmiri Syed , Kim Minsol , Levi Moshe , Shepard Blythe , Ecelbarger Carolyn 
Published: May 2024

SGLT2i has been shown to be protective of renal function and health in type 2 diabetes by unclear means. Recently we reported that empagliflozin (EMPA) treatment of mice on a high-fat diet (HFD) led to marked changes in the renal cortical lipidome, including significant upregulation of many carnitine species (11 species > 35% increased, all p < 0.05). Carnitines are critical in the oxidation of long-chain fatty acids by increasing their uptake into the mitochondria. The mechanism underlying this upregulation was unclear, but the peroxisome proliferator activated receptor, subtype alpha (PPARα) has been demonstrated to upregulate carnitines in other tissues. To the test the impact of EMPA (E) or control (C) treatment on renal cortical PPARα and downstream targets, male (M) and female (F) C57Bl6 mice were treated with HFD (60% by weight) ± EMPA (100 mg/kg·diet) for 12 weeks. EMPA caused a reduction in final body weight (20%) only in females. No differences were observed in final kidney weights (n = 16-18/group). Glomerular filtration rate (GFR) measured by FITC-sinistrin clearance showed a trend (p = 0.052 two-way ANOVA) for an increase by EMPA (mean ± sem, ml/min, n = 5-9): MC- 246 ± 13; ME- 291 ± 5; FC- 252 ± 13; and FE- 275 ± 36. Western blotting of cortex homogenates revealed a modest, insignificant rise in PPARα, itself with EMPA, and a higher overall abundance in females (p = 0.024 for sex, mean band density, % MC): MC-100 ± 14; ME- 108 ±11; FC- 123± 12, FE- 151± 18. Fibroblast growth factor 21 (FGF21) is a reported target of PPARα, and has been shown to be increased in liver in response to treatment with a PPARα agonist. However, FGF21 is also increased compensatorily in metabolic stress conditions, e.g., obesity. We found EMPA treatment substantially reduced circulating FGF21 levels in M, while F levels were low regardless of treatment (ng/ml): MC-3.28 ± 1.32; ME- 0.07 ± 0.027; FC- 0.19 ± 0.08, FE- 0.17 ± 0.08 (p = 0.031, 0.044, and 0.033, for treatment, sex, and interaction, respectively). FGF21 levels in liver, site of most production (measured in males only) was likewise reduced by EMPA (84%, p = 0.029, Mann-Whitney test). In contrast, no significant differences were found for renal cortical FGF21 levels. Previously, we showed PPARα whole-body knockout mice had higher renal expression of Na+K+ATPase, which was associated with higher blood pressure. Western blotting of EMPA-treated mice showed the α-1 subunit of Na+K+ATPase, a surrogate marker of proximal tubule transport activity, was significantly increased in the kidney cortex of EMPA-treated mice (band density % MC): MC-100 ± 26; ME- 145 ± 25; FC- 99 ± 22, FE- 175 ± 21 (p = 0.54, 0.016, and 0.52, for treatment, sex, and interaction, respectively). This was not associated with higher blood pressure in EMPA-treated mice, as measured by tail-cuff. Taken together, these findings do not suggest an overall increase in activity of PPARα in kidney or systemically (in liver) with EMPA. The upregulation of carnitine species in kidney may have resulted from an alternative mechanism. Additional studies are warranted to gauge the role of PPARα activation, emanating from a relatively fasted state, with SGLT2 inhibition, in the kidney and in regard to whole body metabolism. Supported by GHUCCTS (Howard and Georgetown, UL1TR001409) pilot award to CE. This is the full abstract presented at the American Physiology Summit 2024 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.