Effect of Fasting During Time Restricted Feeding on Mitochondrial Beta-Oxidation Enzyme Expression in the Kidney Cortex of Adult Male Salt-Sensitive Dahl Rats
Authors: Yunker Lauren , Reho John J. , Williams Adaysha , Grobe Justin L. , Kriegel Alison 
Published: May 2024

The Dahl salt-sensitive (SS) rat is a well-characterized model of SS hypertension and renal disease that exhibits enhanced Na+ reabsorption in the kidney. Prior research has shown that SS rats experience a reduction in fatty acid beta oxidation (FAO) in the kidney cortex when placed on a high salt (HS) diet. Time restricted feeding (TRF), a type of intermittent fasting in which food consumption is restricted to <10 hrs/day, has been shown to activate FAO. Since the proximal tubule is responsible for the highest amount of Na+ reabsorption, we are interested in understanding if intermittent salt intake via TRF can mitigate dysfunctional cortical metabolism and slow progression of renal damage. We hypothesized that fasting during TRF would activate FAO throughout the body, as well as in the kidney cortex. To study this, 10-week-old male SS rats were provided ad libitum access to 4.0% NaCl (high salt; HS) or 0.4% (low salt; LS) diet for one week. Rats were then placed into a Promethion Core system (Sable Systems International) for metabolic phenotyping, where some continued ad libitum feeding, and others began time restricted feeding (TRF) for an additional week (n=7-9/group). During TRF, food was provided for 8 hours during the active cycle (2200hrs-0600hrs). Rats were euthanized in the last two hours of the final fasting period. We found that during the last hour of the fasting period, when compared to ad libitum rats, both the LS TRF (0.824 ± 0.01 vs 0.986 ± 0.008) and HS TRF (0.830 ± 0.01 vs 0.980 ± 0.006) rats had a significant reduction in their respiratory exchange ratio (2-way ANOVA with Tukey multiple comparisons, p<0.05, mean ± SEM). This suggests that the TRF protocol induced a net whole-body shift in fuel utilization from primarily carbohydrates to a mix of fuel sources by the end of the 16-hour fasting period, regardless of diet. To investigate the effect of fasting during TRF on the kidney cortex, we performed western blot analysis of acyl-CoA dehydrogenase long chain (ACADL) and acetyl-CoA acyltransferase 2 (ACAA2), enzymes involved in initial and final steps of mitochondrial beta-oxidation, respectively. We found that HS rats had lower ACADL and ACAA2 expression than the LS rats (2-way ANOVA; main effect of HS, p<0.05), and there was no difference between ad libitum and TRF groups within LS or HS groups (2-way ANOVA; main effect of TRF, p>0.05). This data suggests that, even though whole-body FAO may be stimulated by TRF fasting, HS-induced suppression of mitochondrial FAO proteins ACADL and ACAA2 was not restored by TRF. Future studies will investigate the effects of the shift in fuel utilization on other metabolic pathways in the cortex and proximal tubules. Supported by the Advancing a Healthier Wisconsin Endowment, the Medical College of Wisconsin, and NIH 5T32HL007852-25. 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.