Cytochrome c Oxidase regulation and mitochondrial dysfunction in the kidney is different in non-salt sensitive (Sprague Dawley) and salt-sensitive (Dahl SS) rats fed a high fructose and high salt diet

Salt-sensitivity of blood pressure is an important driver of cardiovascular disease, yet little is known about the mechanisms involved. We previously showed that fructose feeding (20%) followed by the addition of 4% dietary salt (Fru+HS) for 4 weeks causes a mild increase in mean arterial pressure (MAP; ~5-10 mmHg) in Sprague Dawley rats, a strain that is not otherwise salt-sensitive. Here we show that the addition of dietary salt alone for 4 weeks causes a salt-sensitive increase in MAP in DahlSS rat strain (Mcw) that is much higher in magnitude (~30 mmHg), and that the addition of fructose exacerbates the phenotype (increase of 42 ± 4 mmHg after 6 weeks). The molecular mechanisms of salt-sensitive hypertension have been suggested to involve mitochondrial dysfunction, and it has been shown in Dahl SS rats fed a high salt diet that Drp1 phosphorylation via PINK1 improves mitochondrial fission and alleviates mitochondrial dysfunction in the myocardium. Little else is known in terms of the mechanisms and how other organs relevant to blood pressure control, i.e. the kidney, may be affected. Cytochrome c Oxidase (Complex IV, CIV) is the proposed rate-limiting step of the electron transport chain located in the inner mitochondrial membrane, and its activity is decreased in various disease conditions leading to mitochondrial dysfunction (i.e. inflammatory diseases). In the current study, we set out to determine the CIV-mediated mechanistic differences that govern mitochondrial dysfunction in SD and Dahl SS rats fed a Fru+HS diet. We hypothesized that mitochondrial dysfunction is exacerbated in Dahl SS rats compared to SD rats on Fru+HS diet via CIV-dysfunction in the kidney. We used SD and Dahl SS rats (SS/JrHsdMCwiCrl, both purchased from Charles River Laboratories) that were placed on either Fru+HS diet (TestDiet # 5755) or normal chow for 6 weeks (n = 5 control, n = 7 Fru+HS). To study mitochondrial health and function, we analyzed oxygen consumption rate (OCR) in the kidney and heart, which is a direct measurement of CIV activity, and Blue-Native (BN) PAGE followed by in-gel activity (IGA) and immunoblotting of the electron transport chain (ETC) complexes. In SD rats, there was no difference in the OCR in the hearts nor kidneys in normal vs. Fru+HS diet. In the Dahl SS rats on Fru+HS diet, there was a significant decrease in the OCR in the kidney (35 ± 4%, p < 0.01 ) and the heart (15 ± 4%, p < 0.05), and a decrease in the respiratory control ratio (a measure of mitochondrial coupling) in the kidney cortex (23 ± 5%, p< 0.05) and the heart left ventricle (27 ± 5%, p< 0.05). BN-PAGE was used to investigate the changes in supercomplex (SC) formation and activity in the kidney mitochondria. CIV IGA matched the OCR results, with a decrease in total CIV activity (18 ± 5%, p< 0.01) and in all CIV-related SCs (i.e., a 24 ± 9%, p< 0.05 decrease in III2+IV and a 23 ± 6%, p< 0.001 decrease in I+III2+IVn). However, we found no changes in Complex I (CI) IGA. Immunoblotting found a specific inhibitory tyrosine phosphorylation (Y304) on subunit I of CIV that has been previously associated with a decrease in CIV-specific activity, but not yet investigated in the kidney. We found a significant increase in total Y304 phosphorylation (95 ± 24%, p < 0.05), with a large accumulation in III2+IV SC in the Dahl SS rats on Fru+HS compared to those on a regular diet. The amount and distribution of CI and CIII SCs were unchanged. This suggests that CIV is the primary driver of mitochondrial dysfunction in the Dahl SS model on a Fru+HS diet and makes it an interesting therapeutic target for future treatment of salt-sensitive hypertension. This work was supported by start-up funds to DK. This abstract was presented at the American Physiology Summit 2026 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.