The Role of Superoxide in Sex Differences in Angiotensin II‐induced Hypertensive and Natriuretic Responses in Mice with Proximal Tubule‐Specific Deletion of Mitochondrial Protein Sirtuin 3 in The Kidney

Abstract

Sirtuin 3 (SIRT3), aNAD-dependent deacetylase, is a major mitochondrial protein in the matrix that is encoded by the SIRT3 gene. The key functions of SIRT3 in the mitochondria include anti-oxidative, anti-aging, anti-inflammation, and blood pressure-regulating effects by decreasing reactive oxygen species/superoxide production. However, the role of SIRT3 via superoxide in the proximal tubules (PT) of the kidney in angiotensin II-induced hypertensive or natriuretic responses remains poorly understood. To test our hypothesis, five groups of adult male and female wild-type (WT) and PT-SIRT3-/- mice were treated without (Control) or with Ang II (~0.65 mg/kg/day, i.p.) treated with 2% NaCl diet or tempol, a membrane-permeable radical scavenger and superoxide dismutase-mimetic (50 mg/kg/day, p.o.) for 2 weeks. Under basal conditions, systolic (SBP), diastolic (DBP) and mean arterial pressure (MAP) were significantly lower in adult male and female PT-SIRT3-/- mice than male and female wild-type mice (~13 ± 3 mmHg, P<0.01). Although there were no sex differences in male and female WT mice, SBP and MAP were significantly lower in female than male PT-SIRT3-/- mice (P<0.01). Urinary excretion of electrolytes including sodium (Na+), potassium (K+), chloride (Cl-), and lithium (Li+) were also significantly lower in female PT-SIRT3-/- mice (P<0.01). In response to Ang II infusion and 2% high salt treatment, SBP was increased similarly to 136 ± 7 mmHg in male and 135 ± 7 mmHg in female PT-SIRT3-/- mice (P<0.01). Urinary Na+, K+, Cl-, and Li+ excretion were all significantly increased in male and female PT-SIRT3-/- mice without significant sex differences in these responses to Ang II-induced hypertension. There were also no sex differences found in response to Ang II infusion alone. Tempol treatment alone had no significant effects on blood pressure and urinary electrolyte excretory responses compared with their basal levels. Interestingly, however, tempol treatment of Ang II-infused and 2% NaCl-fed male and female PT-SIRT3-/- mice revealed significant sex differences in these responses (P<0.01). SBP and MAP increased further in male (P<0.01), but not in female PT-SIRT3-/- mice (n.s.), whereas the natriuretic response was significantly greater in female PT-SIRT3-/- mice (P<0.01). Taken together, we concluded that SIRT3 in the mitochondria of the proximal tubules plays an important role in the development of ANG II-dependent hypertension, and that superoxide may be implicated in sex differences in Ang II-induced hypertensive and natriuretic responses in PT-SIRT3-/- mice.