Dietary
nitrate supplementation, and the subsequent serial reduction to
nitric oxide, has been shown to improve
glucose homeostasis in several pre-clinical models of
obesity and
insulin resistance. While the mechanisms remain poorly defined, the beneficial effects of
nitrate appear to be partially dependent on AMPK-mediated signaling events, a central regulator of metabolism and mitochondrial bioenergetics. Since AMPK can activate
SIRT1, we aimed to determine if
nitrate supplementation (4 mM
sodium nitrate via
drinking water) improved skeletal muscle mitochondrial bioenergetics and acetylation status in mice fed a high-fat diet (HFD: 60% fat). Consumption of HFD induced whole-body
glucose intolerance, and within muscle attenuated
insulin-induced Akt phosphorylation, mitochondrial
ADP sensitivity (higher apparent Km), submaximal
ADP-supported respiration, mitochondrial
hydrogen peroxide (mtH2O2) production in the presence of
ADP and increased cellular protein carbonylation alongside mitochondrial-specific acetylation. Consumption of
nitrate partially preserved
glucose tolerance and, within skeletal muscle, normalized
insulin-induced Akt phosphorylation, mitochondrial
ADP sensitivity, mtH2O2, protein carbonylation and global mitochondrial acetylation status.
Nitrate also prevented the HFD-mediated reduction in
SIRT1 protein, and interestingly, the positive effects of
nitrate ingestion on
glucose homeostasis and mitochondrial acetylation levels were abolished in
SIRT1 inducible knock-out mice, suggesting
SIRT1 is required for the beneficial effects of dietary
nitrate. Altogether, dietary
nitrate preserves mitochondrial
ADP sensitivity and global
lysine acetylation in HFD-fed mice, while in the absence of
SIRT1, the effects of
nitrate on
glucose tolerance and mitochondrial acetylation were abrogated.