PPARα-independent effects of nitrate supplementation on skeletal muscle metabolism in hypoxia

Abstract

. (2018). PPAR-independent effects of nitrate supplementation on skeletal muscle metabolism in hypoxia. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR BASIS OF DISEASE. https://doi.org/10.1016/j.bbadis.2018.07.027Citing this paper Please note that where the full-text provided on King's Research Portal is the Author Accepted Manuscript or Post-Print version this may differ from the final Published version. If citing, it is advised that you check and use the publisher's definitive version for pagination, volume/issue, and date of publication details. And where the final published version is provided on the Research Portal, if citing you are again advised to check the publisher's website for any subsequent corrections. General rightsCopyright and moral rights for the publications made accessible in the Research Portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognize and abide by the legal requirements associated with these rights.•Users may download and print one copy of any publication from the Research Portal for the purpose of private study or research.•You may not further distribute the material or use it for any profit-making activity or commercial gain •You may freely distribute the URL identifying the publication in the Research Portal Take down policyIf you believe that this document breaches copyright please contact librarypure@kcl.ac.uk providing details, and we will remove access to the work immediately and investigate your claim. A B S T R A C THypoxia is a feature of many disease states where convective oxygen delivery is impaired, and is known to suppress oxidative metabolism. Acclimation to hypoxia thus requires metabolic remodelling, however hypoxia tolerance may be aided by dietary nitrate supplementation. Nitrate improves tissue oxygenation and has been shown to modulate skeletal muscle tissue metabolism via transcriptional changes, including through the activation of peroxisome proliferator-activated receptor alpha (PPARα), a master regulator of fat metabolism. Here we investigated whether nitrate supplementation protects skeletal muscle mitochondrial function in hypoxia and whether PPARα is required for this effect. Wild-type and PPARα knockout (PPARα) mice were supplemented with sodium nitrate via the drinking water or sodium chloride as control, and exposed to environmental hypoxia (10% O 2 ) or normoxia for 4 weeks. Hypoxia suppressed mitochondrial respiratory function in mouse soleus, an effect partially alleviated through nitrate supplementation, but occurring independently of PPARα. Specifically, hypoxia resulted in 26% lower mass specific fatty acid-supported LEAK respiration and 23% lower pyruvate-supported oxidative phosphorylation capacity. Hypoxia also resulted in 24% lower citrate synthase activity in mouse soleus, possibly indicating a loss of mitochondrial content. These changes were not seen, however, in hypoxic mice when supplemented with dietary nitrate, indicating a nitrate dependent preservation of mitocho...

Inorganic nitrate, hypoxia, and the regulation of cardiac mitochondrial respiration—probing the role of PPARα

“…Body mass, blood hemoglobin, and food, water, and NO 3 − intake have been previously reported for these mice (35). …”

“…Moreover, we only used male mice in this study, which may be a limitation because, for example, gender dimorphic differences in the antiplatelet response to NO 3 − supplementation have been observed in humans (48). As with our previous studies, we were able to precisely control NO 3 − intake using a standardized quality-controlled diet and deionized water (23, 33–35, 49, 50). Although the anorexic effects in the early stages of hypoxic exposure may have confounded our findings, the long duration of the hypoxic exposure proved to be a strength because water intake and therefore NO 3 − intake stabilized in hypoxic mice by wk 2, matching that of their normoxic counterparts for the remainder of the study.…”

“…At the end of the study, Ppara −/− mice were 5% lighter than WTs ( P < 0.01, PPARα main effect), whereas hypoxic mice were 4% lighter than normoxic mice ( P < 0.001, hypoxia main effect) and NO 3 − -treated mice were 3% lighter than chloride-treated mice ( P < 0.05, NO 3 − main effect). [Hb] b , which was measured at the end of the study, was higher in hypoxic mice than normoxic mice (35). …”

“…The overall study design has been previously described (35). Mice were bred on a pure 129Ev/Sv background with 10 backcrosses.…”

“…We therefore investigated this in wild-type (WT) mice ( Ppara +/+ ) and Ppara −/− mice that were exposed to environmental hypoxia or normoxia with and without supplementation with a moderate concentration of dietary NO 3 − . We previously reported that NO 3 − protected aspects of skeletal muscle mitochondrial respiratory function in these mice in hypoxia and found this occurred independently of PPARα (35). However, it has been suggested that in the skeletal muscle of Ppara −/− mice, high expression of PPARβ/δ compensates for the loss of PPARα (36).…”