Cardiac Na/K-ATPase alpha1 isoform-specific role in hypertrophic response: role of metabolic and oxidative signaling

Abstract

Cardiac Na/K-ATPase (NKA) inhibition by cardiotonic steroids (CTS) modulates intracellular Na + and Ca 2+ , leading to increased force of contraction. In contrast, hypertrophy of cardiomyocytes (CM) is triggered by CTS through stimulation of reactive oxygen species (ROS) and fetal gene re-expression independently of changes in intracellular Na + or Ca 2+ . Based on recent evidence that NKAα1 serves an isoform-specific function in the regulation of oxidative metabolism and ROS generation, we used a genetic approach in the mouse and in human cardiac cells (AC16) to test the hypothesis that NKAα1 is required for cardiac hypertrophy. Cardio α1 -/- mice, a conditional KO of NKAα1 in the heart, were viable without overt abnormality of cardiac structure or function. NKAα1 was undetectable in heart lysates or isolated CM of adult cardio α1 -/- mice. Despite a compensatory upregulation of NKAα2, Na/K-ATPase activity in crude heart homogenates and NKA currents in CM were reduced by about 60%. Decreased ROS (assessed by total protein carbonylation) and reduced fatty acid oxidation (FAO) and oxidative phosphorylation pathways (revealed by RNA-seq analysis) were noted at baseline. RT-qPCR revealed downregulated genes involved with FAO and the electron transport chain (such as, Acadl and Ndufa9, about 20% decrease, n=6) in cardio α1 -/- hearts. The activity of the electron transport chain complex I was decreased in cardio α1 -/- hearts (0.3354 vs 0.2732 mOD/min/mg of protein, p<0.05). When 3-month-old male mice were challenged with angiotensin II (1.5 mg.kg -1 .day -1 for 1 week, n=6-15), cardio α1 -/- mice did not develop cardiac hypertrophy, as assessed by heart weight to tibia length ratio, but displayed exacerbated cardiac fibrosis, revealed by Trichrome staining, consistent with the postulated role of CM NKAα1 isoform-specific function in cardiac hypertrophy in vivo. In vitro, CRISPR-Cas9-mediated KO of NKAα1 in AC16 cells led to a drastic downregulation of NKAα1 compared to WT AC16 cells. In contrast to WT AC16 cells, NKAα1 KO cells did not respond to the α-adrenergic agonist phenylephrine (50 μM for 24h) with the expected increase in cell area (2243 vs 3520 μm 2 for WT, p<0.05; 2454 vs 2563 μm 2 for KO, p>0.05). These data suggest that NKAα1 isoform-specific function is required for cardiac hypertrophy. Mechanistically, our data support an isoform-specific regulatory function of NKAα1 in normal FAO, electron transport chain activity, and ROS generation, which are critical for CM hypertrophy. Supported by NIH Grant R15 HL145666 and American Heart Association Grant 22POST917776 (Marco T. Pessoa) This is the full abstract presented at the American Physiology Summit 2023 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.