Kidney‐specific conditional knockout of Klotho causes heart failure via impairing mitochondrial function

Abstract

Background and objectiveHeat function declines with age which ultimately leads to heart failure. In humans, aging is associated with a decrease in serum level of anti‐aging protein, Klotho. Klotho, which was originally discovered as an aging‐suppressor gene, is primarily expressed in renal tubule epithelial cells. This gene encodes a type‐I membrane protein (Klotho protein) that exists in two forms, membrane Klotho and secreted Klotho. Secreted Klotho (sKL) enters blood and may regulate the functions of cells or tissues that do not express Klotho, such as cardiomyocytes. The objective of this study is to investigate whether kidney‐specific conditional knockout of Klotho (KL‐KO) affects mitochondrial function in cardiomyocytes.Methods and ResultsSerum sKL levels were decreased and heart function was impaired in KL‐KO mice as assessed using Doppler. Mitochondrial co‐enzyme (Co‐Q10) and respiratory enzyme Complex I were downregulated in myocytes isolated from KL‐KO mice. Interestingly, treatment with Co‐Q10 rescued KL‐KO‐induced mitochondrial dysfunction and heart failure, suggesting that Klotho deficiency‐induced heart failure may be partly due to impairment in mitochondrial function. We further investigated the underlying molecular mechanism in cultured rat heart H9C2 cells. Treatment with klotho deficient medium (50% reduction in klotho) decreased total mitochondrial DNA copy number and resulted in a downregulation of Complex I expression. Mitochondrial respiratory chain function was decreased as measured by ATP generation using Seahorse. Mitochondrial oxidative phosphorylation was impaired due to klotho deficiency. Klotho‐deficient medium also enhanced mitophagy as evidenced by increased PINK1 and Parkin expression. Klotho deficiency also induced mitochondrial fission in H9C2 cells. Treatment with Co‐Q10 rescued klotho deficiency‐induced downregulation of mitochondrial respiratory chain function and ATP generation and upregulation of mitophagy activity in H9C2 cells.ConclusionKlotho deficiency causes heart failure via downregulation of Co‐Q10 levels which impair mitochondrial respiratory chain enzyme activity and induce mitophagy.Support or Funding InformationNIH R01 Grants ‐ HL122166, HL116863, AG049780 and AG062375