Klf9 is essential for cardiac mitochondrial homeostasis

Mitochondrial dynamics and mitophagy are intimately linked physiological processes that are essential for cardiac homeostasis. Here we show that cardiac Klf9 is dysregulated in human and rodent cardiomyopathy. Young adult global Klf9-knockout mice displayed hypertrophic cardiomyopathy that was characterized by depressed systolic function, increased left ventricular mass and pulmonary congestion. Klf9 knockout led to mitochondrial disarray and fragmentation in cardiomyocytes. Biochemical analysis confirmed that mitochondrial respiratory function was impaired in Klf9-knockout cardiomyocytes, with reduced myocardial ATP levels and elevated ROS. Furthermore, cardiac-specific Klf9-deficient mice phenocopied global Klf9-knockout mice, suggesting that cardiac Klf9 is essential for mitochondrial homeostasis and heart function. Moreover, cardiac Klf9 deficiency inhibited mitophagy induced by angiotensin II (ANGII), thereby leading to accumulation of dysfunctional mitochondria and acceleration of heart failure in mice in response to ANGII treatment. In contrast, cardiac-specific Klf9 transgene improved cardiac systolic function via promoting mitophagy in mice in response to ANGII treatment. Molecular mechanism studies indicated that Klf9 knockout decreased the expression of PGC-1α and its target genes involved in mitochondrial energy metabolism. Moreover, Klf9 controlled the expression of Mfn2 by directly binding to its promoter region, thereby regulating mitochondrial dynamics and mitophagy. Finally, we performed Mfn2 rescue experiments in Klf9-CKO mice and found that AAV-mediated Mfn2 rescue in heart improved cardiac mitochondrial and systolic function in Klf9-CKO mice treated with or without ANGII. Thus, Klf9 integrates cardiac energy metabolism, mitochondrial dynamics and mitophagy. Modulating Klf9 activity may have therapeutic potential in the treatment of heart failure.