Abstract 274: Mitochondrial Translation Machinery Defects Causes Cardiomyopathy and i n vivo Functional Screening of Therapeutic Targets

Abstract

More than 95% of ATP consumed in the heart is derived from oxidative phosphorylation (OxPhos) in the mitochondria. Besides over a thousand proteins encoded by nuclear DNA, mitochondrial gene expression machinery generates 13 proteins for the OxPhos system that employs mitochondrial ribosomal proteins for translation. Mitochondrial ribosome protein S5 (MRPS5) encoded by MRPs gene family, is located at the mammalian mitochondrial ribosome 28S subunit and its importance has not been explored in the heart. Western blotting showed that MRPS5 expression was decreased in TAC-induced hypertrophic mouse hearts ( in vivo ), and in phenylephrine or isoproterenol-stimulated cardiomyocytes ( in vitro ). In the failing hearts of patients, Mrps5-mediated mt-CO1 was markedly decreased as well. To determine the functional role of MRPS5 in the heart, we generated an inducible cardiac-specific knockout mouse and showed that Mrps5-deficient mice developed time-dependent cardiac hypertrophy, fibrosis and heart failure. Mitochondria in the Mrps5-deficient adult cardiomyocytes exhibited membrane swelling and cristae collapsed together with decreased oxygen consumption and ATP production. Mitochondrial calcium homeostasis was also disrupted. Combined analysis of transcriptomics and metabolomics spatiotemporally identified 20 potential target genes associated with Mrps5 deficiency-mediated cardiac pathological processes. Through in vivo functional screening via adeno-associated virus (AAV) mediated gene delivery, we further narrowed down and confirmed that Kruppel-like factor 15 (Klf15) remarkably rescued cardiac phenotype in the Mrps5-deficient mice with maintained mitochondrial homeostasis, suppressed cardiac hypertrophy and fibrosis, as well as preserved cardiac function. Further RNA-sequencing and biochemical analysis mechanistically revealed that genes involved in glycolysis/ gluconeogenesis, PPAR signaling pathway and biosynthesis of amino acids, markedly altered when exploited AAV-Klf15 gene therapy in Mrps5-deficient mice heart. Our results demonstrates Mrps5 is essential for mitochondrial homeostasis and cardiac function and uncovers Klf15 as a potential therapeutic target for treating cardiac mitochondrial diseases.