Abstract 18430: Human Molecular Genetic and Functional Studies Identify TRIM63, Encoding Muscle RING Finger Protein 1, as a Novel Gene for Human Hypertrophic Cardiomyopathy

Abstract

Rationale: A delicate balance between protein synthesis and degradation maintains cardiac size and function. TRIM63 encoding Muscle RING Finger 1 (MuRF1) maintains muscle protein homeostasis by tagging the sarcomere proteins with ubiquitin for subsequent degradation by the Ubiquitin-Proteasome System (UPS). Objectives: To determine the pathogenic role of TRIM63 in human hypertrophic cardiomyopathy (HCM). Methods and Results: Sequencing of TRIM63 gene in 302 HCM probands (250 Caucasians) and 339 controls (262 Caucasians) led to identification of two missense (p.A48V and p.I130M) and a deletion (p.Q247X) variants exclusively in the HCM probands. These three variants were absent in 751 additional controls screened by TaqMan assays. Likewise, rare variants were enriched in the Caucasian HCM population (11/250, 4.4% vs. 3/262, 1.1%, respectively, p=0.024). Expression of the mutant TRIM63 was associated with mislocalization of TRIM63 to sarcomere Z disks, impaired auto-ubiquitination, reduced ubiquitinylation and UPS-mediated degradation of myosin heavy chain 6, cardiac myosin binding protein C, calcineurin (PPP3CB), and p-mTOR in adult cardiac myocytes. Induced expression of the mutant TRIM63 in the mouse heart was associated with cardiac hypertrophy, activation of the mTOR-S6K and calcineurin pathways and expression of the hypertrophic markers, which were normalized upon turning off expression of the mutant protein. Conclusions: TRIM63 mutations, identified in patients with HCM, impart loss-of-function effects on E3 ligase activity and are likely causal mutations in HCM. The findings implicate impaired protein degradation in the pathogenesis of HCM.