Abstract 530: The Ufm1 Specific Ligase 1 Regulates Endoplasmic Reticulum Homeostasis and Protects Against Heart Failure

Protein modifications by ubiquitin and ubiquitin-like proteins are emerging as an important regulatory mechanism of protein function and involved in various cellular processes. Ufm1 (ubiquitin-fold modifier 1) is a novel ubiquitin-like protein that modifies protein targets in a UBA5 (E1) - Ufc1 (E2) - Ufl1 (E3) dependent manner. While defects in ubiquitin- and SUMO-modification have been shown to provoke cardiac remodeling and dysfunction, the importance of Ufm1 modification has not been explored in the normal and stressed heart. Western blotting revealed that Ufm1 specific ligase 1 (Ufl1), an enzyme essential for Ufm1 modification, was increased in hypertrophic mouse hearts but reduced in the failing hearts of patients with dilated cardiomyopathy. To determine the functional role of Ufl1 in the heart, we generated a cardiac-specific knockout mouse and showed that Ufl1-deficient mice developed age-dependent cardiomyopathy and heart failure, as indicated by elevated cardiac fetal gene expression, increased fibrosis and impaired cardiac contractility. When challenged with pressure overload, Ufl1-deficient hearts exhibited remarkably greater hypertrophy, exacerbated fibrosis and worsened cardiac contractility compared with control counterparts. Transcriptome analysis identified that genes associated with the endoplasmic reticulum (ER) function were dysregulated in Ufl1-deficient hearts. Biochemical analysis revealed that excessive ER stress preceded and deteriorated along with the development of cardiomyopathy in Ufl1-deficient hearts. Mechanistically, Ufl1 depletion impaired PERK signaling and aggravated cardiomyocyte cell death following ER stress. Administration of the chemical ER chaperone tauroursodeoxycholic acid to Ufl1-deficient mice alleviated ER stress and attenuated pressure overload-induced cardiac dysfunction. Our results advance a novel concept that the Ufm1 system is essential for cardiac homeostasis through regulation of ER function and that upregulation of myocardial Ufl1 could be protective against heart failure.