Abstract 13056: Endoplasmic Reticulum-Resident Protein TXNDC5 Augments Myocardial Fibrosis by Facilitating Extracellular Matrix Protein Folding in Cardiac Fibroblasts

Introduction: Cardiac fibrosis plays a critical role in fostering heart failure (HF). Excessive accumulation of extracellular matrix (ECM) resulting from cardiac fibrosis impairs cardiac contractile function and increases arrhythmogenicity. Current treatment options for cardiac fibrosis, however, are limited. Exploiting RNA sequencing data from human failing heart and co-expression gene network analysis, we identified thioredoxin domain containing 5 (TXNDC5), a cardiac fibroblast (CF)-enriched endoplasmic reticulum (ER) protein, as a potential novel mediator of cardiac fibrosis. The goal of this study was to test this hypothesis directly. Results: TXNDC5 mRNA and protein were highly upregulated in human failing heart and in the left ventricle (LV) from a mouse model of isoproterenol (ISO)-induced HF. Cardiac TXNDC5 expression showed strong positive correlation with that of ECM protein genes. TXNDC5 increased in CF upon transforming growth factor β (TGFβ) stimulation. Knocking down TXNDC5 in CF abrogated TGFβ-induced ECM protein upregulation and myofibroblast transformation independent of SMAD3 activity. Forced expression of TXNDC5 triggered activation of CF and increased ECM protein production. Further experiments revealed that TXNDC5, a protein disulfide isomerase, facilitated proper ECM protein folding; depletion of TXNDC5 led to ECM protein misfolding and degradation through ER-associated degradation (ERAD) pathway. In addition, TGFβ-induced TXNDC5 upregulation in CF was dependent on increased ER stress and activating transcription factor 6 (ATF6)-mediated regulation. Knocking out TXNDC5 by CRISPR/Cas9 genome editing showed cardioprotective effects including reduced cardiac fibrosis (by 36%), preserved LV contractility (post-ISO LV ejection fraction in WT 40.1±2.6 vs KO 57.5±5.1, P <0.001) and improved survival in mice with ISO-induced HF. Conclusion: ER resident protein TXNDC5 promotes cardiac fibrosis by increasing CF activity and ECM production through facilitating ECM protein folding. Genetic deletion of TXNDC5 protects against β agonist-induced cardiac fibrosis and LV dysfunction. Targeting TXNDC5, therefore, could be a novel approach to mitigate excessive ECM accumulation and fibrosis formation during HF.