Endoplasmic Reticulum Protein TXNDC5 Augments Myocardial Fibrosis by Facilitating Extracellular Matrix Protein Folding and Redox-Sensitive Cardiac Fibroblast Activation

Rationale: Cardiac fibrosis plays a critical role in the pathogenesis of 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 and there is a clear need to identify novel mediators of cardiac fibrosis to facilitate the development of better therapeutics. Exploiting co-expression gene network analysis on RNA sequencing data from failing human heart, we identified thioredoxin domain containing 5 (TXNDC5), a cardiac fibroblast (CF)-enriched endoplasmic reticulum (ER) protein, as a potential novel mediator of cardiac fibrosis and we completed experiments to test this hypothesis directly. Objective: To determine the functional role of TXNDC5 in the pathogenesis of cardiac fibrosis. Methods and Results: RNASeq and Western blot analyses revealed that TXNDC5 mRNA and protein were highly upregulated in failing human left ventricles (LV) and in hypertrophied/failing mouse LV. In addition, cardiac TXNDC5 mRNA expression levels were positively correlated with those of transcripts encoding transforming growth factor β1 (TGFβ1) and ECM proteins in vivo. TXNDC5 mRNA and protein were increased in human CF (hCF) under TGFβ1 stimulation in vitro. Knockdown of TXNDC5 attenuated TGFβ1-induced hCF activation and ECM protein upregulation independent of SMAD3, whereas increasing expression of TXNDC5 triggered hCF activation and proliferation and increased ECM protein production. Further experiments showed that TXNDC5, a protein disulfide isomerase, facilitated ECM protein folding and that depletion of TXNDC5 led to ECM protein misfolding and degradation in CF. In addition, TXNDC5 promotes hCF activation and proliferation by enhancing JNK activity via increased reactive oxygen species, derived from NAD(P)H oxidase 4. TGFβ1-induced TXNDC5 upregulation in hCF was dependent on ER stress and activating transcription factor 6-mediated transcriptional control. Targeted disruption of Txndc5 in mice ( Txndc5 -/- ) revealed protective effects against isoproterenol (ISO)-induced cardiac hypertrophy, reduced fibrosis (by ~70%) and markedly improved LV function; post-ISO LV ejection fraction was 59.1±1.5 vs 40.1±2.5 (P Txndc5 -/- vs wild-type mice, respectively. Conclusions: The ER protein TXNDC5 promotes cardiac fibrosis by facilitating ECM protein folding and CF activation via redox-sensitive JNK signaling. Loss of TXNDC5 protects against β agonist-induced cardiac fibrosis and contractile dysfunction. Targeting TXNDC5, therefore, could be a powerful new therapeutic approach to mitigate excessive cardiac fibrosis, thereby improving cardiac function and outcomes in HF patients.