Abstract 4131128: Cardiomyocyte-specific Deletion of <i>Creg1</i> Impairs Autophagy and Leads to Age-dependent Dilated Cardiomyopathy

CREG1 is a small glycoprotein predominantly localized in the endolysosomal system. In mouse heart, CREG1 expression increases with age. We previously observed cardiac hypertrophy and ventricular non-compaction in a small percentage of constitutive Creg1 knockout mice during the neonatal stage. To elucidate the physiological function of CREG1 in the heart, we generated cardiomyocyte-specific Creg1 knockout (cm Creg1 KO) and knock-in (cm CREG1 KI) mice by crossing Creg1 fl/fl and Rosa hCREG1/hCREG1 with Myh6-Cre mice, respectively. By 6 months of age, the cm Creg1 KO mice developed severe myocardial interstitial fibrosis. Echocardiography at 10 months revealed markedly dilated left ventricles and significantly reduced ejection fractions. All the cm Creg1 KO mice succumbed to heart failure between 10-12 months, while Creg1 fl/fl control littermates exhibited no obvious cardiac abnormalities. Necropsy of deceased cm Creg1 KO mice showed increased heart-to-body weight ratios, enlarged cardiac chambers, and left atrial thromboses. Electron microscopy revealed sparse and elongated myofibers, scant and bizarre-shaped mitochondria, empty cytoplasm, and increased interstitial collagen accumulation. The cm CREG1 KI mice exhibited better endurance to nutritional deprivation than Rosa hCREG1/hCREG1 littermate controls. In sharp contrast to cm Creg1 KO hearts, cm CREG1 KI and Rosa hCREG1/hCREG1 control hearts displayed very mild fibrosis at 8 months, suggesting that CREG1 overexpression may confer cardioprotective effects. In cultured cardiomyocytes, CREG1 colocalizes with the autophagosome marker LC3B following serum deprivation. Immunofluorescence microscopy demonstrated a marked reduction of LC3B puncta in cm Creg1 KO hearts. Analysis of autophagic flux using CAG-RFP-EGFP-LC3 transgenic mice and immunoblotting indicated that the absence of CREG1 impairs both autophagosome formation and degradation, whereas knock-in of CREG1 enhances these autophagic processes. These findings suggest that CREG1 promotes autophagy and protects the heart from age-dependent dilated cardiomyopathy.