Essential Role For UVRAG In Autophagy And Maintenance Of Cardiac Structure And Function

The ultraviolet(UV) radiation resistance-associated gene(UVRAG) was initially identified as a molecule that partially rescues the UV sensitivity of Xeroderma Pigmentosum(XP) group C cells. Subsequently, UVRAG was recognized as a tumor suppressor with putative roles in cell autophagy, endocytosis, and DNA damage repair. In recent years, substantial bodies of work provide new insight into UVRAG structure and multiple biological functions. But, the physiological role of UVRAG in the heart remains poorly understood.We determined the role of UVRAG in autophagy and cardiac function by using UVRAG knockout mice generated by piggyback(PB) transposition. The PB transposon was inserted into intron 14 of the UVRAG gene and the disruption of UVRAG gene expression was confirmed at both the mRNA and protein levels. Despite the deficiency for UVRAG, the adult UVRAGPB/PB mice were viable, fertile, and developmentally normal. The abundance of LC3 II protein was markedly increased in the hearts deficient for UVRAG, indicative of increased autophagosomes. The accumulation of autophagosomes in UVRAG-deficient hearts was confirmed by LC3 immunofluorescence staining and transmission electron microscopy. We next analysed autophagic flux in UVRAG-deficient hearts. p62 was significantly increased in UVRAG-deficient hearts compared with WT controls. We then treated UVRAG-deficient mice and WT mice with chloroquine, LC3 II protein levels were significantly increased in UVRAG-deficient hearts. However, the increase in LC3 II protein levels in UVRAG-deficient hearts were not further enhanced significantly by chloroquine treatment, suggesting that accumulated autophagosomes were caused by defective autophagosome removal due to impaired autophagic flux. Assessment of autophagic flux suggests that autophagy process is impaired in the hearts from UVRAG-deficient mice. In agreement with these observations, autophagosomes are accumulated in UVRAG-deficient MEFs, which is caused by impaired autophagic flux. UVRAG-deficient mice exhibit normal cardiac morphology and function at 2 and 6 months of age. However, at 10 months of age, the hearts from UVRAG-deficient mice are larger than the corresponding normal controls. Moreover, UVRAG deficiency in the heart leads to interstitial collagen accumulation, increased cross-sectional area of individual cardiomyocytes, elevated expression of cardiac fetal genes and enhanced apoptosis. In addition, pro-inflammatory cytokine expression is increased in the hearts from UVRAG-deficient mice. Echocardiography reveals that UVRAG-deficient mice at 10 months of age have significantly greater left ventricular end systolic diameter(LVESD) and left ventricular end diastolic diameter(LVEDD). Furthermore, fractional shortening and ejection fraction, two indices of cardiac function, are attenuated in 10-month-old UVRAG-deficient mice. These results demonstrate that UVRAG-deficient mice develop age-related dilated cardiomyopathy accompanied with compromised cardiac function.Overall, the data in this study suggest that UVRAG is essential in autophagic flux and the maintenance of cardiac structure and function.