ORP5 promotes cardiac hypertrophy by regulating the activation of mTORC1 on lysosome

Oxysterol binding protein (OSBP)-related protein 5 (ORP5) mainly functions as a lipid transfer protein at membrane contact sites (MCS). ORP5 facilitates cell proliferation through the activation of mTORC1 signaling. While the pro-hypertrophic effects of mTORC1 are well-documented, the specific role of ORP5 in the context of pathological cardiac hypertrophy remains inadequately understood.

To investigate the role of ORP5 in pathological cardiac hypertrophy, AAV9-treated mice and neonatal rat ventricular myocytes (NRVMs) were utilized. Cardiac function, morphology, and mTORC1 signaling alterations induced by pro-hypertrophic stimuli were assessed in both myocardium and NRVMs. Additionally, a range of molecular techniques were employed to elucidate the regulatory mechanisms of ORP5 on mTORC1 in hypertrophied hearts.

Increased expression of ORP5 was observed in the hearts of patients with hypertrophic cardiomyopathy (HCM), in mice subjected to transverse aortic constriction (TAC), and in NRVMs treated with angiotensin II (AngII). We found that ORP5 binds to mTOR in cardiomyocytes. Upon exposure to TAC surgery, ORP5-deficient hearts exhibited enhanced cardiac function, reduced cardiomyocyte hypertrophy, and diminished collagen deposition than wild type. Conversely, overexpression of ORP5 significantly aggravated hypertrophic responses in both hearts and NRVMs. Notably, the promotion of cardiac hypertrophy induced by ORP5 overexpression was reversed by rapamycin, an inhibitor of mTORC1. Mechanistically, our study elucidated that the ORD domain of ORP5 interacts with mTORC1, facilitating its translocation to the outer membrane of the lysosome for subsequent activation. This activation triggers the downstream signaling pathways involving S6K1 and 4E-BP1, which initiate protein synthesis, thereby promoting pathological cardiac hypertrophy.

Our findings provide the inaugural evidence that ORP5 facilitates pathological ventricular hypertrophy through the translocation of mTORC1 to the lysosome for subsequent activation. Consequently, ORP5 has the potential to serve as a diagnostic biomarker or therapeutic target for pathological cardiac hypertrophy in the future.