A Junctophilin-2-Mitofusin-2 Interaction Links T-Tubule Remodeling to Mitochondrial Dysfunction in Pulmonary Arterial Hypertension-Mediated Right Ventricular Failure

Introduction: Junctophilin-2 (JPH2) plays a crucial role in t-tubule structure/function and gene regulation in cardiomyocytes. In addition, JPH2 downregulation causes mitochondrial dysfunction and mitofusin-2 (MFN2) dysregulation, but the link between JPH2 and mitochondria is undetermined. Here, we investigated the hypothesis that a direct JPH2-MFN2 interaction is important for mitochondrial regulation and subsequent right ventricular (RV) function in pulmonary arterial hypertension (PAH). Methods and Results: Confocal microscopy revealed JPH2 and MFN2 colocalized at t-tubules in isolated cardiomyocytes. Immunoprecipitation demonstrated JPH2 and MFN2 interacted in RV extracts. Pulldown experiments showed JPH2 directly bound MFN2, and that the MFN2 binding domain was localized to the N-terminal third of JPH2. To probe the importance of the JPH2-MFN2 interaction for RV function, we compared the effects of treatment with AAV9-JPH2 to AAV9-GFP in monocrotaline-induced PAH. Consistent with its known role in t-tubule homeostasis, AAV9-JPH2 normalized RV t-tubule architecture. Interestingly, transmission electron microscopy showed AAV9-JPH2 corrected RV mitochondrial morphology. Immunoblots of RV extracts demonstrated AAV9-JPH2 increased JPH2 and MFN2 expression, which may underlie the restoration of mitochondrial morphology. At the organ level, AAV9-JPH2 reduced RV cardiomyocyte hypertrophy and RV fibrosis. AAV9-JPH2 increased tricuspid annular plane systolic excursion and RV free wall thickening as quantified by echocardiography. Pressure-volume loop analysis showed AAV9-JPH2 augmented RV ejection fraction and right ventricular-pulmonary arterial coupling and lowered RV end diastolic pressure and tau. Importantly, the improvements in RV systolic and diastolic function were independent of altering PAH severity as RV systolic pressure, effective arterial elastance, and pulmonary arterial small vessel remodeling were not altered with AAV9-JPH2. Conclusions: Disruption of the JPH2-MFN2 interaction may link altered t-tubule structure to mitochondrial dysfunction in the compromised RV. Strategies to increase JPH2 expression could have therapeutic value for RV failure.