Abstract Body: Background: Recent clinical studies suggest a potential link between right ventricular (RV) fibrosis, poor function of the pressure-overloaded RV, and mortality in patients with pulmonary arterial hypertension (PAH). However, no therapies specifically targeting RV fibrosis are currently available. There is evidence of a significant contribution of an oxidative stress-sensitive tyrosine kinase c-Src in the development of left ventricular hypertrophy and failure, but it is unknown whether c-Src has pathological roles in the RV under PAH. We previously showed that c-Src can phosphorylate mitofusin 2 (Mfn2), a key protein forming a tethering structure between endoplasmic reticulum (ER) and mitochondria (Mito), which decreases the ER-Mito distance, facilitates ER-to-Mito Ca²⁺ transfer, and increases reactive oxygen species (ROS) in adult human cardiac fibroblasts (CFs) from healthy donors.
Aims: To test the role of c-Src-dependent Mfn2 phosphorylation in promoting RV fibrosis under PAH.
Results: Transmitted electron microscope (TEM) images from RV tissues of a preclinical rat SuHx PAH model (Sugen 5416 injection and 3-week hypoxia followed by 4-week normoxia) showed that ER-Mito distance decreased in CFs (not in the cardiomyocyte [CM] area) compared to those from animals maintained under normoxia (NORM) as a control. Increased c-Src activation and tyrosine phosphorylation of Mfn2 were observed specifically in CFs in the RV, but not in RV-CM area in PAH rats. RV-CFs isolated from PAH rats exhibited increased c-Src activity, decreased ER-Mito distance, increased ROS, and the activation of proliferative signaling compared to RV-CFs from NORMs. The in-vivo introduction of adeno-associated virus serotype 9 (AAV9) carrying CF-specific promoter hTCF21 and outer mitochondrial membrane-targeted dominant-negative c-Src in PAH rats partially decreased RV fibrosis and recovered RV function compared to those injected with AAV9-hTCF21-luciferase.
Conclusions: c-Src-dependent Mfn2 phosphorylation decreases ER-Mito distance, facilitates ER-to-Mito Ca²⁺ transport, and increases mitochondrial ROS, which promotes CF activation in PAH. CF- and mitochondria-specific inhibition of c-Src may attenuate RV fibrosis and failure in response to PAH.