Abstract Body (Do not enter title and authors here): Rationale: Right ventricular (RV) function is the major determinant of survival in pulmonary hypertension (PH); however, no RV-directed therapies exist. Apelin is a secreted peptide that plays a vital role in cardiac cellular homeostasis, but its role in RV remodeling remains unexplored.
Hypothesis: Apelin signaling is protective against RV failure through the inhibition of Renin Angiotensin Aldosterone System (RAAS) signaling and activation of ACE2 signaling.
Methods: RV failure was induced in Sprague Dawley rats by pulmonary artery banding (PAB) for 10 days or 10 weeks or by Sugen/hypoxia (SuHx). A subset of PAB or SuHx rats were treated with Pyr-Apelin-13 (200ug/kg/day) or an APLNR antagonist, ML221 (2mg/kg/day). Pressure-volume loops, RV function and molecular changes were assessed. In vitro characterization of apelin signaling was performed in RV endothelial cells (RVECs). RAAS and ACE2 pathway activity were assessed by ACE1, ACE2, MAS1, and AT1R expression via qRT-PCR and Western blot. Angiogenic potential was measured using a Matrigel tube formation, scratch assay, and survival assay. To test the role of apelin and ACE2 signaling, cells were treated with +/1 Pyr-Apelin-13 (100nM, 24hrs), +/- Apelin receptor antagonist ML221 (100uM, 24hrs) or +/- ACE2 inhibitor MLN4670 (100 nM, 24hrs). p<0.05 was considered statistically significant.
Results: Pyr-Apelin-13 prevented PAB-induced decreases in cardiac output (CO) and cardiac index (CI) at both 10 days and 10 weeks and preserved RV-PA coupling (Ees/Ea). Pyr-Apelin-13 reduced PAB-induced collagen deposition, cardiomyocyte surface area, and preserved capillarization. In RVECs, Pyr-Apelin-13 enhanced angiogenesis by ring formation, wound closure and cell survival but this effect was blocked by co-treatment with ML221 or MLN4670. Pyr-Apelin-13 upregulated mas receptor (MAS1) and downregulated angiotensin II type 1 receptor (AT1R) vs control. Apelin decreased angiotensin converting enzyme 1 (ACE1) and increased ACE2 expression. Pyr-Apelin treatment was able to partially restore ring formation in SuHx RVECs and this was blocked by co-treatment with the apelin receptor antagonist, ML221 or with ACE2 inhibitor MNL4670.
Conclusion: Loss of apelin signaling results in more severe RV failure. Identification of pathways and targets engaged by Apelin during RV failure will allow for the development of novel, long-acting and targeted treatment strategies for RV failure.