P505Neuregulin-1 ameliorates right ventricular diastolic dysfunction in pulmonary arterial hypertension

Neuregulin (NRG)-1 is involved in the preservation of left ventricular performance. Nevertheless, the role of NRG-1 in pulmonary arterial hypertension(PAH) and right ventricular(RV) diastolic stiffness is unknown. We analysed the presence and possible underlying mechanisms of RV diastolic dysfunction in an animal model of PAH and the role of NRG-1 in this context. Wistar rats randomly received monocrotaline (MCT,60mg/Kg,sc) or vehicle. After 14 days, rats received NRG-1 (40ug/Kg/day,ip) or vehicle. The study resulted in 4 groups: control(CTRL,n=16); CTRL+NRG(n=15); MCT(n=13); MCT+NRG(n=18). RV invasive hemodynamic studies and sample collection were performed 25-28 days after MCT administration. Isolated cardiomyocytes were stretched to measure resting tension and phosphorylation of titin isoforms was analyzed (ProQ Diamond and SYPRO Ruby protein gel stains). Only significant results (p<0.05) are given. RV diastolic stiffness (β) was increased in MCT rats (MCT vs CTRL:0.016±0.002 vs 0.008±0.001). However, NRG-1 treatment attenuated this change (MCT+NRG:0.007±0.001). Histological analyses revealed increased cardiomyocyte cross-sectional areas (MCT vs CTRL:536.67±59.46 vs 375.39±47.43μm2), indicating RV hypertrophy. In addition, the amount of RV fibrosis was enhanced in PAH tissue (MCT vs CTRL:2.04±0.17 vs 0.98±0.07%). NRG-1 also attenuated both changes (MCT+NRG:409.01±19.72μm2 and 1.00±0.17%, respectively). MCT-group isolated cardiomyocytes developed higher passive force when compared to CTRL-group cells at the sarcomere lengths of 2.0 (MCT vs CTRL:1.90±0.43 vs 1.43±0.29N/m2), 2.2 (MCT vs CTRL:3.66±0.69 vs 2.68±0.24N/m2), and 2.3μm (MCT vs CTRL: 5.76±1.15 vs 3.86±0.87N/m2). NRG-1 restored passive force development to levels similar to the CTRL-group, at 2.0, 2.2, and 2.3μm (MCT+NRG:1.28±0.25, 3.04±0.55, and 3.63±0.89N/m2, respectively). CTRL+NRG-group cells developed less passive force compared to CTRL-group (CTRL+NRG:1.16±0.31, 2.27±0.38, and 3.05±0.54N/m2, at 2.0, 2.2, and 2.3μm respectively). Titin phosphorylation was reduced in RV tissue of MCT rats (MCT vs CTRL:1.06±0.38 vs 1.62±0.85,arbitrary units) and increased in MCT+NRG group (2.28±0.61). RV diastolic stiffness is increased in MCT rats, with important contributions from increased fibrosis and intrinsic stiffening of the RV cardiomyocyte sarcomeres. NRG-1 treatment decreases the passive force and thus myocardial stiffness, either in rats with RV hypertrophy or in healthy animals. These findings show that NRG-1 pathway regulates systolic and diastolic function at the cellular level, suggesting a potential therapeutic role of this pathway in PAH.