Abstract Body (Do not enter title and authors here): Introduction: A mutation in the Bone Morphogenetic Protein Receptor Type 2 (BMPR2) gene is in 70% of hereditary pulmonary arterial hypertension (hPAH) patients the causative mutation of the disease. Previous work demonstrated that right ventricular function is more impaired in hPAH patients with a BMPR2 mutation. However, the underlying mechanism remains elusive. Moreover, natriuretic peptides, such as N-terminal Brain Natriuretic Peptides (NTproBNP) and Mid Regional proAtrial Natriuretic Peptides (MRproANP), are secreted from cardiomyocytes upon stretch as adaptation to increased pressure overload. We hypothesize that the BMPR2 mutation impairs the response to increased pressure overload. For this purpose, we make use of ventricular induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) of hPAH patients carrying a BMPR2 mutation and their isogenic controls in which the mutation was corrected.

Aim: To study the effect of a BMPR2 mutation on the response to pressure overload in vitro.

Methods: iPSCs from 2 hPAH patients and its isogenic controls were used. iPSCs were differentiated into ventricular iPSC-CMs and stretched 10% equiaxially for 24h at 1Hz on the Flexcell FX-6000 system. Natriuretic peptides gene expressions were quantified via RT-PCR. NTproBNP and MRproANP release were measured on cell supernatants throughout specific immunoassays. Normality of the data was checked, and statistics were performed accordingly.

Results: No differences were observed on natriuretic peptides gene expression on static and stretched iPSC-CMs. There is a clear correlation between NTproBNP and MRproANP release (R²=0.83, p<0.0001, Figure 1A). Interestingly, hPAH iPSC-CMs showed higher baseline values for NTproBNP release compared to isogenic iPSC-CMs (p<0.01, Figure 1B). Furthermore, stretching resulted in increased NTproBNP and MRproANP secretion in both hPAH and isogenic iPSC-CMs (Figure 1B-C).

Conclusions: Secretion of NTproBNP and MRproANP was closely correlated in iPSC-CMs. iPSC-CMs of hPAH patients with a BMPR2 mutation showed higher baseline values of NTproBNP. Increased secretion of NTproBNP and MRproANP upon mechanical stimulation was similar between hPAH and isogenic iPSC-CMs. Experiments in atrial iPSC-CMs are currently ongoing to test potential differences in natriuretic peptide secretion between ventricular and atrial cardiomyocytes as the right atrium is also under stretch in PAH.