Abstract Body: A mutation in the Bone Morphogenetic Protein Receptor Type 2 (BMPR2) gene is in 70% of hereditary pulmonary arterial hypertension (PAH) patients the causative mutation. PAH is a rare disease that originates in the lungs but patients eventually die of right heart failure. Previous work demonstrated that right ventricular (RV) function is more impaired in patients carrying a BMPR2 mutation. However, the underlying mechanism remains elusive. We hypothesize that the BMPR2 mutation impairs the response to pressure overload leading to RV maladaptation.
Induced pluripotent stem cells from 2 PAH patients BMPR2-mutation carriers and its isogenic controls (corrected BMPR2 mutation) were differentiated into ventricular cardiomyocytes (iPSC-CMs). iPSC-CMs were characterised at the gene and functional levels using RNA sequencing and the Cytocypher Multicell High Throughput System, respectively. iPSC-CMs were stretched 10% for 24h at 1Hz on the Flexcell FX-6000 system. Bulk RNA sequencing was performed to assess differences in gene expression between BMPR2-mutation carriers and isogenic controls upon stretching. Immunocytofluorescent stainings on static and stretched conditions were performed to evaluate cell morphology and protein expression of main markers (sarcomeric alpha-actinin and atrial natriuretic peptides).
Mutant iPSC-CMs showed increased beating frequency (64.7±4.67 vs 50.3±3.32 bpm), greater force (0.47±0.04 vs 0.36±0.03), reduced peak width (0.49±0.04 vs 0.60±0.03 s) and similar contraction (0.15±0.03 vs 0.16±0.03 s) and relaxation (0.19±0.02 vs 0.24±0.02 s) times compared to isogenic iPSC-CMs. At baseline, bulk RNA sequencing evidenced 11 upregulated genes related to cell survival and quality control and 57 downregulated genes related to systemic mechanobiological deficit on mutant iPSC-CMs compared to isogenic iPSC-CMs. In addition, mutant iPSC-CMs differentially expressed more genes compared to isogenic iPSC-CMs (2449 vs 446 genes) upon stretching. GO analyses showed upregulated genes involved in cytoskeleton, both cell-cell and cell-substrate junctions, and metabolism.
To conclude, under baseline conditions, mutant iPSC-CMs exhibits different contractility and a transcriptomic signature of homeostatic insufficiency and impaired mechanosensing. Therefore, a BMPR2 mutation results in altered cardiac response to mechanical stretching. Further research is needed to understand the molecular mechanism involved and elucidate promising therapeutic targets.