Mutations in the gene encoding the bone morphogenetic protein type 2 receptor (BMPR2) are the most common genetic cause of heritable pulmonary arterial hypertension (PAH). However, given the reduced penetrance of BMPR2 mutations in affected families, a major outstanding question is the identity of additional factors or pathways that are responsible for the manifestation of clinical disease. Furthermore, limited human tissue is available for study and usually only from patients with end-stage disease, making it difficult to understand how PAH is established and progresses. Alternative human models of PAH are therefore required.

This thesis describes the characterisation of the first human iPSC-derived smooth muscle cell (iPSC-SMC) model of PAH and elucidates the role of BMPR2 deficiency in establishing PAH-associated phenotypes in iPSC-derived SMCs. To achieve this, I used CRISPR-Cas9 gene editing to generate wild-type and BMPR2+/- iPSC lines with isogenic backgrounds which were subsequently differentiated into lineage-specific iPSC-SMCs that displayed a gene expression profile and responses to BMP signalling akin to those present in distal pulmonary artery smooth muscle cells (PASMCs).

Using these cells, I found that the introduction of a single BMPR2 mutation in iPSC-SMCs was sufficient to recapitulate the pro-proliferative and anti-apoptotic phenotype of patient-derived BMPR2+/- PASMCs. However, acquisition of the mitochondrial hyperpolarisation phenotype was enhanced by inflammatory signalling and required an interaction between BMPR2 mutations and environmental stimuli provided by exposure to serum over time. Furthermore, I showed that BMPR2+/- iPSC-SMCs had an altered differentiation state and were less contractile compared to wild-type iPSC-SMCs, phenotypes which have not been observed previously in PAH-derived PASMCs. Finally, RNA sequencing analysis identified genes that were differentially expressed between wild-type and BMPR2+/- iPSC-SMCs and may hence provide further insights into PAH pathobiology.

The iPSC-SMC model described in this study will be useful for identifying additional factors involved in disease penetrance and for validating therapeutic approaches that target BMPR2.