Pulmonary arterial hypertension (PAH) in its familial form (FPAH) is a heritable autosomal dominant disorder that, in the majority of patients, results in progressive right heart failure and death within five years of diagnosis. Bone morphogenetic protein receptor (BMPR) 2 haploinsufficiency occurs in over 70% of the FPAH patients, but intriguingly, only 20% of mutation carriers get clinical disease. This proposal aims to uncover the mechanism underlying the reduced penetrance of BMPR2 mutation in causing FPAH using patient-specific induced pluripotent stem cells derived endothelial cells (iPSC-ECs). Understanding the molecular mechanisms underlying the protective phenotype in those BMPR2 mutation carriers without FPAH could lead to novel therapeutic approaches for familial and non-familial forms of PAH as they all share reduced expression or function of BMPR2. These studies also hold the key to understanding penetrance in other genetic conditions related to PAH, such as the caveolin 1 (CAV1) mutation. Studies carried out during Dr. Gu's AHA postdoctoral fellowship utilized iPSC-ECs from three sets of FPAH patients and from their family members with the same BMPR2 mutation but without disease. Dr. Gu uncovered a compensatory p-p38 signaling pathway leading to preserved adhesion and survival of iPSC-ECs from the unaffected mutation carriers. The mechanism accounting for the preserved p-p38 signaling appears to differ among the families.
The first aim (K99 phase) of Dr. Gu's proposed studies is to extend the findings described above, through gain and loss of function studies to pursue the mechanism of `carrier compensation'. She will also determine whether correction of the BMPR2 mutation by CRISPR/Cas9 technology restores BMP signaling pathways and EC functions in FPAH iPSC-EC from all three families.
The second aim (K99 phase) will determine how the transcriptome and epigenome explain the protective phenotype in the unaffected mutation carriers. RNA-Seq was carried out on iPSC-ECs from all family members (n=11). Seventy-one differentially expressed genes were identified by comparing iPSC-ECs from controls and mutation carriers versus FPAH patients, and four genes of interest have been verified by qPCR.
This aim i s strengthened by a collaboration with Dr. Michael Snyder's lab, to help relate gene expression changes with alterations in histone marks identified by ChIP-Seq and polymorphisms called by whole genome sequencing.
The third aim (R00 phase) will extend studies in Specific Aims 1 and 2 to novel mutations associated with FPAH, such as caveolin1. In the fourth aim (R00 phase), Dr. Gu will establish a high-throughput platform for personalized drug screening using iPSC-ECs as a continuous cell source. These studies will help Dr. Gu to launch a research program that optimizes the use of iPSC-derived vascular cells and integrative `omic' technologies to model vascular disease pathophysiology and to develop personalized treatments using either a bioinformatics' approach or high throughput screening to repurpose FDA approved drugs that activate the protective pathway.
Understanding the mechanism underlying reduced penetrance could be the key to a novel therapy for familial and non-familial forms of pulmonary arterial hypertension, as all forms of the disease share reduced expression or function of BMPR2. These studies also build the foundation for using iPSC-derived vascular cells to model vascular disease pathophysiology and for developing personalized treatment using a high throughput approach to screen for FDA approved drugs or bioactive compounds that can activate the protective pathway. This approach can be extended to model other cardiovascular diseases with limited penetrance or with a variable phenotype, e.g., Williams and Marfan syndrome.