Mechanisms underlying the development of pulmonary arterial hypertension

Severe pulmonary arterial hypertension (PAH) is a rare but devastating condition with greatly reduced life expectancy. The disease is defined as high blood pressure confined to the lungs. Existing treatments improve symptoms for a time but the majority of patients eventually deteriorate and require escalation of therapy or lung transplantation. Many will eventually die from heart failure. We would be better placed to find curative treatments for this condition if we had a deeper understanding of the underlying causes. We have already learned much from genetic discoveries in this disease. Approximately 25% of patients with severe PAH carry defects (mutations) in a gene called BMPR2. The BMPR2 gene codes for a protein that is normally found on the surface of cells that line the inner walls of blood vessels. This protein sends signals to the inside of the cell to prevent it leaking and dying. When BMPR2 is mutated, the cells lining the blood vessels behave abnormally which leads to severe narrowing of the lung arteries. Currently available treatments do not affect this underlying problem and so have little if any effect on the disease process. This project will address major research questions in this field with the aim of providing a greater understanding of disease mechanisms and new clues as to how we can best treat this condition. We now intend to employ the power of modern genetic techniques to find further mutations in patients with PAH in whom we have excluded mutations in BMPR2. Over the last ten years since the discovery of mutations in BMPR2 we have found promising leads in terms of treatment, but these are not straightforward. The prediction is that looking closely for further mutations will provide us with additional targets that might be easier to transform into new treatments. We know that in the families of patients with BMPR2 mutations, there are many individuals with mutations who have not yet developed the disease. This group is at major risk of developing PAH but the environmental factors responsible for triggering the disease remain unknown. We plan to follow up subjects with BMPR2 mutations but who do not yet have the disease over the next 5 years. At 6 monthly follow up subjects will give blood samples, be assessed clinically for signs of disease and will compete a questionnaire designed to detect environmental exposures. This part of the study will provide important information on risk to individuals with certain mutations and provide new information on potential triggers for disease that can then be avoided or used to design new approaches to treatment. As part of this study we will also prepare to capitalise on information learned from the genetic and environmental information. To do this we will generate patient-specific stem cells from a blood test from individuals with BMPR2 mutations (with and without disease) and from patients in whom we find new mutations. We will begin to use these cells to understand how mutations cause changes in important cell types in this disease, including heart and blood vessel cells, and use this as a means of screening new drugs. Finally we will begin to use patient derived samples (stem cells and blood vessel cells) to test our best ideas so far, based on what we have learned from the available genetic information to date. This definitive national study has the potential to provide major new insights into our understanding of the genetic and environmental causes of PAH and has potential to provide promising new approaches to disease prevention or treatment based on these findings.

This study seeks to determine novel genetic and environmental factors that contribute to the initiation and/or progression of pulmonary arterial hypertension (PAH). Idiopathic PAH is a rare but devastating condition, predominantly affecting females (2.3:1) in early middle age. The condition continues to carry a poor prognosis (40% mortality at 3 years) despite modern vasodilator therapies. Existing treatment does not target the abnormal vascular cell phenotype that characterises PAH. A major breakthrough in our understanding of the pathobiology was the identification of heterozygous disease-causing mutations in the gene encoding the bone morphogenetic protein type II receptor (BMPR-II) in families with PAH. Although research over the last 10 years has provided important clues, the precise cell and molecular mechanisms leading to disease manifestation remain incompletely understood. In addition, the penetrance of this mutation in families appears low, on average approximately 20%. The existence of discordant monozygotic twins points to important environmental factors. A further 15-26% of apparently sporadic cases of idiopathic PAH harbour mutations in BMPR-II. Identification of the critical environmental and additional genetic factors leading to disease manifestation will lead to strategies for disease prevention and may identify pathways for the development of novel therapies, and provide a basis for reverse translational studies in vitro and in vivo. This study will harness the expertise and unique resources of the UK National Pulmonary Hypertension Centres and allied NIHR BRC next generation sequencing capacity and bioinformatics to identify novel genetic variation underlying PAH. Concurrent epidemiology and biomarker testing will provide clues to environmental triggers. We will derive patient-specific induced pluripotent stem cells to test hypotheses and facilitate target/drug discovery and provide proof-of-concept for targeting the BMPR-II pathway in PAH.

This research will provide both academic and, potentially, economic and societal impact. The academic impacts include enhancing the knowledge of the causes, the gene-environment interactions, the natural history, clinical course of heritable forms of pulmonary arterial hypertension (PAH). Although we are studying a rare form of PAH, it is likely to be highly informative, with much broader implications for patients with other forms of pulmonary hypertension, in terms of disease mechanisms and potential therapy. Thus both academics, clinicians and patients are likely to benefit from this research. The findings are likely to inform policy in the management and screening of families where a family member has PAH. An economic and societal impact might be the identification of novel pathways or approaches to treating patients with PAH and the implementation of these through experimental medicine studies. Promising approaches to therapy will be developed by attracting translational funding from research councils or charities, likely in collaboration with industry.

We anticipate that the use of patient-derived induced pluripotent stem cells (iPSCs) will be a valuable resource for both academia and industry for screening of pathways and compounds in functional assays. These will be made available to the scientific community and industry under the appropriate arrangements for protecting intellectual property. We have already applied for a patent in the UK for our novel method of generating iPSCs from blood outgrowth endothelial cells, using Cambridge Enterprise, the technology transfer arm of the University of Cambridge. With heir help we have non-exclusively licensed the technology to a Cambridge University spin out stem cell company.

As part of this proposal we plan to develop peptidomimetic agents as agonists of the BMPR2 receptor complex. Our preliminary studies with these agents are promising in endothelial cell-based assays. If we can improve the potency of the compounds and confirm their predicted stability in serum we anticipate applying for a patent for these in the near future via Cambridge Enterprise.

The presence of the national cohort will enable studies of prevention and mutation or pathway specific therapies that would otherwise be extremely difficult, given how rare this condition is. This will provide a basis for the identification of novel biomarkers to predict risk of disease in BMPR2 mutation carriers and provide a unique cohort for intervention.

the principal investigator has had previous experience with experimental medicine studies in PAH, taking a drug from proof-of-concept through to a successful international Phase III clinical trial - using the tyrosine kinase inhibitor, imatinib, in patients with advanced PAH.