Dissecting the role of Osteoprotegerin and related signalling pathways in the pathogenesis of pulmonary arterial hypertension

Pulmonary arterial hypertension is a devastating and life threatening condition that often affects the young. The disease is characterised by the loss of blood vessels within the lung. However, the exact mechanisms of the disease process remain unclear. We have evidence from both clinical studies and experiments in the laboratory to suggest that a protein called osteoprotegerin (OPG) is present at abnormally high levels in this condition. I will investigate how OPG and related proteins are controlled and whether the abnormally high level of OPG is actively causing/driving disease or a diagnostic bystander. To do this I will perform studies in animal models of disease and engineer a mouse that over-expresses OPG to test whether these mice develop pulmonary arterial hypertension. In addition I will use new high throughput protein screening techniques to identify the important intermediary molecules with the goal of identifying novel targets for potential new therapies.

Pulmonary arterial hypertension (PAH) is a devastating and life threatening condition often affecting young women, limiting their physical capacity, and decreasing life expectancy (median 2.8 years without treatment). Current drug treatments fail to reverse disease, leaving lung transplant as the only curative treatment. Pathologically PAH is characterised by the obliteration of the distal pulmonary arteries. Early endothelial cell (EC) dysfunction and apoptosis, and the subsequent abnormal proliferation and migration of pulmonary artery smooth muscle cells (PA-SMC) are thought to be the major contributing factors but the molecular mechanisms responsible are unknown. I have recently described heightened expression of osteoprotegerin (OPG) in Pulmonary Arterial Hypertension (PAH) patients, and that OPG induces proliferation and migration of pulmonary artery smooth muscle cells in vitro. These data are the first to demonstrate that OPG is increased in PAH and that it regulates PA-SMC proliferation and migration. It is unclear, and I aim to determine whether OPG is causal and/or a potential new biomarker in PAH. To this end, the objectives for this fellowship are to 1) determine the temporal relationship between the pattern of OPG expression and onset/progression of PAH in animal models 2) Determine whether over-expression of OPG expression causes PAH in a transgenic mouse model. 3) Determine whether blocking OPG with a neutralising OPG antibody prevents and/or reverses PAH in animal models, and 4) Identify associated binding partners and signalling processes involved in OPG-induced PA-SMC proliferation and migration. To achieve these objectives I will use a combination of established rodent models for PAH and generate a transgenic mouse that over-expresses OPG in vascular smooth muscle cells. Finally using a systems biology approach, I will identify OPG binding partners and subsequent signalling mechanisms by a combination of Biacore technology, MALDI-TOF mass spectrometry and protein array to determine the key molecules that mediate OPG-induced PA-SMC proliferation and migration. The data generated will provide valuable insights into the role of OPG in that pathogenesis of PAH and potentially identify novel therapeutic targets for the treatment of PAH.