Abnormal HIF signaling in Down syndrome-related pulmonary hypertension

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PROJECT SUMMARY Down syndrome (DS), the condition that arises from triplication of chromosome 21 (HSA21), occurs in 1:700 live births and is the most common human chromosomal abnormality. A major co-occurring condition in DS is pulmonary hypertension (PH), which can lead to progressive right heart dysfunction, failure, and death, even when aggressively treated. Remarkedly, PH occurs very frequently in newborns and children with DS (28%) when compared with non-DS subjects and can be associated with congenital heart disease. The underlying cause of PH and the increased susceptibility to accelerated PH in in DS remain poorly understood and animal models for preclinical studies of PH in DS have been lacking. Recent studies have shown that early disruption of lung development related to impaired angiogenesis and alveolar growth is evident in DS children with severe PH, but there remains a critical need to define specific genetic and molecular mechanisms that delay lung maturation and increase susceptibility for PH. Furthermore, more selective PH therapies are needed to decrease cardiopulmonary morbidity and mortality in DS. Past studies have suggested that individuals with DS have a low incidence of vascular disease and solid tumors due to overexpression of anti-angiogenic factors, but whether disruption of lung vascular growth is due to abnormal regulation of angiogenesis and related alveolar growth and mechanisms that contribute to PH in DS children remain uncertain. Our laboratory has previously demonstrated that inhibition of angiogenic pathways reduces lung alveolar and vessel growth and causes PH in diverse experimental models. Additionally, we showed that HSA21-encoded potent anti-angiogenic genes are overexpressed in human fetal and neonatal DS lung and show evidence for reduced vascular and alveolar growth, even in the absence of cardiac disease. In line with these findings, our human biomarker studies show that serum anti-angiogenic factor profile is strongly associated with PH in DS children. Our preliminary data show that 2 weeks of very mild hypoxia exposure of Dp16 DS mice leads to PH as characterized by increased pulmonary vascular wall thickening, decreased vascular densities and right ventricular hypertrophy, and delays lung maturation. Such delayed lung maturation and PH development in DS animal model has not been previously studied, and Dp16 DS mice appears to be a valid preclinical model of PH in DS. Hypoxia and hypoxia-inducible (HIF) signals are critical in PH and abnormal lung development, and cells of DS are characterized by pseudo- hypoxic state that drives a variety of functional deficits seen in DS. Our preliminary data show that hypoxia inducible gene network is markedly upregulated with significant alteration in the molecular pathways that regulate pulmonary vessel development and response to hypoxia in this model. Thus, we hypothesize that mild hypoxic exposure of Dp16 neonatal mice leads to the development of PH and delays lung maturation and that aberrant HIF signaling is a critical driver of this process. Overall, these studies will provide novel insights into the risk for PH in DS and potentially identify novel targets for future therapies.