Role of Secreted Protein Acidic Rich in Cysteine in Pulmonary Vascular Remodeling of Pulmonary Hypertension

Abstract

Pulmonary hypertension (PH) is a life-threatening disease, characterized by excessive pulmonary vascular remodeling, leading to elevated pulmonary arterial pressure and right heart hypertrophy. PH is caused among others by chronic hypoxia, vasoconstrictor/vasodilator and/or growth factor imbalance leading to pulmonary arterial smooth muscle cell (PASMC) dysregulation. Upon re-exposure to normoxia, hypoxia-induced PH in mice is reversible.Until now, research in the field of PH concentrates mostly on the onset and development of PH. In this thesis, we aim to identify novel candidate genes for pulmonary vascular remodeling and its reversal specifically in the pulmonary vasculature.Reverse remodeling was investigated in adult mice (C57BL/6J) either exposed to normoxia (21% O2), chronic hypoxia (10% O2), or chronic hypoxia with subsequent re-exposure to normoxia for 1, 3, 7, 14 days. Pulmonary vessels were laser-microdissected followed by RNA isolation and microarray analysis. In addition, the functional role of the candidate gene was confirmed in vitro in human primary PASMC and in vivo in respective knockout mice.In laser-microdissected murine pulmonary vessels, secreted protein acidic and rich in cysteine (SPARC) was identified as one gene consistently down-regulated in all re-oxygenation time points investigated. Up-regulation of SPARC specifically in the pulmonary vasculature was observed in chronic hypoxic mice and in idiopathic pulmonary arterial hypertension patients. Furthermore, TGF-beta1 or hypoxia-HIF-2alpha signaling pathway induced SPARC expression. In in vitro studies, SPARC silencing in primary human PASMC led to reduced proliferation and diminished PI3K/AKT/mTOR activation. However, SPARC in vivo knockout did not attenuate chronic hypoxia-induced PH, possibly due to elevated AKT activation and PASMC proliferation under hypoxic conditions in SPARC knockout PASMC.In summary, SPARC was identified as a novel gene involved in dysregulation of primary human PASMC proliferation. Moreover, to the best to our knowledge this is the first evidence about its associated with the human PH disease.