Shroom expression is attenuated in pulmonary arterial hypertension

Shroom is a PDZ-domain protein involved in the regulation and maintenance of cytoskeletal architecture by binding to actin. Hypertrophy and altered actin organisation of pulmonary arterial smooth muscle cells (PASMC) is a hallmark of pulmonary arterial hypertension (PAH). The aim of the present study was to localise and characterise Shroom expression in the lung in experimental and idiopathic PAH (IPAH). Shroom expression and localisation in hypoxia-induced PAH in mice and IPAH in humans, in vivo, as well as in primary PASMC, in vitro, was assessed by quantitative RT-PCR, immunofluorescence, laser-assisted microdissection and immunohistochemistry. Shroom localised exclusively to PASMC (both bronchial and vascular) in mouse and human lungs. Both in vivo and in primary PASMC, in vitro, Shroom exhibited spatially similar expression with alpha-smooth muscle actin (alpha-SMA). Shroom expression was significantly reduced in the mouse model of PAH, in primary murine PASMC exposed to hypoxia, and in primary PASMC isolated from patients with IPAH. The ratio between Shroom and alpha-SMA RNA expression further confirmed Shroom downregulation in both mouse and human PASMC. In summary, Shroom localises exclusively to pulmonary smooth muscle cells. Shroom downregulation in pulmonary arterial hypertension suggests a link between Shroom expression and pulmonary arterial smooth muscle cell hypertrophy in pulmonary arterial hypertension.