Background: Idiopathic and familial forms of pulmonary arterial hypertension (PAH) occur more frequently in women than men. However, the reason for this remains unknown. Both the calcium binding protein S100A4/Mts1 (Mts1) and its endogenous receptor (receptor for advanced glycosylation end products; RAGE) have been implicated in the development of PAH. We wished to investigate if the Mts1/RAGE pathway may play a role in the gender bias associated with PAH.
Methods: We investigated the effects of gender on development of PAH in mice over-expressing Mts1 (Mts1+ mice) via measurement of pulmonary arterial remodeling, systolic right ventricular pressure (sRVP) and right ventricular hypertrophy (RVH). Gender differences in pulmonary arterial Mts1 and RAGE expression were assessed by qRT-PCR and immunohistochemistry. Western blotting and cell counts were used to investigate interactions between 17β-estradiol, Mts1 and RAGE on proliferation of human pulmonary artery smooth muscle cells (hPASMCs). Statistical analysis was by one-way analysis of variance with Dunnetts post test or two-way analysis of variance with Bonferronis post test, as appropriate.
Results: Female Mts1+ mice developed increased sRVP and pulmonary vascular remodeling, whereas male Mts1+ mice remained unaffected. The development of plexiform-like lesions in Mts1+ mice was specific to females. These lesions stained positive for both Mts1 and RAGE in the endothelial and adventitial layers. Expression of pulmonary arterial Mts1 was greater in female than male Mts1+ mice, and was localised to the medial and adventitial layers in non plexiform-like pulmonary arteries. RAGE gene expression and immunoreactivity were similar between male and female Mts1+ mice and RAGE staining was localised to the endothelial layer in non plexiform-like pulmonary arteries adjacent to airways. In non-plexiform like pulmonary arteries not associated with airways RAGE staining was present in the medial and adventitial layers. Physiological concentrations of 17β-estradiol increased Mts1 expression in hPASMCs. 17β-estradiol-induced hPASMC proliferation was inhibited by soluble RAGE, which antagonises the membrane bound form of RAGE.
Conclusions: Mts1 over-expression combined with female gender is permissive to the development of experimental PAH in mice. Up-regulation of Mts1 and subsequent activation of RAGE may contribute to 17β-estradiol-induced proliferation of hPASMCs.