Pulmonary Hypertension is Associated with Apoptosis, the Downregulation of S100A1, the Upregulation of S100A6 and the Receptor for Advanced Glycation end-Products

Pulmonary arterial hypertension (PH), defined by a resting mean pulmonary artery pressure (PAP) >25 mm Hg, is a syndrome in which pulmonary arterial obstruction increases pulmonary vascular resistance, leading to right ventricular (RV) hypertrophy, failure, and death. Development of PH involves the complex interactions of multiple cell effectors. The possibility that the S100 calcium binding proteins S100A1, S100A6 and their receptor the receptor for advanced glycation end-products (RAGE) may be involved PH and associated apoptosis has not been tested. We examined the levels of S100A1, S100A6, S100B, RAGE and parameters of apoptosis the anti-apoptotic Bcl2 and the pro-apoptotic Bax and terminal deoxynucleotidyl transferase dUTP nick end labelling assay (TUNEL) positive nuclei in lung biopsies negative for malignancy taken by video-assisted thorascopic surgery in 6 control patients (4 male, 2 female) mean age 59.8±4.4 (SEM) years with PA>60 mmHg. S100A1 mRNA and protein as quantified by quantitative reverse-transcription polymerase chain reaction (qRT-PCR) and histological evaluation respectively is decreased 50-60%, whereas RAGE and S100A6 mRNA and protein is increased in the whole lung predominantly in PA endothelial and smooth muscle cells approximately 4-10 fold in PH patients compared to controls. Lung S100B levels did not differ between the control and PH groups. The PH group showed a 2.1-3.5 fold increase in the whole lung BAX/BCL2 mRNA ratio and TUNEL positive nuclei compared to controls. Compared to wild type (WT), 10-12 week old S100A1-knockout mice (KO) exhibited an increased right ventricular weight as quantified by the Fulton index (WT-0.24+0.01 vs. KO-0.28+0.01, p<0.05, n=6/group), an elevation in right ventricular systolic pressures (WT-15.5+3.8 vs. KO-28.8+4.6 mmHg, p<0.05) in the absence of altered left ventricular filling pressures, a 1.5-fold increase in lung caspase-3 activity as a marker of apoptosis and 2-3 fold increase in whole lung RAGE and S100A6 mRNA expression. Our data demonstrating that absence of S100A1 results in PH describes a novel murine model of PH, which displays many of the hallmarks of the human disease, thus makes it an attractive therapeutic target in the treatment of PH.