BackgroundThe present study investigated whether changes in gene expression in the right ventricle following pulmonary hypertension can be attributed to hypoxia or pressure loading.Methodology/Principal FindingsTo distinguish hypoxia from pressure-induced alterations, a group of rats underwent banding of the pulmonary trunk (PTB), sham operation, or the rats were exposed to normoxia or chronic, hypobaric hypoxia. Pressure measurements were performed and the right ventricle was analyzed by Affymetrix GeneChip, and selected genes were confirmed by quantitative PCR and immunoblotting. Right ventricular systolic blood pressure and right ventricle to body weight ratio were elevated in the PTB and the hypoxic rats. Expression of the same 172 genes was altered in the chronic hypoxic and PTB rats. Thus, gene expression of enzymes participating in fatty acid oxidation and the glycerol channel were downregulated. mRNA expression of aquaporin 7 was downregulated, but this was not the case for the protein expression. In contrast, monoamine oxidase A and tissue transglutaminase were upregulated both at gene and protein levels. 11 genes (e.g. insulin-like growth factor binding protein) were upregulated in the PTB experiment and downregulated in the hypoxic experiment, and 3 genes (e.g. c-kit tyrosine kinase) were downregulated in the PTB and upregulated in the hypoxic experiment.Conclusion/SignificancePressure load of the right ventricle induces a marked shift in the gene expression, which in case of the metabolic genes appears compensated at the protein level, while both expression of genes and proteins of importance for myocardial function and remodelling are altered by the increased pressure load of the right ventricle. These findings imply that treatment of pulmonary hypertension should also aim at reducing right ventricular pressure.

The present study was designed to analyze protein expression in lungs from pulmonary hypertensive rats in order to identify novel signaling pathways. This was achieved by proteomic studies in which proteins from lung homogenates from hypoxic were compared to normoxic rats. The expression of these proteins was then investigated in lungs from hypoxic rats treated with either an activator of soluble guanylyl cyclase, BAY 412272, or an inhibitor of phosphodiesterase type 5, sildenafil. The proteomic study revealed an up-regulation of guanine nucleotide-binding protein β, GST-ω-1, cathepsin D, chloride intracellular channel subunit 5, annexin A4, F-actin capping protein CapZ (CapZα), and the translation factor elongation factor 1 δ in lungs from chronic hypoxic rats with pulmonary hypertension. Immunohistochemistry revealed that CapZα, cathepsin D, and annexin A4 were expressed in the pulmonary vascular wall and immunoblotting showed these proteins correlated to alterations in muscularization. Both drugs inhibited hypoxia-induced increase in right ventricular systolic pressure and pulmonary arterial muscularization, and prevented most of the protein regulations observed after hypoxia. These findings suggest that pulmonary pressure is an important factor for initiating signaling pathways leading to protein expression and muscularization in the pulmonary vasculature.