Abstract 602: FoxO3 Mediates Urotensin-II-induced MMP2 Expression In Pulmonary Artery Smooth Muscle Cells
Vascular remodeling in pulmonary hypertension (PH) results from persistent vasoconstriction, extracellular matrix degradation, cell migration and proliferation of vascular cells. However, the mechanisms linking these events are not well understood. Human urotensin-II (hU-II) is a newly identified vasoactive peptide which by binding to a G-protein-coupled receptor termed GPR-14, acts as the most potent vasoconstrictor known. Although hU-II has been associated with vascular remodeling in PH, its precise role in regulating remodeling processes is not well understood. Since degradation of the extracellular matrix plays a pivotal role in pulmonary vascular remodeling, we investigated whether hU-II is linked to expression and activity of matrix metalloproteinases (MMP) in pulmonary artery smooth muscle cells (PASMC). By immunohistochemistry we found high levels of GPR-14 and MMP2 in the media and intima of pulmonary vessels in tissue samples from patients with pulmonary vascular remodeling. In vitro experiments confirmed that hU-II time-dependently enhanced MMP2 mRNA and protein levels as well as MMP2 activity determined by zymography in PASMC. Actinomycin D inhibited hU-II-stimulated MMP2 expression indicating the involvement of a transcriptional mechanism. Bioinformatic analysis of the MMP2 promoter revealed the presence of a consensus site for FoxO3. Reporter gene assays confirmed that hU-II can increase the activity of FoxO transcription factors. Downregulation of FoxO3 by siRNA inhibited hU-II-induced MMP2 expression. Conversely, overexpression of wild type or constitutively active FoxO3 increased MMP2 expression. Consistently, hU-II increased FoxO3 levels in PASMC. FoxO3 was also strongly expressed in the media and intima of pulmonary vessels in tissue samples from patients with pulmonary vascular remodeling. In summary, this study demonstrates that hU-II induces MMP2 via FoxO3. Since the hU-II receptor GPR-14, MMP2 and FoxO3 colocalized in the media and intima of pulmonary vessels from patients with pulmonary vascular remodeling, these findings suggest an important role of this pathway in promoting pulmonary vascular remodeling and implicate FoxO3 as a potential therapeutic target for combating vascular remodeling in PH.