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Hyperhomocysteinemia (HHcy) is an independent risk factor of cardiovascular diseases. Extracellular signal-regulated kinase-1/2 (ERK-1/2) and the JAK/STAT pathway kinase, signal transducer and activator of transcription 3 (STAT3), are involved in matrix metalloproteinase-9 (MMP-9) induction and matrix remodeling. However, their role in homocys-teine (Hcy)-mediated MMP-9 induction and matrix remodeling is unclear. Clinical and experimental evidence indicates that HHcy and activation of the renin-angiotensin system, mediated by angiotensin II type 1 (AT1) receptor, are involved in a variety of vascular pathologies. Despite this fact, the relationship between HHcy and activation of the renin-angiotensin system has not been comprehensively characterized. Therefore, we hypothesized that Hcy activates AT1 receptor that potentiates STAT3 via ERK-1/2 phospho-rylation. STAT3 modulates target MMP-9 and collagen, resulting in vascular remodeling.Mouse aortic endothelial cells (MAEC) were treated with various doses of Hcy for different time periods. The levels of AT1 receptor, ERK-1/2, STAT3, MMP-9 and collagen type-1 were measured by immu-noblot analyses. The activation of ERK-1/2 and STAT3 were determined by measuring ERK-1/2 phosphory-lation and phosphoserine (727) STAT3.Although Hcy dose-dependently induced AT1 receptor expression in the endothelial cells, a significant induction was observed at 100 μM at 48 h. We investigated Hcy-induced ERK-1/2 and STAT3 phos-phorylation through AT1 receptor induction, and our results suggest that Hcy activated AT1 receptor which led to ERK-1/2 and STAT3 phosphorylation. In addition, findings of this study suggest that Hcy-mediated STAT3 activation regulated MMP-9 and collagen type-1. However, AT1 receptor blocker, valsartan, and the specific STAT3 inhibitor peptide attenuated MMP-9 and collagen type-1 induction.These findings demonstrate for the first time the contribution of AT1 receptor in HHcy-induced atherosclerotic diseases; Hcy-induced activation of AT1 receptor involves MMP-9 and collagen type-1 modulation using ERK-1/2 and STAT3 signaling cascades.