Inhibitory mechanism of taurine on the platelet-derived growth factor BB-mediated proliferation in aortic vascular smooth muscle cells

Taurine suppresses platelet-derived growth factor (PDGF) BB-induced PDGF-β receptor phosphorylation by protein tyrosine phosphatase-mediated dephosphorylation in vascular smooth muscle cells

In atherosclerosis, abnormal vascular smooth muscle cell (VSMC) proliferation plays an important role to form fibroproliferative lesions and platelet-derived growth factor (PDGF)-BB is one of the most potent chemoattractants and proliferative factors for VSMCs. Taurine, sulfur-containing beta-amino acid, has been considered to prevent the development of atherosclerosis, although the molecular mechanism remains obscure. Previously, we demonstrated that taurine significantly suppressed PDGF-BB-induced cell proliferation, DNA synthesis, immediate-early gene expressions and extracellular signal-regulated kinase (ERK) 1/2 phosphorylation in VSMCs. The present study was aimed at elucidating the precise molecular mechanism of taurine in PDGF-BB signaling pathway. We showed that taurine significantly suppressed PDGF-BB-induced phosphorylation of PDGF-beta receptor and activation of its downstream signaling molecules such as Ras, MAPK/ERK kinase (MEK)1/2 and Akt. Because taurine did not attenuate phorbol 12-myristate 13-acetate (PMA)-induced PDGF-beta receptor-independent ERK1/2 phosphorylation, we further investigated the suppressive mechanism of taurine in PDGF-beta receptor level. Although taurine did not directly affect PDGF receptor autophosphorylation in vitro, taurine promoted PDGF-beta receptor dephosphorylation and restored PDGF-BB-induced suppression of protein tyrosine phosphatase (PTPase) activity. Taken together, we propose that taurine could prevent or delay the progression of atherosclerosis by PTPase-mediated suppression of PDGF-beta receptor phosphorylation, and by decreasing the activation of its downstream signaling molecules in VSMCs.

[Taurine is a possible anti-atherosclerotic agent]

Atherosclerosis-related ischemic heart diseases are the principal cause of death in the last few years. Recently, several reports implicated that taurine, sulfur-containing beta-amino acid, prevented the progression of atherosclerosis through various anti-pathogenetic modifications. Firstly, taurine treatment inhibited lipid peroxidation and/or lowered serum LDL/VLDL cholesterol and elevated HDL, and as a result, it prevented lipid accumulation on the aortic valve in hypercholesterolaemic animals. Secondly, taurine administration prevented endothelial dysfunction, one of the initial events in the formation of lesions of atherosclerosis, through the amelioration of the impairment of monocyte function. Thirdly, while it is well known that taurine scavenges hypochlorous acid (HOCl) produced by myeloperoxidase in neutrophils and macrophages, recent studies revealed that HOCl was one of the major factors oxidizing LDL, implying that the anti-oxidative role of taurine contributes to the anti-atherosclerotic effect. Additionally, TauCl, produced by the reaction of taurine with HOCl, inhibits the activation of NF-kappaB followed by the inhibition of the production of the pro-inflammatory mediators.