Acrolein activates mitogen-activated protein kinase signal transduction pathways in rat vascular smooth muscle cells

Acrolein, a major component of cigarette smoke, an environmental pollutant and an endogenous lipid peroxidation product, has been implicated in the development of atherosclerosis. Although a link between vascular injury and acrolein has been indicated, the exact molecular mechanism of acrolein-induced toxicity to vasculature is unknown. In an effort to elucidate the molecular basis of acrolein-induced vascular toxicity, the possibility of the intracellular signaling system as one of the targets of acrolein-induced toxicity is investigated in the present study. Exposure of cultured rat vascular smooth muscle cells (VSMCs) to different doses of acrolein not only causes cytotoxicity but also alters cellular morphology in a concentration and time-dependent manner. VSMCs exhibit cytotoxicity to a narrow concentration range of 5-10 microg/ml and display no toxicity to 2 microg/ml acrolein even after 24 h of exposure. Furthermore, exposure to acrolein results in activation of members of the mitogen-activated protein kinase (MAPK) family and protein tyrosine kinases. The extracellular signal-regulated kinases 1 and 2 (ERK1/2), stress-activated protein kinases/c-jun NH2-terminal kinases (SAPK/JNK) and p38MAPK are effectively and transiently activated by acrolein in a concentration and time-dependent fashion. While all three MAPKs exhibit significant activation within 5 min of exposure to acrolein, maximum activation (ERK1/2 and p38MAPK) or close to maximum activation (SAPK/JNK) occurs on exposure to 5 microg/ml acrolein for 2 h. Acrolein-induced activation of MAPKs is further substantiated by the activation of transcription factors, c-jun and activator transcription factor-2 (ATF-2), by acrolein-activated SAPK/JNK and p38MAPK, respectively. Additionally several cellular proteins exhibit spectacular protein tyrosine phosphorylation, particularly in response to 2 and 5 microg/ml of acrolein. Interestingly, the acrolein-induced activation of MAPKs precedes acrolein-stimulated protein tyrosine phosphorylation, which occurs after 2 h of exposure to acrolein. However, the time course of maximum protein tyrosine phosphorylation profile corresponds to the peak activation profile of MAPKs. The activation of MAPKs and protein tyrosine phosphorylation by acrolein appears to be independent of acrolein-induced toxicity. VSMCs exposed to 2 microg/ml acrolein exhibit no toxicity but stimulates significant activation of MAPKs and protein tyrosine phosphorylation. Although acrolein-induced VSMC toxicity is not blocked by MAPK inhibitors, PD98059, an inhibitor of MAPK kinase and SB203580, an inhibitor of p38MAPK, eitheralone or in combination, each MAPK responds differently to the inhibitors. Most prominently, although SB203580, an inhibitor of both SAPK/JNK and p38MAPK, significantly inhibited acrolein-induced activation of p38MAPK, it also stimulated SAPK/JNK activation by acrolein alone and in combination with PD98059. These results provide the first evidence that the activation of both growth-regulated (ERK1/2) and stress-regulated (SAPK/JNK and p38MAPK) MAPKs as well as tyrosine kinases are involved in the mediation of acrolein-induced effects on VSMC, which may play a crucial role in vascular pathogenesis due to environmentally and endogenously produced acrolein.