Receptor Upregulation and MAPK Activity in Arteries and Bronchi Following Secondhand Smoke Exposure

Cigarette smoking is a major risk factor for cardiovascular and respiratory diseases. Contractile receptor changes have been observed in several vascular diseases. The intracellular mitogen activated protein kinase (MAPK) signaling pathways are suggested to be associated with receptor upregulation. The present study therefore aimed to investigate the status of vascular and bronchial receptor changes after secondhand smoke (SHS) exposure, focusing on the involvement of Raf/MEK/ERK1/2 signaling. The results show that upregulation of 5-hydroxytryptamine type 1B (5-HT1B) receptors and endothelin type A (ETA) receptors was found in rat cerebral arteries after exposure to SHS. SHS exposure modified the expression of ETB and ETA receptors in coronary arteries via the Raf/ERK/MAPK pathway. The SHS exposure-induced bronchial hyperreactivity was manifested by transcriptional upregulation of ETB, ETA and 5-HT2A receptors in bronchioles. The receptor upregulation includes the increased contractile characteristic response to the receptor agonists, elevated expression level of mRNA and/or protein for the contractile receptors. The mechanism study involves the protein phosphorylation analysis of Raf/ERK1/2 and inhibition of Raf-1 or MEK1/2 in vivo. The results show that SHS exposure induced Raf/ERK1/2 activation. Treatment together with SHS exposure showed the preventive effect of GW5074 on the SHS-induced receptor upregulation. After the first 8 weeks exposure, the receptor expression and its contractile function were significantly increased. However, the increased receptor expressions were normalized by accompanying of U0126 administration. Our knowledge of the Raf/MEK/ERK1/2 signaling pathway in SHS exposure-induced contractile receptor upregulation may provide a new therapeutic target for treatment of SHS-associated diseases