title: Secondhand smoke exposure causes bronchial hyperreactivity via transcriptionally upregulated endothelin and 5-hydroxytryptamine 2A receptors.
abstract: BACKGROUND
  Cigarette smoke exposure is strongly associated with airway hyperreactivity (AHR) which is the main characteristic seen in asthma. The intracellular MAPK signaling pathways are suggested to be associated with the airway damage to the AHR. In the present study, we hypothesize that secondhand cigarette smoke (SHS) exposure upregulates the bronchial contractile receptors via activation of the Raf/ERK/MAPK pathway.
  
  
  RESULTS
  Rats were exposed to SHS for 3 h daily for up to 8 weeks. The receptor agonists-induced bronchial contractile reactivity was analyzed with a sensitive myograph system. The mRNA transcription and protein translation of the target receptors and the kinases in Raf/ERK/MAPK pathway were investigated by real-time PCR, Western blotting and immunofluorescence, respectively. Compared with exposure to fresh air, SHS induced enhanced bronchial contractile responses mediated by the 5-hydroxytryptamine 2A (5-HT(2A)) receptors as well as the endothelin type B (ET(B)) and type A (ET(A)) receptors. The response curves were shifted toward the left with an increased maximal contraction (E(max)) demonstrating that SHS induced AHR. Additionally, the mRNA and protein levels of the 5-HT(2A), ET(B) and ET(A) receptors were increased. Furthermore, SHS exposure increased the phosphorylation of Raf-1 and ERK1/2, but it did not alter p38 or JNK. A Raf-1 inhibitor (GW5074) suppressed the SHS-induced increase in the expression of 5-HT(2A) and ET(A) receptors and the receptor-mediated AHR.
  
  
  CONCLUSIONS
  Our findings show that SHS exposure induces transcriptional upregulation of the 5-HT(2A), ET(B) and ET(A) receptors in rat bronchial smooth muscle cells, which mediates AHR. The Raf/ERK/MAPK pathway is involved in SHS-associated receptor upregulation and AHR.
authors.affiliation: Division of Experimental Vascular Research, Institute of Clinical Science in Lund, Lund University, Lund, Sweden.
authors.forename: Lei
authors.initials: L
authors.lastname: Cao
authors.forename: Yaping
authors.initials: Y
authors.lastname: Zhang
authors.forename: Yong-Xiao
authors.initials: YX
authors.lastname: Cao
authors.forename: Lars
authors.initials: L
authors.lastname: Edvinsson
authors.forename: Cang-Bao
authors.initials: CB
authors.lastname: Xu
mesh_terms: D000818:Animals; D016535:Bronchial Hyperreactivity / Q000201:enzymology / Q000235:genetics* / Q000473:pathology / Q000503:physiopathology; D004781:Environmental Exposure; D004789:Enzyme Activation / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D010636:Phenols / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D044022:Receptor, Endothelin A / Q000235:genetics* / Q000378:metabolism; D044023:Receptor, Endothelin B / Q000235:genetics* / Q000378:metabolism; D044402:Receptor, Serotonin, 5-HT2A / Q000235:genetics* / Q000378:metabolism; D058826:Serotonin 5-HT2 Receptor Agonists / Q000494:pharmacology; D014028:Tobacco Smoke Pollution; D014158:Transcription, Genetic / Q000187:drug effects; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics*; D048490:raf Kinases / Q000378:metabolism
chemical_list: D007211:Indoles; D010636:Phenols; D012333:RNA, Messenger; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D044402:Receptor, Serotonin, 5-HT2A; D058826:Serotonin 5-HT2 Receptor Agonists; D014028:Tobacco Smoke Pollution; D048490:raf Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; C489251:5-iodo-3-((3,5-dibromo-4-hydroxyphenyl)methylene)-2-indolinone