YKL-40-induced IL-8 Expression From Bronchial Epithelium Leads To Bronchial Smooth Muscle Proliferation And Migration

Background and Objectives:YKL-40, also called Human Cartilage glycoprotein-39 or Chitinase-3-like-1, is one kind of chitinase-like proteins, which belong to the chitinase and chitinase-like family of proteins. It can bind to the chitin, however has no activity of chitinase and consequently has no ability to degrade chitin. Since the last three amino acids in the N-terminal of CHI3L1 are tyrosine, lysine and leucine, and its molecular weight is 40 KD, CHI3L1 is also named as YKL-40. Previous studies showed that YKL-40 plays important roles in tissue remodeling, fibrosis and genesis of solid tumors. Further investigations found that YKL-40 was highly expressed in Th2 inflammation subjects implying the close relationship between YKL-40 and Th2 inflammation. Besides, YKL-40 can regulate the procedure of proliferation and differentiation and subsequently plays important roles in tissue remodeling. Our previous study had proved that in asthmatic patients with exacerbation, serum YKL-40 levels are much higher than in stable asthmatic patients, which shows close correlations between YKL-40 and exacerbation of asthma. As the main barrier of resistant to outer stimuli and pathogens, human bronchial epithelial cells also play important roles in pathogenesis and exacerbation of asthma. Previous studies demonstrated that YKL-40 expression was obviously upgraded in bronchial epithelial cells of asthmatic patients through immunohistochemical method, indicating that YKL-40 may have influence on the occurrence and development of asthma through bronchial epithelial cells.The main purpose of this study is to investigate how YKL-40 can mediate inflammation in human bronchial epithelial cells, including what the corresponding inflammatory cytokines are and the variation trends, and whether these inflammatory cytokines are responsible for increasing proliferation and migration of primary normal human bronchial smooth muscle cells (BSMCs).Methods:YKL-40-induced inflammation was assayed in two human bronchial epithelial cells (BEAS-2B cell line and primary human bronchial epithelial cells, namely HBECs). We treated BEAS-2B cells and HBECs with YKL-40 for different times in gradient, and measured the protein levels of IL-8, RANTES, Eotaxin, and TNF-ain supernatant by ELISA and the mRNA of these four inflammatory cytokines in these two kind of cells by real-time reverse transcription PCR. Afterwards, we added the conditioned culture media of BEAS-2B cells (YKL-40-BEAS-2B-CM) and that of HBEC cells (YKL-40-HBECs-CM) to BSMCs after 6 hours of YKL-40 stimulation. The proliferation and migration of BSMCs were determined by premixed WST-1 cell proliferation reagent and QCM chemotaxis migration assay, respectively.Results:Both BEAS-2B cells and HBECs treated with YKL-40 resulted in a significant increase of IL-8 not only in protein production but also in mRNA transcription, in time-dependent and dose-dependent manners. However, the similar effects could not be observed concerning to RANTES, Eotaxin and TNF-a. The supernatant of BEAS-2B cells and HBECs treated with YKL-40 (YKL-40-BEAS-2B-CM and YKL-40-HBECs-CM) was found to further stimulate proliferation and migration of BSMCs, and the effects were inhibited after neutralizing IL-8.Conclusions:Through investigating the interaction of airway epithelium and smooth muscle, our findings implicate that YKL-40 may be involved in the inflammation of asthma by induction of IL-8 from epithelium, subsequently contributing to BSMCs proliferation and migration. Moreover, inhibition of IL-8 signaling is a potential therapeutic target for YKL-40-induced inflammation and remodeling of asthma.