Mechanisms Of Inflammation And Oxidative Damage In Sheep Bronchial Epithelial Cells Induced By Capsular Polysaccharide Of Mycoplasma Ovipneumoniae

Mycoplasma ovipneumoniae(M.ovipneumoniae,MO)has been identified as a pathogenic agent of chronic non-progressive infection of pneumonia in sheep and goats,the nature between a protective and a pathological host response of MO infection currently remains largely unknown.In this regard,the role of capsular polysaccharide(CPS),a major active component for cellular adherence,invasion,immune modulation and virulence of M.ovipneumoniae remains undefined,despite several lines of evidences have shown that M.ovipneumoniae is able to produce polysaccharide capsules for facilitating its adherence to ciliated epithelium.Together with the pivotal role of CPS in the adherence of M.ovipneumoniae to host cells,it is therefore of importance to characterize biological functions and underlying mechanisms of immune responses of the CPS in respiratory epithelial cells.In the present study,we interrogated the biological activity and mechanism of capsular polysaccharides(CPS)of M.ovipneumoniae-induced respiratory epithelial cell inflammation and apoptosis using air-liquid interface(ALI)-cultured epithelial cells generated with primary bronchial epithelial cells of Tan sheep.Results showed that CPS derived from M.vipenumoniae could activate Toll-like receptor(TLR)-mediated inflammatory responses,along with an elevated expression of various inflammatory-associated mediators,representatively including pro-inflammatory cytokines such as ILI?,TNFa,and IL8,and anti-inflammatory cytokines such as IL10 and TGF? of TLR signaling cascade.Mechanistically,the CPS-induced inflammation was TLRs-initiated and was mediated by activations of both MyD88-dependent and MyD88-independent signaling pathways.Of importance,a blockage of CPS with specific antibody led a significantly reduction of M.ovipenumoniae-induced inflammatory responses in sheep bronchial epithelial cells.These results suggested that CPS is a key component of M.ovipenumoniae,which may play a crucial role in the inflammatory response induced by M.ovipenumoniae infections.In addition,our results showed that CPS of M.ovipenumoniae induce a caspase-dependent apoptosis via both intrinsic and extrinsic apoptotic pathways in sheep bronchial epithelial cells,and which may be mainly attributed by a ROS-dependent JNK-and p38 MAPK signaling pathways,but not ERK MAPK-mediated apoptotic pathways.Collectively,the results from our studies using an ALI culture of primary sheep bronchial epithelial cells suggest that CPS,which is the major capsular component of M.ovipneumoniae,might serve as main endogenous PAMPs of this pathogen to activate the epithelial inflammation.Moreover,CPS may contribute to M.ovipneumoniae-induced apoptosis through both ROS-dependent intrinsic and extrinsic apoptotic pathways.These findings herein provide insights into the M.ovipneumoniae-mediated pathogenicity mechanism in modulating the host immune system,which also warrants further study for development of specific agents that can suppress M.ovipneumoniae-induced inflammation and apoptosis in veterinary clinic settings.