Effects of LDH in Mesomycoplasma(Mycoplasma)hyopneumoniae on Apoptosis of Porcine Bronchial Epithelial Cells
Mesomycoplasma(Mycoplasma)hyopneumoniae(Mhp)infection can cause damage and apoptosis of host epithelial cells,and the breakdown of the epithelial barrier often leads to the secondary infection of other bacteria and viruses,causing serious economic losses to the swine industry.However,the pathogenicity and virulence determinants of Mhp are not yet completely elucidated.Previous studies have found that Mhp lactate dehydrogenase(LDH)not only involved in the metabolism of Mhp,but also related to its virulence.Therefore,in this study,recombinant LDH(rLDH)was obtained through prokaryotic expression and affinity chromatography,and different concentrations of rLDH were used to interact with porcine bronchial epithelial cell(PBEC).The effect of rLDH on cellular morphology was observed by microscope,and the effect of rLDH on cellular viability was detected by CCK-8 method.The rLDH concentrations(50 and 100 μg·mL-1)were selected for further analysis by that there was no significant effect on cellular morphology and viability when it incubated with PBEC,and the apoptosis rate of cells was detected by flow cytometry.The transcriptional and expression levels of apoptosis-related genes caspase3,caspase 8,caspase 9,Bax and BCL-2 were detected by reverse transcription-quantitative polymerase chain reaction(RT-qPCR)and Western blot.The results showed that rLDH induced apoptosis of PBEC in a dose-dependent manner,the function of that was similar with Mhp.The mRNA levels of caspase 3,caspase 9,and Bax of PBEC after incubation with rLDH and Mhp 168 were significantly up-regulated and the mRNA level of BCL-2 was significantly down-regulated,while the mRNA of caspase 8 was not changed significantly.The protein expression levels of caspase 3 and Bax were significantly up-regulated and the protein expression level of BCL-2 was significantly down-regulated.The results showed that Mhp could induce the endogenous apoptosis of PBEC through LDH,in which the apoptosis-related factors caspase 3,caspase 9,Bax and BCL-2 playing important roles.