The Mechanism Of Neonatal Streptococcus Pneumoniae Pneumonia Altering The Phenotype Of Airway Smooth Muscle And Airway Hyperresponsiveness

Background:Streptococcus pneumoniae is the vital bacterial pathogen of acquired respiratory infection in children.Our previous studies have shown that neonatal Streptococcus pneumoniae infection can promote airway inflammation and airway hyperresponsiveness(AHR)in an OVA-induced allergic asthma.Airway smooth muscle(ASM)plays a pivotal role in AHR development.Whether neonatal Streptococcus pneumoniae infection alters airway smooth muscle phenotype and promotes AHR remains unclear.Objective:To investigate the effect of Streptococcus pneumoniae pneumonia(S.pp)on airway smooth muscle(ASM)phenotypes and AHR.Methods:Non-lethal neonatal pneumonia was established by intranasally infecting 1-week-old BALB/C mice with the S.pneumoniae strain D39.The mice were divided into control group and S.pp group.The body weight and lung weight were monitored.Lungs were collected to detecte AHR by means of whole-body plethysmography,and to assess the levels ofα-SMA and the contractile proteins of ASM.Result:Our results indicate that the body weight and lung weight were recovered within 7 days,and AHR in S.pp group was significantly higher than that in control group(p<0.001).The thickness of bronchial wall was significantly higher in S.pp group compared with control group(p<0.01),the thickness of alveolar septum was also significantly higher in S.pp group compared with control group(p<0.05).The airway smooth muscle area(α-SMA~+area/Pbm)was remarkably higher in S.pp group compared with control group(P<0.01).The airway smooth muscle myosin heavy chain area(SMMHC~+area/Pbm)was significantly higher in S.pp group compared with control group(P<0.05).And there was no significant difference in airway smooth muscle 22 alpha area(SM22α~+area/Pbm)between two groups(P>0.05).As expected,western blot analysis ofα-SMA protein was significantly higher in S.pp group compared with control group(P<0.01).SMMHC protein was significantly higher in S.pp group than that in control group(P<0.01).While SM22αprotein was similar between two groups(P>0.05).Meanwhile,Acta 2-mRNA was significantly higher in S.pp group compared with control group(P<0.01).And Myh11-mRNA were significantly higher in S.pp group than those in control mice(P<0.01).Similarly Tagln-mRNA was no significant difference between two groups(P>0.05).Conclusion:Neonatal S.pp may alter the phenotype of ASM and promote AHR development.