Role and pathogenic mechanism of TcpC in uropathogenic Escherichia coli-induced mouse model of cystitis / 中华微生物学和免疫学杂志

ABSTRACT

Objective:To investigate the role of TcpC in uropathogenic Escherichia coli (UPEC)-induced cystitis in mice and to preliminarily analyze the pathogenic mechanism. Methods:C57BL/6 mice were injected with 10 9 CFU wild-type UPEC CFT073 (CFT073 wt) or tcpc gene-deleted mutant (CFT073 Δ tcpc) from urethra into bladder to construct the mouse model of cystitis. The mice were sacrificed 3 d after infection and the bladders were taken to observe the gross pathological changes. Histopathological changes in bladder tissues were observed after HE staining. Immunohistochemistry was used to detect TcpC in bladder tissues. Bacterial loads in urine samples of UPEC-infected mice were counted by tenfold dilution method, and the presence of tcpc gene in the genomic DNA of bacteria from the bladder and urine samples of CFT073 wt-infected mice was measured by PCR. Real-time quantitative RT-PCR (qRT-PCR) and Western blot were performed to detect the expression of TcpC at mRNA and protein levels in macrophages after CFT073 wt infection. The influence of UPEC strains on the activation of NF-κB signaling pathway in macrophages were determined by Western blot. The levels of proinflammatory factors and the bacterial and cell activity after infecting macrophages with UPEC strains were detected by ELISA, laser confocal microscope and fluorescence microscope, respectively. Results:Compared with the mice with CFT073 Δ tcpc infection, CFT073 wt-infected mice had significantly enlarged bladder and severe neutrophil infiltration and abundant TcpC in bladder tissues. The number of bacteria in the urine of CFT073 wt-infected mice was significantly greater than that of the CFT073 Δ tcpc group. PCR results showed that the bacteria in bladder or urine were CFT073 wt. The expression of TcpC at both mRNA and protein levels in macrophages increased significantly after CFT073 wt infection. Moreover, in CFT073 wt-infected macrophages, the expression of IκBα was promoted and the phosphorylation of p65 and the production of proinflammatory factors were suppressed. TcpC was instrumental in the survival and invasion of CFT073 wt in macrophages. Conclusions:TcpC expression increased significantly in mice with CFT073 wt-induced cystitis. TcpC inhibited the activation of NF-κB signaling pathway and the production of proinflammatory factors in macrophages to improve the survival rate of CFT073 wt, which was closely related to the pathogenesis and immune evasion of UPEC.