Mycobacterium tuberculosis Lipoprotein MPT83 Induces Apoptosis of Infected Macrophages by Activating the TLR2/p38/COX-2 Signaling Pathway

Tuberculosis caused by Mycobacterium tuberculosis continues to pose a serious global health threat. The attenuated Mycobacterium bovis bacillus Calmette-Guérin, as the only licensed vaccine, has limited protective efficacy against TB. The development of more effective antituberculosis vaccines is urgent and demands for further identification and understanding of M. tuberculosis Ags. MPT83 (Rv2873), a secreted mycobacterial lipoprotein, has been applied into subunit vaccine development and shown protective effects against M. tuberculosis infection in animals; however, the understanding of the underlying mechanism is limited. In present study, we systematically studied the effect of MPT83 on macrophage apoptosis by constructing Mycobacterium smegmatis strain overexpressing MPT83 (MS_MPT83) and purifying rMPT83 protein. We found that MPT83 induced apoptosis in both human and mouse macrophages. MPT83 induced cyclooxygenase-2 (COX-2) expression at both the transcriptional and protein levels in macrophages, whereas silencing or inhibiting COX-2 blocked rMPT83-induced apoptosis or the enhanced apoptotic response to MS_MPT83 in comparison with M. smegmatis transfected with pMV261 vector (MS_Vec), indicating that COX-2 is required for MPT83-induced apoptosis. Additionally, tlr2 deficiency led to significant reduction of COX-2 expression, accompanied by less apoptosis in macrophages stimulated with rMPT83 or infected with MS_MPT83. Moreover, the activation of p38 accounted for MPT83-induced COX-2 expression. Finally, lower bacteria burdens in the lungs and spleens and enhanced survival were observed in mice i.v. infected with MS_MPT83 compared with MS_Vec. Taken together, our results established a proapoptotic effect of MPT83 and identified the TLR2/p38/COX-2 axis in MPT83-induced macrophage apoptosis.

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