The Role of Matrix Metalloproteinases in the Immunopathology of Cerebral Tuberculosis

Abstract

Introduction: Central nervous system tuberculosis (CNS TB) has a high mortality. Microglial derived matrix metalloproteinases (MMPs) are implicated in the intense inflammatory response to Mycobacterium tuberculosis (M.tb) as the blood brain barrier is rich in MMP substrates. Methods: In a cellular model of CNS TB human microglial cells were stimulated with M.tb and conditioned media from M.tb infected human monocytes (CoMTb). Gene expression of all 23 MMPs and the 4 tissue inhibitors of MMP (TIMPs) was analysed by real time RT-PCR and secretion by Luminex and Western blotting. MMP gene transcription regulation was studied by luciferase promoter reporter assays and NFkB/AP-1 ELISAs. MAP kinases were studied by Western blotting. Immunohistochemistry of CNS TB biopsies and ELISA analysis of cerebrospinal fluid (CSF) was performed. Results: CoMTb up-regulated expression of MMP-1, -3 and -9, which was suppressed by dexamethasone. In contrast CoMTb did not alter TIMP-1 and reduced TIMP-2, -3 and -4 expression. M.tb up-regulated MMP-1 and -3 secretion. However, CoMTb drove MMP-1 and -3 secretion more potently than M.tb but suppressed MMP-2 secretion. Nuclear NFkB p50-p65 heterodimers and AP-1 cJun/FosB increased in CoMTb stimulated cells, with concomitant degradation of IkBα. Mutation of NFkB and AP-1 sites in the MMP-1 promoter abrogated CoMTb promoter activity. CoMTb drove early p38 and ERK MAP kinase phosphorylation. Chemical inhibition of both NFkB and p38 returned MMP-1 and 3 secretion to control levels but enhanced MMP-2 secretion that was also caspase 8 dependent. MMP/TIMP concentrations in CSF samples from TBM patients were predictive of coma severity and outcome and demonstrated that dexamethasone preferentially suppressed MMP-9. Conclusions: In CNS TB unopposed MMP-1 and -3 expression and secretion are driven by M.tb-infected monocyte networks and regulated by p38, NFkB and AP-1. CSF MMP/TIMP concentrations predict disease severity and offer a mechanism for the beneficial effect of dexamethasone therapy.