Matrix Metalloproteinases in Pulmonary and Central Nervous System Tuberculosis-A Review

Tuberculosis (TB) remains the single biggest infectious cause of death globally, claiming almost two million lives and causing disease in over 10 million individuals annually. Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes with various physiological roles implicated as key factors contributing to the spread of TB. They are involved in the breakdown of lung extracellular matrix and the consequent release of Mycobacterium tuberculosis bacilli into the airways. Evidence demonstrates that MMPs also play a role in central nervous system (CNS) tuberculosis, as they contribute to the breakdown of the blood brain barrier and are associated with poor outcome in adults with tuberculous meningitis (TBM). However, in pediatric TBM, data indicate that MMPs may play a role in both pathology and recovery of the developing brain. MMPs also have a significant role in HIV-TB-associated immune reconstitution inflammatory syndrome in the lungs and the brain, and their modulation offers potential novel therapeutic avenues. This is a review of recent research on MMPs in pulmonary and CNS TB in adults and children and in the context of co-infection with HIV. We summarize different methods of MMP investigation and discuss the translational implications of MMP inhibition to reduce immunopathology.

l-Glutamate in Middlebrook 7H9 culture medium upregulates matrix metalloproteinase-2 secretion from human astrocytoma cells

Matrix metalloproteinases (MMPs) are implicated in the pathology of CNS tuberculosis. Whilst investigating the secretion of MMP-2 from human U373-MG astrocytoma cells, we observed elevated MMP-2 secretion in response to Middlebrook 7H9 media but not to Mycobacterium tuberculosis itself. Middlebrook 7H9 media did not stimulate MMP-1 or MMP-9 secretion from astrocytoma cells. The excitatory neurotransmitter l-glutamate, at concentrations found in Middlebrook 7H9 media, induced significant astrocytoma MMP-2 secretion (p<0.05). l-Glutamate-induced MMP-2 activity may contribute to neuropathology in various CNS diseases and may generate misleading data in pathogen studies where Middlebrook 7H9 is the culture medium.

Astrocyte-leucocyte interactions and the mechanisms regulating matrix degradation in CNS tuberculosis

The CNS (central nervous system) has a unique pattern of immune response to infection. TB (tuberculosis) of the CNS is devastating with widespread tissue destruction. In TB, astrocyte-leucocyte interactions are key in regulating MMP (matrix metalloproteinase) activity and are regulated by complex signalling pathways. A synergistic interaction between interferon gamma and monocyte-derived mediators drives high-level astrocyte MMP-9 secretion; this and other networking effects are inhibited by steroids. Better understanding of regulatory mechanisms may identify potential switch points that could be future therapeutic targets.

Monocyte-Astrocyte Networks Regulate Matrix Metalloproteinase Gene Expression and Secretion in Central Nervous System Tuberculosis In Vitro and In Vivo

CNS tuberculosis (CNS-TB) is the most deadly form of tuberculous disease accounting for 10% of clinical cases. CNS-TB is characterized by extensive tissue destruction, in which matrix metalloproteinases (MMPs) may play a critical role. We investigated the hypothesis that Mycobacterium tuberculosis activates monocyte-astrocyte networks increasing the activity of key MMPs. We examined the expression of all human MMPs and the tissue inhibitors of metalloproteinases (TIMPs) in human astrocytes stimulated by conditioned medium from M. tuberculosis-infected monocytes (CoMTB). Real-time RT-PCR showed that gene expression of MMP-1, -2, -3, -7, and -9 was increased (p < 0.05). MMP-9 secretion was significantly up-regulated at 24 h and increased over 120 h (p < 0.01). MMP-1, -3, and -7 secretion was not detected. Secretion of MMP-2 was constitutive and unaffected by CoMTB. Astrocyte gene expression and secretion of TIMP-1 was not affected by CoMTB although TIMP-2 secretion increased 3-fold at 120 h. Immunohistochemical analysis of human brain biopsies confirmed that astrocyte MMP-9 secretion is a predominant feature in CNS-TB in vivo. Dexamethasone inhibited astrocyte MMP-9, but not TIMP-1/2 secretion in response to CoMTB. CoMTB stimulated the nuclear translocation of NF-kappaB, inducing a 6-fold increase in nuclear p65 and a 2-fold increase in nuclear p50. This was associated with degradation of IkappaBalpha and beta within 30 min, persisting for 24 h. In summary, networks active between monocytes and astrocytes regulate MMP-9 activity in tuberculosis and astrocytes are a major source of MMP-9 in CNS-TB. Astrocytes may contribute to a matrix degrading environment within the CNS and subsequent morbidity and mortality.