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T1 Matrix metalloproteinase-driven tissue destruction in Human Tuberculosis (TB) is mediated by Th-17 cytokines and the PI3K/p110a/p70S6K cascade
  1. S Singh1,
  2. U K Singh2,
  3. P T Elkington1,
  4. J S Friedland1
  1. 1Imperial College London, London, UK
  2. 2Nalanda Medical College and Hospitals, Patna, India

Abstract

Mycobacterium tuberculosis (Mtb) kills 1.7 million people annually. The Th1 paradigm does not explain TB-driven cavitation. Current treatment is lengthy with many adverse effects. The Interleukin-23/Th17 axis plays a critical role in early Mtb containment. Respiratory stromal cells are important first-line defence and secrete Matrix metalloproteinases (MMPs). Role of MMPs, which are substrate-specific proteases causing extracellular matrix degradation/remodelling, was investigated in TB. Human bronchoalveolar lavage (BAL) samples from 35 well-characterised TB and control patients were analysed for MMPs and Th17 cytokines. TB/Control lung biopsies were stained for MMPs/IL-17. Primary normal human bronchial epithelial cells (NHBEs) and MRC-5 fibroblasts were stimulated with IL-17/IL-22/IL-23, alone and in combination with conditioned medium from Mtb-infected monocytes (CoMTb). Secretion, gene expression, gene silencing, intracellular signalling were investigated by luminex, ELISA, zymography, dual-luciferase promoter-reporter, realtime RT-PCR, siRNA transfection. MMPs were up-regulated in Human TB BALs (p<0.0001). This positively correlated with cavitation score on CXRs. TIMPs (tissue inhibitor of metalloproteinase) and IL-17/IL-23 were unaltered but IL-22 was increased in TB BAL. IL-17 and MMP-3 were co-expressed in pneumocytes around granulomas in TB lung biopsies. CoMTb (but not direct infection) up-regulated secretion and gene expression of MMP-1 (collagenase, p<0.0001), MMP-3 (stromelysin, p<0.001) and MMP-9 (gelatinase, p<0.0001) from NHBEs. MMP-3 protein and promoter activity in MRC-5s was also increased (p<0.001). AKT inhibition suppressed all MMPs (p<0.01) whereas siRNA and chemical inhibition of the proximal PI3Kp110a subunit abrogated MMP-3 only (p<0.001). Distally, p70S6K (mTOR) blockade with rapamycin abrogated TB-driven MMP-1 and MMP-3 (p<0.001). MMP-9 production was unaffected by proximal/distal inhibition of PI3K.IL-17 independently and also synergistically with CoMTb augmented MMP-3 secretion/gene expression from NHBEs and MRC-5s in a dose-dependent manner (peak 8ng/ml, p<0.0001). This was p38-dependent, confirmed by p38-specific siRNA. In contrast, IL-17 down-regulated CoMTb-driven MMP-9 to baseline (p<0.01). IL-22 augmented MMP-3 from fibroblasts but not from NHBEs. IL-23 did not drive MMPs.

Summary MMPs are key mediators of tissue damage in human pulmonary TB and are regulated in a cell- and stimulus-specific manner. IL-17 and IL-22 drive MMP-3 but suppress MMP-9 in airway epithelium. The PI3Kinase/p110a/p70S6K pathway is a crucial target and its immuno-modulation (eg, rapamycin) is a potential adjunctive therapy to limit tissue destruction and shorten chemotherapy in TB.

Abstract T1 Figure 1

Pulmonary epithelial cells around a TB granuloma expressed IL-17 (A). Strong immunoreactivity for MMP-3 (B) in pulmonary epithelial cells around TB granulomas was also detected. Control lungs (not shown) were negative.

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