Non-acylated Mycobacterium bovis glycoprotein MPB83 binds to TLR1/2 and stimulates production of matrix metalloproteinase 9

A variety of Mycobacterium tuberculosis cell wall components induce expression of matrix metalloproteinase 9 (MMP-9) by monocytic cells and levels of MMP-9 in vivo positively correlate with severity of disease. Toll-like receptor (TLR)2 mediates cellular responses to acylated molecules but can also mediate responsiveness to diverse molecular structures, including non-acylated native viral and bacterial proteins. MPT/B-83 is a cell-associated lipoglycoprotein common to M. tuberculosis and M. bovis and an important antigen during infection of cattle. Since MPB83 is acylated and glycosylated, we investigated whether MPB83 would induce MMP-9 expression via interaction with TLR2, and assessed the contribution of the lipid, glycan and polypeptide components to its activity. Acylated peptide derived from MPB83 stimulated MMP-9 expression by human macrophage cells via interaction with both TLR2 and TLR1, but not TLR4. Lesser induction was found with secreted (non-acylated, but glycosylated) MPB83 protein purified from culture of M. bovis. Stimulation of cells with MPB83 induced TNF-α production which acted to upregulate MMP-9 expression. Surprisingly, recombinant MPB83 protein devoid of any post-translational modification also induced MMP-9 expression. Direct interaction of RecMPB83 with TLR2 was demonstrated by surface plasmon-resonance. MPB83 may act as a virulence factor through TLR2 mediated induction of MMP-9.

Research highlights
► M. bovis antigen MPB83 induced expression of TNF-α and MMP-9 by macrophages.
► MPB83 lipopeptide was more potent than glycosylated secreted MPB83 protein.
► Unmodified recombinant MPB83 protein also induced MMP-9 expression.
► The stimulatory effect of MPB83 is mediated through a TLR2/TLR1 dependent mechanism.
► Surface Plasmon Resonance revealed a high affinity binding of TLR2 for MPB83.