Comparison of the effects of matrix metalloproteinase inhibitors on TNF-α release from activated microglia and TNF-α converting enzyme activity

Matrix metalloproteinases (MMPs) are zinc-dependent endopeptidases that regulate cell-matrix composition and are also involved in processing various bioactive molecules such as cell-surface receptors, chemokines, and cytokines. Our group recently reported that MMP-3, -8, and -9 are upregulated during microglial activation and play a role as proinflammatory mediators (Lee et al., 2010, 2014). In particular, we demonstrated that MMP-8 has tumor necrosis factor alpha (TNF-α)-converting enzyme (TACE) activity by cleaving the prodomain of TNF-α and that inhibition of MMP-8 inhibits TACE activity. The present study was undertaken to compare the effect of MMP-8 inhibitor (M8I) with those of inhibitors of other MMPs, such as MMP-3 (NNGH) or MMP-9 (M9I), in their regulation of TNF-α activity. We found that the MMP inhibitors suppressed TNF-α secretion from lipopolysaccharide (LPS)- stimulated BV2 microglial cells in an order of efficacy: M8I>NNGH>M9I. In addition, MMP inhibitors suppressed the activity of recombinant TACE protein in the same efficacy order as that of TNF-α inhibition (M8I>NNGH>M9I), proving a direct correlation between TACE activity and TNF-α secretion. A subsequent pro-TNF-α cleavage assay revealed that both MMP-3 and MMP-9 cleave a prodomain of TNF-α, suggesting that MMP-3 and MMP-9 also have TACE activity. However, the number and position of cleavage sites varied between MMP-3, -8, and -9. Collectively, the concurrent inhibition of MMP and TACE by NNGH, M8I, or M9I may contribute to their strong anti-inflammatory and neuroprotective effects.