gms | German Medical Science

Introduction: The pro-inflammatory cytokine tumour necrosis factor-α (TNF-α) is involved in a variety of inflammatory processes in different organs. Increased TNF-α levels are accused for failure of acute wound healing in skin and intestine and of chronic skin ulcers. The mechanisms are unknown although it is well-documented that TNF-α induces different matrix metalloproteinases (MMPs). We hypothesized that TNF-α contributes to tissue destruction through increased MMP activity.

Materials and methods: The effect of exogenous TNF-α on collagen degradation was evaluated using an ex vivo human skin culture model. Skin explants (8 mm) from six healthy female donors were cultured in serum-free media without or with TNF-α (10 ng/ml), the broad-spectrum MMP inhibitor GM6001, a selective p38 mitogen-activated protein kinase (MAPK) inhibitor or cycloheximide, an inhibitor of protein synthesis. Fragmented collagen molecules in the tissue were measured by hydroxyproline released into the media. Degradation and synthesis of type I collagen specifically were measured in the conditioned medium by the markers carboxyterminal telopeptide of type I collagen and type I C-terminal collagen propeptide.

Results: We could clearly demonstrate that collagen degradation: a) is time-dependent; b) is accelerated by TNF-α (p<0.01); c) is accomplished by MMPs; d) requires de novo protein synthesis; and e) is mediated by the TNF-α-activated p38 MAPK pathway. TNF-α specifically increased cleavage of type I collagen but had no significant effect on type I collagen synthesis.

Conclusion: In conclusion, TNF-α induces excessive MMP activity via the p38 MAPK pathway that leads to a collagen net loss in human skin. This may explain some of the detrimental effect of elevated TNF-α in non-healing acute and chronic skin wounds.