The regulation of proteases and mechanical loading during fibroblast populated collagen lattice contraction

Dermal wound healing is a complex multi-stage process involving many cell types, several cell-matrix interactions, and is influenced by internal and external environmental factors. Of these, mechanical stimulation of the wound region has been shown to be highly significant influencing tissue formation and remodelling. The hypothesis here has been "Protease production is closely associated with external mechanical stimulation of fibroblast populated collagen lattices". This was investigated using three in vitro lattice models of mechanical loading (1) non-load, (2) endogenous static load, and (3) exogenous loading (cyclical and continuous loads). Exogenous loading regimes were applied across the lattice using a computer controlled drive unit incorporated into a culture system known as tension-Culture Force Monitor. Proteases released into the media were analysed by zymography and Western blotting. Whole lattices were examined by immunohistochemistry. A wide range of Matrix metalloproteases (MMPs) and Serine proteases were detected in media from human dermal and pathological (scar and keloid) fibroblast cultures following mechanical loading. Different profiles were present for each of the enzymes monitored. Substantial increases of MMP-1 (collagenase) and MMP-9 (gelatinase B), and tissue-type plasminogen activator (tPA) were demonstrated following exogenous loading, whilst, MMP-2 (gelatinase A) was mostly unaffected. MMP-3 (stromelysin) and urokinase-type plasminogen activator (uPA) were mainly reduced following loading regimes. In conclusion, fibroblasts within collagen matrices produced different protease responses following mechanical loading, indicating that each protease had a differential role relevant to cell-matrix interactions-attachment, locomotion, and contraction. Clinically, scar contraction following injury or surgery could be reduced by protease production influencing matrix remodelling