In vivo mechanism of action of matrix metalloprotease (MMP) in the autolysis of sea cucumber (Stichopus japonicus)

Matrix metalloprotease (MMP) is the key endogenous protease that boosts the autolysis of sea cucumber, while its action and mechanism in vivo are still unclear. MMP inhibitor (1,10-phenanthroline) was injected into coelomic cavity of sea cucumber (Stichopus japonicus) and its effects on autolysis and mechanism of action were investigated for the first time by using scanning electron microscopy, multi-functional in vivo imaging system, and confocal laser scanning microscopy. In response to external stimuli, the level of Ca2+ in live sea cucumber dermis increased, which may activate MMP activity. MMP inhibitor could diffuse from coelomic cavity into body wall and significantly prevented the activation of MMP by chelating Ca2+, and thus, retarded the autolysis of fresh sea cucumber by preventing degradation of interfibrillar proteoglycan bridges between adjacent collagen fibrils. This work provides information toward understanding the mechanism behind the sea cucumber autolysis and demonstrate a potential approach to prevent the autolysis. Practical applications Autolysis occurs in sea cucumber in response to external stimulation. Matrix metalloproteinase (MMP) has been found to be the key endogenous protease that boosts the autolysis of sea cucumber body wall (SCBW). However, the role of MMP in the autolysis of SCBW in vivo and the mechanisms involved remain unclear. In this study, MMP inhibitor (1,10-phenanthroline) was injected into the body cavity of live sea cucumber, and its effects on in situ changes in SCBW were studied. Our results indicated that the activity of endogenous MMP in live SCBW was activated in response to external stimulation, which may be responsible for the autolysis. After injection into coelomic cavity, MMP inhibitor could diffuse into SCBW and significantly reduced the progress of typical morphological and microstructural changes of autolytic sea cucumber. Through chelating Ca2+, the MMP inhibitor could prevent the activation of MMP, and thus reduced the autolysis of fresh sea cucumber.