Collaborative Effect\nof Matrix Metalloproteinases\non Type I Collagen Degradation and Muscle Softening in Sea Bass (Lateolabrax japonicus) during Cold Storage

Matrix metalloproteinases (MMPs)\nplay critical roles\nin the degradation\nof collagens, while their mechanism remains unclear. In the present\nstudy, the involvement of matrix metalloproteinases (MMPs) in collagen\ndegradation of sea bass muscle during cold storage was explored. Immunohistochemical\nstaining results showed significant degradation of type I collagen\nin the connective tissue of muscle endomysium during cold storage,\nthus affecting the muscle structural integrity and quality. Western\nblot analysis revealed an increment in the α1 chain and a decrease\nin the β and γ chains of type I collagen. Immunofluorescence\nstaining showed that MMP-2, MMP-9, and MMP-13 were distributed in\nthe endomysium surrounding the muscle fibers. Additionally, the catalytic\ndomains of MMP-2, MMP-9, and MMP-13 with biological activities were\nsuccessfully expressed. The degradation trend of type I collagen by\nMMPs under 4 °C was similar to that of muscle collagen during\ncold storage, suggesting that the degradation of type I collagen was\nattributed to the cooperative action of the MMPs. In conclusion, our\nstudy elucidated that the MMPs-engaged degradation of type I collagen\nis quite possibly the leading cause of sea bass muscle softening during\ncold storage.