Abstract: BACKGROUND: Collagen is the most abundant extracellular matrix component, which is closely related to the structure and function of the extracellular matrix of skeletal muscle, but the effect and mechanism of recombinant human collagen (rhC) produced by bioengineering technology on the extracellular matrix of skeletal muscle are unclear.
OBJECTIVE: To investigate the effect of rhC supplementation on the remodeling of skeletal muscle extracellular matrix after eccentric exercise, thereby revealing the possible mechanism by which rhC improves the injury of skeletal muscle extracellular matrix and promote the recovery after exercise.
METHODS: A total of 104 healthy male C57 mice aged 8 weeks old were randomly divided into control group (normal saline), low-dose rhC group (0.2 g/kg), medium-dose rhC group (1.0 g/kg), and high-dose rhC group (2.0 g/kg). Two mice in each group were selected after continuous 7 days of intragastric intervention, and organs were dissected for hematoxylin-eosin staining to determine inflammatory infiltrates. On the 8th day, the remaining mice were subjected to eccentric exercise. The structural changes of the skeletal muscle extracellular matrix were observed under scanning electron microscopy immediately (0), 24, 48, and 96 hours  after eccentric exercise. Meanwhile, grip strength, creatine kinase activity, and protein levels of matrix metalloproteinases 2, 9, 14 and tissue inhibitor of metalloproteinase-2 in skeletal muscle were detected by western blot assay.
RESULTS AND CONCLUSION: Hematoxylin-eosin staining results indicated that short-term rhC supplementation showed no significant effects on the morphology of the heart, liver, spleen and kidney. After one-time eccentric exercise, the recovery rate of grip strength in the medium- and high-dose rhC groups was significantly increased (P < 0.01). The trend of creatine kinase changes was consistent in all groups and there was no significant difference between groups. The recovery process of the extracellular matrix in the low-dose rhC group was faster than that in the control group, and the muscle tract membrane in the medium- and high-dose rhC groups was more complete. The protein level of matrix metalloproteinase 9 in the high-dose rhC group was significantly decreased (P < 0.05). The protein levels of matrix metalloproteinase 14 in the medium- and high-dose rhC groups were significantly decreased (P < 0.05). The protein levels of matrix metalloproteinase 2 in the medium- and high-dose rhC groups were significantly decreased (P < 0.05). Tissue inhibitor of metalloproteinase-2 protein levels in the medium- and high-dose rhC groups were significantly increased (P < 0.05). The ratio of matrix metalloproteinase 2 to tissue inhibitor of metalloproteinase-2 in each rhC group was significantly decreased (P < 0.05). To conclude, pre-supplementation of 1.0 and 2.0 g/kg rhC for 7 days can inhibit extracellular matrix degradation in skeletal muscle after exercise by modulating matrix metalloproteinases and matrix metalloproteinase inhibitors, thereby promoting recovery of skeletal muscle strength in mice.

Key words: recombinant human collagen, eccentric exercise, skeletal muscle extracellular matrix, matrix metalloproteinase, tissue inhibitor of metalloproteinases