Effect of human adipose stem cell-derived mitochondrial transplantation on the activity of chronically injured anterior cruciate ligament cells.

AIMS: Mitochondrial transplantation has been proposed as a potential treatment for injured ligament tissue. This study aimed to investigate the relationship between the time from injury to surgery and the activity of injured anterior cruciate ligament (ACL) cells. Additionally, we evaluated the effectiveness of mitochondrial transplantation in chronically injured ACL cells and in an in vivo ACL partial tear animal model. METHODS: First, ACL injured tissue from rabbits (n = 6 for each timepoint) was harvested at two (acute), four (subacute), and eight (chronic) weeks following ACL transection. We investigated cell proliferation, migration capability, and the expression of collagen synthesis, vascular endothelial growth factor (VEGF), and transforming growth factor-β (TGF-β) genes in injured ACL cells at different injury timepoints. Second, we isolated mitochondria from human adipose-derived stem cells (hADSCs) and transplanted them into the ACL cells. Lastly, we evaluated the in vivo effects of hADSCs-mitochondrial transplantation in a rabbit knee model with partial ACL tear. RESULTS: After injury, the highest cell activity was observed at four weeks. Immunohistochemical staining showed that hADSCs-mitochondria were taken up by the eight-week injured ACL cells, leading to subsequent improvements in cell viability, migration capability, and collagen synthesis, and VEGF gene expression which were superior to those of untreated cells. At eight weeks, treated injured ACL cells achieved cell proliferation and collagen type I, type III, and VEGF expression levels comparable to those of four-week injured cells. In the in vivo study, enhanced collagen synthesis was observed in the histological analysis following hADSCs-mitochondrial transplantation. CONCLUSION: The optimal timing of ACL reconstruction is four to six weeks after injury due to peak cell activity. Mitochondrial transplantation improves the activity of chronically injured ACL cells and enhances collagen synthesis in ACL partial tears, highlighting its potential as a treatment for improving their regenerative capability.