Dermal Fibroblast-Derived Exosomes Promotes Bone-to-Tendon Interface Healing of Chronic Rotator Cuff Tear in Rabbit Model.

Abstract

Purpose: To investigate the efficacy of exosomes derived from dermal fibroblasts (DF-Ex) on bone-to-tendon interface (BTI) healing in a chronic rotator cuff tear (RCT) model of rabbit.

Methods: After extraction of DF-Ex, the characterization of DF-Ex was identified in the in vitro study. In the in vivo experiment, forty-eight rabbits were randomly allocated into three groups. To create chronic RCT models, transected tendons were left untreated for 6 weeks, and then were repaired in a transosseous manner. Different materials were injected into repair site according to the allocated group (group A: saline, group B: fibrin glue only, group C: DF-Ex with fibrin glue; n = 16 for each). Genetic and immunofluorescence analyses were conducted at 4 weeks post-surgery. Furthermore, genetic, histologic, and biomechanical analyses were conducted at 12 weeks post-surgery.

Results: In vitro analyses revealed the exosomal marker proteins, CD9, CD63, and ALIX were positively expressed in DF-Ex, while negative control Calnexin was nearly absent. In vivo analyses showed that group C had the highest mRNA expression levels of COL1A1, COL3A1, and ACAN among all groups (P < 0.001, P = 0.007, and P = 0.002, respectively) at 4 weeks post-surgery. Meanwhile, there were more preliminary fibrocartilaginous matrix (aggrecan+/collagen II+) formation in group C. At 12 weeks post-surgery, group C demonstrated better collagen fiber continuity and orientation, denser collagen fibers, more mature bone-to-tendon junction, and greater fibrocartilage layer formation compared to the other groups (all P < 0.05). Moreover, group C also demonstrated higher load-to-failure value (53.3 ± 6.1 N/kg, P < 0.001).

Conclusion: Topical DF-Ex administration effectively promoted BTI healing by upregulating the COL1A1, COL3A1, and ACAN mRNA expression levels at an early stage and enhancing the structural and biomechanical properties at 12 weeks after surgical repair of a chronic RCT model of rabbit.

Clinical relevance: The study could be a transitional study to investigate the efficacy of DF-Ex on BTI healing for surgical repair of chronic RCTs as a powerful biological agent in humans.