Adipose Stem Cell-Derived Exosomes Recover Impaired Matrix Metabolism of Torn Human Rotator Cuff Tendons by Maintaining Tissue Homeostasis.

BACKGROUND: Adipose stem cell-derived exosomes (ASC-Exos) are reported to effectively prevent muscle atrophy and degeneration of torn rat rotator cuff, but their influence on human samples and their potential mechanism are still unclear.

PURPOSE: We aimed to investigate the effects of ASC-Exos on the metabolic activities of torn human rotator cuff tendons and explore the potential mechanism behind it.

STUDY DESIGN: Controlled laboratory study.

METHODS: Diseased supraspinatus tendons were harvested from 15 patients with a mean ± SD age of 65.8 ± 3.2 years who underwent reverse shoulder arthroplasty for chronic rotator cuff tears associated with glenohumeral pathological changes. Each tendon was dissected into 3 × 4 × 4-mm explants: the ones derived from the same tendon were placed into 12-well plates and cultured in complete culture media (control) or in complete culture media supplemented with ASC-Exos for 72 hours. Afterward, the concentrations of cytokines secreted into the culture media-including interleukin 1β (IL-1β), IL-6, IL-8, and matrix metalloproteinase 9 (MMP-9)-were measured using enzyme-linked immunosorbent assay (ELISA). Tendons were stained with hematoxylin and eosin and immunohistochemistry (type I and III collagens) for histological analyses. Moreover, the expression of anabolic genes ( TIMP-1 and TIMP-3 ; type I and III collagen encoding) and catabolic genes ( MMP-9 and MMP-13 ) in tendons were measured using real-time quantitative polymerase chain reaction. Phosphorylated AMPKα and Wnt/β-catenin pathways were assayed by western blotting to explore the potential mechanism of action of ASC-Exos.

RESULTS: Secretion of proinflammatory cytokines, including IL-1β, IL-6, and MMP-9, was significantly reduced in the ASC-Exos group as compared with the control group. Supraspinatus tendons in the ASC-Exos group exhibited superior histological properties, as demonstrated by higher tendon maturing scores and more type I collagen content, but there was no significant difference in type III collagen content between groups. Expression of MMP-9 and MMP-13 genes was decreased in the ASC-Exos group versus the control group. Increased expression of type I and III collagens and an elevated type I/III ratio were found in the ASC-Exos group when compared with the control group. There was no significant difference in the secretion of IL-8 and expression of TIMP-1 and TIMP-3 genes between the ASC-Exos and control groups. Western blotting revealed that ASC-Exos enhanced phosphorylated AMPKα and decreased β-catenin levels to prevent tendon degeneration.

CONCLUSION: ASC-Exos maintained metabolic homeostasis of torn human rotator cuff tendons to improve their histological properties, which might be achieved by enhancing AMPK signaling to suppress Wnt/β-catenin activity.

CLINICAL RELEVANCE: ASC-Exos could be used as an effective biological tool to promote healing in torn human rotator cuff tendons.