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Bone & Joint Research
Vol. 12, Issue 10 | Pages 657 - 666
17 Oct 2023
Sung J Barratt KR Pederson SM Chenu C Reichert I Atkins GJ Anderson PH Smitham PJ

Aims

Impaired fracture repair in patients with type 2 diabetes mellitus (T2DM) is not fully understood. In this study, we aimed to characterize the local changes in gene expression (GE) associated with diabetic fracture. We used an unbiased approach to compare GE in the fracture callus of Zucker diabetic fatty (ZDF) rats relative to wild-type (WT) littermates at three weeks following femoral osteotomy.

Methods

Zucker rats, WT and homozygous for leptin receptor mutation (ZDF), were fed a moderately high-fat diet to induce T2DM only in the ZDF animals. At ten weeks of age, open femoral fractures were simulated using a unilateral osteotomy stabilized with an external fixator. At three weeks post-surgery, the fractured femur from each animal was retrieved for analysis. Callus formation and the extent of healing were assessed by radiograph and histology. Bone tissue was processed for total RNA extraction and messenger RNA (mRNA) sequencing (mRNA-Seq).


Aims. Exosomes derived from bone marrow mesenchymal stem cells (BMSCs) have been reported to be a promising cellular therapeutic approach for various human diseases. The current study aimed to investigate the mechanism of BMSC-derived exosomes carrying microRNA (miR)-136-5p in fracture healing. Methods. A mouse fracture model was initially established by surgical means. Exosomes were isolated from BMSCs from mice. The endocytosis of the mouse osteoblast MC3T3-E1 cell line was analyzed. CCK-8 and disodium phenyl phosphate microplate methods were employed to detect cell proliferation and alkaline phosphatase (ALP) activity, respectively. The binding of miR-136-5p to low-density lipoprotein receptor related protein 4 (LRP4) was analyzed by dual luciferase reporter gene assay. HE staining, tartrate-resistant acid phosphatase (TRAP) staining, and immunohistochemistry were performed to evaluate the healing of the bone tissue ends, the positive number of osteoclasts, and the positive expression of β-catenin protein, respectively. Results. miR-136-5p promoted fracture healing and osteoblast proliferation and differentiation. BMSC-derived exosomes exhibited an enriched miR-136-5p level, and were internalized by MC3T3-E1 cells. LRP4 was identified as a downstream target gene of miR-136-5p. Moreover, miR-136-5p or exosomes isolated from BMSCs (BMSC-Exos) containing miR-136-5p activated the Wnt/β-catenin pathway through the inhibition of LRP4 expression. Furthermore, BMSC-derived exosomes carrying miR-136-5p promoted osteoblast proliferation and differentiation, thereby promoting fracture healing. Conclusion. BMSC-derived exosomes carrying miR-136-5p inhibited LRP4 and activated the Wnt/β-catenin pathway, thus facilitating fracture healing. Cite this article: Bone Joint Res 2021;10(12):744–758