Ageing attenuates bone healing by mesenchymal stem cells in a microribbon hydrogel with a murine long bone critical-size defect model

Abstract

Background Despite the high incidence of fractures and pseudoarthrosis in the aged population, a potential role for the use of mesenchymal stem cells (MSCs) in the treatment of bone defects in elderly patients has not been elucidated. Inflammation and the innate immune system, including macrophages, play crucial roles in the differentiation and activation of MSCs. We have developed lentivirus-transduced interleukin 4 (IL4) over-expressing MSCs (IL4-MSCs) to polarize macrophages to an M2 phenotype to promote bone healing in an established young murine critical size bone defect model. In the current study, we explore the potential of IL4-MSCs in aged mice. Methods A 2 mm femoral diaphyseal bone defect was created and fixed with an external fixation device in 15- to 17-month-old male and female BALB/c mice. Microribbon (µRB) scaffolds (Sc) with or without encapsulation of MSCs were implanted in the defect sites. Accordingly, the mice were divided into three treatment groups: Sc-only, Sc + MSCs, and Sc + IL4-MSCs. Mice were euthanized six weeks after the surgery; subsequently, MicroCT (µCT), histochemical and immunohistochemical analyses were performed. Results µCT analysis revealed that bone formation was markedly enhanced in the IL4-MSC group. Compared with the Sc-only, the amount of new bone increased in the Sc + MSCs and Sc + IL4-MSC groups. However, no bridging of bone was observed in all groups. H&E staining showed fibrous tissue within the defect in all groups. Alkaline phosphatase (ALP) staining was increased in the Sc + IL4-MSC group. The Sc + IL4-MSCs group showed a decrease in the number of M1 macrophages and an increase in the number of M2 macrophages, with a significant increase in the M2/M1 ratio. Discussion IL4 promotes macrophage polarization to an M2 phenotype, facilitating osteogenesis and vasculogenesis. The addition of IL4-MSCs in the µRB scaffold polarized macrophages to an M2 phenotype and increased bone formation; however, complete bone bridging was not observed in any specimens. These results suggest that IL4-MSCs are insufficient to heal a critical size bone defect in aged mice, as opposed to younger animals. Additional therapeutic strategies are needed in this challenging clinical scenario.

Differential dynamics of bone graft transplantation and mesenchymal stem cell therapy during bone defect healing in a murine critical size defect

“…We also quantified the non-leukocyte (CD45 - ) population, including chondrocytes (CD45 - , Sox9 + ), endothelial cells (CD45 - , CD31 + ), and muscle satellite cells (CD45 - , Pax7 + ). Chondrocytes were not detected in any of the samples, which is similar to our previous studies using this model [ 9 , 36 , 37 ]. Very few endothelial cells and muscle satellite cells were detected on Day 7.…”

“…Previous studies have suggested that crosstalk among different types of cells may collectively contribute to the bone healing process [ [36] , [37] , [38] , [39] ]. We therefore sought to elucidate cell compositions in tissues from bone defect sites that contained either the MSCs-embedded scaffold or the bone graft and compare them with that of the original bone graft.…”

Leukemia Inhibitory Factor Facilitates Self-Renewal and Differentiation and Attenuates Oxidative Stress of BMSCs by Activating PI3K/AKT Signaling

“…Bone defects caused by various traumas and diseases have become one of the most common clinical diseases [ 1 ]. At present, bone transplantation is the main method to solve the repair of bone defects [ 2 ].…”

Injectable and Microporous Microgel‐Fiber Granular Hydrogel Loaded with Bioglass and siRNA for Promoting Diabetic Wound Healing

“…[12,20,21,53,54] However, existing microribbons and microfibers produced using the wet spinning technique consist solely of polymers. [12,53,[55][56][57][58] There is currently no research available on microribbons or microfibers composed of a combination of polymers and insoluble inorganic biomaterials. This gap in knowledge may be attributed to the fact that traditional wet spinning techniques involve injecting a precursor solution into a cross-linking solution through a needle.…”