A distinct "repair" role of regulatory T cells in fracture healing.

Regulatory T cells (Tregs) suppress immune responses and inflammation. Here, we described the distinct nonimmunological role of Tregs in fracture healing. The recruitment from the circulation pool, peripheral induction, and local expansion rapidly enriched Tregs in the injured bone. The Tregs in the injured bone displayed superiority in direct osteogenesis over Tregs from lymphoid organs. Punctual depletion of Tregs compromised the fracture healing process, which leads to increased bone nonunion. In addition, bone callus Tregs showed unique T-cell receptor repertoires. Amphiregulin was the most overexpressed protein in bone callus Tregs, and it can directly facilitate the proliferation and differentiation of osteogenic precursor cells by activation of phosphatidylinositol 3-kinase/protein kinase B signaling pathways. The results of loss- and gain-function studies further evidenced that amphiregulin can reverse the compromised healing caused by Treg dysfunction. Tregs also enriched in patient bone callus and amphiregulin can promote the osteogenesis of human pre-osteoblastic cells. Our findings indicate the distinct and nonredundant role of Tregs in fracture healing, which will provide a new therapeutic target and strategy in the clinical treatment of fractures.

Neddylation suppression by a macrophage membrane-coated nanoparticle promotes dual immunomodulatory repair of diabetic wounds.

Oxidative stress, infection, and vasculopathy caused by hyperglycemia are the main barriers for the rapid repair of foot ulcers in patients with diabetes mellitus (DM). In recent times, the discovery of neddylation, a new type of post-translational modification, has been found to regulate various crucial biological processes including cell metabolism and the cell cycle. Nevertheless, its capacity to control the healing of wounds in diabetic patients remains unknown. This study shows that MLN49224, a compound that inhibits neddylation at low concentrations, enhances the healing of diabetic wounds by inhibiting the polarization of M1 macrophages and reducing the secretion of inflammatory factors. Moreover, it concurrently stimulates the growth, movement, and formation of blood vessel endothelial cells, leading to expedited healing of wounds in individuals with diabetes. The drug is loaded into biomimetic macrophage-membrane-coated PLGA nanoparticles (M-NPs/MLN4924). The membrane of macrophages shields nanoparticles from being eliminated in the reticuloendothelial system and counteracts the proinflammatory cytokines to alleviate inflammation in the surrounding area. The extended discharge of MLN4924 from M-NPs/MLN4924 stimulates the growth of endothelial cells and the formation of tubes, along with the polarization of macrophages towards the anti-inflammatory M2 phenotype. By loading M-NPs/MLN4924 into a hydrogel, the final formulation is able to meaningfully repair a diabetic wound, suggesting that M-NPs/MLN4924 is a promising engineered nanoplatform for tissue engineering.

Circulating MiRNA-21-enriched extracellular vesicles promote bone remodeling in traumatic brain injury patients.

Fracture combined with traumatic brain injury (TBI) is one of the most common and serious types of compound trauma in the clinic and is characterized by dysfunction of cellular communication in injured organs. Our prior studies found that TBI was capable of enhancing fracture healing in a paracrine manner. Exosomes (Exos), as small extracellular vesicles, are important paracrine vehicles for noncell therapy. However, whether circulating Exos derived from TBI patients (TBI-Exos) regulate the prohealing effects of fractures remains unclear. Thus, the present study aimed to explore the biological effects of TBI-Exos on fracture healing and reveal the potential molecular mechanism. TBI-Exos were isolated by ultracentrifugation, and the enriched miR-21-5 p was identified by qRT‒PCR analysis. The beneficial effects of TBI-Exos on osteoblastic differentiation and bone remodeling were determined by a series of in vitro assays. Bioinformatics analyses were conducted to identify the potential downstream mechanisms of the regulatory effect of TBI-Exos on osteoblasts. Furthermore, the role of the potential signaling pathway of TBI-Exos in mediating the osteoblastic activity of osteoblasts was assessed. Subsequently, a murine fracture model was established, and the effect of TBI-Exos on bone modeling was demonstrated in vivo. TBI-Exos can be internalized by osteoblasts, and in vitro, suppression of SMAD7 promoted osteogenic differentiation, whereas knockdown of miR-21-5 p in TBI-Exos strongly inhibited this bone-beneficial effect. Similarly, our results confirmed that preinjection of TBI-Exos led to enhanced bone formation, whereas knockdown of exosomal miR-21-5 p substantially impaired this bone-beneficial effect in vivo.

E3 Ubiquitin Ligases: Potential Therapeutic Targets for Skeletal Pathology and Degeneration.

The ubiquitination-proteasome system (UPS) is crucial in regulating a variety of cellular processes including proliferation, differentiation, and survival. Ubiquitin protein ligase E3 is the most critical molecule in the UPS system. Dysregulation of the UPS system is associated with many conditions. Over the past few decades, there have been an increasing number of studies focusing on the UPS system and how it affects bone metabolism. Multiple E3 ubiquitin ligases have been found to mediate osteogenesis or osteolysis through a variety of pathways. In this review, we describe the mechanisms of UPS, especially E3 ubiquitin ligases on bone metabolism. To date, many E3 ubiquitin ligases have been found to regulate osteogenesis or osteoclast differentiation. We review the classification of these E3 enzymes and the mechanisms that influence upstream and downstream molecules and transduction pathways. Finally, this paper reviews the discovery of the relevant UPS inhibitors, drug molecules, and noncoding RNAs so far and prospects the future research and treatment.