This review explores the regenerative potential of key progenitor cell types and therapeutic strategies to improve healing of complex fractures and bone defects. We define, summarize, and discuss the differentiation potential of totipotent, pluripotent, and multipotent stem cells, emphasizing the advantages and shortcomings of cell therapy for bone repair and regeneration. The fundamental role of mesenchymal stem cells (MSCs) is highlighted due to their multipotency to differentiate into the key lineage cells including osteoblasts, osteocytes, and chondrocytes, which are crucial for bone formation and remodeling. Hematopoietic stem cells (HSCs) also play a significant role; immune cells such as macrophages and T cells modulate inflammation and tissue repair. Osteoclasts are multi-nucleated cells that are important to bone remodeling. Vascular progenitor cells are critical to oxygen and nutrient supply. The dynamic interplay among these lineages and their microenvironment is essential for effective bone restoration. Therapies involving cells that are more than "minimally manipulated" are controversial and include embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). ESCs, derived from early-stage embryos, possess pluripotent capabilities and have shown promise in preclinical studies for bone healing. iPSCs, reprogrammed from somatic cells, offer personalized medicine applications and can differentiate into various tissue-specific cell lines. Minimally manipulative cell therapy approaches such as the use of concentrated bone marrow aspirate (BMAC), exosomes, and various biomaterials for local delivery are explored for their effectiveness in bone regeneration. BMAC, which contains mostly immune cells but few mesenchymal and vascular progenitors, probably improves bone healing by facilitating paracrine mediated intercellular communication. Exosome isolation harnesses the biological signals and cellular byproducts that are a primary source for cell crosstalk and activation. Safe, efficacious, and cost-effective strategies to enhance bone healing using novel cellular therapies are part of a changing paradigm to modulate the inflammatory, repair and regenerative pathways to achieve earlier more robust tissue healing and improved physical function.

Joint replacement is a common surgery and is predominantly utilized for treatment of osteoarthritis in the aging population. The longevity of many of these implants depends on bony ingrowth. Here, we provide an overview of current techniques in osteogenesis (inducing bone growth onto an implant), which is affected by aging and inflammation. In this review we cover the biologic underpinnings of these processes as well as the clinical applications. Overall, aging has a significant effect at the cellular and macroscopic level that impacts osteosynthesis at bone-metal interfaces after joint arthroplasty; potential solutions include targeting prolonged inflammation, preventing microbial adhesion, and enhancing osteoinductive and osteoconductive properties.

Mesenchymal stem cells (MSCs) play an important role in regenerative medicine and drug discovery due to their multipotential differentiation capabilities and immunomodulatory effects. Compared with traditional 2D cultures of MSCs, 3D cultures of MSCs have emerged as an effective approach to enhance cell viability, proliferation, and functionality, and provide a more relevant physiological environment. Here, we review the therapeutic potential of 3D-cultured MSCs, highlighting their roles in tissue regeneration and repair and drug screening. We further summarize successful cases that apply 3D MSCs in modeling disease states, enabling the identification of novel therapeutic strategies. Despite these promising applications, we discuss challenges that remain in the clinical translation of 3D MSC technologies, including stability, cell heterogeneity, and regulatory issues. We conclude by addressing these obstacles and emphasizing the need for further research to fully exploit the potential of 3D MSCs in clinical practice.

Background: Corticosteroids provide well-established therapeutic benefits; however, they are also accompanied by adverse effects on bone. Metformin is a widely used medication for managing type 2 diabetes mellitus. Recent studies have highlighted additional therapeutic benefits of metformin, particularly concerning bone health and oxidative stress. Objective: This research investigates the effects of prednisolone on cellular metabolic functions and bone formation using a 3D in vitro model. Then, we demonstrate the potential therapeutic effects of metformin on oxidative stress and the formation of calcified matrix due to corticosteroids. Methods: Human mesenchymal stem cells (MSCs) and macrophages were cultured in a 3D GelMA scaffold and stimulated with prednisolone, with and without metformin. The adverse effects of prednisolone and metformin’s therapeutic effect(s) were assessed by analyzing cell viability, osteogenesis markers, bone mineralization, and inflammatory markers. Oxidative stress was measured by evaluating reactive oxygen species (ROS) levels and ATP production. Results: Prednisolone exhibited cytotoxic effects, reducing the viability of MSCs and macrophages. Lower osteogenesis potential was also detected in the MSC group. Metformin positively affected cell functions, including enhanced osteoblast activity and increased bone mineralization. Furthermore, metformin effectively reduced oxidative stress, as evidenced by decreased ROS levels and increased ATP production. These findings indicate that metformin protects against oxidative damage, thus supporting osteogenesis. Conclusion: Metformin exhibits promising therapeutic potential beyond its role in diabetes management. The capacity to alleviate oxidative stress highlights the potential of metformin in supporting bone formation in inflammatory environments.

Max L. Lee was not included as an author in the original publication

“Inflammaging” is the presence of continuous systemic low-level chronic inflammation with increasing age, and impairs bone healing. C-C motif chemokine ligand 2 (CCL2) promotes the migration of macrophages during acute inflammation, and subsequent macrophage–mesenchymal stromal cell (MSC) crosstalk. We hypothesized that CCL2 would enhance bone regeneration in both young and aged primary murine cells and investigated the effects of CCL2 on osteogenesis and osteoclastogenesis. In the following experiments, 10–12-week-old and 15–17-month-old female mice were used. For the osteogenic differentiation, MSCs and naïve uncommitted macrophages (M0) were isolated and co-cultured to investigate the effect of CCL2 on the cell–cell interaction, alkaline phosphatase (ALP), and Alizarin-Red staining. For the osteoclastogenic differentiation, primary bone marrow cells were isolated and cultured, then TRAP and Cathepsin K staining and quantitative real-time RT-PCR were performed. In the CCL2-treated group, cells were cultured with recombinant CCL2 for an initial 24 h. MSCs from young mice showed greater osteogenic ability than aged mice. The CCL2-treated group showed a greater Alizarin-Red-positive area both in young and aged cells. In the osteoclastogenic differentiation assays, the number of tartrate-resistant acid phosphatase (TRAP)-positive cells and the expression level of C-fos and Dc-stamp were increased in the CCL2-treated group both in young and aged cells. These findings indicate that CCL2 promotes osteogenesis, particularly mineralization, and enhances selected osteoclastogenic features in both young and aged primary murine cells. These effects suggest that CCL2 may have a potential role in bone remodeling, including in the context of aging.