Dextran sulfate-amplified extracellular matrix deposition promotes osteogenic differentiation of mesenchymal stem cells.

The development of bone-like tissues in vitro that exhibit key features similar to those in vivo is needed to produce tissue models for drug screening and the study of bone physiology and disease pathogenesis. Extracellular matrix (ECM) is a predominant component of bone in vivo; however, as ECM assembly is sub-optimal in vitro, current bone tissue engineering approaches are limited by an imbalance in ECM-to-cell ratio. We amplified the deposition of osteoblastic ECM by supplementing dextran sulfate (DxS) into osteogenically induced cultures of human mesenchymal stem cells (MSCs). DxS, previously implicated to act as a macromolecular crowder, was recently demonstrated to aggregate and co-precipitate major ECM components, including collagen type I, thereby amplifying its deposition. This effect was re-confirmed for MSC cultures undergoing osteogenic induction, where DxS supplementation augmented collagen type I deposition, accompanied by extracellular osteocalcin accumulation. The resulting differentiated osteoblasts exhibited a more mature osteogenic gene expression profile, indicated by a strong upregulation of the intermediate and late osteogenic markers ALP and OCN, respectively. The associated cellular microenvironment was also enriched in bone morphogenetic protein 2 (BMP-2). Interestingly, the resulting decellularized matrices exhibited the strongest osteo-inductive effects on re-seeded MSCs, promoted cell proliferation, osteogenic marker expression and ECM calcification. Taken together, these findings suggest that DxS-mediated enhancement of osteogenic differentiation by MSCs is mediated by the amplified ECM, which is enriched in osteo-inductive factors. We have thus established a simple and reproducible approach to generate ECM-rich bone-like tissue in vitro with sequestration of osteo-inductive factors. STATEMENT OF SIGNIFICANCE: As extracellular matrix (ECM) assembly is significantly retarded in vitro, the imbalance in ECM-to-cell ratio hampers current in vitro bone tissue engineering approaches in their ability to faithfully resemble their in vivo counterpart. We addressed this limitation by leveraging a poly-electrolyte mediated co-assembly and amplified deposition of ECM during osteogenic differentiation of human mesenchymal stem cells (MSCs). The resulting pericelluar space in culture was enriched in organic and inorganic bone ECM components, as well as osteo-inductive factors, which promoted the differentiation of MSCs towards a more mature osteoblastic phenotype. These findings thus demonstrated a simple and reproducible approach to generate ECM-rich bone-like tissue in vitro with a closer recapitulation of the in vivo tissue niche.

The Crosstalk between Mesenchymal Stem Cells and Macrophages in Bone Regeneration: A Systematic Review.

Bone regeneration is a complex and well-coordinated process that involves crosstalk between immune cells and resident cells in the injury site. Transplantation of mesenchymal stem cells (MSCs) is a promising strategy to enhance bone regeneration. Growing evidence suggests that macrophages have a significant impact on osteogenesis during bone regeneration. However, the precise mechanisms by which macrophage subtypes influence bone regeneration and how MSCs communicate with macrophages have not yet been fully elucidated. In this systematic literature review, we gathered evidence regarding the crosstalk between MSCs and macrophages during bone regeneration. According to the PRISMA protocol, we extracted literature from PubMed and Embase databases by using "mesenchymal stem cells" and "macrophages" and "bone regeneration" as keywords. Thirty-three studies were selected for this review. MSCs isolated from both bone marrow and adipose tissue and both primary macrophages and macrophage cell lines were used in the selected studies. In conclusion, anti-inflammatory macrophages (M2) have significantly more potential to strengthen bone regeneration compared with naïve (M0) and classically activated macrophages (M1). Transplantation of MSCs induced M1-to-M2 transition and transformed the skeletal microenvironment to facilitate bone regeneration in bone fracture and bone defect models. This review highlights the complexity between MSCs and macrophages, providing more insight into the polarized macrophage behavior in this evolving field of osteoimmunology. The results may serve as a useful reference for definite success in MSC-based therapy based on the critical interaction with macrophages.

Ginkgolide B monotherapy reverses osteoporosis by regulating oxidative stress-mediated bone homeostasis.

Osteoporosis is characterized by reductions in bone mass, which could be attributed to the dysregulation of bone homeostasis, such as the loss of balance between bone-resorbing osteoclasts and bone-forming osteoblasts. Elevated levels of oxidative stress increase bone resorption by promoting osteoclastogenesis and inhibiting the osteogenesis. Ginkgolide B (GB), a small natural molecule from Ginkgo biloba, has been reported to possess pharmacological activities by regulating reactive oxygen species (ROS) in aging-related degenerative diseases. Herein, we assessed the therapeutic effects of GB on the bone phenotypes of mice with osteoporosis induced by (I) aging, (II) ovariectomy, and (III) glucocorticoids. In all three animal models, oral gavage of GB significantly improved bone mass consistent with the increase in the OPG-to-RANKL ratio. In the in vitro experiments, GB promoted osteogenesis in aged mesenchymal stem cells (MSCs) and repressed osteoclastogenesis in aged macrophages by reducing ROS. The serum protein profile in GB-treated aged mice revealed moderate rejuvenating effects; signaling pathways associated with ROS were also regulated. The anabolic and anti-catabolic effects of GB were illustrated by the reduction in ROS. Our results indicate that GB is effective in treating osteoporosis. The use of GB in patients with osteoporosis is worthy of further clinical investigation.