The therapeutic potential of mesenchymal stem cells in treating osteoporosis

Endogenous Tissue Engineering for Chondral and Osteochondral Regeneration: Strategies and Mechanisms

Increasing attention has been paid to the development of effective strategies for articular cartilage (AC) and osteochondral (OC) regeneration due to their limited self-reparative capacities and the shortage of timely and appropriate clinical treatments. Traditional cell-dependent tissue engineering faces various challenges such as restricted cell sources, phenotypic alterations, and immune rejection. In contrast, endogenous tissue engineering represents a promising alternative, leveraging acellular biomaterials to guide endogenous cells to the injury site and stimulate their intrinsic regenerative potential. This review provides a comprehensive overview of recent advancements in endogenous tissue engineering strategies for AC and OC regeneration, with a focus on the tissue engineering triad comprising endogenous stem/progenitor cells (ESPCs), scaffolds, and biomolecules. Multiple types of ESPCs present within the AC and OC microenvironment, including bone marrow-derived mesenchymal stem cells (BMSCs), adipose-derived mesenchymal stem cells (AD-MSCs), synovial membrane-derived mesenchymal stem cells (SM-MSCs), and AC-derived stem/progenitor cells (CSPCs), exhibit the ability to migrate toward injury sites and demonstrate pro-regenerative properties. The fabrication and characteristics of scaffolds in various formats including hydrogels, porous sponges, electrospun fibers, particles, films, multilayer scaffolds, bioceramics, and bioglass, highlighting their suitability for AC and OC repair, are systemically summarized. Furthermore, the review emphasizes the pivotal role of biomolecules in facilitating ESPCs migration, adhesion, chondrogenesis, osteogenesis, as well as regulating inflammation, aging, and hypertrophy-critical processes for endogenous AC and OC regeneration. Insights into the applications of endogenous tissue engineering strategies for in vivo AC and OC regeneration are provided along with a discussion on future perspectives to enhance regenerative outcomes.

PMAIP1 regulates autophagy in osteoblasts via the AMPK/mTOR pathway in osteoporosis

Osteoporosis (OP) is a highly prevalent disorder characterized by low bone mass that severely reduces patient quality of life. Although numerous treatments for OP have been introduced in clinic, many have side effects and high costs. Therefore, there is still an unmet need for optimal solutions. Here, raw signal analysis was used to identify potential high-risk factors for OP, and the biological functions and possible mechanisms of action (MOAs) of these factors were explored via gene set enrichment analysis (GSEA). Subsequently, molecular biological experiments were performed to verify and analyze the discovered risk factors in vitro and in vivo. PMAIP1 was identified as a potential risk factor for OP and significantly suppressed autophagy in osteoblasts via the AMPK/mTOR pathway, thereby inhibiting the proliferation and differentiation of osteoblasts. Furthermore, we constructed an ovariectomy (OVX) model of OP in rats and simultaneously applied si-PMAIP1 for in vivo interference. si-PMAIP1 upregulated the expression of LC3B and p-AMPK and downregulated the expression of p-mTOR, and these effects were reversed by the autophagy inhibitor. Micro-CT revealed that, si-PMAIP1 significantly inhibited the development of osteoporosis in OVX model rats, and this therapeutic effect was attenuated by treatment with an autophagy inhibitor. This study explored the role and mechanism of PMAIP1 in OP and demonstrated that PMAIP1 may serve as a novel target for OP treatment.

Comprehensive analysis of circRNA expression profiles in postmenopausal women differing in bone mineral density

Postmenopausal osteoporosis (PMOP) seriously endangers the bone health of older women. Although there are currently indicators to diagnose PMOP, early diagnostic biomarkers are lacking. Circular ribonucleic acid (circRNA) has a stable structure, regulates gene expression, participates in the pathological process of disease, and has the potential to become a biomarker. The purpose of this study was to investigate circRNAs that could be used to predict patients with early PMOP. Ribonucleic acid (RNA) sequencing was performed on peripheral blood leukocytes from 15 female patients to identify differential circRNAs between different groups. Using bioinformatics analysis, enrichment analysis was performed to discover relevant functions and pathways. CircRNA-micro ribonucleic acid (miRNA) interaction analysis and messenger ribonucleic acid (mRNA) prediction and network construction help us to understand the relationship between circRNA, miRNA, and mRNA. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to validate the gene expression of candidate circRNAs. We screened out 2 co-expressed differential circRNAs, namely hsa_circ_0060849 and hsa_circ_0001394. By analyzing the regulatory network, a total of 54 miRNAs and 57 osteoporosis-related mRNAs were identified, which, as potential downstream target genes of hsa_circ_0060849 and hsa_circ_0001394, may play a key role in the occurrence and development of PMOP. The occurrence and development of PMOP is regulated by circRNAs, and hsa_circ_0060849 and hsa_circ_0001394 can be used as new diagnostic markers and therapeutic targets for early PMOP.

Comparison of the therapeutic effects of mesenchymal stem cells derived from human dental pulp (DP), adipose tissue (AD), placental amniotic membrane (PM), and umbilical cord (UC) on postmenopausal osteoporosis

Background: Osteoporosis is a systemic bone disease characterized by bone loss and microstructural degeneration. Recent preclinical and clinical trials have further demonstrated that the transplantation of mesenchymal stem cells (MSCs) derived from human adipose tissue (AD), dental pulp (DP), placental amniotic membrane (AM), and umbilical cord (UC) tissues can serve as an effective form of cell therapy for osteoporosis. However, MSC-mediated osteoimmunology and the ability of these cells to regulate osteoclast-osteoblast differentiation varies markedly among different types of MSCs. Methods: In this study, we investigated whether transplanted allogeneic MSCs derived from AD, DP, AM, and UC tissues were able to prevent osteoporosis in an ovariectomy (OVX)-induced mouse model of osteoporosis. The homing and immunomodulatory ability of these cells as well as their effects on osteoblastogenesis and the maintenance of bone formation were compared for four types of MSCs to determine the ideal source of MSCs for the cell therapy-based treatment of OVX-induced osteoporosis. The bone formation and bone resorption ability of these four types of MSCs were analyzed using micro-computed tomography analyses and histological staining. In addition, cytokine array-based analyses of serological markers and bioluminescence imaging assays were employed to evaluate cell survival and homing efficiency. Immune regulation was determined by flow cytometer assay to reflect the mechanisms of osteoporosis treatment. Conclusion: These analyses demonstrated that MSCs isolated from different tissues have the capacity to treat osteoporosis when transplanted in vivo. Importantly, DP-MSCs infusion was able to maintain trabecular bone mass more efficiently with corresponding improvements in trabecular bone volume, mineral density, number, and separation. Among the tested MSC types, DP-MSCs were also found to exhibit greater immunoregulatory capabilities, regulating the Th17/Treg and M1/M2 ratios. These data thus suggest that DP-MSCs may represent an effective tool for the treatment of osteoporosis.

Chitosan derived chito-oligosaccharides promote osteoblast differentiation and offer anti-osteoporotic potential: Molecular and morphological evidence from a zebrafish model

This study delves into the potential of chito-oligosaccharides (COS) to promote osteoblast differentiation and prevent osteoporosis, utilizing experiments with mouse MSCs and the zebrafish model. The preliminary biocompatibility study affirms the non-toxic nature of COS across various concentrations. In the osteoblast differentiation study, COS enhances ALP activity and calcium deposition at the cellular level. Moreover, COS induces the upregulation of molecular markers, including Runx2, Type I collagen, ALP, osteocalcin, and osteonectin in mouse MSCs. Zebrafish studies further demonstrate COS's anti-osteoporotic effects, showcasing its ability to expedite fin fracture repair, vertebral mineralization, and bone mineralization in dexamethasone-induced osteoporosis models. The scale regenerative study reveals that COS mitigates the detrimental effects of dexamethasone induced osteoclastic activity, reducing TRAP and hydroxyproline levels while elevating the expression of Runx2a MASNA isoform, collagen2α, OC, and ON mRNAs. Additionally, COS enhances calcium and phosphorus levels in regenerated scales, impacting the bone-healthy calcium-to‑phosphorus ratio. The study also suggests that COS modulates the MMP3-Osteopontin-MAPK signaling pathway. Overall, this comprehensive investigation underscores the potential of COS to prevent and treat osteoporosis. Its multifaceted cellular and molecular effects, combined with in vivo bone regeneration and repair, propose that COS may be effective in addressing osteoporosis and related bone disorders. Nonetheless, further research is imperative to unravel underlying mechanisms and optimize clinical applications.

Network pharmacology identifies fisetin as a treatment for osteoporosis that activates the Wnt/β-catenin signaling pathway in BMSCs

BACKGROUND

Although fisetin may exist widely in many natural herbs, its anti-OP mechanism is still unclear. The aim of this study is to explore the molecular anti-osteoporosis (OP) mechanism of fisetin based on network pharmacology and cell experiments.

METHODS

The target of fisetin was extracted by the Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform (TCMSP). The targets of OP were obtained by DisGeNET, GeneCards and the Comparative Toxicogenomics Database, and the targets of fisetin in OP were screened by cross-analysis. The protein-protein interaction (PPI) network was constructed by STRING, and the core targets were obtained. We performed gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses on common targets via the Database for Annotation, Visualization and Integrated Discovery. Finally, an in vitro cell experiment was used to verify the anti-OP effect and mechanism of fisetin.

RESULTS

There are 44 targets of fisetin related to the treatment of OP. The PPI results suggest that CTNNB1, CCND1, TP53, JUN, and AKT1 are the core targets. A total of 259 biological process, 57 molecular function and 26 cell component terms were obtained from GO enrichment analysis. The results of KEGG pathway enrichment analysis suggested that fisetin treatment of OP may be related to the Wnt signaling pathway, estrogen signaling pathway, PI3K-Akt signaling pathway and other signaling pathways. In vitro cell experiments showed that fisetin significantly increased the expression levels of ALP, collagen I, osteopontin and RUNX2 in bone marrow mesenchymal stem cells (BMSCs) (p < 0.05). Fisetin also increased the gene expression levels of Wnt3 and β-catenin (CTNNB1) in BMSCs, which indicates that fisetin can regulate the Wnt/β-catenin signaling pathway and promote the osteogenic differentiation of BMSCs.

CONCLUSIONS

Fisetin acts on multiple targets and pathways in the treatment of OP; mechanistically, it regulates the Wnt/β-catenin signaling pathway, which promotes the osteogenic differentiation of BMSCs and maintains bone homeostasis. The results of this study provide a theoretical basis for further study on the complex anti-OP mechanism of fisetin.

Mesenchymal stem/stromal cells-derived exosomes for osteoporosis treatment

Osteoporosis is a systemic bone disease, which leads to decreased bone mass and an increased risk of fragility fractures. Currently, there are many anti-resorption drugs and osteosynthesis drugs, which are effective in the treatment of osteoporosis, but their usage is limited due to their contraindications and side effects. In regenerative medicine, the unique repair ability of mesenchymal stem cells (MSCs) has been favored by researchers. The exosomes secreted by MSCs have signal transduction and molecular delivery mechanisms, which may have therapeutic effects. In this review, we describe the regulatory effects of MSCs-derived exosomes on osteoclasts, osteoblasts, and bone immunity. We aim to summarize the preclinical studies of exosome therapy in osteoporosis. Furthermore, we speculate that exosome therapy can be a future direction to improve bone health.

Downregulation of METTL14 improves postmenopausal osteoporosis via IGF2BP1 dependent posttranscriptional silencing of SMAD1

Osteoporosis (OP) tends to occur in postmenopausal women, making them prone to fractures. N6-methyladenosine (m6A) methylation plays a crucial role in OP. Herein, we aimed to explore the effects of METTL14 on osteogenesis and the underlying mechanism. Osteogenic differentiation was assessed through osteoblast markers expression, cell proliferation, ALP activity, and mineralization, which were detected by qRT-PCR, CCK-8, EdU assay, ALP staining assay, and ARS staining assay, respectively. Osteoporosis was evaluated in OVX mice using qRT-PCR, microcomputed tomography, and H&E staining assay. The levels of METTL14 and SMAD1 were measured using qRT-PCR and western blot, and their interaction was assessed using RIP and luciferase reporter assay. M6A methylation was analyzed using the Me-RIP assay. The results indicated that m6A, METTL14, and SMAD1 levels were downregulated in patients with OP and OVX mice, and upregulated in osteogenic BMSCs. Knockdown of METTL14 suppressed osteogenesis of BMSCs and reduced bone mass of OVX mice. Moreover, silencing of METTL14 positively related to SMAD1 and inhibited m6A modification of SMAD1 by suppressing its stability. IGF2BP1 was identified as the methylation reader, and which knockdown reversed the upregulation induced by SMAD1. Overexpression of SMAD1 reversed the suppression of osteogenic differentiation induced by METTL14 knockdown. In conclusion, interference with METTL14 inhibited osteogenic differentiation of BSMCs by m6A modification of SMAD1 in an IGFBP1 manner, suggesting that METTL14 might be a novel approach for improving osteoporosis.

Therapeutic Benefits of Mesenchymal Stem Cells in Acute Respiratory Distress Syndrome: Potential Mechanisms and Challenges

Acute respiratory distress syndrome (ARDS) presents as a form of acute respiratory failure resulting from non-cardiogenic pulmonary edema due to excessive alveolocapillary permeability, which may be pulmonary or systemic in origin. In the last 3 years, the coronavirus disease 2019 pandemic has resulted in an increase in ARDS cases and highlighted the challenges associated with this syndrome, as well as the unacceptably high mortality rates and lack of effective treatments. Currently, clinical treatment remains primarily supportive, including mechanical ventilation and drug-based therapy. Mesenchymal stem cell (MSC) therapies are emerging as a promising intervention in patients with ARDS and have promising therapeutic effects and safety. The therapeutic mechanisms include modifying the immune response and assisting with tissue repair. This review provides an overview of the general properties of MSCs and outlines their role in mitigating lung injury and promoting tissue repair in ARDS. Finally, we summarize the current challenges in the study of translational MSC research and identify avenues by which the discipline may progress in the coming years.

RRM2 regulates osteogenesis of mouse embryo fibroblasts via the Wnt/β‑catenin signaling pathway

Osteoporosis is a widespread bone metabolic disease characterized by reduced bone mass and bone microstructure deterioration. Ribonucleotide reductase M2 (RRM2) is a key enzyme in DNA synthesis and repair. The present study investigated the effect of RRM2 on osteogenesis of mouse embryo fibroblasts (MEFs) and its molecular mechanism. Bioinformatics analysis revealed that RRM2 expression was increased during osteogenesis of MEFs triggered by bone morphogenetic protein 9. Subsequently, MEFs were used as a mesenchymal stem cell model and osteogenic inducing medium was used to induce osteogenic differentiation. RRM2 protein expression was measured by western blotting during osteogenic differentiation induction of MEFs. RRM2 levels in MEFs were upregulated and downregulated by RRM2-overexpressing recombinant adenovirus and small interfering RNA-RRM2, respectively. Bone formation markers (RUNX family transcription factor 2, osterix, distal-less homeobox 5, collagen type I α1 chain, osteopontin and osteocalcin) were detected by reverse transcription-quantitative (RT-q) PCR and alkaline phosphatase (ALP) and Alizarin Red S staining were examined. The protein expression levels of β-catenin and the ratio of phosphorylated (p-)GSK-3β to GSK-3β were detected by western blotting and the RNA expression of downstream related target genes (β-catenin, axis inhibition protein 2 (AXIN2), transcription factor 7 like 2, lymphoid enhancer binding factor 1, c-MYC and Cyclin D1) in the Wnt/β-catenin signaling pathway was measured by RT-qPCR. RRM2 protein expression increased as the osteogenic differentiation induction period was extended. RRM2 overexpression increased osteogenic marker RNA expression, ALP activity, bone mineralization, the protein expression levels of β-catenin, the ratio of p-GSK-3β to GSK-3β and the RNA expression of downstream related target genes in the Wnt/β-catenin signaling pathway, whereas RRM2 knockdown had the opposite effect. The findings of the present study revealed that RRM2 overexpression enhanced osteogenic differentiation, while RRM2 knockdown reduced osteogenic differentiation. RRM2 may regulate osteogenic differentiation of MEFs via the canonical Wnt/β-catenin signaling pathway, providing a possible therapeutic target for osteoporosis.

Mesobiliverdin IXα ameliorates osteoporosis via promoting osteogenic differentiation of mesenchymal stem cells

Heme oxygenase-1 (HO-1) expression promotes osteogenesis, but the mechanisms remain unclear and therapeutic strategies using it to target bone disorders such as osteoporosis have not progressed. Mesobiliverdin IXα is a naturally occurring bilin analog of HO-1 catalytic product biliverdin IXα. Inclusion of mesobiliverdin IXα in the feed diet of ovariectomized osteoporotic mice was observed to increase femur bone volume, trabecular thickness and osteogenesis serum markers osteoprotegrin and osteocalcin and to decrease bone resorption serum markers cross-linked N-teleopeptide and tartrate-resistant acid phosphatase 5b. Moreover, in vitro exposure of human bone marrow mesenchymal stem cells to mesobiliverdin IXα enhanced osteogenic differentiation efficiency by two-fold over non-exposed controls. Our results imply that mesobiliverdin IXα promotes osteogenesis in ways that reflect the potential therapeutic effects of induced HO-1 expression in alleviating osteoporosis.

Exendin-4 enhances osteogenic differentiation of adipose tissue mesenchymal stem cells through the receptor activator of nuclear factor-kappa B and osteoprotegerin signaling pathway

The capability of mesenchymal stem cells (MSCs) to repair bone damage and defects has long been investigated. The receptor activator of nuclear factor-kappa B (RANK), its ligand (RANKL) and the decoy receptor osteoprotegerin (OPG) axis is crucial to keep the equilibrium between osteoblastic and osteoclastic activity. Exendin-4 utilization increased bone formation and enhanced bone integrity. This study aimed to investigate the mentioned axis and determine the effect of exendin-4 upon adipose mesenchymal stem cells (Ad-MSCs) osteogenic differentiation. Ad-MSCs were isolated from rat epididymal fat, followed by characterization and then differentiation into osteocytes both in the presence or absence of exendin-4. Osteogenic differentiation was evaluated by alizarin red staining and the expression of osteogenic markers; using reverse transcriptase-quantitative polymerase chain reaction, western blotting and enzyme-linked immunoassay. MSCs derived from rat epididymal fat were isolated and characterized, along with their differentiation into osteocytes. The differentiated cells were alizarin red-stained, showing increased staining intensity upon addition of exendin-4. Moreover, the addition of exendin-4 elevated the messenger RNA expression levels of osteogenic markers; runt-related transcription factor-2 (RUNX-2), osteocalcin, and forkhead box protein O-1 while reducing the expression of the adipogenic marker peroxisome-proliferator-activated receptor-gamma. Exendin-4 addition elevated OPG levels in the supernatant of osteogenic differentiated cells. Moreover, exendin-4 elevated the protein levels of glucagon-like peptide-1 receptor and RUNX-2, while decreasing both RANK and RANKL. In conclusion, osteogenic differentiation of Ad-MSCs is associated with increased osteoblastic rather than osteoclastic activity. The findings of this study suggest that exendin-4 can enhance Ad-MSCs osteogenic differentiation partially through the RANK/RANKL/OPG axis.