Advances in the application of mesenchymal stem cells, exosomes, biomimetic materials, and 3D printing in osteoporosis treatment

Therapeutic potential of mesenchymal stem cell-derived exosomes in skeletal diseases

Skeletal diseases impose a considerable burden on society. The clinical and tissue-engineering therapies applied to alleviate such diseases frequently result in complications and are inadequately effective. Research has shifted from conventional therapies based on mesenchymal stem cells (MSCs) to exosomes derived from MSCs. Exosomes are natural nanocarriers of endogenous DNA, RNA, proteins, and lipids and have a low immune clearance rate and good barrier penetration and allow targeted delivery of therapeutics. MSC-derived exosomes (MSC-exosomes) have the characteristics of both MSCs and exosomes, and so they can have both immunosuppressive and tissue-regenerative effects. Despite advances in our knowledge of MSC-exosomes, their regulatory mechanisms and functionalities are unclear. Here we review the therapeutic potential of MSC-exosomes for skeletal diseases.

Apoptotic vesicles rescue impaired mesenchymal stem cells and their therapeutic capacity for osteoporosis by restoring miR-145a-5p deficiency

Apoptotic vesicles (apoVs) play a vital role in various pathological conditions; however, we have yet to fully understand their precise biological effects in rescuing impaired mesenchymal stem cells (MSCs) and regulating tissue homeostasis. Here, we proved that systemic infusion of bone marrow MSCs derived from wild-type (WT) mice effectively improved the osteopenia phenotype and hyperimmune state in ovariectomized (OVX) mice. Importantly, the WT MSCs rescued the impairment of OVX MSCs both in vivo and in vitro, whereas OVX MSCs did not show the same efficacy. Interestingly, treatment with apoVs derived from WT MSCs (WT apoVs) restored the impaired biological function of OVX MSCs and their ability to improve osteoporosis. This effect was not observed with OVX MSCs-derived apoVs (OVX apoVs) treatment. Mechanistically, the reduced miR-145a-5p expression hindered the osteogenic differentiation and immunomodulatory capacity of OVX MSCs by affecting the TGF-β/Smad 2/3-Wnt/β-catenin signaling axis, resulting in the development of osteoporosis. WT apoVs directly transferred miR-145a-5p to OVX MSCs, which were then reused to restore their impaired biological functions. Conversely, treatment with OVX apoVs did not produce significant effects due to their limited expression of miR-145a-5p. Overall, our findings unveil the remarkable potential of apoVs in rescuing the biological function and therapeutic capability of MSCs derived from individuals with diseases. This discovery offers a new avenue for exploring apoVs-based MSC engineering and expands the application scope of stem cell therapy, contributing to the maintenance of bone homeostasis through a previously unrecognized mechanism.

Intercellular crosstalk between cancer cells and cancer-associated fibroblasts via exosomes in gastrointestinal tumors

Gastrointestinal (GI) tumors are a significant global health threat, with high rates of morbidity and mortality. Exosomes contain various biologically active molecules like nucleic acids, proteins, and lipids and can serve as messengers for intercellular communication. They play critical roles in the exchange of information between tumor cells and the tumor microenvironment (TME). The TME consists of mesenchymal cells and components of the extracellular matrix (ECM), with fibroblasts being the most abundant cell type in the tumor mesenchyme. Cancer-associated fibroblasts (CAFs) are derived from normal fibroblasts and mesenchymal stem cells that are activated in the TME. CAFs can secrete exosomes to modulate cell proliferation, invasion, migration, drug resistance, and other biological processes in tumors. Additionally, tumor cells can manipulate the function and behavior of fibroblasts through direct cell-cell interactions. This review provides a summary of the intercellular crosstalk between GI tumor cells and CAFs through exosomes, along with potential underlying mechanisms.

Exosome-mediated Repair of Intervertebral Disc Degeneration: The Potential Role of miRNAs

Intervertebral disc degeneration (IVDD) is a serious condition that manifests as low back pain, intervertebral disc protrusion, and spinal canal stenosis. At present, the main treatment methods for IVDD are surgical interventions such as discectomy, total disc replacement, and spinal fusion. However, these interventions have shown limitations, such as recurrent lumbar disc herniation after discectomy, lesions in adjacent segments, and failure of fixation. To overcome these shortcomings, researchers have been exploring stem cell transplantation therapy, such as mesenchymal stem cell (MSC) transplantation, but the treatment results are still controversial. Therefore, researchers are in search of new methods that are more efficient and have better outcomes. The exosomes from stem cells contain a variety of bioactive molecules that mediate cell interactions, and these components have been investigated for their potential therapeutic role in the repair of various tissue injuries. Recent studies have shown that MSC-derived miRNAs in exosomes and vesicles have therapeutic effects on nucleus pulposus cells, annulus fibrosus, and cartilage endplate. miRNAs play a role in many cell activities, such as cell proliferation, apoptosis, and cytokine release, by acting on mRNA translation, and they may have immense therapeutic potential, especially when combined with stem cell therapy. This article reviews the current status of research on intervertebral disc repair, especially with regard to the latest research findings on the molecular biological mechanisms of miRNAs in MSC-derived exosomes in intervertebral disc repair.

Advancements in the pathogenesis of hepatic osteodystrophy and the potential therapeutic of mesenchymal stromal cells

Hepatic osteodystrophy (HOD) is a metabolically associated bone disease mainly manifested as osteoporosis with the characteristic of bone loss induced by chronic liver disease (CLD). Due to its high incidence in CLD patients and increased risk of fracture, the research on HOD has received considerable interest. The specific pathogenesis of HOD has not been fully revealed. While it is widely believed that disturbance of hormone level, abnormal secretion of cytokines and damage of intestinal barrier caused by CLD might jointly affect the bone metabolic balance of bone formation and bone absorption. At present, the treatment of HOD is mainly to alleviate the bone loss by drug treatment, but the efficacy and safety are not satisfactory. Mesenchymal stromal cells (MSCs) are cells with multidirectional differentiation potential, cell transplantation therapy based on MSCs is an emerging therapeutic approach. This review mainly summarized the pathogenesis and treatment of HOD, reviewed the research progress of MSCs therapy and the combination of MSCs and scaffolds in the application of osteoporotic bone defects, and discussed the potential and limitations of MSCs therapy, providing theoretical basis for subsequent studies.

Forged to heal: The role of metallic cellular solids in bone tissue engineering

Metallic cellular solids, made of biocompatible alloys like titanium, stainless steel, or cobalt-chromium, have gained attention for their mechanical strength, reliability, and biocompatibility. These three-dimensional structures provide support and aid tissue regeneration in orthopedic implants, cardiovascular stents, and other tissue engineering cellular solids. The design and material chemistry of metallic cellular solids play crucial roles in their performance: factors such as porosity, pore size, and surface roughness influence nutrient transport, cell attachment, and mechanical stability, while their microstructure imparts strength, durability and flexibility. Various techniques, including additive manufacturing and conventional fabrication methods, are utilized for producing metallic biomedical cellular solids, each offering distinct advantages and drawbacks that must be considered for optimal design and manufacturing. The combination of mechanical properties and biocompatibility makes metallic cellular solids superior to their ceramic and polymeric counterparts in most load bearing applications, in particular under cyclic fatigue conditions, and more in general in application that require long term reliability. Although challenges remain, such as reducing the production times and the associated costs or increasing the array of available materials, metallic cellular solids showed excellent long-term reliability, with high survival rates even in long term follow-ups.

Drug Delivery and Therapy Strategies for Osteoporosis Intervention

With the advent of the aging society, osteoporosis (OP) risk increases yearly. Currently, the clinical usage of anti-OP drugs is challenged by recurrent side effects and poor patient compliance, regardless of oral, intravenous, or subcutaneous administration. Properly using a drug delivery system or formulation strategy can achieve targeted drug delivery to the bone, diminish side effects, improve bioavailability, and prolong the in vivo residence time, thus effectively curing osteoporosis. This review expounds on the pathogenesis of OP and the clinical medicaments used for OP intervention, proposes the design approach for anti-OP drug delivery, emphatically discusses emerging novel anti-OP drug delivery systems, and enumerates anti-OP preparations under clinical investigation. Our findings may contribute to engineering anti-OP drug delivery and OP-targeting therapy.

Osteoporosis treatment using stem cell-derived exosomes: a systematic review and meta-analysis of preclinical studies

BACKGROUND

The increasing incidence of osteoporosis in recent years has aroused widespread public concern; however, existing effective treatments are limited. Therefore, new osteoporosis treatment methods, including stem cell transplantation and exosome therapy, have been proposed and are gaining momentum. Exosomes are considered to have greater potential for clinical application owing to their immunocompatibility. This study summarises the latest evidence demonstrating the efficacy of exosomes in improving bone loss in the treatment of osteoporosis.

MAIN TEXT

This systematic review and meta-analyses searched PubMed, Embase, and Cochrane Library databases from inception to 26 March 2022 for osteoporosis treatment studies using stem cell-derived exosomes. Six endpoints were selected to determine efficacy: bone mineral density, trabecular bone volume/tissue volume fraction, trabecular number, trabecular separation, trabecular thickness, and cortical thickness. The search generated 366 citations. Eventually, 11 articles that included 15 controlled preclinical trials and 242 experimental animals (rats and mice) were included in the meta-analysis.

CONCLUSION

The results were relatively robust and reliable despite some publication biases, suggesting that exosome treatment increased bone mass, improved bone microarchitecture, and enhanced bone strength compared with placebo treatments. Moreover, stem cell-derived exosomes may favour anabolism over catabolism, shifting the dynamic balance towards bone regeneration.

Advances in materials-based therapeutic strategies against osteoporosis

Osteoporosis is caused by the disruption in homeostasis between bone formation and bone resorption. Conventional management of osteoporosis involves systematic drug administration and hormonal therapy. These treatment strategies have limited curative efficacy and multiple adverse effects. Biomaterials-based therapeutic strategies have recently emerged as promising alternatives for the treatment of osteoporosis. The present review summarizes the current status of biomaterials designed for managing osteoporosis. The advantages of biomaterials-based strategies over conventional systematic drug treatment are presented. Different anti-osteoporotic delivery systems are concisely addressed. These materials include injectable hydrogels and nanoparticles, as well as anti-osteoporotic bone tissue engineering materials. Fabrication techniques such as 3D printing, electrostatic spinning and artificial intelligence are appraised in the context of how the use of these adjunctive techniques may improve treatment efficacy. The limitations of existing biomaterials are critically analyzed, together with deliberation of the future directions in biomaterials-based therapies. The latter include discussion on the use of combination strategies to enhance therapeutic efficacy in the osteoporosis niche.

3D printing of bone and cartilage with polymer materials

Damage and degeneration to bone and articular cartilage are the leading causes of musculoskeletal disability. Commonly used clinical and surgical methods include autologous/allogeneic bone and cartilage transplantation, vascularized bone transplantation, autologous chondrocyte implantation, mosaicplasty, and joint replacement. 3D bio printing technology to construct implants by layer-by-layer printing of biological materials, living cells, and other biologically active substances in vitro, which is expected to replace the repair mentioned above methods. Researchers use cells and biomedical materials as discrete materials. 3D bio printing has largely solved the problem of insufficient organ donors with the ability to prepare different organs and tissue structures. This paper mainly discusses the application of polymer materials, bio printing cell selection, and its application in bone and cartilage repair.

Aging of mesenchymal stem cell: machinery, markers, and strategies of fighting

Human mesenchymal stem cells (MSCs) are primary multipotent cells capable of differentiating into osteocytes, chondrocytes, and adipocytes when stimulated under appropriate conditions. The role of MSCs in tissue homeostasis, aging-related diseases, and cellular therapy is clinically suggested. As aging is a universal problem that has large socioeconomic effects, an improved understanding of the concepts of aging can direct public policies that reduce its adverse impacts on the healthcare system and humanity. Several studies of aging have been carried out over several years to understand the phenomenon and different factors affecting human aging. A reduced ability of adult stem cell populations to reproduce and regenerate is one of the main  contributors to the human aging process. In this context, MSCs senescence is a major challenge in front of cellular therapy advancement. Many factors, ranging from genetic and metabolic pathways to extrinsic factors through various cellular signaling pathways, are involved in regulating the mechanism of MSC senescence. To better understand and reverse cellular senescence, this review highlights the underlying mechanisms and signs of MSC cellular senescence, and discusses the strategies to combat aging and cellular senescence.

Osteoporosis pathogenesis and treatment: existing and emerging avenues

Osteoporotic fractures lead to increased disability and mortality in the elderly population. With the rapid increase in the aging population around the globe, more effective treatments for osteoporosis and osteoporotic fractures are urgently required. The underlying molecular mechanisms of osteoporosis are believed to be due to the increased activity of osteoclasts, decreased activity of osteoblasts, or both, which leads to an imbalance in the bone remodeling process with accelerated bone resorption and attenuated bone formation. Currently, the available clinical treatments for osteoporosis have mostly focused on factors influencing bone remodeling; however, they have their own limitations and side effects. Recently, cytokine immunotherapy, gene therapy, and stem cell therapy have become new approaches for the treatment of various diseases. This article reviews the latest research on bone remodeling mechanisms, as well as how this underpins current and potential novel treatments for osteoporosis.

Bibliometric and visual analysis of mesenchymal stem cells in the treatment of osteoporosis based on CiteSpace software

BACKGROUND

The focus of research in the treatment of osteoporosis (OP) has evolved from promoting bone formation and inhibiting bone resorption to current stem cell therapy. Due to their multipotent differentiation properties, mesenchymal stem cells (MSCs) can repair degenerated bones through transplantation, and have become a new method for the treatment of OP.

METHODS

Relevant literatures included in the Web of Science database core collection database from 2012 to 2021 were retrieved. CiteSpace software was used to analyze the cooperative relationship among authors, journals, institutions, and countries, and to analyze the co-citation situation of the literature. And performed co-occurrence analysis, cluster analysis and burst analysis of keywords, draw visual maps and analyzed the results.

RESULTS

A total of 2100 papers were included, and the number of papers published from 2012 to 2021 was on the rise. A total of 484 authors were included, and 176 authors published more than 3 papers. The high-yield authors were mainly represented by YAN JIN and BO GAO. A total of 99 journals were included, and the journal with the most publications was J BONE MINER RES. A total of 787 institutions were included, and the institution with the largest number of publications was Shanghai Jiao Tong University. A total of 65 countries were included. The country with the largest number of publications was China, and the United States had the highest centrality. The co-citation analysis of the literature found 2 articles with high citation frequency and high centrality. The main research direction was the mechanism of MSCs in the treatment of osteoporosis. A total of 133 keywords were included, and the hot keywords were osteogenic differentiation, expression, proliferation, bone marrow, etc.

CONCLUSIONS

The research hotspots in this field mainly focused on the mechanism of bone regeneration, proliferation and osteogenic differentiation of bone marrow MSCs, and the expression of osteogenic-related genes. The future research trends in this field are predicted to be the mechanism of action of microRNA and long non-coding RNA on MSCs and their relationship with OP, the mechanism of MSCs adipogenic and osteogenic differentiation, and tissue engineering scaffolds applications.

Extracellular Vesicles in Tissue Engineering: Biology and Engineered Strategy

Extracellular vesicles (EVs), acting as an important ingredient of intercellular communication through paracrine actions, have gained tremendous attention in the field of tissue engineering (TE). Moreover, these nanosized extracellular particles (30-140 nm) can be incorporated into biomaterials according to different principles to facilitate signal delivery in various regenerative processes directly or indirectly. Bioactive biomaterials as the carrier will extend the retention time and realize the controlled release of EVs, which further enhance their therapeutic efficiency in tissue regeneration. Herein, the basic biological characteristics of EVs are first introduced, and then their outstanding performance in exerting direct impacts on target cells in tissue regeneration as well as indirect effects on promoting angiogenesis and regulating the immune environment, due to specific functional components of EVs (nucleic acid, protein, lipid, etc.), is emphasized. Furthermore, different design ideas for suitable EV-loaded biomaterials are also demonstrated. In the end, this review also highlights the engineered strategies, which aim at solving the problems related to natural EVs such as highly heterogeneous functions, inadequate tissue targeting capabilities, insufficient yield and scalability, etc., thus promoting the therapeutic pertinence and clinical potential of EV-based approaches in TE.

Anti-aging effect of β-carotene through regulating the KAT7-P15 signaling axis, inflammation and oxidative stress process

Background

Research on aging is growing as the elderly make up a greater share of the population, focusing on reversing and inhibiting the aging process. The exhaustion and senescence of stem cells are the fundamental drivers behind aging. β-Carotene has been depicted to have many biological functions, and we speculate that it may have an anti-aging effect.

Methods

Firstly, the anti-aging property of β-carotene was investigated in vitro using mesenchymal stem cells (MSCs) induced by H₂O₂. The anti-aging effect was characterized using Western-bloting, confocal laser scanning microscopy, indirect immunofluorescence, and immunohistochemistry. The anti-aging property was also tested in vivo using aged mice.

Results

The in vitro experiment revealed that β-carotene could relieve the aging of MSCs, as evidenced by a series of aging marker molecules such as p16 and p21. β-Carotene appeared to inhibit aging by regulating the KAT7-P15 signaling axis. The in vivo experiment revealed that β-carotene treatment has significantly down-regulated the aging level of tissues and organs.

Conclusions

In this work, we explored the anti-aging effect of β-carotene in vivo and in vitro. The experimental results indicate that β-carotene may be an important potential anti-aging molecule, which can be used as a drug or in functional food to treat aging in the future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s11658-022-00389-7.

The role of macrophage subtypes and exosomes in immunomodulation

Macrophages are influential members of the innate immune system that can be reversibly polarized by different microenvironment signals. Cell polarization leads to a wide range of features, involving the migration, development, and organization of the cells. There is mounting evidence that macrophage polarization plays a key role in the initiation and development of a wide range of diseases. This study aims to give an overview of macrophage polarization, their different subtypes, and the importance of alternatively activated M2 macrophage and classically activated M1 macrophage in immune responses and pathological conditions. This review provides insight on the role of exosomes in M1/M2-like macrophage polarization and their potential as a promising therapeutic candidate.

Mesenchymal stem cell-derived extracellular vesicles: a possible therapeutic strategy for orthopaedic diseases: a narrative review

Accumulating evidence suggests that the therapeutic role of mesenchymal stem cells (MSCs) in bone diseases is closely related to paracrine-generated extracellular vesicles (EVs). MSC-derived EVs (MSC-EVs) carry proteins, nucleic acids, and lipids to the extracellular space and affect the bone microenvironment. They have similar biological functions to MSCs, such as the ability to repair organ and tissue damage. In addition, MSC-EVs also have the advantages of long half-life, low immunogenicity, attractive stability, ability to pass through the blood-brain barrier, and demonstrate excellent performance with potential practical applications in bone diseases. In this review, we summarise the current applications and mechanisms of MSC-EVs in osteoporosis, osteoarthritis, bone tumours, osteonecrosis of the femoral head, and fractures, as well as the development of MSC-EVs combined with materials science in the field of orthopaedics. Additionally, we explore the critical challenges involved in the clinical application of MSC-EVs in orthopaedic diseases.

Interleukin-10 genetically modified clinical-grade mesenchymal stromal cells markedly reinforced functional recovery after spinal cord injury via directing alternative activation of macrophages

Background

After spinal cord injury (SCI), dysregulated or nonresolving inflammatory processes can severely disturb neuronal homeostasis and drive neurodegeneration. Although mesenchymal stromal cell (MSC)-based therapies have showed certain therapeutic efficacy, no MSC therapy has reached its full clinical goal. In this study, we examine interleukin-10 (IL10) genetically modified clinical-grade MSCs (IL10-MSCs) and evaluate their clinical safety, effectiveness, and therapeutic mechanism in a completely transected SCI mouse model.

Methods

We established stable IL10-overexpressing human umbilical-cord-derived MSCs through electric transduction and screened out clinical-grade IL10-MSCs according to the criteria of cell-based therapeutic products, which were applied to mice with completely transected SCI by repeated tail intravenous injections. Then we comprehensively investigated the motor function, histological structure, and nerve regeneration in SCI mice, and further explored the potential therapeutic mechanism after IL10-MSC treatment.

Results

IL10-MSC treatment markedly reinforced locomotor improvement, accompanied with decreased lesion volume, regeneration of axons, and preservation of neurons, compared with naïve unmodified MSCs. Further, IL10-MSC transplantation increased the ratio of microglia to infiltrated alternatively activated macrophages (M2), and reduced the ratio of classically activated macrophages (M1) at the injured spinal cord, meanwhile increasing the percentage of Treg and Th2 cells, and reducing the percentage of Th1 cells in the peripheral circulatory system. In addition, IL10-MSC administration could prevent apoptosis and promote neuron differentiation of neural stem cells (NSCs) under inflammatory conditions in vitro.

Conclusions

IL10-MSCs exhibited a reliable safety profile and demonstrated promising therapeutic efficacy in SCI compared with naïve MSCs, providing solid support for future clinical application of genetically engineered MSCs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s11658-022-00325-9.

Cryo-Temperature Pretreatment Increases the Pro-Angiogenic Capacity of Three-Dimensional Mesenchymal Stem Cells via the PI3K-AKT Pathway

To increase the potential and effectiveness of three-dimensional (3D) mesenchymal stem cells (MSCs) for clinical applications, this study explored the effects of short cryo-temperature pretreatment on MSC function. Adipose-derived MSCs (A-MSCs) were cultured via the ordinary monolayer method and 3D hanging drop spheroid method. When the cells adhered to the wall or formed a spheroid, they were subjected to hypothermic stress at 4°C for 1 h and then divided into three recovery periods at 37°C, specifically 0, 12, and 24 h. The control group was not subjected to any treatment throughout the study. Monolayer and 3D spheroid A-MSCs were analyzed via RNA sequencing after hypothermic stress at 4°C for 1 h. Subsequently, each group of cells was collected and subjected to phenotype identification via flow cytometry, and mRNA expression was detected via reverse transcription-quantitative polymerase chain reaction analysis. Western blot analysis was performed to analyze the PI3K-AKT signaling pathway in A-MSCs. The effects of A-MSCs on angiogenesis in vivo were examined using a chick chorioallantoic membrane assay. Transwell assays were performed to determine whether the culture supernatant from each group could induce the chemotaxis of human umbilical vein endothelial cells (HUVECs). Three-dimensional spheroid culture did not change the phenotype of A-MSCs. The expression of fibroblast growth factors, hepatocyte growth factors, and other angiogenesis-related factors in A-MSCs was upregulated. A-MSCs subjected to hypothermic stress promoted angiogenesis under both monolayer and 3D spheroid cultures. Moreover, the chemotaxis of HUVECs to the 3D spheroid culture supernatant increased substantially. Short cryo-temperature pretreatment could stimulate 3D spheroid A-MSCs and activate the PI3K-AKT pathway. This approach has the advantages of promoting angiogenesis and maintaining cell viability.