Conditioned medium of mesenchymal stem cells delays osteoarthritis progression in a rat model by protecting subchondral bone, maintaining matrix homeostasis, and enhancing autophagy

Forkhead box C1 promotes the pathology of osteoarthritis in subchondral bone osteoblasts via the Piezo1/YAP axis

Subchondral bone sclerosis is a key characteristic of osteoarthritis (OA). Prior research has shown that Forkhead box C1 (FoxC1) plays a role in the synovial inflammation of OA, but its specific role in the subchondral bone of OA has not been explored. Our research revealed elevated expression levels of FoxC1 and Piezo1 in OA subchondral bone tissues. Further experiments on OA subchondral bone osteoblasts with FoxC1 or Piezo1 overexpression showed increased cell proliferation activity, expression of Yes-associated Protein 1 (YAP) and osteogenic markers, and secretion of proinflammatory factors. Mechanistically, the overexpression of FoxC1 through Piezo1 activation, in combination with downstream YAP signaling, led to increased levels of alkaline phosphatase (ALP), collagen type 1 (COL1) A1, RUNX2, Osteocalcin, matrix metalloproteinase (MMP) 3, and MMP9 expression. Notably, inhibition of Piezo1 reversed the regulatory function of FoxC1. The binding of FoxC1 to the targeted area (ATATTTATTTA, residues +612 to +622) and the activation of Piezo1 transcription were verified by the dual luciferase assays. Additionally, Reduced subchondral osteosclerosis and microangiogenesis were observed in knee joints from FoxC1-conditional knockout (CKO) and Piezo1-CKO mice, indicating reduced lesions. Collectively, our study reveals the significant involvement of FoxC1 in the pathologic process of OA subchondral bone via the Piezo1/YAP signaling pathway, potentially establishing a novel therapeutic target.

Research hotspots and trends of mesenchymal stem cell-derived extracellular vesicles for drug delivery: a bibliometric and visualization analysis from 2013 to 2023

Introduction

Our study aims to provide a comprehensive overview of mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) in drug delivery research, focusing on the period between 2013 and 2023. Given the increasing global interest in this field, we utilized bibliometric tools to explore publication trends, key contributors, and thematic research clusters.

Methods

Data was collected from the Web of Science (WoS) database, and an in-depth bibliometric analysis was conducted using VOSviewer. The analysis encompassed bibliographic coupling, co-citation, co-authorship, and co-occurrence trends, offering a structured insight into global research activity. We also employed Citespace to further analyze thematic clusters in this domain.

Results

Our analysis revealed a total of 1,045 publications related to MSC-EVs in drug delivery over the past decade, showing a steady increase in research output. China led in publication count, H-index, prolific authors, and research funding, while the United States ranked highest in total citations, average citation counts, and H-index performance. Pharmaceutics emerged as the leading journal by publication volume, with the Journal of Controlled Release having the strongest total link strength. Top institutions driving research included Shanghai Jiao Tong University, Zhejiang University, and Harvard University. VOSviewer analysis identified four major research clusters: tissue engineering, cancer, neurological diseases, and targeted delivery. Citespace analysis refined this further into ten thematic areas, including differentiation, tissue regeneration, and drug resistance.

Discussion

This bibliometric assessment provides a holistic visualization of the research landscape for MSC-EVs in drug delivery, underlining the significant contributions of China and the United States. Our findings underscore the increasing global importance of MSC-EV research and highlight emerging themes that will likely guide future research directions. The insights from this study offer a foundational framework for identifying nascent frontiers in MSC-EV-based drug delivery.

The iPSC secretome is beneficial for in vitro propagation of primary osteoarthritic chondrocytes cell lines

BACKGROUND

One of the obstacles to autologous chondrocyte implantation (ACI) is obtaining a large quantity of chondrocytes without depletion of their properties. The conditioned medium (CM) from different subpopulations of stem cells (mesenchymal stromal cells (MSC) or induced pluripotent stem cells (iPSC)) could be a gamechanger. MSCs' potential is related to the donor's health and age, which could be omitted when, as a source, iPSCs are used. There is a lack of data regarding their use in the chondrocyte culture expansion. Thus, we wanted to verify whether iPSC-CM could be beneficial for the cell culture of primary chondrocyte cells.

METHODS

We added the iPSC-CMs from GPCCi001-A and ND 41658*H cells to the culture of primary chondrocyte cell lines isolated from OA patients (n = 6) for other two passages. The composition of the CM was evaluated using Luminex technology. Then, we analysed the senescence, proliferation rate and using flow cytometry: viability, distribution of cell cycle phases, production of reactive oxygen species (ROS) and double-strand breaks. The cartilage-related markers were evaluated using Western blot and immunofluorescence. Additionally, a three-dimensional cell culture was used to determine the potential to form cartilage particles.

RESULTS

iPSC-CM increased proliferation and diminished cell ROS production and senescence. CM influenced the cartilage-related protein expression and promoted the growth of cartilage particles. The cell exposed to CM did not lose the ECM proteins, suggesting the chondroprotective effect for prolonged culture time.

CONCLUSION

Our preliminary results suggest a beneficial effect on maintaining chondrocyte biology during in vitro expansion.

Comparison of the Therapeutic Efficacy and Autophagy-Mediated Mechanisms of Action of Urine-Derived and Adipose-Derived Stem Cells in Osteoarthritis

BACKGROUND

Osteoarthritis (OA) is a prevalent and disabling disease that affects a significant proportion of the global population. Urine-derived stem cells (USCs) have shown great prospects in the treatment of OA, but there is no study that has compared them with traditional stem cells.

PURPOSE

This study aimed to compare the therapeutic efficacy and mechanisms of USCs and adipose-derived stem cells (ADSCs) for OA treatment.

STUDY DESIGN

Controlled laboratory study.

METHODS

We compared the biological properties of USCs and ADSCs using CCK-8, colony formation, EdU, adhesion, and apoptosis assays. We evaluated the protective effects of USCs and ADSCs on IL-1β-treated OA chondrocytes by chemical staining, immunofluorescence, and Western blotting. We assessed the effects of USCs and ADSCs on chondrocyte autophagy by transmission electron microscopy, immunofluorescence, and Western blotting. We also compared the therapeutic efficacy of intra-articular injections of USCs and ADSCs by gross, histological, micro-computed tomography, and immunohistochemical analyses in an OA rat model induced by anterior cruciate ligament transection.

RESULTS

USCs showed higher proliferation, colony formation, DNA synthesis, adhesion, and anti-apoptotic abilities than ADSCs. Both USCs and ADSCs increased the expression of cartilage-specific proteins and decreased the expression of matrix degradation-related proteins and inflammatory factors in OA chondrocytes. USCs had a greater advantage in suppressing MMP-13 and inflammatory factors than ADSCs. Both USCs and ADSCs enhanced autophagy in OA chondrocytes, with USCs being more effective than ADSCs. The autophagy inhibitor 3-MA reduced the enhanced autophagy and protective effects of USCs and ADSCs on OA chondrocytes.

CONCLUSION

To our knowledge, this is the first study to explore the efficacy of USCs in the treatment of knee OA and to compare them with ADSCs. Considering the superior properties of USCs in terms of noninvasive acquisition, a high cost-benefit ratio, and low ethical concerns, our study suggests that they may be a more promising therapeutic option than ADSCs for OA treatment under rigorous regulatory pathways.

CLINICAL RELEVANCE

USCs may be a superior cell source for stem cells to treat knee OA, and this study strengthens the evidence for the application of USCs.

Conditioned Medium of Infrapatellar Fat Stem Cells Alleviates Degradation of Chondrocyte Extracellular Matrix and Delays Development of Osteoarthritis

INTRODUCTION

Osteoarthritis (OA) is a prevalent clinical chronic degenerative condition characterized by the degeneration of articular cartilage. Currently, drug treatments for OA come with varying degrees of side effects, making the development of new therapeutic approaches for OA imperative. Mesenchymal stem cells (MSCs) are known to mitigate the progression of OA primarily through paracrine effects. The conditioned medium (CM) derived from MSCs encapsulates a variety of paracrine factors secreted by these cells.

METHODS

In this study, we investigated the effect of the CM of infrapatellar fat pad-derived MSCs (IPFSCs) on OA in vitro and in vivo, as well as and the potential underlying mechanisms. We established three experimental groups: the normal group, the OA group, and the CM intervention group. In vitro experiments, we used methods such as qPCR, Western blot, immunofluorescence, and flow cytometry to detect the impact of CM on OA chondrocytes. In vivo experiments, we evaluated the changes in the knee joints of OA rats after intra-articular injection of CM treatment.

RESULTS

The results showed that injection of CM into the knee joint inhibited OA development in a rat model induced by destabilization of the medial meniscus and anterior cruciate ligament transection. The CM increased the deposition of extracellular matrix-related components (type II collagen and Proteoglycan). The activation of PI3K/AKT/NF-κB signaling pathway was induced by IL-1β in chondrocytes, which was finally inhibited by CM-IPFSCs treatment.

CONCLUSION

In summary, IPFSCs-CM may have therapeutic potential for OA.

Therapeutics of the future: Navigating the pitfalls of extracellular vesicles research from an osteoarthritis perspective

Extracellular vesicles have gained wide momentum as potential therapeutics for osteoarthritis, a highly prevalent chronic disease that still lacks an approved treatment. The membrane-bound vesicles are secreted by all cells carrying different cargos that can serve as both disease biomarkers and disease modifiers. Nonetheless, despite a significant peak in research regarding EVs as OA therapeutics, clinical implementation seems distant. In addition to scalability and standardization challenges, researchers often omit to focus on and consider the proper tropism of the vesicles, the practicality and relevance of their source, their low native therapeutic efficacy, and whether they address the disease as a whole. These considerations are necessary to better understand EVs in a clinical light and have been comprehensively discussed and ultimately summarized in this review into a conceptualized framework termed the nanodiamond concept. Future perspectives are also discussed, and alternatives are presented to address some of the challenges and concerns.

The role of autophagy in mitigating osteoarthritis progression via regulation of chondrocyte apoptosis: A review

Osteoarthritis (OA) is the most prevalent chronic joint disease with an immense socioeconomic burden; however, no treatment has achieved complete success in effectively halting or reversing cartilage degradation, which is the central pathophysiological feature of OA. Chondrocytes loss or dysfunction is a significant contributing factor to the progressive cartilage deterioration as these sole resident cells have a crucial role to produce extracellular matrix proteins, thus maintaining cartilage structure and homeostasis. It has been previously suggested that death of chondrocytes occurring through apoptosis substantially contributes to cartilage degeneration. Although the occurrence of apoptosis in osteoarthritic cartilage and its correlation with cartilage degradation is evident, the causes of chondrocyte apoptosis leading to matrix loss are still not well-understood. Autophagy, an intracellular degradative mechanism that eliminates dysfunctional cytoplasmic components to aid cell survival in unfavourable conditions, is a potential therapeutic target to inhibit chondrocyte apoptosis and reduce OA severity. Despite accumulating evidence indicating significant cytoprotective effects of autophagy against chondrocyte apoptosis, the mechanistic link between autophagy and apoptosis in chondrocytes remains to be further explored. In this review, we summarize the relevant mechanistic events that perpetuate chondrocyte apoptosis and highlight the prominent role of autophagy in modulating these events to mitigate OA progression.

Enhancing cartilage regeneration through spheroid culture and hyaluronic acid microparticles: A promising approach for tissue engineering

Cell therapy using chondrocytes has shown promise for cartilage regeneration, but maintaining functional characteristics during in vitro culture and ensuring survival after transplantation are challenges. Three-dimensional (3D) cell culture methods, such as spheroid culture, and hydrogels can improve cell survival and functionality. In this study, a new method of culturing spheroids using hyaluronic acid (HA) microparticles was developed. The spheroids mixed with HA microparticles effectively maintained the functional characteristics of chondrocytes during in vitro culture, resulting in improved cell survival and successful cartilage formation in vivo following transplantation. This new method has the potential to improve cell therapy production for cartilage regeneration.

Epigenetic modification and exosome effects on autophagy in osteoarthritis

Osteoarthritis (OA) is a degenerative disease that leads to joint pain and stiffness and is one of the leading causes of disability and pain worldwide. Autophagy is a highly conserved self-degradation process, and its abnormal function is closely related to human diseases, including OA. Abnormal autophagy regulates cell aging, matrix metalloproteinase metabolism, and reactive oxygen metabolism, which are key in the occurrence and development of OA. There is evidence that drugs directly or indirectly targeting autophagy significantly hinder the progress of OA. In addition, the occurrence and development of autophagy in OA are regulated by many factors, including epigenetic modification, exosomes, crucial autophagy molecules, and signaling pathway regulation. Autophagy, as a new therapeutic target for OA, has widely influenced the pathological mechanism of OA. However, determining how autophagy affects OA pathology and its use in the treatment and diagnosis of targets still need further research.

Managing Temporomandibular Joint Osteoarthritis by Dental Stem Cell Secretome

The potential therapeutic role of the Dental Pulp Stem Cells Secretome (SECR) in a rat model of experimentally induced Temporomandibular Joint (TMJ) Osteoarthritis (OA) was evaluated. Proteomic profiling of the human SECR under specific oxygen tension (5% O2) and stimulation with Tumor Necrosis Factor-alpha (TNF-α) was performed. SECR and respective cell lysates (CL) samples were collected and subjected to SDS-PAGE, followed by LC-MS/MS analysis. The identified proteins were analyzed with Bioinformatic tools. The anti-inflammatory properties of SECR were assessed via an in vitro murine macrophages model, and were further validated in vivo, in a rat model of chemically-induced TMJ-OA by weekly recording of the head withdrawal threshold, the food intake, and the weight change, and radiographically and histologically at 4- and 8-weeks post-treatment. SECR analysis revealed the presence of 50 proteins that were enriched and/or statistically significantly upregulated compared to CL, while many of those proteins were involved in pathways related to "extracellular matrix organization" and "immune system". SECR application in vitro led to a significant downregulation on the expression of pro-inflammatory genes (MMP-13, MMP-9, MMP-3 and MCP-1), while maintaining an increased expression of IL-10 and IL-6. SECR application in vivo had a significant positive effect on all the clinical parameters, resulting in improved food intake, weight, and pain suppression. Radiographically, SECR application had a significant positive effect on trabecular bone thickness and bone density compared to the saline-treated group. Histological analysis indicated that SECR administration reduced inflammation, enhanced ECM and subchondral bone repair and regeneration, thus alleviating TMJ degeneration.

Photobiostimulation conjugated with stem cells or their secretome for temporomandibular joint arthritis in a rat model

BACKGROUND

Temporomandibular joint (TMJ) arthritis is a debilitating, challenging condition and different methods have been implicated for its treatment. This study aimed to test the therapeutic potentials of low-level laser therapy (LLLT) associated with adipose derived stem cells (ADSC) or their derived secretome on a murine model induced arthritis.

METHODS

Forty eight rats were divided into four groups where group I was the sham control, the rest of animals were subjected to arthritis induction using complete Freund's adjuvant, then divided as follows: group II received phosphate buffered saline (PBS) intraarticular injection and irradiation of 0 j/cm2, group III received ADSCs derived secretome and irradiation of 38 j/cm2, and group IV received ADSCs and irradiation of 38 j/cm2 as well. One and three weeks after treatment, animals were euthanized, and paraffin blocks were processed for histological assessment by hematoxylin and eosin stain with histomorphometrical analysis. Histochemical evaluation of joint proteoglycan content was performed through toluidine blue stain, and immunohistochemical staining by the proinflammatory marker tumor necrosis factor-α (TNF-α) was performed followed by the relevant statistical tests.

RESULTS

The arthritis group showed histological signs of joint injury including cartilage atrophy, articular disc fibrosis, irregular osteochondral interface, and condylar bone resorption together with high inflammatory reaction and defective proteoglycan content. In contrast, the treated groups III and IV showed much restoration of the joint structure with normal cartilage and disc thickness. The inflammation process was significantly suppressed especially after three weeks as confirmed by the significant reduction in TNF-α positive immunostaining compared to the arthritic group, and the cartilage proteoglycan content also showed significant increase relative to the arthritic group. However, no significant difference between the results of the two treated groups was detected.

CONCLUSION

LLLT conjugated with ADSCs or ADSCs derived secretome can efficiently enhance the healing of arthritic TMJs. Stem cell secretome can be applied as a safe, potent therapy. However, further investigations are required to unravel its mechanism of action and pave its way as a safe, novel, cell free therapy.

Thermo-Responsive Hyaluronan-Based Hydrogels Combined with Allogeneic Cytotherapeutics for the Treatment of Osteoarthritis

Thermo-responsive hyaluronan-based hydrogels and FE002 human primary chondroprogenitor cell sources have both been previously proposed as modern therapeutic options for the management of osteoarthritis (OA). For the translational development of a potential orthopedic combination product based on both technologies, respective technical aspects required further optimization phases (e.g., hydrogel synthesis upscaling and sterilization, FE002 cytotherapeutic material stabilization). The first aim of the present study was to perform multi-step in vitro characterization of several combination product formulas throughout the established and the optimized manufacturing workflows, with a strong focus set on critical functional parameters. The second aim of the present study was to assess the applicability and the efficacy of the considered combination product prototypes in a rodent model of knee OA. Specific characterization results (i.e., spectral analysis, rheology, tribology, injectability, degradation assays, in vitro biocompatibility) of hyaluronan-based hydrogels modified with sulfo-dibenzocyclooctyne-PEG4-amine linkers and poly(N-isopropylacrylamide) (HA-L-PNIPAM) containing lyophilized FE002 human chondroprogenitors confirmed the suitability of the considered combination product components. Specifically, significantly enhanced resistance toward oxidative and enzymatic degradation was shown in vitro for the studied injectable combination product prototypes. Furthermore, extensive multi-parametric (i.e., tomography, histology, scoring) in vivo investigation of the effects of FE002 cell-laden HA-L-PNIPAM hydrogels in a rodent model revealed no general or local iatrogenic adverse effects, whereas it did reveal some beneficial trends against the development of knee OA. Overall, the present study addressed key aspects of the preclinical development process for novel biologically-based orthopedic combination products and shall serve as a robust methodological basis for further translational investigation and clinical work.

Potential of secretome of human fetal cartilage progenitor cells as disease modifying agent for osteoarthritis

AIMS

Osteoarthritis (OA) is caused by an imbalance in the synthesis and degradation of cartilage tissue by chondrocytes. Therefore, a therapeutic agent for OA patients that can positively affect both synthesis and degradation is needed. However, current nonsurgical treatments for OA can barely achieve satisfactory long-term outcomes in cartilage repair. Human fetal cartilage progenitor cells-secretome (ShFCPC) has shown potent anti-inflammatory and tissue-repair effects; however, its underlying mechanisms and effects on OA have rarely been systematically elucidated. This study aims to analyze and evaluate the potency of ShFCPC in modifying OA process.

MAIN METHODS

Herein, secreted proteins enriched in ShFCPC have been characterized, and their biological functions both in vitro and in vivo in an OA model are compared with those of human bone marrow-derived mesenchymal stem cells-secretome (ShBMSC) and hyaluronan (HA).

KEY FINDINGS

Secretome analysis has shown that ShFCPC is significantly enriched with extracellular matrix molecules involved in many effects of cellular processes required for homeostasis during OA progression. Biological validation in vitro has shown that ShFCPC protects chondrocyte apoptosis by suppressing the expression of inflammatory mediators and matrix-degrading proteases and promotes the secretion of pro-chondrogenic cytokines in lipopolysaccharide-induced coculture of human chondrocytes and SW982 synovial cells compared with ShBMSC. Moreover, in a rat OA model, ShFCPC protects articular cartilage by reducing inflammatory cell infiltration and M1/M2 macrophage ratio in the synovium, which directly contributes to an increase in immunomodulatory atmosphere and enhances cartilage repair compared to ShBMSC and HA.

SIGNIFICANCE

Our findings support clinical translations of ShFCPC as a novel agent for modifying OA process.

Conditioned Medium - Is it an Undervalued Lab Waste with the Potential for Osteoarthritis Management?

BACKGROUND

The approaches currently used in osteoarthritis (OA) are mainly short-term solutions with unsatisfactory outcomes. Cell-based therapies are still controversial (in terms of the sources of cells and the results) and require strict culture protocol, quality control, and may have side-effects. A distinct population of stromal cells has an interesting secretome composition that is underrated and commonly ends up as biological waste. Their unique properties could be used to improve the existing techniques due to protective and anti-ageing properties.

SCOPE OF REVIEW

In this review, we seek to outline the advantages of the use of conditioned media (CM) and exosomes, which render them superior to other cell-based methods, and to summarise current information on the composition of CM and their effect on chondrocytes.

MAJOR CONCLUSIONS

CM are obtainable from a variety of mesenchymal stromal cell (MSC) sources, such as adipose tissue, bone marrow and umbilical cord, which is significant to their composition. The components present in CMs include proteins, cytokines, growth factors, chemokines, lipids and ncRNA with a variety of functions. In most in vitro and in vivo studies CM from MSCs had a beneficial effect in enhance processes associated with chondrocyte OA pathomechanism.

GENERAL SIGNIFICANCE

This review summarises the information available in the literature on the function of components most commonly detected in MSC-conditioned media, as well as the effect of CM on OA chondrocytes in in vitro culture. It also highlights the need to standardise protocols for obtaining CM, and to conduct clinical trials to transfer the effects obtained in vitro to human subjects.

Autophagy in the pathogenesis and therapeutic potential of post-traumatic osteoarthritis

Autophagy, as a fundamental mechanism for cellular homeostasis, is generally involved in the occurrence and progression of various diseases. Osteoarthritis (OA) is the most common musculoskeletal disease that often leads to pain, disability and economic loss in patients. Post-traumatic OA (PTOA) is a subtype of OA, accounting for >12% of the overall burden of OA. PTOA is often caused by joint injuries including anterior cruciate ligament rupture, meniscus tear and intra-articular fracture. Although a variety of methods have been developed to treat acute joint injury, the current measures have limited success in effectively reducing the incidence and delaying the progression of PTOA. Therefore, the pathogenesis and intervention strategy of PTOA need further study. In the past decade, the roles and mechanisms of autophagy in PTOA have aroused great interest in the field. It was revealed that autophagy could maintain the homeostasis of chondrocytes, reduce joint inflammatory level, prevent chondrocyte death and matrix degradation, which accordingly improved joint symptoms and delayed the progression of PTOA. Moreover, many strategies that target PTOA have been revealed to promote autophagy. In this review,  we summarize the roles and mechanisms of autophagy in PTOA and the current strategies for PTOA treatment that depend on autophagy regulation, which may be beneficial for PTOA patients in the future.

Lithium-Containing Biomaterials Stimulate Cartilage Repair through Bone Marrow Stromal Cells-Derived Exosomal miR-455-3p and Histone H3 Acetylation

The repair of damaged cartilage still remains a great challenge in clinic. It is demonstrated that bone marrow stromal cells (BMSCs)-chondrocytes communication is of great significance for cartilage repair. Moreover, BMSCs have been confirmed to enhance biological function of chondrocytes via exosome-mediated paracrine pathway. Lithium-containing scaffolds have been reported to effectively promote cartilage regeneration; however, whether lithium-containing biomaterial could facilitate cartilage regeneration through regulating BMSCs-derived exosomes has not been illustrated. In the study, the model lithium-substituted bioglass ceramic (Li-BGC) is selected and regulatory effects of BMSCs-derived exosomes after Li-BGC treatment (Li-BGC-Exo) are systemically evaluated. The data reveal that Li-BGC-Exo notably promotes chondrogenesis, which attributes to the upregulated exosomal miR-455-3p transfer, consequently leads to suppression of histone deacetylase 2 (HDAC2) and enhanced histone H3 acetylation in chondrocytes. Notably, BMSCs-derived exosomes after LiCl treatment (LiCl-Exo) exhibits the similar regulatory effect with Li-BGC-Exo, indicating that the pro-chondrogenesis capability of them is mainly owing to the lithium ions. Furthermore, the in vivo study proves that LiCl-Exo remarkably facilitates cartilage regeneration. The research may provide novel possibility for the intrinsic mechanism of chondrogenesis trigged by lithium-containing biomaterials, and suggests that application of lithium-containing scaffolds may be a promising strategy for cartilage regeneration.

Human Adipose- and Amnion-Derived Mesenchymal Stromal Cells Similarly Mitigate Osteoarthritis Progression in the Dunkin Hartley Guinea Pig

BACKGROUND

Clinical trials are currently underway to investigate the efficacy of intra-articular administration of mesenchymal stromal cells (MSCs) to mitigate osteoarthritis (OA) progression in the knee. Although multiple MSC sources exist, studies have yet to determine whether differences in therapeutic efficacy exist between them.

PURPOSE

To compare the ability of intra-articularly injected adipose-derived MSCs (AD-MSCs) and amnion-derived MSCs (AM-MSCs) to mitigate the progression of knee OA in a small animal model of spontaneous OA, as well as to compare the therapeutic potential of MSCs in hyaluronic acid (HA) and in HA only with saline (OA) controls.

STUDY DESIGN

Controlled laboratory study.

METHODS

Injections of AD-MSCs or AM-MSCs suspended in HA or HA only were performed in the rear stifle joints of 3-month-old Dunkin Hartley guinea pigs (DHGPs). Repeat injections occurred at 2 and 4 months after the initial injection in each animal. Contralateral limbs received saline injections and served as untreated controls. Subsequently, joints were analyzed for osteoarthritic changes of the cartilage and subchondral bone via histologic and biochemical analyses. To evaluate MSC retention time in the joint space, DHGPs received a single intra-articular injection of fluorescently labeled AD-MSCs or AM-MSCs, and the fluorescence intensity was longitudinally tracked via an in vivo imaging system.

RESULTS

No statistically significant differences in outcomes were found when comparing the ability of AD-MSCs and AM-MSCs to mitigate OA. However, the injection of AD-MSCs, AM-MSCs, and HA-only treatments more effectively mitigated cartilage damage compared with that of saline controls by demonstrating higher amounts of cartilage glycosaminoglycan content and improved histological proteoglycan scoring while reducing the percentage of osteophytes present.

CONCLUSION

Intra-articular injection of AD-MSCs, AM-MSCs, or HA only was able to similarly mitigate the progression of cartilage damage and reduce the percentage of osteophytes compared with that of saline controls in the DHGP. However, this study was unable to establish the superiority of AD-MSCs versus AM-MSCs as a treatment to mitigate spontaneous OA.

CLINICAL RELEVANCE

MSCs demonstrate the ability to mitigate the progression of knee OA and thus may be used in a prophylactic approach to delay the need for end-stage treatment strategies.

Current understanding of MSC-derived exosomes in the management of knee osteoarthritis

Mesenchymal stem cell-derived exosomes (MSC-Exos) have been utilized as medicinal agents or as delivery vehicles in cartilage injuries and cartilage-based diseases. Given the ongoing emergence of evidence on the effector mechanisms and methods of the utility of the MSC-Exos in knee osteoarthritis, a comprehensive review of the current evidence is the need of the hour. Hence, in this article, we review the current understanding of the role of MSC-Exos in the management of knee osteoarthritis in view of their classification, characterization, biogenesis, mechanism of action, pathways involved in their therapeutic action, in-vitro evidence on cartilage regeneration, in-vivo evidence in OA knee models and recent advances in using MSC-Exos to better streamline future research from bench to bedside for OA knee.

Engineering of MSC-Derived Exosomes: A Promising Cell-Free Therapy for Osteoarthritis

Osteoarthritis (OA) is characterized by progressive cartilage degeneration with increasing prevalence and unsatisfactory treatment efficacy. Exosomes derived from mesenchymal stem cells play an important role in alleviating OA by promoting cartilage regeneration, inhibiting synovial inflammation and mediating subchondral bone remodeling without the risk of immune rejection and tumorigenesis. However, low yield, weak activity, inefficient targeting ability and unpredictable side effects of natural exosomes have limited their clinical application. At present, various approaches have been applied in exosome engineering to regulate their production and function, such as pretreatment of parental cells, drug loading, genetic engineering and surface modification. Biomaterials have also been proved to facilitate efficient delivery of exosomes and enhance treatment effectiveness. Here, we summarize the current understanding of the biogenesis, isolation and characterization of natural exosomes, and focus on the large-scale production and preparation of engineered exosomes, as well as their therapeutic potential in OA, thus providing novel insights into exploring advanced MSC-derived exosome-based cell-free therapy for the treatment of OA.

Characterization of the Secretome of a Specific Cell Expressing Mutant Methionyl-tRNA Synthetase in Co-Culture Using Click Chemistry

Co-culture system, in which two or more distinct cell types are cultured together, is advantageous in that it can mimic the environment of the in vivo niche of the cells. In this study, we presented a strategy to analyze the secretome of a specific cell type under the co-culture condition in serum-supplemented media. For the cell-specific secretome analysis, we expressed the mouse mutant methionyl-tRNA synthetase for the incorporation of the non-canonical amino acid, azidonorleucine into the newly synthesized proteins in cells of which the secretome is targeted. The azidonorleucine-tagged secretome could be enriched, based on click chemistry, and distinguished from any other contaminating proteins, either from the cell culture media or the other cells co-cultured with the cells of interest. In order to have more reliable true-positive identifications of cell-specific secretory bodies, we established criteria to exclude any identified human peptide matched to bovine proteins. As a result, we identified a maximum of 719 secreted proteins in the secretome analysis under this co-culture condition. Last, we applied this platform to profile the secretome of mesenchymal stem cells and predicted its therapeutic potential on osteoarthritis based on secretome analysis.

Functionalized Hydrogels for Cartilage Repair: The Value of Secretome-Instructive Signaling

Cartilage repair has been a challenge in the medical field for many years. Although treatments that alleviate pain and injury are available, none can effectively regenerate the cartilage. Currently, regenerative medicine and tissue engineering are among the developed strategies to treat cartilage injury. The use of stem cells, associated or not with scaffolds, has shown potential in cartilage regeneration. However, it is currently known that the effect of stem cells occurs mainly through the secretion of paracrine factors that act on local cells. In this review, we will address the use of the secretome—a set of bioactive factors (soluble factors and extracellular vesicles) secreted by the cells—of mesenchymal stem cells as a treatment for cartilage regeneration. We will also discuss methodologies for priming the secretome to enhance the chondroregenerative potential. In addition, considering the difficulty of delivering therapies to the injured cartilage site, we will address works that use hydrogels functionalized with growth factors and secretome components. We aim to show that secretome-functionalized hydrogels can be an exciting approach to cell-free cartilage repair therapy.

The secretion profile of mesenchymal stem cells and potential applications in treating human diseases

Mesenchymal stromal/stem cells (MSCs) possess multi-lineage differentiation and self-renewal potentials. MSCs-based therapies have been widely utilized for the treatment of diverse inflammatory diseases, due to the potent immunoregulatory functions of MSCs. An increasing body of evidence indicates that MSCs exert their therapeutic effects largely through their paracrine actions. Growth factors, cytokines, chemokines, extracellular matrix components, and metabolic products were all found to be functional molecules of MSCs in various therapeutic paradigms. These secretory factors contribute to immune modulation, tissue remodeling, and cellular homeostasis during regeneration. In this review, we summarize and discuss recent advances in our understanding of the secretory behavior of MSCs and the intracellular communication that accounts for their potential in treating human diseases.

Attenuation of osteoarthritis progression through intra-articular injection of a combination of synovial membrane-derived MSCs (SMMSCs), platelet-rich plasma (PRP) and conditioned medium (secretome)

PURPOSE

Osteoarthritis (OA) as a progressive destructive disease of articular cartilage is the most common joint disease characterized by reduction of joint cartilage thickness, demolition of cartilage surface and new bone formation. To overcome these problems, the purpose of the current research was to evaluate and compare the in vivo effects of synovial membrane-derived mesenchymal stem cell (SMMSCs), platelet-rich plasma (PRP) and conditioned medium (secretome) on collagenase II-induced rat knee osteoarthritis (KOA) remedy.

METHODS

For the first step, SMMSCs were isolated and characterized. Also, secretome was collected from SMMSCs culture. Furthermore, PRP was collect from the rat heart venous blood. Second, two injection of collagenase II with an interval of 3 days was performed in the knee intra-articular space to induce osteoarthritis. Two weeks later, animals were randomly divided into 6 groups. Control group without treatment, positive group: taken an intra-articular sodium hyaluronate injection (0.1 ml), treatment groups taken an intra-articular injection of; treatment 1: SMMSCs (5 × 10⁶), treatment 2: SMMSCs (5 × 10⁶)/secretome (50 µl), treatment 3: SMMSCs (5 × 10⁶)/PRP (50 µl), and treatment 4: SMMSCs (5 × 10⁶)/ secretome (50 µl)/ PRP (50 µl). Three months later, rats were killed and the following assessments were executed: radiography, histopathology, and immunohistochemistry.

RESULTS

Our findings represented that a combination of the SMMSCs/secretome/PRP had a considerable effect on glycosaminoglycans (GAGs) and collagen II contents, articular cartilage preservation, compared with other groups. In addition, combination of the SMMSCs with PRP and secretome showed the lowest expression of mmp3, while SOX9 had the highest expression in comparison with other groups. Also, SMMSCs-injected groups demonstrated better results compared with positive and control groups.

CONCLUSIONS

Injecting a combination of the SMMSCs/secretome/PRP resulted in better efficacy in terms of joint space width, articular cartilage surface continuity and integrity, sub-chondral bone and ECM constituents such as collagen II. Indeed, transplantation of this combination could be considered as a preliminary therapy for clinical trial study in the future.

Sec62 promotes gastric cancer metastasis through mediating UPR-induced autophagy activation

BACKGROUND AND AIMS

Sec62 is a membrane protein of the endoplasmic reticulum that facilitates protein transport. Its role in cancer is increasingly recognised, but remains largely unknown. We investigated the functional role of Sec62 in gastric cancer (GC) and its underlying mechanism.

METHODS

Bioinformatics, tissue microarray, immunohistochemistry (IHC), western blotting (WB), quantitative polymerase chain reaction (qPCR), and immunofluorescence were used to examine the expression of target genes. Transwell, scratch healing assays, and xenograft models were used to evaluate cell migration and invasion. Transmission electron microscopy and mRFP-GFP-LC3 double-labeled adenoviruses were used to monitor autophagy. Co-immunoprecipitation (CO-IP) was performed to evaluate the binding activity between the proteins.

RESULTS

Sec62 expression was upregulated in GC, and Sec62 upregulation was an independent predictor of poor prognosis. Sec62 overexpression promoted GC cell migration and invasion both in vitro and in vivo. Sec62 promoted migration and invasion by affecting TIMP-1 and MMP2/9 balance. Moreover, Sec62 could activate autophagy by upregulating PERK/ATF4 expression and binding to LC3II with concomitant FIP200/Beclin-1/Atg5 activation. Furthermore, autophagy blockage impaired the promotive effects of Sec62 on GC cell migration and invasion, whereas autophagy activation rescued the inhibitory effect of Sec62 knockdown on GC metastasis. Notably, Sec62 inhibition combined with autophagy blockage exerted a synergetic anti-metastatic effect in vitro and in vivo.

CONCLUSION

Sec62 promotes GC metastasis by activating autophagy and subsequently regulating TIMP-1 and MMP2/9 balance. The activation of autophagy by Sec62 may involve the unfolded protein response (UPR)-related PERK/ATF4 pathway and binding of LC3II during UPR recovery involving FIP200/Beclin-1/Atg5 upregulation. Specifically, the dual inhibition of Sec62 and autophagy may provide a promising therapeutic strategy for GC metastasis.

Mesenchymal stromal cell-based therapy for cartilage regeneration in knee osteoarthritis

Osteoarthritis, as a degenerative disease, is a common problem and results in high socioeconomic costs and rates of disability. The most commonly affected joint is the knee and characterized by progressive destruction of articular cartilage, loss of extracellular matrix, and progressive inflammation. Mesenchymal stromal cell (MSC)-based therapy has been explored as a new regenerative treatment for knee osteoarthritis in recent years. However, the detailed functions of MSC-based therapy and related mechanism, especially of cartilage regeneration, have not been explained. Hence, this review summarized how to choose, authenticate, and culture different origins of MSCs and derived exosomes. Moreover, clinical application and the latest mechanistical findings of MSC-based therapy in cartilage regeneration were also demonstrated.

Icariin accelerates cartilage defect repair by promoting chondrogenic differentiation of BMSCs under conditions of oxygen-glucose deprivation

This study explored the role played by combined ICA and bone mesenchymal stem cells (BMSCs) in repairing rabbit knee cartilage defects. Firstly, rabbit BMSCs were isolated and used to construct an in vitro cellular model of oxygen‐glucose deprivation/reoxygenation (OGD/R). Subsequently, ICA processing, Alcian blue staining, immunofluorescence and Western blot studies were performed to evaluate the ability of BMSCs to display signs of chondrogenic differentiation. Furthermore, a rabbit knee cartilage injury model was established in vivo. International Cartilage Repair Society (ICRS) macroscopic evaluations, H&E, Alcian blue and EdU staining, as well as immunohistochemistry, were analysed cartilage repair and pathological condition of the knee cartilage tissue. Our in vitro results showed that ICA promoted the chondrogenic differentiation of BMSCs, as well as aggrecan (AGR), bone morphogenetic protein 2 (BMP2) and COL2A1 protein expression in BMSCs. In vivo experiments showed that rabbits in the BMSCs or ICA treatment group had higher ICRS scores and displayed a better restoration of cartilage‐like tissue and chondrocyte expression on the surface of their cartilage defects. In conclusion, ICA or BMSCs alone could repair rabbit knee cartilage damage, and combined treatment with ICA and BMSCs showed a better ability to repair rabbit knee cartilage damage.

Dental Pulp Stem Cell-Derived Secretome and Its Regenerative Potential

The therapeutic potential of the dental pulp stem (DSC) cell-derived secretome, consisting of various biomolecules, is undergoing intense research. Despite promising in vitro and in vivo studies, most DSC secretome-based therapies have not been implemented in human medicine because the paracrine effect of the bioactive factors secreted by human dental pulp stem cells (hDPSCs) and human exfoliated deciduous teeth (SHEDs) is not completely understood. In this review, we outline the current data on the hDPSC- and SHED-derived secretome as a potential candidate in the regeneration of bone, cartilage, and nerve tissue. Published reports demonstrate that the dental MSC-derived secretome/conditional medium may be effective in treating neurodegenerative diseases, neural injuries, cartilage defects, and repairing bone by regulating neuroprotective, anti-inflammatory, antiapoptotic, and angiogenic processes through secretome paracrine mechanisms. Dental MSC-secretomes, similarly to the bone marrow MSC-secretome activate molecular and cellular mechanisms, which determine the effectiveness of cell-free therapy. Many reports emphasize that dental MSC-derived secretomes have potential application in tissue-regenerating therapy due to their multidirectional paracrine effect observed in the therapy of many different injured tissues.

New Generation of Meso and Antiprogestins (SPRMs) into the Osteoporosis Approach

Receptor activator of nuclear factor κB (RANK) and its ligand (RANKL) play key roles in bone metabolism and the immune system. The RANK/RANKL complex has also been shown to be critical in the formation of mammary epithelia cells. The female hormones estradiol and progesterone closely control the action of RANKL with RANK. Blood concentration of these sex hormones in the postmenopausal period leads to an increase in RANK/RANKL signaling and are a major cause of women's osteoporosis, characterized by altered bone mineralization. Knowledge of the biochemical relationships between hormones and RANK/RANKL signaling provides the opportunity to design novel therapeutic agents to inhibit bone loss, based on the anti-RANKL treatment and inhibition of its interaction with the RANK receptor. The new generation of both anti- and mesoprogestins that inhibit the NF-κB-cyclin D1 axis and blocks the binding of RANKL to RANK can be considered as a potential source of new RANK receptor ligands with anti-RANKL function, which may provide a new perspective into osteoporosis treatment itself as well as limit the osteoporosis rise during breast cancer metastasis to the bone.

Beneficial effects of secretome derived from mesenchymal stem cells with stigmasterol to negate IL-1β-induced inflammation in-vitro using rat chondrocytes-OA management

Osteoarthritis (OA) is the most prevalent joint disease predominantly characterized by inflammation which drives cartilage destruction. Mesenchymal stem cells-condition medium (MSC-CM) or the secretome is enriched with bioactive factors and possesses anti-inflammatory and regenerative effects. The present study aimed at evaluating the effects of combining MSC-conditioned medium with stigmasterol compared with the individual treatments in alleviating interleukin-1 beta (IL-1β)-induced inflammation in rat chondrocytes. Stigmasterol is a phytosterol exhibiting anti-inflammatory effects. IL-1β (10 ng/ml) was used to induce inflammation and mimic OA in-vitro in primary rat articular chondrocytes. The IL-1β-stimulated chondrocytes were treated with MSC-CM, stigmasterol, and a combination of MSC-CM and stigmasterol for 24 h. Cell viability was measured using MTT assay. Protein expression of inducible nitric oxide synthase (iNOS), interleukin-6 (IL-6), collagen II (COL2A1) and matrix metalloproteinase (MMP)-13 were evaluated by immunofluorescence. Gene expression levels of MMP-3, MMP-13 and A Disintegrin-like and Metalloproteinases with Thrombospondin Motifs (ADAMTS)-5 were measured using qRT-PCR. NF-κB signaling pathway was studied using western blotting. A significant reduction in the expression of iNOS, IL-6, MMP-3, MMP-13 and ADAMTS-5, and a significant increase in COL2A1 expression was observed in the rat chondrocytes across all the treatment groups. However, the combination treatment of MSC-CM and stigmasterol remarkably reversed the IL-1β-induced pro-inflammatory/pro-catabolic responses to near normal levels comparable to the control group. The combination treatment (MSC-CM + stigmasterol) elicited a superior anti-inflammatory/anti-catabolic effect by inhibiting the IL-1β-induced NF-κB activation evidenced by the negligible phosphorylation of p65 and IκBα subunits, thereby emphasizing the benefit of the combination therapy over the individual treatments.

The role of inflammation in mesenchymal stromal cell therapy in osteoarthritis, perspectives for post-traumatic osteoarthritis: a review

OA is a complex and highly prevalent degenerative disease affecting the whole joint, in which factors like genetic predisposition, gender, age, obesity and traumas contribute to joint destruction. ∼50-80% of OA patients develop synovitis. OA-associated risk factors contribute to joint instability and the release of cartilage matrix fragments, activating the synovium to release pro-inflammatory factors and catabolic enzymes in turn damaging the cartilage and creating a vicious circle. Currently, no cure is available for OA. Mesenchymal stromal cells (MSCs) have been tested in OA for their chondrogenic and anti-inflammatory properties. Interestingly, MSCs are most effective when administered during synovitis. This review focusses on the interplay between joint inflammation and the immunomodulation by MSCs in OA. We discuss the potential of MSCs to break the vicious circle of inflammation and describe current perspectives and challenges for clinical application of MSCs in treatment and prevention of OA, focussing on preventing post-traumatic OA.

Proteomic Analysis Reveals Commonly Secreted Proteins of Mesenchymal Stem Cells Derived from Bone Marrow, Adipose Tissue, and Synovial Membrane to Show Potential for Cartilage Regeneration in Knee Osteoarthritis

Paracrine factors secreted by mesenchymal stem cells (MSCs) reportedly modulate inflammation and reparative processes in damaged tissues and have been explored for knee osteoarthritis (OA) therapy. Although various studies have reported the effects of paracrine factors in knee OA, it is not yet clear which paracrine factors directly affect the regeneration of damaged cartilage and which are secreted under various knee OA conditions. In this study, we cultured MSCs derived from three types of tissues and treated each type with IL-1β and TNF-α or not to obtain conditioned medium. Each conditioned medium was used to analyse the paracrine factors related to cartilage regeneration using liquid chromatography-tandem mass spectrometry. Bone marrow-, adipose tissue-, and synovial membrane-MSCs (all-MSCs) exhibited expression of 93 proteins under normal conditions and 105 proteins under inflammatory conditions. It was confirmed that the types of secreted proteins differed depending on the environmental conditions, and the proteins were validated using ELISA. The results of Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analysis using a list of proteins secreted by all-MSCs under each condition confirmed that the secreted proteins were closely related to cartilage repair under inflammatory conditions. Protein-protein interaction networks were confirmed to change depending on environmental differences and were found to enhance the secretion of paracrine factors related to cartilage regeneration under inflammatory conditions. In conclusion, our results demonstrated that compared with knee OA conditions, the differential expression proteins may contribute to the regeneration of damaged cartilage. In addition, the detailed information on commonly secreted proteins by all-MSCs provides a comprehensive basis for understanding the potential of paracrine factors to influence tissue repair and regeneration in knee OA.

Mesenchymal stem cells and extracellular vesicles for the treatment of pain: Current status and perspectives

Mesenchymal stem/stromal cells (MSCs) are multipotent progenitor cells of mesodermal origin. Due to their capacity for self-renewal and differentiation into several cell types, MSCs have been extensively studied in experimental biology and regenerative medicine in recent years. Moreover, MSCs release extracellular vesicles (EVs), which might be partly responsible for their regenerative properties. MSCs regulate several processes in target cells via paracrine signalling, such as immunomodulation, anti-apoptotic signalling, tissue remodelling, angiogenesis and anti-fibrotic signalling. The aim of this review is to provide a detailed description of the functional properties of MSCs and EVs and their potential clinical applications, with a special focus on pain treatment. The analgesic, anti-inflammatory and regenerative properties of MSCs and EVs will be discussed for several diseases, such as neuropathic pain, osteoarthritis and spinal cord injury.

Is Extracellular Vesicle-Based Therapy the Next Answer for Cartilage Regeneration?

"Extracellular vesicles" (EVs) is a term gathering biological particles released from cells that act as messengers for cell-to-cell communication. Like cells, EVs have a membrane with a lipid bilayer, but unlike these latter, they have no nucleus and consequently cannot replicate. Several EV subtypes (e.g., exosomes, microvesicles) are described in the literature. However, the remaining lack of consensus on their specific markers prevents sometimes the full knowledge of their biogenesis pathway, causing the authors to focus on their biological effects and not their origins. EV signals depend on their cargo, which can be naturally sourced or altered (e.g., cell engineering). The ability for regeneration of adult articular cartilage is limited because this avascular tissue is partly made of chondrocytes with a poor proliferation rate and migration capacity. Mesenchymal stem cells (MSCs) had been extensively used in numerous in vitro and preclinical animal models for cartilage regeneration, and it has been demonstrated that their therapeutic effects are due to paracrine mechanisms involving EVs. Hence, using MSC-derived EVs as cell-free therapy tools has become a new therapeutic approach to improve regenerative medicine. EV-based therapy seems to show similar cartilage regenerative potential compared with stem cell transplantation without the associated hindrances (e.g., chromosomal aberrations, immunogenicity). The aim of this short review is to take stock of occurring EV-based treatments for cartilage regeneration according to their healing effects. The article focuses on cartilage regeneration through various sources used to isolate EVs (mature or stem cells among others) and beneficial effects depending on cargos produced from natural or tuned EVs.

ADAMTS5 is required for normal trabeculated bone development in the mandibular condyle

OBJECTIVE

Determine the role of the extracellular matrix protease ADAMTS5 in development of the trabeculated bone of the mandibular condyle.

METHODS

The mandibular condyles of wild type and mice deficient in the protease ADAMTS5 were examined for histopathology with Safranin O staining. Microcomputed tomography was performed to analyze the developing bone of the mandibular condyle. RNAscope and immunohistochemistry were utilized to investigate cell type and extracellular matrix expression.

RESULTS

Mice deficient in Adamts5, (Adamts5tm1Dgen/J) exhibit an increase in trabecular separation (n = 37 wild type; n = 27: P < 0.0001) and reduction of trabecular thickness P = 0.0116 and bone volume fraction P = 0.0869 in the mandibular condylar head compared to wild type littermates. The altered bone parameters were more pronounced in male Adamts5-/- mice compared to female Adamts5-/- mice (TbSp; P = 0.03). Adamts5 was co-expressed with versican and Gli1 in mesenchymal, stem-like cells in the transition zone where the trabeculated bone is adjacent to mature hypertrophic chondrocytes. Loss of Adamts5 caused a reduction of Bglap expressing osteoblasts throughout mandibular condylar development and in young adult mice. The protease Mmp13, that is involved in mineralization and is expressed by hypertrophic chondrocytes and osteoblasts, was reduced in the mandibular condyle of Adamts5 deficient mice.

CONCLUSION

This is the first report of a novel and critical role for Adamts5 in bone formation within the mandibular condyle of the temporomandibular joint. These data indicate Adamts5 may be required in the transdifferentiation of hypertrophic chondrocytes to osteoblasts during trabecular bone formation in development of the mandibular condyle.

Mesenchymal stem/stromal cells as a valuable source for the treatment of immune-mediated disorders

Over recent years, mesenchymal stem/stromal cells (MSCs) and their potential biomedical applications have received much attention from the global scientific community in an increasing manner. Firstly, MSCs were successfully isolated from human bone marrow (BM), but in the next steps, they were also extracted from other sources, mostly from the umbilical cord (UC) and adipose tissue (AT). The International Society for Cellular Therapy (ISCT) has suggested minimum criteria to identify and characterize MSCs as follows: plastic adherence, surface expression of CD73, D90, CD105 in the lack of expression of CD14, CD34, CD45, and human leucocyte antigen-DR (HLA-DR), and also the capability to differentiate to multiple cell types including adipocyte, chondrocyte, or osteoblast in vitro depends on culture conditions. However, these distinct properties, including self-renewability, multipotency, and easy accessibility are just one side of the coin; another side is their huge secretome which is comprised of hundreds of mediators, cytokines, and signaling molecules and can effectively modulate the inflammatory responses and control the infiltration process that finally leads to a regulated tissue repair/healing or regeneration process. MSC-mediated immunomodulation is a direct result of a harmonic synergy of MSC-released signaling molecules (i.e., mediators, cytokines, and chemokines), the reaction of immune cells and other target cells to those molecules, and also feedback in the MSC-molecule-target cell axis. These features make MSCs a respectable and eligible therapeutic candidate to be evaluated in immune-mediated disorders, such as graft versus host diseases (GVHD), multiple sclerosis (MS), Crohn's disease (CD), and osteoarthritis (OA), and even in immune-dysregulating infectious diseases such as the novel coronavirus disease 2019 (COVID-19). This paper discussed the therapeutic applications of MSC secretome and its biomedical aspects related to immune-mediated conditions. Sources for MSC extraction, their migration and homing properties, therapeutic molecules released by MSCs, and the pathways and molecular mechanisms possibly involved in the exceptional immunoregulatory competence of MSCs were discussed. Besides, the novel discoveries and recent findings on immunomodulatory plasticity of MSCs, clinical applications, and the methods required for their use as an effective therapeutic option in patients with immune-mediated/immune-dysregulating diseases were highlighted.

Conditioned medium from mesenchymal stem cells improves condylar resorption induced by mandibular distraction osteogenesis in a rat model

Condylar resorption (CR) after surgical orthognathic treatment is defined as dysfunctional remodeling of the temporomandibular joint manifested by morphological changes with decreased condylar head volume that cause occlusal and esthetic changes. Although both conservative and surgical treatment strategies have been employed for the treatment of CR, effective procedures have not been established till date. In this study, the effects of MSC-CM on CR were investigated. Bone marrow-derived MSCs of rats (rMSCs) were cultured until 80% confluent, cultured in serum-free conditioned medium for 48 h; the collected medium was defined as MSC-CM. Osteogenesis, chondrogenesis, and angiogenesis-related gene expression in rMSCs cultured with MSC-CM was evaluated by quantitative real-time polymerase chain reaction. A rat CR model was used for animal studies, in which CR occurred after mandibular distraction osteogenesis for 10 days. MSC-CM was injected via the tail vein and quantitative and qualitative evaluations were performed by micro-computed tomography (micro-CT) and histology.

MSC-CM enhanced osteogenesis-, chondrogenesis-, and angiogenesis-related gene expression in rMSCs. Micro-CT showed CR in control groups; however, it was observed to be improved in the MSC-CM group. Histologically, an enlarged cartilage layer was seen in the MSC-CM group, while cartilage layers had almost thinned or disappeared in control groups. These results indicate that MSC-CM improved CR.

Research Progress on Stem Cell Therapies for Articular Cartilage Regeneration

Injury of articular cartilage can cause osteoarthritis and seriously affect the physical and mental health of patients. Unfortunately, current surgical treatment techniques that are commonly used in the clinic cannot regenerate articular cartilage. Regenerative medicine involving stem cells has entered a new stage and is considered the most promising way to regenerate articular cartilage. In terms of theories on the mechanism, it was thought that stem cell-mediated articular cartilage regeneration was achieved through the directional differentiation of stem cells into chondrocytes. However, recent evidence has shown that the stem cell secretome plays an important role in biological processes such as the immune response, inflammation regulation, and drug delivery. At the same time, the stem cell secretome can effectively mediate the process of tissue regeneration. This new theory has attributed the therapeutic effect of stem cells to their paracrine effects. The application of stem cells is not limited to exogenous stem cell transplantation. Endogenous stem cell homing and in situ regeneration strategies have received extensive attention. The application of stem cell derivatives, such as conditioned media, extracellular vesicles, and extracellular matrix, is an extension of stem cell paracrine theory. On the other hand, stem cell pretreatment strategies have also shown promising therapeutic effects. This article will systematically review the latest developments in these areas, summarize challenges in articular cartilage regeneration strategies involving stem cells, and describe prospects for future development.

Conditioned medium of human bone marrow-derived stem cells promotes tendon-bone healing of the rotator cuff in a rat model

Rotator cuff repair is a common surgery in sports medicine. During the surgery, torn tendon was re-fixed onto the bony surface. The majority of patients gain good results. However, re-tear occurs in some patients. The reason under this phenomenon is that the normal tendon-bone enthesis cannot be reconstructed. In order to strengthen the tendon-bone healing and promote enthesis regeneration, numerous manners are tested, among which stem cell related therapies are preferred. Stem cells, due to the ability of multi-lineage differentiation, are widely used in regenerative medicine. However, safety and ethics concerns limit its clinical use. Recent studies found that it is the secretome of stem cells that is biologically effective. On ground of this, we, in the current study, collected the conditioned medium of human bone marrow-derived stem cells (hBMSC-CM) and tested whether this acellular method could promote tendon-bone healing in a rat model of rotator cuff repair. By using histological, radiological, and biomechanical methods, we found that hBMSC-CM promoted tendon-bone healing of the rat rotator cuff. Then, we noticed that hBMSC-CM exerted an impact on macrophage polarization both in vivo and in vitro by inhibiting M1 phenotype and promoting M2 phenotype. Further, we proved that the benefit of hBMSC-CM on tendon-bone healing was related to its regulation on macrophage. Finally, we proved that, hBMSC-CM influenced macrophage polarization, which was, at least partially, related to Smad2/3 signaling pathway. Based on the experiments above, we confirmed the benefit of hBMSC-CM on tendon-bone healing, which relied on its immune-regulative property. Considering the accessibility and safety of acellular hBMSC-CM, we believe it is a promising candidate clinically for tendon-bone healing.

Electrospun fibers enhanced the paracrine signaling of mesenchymal stem cells for cartilage regeneration

BACKGROUND

Secretome profiles of mesenchymal stem cells (MSCs) are reflective of their local microenvironments. These biologically active factors exert an impact on the surrounding cells, eliciting regenerative responses that create an opportunity for exploiting MSCs towards a cell-free therapy for cartilage regeneration. The conventional method of culturing MSCs on a tissue culture plate (TCP) does not provide the physiological microenvironment for optimum secretome production. In this study, we explored the potential of electrospun fiber sheets with specific orientation in influencing the MSC secretome production and its therapeutic value in repairing cartilage.

METHODS

Conditioned media (CM) were generated from MSCs cultured either on TCP or electrospun fiber sheets of distinct aligned or random fiber orientation. The paracrine potential of CM in affecting chondrogenic differentiation, migration, proliferation, inflammatory modulation, and survival of MSCs and chondrocytes was assessed. The involvement of FAK and ERK mechanotransduction pathways in modulating MSC secretome were also investigated.

RESULTS

We showed that conditioned media of MSCs cultured on electrospun fiber sheets compared to that generated from TCP have improved secretome yield and profile, which enhanced the migration and proliferation of MSCs and chondrocytes, promoted MSC chondrogenesis, mitigated inflammation in both MSCs and chondrocytes, as well as protected chondrocytes from apoptosis. Amongst the fiber sheet-generated CM, aligned fiber-generated CM (ACM) was better at promoting cell proliferation and augmenting MSC chondrogenesis, while randomly oriented fiber-generated CM (RCM) was more efficient in mitigating the inflammation assault. FAK and ERK signalings were shown to participate in the modulation of MSC morphology and its secretome production.

CONCLUSIONS

This study demonstrates topographical-dependent MSC paracrine activities and the potential of employing electrospun fiber sheets to improve the MSC secretome for cartilage regeneration.

Bone Marrow Stromal Cell-Derived Exosomes Promote Muscle Healing Following Contusion Through Macrophage Polarization

Skeletal muscle contusion is among the most common injuries in traumatology and clinics of sports medicine. The injured muscle is vulnerable to re-injury owing to fibrosis formation. Given that the bone marrow stromal cell-derived exosomes (BMSC-Exos) displayed promising therapeutic effect for various tissues, we used BMSC-Exos to treat skeletal muscle contusion and investigated its effects on muscle healing. In this study, the in vivo model of skeletal muscle contusion was established by subjecting the tibialis anterior of young male mice to hit injury, and the in vitro inflammation model was established by lipopolysaccharide treatment on macrophages. Macrophage depletion model was built by intraperitoneal injection with clodronate-containing liposomes. Exosomes were isolated and purified from the supernatant of BMSCs using gradient centrifugation. Nanoparticle tracking analysis, transmission electron microscope, and western blot were used to identify the exosomes. HE stain, Masson stain, immunofluorescence, and biomechanical testing were carried out on the muscle tissue. In addition, enzyme-linked immunosorbent assay (ELISA) assays, real-time qPCR, flow cytometry, and PKH67 fluorescence trace were conducted in vitro. Intramuscular injection of BMSC-Exos to mice after muscle contusion alleviated inflammation level, reduced fibrosis size, promoted muscle regeneration, and improved biomechanical property. After macrophages depletion, the effects of BMSC-Exos were inhibited. In vitro, PKH-67 fluorescence was internalized into macrophages. BMSC-Exos promoted M2 macrophages polarization both in vivo and in vitro. At the same time, BMSC-Exos reduced the production of inflammatory cytokines under the inflammatory microenvironment and upregulated anti-inflammatory factors expression. In conclusion, BMSC-Exos attenuated muscle contusion injury and promoted muscle healing in mice by modifying the polarization status of macrophages and suppressing the inflammatory reaction.

Osteoarthritis year in review 2020: biology

This year in review about osteoarthritis biology highlights a selection of articles published between the 2019 and 2020 Osteoarthritis Research Society International (OARSI) World Congress meetings, within the field of osteoarthritis biology. Highlights were selected from PubMed searches covering osteoarthritis (OA) cartilage, subchondral bone, synovium and aging. Subsequently, a personal selection was based on new and emerging themes together with common research topics that were studied by multiple groups. Themes discussed include novel insights into the inflammatory changes during OA, with a number of noteworthy publications concerning the role of macrophages in healthy and osteoarthritic joints. Next, the application of mesenchymal stem cells as OA-dampening therapy is discussed, including possible ways to improve their efficacy by pre-treatment. Other significant themes including treatment of OA with metformin, enhancing autophagy to alleviate OA and the involvement of the gastro-intestinal microbiome in development of OA symptoms and structural damage are discussed. An effort was made to connect the seemingly distant topics from which the overarching conclusion can be drawn that over the last year promising breakthroughs have been achieved in further understanding the biology of OA development and that new therapeutic possibilities have been explored.

The Serum from Patients with Secondary Frozen Shoulder Following Rotator Cuff Repair Induces Shoulder Capsule Fibrosis and Promotes Macrophage Polarization and Fibroblast Activation

PURPOSE

Disorders with systematic inflammation were prognostic for secondary frozen shoulder (sFS) following rotator cuff repair (RCR); however, how systematic inflammation affects sFS remains unclear. The aim of this study was to observe the effect of pre-operative serum from patients with sFS and the serum from those without on shoulder capsule in mice, and on macrophages and fibroblasts in vitro.

METHODS

Serum samples of a consecutive cohort of patients for RCR were collected pre-operatively. Three months after RCR, patients who developed sFS (Group S) were identified. Serum samples from gender- and age-matched controls without sFS (group NS) were also picked out. Firstly, the effect of serum on shoulder capsule fibrosis was observed histologically and biomechanically in a mouse model of RCR. Secondly, the roles of the serum on macrophage polarization and fibroblast activation were investigated, and the potentially involved signaling pathways were identified. Finally, inflammation and fibrosis-related cytokines in serum were quantified.

RESULTS

In our cohort, all patients had free pre-operative shoulder range of motion. Seven patients developed sFS at 3 months after surgery. Seven matched patients without sFS were selected as control. The inter-group difference of basic characteristics was not significant. Compared to the serum of group NS, the serum of group S significantly induced hypercellularity, capsular thickening, and range of motion deficiency in mice shoulders after RCR. Compared to the serum of group NS, samples of group S significantly promoted M2 polarization of THP-1 human macrophages and the activation of human capsule-derived fibroblasts. Meanwhile, Smad3 and p-Smad3 in macrophages and fibroblasts were significantly up-regulated. On the other hand, levels of inflammation and fibrosis-related cytokines were not significantly different between serum in group S and group NS.

CONCLUSION

Although all patients in this cohort had free range of motion pre-operatively, the pre-operative serum from patients with sFS at 3 months after RCR could act as a trigger of shoulder capsule fibrosis post-operatively. This effect may be related to its promotion on macrophage polarization to M2 phenotype and fibroblast activation.

Molecular Crosstalk Between Macrophages and Mesenchymal Stromal Cells

Mesenchymal stromal cells (MSCs) have been widely investigated for regenerative medicine applications, from treating various inflammatory diseases as a cell therapy to generating engineered tissue constructs. Numerous studies have evaluated the potential effects of MSCs following therapeutic administration. By responding to their surrounding microenvironment, MSCs may mediate immunomodulatory effects through various mechanisms that directly (i.e., contact-dependent) or indirectly (i.e., paracrine activity) alter the physiology of endogenous cells in various disease pathologies. More specifically, a pivotal crosstalk between MSCs and tissue-resident macrophages and monocytes (TMφ) has been elucidated using in vitro and in vivo preclinical studies. An improved understanding of this crosstalk could help elucidate potential mechanisms of action (MOAs) of therapeutically administered MSCs. TMφ, by nature of their remarkable functional plasticity and prevalence within the body, are uniquely positioned as critical modulators of the immune system - not only in maintaining homeostasis but also during pathogenesis. This has prompted further exploration into the cellular and molecular alterations to TMφ mediated by MSCs. In vitro assays and in vivo preclinical trials have identified key interactions mediated by MSCs that polarize the responses of TMφ from a pro-inflammatory (i.e., classical activation) to a more anti-inflammatory/reparative (i.e., alternative activation) phenotype and function. In this review, we describe physiological and pathological TMφ functions in response to various stimuli and discuss the evidence that suggest specific mechanisms through which MSCs may modulate TMφ phenotypes and functions, including paracrine interactions (e.g., secretome and extracellular vesicles), nanotube-mediated intercellular exchange, bioenergetics, and engulfment by macrophages. Continued efforts to elucidate this pivotal crosstalk may offer an improved understanding of the immunomodulatory capacity of MSCs and inform the development and testing of potential MOAs to support the therapeutic use of MSCs and MSC-derived products in various diseases.

Endogenous cell recruitment strategy for articular cartilage regeneration

In the absence of timely and proper treatments, injuries to articular cartilage (AC) can lead to cartilage degeneration and ultimately result in osteoarthritis. Regenerative medicine and tissue engineering techniques are emerging as promising approaches for AC regeneration and repair. Although the use of cell-seeded scaffolds prior to implantation can regenerate and repair cartilage lesions to some extent, these approaches are still restricted by limited cell sources, excessive costs, risks of disease transmission and complex manufacturing practices. Recently developed acellular scaffold approaches that rely on the recruitment of endogenous cells to the injured sites avoid these drawbacks and offer great promise for in situ AC regeneration. Multiple endogenous stem/progenitor cells (ESPCs) are found in joint-resident niches and have the capability to migrate to sites of injury to participate in AC regeneration. However, the natural recruitment of ESPCs is insufficient, and the local microenvironment is hostile after injury. Hence, an endogenous cell recruitment strategy based on the combination of chemoattractants and acellular scaffolds to effectively and specifically recruit ESPCs and improve local microenvironment may provide new insights into in situ AC regeneration. This review provides a brief overview of: (1) the status of endogenous cell recruitment strategy; (2) the subpopulations, potential migration routes (PMRs) of joint-resident ESPCs and their immunomodulatory and reparative effects; (3) chemoattractants and their potential adverse effects; (4) scaffold-based drug delivery systems (SDDSs) that are utilized for in situ AC regeneration; and (5) the challenges and future perspectives of endogenous cell recruitment strategy for AC regeneration. STATEMENT OF SIGNIFICANCE: Although the endogenous cell recruitment strategy for articular cartilage (AC) regeneration has been investigated for several decades, much work remains to be performed in this field. Future studies should have the following aims: (1) reporting the up-to-date progress in the endogenous cell recruitment strategies; (2) determining the subpopulations of ESPCs, the cellular and molecular mechanisms underlying the migration of these cells and their anti-inflammatory, immunomodulatory and reparative effects; (3) elucidating the chemoattractants that enhance ESPC recruitment and their potential adverse effects; and (4) developing advanced SDDSs for chemoattractant dispatch. Herein, we present a systematic overview of the aforementioned issues to provide a better understanding of endogenous cell recruitment strategies for AC regeneration and repair.

Human Levels of MMP-1 in Degenerated Disks Can Be Mitigated by Signaling Peptides from Mesenchymal Stem Cells

Degradation of extracellular matrix (ECM) in intervertebral disks (IVDs) during IVD degeneration plays a vital role in low back pain (LBP). In healthy IVDs, synthesis and degradation of ECM are kept in balance by matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs. MMPs are enzymes responsible for ECM degradation, and their expression levels are known to increase in degenerated disks. However, the exact pathophysiological concentration of MMP-1 in the degenerated disks of patients with chronic LBP has not been reported previously. Factors secreted by human mesenchymal stem cells (hMSCs) have shown positive results in cell therapy of degenerated disks. The aim of this study was to investigate the pathophysiological MMP-1 concentration (in ng/mL) in degenerated disk tissue and to evaluate if conditioned media (CM) from hMSCs could mitigate the effects of MMP-1 at the detected levels in a 3D in vitro disk cell (DC) pellet model. Tissue levels of MMP-1 were quantified in disk tissue collected from 6 chronic LBP patients undergoing surgery. DC pellet cultures were performed to investigate the effects of MMP-1 alone and the effects of conditioned media (CM) in the presence of MMP-1. MMP-1 was introduced in the pellets on day 14 at concentrations of 5, 50, or 100 ng/mL. The pellets were harvested on day 28 and evaluated for cell viability, proliferation, and ECM production. The mean concentration of MMP-1 in disk tissue was 151 ng/mL. Results from pellet cultures demonstrated a higher number of viable cells, glycosaminoglycan production, and ECM accumulation in the CM group even in the presence of MMP-1 compared to the controls. However, the level decreased with increasing MMP-1 concentration. The results demonstrated that CM has the ability to mitigate matrix degradation property of MMP-1 up to 50 ng/mL suggesting that CM could potentially be used to treat early stages of disk degeneration.

The Role of Autophagy and Mitophagy in Bone Metabolic Disorders

Bone metabolic disorders include osteolysis, osteoporosis, osteoarthritis and rheumatoid arthritis. Osteoblasts and osteoclasts are two major types of cells in bone constituting homeostasis. The imbalance between bone formation by osteoblasts and bone resorption by osteoclasts has been shown to have a direct contribution to the onset of these diseases. Recent evidence indicates that autophagy and mitophagy, the selective autophagy of mitochondria, may play a vital role in regulating the proliferation, differentiation and function of osteoblasts and osteoclasts. Several signaling pathways, including PINK1/Parkin, SIRT1, MAPK8/FOXO3, Beclin-1/BECN1, p62/SQSTM1, and mTOR pathways, have been implied in the regulation of autophagy and mitophagy in these cells. Here we review the current progress about the regulation of autophagy and mitophagy in osteoblasts and osteoclasts in these bone metabolic disorders, as well as the molecular signaling activated or deactivated during this process. Together, we hope to draw attention to the role of autophagy and mitophagy in bone metabolic disorders, and their potential as a new target for the treatment of bone metabolic diseases and the requirements of further mechanism studies.

Novel Aptamer-Functionalized Nanoparticles Enhances Bone Defect Repair By Improving Stem Cell Recruitment

BACKGROUND

The restoration and repair method in the clinic of delayed fracture healing and non-union after comminuted fractures are urgently needed to improve the prognosis of patients. The recruitment of endogenous stem cells has been considered a promising approach in bone defect repair.

PROPOSE

The aim of this study was to generate a de novel MSCs aptamer and developed the first, feasible, economical, bio-compatible, and functional MSCs aptamer-directed nanoparticles without complex manufacture to recruit mesenchymal stem cells (MSCs) for bone defect regeneration.

METHODS

Whole-cell SELEX was used to generate a de novel MSCs aptamer. Flow cytometry was applied to assess the binding specificities, affinities and sorting abilities of the aptamers. Nano-Aptamer Ball (NAB) was constructed by NHS/EDC reaction. The diameter and zeta of NAB were assessed by dynamic light scattering. CCK8 assay was utilized to evaluate whether NAB could cause non-specific cytotoxicity and induce cell proliferation. To evaluate the bone repair capacity of NAB, histomorphological staining, alizarin red and micro X-ray were used to observe the repair degree of defect in vivo. ELISA was used to detect osteopontin (OPN), osteocalcin (BGP) by, and alkaline phosphatase (ALP) in peripheral blood.

RESULTS

MSCs aptamer termed as HM69 could bind with MSCs with high specificity and Kd of 9.67 nM, while has minimal cross-reactivities to other negative cells. HM69 could capture MSCs with a purity of >89%. In vitro, NAB could bind and capture MSCs effectively, whereas did not cause obvious cytotoxicity. In vivo, serum OPN, BGP, and ALP levels in the NAB group of rats were increased at both 2 and 4 weeks, indicating the repair and osteogenesis generation. The healing of bone defects in the NAB group was significantly better than control groups, the defects became blurred, and local trabecular bone growth could be observed in X-ray. The organized hematoma and cell growth in the bone marrow of the NAB group were more vigorous in bone sections staining.

CONCLUSION

These suggested that HM69 and HM69-functionalized nanoparticles NAB exhibited the ability to recruit MSCs both in vitro and in vivo and achieved a better outcome of bone defect repair in a rat model. The findings demonstrate a promising strategy of using aptamer-functionalized bio-nanoparticles for the restoration of bone defects via aptamer-introduced homing of MSCs.