Hypoxia Pretreatment Promotes Chondrocyte Differentiation of Human Adipose-Derived Stem Cells via Vascular Endothelial Growth Factor

NPTX1 Mediates the Facilitating Effects of Hypoxia-Stimulated Human Adipocytes on Adipose-Derived Stem Cell Activation and Autologous Adipose Graft Survival Rate

BACKGROUND

Autologous adipose tissue is an ideal material for soft tissue filling and transplantation; however, high volumes of fat absorption over time lead to a relatively low overall survival percentage. The survival and differentiation of adipose-derived stem cells (ADSCs) in the transplanted microenvironment might improve adipose graft survival. Adipocytes have been reported to affect ADSC activation. However, its underlying mechanisms remain unclear.

METHODS

Human ADSCs were incubated in a culture medium supplemented with hypoxic or normoxic conditioned culture medium (CM) derived from human adipocytes. Neuronal Pentraxin 1 (NPTX1) was overexpressed or knocked down in human adipocytes using an overexpression vector (NPTX1 OE) or small interfering RNA (siRNA) transfection, respectively. ADSC differentiation and paracrine secretion were assessed. Nude mice were implanted with human adipocytes and ADSCs. The adipose tissue was subsequently evaluated by histological analysis.

RESULTS

CM from hypoxic-stimulated human adipocytes significantly facilitated the differentiation ability and paracrine levels of ADSCs. NPTX1 was significantly up-regulated in human adipocytes exposed to hypoxic conditions. In vitro, CM derived from hypoxia-stimulated human adipocytes or NPTX1-overexpressing human adipocytes exposed to normoxia promoted ADSC differentiation and paracrine; after silencing NPTX1, the facilitating effects of hypoxia-treated human adipocytes on ADSC activation were eliminated. Similarly, in vivo, the NPTX1 OE + normoxia-CM group saw improved histological morphology and fat integrity, less fibrosis and inflammation, and increased vessel numbers compared with the OE NC + normoxia-CM group; the adipocyte grafts of the si-NC + hypoxia-CM group yielded the most improved histological morphology, fat integrity, and the most vessel numbers. However, these enhancements of ADSC activation and adipose graft survival were partially abolished by NPTX1 knockdown in human adipocytes.

CONCLUSION

NPTX1 might mediate the facilitating effects of hypoxia-stimulated human adipocytes on ADSC activation, thereby improving adipose tissue survival rate after autologous fat transplantation and the effectiveness of autologous fat transplantation through promoting ADSC activation.

LEVEL OF EVIDENCE III

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Multiple pretreatments can effectively improve the functionality of mesenchymal stem cells

In this editorial, we offer our perspective on the groundbreaking study entitled "Hypoxia and inflammatory factor preconditioning enhances the immunosuppressive properties of human umbilical cord mesenchymal stem cells", recently published in World Journal of Stem Cells. Despite over three decades of research on the clinical application of mesenchymal stem cells (MSCs), only a few therapeutic products have made it to clinical use, due to multiple preclinical and clinical challenges yet to be addressed. The study proved the hypoxia and inflammatory factor preconditioning led to higher immunosuppressive effects of MSCs without damaging their biological characteristics, which revealed the combination of inflammatory factors and hypoxic preconditioning offers a promising approach to enhance the function of MSCs. As we delve deeper into the intricacies of pretreatment methodologies, we anticipate a transformative shift in the landscape of MSC-based therapies, ultimately contributing to improved patient outcomes and advancing the field as a whole.

Hypoxia and Hypoxia Mimetic Agents As Potential Priming Approaches to Empower Mesenchymal Stem Cells

Mesenchymal stem cells (MSC) exhibit self-renewal capacity and multilineage differentiation potential, making them attractive for research and clinical application. The properties of MSC can vary depending on specific micro-environmental factors. MSC resides in specific niches with low oxygen concentrations, where oxygen functions as a metabolic substrate and a signaling molecule. Conventional physical incubators or chemically hypoxia mimetic agents are applied in cultures to mimic the original low oxygen tension settings where MSC originated. This review aims to focus on the current knowledge of the effects of various physical hypoxic conditions and widely used hypoxia-mimetic agents-PHD inhibitors on mesenchymal stem cells at a cellular and molecular level, including proliferation, stemness, differentiation, viability, apoptosis, senescence, migration, immunomodulation behaviors, as well as epigenetic changes.

Long-term hypoxic hUCMSCs-derived extracellular vesicles alleviates allergic rhinitis through triggering immunotolerance of their VEGF-mediated inhibition of dendritic cells maturation

BACKGROUND

Extensions of mesenchymal stem cells (MSCs) in vitro may lead to the loss of their biological functions. However, hypoxic culturation has been shown to enhance the proliferation, survival, and immunomodulatory capacity of MSCs.

OBJECTIVE

We aimed to investigate the effects of long-term hypoxic cultivation on the properties of human umbilical cord-derived MSCs (hUCMSCs) and the therapeutic effects of their extracellular vesicles (EVs) in allergic rhinitis (AR).

METHODS

Proliferation, senescence, telomerase activity and multipotent properties of hUCMSCs were analyzed under long-term culturation of hypoxia (1%) or normoxia (21%), and the therapeutic effects of their conditional medium (CM) and EVs were evaluated in OVA-induced AR mice. Effects of hypoxia-EVs (Hy-EVs) or normoxia-EVs (No-EVs) on human monocyte-derived dendritic cells (DCs) were investigated, and the possible mechanisms of Hy-EVs in induction of immunotolerance were further explored.

RESULTS

Long-term hypoxia significantly promoted the proliferation, inhibited cell senescence, maintained the multipotent status of hUCMSCs. Hy-CM and Hy-EVs showed better therapeutic effects in AR mice compared to No-EVs, seen as improvement of AR-related behaviors such as rubbing and sneezing, and attenuation of inflammation in nasal tissues. In addition, Hy-EVs significantly reduced the expressions of HLA-DR, CD80, CD40, and CD83 induced by OVA plus LPS in DCs, inhibiting the maturation of DCs. Furthermore, we observed that VEGF was remarkably enriched in Hy-EVs, but not in No-EVs, and the inhibition of DCs maturation was markedly neutralized by VEGF antibodies, suggesting that VEGF derived from Hy-EVs was responsible for the inhibition of DCs maturation.

CONCLUSION

Our results demonstrated that long-term hypoxia significantly promoted the proliferation, inhibited cell senescence, maintained the multipotent status of hUCMSCs, and hypoxia treated hUCMSCs-derived EVs enhanced their therapeutic effects in AR mice through VEGF-mediated inhibition of DCs maturation.

Secretive derived from hypoxia preconditioned mesenchymal stem cells promote cartilage regeneration and mitigate joint inflammation via extracellular vesicles

Secretome derived from mesenchymal stem cells (MSCs) have profound effects on tissue regeneration, which could become the basis of future MSCs therapies. Hypoxia, as the physiologic environment of MSCs, has great potential to enhance MSCs paracrine therapeutic effect. In our study, the paracrine effects of secretome derived from MSCs preconditioned in normoxia and hypoxia was compared through both in vitro functional assays and an in vivo rat osteochondral defect model. Specifically, the paracrine effect of total EVs were compared to that of soluble factors to characterize the predominant active components in the hypoxic secretome. We demonstrated that hypoxia conditioned medium, as well as the corresponding EVs, at a relatively low dosage, were efficient in promoting the repair of critical-sized osteochondral defects and mitigated the joint inflammation in a rat osteochondral defect model, relative to their normoxia counterpart. In vitro functional test shows enhancement through chondrocyte proliferation, migration, and matrix deposition, while inhibit IL-1β-induced chondrocytes senescence, inflammation, matrix degradation, and pro-inflammatory macrophage activity. Multiple functional proteins, as well as a change in EVs' size profile, with enrichment of specific EV-miRNAs were detected with hypoxia preconditioning, implicating complex molecular pathways involved in hypoxia pre-conditioned MSCs secretome generated cartilage regeneration.

Exosomes Derived from Hypoxia-Cultured Human Adipose Stem Cells Alleviate Articular Chondrocyte Inflammaging and Post-Traumatic Osteoarthritis Progression

Osteoarthritis (OA) is the most common age-related degenerative joint disease. Inflammaging, linking inflammation and aging, is found in senescent cells with the secretions of matrix-degrading proteins and proinflammatory cytokines. The senescence-associated secretory phenotype (SASP) plays a very important role in OA progression. However, there remains no effective way to suppress OA progression, especially by suppressing inflammaging and/or the chondrocyte SASP. Recent studies have shown that exosomes derived from hypoxia-cultured BMSCs can regenerate cartilage in OA animal models. Some reports have further indicated that exosomes secreted from MSCs contribute to the efficacy of MSC therapy in OA. However, whether hypoxia-cultured ADSC-secreted exosomes (hypoxia-ADSC-Exos) can alleviate the chondrocyte SASP or OA progression remains unclear. Accordingly, we hypothesized that hypoxia-ADSC-Exos have a beneficial effect on the normal functions of human articular chondrocytes (HACs), can attenuate the SASP of OA-like HACs in vitro, and further suppress OA progression in rats. Hypoxia-ADSC-Exos were derived from ADSCs cultured in 1% O2 and 10% de-Exo-FBS for 48 h. The molecular and cell biological effects of hypoxia-ADSC-Exos were tested on IL1-β-induced HACs as OA-like HACs in vitro, and the efficacy of OA treatment was tested in ACLT-induced OA rats. The results showed that hypoxia-ADSC-Exos had the best effect on GAG formation in normal HACs rather than those cultured in normoxia or hypoxia plus 2% de-Exo-FBS. We further found that hypoxia-ADSC-Exos alleviated the harmful effect in OA-like HACs by decreasing markers of normal cartilage (GAG and type II collagen) and increasing markers of fibrous or degenerative cartilage (type I or X collagen), matrix degradation enzymes (MMP13 and ADAMT5), and inflammatory cytokines (TNFα and IL-6). More importantly, intra-articular treatment with hypoxia-ADSC-Exos suppressed OA progression, as evidenced by the weight-bearing function test and cartilage GAG quantification in ACLT rats. Moreover, through NGS and bioinformatic analysis, seven potential miRNAs were found in hypoxia-ADSC-Exos, which may contribute to regulating cellular oxidative stress and attenuating cell senescence. In summary, we demonstrated that hypoxia-ADSC-Exos, carrying potent miRNAs, not only improve normal HAC function but also alleviate HAC inflammaging and OA progression. The results suggest that hypoxia-ADSC-Exo treatment may offer another strategy for future OA therapy.

Advances in Hypoxia-Inducible Factor-1α Stabilizer Deferoxamine in Tissue Engineering

Deferoxamine (DFO) is an iron chelator with FDA approval for the clinical treatment of iron excess. As a well-established stabilizer of hypoxia-inducible factor-1α (HIF-1α), DFO can efficiently upregulate HIF-1α and relevant downstream angiogenic factors, leading to accelerated vascularization. Moreover, as increasing studies have focused on DFO as a hypoxia-mimetic agent in recent years, it has been shown that DFO exhibited multiple functions, including stem cell regulation, immunoregulation, provascularization, and pro-osteogenesis. On the contrary, DFO can bind excess iron ions in wounds of chronic inflammation, while serving as an antioxidant with the characteristic of removing reactive oxygen species. Collectively, these characteristics make DFO a potent modulator in tissue engineering for increasing tissue integration of biomaterials in vivo and facilitating wound healing. This review outlines the activity of DFO as a representative hypoxia-mimetic agent in cells as well as the evolution of its application in tissue engineering. It can be concluded that DFO is a medication with tremendous promise and application value in future trends, which can optimize biomaterials and existing tissue engineering techniques for tissue regeneration.

Factors affecting osteogenesis and chondrogenic differentiation of mesenchymal stem cells in osteoarthritis

Osteoarthritis (OA) is a common degenerative joint disease that often involves progressive cartilage degeneration and bone destruction of subchondral bone. At present, clinical treatment is mainly for pain relief, and there are no effective methods to delay the progression of the disease. When this disease progresses to the advanced stage, the only treatment option for most patients is total knee replacement surgery, which causes patients great pain and anxiety. As a type of stem cell, mesenchymal stem cells (MSCs) have multidirectional differentiation potential. The osteogenic differentiation and chondrogenic differentiation of MSCs can play vital roles in the treatment of OA, as they can relieve pain in patients and improve joint function. The differentiation direction of MSCs is accurately controlled by a variety of signaling pathways, so there are many factors that can affect the differentiation direction of MSCs by acting on these signaling pathways. When MSCs are applied to OA treatment, the microenvironment of the joints, injected drugs, scaffold materials, source of MSCs and other factors exert specific impacts on the differentiation direction of MSCs. This review aims to summarize the mechanisms by which these factors influence MSC differentiation to produce better curative effects when MSCs are applied clinically in the future.

Hypoxia activates the PI3K/AKT/HIF-1α pathway to promote the anti-inflammatory effect of adipose mesenchymal stem cells

This study aimed to investigate the effect of hypoxia on the anti-inflammatory effect of adipose-derived mesenchymal stem cells (AMSCs) in vitro and its possible mechanism. AMSCs were cultured in vitro in a hypoxic environment with 3% O₂, and a normoxic (21% O₂) environment was used as the control. The cells were identified by in vitro adipogenic and osteogenic differentiation and cell surface antigen detection, and the cell viability were detected. The effect of hypoxic AMSCs on macrophage inflammation was analyzed by co-culture. The results showed that under hypoxia, AMSCs had better viability, significantly downregulated the expression of inflammatory factors, alleviated macrophage inflammation, and activated the PI3K/AKT/HIF-1α pathway.

Adipose-Derived Stem Cells Improve Angiogenesis and Lymphangiogenesis in a Hypoxic Dermal Regeneration Model In Vitro

Background and Objectives: Impaired wound healing represents an unsolved medical issue with a high impact on patients’ quality of life and global health care. Even though hypoxia is a significant limiting factor for wound healing, it reveals stimulating effects in gene and protein expression at cellular levels. In particular, hypoxically treated human adipose tissue-derived stem cells (ASCs) have previously been used to stimulate tissue regeneration. Therefore, we hypothesized that they could promote lymphangiogenesis or angiogenesis. Materials and Methods: Dermal regeneration matrices were seeded with human umbilical vein endothelial cells (HUVECs) or human dermal lymphatic endothelial cells (LECs) that were merged with ASCs. Cultures were maintained for 24 h and 7 days under normoxic or hypoxic conditions. Finally, gene and protein expression were measured regarding subtypes of VEGF, corresponding receptors, and intracellular signaling pathways, especially hypoxia-inducible factor-mediated pathways using multiplex-RT-qPCR and ELISA assays. Results: All cell types reacted to hypoxia with an alteration of gene expression. In particular, vascular endothelial growth factor A (VEGFA), vascular endothelial growth factor B (VEGFB), vascular endothelial growth factor C (VEGFC), vascular endothelial growth factor receptor 1 (VEGFR1/FLT1), vascular endothelial growth factor receptor 2 (VEGFR2/KDR), vascular endothelial growth factor receptor 3 (VEGFR3/FLT4), and prospero homeobox 1 (PROX1) were overexpressed significantly depending on upregulation of hypoxia-inducible factor 1 alpha (HIF-1a). Moreover, co-cultures with ASCs showed a more intense change in gene and protein expression profiles and gained enhanced angiogenic and lymphangiogenic potential. In particular, long-term hypoxia led to continuous stimulation of HUVECs by ASCs. Conclusions: Our findings demonstrated the benefit of hypoxic conditioned ASCs in dermal regeneration concerning angiogenesis and lymphangiogenesis. Even a short hypoxic treatment of 24 h led to the stimulation of LECs and HUVECs in an ASC-co-culture. Long-term hypoxia showed a continuous influence on gene expressions. Therefore, this work emphasizes the supporting effects of hypoxia-conditioned-ASC-loaded collagen scaffolds on wound healing in dermal regeneration.

Decellularization of cartilage microparticles: Effects of temperature, supercritical carbon dioxide and ultrasound on biochemical, mechanical, and biological properties

One of the approaches to restoring the structure of damaged cartilage tissue is an intra-articular injection of tissue-engineered medical products (TEMPs) consisting of biocompatible matrices loaded with cells. The most interesting are the absorbable matrices from decellularized tissues, provided that the cellular material is completely removed from them with the maximum possible preservation of the structure and composition of the natural extracellular matrix. The present study investigated the mechanical, biochemical, and biological properties of decellularized porcine cartilage microparticles (DCMps) obtained by techniques, differing only in physical treatments, such as freeze-thaw cycling (Protocol 1), supercritical carbon dioxide fluid (Protocol 2) and ultrasound (Protocol 3). Full tissue decellularization was achieved, as confirmed by the histological analysis and DNA quantification, though all the resultant DCMps had reduced glycosaminoglycans (GAGs) and collagen. The elastic modulus of all DCMp samples was also significantly reduced. Most notably, DCMps prepared with Protocol 3 significantly outperformed other samples in viability and the chondroinduction of the human adipose-derived stem cells (hADSCs), with a higher GAG production per DNA content. A positive ECM staining for type II collagen was also detected only in cartilage-like structures based on ultrasound-treated DCMps. The biocompatibility of a xenogenic DCMps obtained with Protocol 3 has been confirmed for a 6-month implantation in the thigh muscle tissue of mature rats (n = 18). Overall, the results showed that the porcine cartilage microparticles decellularized by a combination of detergents, ultrasound and DNase could be a promising source of scaffolds for TEMPs for cartilage reconstruction.

Cartilage 3D bioprinting for rhinoplasty using adipose-derived stem cells as seed cells: Review and recent advances

Nasal deformities due to various causes affect the aesthetics and use of the nose, in which case rhinoplasty is necessary. However, the lack of cartilage for grafting has been a major problem and tissue engineering seems to be a promising solution. 3D bioprinting has become one of the most advanced tissue engineering methods. To construct ideal cartilage, bio-ink, seed cells, growth factors and other methods to promote chondrogenesis should be considered and weighed carefully. With continuous progress in the field, bio-ink choices are becoming increasingly abundant, from a single hydrogel to a combination of hydrogels with various characteristics, and more 3D bioprinting methods are also emerging. Adipose-derived stem cells (ADSCs) have become one of the most popular seed cells in cartilage 3D bioprinting, owing to their abundance, excellent proliferative potential, minimal morbidity during harvest and lack of ethical considerations limitations. In addition, the co-culture of ADSCs and chondrocytes is commonly used to achieve better chondrogenesis. To promote chondrogenic differentiation of ADSCs and construct ideal highly bionic tissue-engineered cartilage, researchers have used a variety of methods, including adding appropriate growth factors, applying biomechanical stimuli and reducing oxygen tension. According to the process and sequence of cartilage 3D bioprinting, this review summarizes and discusses the selection of hydrogel and seed cells (centered on ADSCs), the design of printing, and methods for inducing the chondrogenesis of ADSCs.

Composite Multicellular Spheroids Containing Fibers with Pores and Epigallocatechin Gallate (EGCG) Coating on the Surface for Enhanced Proliferation of Stem Cells

Multicellular spheroids are formed by strong cell-cell and cell-extracellular matrix interactions and are widely utilized in tissue engineering for therapeutic treatments or ex vivo tissue modeling. However, diffusion of oxygen into the spheroid gradually decreases, forming a necrotic core. In this study, polycaprolactone (PCL) fibers with pores and epigallocatechin gallate (EGCG) coating on their surface to provide a structural framework within the spheroids and investigated their ability to mitigate diffusional limitation and control over the proliferation of human adipose-derived stem cells (hADSCs) is engineered. The DNA content of composite spheroids prepared from fibers and hADSCs decreased in unadjusted cells (1224 ± 134 ng), in those with fibers with a smooth surface (SF) (1447 ± 331 ng), and in those EGCG-coated with SF (E-SF) (1437 ± 289 ng). Cells with fibers with pores on the surface (PF) (2020 ± 32 ng) and those with EGCG-coated PF (E-PF) (1911 ± 80 ng) increased after 7 days of culture, with a significantly greater number of proliferating cells (29 ± 8% and 30 ± 8%, respectively). These results indicate that physical modification through the formation of pores on the fiber surface alleviates diffusion limitation of composite spheroids, playing a dominant role over chemical modification.

Identification of hub genes regulating the cell activity and function of adipose-derived stem cells under oxygen-glucose deprivation

While oxygen-glucose deprivation (OGD) has been widely utilized in many cell lines to mimic certain biological changes, it has yet to be validated in mesenchymal stem cells. We performed RNA sequencing on adipose-derived stem cells (ADSCs) under hypoxic and glucose-free conditions after 4 h and 8 h. A total of 335 common differentially expressed genes (DEGs) were identified in the two OGD groups compared with the normal control group, consisting of 292 upregulated and 43 downregulated genes. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses indicated that DEGs are mainly involved in metabolic processes, programmed cell death, and DNA-binding transcription activator activity. Protein‒protein interaction and hub gene analysis revealed various potential hub genes, in which response to oxygen levels, the IL-17-related biological function and the hypoxia-inducible factor 1 signaling pathway have been of vital importance. In summary, changes in transcription factor activity may play pivotal roles in oxygen-glucose deprivation. Through RNA sequencing, we have a deeper understanding of the changes in ADSCs after OGD treatment, providing more precise insight into predicting and regulating the stemness of ADSCs.

The Influence of Intervertebral Disc Microenvironment on the Biological Behavior of Engrafted Mesenchymal Stem Cells

Intervertebral disc degeneration is the main cause of low back pain. Traditional treatment methods cannot repair degenerated intervertebral disc tissue. The emergence of stem cell therapy makes it possible to regenerate and repair degenerated intervertebral disc tissue. At present, mesenchymal stem cells are the most studied, and different types of mesenchymal stem cells have their own characteristics. However, due to the harsh and complex internal microenvironment of the intervertebral disc, it will affect the biological behaviors of the implanted mesenchymal stem cells, such as viability, proliferation, migration, and chondrogenic differentiation, thereby affecting the therapeutic effect. This review is aimed at summarizing the influence of each intervertebral disc microenvironmental factor on the biological behavior of mesenchymal stem cells, so as to provide new ideas for using tissue engineering technology to assist stem cells to overcome the influence of the microenvironment in the future.

Netrin-1 promotes the vasculogenic capacity of human adipose-derived stem cells

Adipose derived stem cells (ADSCs) have been increasingly explored for use in cell-based therapy against ischemic diseases. However, unsatisfactory angiogenesis limits the therapeutic efficacy. Netrin-1, a known axon guidance molecule, improves neovascularization in the ischemic region. Thus, our study was performed to evaluate the potential effect of Netrin-1 on the angiogenic behaviors of human ADSCs (hADSCs). hADSCs acquired from human abdominal adipose tissue were modified by liposome transfection of Netrin-1 plasmid, and the proliferation of hADSCs was determined by Cell Counting Kit-8 (CCK-8) assay. The transcript levels of pro-invasive proteins such as matrix metalloproteinase 2 (MMP2) and matrix metalloproteinase 9 (MMP-9), were measured to test migratory and invasive capabilities, and the levels of vascular endothelial growth factors were assayed to monitor angiogenic activity. Our results showed that Netrin-1 overexpression enhanced the proliferation of hADSCs, and promoted the migration and invasion of hADSCs, as indicated by increased levels of MMP-2 and MMP-9. Furthermore, Netrin-1 overexpression increased the expression of vascular endothelial growth factor and placental growth factor in hADSCs. Our results highlighted the possibility that genetic modification of hADSCs by Netrin-1 overexpression might be beneficial for cell transplantation therapy against ischemic diseases.

Current applications of adipose-derived mesenchymal stem cells in bone repair and regeneration: A review of cell experiments, animal models, and clinical trials

In the field of orthopaedics, bone defects caused by severe trauma, infection, tumor resection, and skeletal abnormalities are very common. However, due to the lengthy and painful process of related surgery, people intend to shorten the recovery period and reduce the risk of rejection; as a result, more attention is being paid to bone regeneration with mesenchymal stromal cells, one of which is the adipose-derived mesenchymal stem cells (ASCs) from adipose tissue. After continuous subculture and cryopreservation, ASCs still have the potential for multidirectional differentiation. They can be implanted in the human body to promote bone repair after induction in vitro, solve the problems of scarce sources and large damage, and are expected to be used in the treatment of bone defects and non-union fractures. However, the diversity of its differentiation lineage and the lack of bone formation potential limit its current applications in bone disease. Here, we concluded the current applications of ASCs in bone repair, especially with the combination and use of physical and biological methods. ASCs alone have been proved to contribute to the repair of bone damage in vivo and in vitro. Attaching to bone scaffolds or adding bioactive molecules can enhance the formation of the bone matrix. Moreover, we further evaluated the efficiency of ASC-committed differentiation in the bone in conditions of cell experiments, animal models, and clinical trials. The results show that ASCs in combination with synthetic bone grafts and biomaterials may affect the regeneration, augmentation, and vascularization of bone defects on bone healing. The specific conclusion of different materials applied with ASCs may vary. It has been confirmed to benefit osteogenesis by regulating osteogenic signaling pathways and gene transduction. Exosomes secreted by ASCs also play an important role in osteogenesis. This review will illustrate the understanding of scientists and clinicians of the enormous promise of ASCs’ current applications and future development in bone repair and regeneration, and provide an incentive for superior employment of such strategies.

ADSCs stimulated by VEGF-C alleviate intestinal inflammation via dual mechanisms of enhancing lymphatic drainage by a VEGF-C/VEGFR-3-dependent mechanism and inhibiting the NF-κB pathway by the secretome

Background

Adipose-derived stem cells (ADSCs) have provided promising applications for Crohn’s disease (CD). However, the practical efficacy of ADSCs remains controversial, and their mechanism is still unclear. Based on the pathogenesis of dysregulated immune responses and abnormal lymphatic alterations in CD, vascular endothelial growth factor-C (VEGF-C) is thought to be a favourable growth factor to optimize ADSCs. We aimed to investigate the efficacy of VEGF-C-stimulated ADSCs and their dual mechanisms in both inhibiting inflammation “IN” and promoting inflammation “OUT” in the intestine.

Methods

Human stem cells isolated from adipose tissues were identified, pretreated with or without 100 ng/ml VEGF-C and analysed for the secretion of cell culture supernatants in vitro. Lymphatic endothelial cells (LECs) were treated with ADSCs-conditioned medium or co-cultured with ADSCs and VEGF-C stimulated ADSCs. Changes in LECs transmigration, and VEGF-C/VEGFR-3 mRNA levels were assessed by transwell chamber assay and qRT–PCR. ADSCs and VEGF-C-stimulated ADSCs were intraperitoneally injected into mice with TNBS-induced chronic colitis. ADSCs homing and lymphatic vessel density (LVD) were evaluated by immunofluorescence staining. Lymphatic drainage was assessed using Evans blue. Cytokines and growth factors expression was detected respectively by ELISA and qRT–PCR. The protein levels of VEGF-C/VEGFR-3-mediated downstream signals and the NF-κB pathway were assayed by western blot. Faecal microbiota was measured by 16S rRNA sequencing.

Results

ADSCs stimulated with VEGF-C released higher levels of growth factors (VEGF-C, TGF-β1, and FGF-2) and lower expression of cytokines (IFN-γ and IL-6) in cell supernatants than ADSCs in vitro (all P < 0.05). Secretome released by VEGF-C stimulated ADSCs exhibited a stronger LEC migratory capability and led to elevated VEGF-C/VEGFR-3 expression, but these effects were markedly attenuated by VEGFR-3 inhibitor. VEGF-C-stimulated ADSCs homing to the inflamed colon and mesenteric lymph nodes (MLNs) can exert stronger efficacy in improving colitis symptoms, reducing inflammatory cell infiltration, and significantly enhancing lymphatic drainage. The mRNA levels and protein concentrations of anti-inflammatory cytokines and growth factors were markedly increased with decreased proinflammatory cytokines in the mice treated with VEGF-C-stimulated ADSCs. Systemic administration of VEGF-C-stimulated ADSCs upregulated the colonic VEGF-C/VEGFR-3 pathway and activated downstream AKT and ERK phosphorylation signalling, accompanied by decreased NF-κB p65 expression. A higher abundance of faecal p-Bacteroidetes and lower p-Firmicutes were detected in mice treated with VEGF-C-stimulated ADSCs (all P < 0.05).

Conclusion

VEGF-C-stimulated ADSCs improve chronic intestinal inflammation by promoting lymphatic drainage and enhancing paracrine signalling via activation of VEGF-C/VEGFR-3-mediated signalling and inhibition of the NF-κB pathway. Our study may provide a new insight into optimizing ADSCs treatment and investigating potential mechanisms in CD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03132-3.

The role of microenvironment in stem cell-based regeneration of intervertebral disc

Regenerative medicine for intervertebral disc (IVD) disease, by utilizing chondrocytes, IVD cells, and stem cells, has progressed to clinical trials in the treatment of back pain, and has been studied in various animal models of disc degeneration in the past decade. Stem cells exist in their natural microenvironment, which provides vital dynamic physical and chemical signals for their survival, proliferation and function. Long-term survival, function and fate of mesenchymal stem cells (MSCs) depend on the microenvironment in which they are transplanted. However, the transplanted MSCs and the endogenous disc cells were influenced by the complicated microenvironment in the degenerating disc with the changes of biochemical and biophysical components. It is important to understand how the MSCs and endogenous disc cells survive and thrive in the harsh microenvironment of the degenerative disc. Furthermore, materials containing stem cells and their natural microenvironment have good clinical effects. However, the implantation of tissue engineering IVD (TE-IVD) cannot provide a complete and dynamic microenvironment for MSCs. IVD graft substitutes may need further improvement to provide the best engineered MSC microenvironment. Additionally, the IVD progenitor cells inside the stem cell niches have been regarded as popular graft cells for IVD regeneration. However, it is still unclear whether actual IVD progenitor cells exist in degenerative spinal conditions. Therefore, the purpose of this review is fourfold: to discuss the presence of endogenous stem cells; to review and summarize the effects of the microenvironment in biological characteristics of MSC, especially those from IVD; to explore the feasibility and prospects of IVD graft substitutes and to elaborate state of the art in the use of MSC transplantation for IVD degeneration in vivo as well as their clinical application.

Hypoxia: molecular pathophysiological mechanisms in human diseases

Hypoxia, a low O2 tension, is a fundamental feature that occurs in physiological events as well as pathophysiological conditions, especially mentioned for its role in the mechanism of angiogenesis, glucose metabolism, and cell proliferation/survival. The hypoxic state through the activation of specific mechanisms is an aggravating circumstance commonly noticed in multiple sclerosis, cancer, heart disease, kidney disease, liver disease, lung disease, and in inflammatory bowel disease. On the other hand, hypoxia could play a key role in tissue regeneration and repair of damaged tissues, especially by acting on specific tissue stem cells, but their features may result as a disadvantage when it is concerned for neoplastic stem cells. Furthermore, hypoxia could also have a potential role in tissue engineering and regenerative medicine due to its capacity to improve the performance of biomaterials. The current review aims to highlight the hypoxic molecular mechanisms reported in different pathological conditions to provide an overview of hypoxia as a therapeutic agent in regenerative and molecular therapy.

Graphical abstract

Inhibition of RIP3 increased ADSC viability under OGD and modified the competency of adipogenesis, angiogenesis, and inflammation regulation

Adipose-derived stem cells (ADSCs) showed decreased cell viability and increased cell death under oxygen-glucose deprivation (OGD). Meanwhile, vital necroptotic proteins, including receptor-interacting protein kinase (RIP) 3 (RIP3) and mixed lineage kinase domain-like pseudokinase (MLKL), were expressed in the early stage. The present study aims to explore the effect of necroptosis inhibition on ADSCs. ADSCs were obtained from normal human subcutaneous fat and verified by multidirectional differentiation and flow cytometry. By applying cell counting kit-8 (CCK-8), calcein/propidium iodide (PI) staining and immunostaining, we determined the OGD treatment time of 4 h, a timepoint when the cells showed a significant decrease in viability and increased protein expression of RIP3, phosphorylated RIP3 (pRIP3) and phosphorylated MLKL (pMLKL). After pretreatment with the inhibitor of RIP3, necroptotic protein expression decreased under OGD conditions, and cell necrosis decreased. Transwell assays proved that cell migration ability was retained. Furthermore, the expression of the adipogenic transcription factor peroxisome proliferator-activated receptor γ (PPARγ) and quantitative analysis of Oil Red O staining increased in the inhibitor group. The expression of vascular endothelial growth factor-A (VEGFA) and fibroblast growth factor 2 (FGF2) and the migration test suggest that OGD increases the secretion of vascular factors, promotes the migration of human umbilical vein endothelial cells (HUVECs), and forms unstable neovascularization. ELISA revealed that inhibition of RIP3 increased the secretion of the anti-inflammatory factor, interleukin (IL)-10 (IL-10) and reduced the expression of the proinflammatory factor IL-1β. Inhibition of RIP3 can reduce the death of ADSCs, retain their migration ability and adipogenic differentiation potential, reduce unstable neovascularization and inhibit the inflammatory response.

Hypoxia-preconditioning of human adipose-derived stem cells enhances cellular proliferation and angiogenesis: A systematic review

BACKGROUND

Human adipose-derived stem cells (hADSCs) have gained attention lately because of their ease of harvesting and ability to be substantially multiplied in laboratory cultures. Stem cells are usually cultured under atmospheric conditions; however, preconditioning stem cells under hypoxic conditions seems beneficial.

AIM

This systematic review aims to investigate the effect of hypoxia preconditioning and its impact on the proliferation and angiogenic capacity of the hADSCs.

METHODS

We performed a systematic review by searching PubMed, Scopus, Embase, and Google Scholar databases from all years through March 22, 2021, following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Medical Subject Headings terms "adipose-derived stem cell," "Hypoxia," "cell proliferation," and "angiogenesis" guided our search. Only articles written in English using experimental models comparing a preconditioned group against a control group of hADSCs with data on proliferation and angiogenic capacity were included.

RESULTS

Our search yielded a total of 321 articles. 11 articles met our inclusion criteria and were ultimately included in this review. Two studies induced hypoxia using hypoxia-inducible factor-1 alpha stabilizing agents, while nine reached hypoxia by changing oxygen tension conditions around the cells. Four articles conducted in-vivo studies to correlate their in-vitro findings, which proved to be consistent. Although 1 article indicated cell proliferation inhibition with hypoxia preconditioning, the remaining 10 found enhanced proliferation in preconditioned groups compared to controls. All articles showed an enhanced angiogenic capacity of hADSCs after hypoxia preconditioning.

CONCLUSION

In this review, we found evidence to support hypoxia preconditioning of hADSCs before implantation. Benefits include enhanced cell proliferation with a faster population doubling rate and increased secretion of multiple angiogenic growth factors, enhancing angiogenesis capacity.

RELEVANCE FOR PATIENTS

Although regenerative therapy is a promising field of study and treatment in medicine, much is still unknown. The potential for angiogenic therapeutics with stem cells is high, but more so, if we discover ways to enhance their natural angiogenic properties. Procedures and pathologies alike require the assistance of angiogenic treatments to improve outcome, such is the case with skin grafts, muscle flaps, skin flaps, or myocardial infarction to mention a few. Enhanced angiogenic properties of stem cells may pave the way for better outcomes and results for patients.

Extracellular Vesicles Derived From Hypoxia-Conditioned Adipose-Derived Mesenchymal Stem Cells Enhance Lymphangiogenesis

Extracellular vesicles from adipose-derived mesenchymal stem cells (ADSCs) play an important role in lymphangiogenesis; however, the underlying mechanisms are not fully understood. In this study, we aimed to investigate the function of extracellular vesicles secreted by hypoxia-conditioned ADSCs in lymphangiogenesis and explore the potential molecular mechanisms. Extracellular vesicles were extracted from ADSCs cultured under hypoxia or normoxia conditions. The uptake of extracellular vesicles by lymphatic endothelial cells (LECs) was detected by immunofluorescence staining. The effects of extracellular vesicles on the viability, migration, and tube formation of LECs were determined by CCK-8 assay, migration assay, and tube formation assay, respectively. Molecules and pathway involved in lymphangiogenesis mediated by ADSC-derived extracellular vesicles were analyzed by luciferase reporter assay, qRT-polymerase chain reaction (PCR), and Western blot. Hypoxia ADSC-derived extracellular vesicles (H-ADSC/evs) significantly enhanced the proliferation, migration, and tube formation of LECs. Hypoxia decreased the expression of miR-129 in ADSC-derived extracellular vesicles. Overexpression of miR-129 counteracted the promoting effect of H-ADSC/evs on lymphangiogenesis. In addition, decreased exosomal miR-129 expression resulted in upregulation of HMGB1 in LECs, which led to AKT activation and lymphangiogenesis enhancement. Our data reveal that extracellular vesicles derived from hypoxia-conditioned ADSCs induce lymphangiogenesis, and this effect is mediated by miR-129/HMGB1/AKT signaling. Our findings imply that hypoxia ADSC-isolated extracellular vesicles may represent as a valuable target for the treatment of diseases associated with lymphatic remodeling.

Soft substrates direct stem cell differentiation into the chondrogenic lineage without the use of growth factors

Mesenchymal stem cells (MSCs) hold great promise for the treatment of cartilage related injuries. However, selectively promoting stem cell differentiation in vivo is still challenging. Chondrogenic differentiation of MSCs usually requires the use of growth factors that lead to the overexpression of hypertrophic markers. In this study, for the first time the effect of stiffness on MSC differentiation has been tested without the use of growth factors. Three-dimensional collagen and alginate scaffolds were developed and characterised. Stiffness significantly affected gene expression and ECM deposition. While, all hydrogels supported chondrogenic differentiation and allowed deposition of collagen type II and aggrecan, the 5.75 kPa hydrogel showed limited production of collagen type I compared to the other two formulations. These findings demonstrated for the first time that stiffness can guide MSCs differentiation without the use of growth factors within a tissue engineering scaffold suitable for the treatment of cartilage defects.

Exploring microenvironment strategies to delay mesenchymal stem cell senescence

Mesenchymal stem cells (MSCs) have recently emerged as an important candidate for cell therapy and tissue regeneration. However, some limitations in translational research and therapies still exist, such as insufficient cell supply, inadequate differentiation potential, and decreased immune capacity, all of which result from replicative senescence during long-term in vitro culture. In vitro, stem cells lack a protective microenvironment owing to the absence of physical and biochemical cues compared with the in vivo niche, which provides dynamic physicochemical and biological cues. This difference results in accelerated aging after long-term in vitro culture. Therefore, it remains a great challenge to delay replicative senescence in culture. Constructing a microenvironment to delay replicative senescence of MSCs by maintaining their phenotypes, properties, and functions is a feasible strategy to solve this problem and has made measurable progress both in preclinical studies and clinical trials. Here, we review the current knowledge on the characteristics of senescent MSCs, explore the molecular mechanisms of MSCs senescence, describe the niche of MSCs, and discuss some current microenvironment strategies to delay MSCs replicative senescence that can broaden their range of therapeutic applications.

Mesenchymal Stem Cell-Derived Extracellular Vesicle: A Promising Alternative Therapy for Osteoporosis

Osteoporosis is the chronic metabolic bone disease caused by the disturbance of bone remodeling due to the imbalance of osteogenesis and osteoclastogenesis. A large population suffers from osteoporosis, and most of them are postmenopausal women or older people. To date, bisphosphonates are the main therapeutic agents in the treatment of osteoporosis. However, limited therapeutic effects with diverse side effects caused by bisphosphonates hindered the therapeutic applications and decreased the quality of life. Therefore, an alternative therapy for osteoporosis is still needed. Stem cells, especially mesenchymal stem cells, have been shown as a promising medication for numerous human diseases including many refractory diseases. Recently, researchers found that the extracellular vesicles derived from these stem cells possessed the similar therapeutic potential to that of parental cells. To date, a number of studies demonstrated the therapeutic applications of exogenous MSC-EVs for the treatment of osteoporosis. In this article, we reviewed the basic back ground of EVs, the cargo and therapeutic potential of MSC-EVs, and strategies of engineering of MSC-EVs for osteoporosis treatment.

Hypoxia-inducible factor 2α is a novel inhibitor of chondrocyte maturation

Hypoxic environment is essential for chondrocyte maturation and longitudinal bone growth. Although hypoxia-inducible factor 1 alpha (Hif-1α) has been known as a key player for chondrocyte survival and function, the function of Hif-2α in cartilage is mechanistically and clinically relevant but remains unknown. Here we demonstrated that Hif-2α was a novel inhibitor of chondrocyte maturation through downregulation of Runx2 stability. Mechanistically, Hif-2α binding to Runx2 inhibited chondrocyte maturation by Runx2 degradation through disrupting Runx2/Cbfβ complex formation. The Hif-2α-mediated-Runx2 degradation could be rescued by Cbfβ transfection due to the increase of Runx2/Cbfβ complex formation. Consistently, mesenchymal cells derived from Hif-2α heterozygous mice were more rapidly differentiated into hypertrophic chondrocytes than those of wild-type mice in a micromass culture system. Collectively, these findings demonstrate that Hif-2α is a novel inhibitor for chondrocyte maturation by disrupting Runx2/Cbfβ complex formation and consequential regulatory activity.

Metal Ion Releasing Gold Nanoparticles for Improving Therapeutic Efficiency of Tumor Targeted Photothermal Therapy

BACKGROUND

Owing to the tumor-targeted migration capacity of human mesenchymal stem cells (hMSCs), they have been combined with nanoparticles for photothermal therapy. However, the low viability of hMSCs following transplantation remains a problem. Here, we developed iron (Fe) ion-releasing gold (Au) nanoparticles (IIAuNPs) for advanced tumor-targeted photothermal therapy using hMSCs.

METHODS

IIAuNPs were designed to undergo degradation under low pH conditions, such as the endosomal microenvironment, for Fe ion release in hMSCs. After evaluating the properties of IIAuNP, the IIAuNP concentration for treating hMSCs was optimized in terms of cytotoxicity. In vitro cell migration and antiapoptotic factor secretion were observed in hMSCs. Additionally, IIAuNPs-treated hMSCs were intravenously injected into tumor-bearing mice, and enhanced tumor targeting based on improved cell viability and cell migration was evaluated. Three days after the injection, the mice were irradiated with 660 nm laser to confirm the enhanced photothermal effect.

RESULTS

In vitro studies revealed that treating hMSCs with an optimum concentration of IIAuNPs enhanced cell migration and anti-apoptotic gene expression through intracellular Fe ion delivery. The viability of hMSCs under hypoxic cell culture conditions that mimic the in vivo microenvironment was also improved when hMSCs were treated with IIAuNPs, compared to hMSCs without IIAuNPs treatment. IIAuNPs-treated hMSCs showed significantly enhanced tumor-targeting efficiency and subsequent photothermal effect compared to hMSCs without IIAuNP treatment.

CONCLUSION

Our results suggest that our metal-ion-releasing photothermal nanoparticles may provide a promising platform for future photothermal therapies and related applications.

Hypoxic Pretreatment of Adipose-Derived Stem Cells Accelerates Diabetic Wound Healing via circ-Gcap14 and HIF-1α/VEGF Mediated Angiopoiesis

Background and Objectives

Adipose-derived stem cell (ADSC) transplantation improves stem cell paracrine function and can enhance wound healing. However, in diabetic patients, glucose-associated effects on this function and cell survival lead to impaired wound closure, thereby limiting ADSC transplantation efficiency. The hypoxia-inducible factor HIF-1α has an important protective function during wound healing. Here, we aim to clarify the regulatory mechanism of ADSCs.

Methods and Results

ADSCs were isolated from BALB/C mice adipose samples. We then used high-throughput sequencing to assess abnormal expression of circular RNAs (circRNAs). We also used an in vivo full-thickness skin defect mouse model to assess the effects of transplanted ADSC on diabetic wound closure. Hypoxic pretreatment of ADSCs accelerated diabetic wound closure, which enhanced angiogenic growth factor expression in our mouse model. High-throughput sequencing and RT-qPCR indicated that circ-Gcap14 was upregulated in hypoxic pretreated ADSCs. Similarly, circ-Gcap14 downregulation also decreased the therapeutic effects of ADSCs; however, circ-Gcap14 overexpression increased the effects of ADSC by promoting angiopoiesis. We also used a luciferase reporter assay to confirm that miR-18a-5p and HIF-1α were downstream targets of circ-Gcap14. HIF-1α expression plays an important role in increased VEGF level.

Conclusions

Based on our data, we suggest that circ-Gcap14 plays an important role in accelerating hypoxic ADSC-mediated diabetic wound closure, by enhancing mouse angiogenic growth factor expression and regulating downstream miR-18a-5p/HIF-1α expression.

Adipose Derived Mesenchymal Stem Cells from a Hypoxic Culture Reduce Cartilage Damage

The method to benifit tissue engineering of adipose-derived stem cells (ADSCs) to cartilage has been an objective of intense research in treating increasing cartilage-related disease. In this study, whether hypoxic expansion would enhance the proliferation and in vitro chondrogenic differentiation of ADSCs was studied, and then hypoxic expansion was applied to reduce cartilage damage in a rat model in vivo. Hypoxic expansion increased the proliferation and decreased the expression of aging-related genes, including p16, p21, and p53, of human ADSCs in comparison with normoxic expansion. In addition, the γH2AX expression was reduced in the hypoxic ADSCs. The chondrogenic markers were enhanced in the hypoxic ADSC differentiated chondrogenic pellets, including SOX9 on day 7 and gene expressions of COL 2 and COL 10 on day 21. To determine the in vitro chondrogenic differentiation potential of ADSCs, ADSC differentiated 21-day chondrogenic pellets were stained by Alcian blue staining and the immunostaining of COL 2 and COL 10, the results of which confirmed the enhancement of differentiation potential after the hypoxic expansion. Moreover, cartilage injury in a rat model was reduced by hypoxic ADSC treatment that was determined by histological and immunohistochemical staining detections. The effects of hypoxic expansion of ADSCs and bone marrow-derived stem cells (BMSCs) on chondrogenic differentiation potential were also compared. Smaller sizes were presented in the in vitro hypoxic BMSC differentiated chondrogenic pellets, whereas the chondrogenic marker expressions were significantly higher than those of the hypoxic ADSCs. However, there was no significant difference between the treatments of the hypoxic ADSCs and BMSCs in the cartilage injury in vivo. In conclusion, hypoxic expansion increases the chondrogenic differentiation potential of ADSCs and BMSCs in vitro and enhances them to reduce cartilage damage in vivo. Although the hypoxic BMSCs showed compact chondrogenic pellet formation and higher potential of chondrogenesis, the easy access and large resources of ADSCs still uplifted the application.

Towards Physiologic Culture Approaches to Improve Standard Cultivation of Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are of great interest for their use in cell-based therapies due to their multipotent differentiation and immunomodulatory capacities. In consequence of limited numbers following their isolation from the donor tissue, MSCs require extensive expansion performed in traditional 2D cell culture setups to reach adequate amounts for therapeutic use. However, prolonged culture of MSCs in vitro has been shown to decrease their differentiation potential and alter their immunomodulatory properties. For that reason, preservation of these physiological characteristics of MSCs throughout their in vitro culture is essential for improving the efficiency of therapeutic and in vitro modeling applications. With this objective in mind, many studies already investigated certain parameters for enhancing current standard MSC culture protocols with regard to the effects of specific culture media components or culture conditions. Although there is a lot of diversity in the final therapeutic uses of the cells, the primary stage of standard isolation and expansion is imperative. Therefore, we want to review on approaches for optimizing standard MSC culture protocols during this essential primary step of in vitro expansion. The reviewed studies investigate and suggest improvements focused on culture media components (amino acids, ascorbic acid, glucose level, growth factors, lipids, platelet lysate, trace elements, serum, and xenogeneic components) as well as culture conditions and processes (hypoxia, cell seeding, and dissociation during passaging), in order to preserve the MSC phenotype and functionality during the primary phase of in vitro culture.

Enhanced wound healing using a 3D printed VEGF-mimicking peptide incorporated hydrogel patch in a pig model

There is a need for effective wound healing through rapid wound closure, reduction of scar formation, and acceleration of angiogenesis. Hydrogel is widely used in tissue engineering, but it is not an ideal solution because of its low vascularization capability and poor mechanical properties. In this study, gelatin methacrylate (GelMA) was tested as a viable option with tunable physical properties. GelMA hydrogel incorporating a vascular endothelial growth factor (VEGF) mimicking peptide was successfully printed using a three-dimensional (3D) bio-printer owing to the shear-thinning properties of hydrogel inks. The 3D structure of the hydrogel patch had high porosity and water absorption properties. Furthermore, the bioactive characterization was confirmed by cell culture with mouse fibroblasts cell lines (NIH 3T3) and human umbilical vein endothelial cells. VEGF peptide, which is slowly released from hydrogel patches, can promote cell viability, proliferation, and tubular structure formation. In addition, a pig skin wound model was used to evaluate the wound-healing efficacy of GelMA-VEGF hydrogel patches; the results suggest that the GelMA-VEGF hydrogel patch can be used for wound dressing.

Repair of articular cartilage defect using adipose-derived stem cell-loaded scaffold derived from native cartilage extracellular matrix

The purpose of this study was to investigate the feasibility of adipose-derived stem cells (ADSCs) as the seed cells of cartilage tissue engineering. ADSCs were isolated from adipose tissue that was harvested under sterile conditions from the inguen fold of porcines and cultured in vitro. Acellular cartilage extracellular matrix (ACECM) scaffolds of pigs were then constructed. Moreover, inflammatory cells, as well as cellular and humoral immune responses, were detected using hematoxylin and eosin staining staining, immunohistochemical staining, and western blot analysis. The results showed that the cartilage complex constructed by ADSCs and ACECM through tissue engineering successfully repaired the cartilage defect of the pig knee joint. The in vivo repair experiment showed no significant difference between chondrocytes, ADSCs, and induced ADSCs, indicating that ADSCs do not require in vitro induction and have the potential for chondrogenic differentiation in the environment around the knee joint. In addition, pig-derived acellular cartilage scaffolds possess no obvious immune inflammatory response when used in xenotransplantation. ADSCs may serve as viable seed cells for cartilage tissue engineering.

Roles of oxygen level and hypoxia-inducible factor signaling pathway in cartilage, bone and osteochondral tissue engineering

The repair and treatment of articular cartilage injury is a huge challenge of orthopedics. Currently, most of the clinical methods applied in treating cartilage injuries are mainly to relieve pains rather than to cure them, while the strategy of tissue engineering is highly expected to achieve the successful repair of osteochondral defects. Clear understandings of the physiological structures and mechanical properties of cartilage, bone and osteochondral tissues have been established, but the understanding of their physiological heterogeneity still needs further investigation. Apart from the gradients in the micromorphology and composition of cartilage-to-bone extracellular matrixes, an oxygen gradient also exists in natural osteochondral tissue. The response of hypoxia-inducible factor (HIF)-mediated cells to oxygen would affect the differentiation of stem cells and the maturation of osteochondral tissue. This article reviews the roles of oxygen level and HIF signaling pathway in the development of articular cartilage tissue, and their prospective applications in bone and cartilage tissue engineering. The strategies for regulating HIF signaling pathway and how these strategies finding their potential applications in the regeneration of integrated osteochondral tissue are also discussed.

The Application of Bioreactors for Cartilage Tissue Engineering: Advances, Limitations, and Future Perspectives

Tissue engineering (TE) has brought new hope for articular cartilage regeneration, as TE can provide structural and functional substitutes for native tissues. The basic elements of TE involve scaffolds, seeded cells, and biochemical and biomechanical stimuli. However, there are some limitations of TE; what most important is that static cell culture on scaffolds cannot simulate the physiological environment required for the development of natural cartilage. Recently, bioreactors have been used to simulate the physical and mechanical environment during the development of articular cartilage. This review aims to provide an overview of the concepts, categories, and applications of bioreactors for cartilage TE with emphasis on the design of various bioreactor systems.

Novel insights for improving the therapeutic safety and efficiency of mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) have attracted great interest in the field of regenerative medicine. They can home to damaged tissue, where they can exert pro-regenerative and anti-inflammatory properties. These therapeutic effects involve the secretion of growth factors, cytokines, and chemokines. Moreover, the functions of MSCs could be mediated by extracellular vesicles (EVs) that shuttle various signaling messengers. Although preclinical studies and clinical trials have demonstrated promising therapeutic results, the efficiency and the safety of MSCs need to be improved. After transplantation, MSCs face harsh environmental conditions, which likely dampen their therapeutic efficacy. A possible strategy aiming to improve the survival and therapeutic functions of MSCs needs to be developed. The preconditioning of MSCs ex vivo would strength their capacities by preparing them to survive and to better function in this hostile environment. In this review, we will discuss several preconditioning approaches that may improve the therapeutic capacity of MSCs. As stated above, EVs can recapitulate the beneficial effects of MSCs and may help avoid many risks associated with cell transplantation. As a result, this novel type of cell-free therapy may be safer and more efficient than the whole cell product. We will, therefore, also discuss current knowledge regarding the therapeutic properties of MSC-derived EVs.

Intervertebral Disc Regeneration Using Stem Cell/Growth Factor-Loaded Porous Particles with a Leaf-Stacked Structure

Although biological therapies based on growth factors and transplanted cells have demonstrated some positive outcomes for intervertebral disc (IVD) regeneration, repeated injection of growth factors and cell leakage from the injection site remain considerable challenges for human therapeutic use. Herein, we prepare human bone marrow-derived mesenchymal stem cells (hBMSCs) and transforming growth factor-β3 (TGF-β3)-loaded porous particles with a unique leaf-stack structural morphology (LSS particles) as a combination bioactive delivery matrix for degenerated IVD. The LSS particles are fabricated with clinically acceptable biomaterials (polycaprolactone and tetraglycol) and procedures (simple heating and cooling). The LSS particles allow sustained release of TGF-β3 for 18 days and stable cell adhesiveness without additional modifications of the particles. On the basis of in vitro and in vivo studies, it was observed that the hBMSCs/TGF-β3-loaded LSS particles can provide a suitable milieu for chondrogenic differentiation of hBMSCs and effectively induce IVD regeneration in a beagle dog model. Thus, therapeutically loaded LSS particles offer the promise of an effective bioactive delivery system for regeneration of various tissues including IVD.