Effect of low oxygen tension on the biological characteristics of human bone marrow mesenchymal stem cells

The current insights of mitochondrial hormesis in the occurrence and treatment of bone and cartilage degeneration

It is widely acknowledged that aging, mitochondrial dysfunction, and cellular phenotypic abnormalities are intricately associated with the degeneration of bone and cartilage. Consequently, gaining a comprehensive understanding of the regulatory patterns governing mitochondrial function and its underlying mechanisms holds promise for mitigating the progression of osteoarthritis, intervertebral disc degeneration, and osteoporosis. Mitochondrial hormesis, referred to as mitohormesis, represents a cellular adaptive stress response mechanism wherein mitochondria restore homeostasis and augment resistance capabilities against stimuli by generating reactive oxygen species (ROS), orchestrating unfolded protein reactions (UPRmt), inducing mitochondrial-derived peptides (MDP), instigating mitochondrial dynamic changes, and activating mitophagy, all prompted by low doses of stressors. The varying nature, intensity, and duration of stimulus sources elicit divergent degrees of mitochondrial stress responses, subsequently activating one or more signaling pathways to initiate mitohormesis. This review focuses specifically on the effector molecules and regulatory networks associated with mitohormesis, while also scrutinizing extant mechanisms of mitochondrial dysfunction contributing to bone and cartilage degeneration through oxidative stress damage. Additionally, it underscores the potential of mechanical stimulation, intermittent dietary restrictions, hypoxic preconditioning, and low-dose toxic compounds to trigger mitohormesis, thereby alleviating bone and cartilage degeneration.

The role of oxygen tension in cell fate and regenerative medicine: implications of hypoxia/hyperoxia and free radicals

Oxygen pressure plays an integral role in regulating various aspects of cellular biology. Cell metabolism, proliferation, morphology, senescence, metastasis, and angiogenesis are some instances that are affected by different tensions of oxygen. Hyperoxia or high oxygen concentration, enforces the production of reactive oxygen species (ROS) that disturbs physiological homeostasis, and consequently, in the absence of antioxidants, cells and tissues are directed to an undesired fate. On the other side, hypoxia or low oxygen concentration, impacts cell metabolism and fate strongly through inducing changes in the expression level of specific genes. Thus, understanding the precise mechanism and the extent of the implication of oxygen tension and ROS in biological events is crucial to maintaining the desired cell and tissue function for application in regenerative medicine strategies. Herein, a comprehensive literature review has been performed to find out the impacts of oxygen tensions on the various behaviors of cells or tissues.

Research hotspots and frontiers of preconditioning in cerebral ischemia: A bibliometric analysis

Background

Preconditioning is a promising strategy against ischemic brain injury, and numerous studies in vitro and in vivo have demonstrated its neuroprotective effects. However, at present there is no bibliometric analysis of preconditioning in cerebral ischemia. Therefore, a comprehensive overview of the current status, hot spots, and emerging trends in this research field is necessary.

Materials and methods

Studies on preconditioning in cerebral ischemia from January 1999-December 2022 were retrieved from the Web of Science Core Collection (WOSCC) database. CiteSpace was used for data mining and visual analysis.

Results

A total of 1738 papers on preconditioning in cerebral ischemia were included in the study. The annual publications showed an upwards and then downwards trend but currently remain high in terms of annual publications. The US was the leading country, followed by China, the most active country in recent years. Capital Medical University published the largest number of articles. Perez-Pinzon, Miguel A contributed the most publications, while KITAGAWA K was the most cited author. The focus of the study covered three areas: (1) relevant diseases and experimental models, (2) types of preconditioning and stimuli, and (3) mechanisms of ischemic tolerance. Remote ischemic preconditioning, preconditioning of mesenchymal stem cells (MSCs), and inflammation are the frontiers of research in this field.

Conclusion

Our study provides a visual and scientific overview of research on preconditioning in cerebral ischemia, providing valuable information and new directions for researchers.

Regulation Mechanisms and Maintenance Strategies of Stemness in Mesenchymal Stem Cells

Stemness pertains to the intrinsic ability of mesenchymal stem cells (MSCs) to undergo self-renewal and differentiate into multiple lineages, while simultaneously impeding their differentiation and preserving crucial differentiating genes in a state of quiescence and equilibrium. Owing to their favorable attributes, including uncomplicated isolation protocols, ethical compliance, and ease of procurement, MSCs have become a focal point of inquiry in the domains of regenerative medicine and tissue engineering. As age increases or ex vivo cultivation is prolonged, the functionality of MSCs decreases and their stemness gradually diminishes, thereby limiting their potential therapeutic applications. Despite the existence of several uncertainties surrounding the comprehension of MSC stemness, considerable advancements have been achieved in the clarification of the potential mechanisms that lead to stemness loss, as well as the associated strategies for stemness maintenance. This comprehensive review provides a systematic overview of the factors influencing the preservation of MSC stemness, the molecular mechanisms governing it, the strategies for its maintenance, and the therapeutic potential associated with stemness. Finally, we underscore the obstacles and prospective avenues in present investigations, providing innovative perspectives and opportunities for the preservation and therapeutic utilization of MSC stemness.

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.

Regenerative capacity of trophoblast stem cell-derived extracellular vesicles on mesenchymal stem cells

BACKGROUND

Human mesenchymal stem cells (MSCs) are therapeutic for clinical applications because of their excellent immunomodulatory and multiple lineage differentiation abilities at tissue injury sites. However, insufficient number of cells and lack of regenerative properties during in vitro expansion still limit the clinical applicability of MSC therapies. Here, we demonstrated a preconditioning strategy with trophoblast stem cell-derived extracellular vesicles (TSC-EVs) to boost the proliferation and regenerative capacity of MSCs.

METHODS

We employed cell proliferation analyses such as CCK8 and BrdU assays to determine the proliferation-promoting role of TSC-EVs on MSCs. Osteogenic effects of TSC-EVs on MSCs were assessed by alkaline phosphatase (ALP) activity, calcium assays, and calvarial bone defect animal models. For skin regenerative effects, skin wound mice model was exploited to analyze wound-healing rate in this study, as well as immunofluorescence and histological staining evaluates. We also performed the small RNA profiling and RNA-sequencing analyzes to understand the cellular mechanism of TSC-EVs on MSCs.

RESULTS

TSC-EVs significantly promoted MSC proliferation under xeno-free conditions and facilitated the therapeutic effects of MSCs, including osteogenesis, anti-senescence, and wound healing. Transcriptomic analysis also provided evidence that specific microRNAs in TSC-EVs and differentially expressed genes (DEGs) in TSC-EV-treated MSCs showed the possibility of TSC-EVs triggering the regenerative abilities of MSCs with cytokine interaction. Hence, we found that NGF/Akt signaling mediated the regenerative effects of TSC-EVs on MSCs as a particular cellular signaling pathway.

CONCLUSION

The results of this study demonstrated the functional properties of TSC-EVs on MSCs for MSC-based therapeutic applications, suggesting that TSC-EVs may serve as a potential preconditioning source for MSC therapy in the clinical field of regenerative medicine.

Oxygen availability influences the incidence of testicular teratoma in Dnd1Ter/+ mice

Testicular teratomas and teratocarcinomas are the most common testicular germ cell tumors in early childhood and young men, and they are frequently found unilaterally in the left testis. In 129/SvJ mice carrying a heterozygous copy of the potent modifier of tumor incidence Ter, a point mutation in the dead-end homolog one gene (Dnd1 Ter/+), ∼70% of the unilateral teratomas arise in the left testis. We previously showed that in mice, left/right differences in vascular architecture are associated with reduced hemoglobin saturation and increased levels of the hypoxia inducible factor-1 alpha (HIF-1α) in the left compared to the right testis. To test the hypothesis that systemic reduction of oxygen availability in Dnd1 Ter/+ mice would lead to an increased incidence of bilateral tumors, we placed pregnant females from 129/SvJ Dnd1 Ter/+ intercross matings in a hypobaric chamber for 12-h intervals. Our results show that in 129/SvJ Dnd1 Ter/+ male gonads, the incidence of bilateral teratoma increased from 3.3% to 64% when fetuses were exposed to acute low oxygen conditions for 12-h between E13.8 and E14.3. The increase in tumor incidence correlated with the maintenance of high expression of pluripotency genes Oct4, Sox2 and Nanog, elevated activity of the Nodal signaling pathway, and suppression of germ cell mitotic arrest. We propose that the combination of heterozygosity for the Ter mutation and hypoxia causes a delay in male germ cell differentiation that promotes teratoma initiation.

Low oxygen tension affects proliferation and senescence of caprine bone marrow mesenchymal stem cells in in vitro culture condition

The culture system of bone marrow mesenchymal stem cells (bmMSCs) in the normoxic environment does not imitate the hypoxic milieu of typical biological conditions, thus hypoxic culture conditions may improve survival, and growth attributes of bmMSCs during in vitro culture. Therefore, the present study was conducted at ICAR-CIRG, Makhdoom during year 2020 with the objective to investigate the changes in biological characteristics of cultured caprine bmMSCs (cbmMSCs) including the cellular senescence, survival, rate of proliferation, immuno-phenotypic characteristics, and gene expression pattern in a normal and hypoxic microenvironment condition. For this, cbmMSCs isolated from bone marrow collected from iliac crest were enriched and grown under either hypoxic (5% O2) or normoxic (20% O2) conditions. Thereafter, the outcome of hypoxic (5% O2) culturing of cbmMSCs on growth characteristics, proliferation, senescence, and expression profile of important stemness-associated (OCT-4) and oxidative stress [glutathione peroxidase (GPx1) and copper-zinc superoxide dismutase (CuZnSOD)] marker genes was evaluated. cbmMSCs cultivated in hypoxic conditions showed higher proliferation and decreased population doubling time and senescence-associated β-GAL expression; however, the immune-phenotypic characteristics of the cells remain unchanged. Furthermore, the culture of cbmMSCs in hypoxia increased the expression of OCT-4, GPx1, and CuZnSOD, compared with the cells grown under normoxia. In conclusion, the culture condition with low O2 level improved the growth characteristics and proliferation of cbmMSCs. These outcomes would provide information to formulate strategies for the collection and efficient in vitro expansion of bmMSCs from goats and other farm animals before their downstream applications.

Proteomics profile of mesenchymal stromal cells and extracellular vesicles in normoxic and hypoxic conditions

BACKGROUND AIMS

Although bone marrow-derived mesenchymal stromal cells (MSCs) have demonstrated success in pre-clinical studies, they have shown only mild therapeutic effects in clinical trials. Hypoxia pre-conditioning may optimize the performance of bone marrow-derived MSCs because it better reflects the physiological conditions of their origin. It is not known whether changes in the protein profile caused by hypoxia in MSCs can be extended to the extracellular vesicles (EVs) released from them. The aim of this study was to evaluate the proteomics profile of MSCs and their EVs under normoxic and hypoxic conditions.

METHODS

Bone marrow-derived MSCs were isolated from six healthy male Wistar rats. After achieving 80% confluence, MSCs were subjected to normoxia (MSC-Norm) (21% oxygen, 5% carbon dioxide, 74% nitrogen) or hypoxia (MSC-Hyp) (1% oxygen, 5% carbon dioxide, 94% nitrogen) for 48 h. Cell viability and oxygen consumption rate were assessed. EVs were extracted from MSCs for each condition (EV-Norm and EV-Hyp) by ultracentrifugation. Total proteins were isolated from MSCs and EVs and prepared for mass spectrometry. EVs were characterized by nanoparticle tracking analysis. Proteomics data were analyzed by PatternLab 4.0, Search Tool for the Retrieval of Interacting Genes/Proteins, Gene Ontology, MetaboAnalyst and Reactome software.

RESULTS

Cell viability was higher in MSC-Hyp than MSC-Norm (P = 0.007). Basal respiration (P = 0.001), proton leak (P = 0.004) and maximal respiration (P = 0.014) were lower in MSC-Hyp than MSC-Norm, and no changes in adenosine triphosphate-linked and residual respiration were observed. The authors detected 2177 proteins in MSC-Hyp and MSC-Norm, of which 147 were identified in only MSC-Hyp and 512 were identified in only MSC-Norm. Furthermore, 718 proteins were identified in EV-Hyp and EV-Norm, of which 293 were detected in only EV-Hyp and 30 were detected in only EV-Norm. Both MSC-Hyp and EV-Hyp showed enrichment of pathways and biological processes related to glycolysis, the immune system and extracellular matrix organization.

CONCLUSIONS

MSCs subjected to hypoxia showed changes in their survival and metabolic activity. In addition, MSCs under hypoxia released more EVs, and their content was related to expression of regulatory proteins of the immune system and extracellular matrix organization. Because of the upregulation of proteins involved in glycolysis, gluconeogenesis and glucose uptake during hypoxia, production of reactive oxygen species and expression of immunosuppressive properties may be affected.

Study on βTCP/P(3HB) Scaffolds-Physicochemical Properties and Biological Performance in Low Oxygen Concentration

The search for new materials for bone regenerative purposes is still ongoing. Therefore, we present a series of newly constructed composites based on β tricalcium phosphate (βTCP) and poly(3-hydroxybutyrate) bacteria-derived biopolymer (P(3HB)) in the form of 3D scaffolds with different pore sizes. To improve the polymer attachment to the βTCP surface, the etching of ceramic sinters, using citric acid, was applied. As expected, pre-treatment led to the increase in surface roughness and the creation of micropores facilitating polymer adhesion. In this way, the durability and compressive strength of the ceramic-polymer scaffolds were enhanced. It was confirmed that P(3HB) degrades to 3-hydroxybutyric acid, which broadens applications of developed materials in bone tissue engineering as this compound can potentially nourish surrounding tissues and reduce osteoporosis. Moreover, to the best of our knowledge, it is one of the first studies where the impact of βTCP/P(3HB) scaffolds on mesenchymal stem cells (MSCs), cultured in lowered (5%) oxygen concentration, was assessed. It was decided to use a 5% oxygen concentration in the culture to mimic the conditions that would be found in damaged bone in a living organism during regeneration. Scaffolds enabled cell migration and sufficient flow of the culture medium, ensuring high cell viability. Furthermore, in composites with etched βTCP, the MSCs adhesion was facilitated by hydrophilic ceramic protrusions which reduced hydrophobicity. The developed materials are potential candidates for bone tissue regeneration. Nevertheless, to confirm this hypothesis, in vivo studies should be performed.

Heterogeneity of In Vitro Expanded Mesenchymal Stromal Cells and Strategies to Improve Their Therapeutic Actions

Beneficial properties of mesenchymal stromal cells (MSCs) have prompted their use in preclinical and clinical research. Accumulating evidence has been provided for the therapeutic effects of MSCs in several pathologies, including neurodegenerative diseases, myocardial infarction, skin problems, liver disorders and cancer, among others. Although MSCs are found in multiple tissues, the number of MSCs is low, making in vitro expansion a required step before MSC application. However, culture-expanded MSCs exhibit notable differences in terms of cell morphology, physiology and function, which decisively contribute to MSC heterogeneity. The changes induced in MSCs during in vitro expansion may account for the variability in the results obtained in different MSC-based therapy studies, including those using MSCs as living drug delivery systems. This review dissects the different changes that occur in culture-expanded MSCs and how these modifications alter their therapeutic properties after transplantation. Furthermore, we discuss the current strategies developed to improve the beneficial effects of MSCs for successful clinical implementation, as well as potential therapeutic alternatives.

Hypoxia pretreatment enhances the therapeutic potential of mesenchymal stem cells (BMSCs) on ozone-induced lung injury in rats

Ozone (O₃) gas is a double-sided weapon. It provides a shield that protects life on earth from the harmful ultraviolet (UV) rays, but ground-level O₃ is considered an urban air pollutant. So, a rat model of chronic O₃ inhalation was established to assess the biochemical and morphological alterations in the lung tissue and to investigate the ameliorative effects of bone marrow-derived mesenchymal stem cells (BMSCs) with or without hypoxia pre-treatment. Forty-two adult male albino rats were divided into four groups: control, ozone-exposed, normoxic BMSC-treated, and hypoxic BMSC-treated groups. Lung tissue sections were processed for light and electron microscope examination, immunohistochemical staining for caspase 3, and iNOS. Quantitative real-time PCR for IL-1α, IL-17, TNF-α, and Nrf2 mRNA gene expression were also performed. Chronic O₃ exposure caused elevated inflammatory cytokines and decreased antioxidant Nrf2 mRNA expression. Marked morphological alterations with increased collagen deposition and elevated apoptotic markers and iNOS were evident. BMSC treatment showed immunomodulatory (decreased inflammatory cytokine gene expression), antioxidant (increased Nrf2 expression and decreased iNOS), and anti-apoptotic (decreased caspase3 expression) effects. Consequently, ameliorated lung morphology with diminished collagen deposition was observed. Hypoxia pretreatment enhanced BMSC survival by MTT assay. It also augmented the previously mentioned effects of BMSCs on the lung tissue as proved by statistical analysis. Lung morphology was similar to that of control group. In conclusion, hypoxia pretreatment represents a valuable intervention to enhance the effects of MSCs on chronic lung injury.

Remodeling Osteoarthritic Articular Cartilage under Hypoxic Conditions

Osteoarthritis (OA) is one of the leading joint diseases induced by abnormalities or inflammation in the synovial membrane and articular cartilage, causing severe pain and disability. Along with the cartilage malfunction, imbalanced oxygen uptake occurs, changing chondrocytes into type I collagen- and type X collagen-producing dedifferentiated cells, contributing to OA progression. However, mounting evidence suggests treating OA by inducing a hypoxic environment in the articular cartilage, targeting the inhibition of several OA-related pathways to bring chondrocytes into a normal state. This review discusses the implications of OA-diseased articular cartilage on chondrocyte phenotypes and turnover and debates the hypoxic mechanism of action. Furthermore, this review highlights the new understanding of OA, provided by tissue engineering and a regenerative medicine experimental design, modeling the disease into diverse 2D and 3D structures and investigating hypoxia and hypoxia-inducing biomolecules and potential cell therapies. This review also reports the mechanism of hypoxic regulation and highlights the importance of activating and stabilizing the hypoxia-inducible factor and related molecules to protect chondrocytes from mitochondrial dysfunction and apoptosis occurring under the influence of OA.

Efficiency assessment of irrigation as an alternative method for improving the regenerative potential of nonhealing wounds

The application of mesenchymal stem/stromal cells (MSC) in regenerative medicine offers hope for the effective treatment of incurable or difficult‐to‐heal diseases. However, it requires the development of unified protocols for both safe and efficient cell acquisition and clinical usage. The therapeutic effect of fat grafts (containing stem cells) in non‐healing wounds has been discussed in previous studies, although the application requires local or general anaesthesia. The treatment of MSC derived from adipose tissue (ASC) could be a less invasive method, and efficient delivery could lead to more favourable outcomes, which should encourage clinicians to use such therapeutic approaches more frequently. Therefore, the aim of this study was to optimise the methods of ASC isolation, culture and administration while maintaining their high survival, proliferation and colonisation potential. The ASC were isolated by an enzymatic method and were characterised according to International Society for Cellular Therapy and International Federation for Adipose Therapeutics and Science guidelines. To assess the opportunity to obtain a sufficient number of cells for transplantation, long‐term cell cultures in two oxygen concentrations (5% vs. 21%) were conducted. For these cultures, the population doubling time, the cumulative time for cell population doublings and the rate of cell senescence were estimated. In a developed and pre‐defined protocol, ASC can be efficiently cultured at physiological oxygen concentrations (5%), which leads to faster proliferation and slower cell senescence. Subsequently, to select the optimal and minimally invasive methods of ASC transplantation, direct cell application with an irrigator or with skin dressings was analysed. Our results confirmed that both the presented methods of cell application allow for the safe delivery of isolated ASC into wounds without losing their vitality. Cells propagated in the described conditions and applied in non‐invasive cell application (with an irrigation system and dressings) to treat chronic wounds can be a potential alternative or supplement to more invasive clinical approaches.

Hypoxia preconditioning elicit differential response in tissue-specific MSCs via immunomodulation and exosomal secretion

Mesenchymal stromal cells (MSCs) are emerging as an ideal candidate for regenerative medicine. It is known that the culture conditions impact the cellular properties of MSCs and their therapeutic behavior. Moreover, maintenance of MSCs in low oxygen tension for a short duration has shown to be beneficial for MSCs as it is similar to that of their physiological niche. However, the precise mechanism through which hypoxia pre-conditioning affects MSCs is not clear yet. Thus, in this study, we have investigated the effect of hypoxia exposure (1% O₂) on tissue-specific MSCs over a period of time under serum-free culture conditions and evaluated the changes in expression of immuno-modulatory molecules and exosome biogenesis and secretion markers. It was observed that all MSCs responded differentially towards hypoxia exposure as indicated by the expression of HIF-1α. Moreover, this short-term exposure did not induce any changes in MSCs cellular morphology, proliferation rate, and surface marker profiling. In addition, we observed an enhancement in the expression of immunomodulatory factors (HLA-G, PGE-2, and IDO) after hypoxia exposure of 12 to 24 h in all tissue-specific MSCs. Interestingly, we have also observed the upregulation in exosome secretion that was further corelated to the upregulation of expression of exosome biogenesis and secretion markers (ALIX, TSG101, RAB27a, RAB27b). Though there was a differential response of MSCs where WJ-MSCs and BM-MSCs showed upregulation of these markers at 6-12 h of hypoxia pre-conditioning, while AD-MSCs showed similar changes beyond 24 h of hypoxia exposure.

Inflammation Regulates Haematopoietic Stem Cells and Their Niche

Haematopoietic stem cells (HSCs) reside in the bone marrow and are supported by the specialised microenvironment, a niche to maintain HSC quiescence. To deal with haematopoietic equilibrium disrupted during inflammation, HSCs are activated from quiescence directly and indirectly to generate more mature immune cells, especially the myeloid lineage cells. In the process of proliferation and differentiation, HSCs gradually lose their self-renewal potential. The extensive inflammation might cause HSC exhaustion/senescence and malignant transformation. Here, we summarise the current understanding of how HSC functions are maintained, damaged, or exhausted during acute, prolonged, and pathological inflammatory conditions. We also highlight the inflammation-altered HSC niche and its impact on escalating the insults on HSCs.

Decrescent role of recombinant HSP60 antibody against atherosclerosis in high-cholesterol diet immunized rabbits

OBJECTIVES

Atherosclerosis is the main cause of cardiovascular disease (CVD) which has a key role in the development of coronary artery disease (CAD). Based on clinical studies, HSP60 is the only HSP that can cause atherosclerosis. In this paper, the expression level of HSP60 and the pathogenic degree of its cloned part was investigated in atherosclerosis condition.

MATERIALS AND METHODS

After the designation of the specific primers for HSP60, PCR was done by the Pfu enzyme. Subsequently, the PCR products were cloned into a prokaryotic expression vector pET-28a. The resultant recombinant vector was transferred in BL21 and purified. Purification of protein was done by the Nickel affinity column. After confirmation of Western blotting and HSP60 protein purification, purified protein concentration was measured by the Bradford method, and purity was analyzed by SDS PAGE 12%. New Zealand rabbits were tested as an animal model. At the next step, the recombinant protein was injected into the animal model that was on a fatty diet.

RESULTS

The prokaryotic expression plasmid pET28a-hps60 was successfully constructed, the HSP60 protein was expressed and purified in Escherichia coli BL21 (DE3). We found that the rabbit that was receiving the recombinant vaccine with the fatty diet showed a lower amount of fat deposition at the media endothelial level than the rabbit which received only the fatty diet.

CONCLUSION

Taking recombinant protein concomitant with a fatty diet, causes betterment of atherosclerosis via decreasing aggregation of cholesterol and thickness of the endothelial media.

Causes and Preventive Measures of Sports Injuries in Physical Fitness Tests in Colleges and Universities Based on Biological Characteristics

Biological characteristics refer to the morphological and physiological characteristics exhibited by individual organisms. The indicators of individual biological characteristics mainly include physical indicators such as height, weight, chest circumference, and health-related physical indicators such as blood pressure, grip strength, and vital capacity. This article mainly introduces the cause analysis and preventive measures of a physical fitness test in colleges and universities based on biological characteristics and intends to provide ideas and directions for the cause analysis and preventive measures of a physical fitness test in colleges and universities. This paper proposes a research method for the cause analysis and preventive measures of sports injuries in college physical fitness tests based on biological characteristics. Research experiments on the cause analysis and preventive measures of sports injuries in the physical fitness test of colleges and universities. The experimental results in this paper show that the most frequent cause of sports injuries among boys is lack of self-protection awareness, with a probability of 24.24%; among girls, the most frequent cause of sports injuries is insufficient flexibility, with a probability of 22.86%.

Hypoxia conditioned mesenchymal stem cells in tissue regeneration application

Mesenchymal stem cells (MSCs) have been demonstrated as promising cell sources for tissue regeneration due to their capability of self-regeneration, differentiation and immunomodulation. MSCs also exert extensive paracrine effects through release of trophic factors and extracellular vesicles. However, despite extended exploration of MSCs in pre-clinical studies, the results are far from satisfactory due to the poor engraftment and low level of survival after implantation. Hypoxia preconditioning has been proposed as an engineering approach to improve the therapeutic potential of MSCs. During in vitro culture, hypoxic conditions can promote MSC proliferation, survival and migration through various cellular responses to the reduction of oxygen tension. The multilineage differentiation potential of MSCs is altered under hypoxia, with consistent reports of enhanced chondrogenesis. Hypoxia also stimulates the paracrine activities of MSCs and increases the production of secretome both in terms of soluble factors as well as extracellular vesicles. The secretome from hypoxia preconditioned MSCs play important roles in promoting cell proliferation and migration, enhancing angiogenesis while inhibiting apoptosis and inflammation. In this review, we summarise current knowledge of hypoxia-induced changes in MSCs and discuss the application of hypoxia preconditioned MSCs as well as hypoxic secretome in different kinds of disease models.

Insight into Hypoxia Stemness Control

Recently, the research on stemness and multilineage differentiation mechanisms has greatly increased its value due to the potential therapeutic impact of stem cell-based approaches. Stem cells modulate their self-renewing and differentiation capacities in response to endogenous and/or extrinsic factors that can control stem cell fate. One key factor controlling stem cell phenotype is oxygen (O₂). Several pieces of evidence demonstrated that the complexity of reproducing O₂ physiological tensions and gradients in culture is responsible for defective stem cell behavior in vitro and after transplantation. This evidence is still worsened by considering that stem cells are conventionally incubated under non-physiological air O₂ tension (21%). Therefore, the study of mechanisms and signaling activated at lower O₂ tension, such as those existing under native microenvironments (referred to as hypoxia), represent an effective strategy to define if O₂ is essential in preserving naïve stemness potential as well as in modulating their differentiation. Starting from this premise, the goal of the present review is to report the status of the art about the link existing between hypoxia and stemness providing insight into the factors/molecules involved, to design targeted strategies that, recapitulating naïve O₂ signals, enable towards the therapeutic use of stem cell for tissue engineering and regenerative medicine.

Low oxygen tension potentiates proliferation and stemness but not multilineage differentiation of caprine male germline stem cells

The milieu of male germline stem cells (mGSCs) is characterized as a low-oxygen (O₂) environment, whereas, their in-vitro expansion is typically performed under normoxia (20-21% O₂). The comparative information about the effects of low and normal O₂ levels on the growth and differentiation of caprine mGSCs (cmGSCs) is lacking. Thus, we aimed to investigate the functional and multilineage differentiation characteristics of enriched cmGSCs, when grown under hypoxia and normoxia. After enrichment of cmGSCs through multiple methods (differential platting and Percoll-density gradient centrifugation), the growth characteristics of cells [population-doubling time (PDT), viability, proliferation, and senescence], and expression of key-markers of adhesion (β-integrin and E-Cadherin) and stemness (OCT-4, THY-1 and UCHL-1) were evaluated under hypoxia (5% O₂) and normoxia (21% O₂). Furthermore, the extent of multilineage differentiation (neurogenic, adipogenic, and chondrogenic differentiation) under different culture conditions was assessed. The survival, viability, and proliferation were significantly (p < 0.05) improved, thus, yielding a significantly (p < 0.05) higher number of viable cells with larger colonies under hypoxia. Furthermore, the expression of stemness and adhesion markers were distinctly upregulated under lowered O₂ conditions. Conversely, the differentiated regions and expression of differentiation-specific genes [C/EBPα (adipogenic), nestin and β-tubulin (neurogenic), and COL2A1 (chondrogenic)] were significantly (p < 0.05) reduced under hypoxia. Overall, the results demonstrate that culturing cmGSCs under hypoxia augments the growth characteristics and stemness but not the multilineage differentiation of cmGSCs, as compared with normoxia. These data are important to develop robust methodologies for ex-vivo expansion and lineage-committed differentiation of cmGSCs for clinical applications.

LncRNA DNM3OS regulates GREM2 via miR-127-5p to suppress early chondrogenic differentiation of rat mesenchymal stem cells under hypoxic conditions

Background

Improved chondrogenic differentiation of mesenchymal stem cells (MSCs) by genetic regulation is a potential method for regenerating articular cartilage. MiR-127-5p has been reported to promote cartilage differentiation of rat bone marrow MSCs (rMSCs); however, the regulatory mechanisms underlying hypoxia-stimulated chondrogenic differentiation remain unknown.

Methods

rMSCs were induced to undergo chondrogenic differentiation under normoxic or hypoxic conditions. Expression of lncRNA DNM3OS, miR-127-5p, and GREM2 was detected by quantitative real-time PCR. Proteoglycans were detected by Alcian blue staining. Western blot assays were performed to examine the relative levels of GREM2 and chondrogenic differentiation related proteins. Luciferase reporter assays were performed to assess the association among DNM3OS, miR-127-5p, and GREM2.

Results

MiR-127-5p levels were upregulated, while DNM3OS and GREM2 levels were downregulated in rMSCs induced to undergo chondrogenic differentiation, and those changes were attenuated by hypoxic conditions (1% O₂). Further in vitro experiments revealed that downregulation of miR-127-5p reduced the production of proteoglycans and expression of chondrogenic differentiation markers (COL1A1, COL2A1, SOX9, and ACAN) and osteo/chondrogenic markers (BMP-2, p-SMAD1/2). MiR-127-5p overexpression produced the opposite results in rMSCs induced to undergo chondrogenic differentiation under hypoxic conditions. GREM2 was found to be a direct target of miR-127-5p, which was suppressed in rMSCs undergoing chondrogenic differentiation. Moreover, DNM3OS could directly bind to miR-127-5p and inhibit chondrogenic differentiation of rMSCs via regulating GREM2.

Conclusions

Our study revealed a novel molecular pathway (DNM3OS/miR-127-5p/GREM2) that may be involved in hypoxic chondrogenic differentiation.

Assessment of the Neuroprotective and Stemness Properties of Human Wharton's Jelly-Derived Mesenchymal Stem Cells under Variable (5% vs. 21%) Aerobic Conditions

To optimise the culture conditions for human Wharton's jelly-derived mesenchymal stem cells (hWJ-MSCs) intended for clinical use, we investigated ten different properties of these cells cultured under 21% (atmospheric) and 5% (physiological normoxia) oxygen concentrations. The obtained results indicate that 5% O2 has beneficial effects on the proliferation rate, clonogenicity, and slowdown of senescence of hWJ-MSCs; however, the oxygen level did not have an influence on the cell morphology, immunophenotype, or neuroprotective effect of the hWJ-MSCs. Nonetheless, the potential to differentiate into adipocytes, osteocytes, and chondrocytes was comparable under both oxygen conditions. However, spontaneous differentiation of hWJ-MSCs into neuronal lineages was observed and enhanced under atmospheric oxygen conditions. The cells relied more on mitochondrial respiration than glycolysis, regardless of the oxygen conditions. Based on these results, we can conclude that hWJ-MSCs could be effectively cultured and prepared under both oxygen conditions for cell-based therapy. However, the 5% oxygen level seemed to create a more balanced and appropriate environment for hWJ-MSCs.

Oxygen releasing materials: Towards addressing the hypoxia-related issues in tissue engineering

Manufacturing macroscale cell-laden architectures is one of the biggest challenges faced nowadays in the domain of tissue engineering. Such living constructs, in fact, pose strict requirements for nutrients and oxygen supply that can hardly be addressed through simple diffusion in vitro or without a functional vasculature in vivo. In this context, in the last two decades, a substantial amount of work has been carried out to develop smart materials that could actively provide oxygen-release to contrast local hypoxia in large-size constructs. This review provides an overview of the currently available oxygen-releasing materials and their synthesis and mechanism of action, highlighting their capacities under in vitro tissue cultures and in vivo contexts. Additionally, we also showcase an emerging concept, herein termed as "living materials as releasing systems", which relies on the combination of biomaterials with photosynthetic microorganisms, namely algae, in an "unconventional" attempt to supply the damaged or re-growing tissue with the necessary supply of oxygen. We envision that future advances focusing on tissue microenvironment regulated oxygen-supplying materials would unlock an untapped potential for generating a repertoire of anatomic scale, living constructs with improved cell survival, guided differentiation, and tissue-specific biofunctionality.

Physiological Oxygen Tension Enhances Competence and Functional Properties of Murine Cardiac Mesenchymal Cells

Cardiac mesenchymal cells (CMCs), a newly-discovered and promising type of progenitor cells, are effective in improving cardiac function in rodents after myocardial infarction. Stem/progenitor cells are usually cultured at atmospheric O₂ tension (21%); however, the physiologic O₂ tension in the heart is ~5%, raising the concern that 21% O₂ may cause toxicity due to oxidative stress. Thus, we compared mouse CMCs cultured at 21% or 5% O₂ beginning at passage 2. At passage 5, CMCs underwent severe hypoxic stress (1% O₂ for 24 h). Compared with CMCs cultured at 21% O₂, culture at 5% O₂ consistently improved cell morphology throughout 5 passages, markedly decreased cell size, increased cell number, shortened cell doubling time, and dramatically reduced lactate dehydrogenase release from CMCs into culture media after hypoxic stress. Furthermore, culture at 5% O₂ increased telomerase activity and telomere length, implying that 21% O₂ tension impairs telomerase activity, resulting in telomere shortening and decreased cell proliferation. Thus far, almost all preclinical and clinical studies of cell therapy for the heart disease have used atmospheric (21%) O₂ to culture cells. Our data challenge this paradigm. Our results demonstrate that, compared with 21% O₂, 5% O₂ tension greatly enhances the competence and functional properties of CMCs. The increased proliferation rate at 5% O₂ means that target numbers of CMCs can be achieved with much less time and cost. Furthermore, since this increased proliferation may continue in vivo after CMC transplantation, and since cells grown at 5% O₂ are markedly resistant to severe hypoxic stress, and thus may be better able to survive after transplantation into scarred regions of the heart where O₂ is very low, culture at 5% O₂ may enhance the reparative properties of CMCs (and possibly other cell types). In conclusion, our data support a change in the methods used to culture CMCs and possibly other progenitor cells.

Modulation of Heat-Shock Proteins Mediates Chicken Cell Survival against Thermal Stress

Heat stress is one of the most challenging environmental stresses affecting domestic animal production, particularly commercial poultry, subsequently causing severe yearly economic losses. Heat stress, a major source of oxidative stress, stimulates mitochondrial oxidative stress and cell dysfunction, leading to cell damage and apoptosis. Cell survival under stress conditions needs urgent response mechanisms and the consequent effective reinitiation of cell functions following stress mitigation. Exposure of cells to heat-stress conditions induces molecules that are ready for mediating cell death and survival signals, and for supporting the cell's tolerance and/or recovery from damage. Heat-shock proteins (HSPs) confer cell protection against heat stress via different mechanisms, including developing thermotolerance, modulating apoptotic and antiapoptotic signaling pathways, and regulating cellular redox conditions. These functions mainly depend on the capacity of HSPs to work as molecular chaperones and to inhibit the aggregation of non-native and misfolded proteins. This review sheds light on the key factors in heat-shock responses for protection against cell damage induced by heat stress in chicken.

Effect of low oxygen tension on transcriptional factor OCT4 and SOX2 expression in New Zealand rabbit bone marrow-derived mesenchymal stem cells

Background and Aim:

Octamer-binding transcription factor 4 (OCT4) and sex-determining region Y-box 2 (SOX2) are transcription factors whose functions are essential to maintain the pluripotency of embryonic stem cells. The purpose of this study was to derive stem cells for in vitro culture and to maintain their viability and pluripotency, with the goal to obtain a cell line for transplantation in patients with degenerative diseases or injuries. This research focused on examining the effect of low oxygen tension on the ability of bone marrow-derived mesenchymal stem cells (BM-MSCs) to express OCT4 and SOX2 in vitro.

Materials and Methods:

BM-MSCs were obtained from femurs of 2000 to 3000 g New Zealand male rabbits. BM-MSCs were divided into three groups to test different culture conditions: A control group under hyperoxia condition (21% O₂) and two treatment groups with low oxygen tension (1% and 3% O₂). We characterized the BM-MSCs using flow cytometric measurement of cluster differentiation 44 (CD44) and cluster differentiation 90 (CD90) expression. The expression of OCT4 and SOX2 was measured by immunofluorescence staining after 48 h of incubation in chambers with normal or low oxygen tension with controlled internal atmosphere consisting of 95% N₂, 5% CO₂, and 1% O₂ (T1) and 3% O₂ (T2). We considered OCT4 and SOX2 as two markers of pluripotency induction. All immunofluorescence data were subjected to a post hoc normality Tukey’s honestly significant difference test; all differences with p<5% were considered significant.

Results:

BM-MSCs were positive for CD44 and CD90 expression after isolation. Oxygen tension culture conditions of 1% and 3% O₂ led to OCT4 and SOX2 expression on culture days 2 and 4 (p<0.05), respectively, as compared to the hyperoxia condition (21% O₂).

Conclusion:

Based on the OCT4 and SOX2 immunofluorescence data, we conclude that the stem cells were pluripotent at low O₂ tension (at 1% O₂ on day 2 and at 3% O₂ on day 4), whereas under 21% O₂ the OCT4 and SOX2 were not expressed.

Vadadustat, a HIF Prolyl Hydroxylase Inhibitor, Improves Immunomodulatory Properties of Human Mesenchymal Stromal Cells

The therapeutic potential of mesenchymal stromal cells (MSCs) is largely attributed to their immunomodulatory properties, which can be further improved by hypoxia priming. In this study, we investigated the immunomodulatory properties of MSCs preconditioned with hypoxia-mimetic Vadadustat (AKB-6548, Akebia). Gene expression analysis of immunomodulatory factors was performed by real-time polymerase chain reaction (real-time PCR) on RNA isolated from six human bone-marrow derived MSCs populations preconditioned for 6 h with 40 μM Vadadustat compared to control MSCs. The effect of Vadadustat preconditioning on MSCs secretome was determined using Proteome Profiler and Luminex, while their immunomodulatory activity was assessed by mixed lymphocyte reaction (MLR) and Culturex transwell migration assays. Real-time PCR revealed that Vadadustat downregulated genes related to immune system: IL24, IL1B, CXCL8, PDCD1LG1, PDCD1LG2, HIF1A, CCL2 and IL6, and upregulated IL17RD, CCL28 and LEP. Vadadustat caused a marked decrease in the secretion of IL6 (by 51%), HGF (by 47%), CCL7 (MCP3) (by 42%) and CXCL8 (by 40%). Vadadustat potentiated the inhibitory effect of MSCs on the proliferation of alloactivated human peripheral blood mononuclear cells (PBMCs), and reduced monocytes-enriched PBMCs chemotaxis towards the MSCs secretome. Preconditioning with Vadadustat may constitute a valuable approach to improve the therapeutic properties of MSCs.

Non-viral gene delivery of HIF-1α promotes angiogenesis in human adipose-derived stem cells

Stable and mature vascular formation is a current challenge in engineering functional tissues. Transient, non-viral gene delivery presents a unique platform for delivering genetic information to cells for tissue engineering purposes and to restore blood flow to ischemic tissue. The formation of new blood vessels can be induced by upregulation of hypoxia-inducible factor-1α (HIF-1), among other factors. We hypothesized that biodegradable polymers could be used to efficiently deliver the HIF-1α gene to human adipose-derived stromal/stem cells (hASCs) and that this treatment could recruit an existing endogenous endothelial cell population to induce angiogenesis in a 3D cell construct in vitro. In this study, end-modified poly(β-amino ester) (PBAE) nanocomplexes were first optimized for transfection of hASCs and a new biodegradable polymer with increased hydrophobicity and secondary amine structures, N'-(3-aminopropyl)-N,N-dimethylpropane-1,3-diamine end-modified poly(1,4-butanediol diacrylate-co-4-amino-1-butanol), was found to be most effective. Optimal PBAE nanocomplexes had a hydrodynamic diameter of approximately 140 nm and had a zeta potential of 30 mV. The PBAE polymer self-assembled with HIF-1α plasmid DNA and treatment of hASCs with these nanocomplexes induced 3D vascularization. Cells transfected with this polymer-DNA complex were found to have 106-fold upregulation HIF-1α expression, an approximately 2-fold increase in secreted VEGF, and caused the formation of vessel tubules compared to an untransfected control. These gene therapy biomaterials may be useful for regenerative medicine. STATEMENT OF SIGNIFICANCE: Not only is the formation of stable vasculature a challenge for engineering human tissues in vitro, but it is also of valuable interest to clinical applications such as peripheral artery disease. Previous studies using HIF-1α to induce vascular formation have been limited by the necessity of hypoxic chambers. It would be advantageous to simulate endogenous responses to hypoxia without the need for physical hypoxia. In this study, 3D vascular formation was shown to be inducible through non-viral gene delivery of HIF-1α with new polymeric nanocomplexes. A biodegradable polymer N'-(3-aminopropyl)-N,N-dimethylpropane-1,3-diamine end-modified poly(1,4-butanediol diacrylate-co-4-amino-1-butanol) demonstrates improved transfection of human adipose-derived stem cells. This nanobiotechnology could be a promising strategy for the creation of vasculature for tissue engineering and clinical applications.

HIF1α-dependent metabolic reprogramming governs mesenchymal stem/stromal cell immunoregulatory functions

Hypoxia-inducible factor 1 α (HIF1α), a regulator of metabolic change, is required for the survival and differentiation potential of mesenchymal stem/stromal cells (MSC). Its role in MSC immunoregulatory activity, however, has not been completely elucidated. In the present study, we evaluate the role of HIF1α on MSC immunosuppressive potential. We show that HIF1α silencing in MSC decreases their inhibitory potential on Th1 and Th17 cell generation and limits their capacity to generate regulatory T cells. This reduced immunosuppressive potential of MSC is associated with a metabolic switch from glycolysis to OXPHOS and a reduced capacity to express or produce some immunosuppressive mediators including Intercellular Adhesion Molecule (ICAM), IL-6, and nitric oxide (NO). Moreover, using the Delayed-Type Hypersensitivity murine model (DTH), we confirm, in vivo, the critical role of HIF1α on MSC immunosuppressive effect. Indeed, we show that HIF1α silencing impairs MSC capacity to reduce inflammation and inhibit the generation of pro-inflammatory T cells. This study reveals the pivotal role of HIF1α on MSC immunosuppressive activity through the regulation of their metabolic status and identifies HIF1α as a novel mediator of MSC immunotherapeutic potential.

Bone marrow- and adipose tissue-derived mesenchymal stem cells from donors with coronary artery disease; growth, yield, gene expression and the effect of oxygen concentration

Mesenchymal stem cells (MSCs) for cardiovascular cell therapy are procured from different sources including bone marrow and adipose tissue. Differently located MSCs differ in growth potential, differentiation ability and gene expression when cultured in vitro, and studies show different healing abilities for different MSC subgroups. In this study, bone marrow derived MSCs (BMSCs) and adipose tissue derived MSCs (ADSCs) from six human donors with coronary artery disease were compared for growth potential and expression of target genes (Angpt1, LIF, HGF, TGF-β1 and VEGF-A) in response to exposure to 1% and 5% O₂, for up to 48 h. We found greater growth of ADSCs compared to BMSCs. ADSCs expressed higher levels of Angpt1, LIF and TGF-β1 and equal levels of VEGF-A and HGF as BMSCs. In BMSCs, exposure to low oxygen resulted in upregulation of TGF-β1, whereas other target genes were unaffected. Upregulation was only present at 1% O₂. In ADSCs, LIF was upregulated in both oxygen concentrations, whereas Angpt1 was upregulated only at 1% O₂. Different response to reduced oxygen culture conditions is of relevance when expanding cells in vitro prior to administration. These findings indicate ADSCs as better suited for cardiovascular cell therapy compared to BMSCs.

Scaffold channel size influences stem cell differentiation pathway in 3-D printed silica hybrid scaffolds for cartilage regeneration

We report that 3-D printed scaffold channel size can direct bone marrow derived stem cell differentiation. Treatment of articular cartilage trauma injuries, such as microfracture surgery, have limited success because durability is limited as fibrocartilage forms. A scaffold-assisted approach, combining microfracture with biomaterials has potential if the scaffold can promote articular cartilage production and share load with cartilage. Here, we investigated human bone marrow derived stromal cell (hBMSC) differentiation in vitro in 3-D printed silica/poly(tetrahydrofuran)/poly(ε-caprolactone) hybrid scaffolds with specific channel sizes. Channel widths of ∼230 μm (210 ± 22 μm mean strut size, 42.4 ± 3.9% porosity) provoked hBMSC differentiation down a chondrogenic path, with collagen Type II matrix prevalent, indicative of hyaline cartilage. When pores were larger (∼500 μm, 229 ± 29 μm mean strut size, 63.8 ± 1.6% porosity) collagen Type I was dominant, indicating fibrocartilage. There was less matrix and voids in smaller channels (∼100 μm, 218 ± 28 μm mean strut size, 31.2 ± 2.9% porosity). Our findings suggest that a 200-250 μm pore channel width, in combination with the surface chemistry and stiffness of the scaffold, is optimal for cell-cell interactions to promote chondrogenic differentiation and enable the chondrocytes to maintain their phenotype.

Improved therapeutics of modified mesenchymal stem cells: an update

Background

Mesenchymal stromal cells (MSCs) have attracted intense interest due to their powerful intrinsic properties of self-regeneration, immunomodulation and multi-potency, as well as being readily available and easy to isolate and culture. Notwithstanding, MSC based therapy suffers reduced efficacy due to several challenges which include unfavorable microenvironmental factors in vitro and in vivo.

Body

In the quest to circumvent these challenges, several modification techniques have been applied to the naïve MSC to improve its inherent therapeutic properties. These modification approaches can be broadly divided into two groups to include genetic modification and preconditioning modification (using drugs, growth factors and other molecules). This field has witnessed great progress and continues to gather interest and novelty. We review these innovative approaches in not only maintaining, but also enhancing the inherent biological activities and therapeutics of MSCs with respect to migration, homing to target site, adhesion, survival and reduced premature senescence. We discuss the application of the improved modified MSC in some selected human diseases. Possible ways of yet better enhancing the therapeutic outcome and overcoming challenges of MSC modification in the future are also elaborated.

Conclusion

The importance of prosurvival and promigratory abilities of MSCs in their therapeutic applications can never be overemphasized. These abilities are maintained and even further enhanced via MSC modifications against the inhospitable microenvironment during culture and transplantation. This is a turning point in MSC-based therapy with promising preclinical studies and higher future prospect.

Natural Compounds as a Strategy to Optimize "In Vitro" Expansion of Stem Cells

The efficient use of stem cells for transplantation is often limited by the relatively low number of stem cells collected. The ex vivo expansion of human stem cells for clinical use is a potentially valuable approach to increase stem cell number. Currently, most of the procedures used to expand stem cells are carried out using a 21% oxygen concentration, which is about 4- to 10-fold greater than the concentration characteristic of their natural niches. Hyperoxia might cause oxidative stress with a deleterious effect on the physiology of cultured stem cells. In this review, we investigate and critically examine the available information on the ability of natural compounds to counteract hyperoxia-induced damage in different types of stem cells ex vivo. In particular, we focused on proliferation and stemness maintenance in an attempt to draw up useful indications to define new culture media with a promoting activity on cell expansion in vitro.

Effects of cobalt chloride on the stem cell marker expression and osteogenic differentiation of stem cells from human exfoliated deciduous teeth

Stem cells from human exfoliated deciduous teeth (SHEDs) are a promising source for tissue engineering and stem cell transplantation. However, long-term in vitro culture and expansion lead to the loss of stemness of SHEDs, compromising their therapeutic benefits. Hypoxia plays an essential role in controlling the stem cell behavior of mesenchymal stem cells (MSCs). Thus, this study aimed to investigate the effects of cobalt chloride (CoCl2), a hypoxia-mimetic agent, on the stem cell marker expression and osteogenic differentiation of SHEDs. SHEDs were cultured with or without 50 or 100 μM CoCl2. Their proliferation, apoptosis, stem cell marker expression, migration ability, and osteogenic differentiation were examined. Culture with 50 and 100 μM CoCl2 increased the hypoxia-inducible factor-1 alpha (HIF-1α) protein levels in a dose-dependent manner in SHEDs without inducing significant cytotoxicity. This effect was accompanied by an increase in the proportion of STRO-1+ cells. CoCl2 significantly increased the expression of stem cell markers (OCT4, NANOG, SOX2, and c-Myc) in a dose-dependent manner. The migration ability was also promoted by CoCl2 treatment. Furthermore, SHEDs cultured in osteogenic medium with CoCl2 showed a dose-dependent reduction in alkaline phosphatase (ALP) activity and calcium deposition. The expression of osteogenic-related genes was also suppressed by CoCl2, especially in the 100-μM CoCl2 group. In conclusion, CoCl2 increased the expression of stem cell markers and inhibited the osteogenic differentiation of SHEDs. These findings may provide evidence supporting the use of in vitro hypoxic environments mimicked by CoCl2 in assisting the clinical application of SHEDs.

Atypical Chemokine Receptor 3 (ACKR3): A Comprehensive Overview of its Expression and Potential Roles in the Immune System

Atypical chemokine receptor 3 (ACKR3), previously known as C-X-C chemokine receptor type 7 (CXCR7), has emerged as a key player in several biologic processes, particularly during development. Its CXCL11 and CXCL12 scavenging activity and atypical signaling properties, together with a new array of other nonchemokine ligands, have established ACKR3 as a main regulator of physiologic processes at steady state and during inflammation. Here, we present a comprehensive review of ACKR3 expression in mammalian tissues in search of a possible connection with the receptor function. Besides the reported roles of ACKR3 during development, we discuss the potential contribution of ACKR3 to the function of the immune system, focusing on the myeloid lineage.

The effects of mechanical stretch on the biological characteristics of human adipose-derived stem cells

Adipose‐derived stem cells (ADSCs) are a subset of mesenchymal stem cells (MSCs), which have promised a vast therapeutic potential in tissue regeneration. Recent studies have demonstrated that combining stem cells with mechanical stretch may strengthen the efficacy of regenerative therapies. However, the exact influences of mechanical stretch on MSCs still remain inconclusive. In this study, human ADSCs (hADSCs) were applied cyclic stretch stimulation under an in vitro stretching model for designated duration. We found that mechanical stretch significantly promoted the proliferation, adhesion and migration of hADSCs, suppressing cellular apoptosis and increasing the production of pro‐healing cytokines. For differentiation of hADSCs, mechanical stretch inhibited adipogenesis, but enhanced osteogenesis. Long‐term stretch could promote ageing of hADSCs, but did not alter the cell size and typical immunophenotypic characteristics. Furthermore, we revealed that PI3K/AKT and MAPK pathways might participate in the effects of mechanical stretch on the biological characteristics of hADSCs. Taken together, mechanical stretch is an effective strategy for enhancing stem cell behaviour and regulating stem cell fate. The synergy between hADSCs and mechanical stretch would most likely facilitate tissue regeneration and promote the development of stem cell therapy.

Relevance of Oxygen Concentration in Stem Cell Culture for Regenerative Medicine

The key hallmark of stem cells is their ability to self-renew while keeping a differentiation potential. Intrinsic and extrinsic cell factors may contribute to a decline in these stem cell properties, and this is of the most importance when culturing them. One of these factors is oxygen concentration, which has been closely linked to the maintenance of stemness. The widely used environmental 21% O₂ concentration represents a hyperoxic non-physiological condition, which can impair stem cell behaviour by many mechanisms. The goal of this review is to understand these mechanisms underlying the oxygen signalling pathways and their negatively-associated consequences. This may provide a rationale for culturing stem cells under physiological oxygen concentration for stem cell therapy success, in the field of tissue engineering and regenerative medicine.

Impact of c-MYC expression on proliferation, differentiation, and risk of neoplastic transformation of human mesenchymal stromal cells

BACKGROUND

Mesenchymal stromal cells isolated from bone marrow (MSC) represent an attractive source of adult stem cells for regenerative medicine. However, thorough research is required into their clinical application safety issues concerning a risk of potential neoplastic degeneration in a process of MSC propagation in cell culture for therapeutic applications. Expansion protocols could preselect MSC with elevated levels of growth-promoting transcription factors with oncogenic potential, such as c-MYC. We addressed the question whether c-MYC expression affects the growth and differentiation potential of human MSC upon extensive passaging in cell culture and assessed a risk of tumorigenic transformation caused by MSC overexpressing c-MYC in vivo.

METHODS

MSC were subjected to retroviral transduction to induce expression of c-MYC, or GFP, as a control. Cells were expanded, and effects of c-MYC overexpression on osteogenesis, adipogenesis, and chondrogenesis were monitored. Ectopic bone formation properties were tested in SCID mice. A potential risk of tumorigenesis imposed by MSC with c-MYC overexpression was evaluated.

RESULTS

C-MYC levels accumulated during ex vivo passaging, and overexpression enabled the transformed MSC to significantly overgrow competing control cells in culture. C-MYC-MSC acquired enhanced biological functions of c-MYC: its increased DNA-binding activity, elevated expression of the c-MYC-binding partner MAX, and induction of antagonists P19ARF/P16INK4A. Overexpression of c-MYC stimulated MSC proliferation and reduced osteogenic, adipogenic, and chondrogenic differentiation. Surprisingly, c-MYC overexpression also caused an increased COL10A1/COL2A1 expression ratio upon chondrogenesis, suggesting a role in hypertrophic degeneration. However, the in vivo ectopic bone formation ability of c-MYC-transduced MSC remained comparable to control GFP-MSC. There was no indication of tumor growth in any tissue after transplantation of c-MYC-MSC in mice.

CONCLUSIONS

C-MYC expression promoted high proliferation rates of MSC, attenuated but not abrogated their differentiation capacity, and did not immediately lead to tumor formation in the tested in vivo mouse model. However, upregulation of MYC antagonists P19ARF/P16INK4A promoting apoptosis and senescence, as well as an observed shift towards a hypertrophic collagen phenotype and cartilage degeneration, point to lack of safety for clinical application of MSC that were manipulated to overexpress c-MYC for their better expansion.

Oxygen Tension Strongly Influences Metabolic Parameters and the Release of Interleukin-6 of Human Amniotic Mesenchymal Stromal Cells In Vitro

The human amniotic membrane (hAM) has been used for tissue regeneration for over a century. In vivo (in utero), cells of the hAM are exposed to low oxygen tension (1-4% oxygen), while the hAM is usually cultured in atmospheric, meaning high, oxygen tension (20% oxygen). We tested the influence of oxygen tensions on mitochondrial and inflammatory parameters of human amniotic mesenchymal stromal cells (hAMSCs). Freshly isolated hAMSCs were incubated for 4 days at 5% and 20% oxygen. We found 20% oxygen to strongly increase mitochondrial oxidative phosphorylation, especially in placental amniotic cells. Oxygen tension did not impact levels of reactive oxygen species (ROS); however, placental amniotic cells showed lower levels of ROS, independent of oxygen tension. In contrast, the release of nitric oxide was independent of the amniotic region but dependent on oxygen tension. Furthermore, IL-6 was significantly increased at 20% oxygen. To conclude, short-time cultivation at 20% oxygen of freshly isolated hAMSCs induced significant changes in mitochondrial function and release of IL-6. Depending on the therapeutic purpose, cultivation conditions of the cells should be chosen carefully for providing the best possible quality of cell therapy.

Hypoxic condition enhances chondrogenesis in synovium-derived mesenchymal stem cells

Background

The chondrogenic differentiation of mesenchymal stem cells (MSCs) is regulated by many factors, including oxygen tensions, growth factors, and cytokines. Evidences have suggested that low oxygen tension seems to be an important regulatory factor in the proliferation and chondrogenic differentiation in various MSCs. Recent studies report that synovium-derived mesenchymal stem cells (SDSCs) are a potential source of stem cells for the repair of articular cartilage defects. But, the effect of low oxygen tension on the proliferation and chondrogenic differentiation in SDSCs has not characterized. In this study, we investigated the effects of hypoxia on proliferation and chondrogenesis in SDSCs.

Method

SDSCs were isolated from patients with osteoarthritis at total knee replacement. To determine the effect of oxygen tension on proliferation and colony-forming characteristics of SDSCs, A colony-forming unit (CFU) assay and cell counting-based proliferation assay were performed under normoxic (21% oxygen) or hypoxic (5% oxygen). For in vitro chondrogenic differentiation, SDSCs were concentrated to form pellets and subjected to conditions appropriate for chondrogenic differentiation under normoxia and hypoxia, followed by the analysis for the expression of genes and proteins of chondrogenesis. qRT-PCR, histological assay, and glycosoaminoglycan assays were determined to assess chondrogenesis.

Results

Low oxygen condition significantly increased proliferation and colony-forming characteristics of SDSCs compared to that of SDSCs under normoxic culture. Similar pellet size and weight were found for chondrogensis period under hypoxia and normoxia condition. The mRNA expression of types II collagen, aggrecan, and the transcription factor SOX9 was increased under hypoxia condition. Histological sections stained with Safranin-O demonstrated that hypoxic conditions had increased proteoglycan synthesis. Immunohistochemistry for types II collagen demonstrated that hypoxic culture of SDSCs increased type II collagen expression. In addition, GAG deposition was significantly higher in hypoxia compared with normoxia at 21 days of differentiation.

Conclusion

These findings show that hypoxia condition has an important role in regulating the synthesis ECM matrix by SDSCs as they undergo chondrogenesis. This has important implications for cartilage tissue engineering applications of SDSCs.

Mathematical Modeling Reveals the Role of Hypoxia in the Promotion of Human Mesenchymal Stem Cell Long-Term Expansion

Many experimental studies have found that human mesenchymal stem cells (MSCs) in long-term culture exhibited enhanced cell proliferation and prolonged lifespan under hypoxia (around 1%–7% oxygen) against the normoxic condition (about 21% oxygen). Inspired by the experimental findings, we aimed to investigate the hypoxic effects on MSC expansion quantitatively through mathematical modeling to elucidate the corresponding biological mechanism. A two-compartment model based on ordinary differential equations (ODEs), which incorporate cellular division and senescence via state transition, was developed to describe the MSC expansion process. Parameters of this model were fitted to experimental data and used to interpret the different proliferative capacities of MSCs under hypoxia and normoxia along with model sensitivity analysis. The proposed model was tested on data from two separate experimental studies, and it could reproduce the observed growth characteristics in both conditions. Overall, this compartmental model with a logistic state transition rate was sufficient to explain the experimental findings and highlighted the promotive role of hypoxia in MSC proliferation. This in silico study suggests that hypoxia can enhance MSC long-term expansion mainly by delaying replicative senescence, which is indicated by the slowdown of the state transition rate in our model. Therefore, this explanatory model may provide theoretical proof for the experimentally observed MSC growth superiority under hypoxia and has the potential to further optimize MSC culture protocols for regenerative medicine applications.

Comparative Study on In Vitro Culture of Mouse Bone Marrow Mesenchymal Stem Cells

In vitro culture of mesenchymal stem cells (MSCs) from mouse bone marrow (BM) has been hampered because of the low yield of MSCs during isolation and the contamination of hematopoietic cells during expansion. The lack of specific mouse BM-MSC markers increases the difficulty. Several techniques have been reported to improve the purity and in vitro growth of mouse BM-MSCs. However, systematic report on comparison of characteristics in primary BM-MSCs between different culture conditions is rare. Here, we studied the effects of oxygen concentrations and initial medium replacement intervals, along with cell passages, on mouse BM-MSCs isolated with differential adhesion method. BM-MSCs exhibited elevated proliferative and clonogenic abilities in 5% oxygen compared with 10% and 21% oxygen, as well as a better expression of the MSC marker Sca-1. Adipogenic and osteogenetic differentiation of BM-MSCs can be observed in both 21% and 5% oxygen. Adipogenic differentiation appeared stronger under normoxia conditions. BM-MSCs showed increased proliferative capacity and adipogenic/osteogenetic differentiation potential when initial medium replacement interval was 4 days compared with 1 day. As passage number increased, cells were more MSC-like in morphology and in expression of surface markers (positive for CD29, CD44, and Sca-1 and negative for CD11b, CD19, and CD45). These data provide new insight into optimizing the culture method and understanding the biological characteristics of mouse BM-MSCs during in vitro expansion.

Oxygen concentration modulates cellular senescence and autophagy in human trophoblast cells

PROBLEM

We investigated the effect of oxygen concentrations on cellular senescence and autophagy and examined the role of autophagy in human trophoblast cells.

METHOD OF STUDY

Human first-trimester trophoblast cells (Sw.71) were incubated under 21%, 5%, or 1% O₂ concentrations for 24 hours. We examined the extent of senescence caused using senescence-associated β-galactosidase (SA-β-Gal) and senescence-associated secretory phenotype (SASP) as markers. Moreover, we examined the role of autophagy in causing cellular senescence using an autophagy inhibitor (3-methyladenine, 3MA).

RESULTS

Physiological normoxia (5% O₂ ) decreased SA-β-Gal-positive cells and SASP including interleukin-6 (IL-6) and IL-8 compared with cultured cells in 21% O₂ . Pathophysiological hypoxia (1% O₂ ) caused cytotoxicity, including extracellular release of ATP and lactate dehydrogenase, and decreased senescence phenotypes. 3MA-treated trophoblast cells significantly suppressed senescence markers (SA-β-Gal-positive cells and SASP secretion) in O₂ -independent manner.

CONCLUSION

We conclude that O₂ concentration modulates cellular senescence phenotypes regulating autophagy in the human trophoblast cells. Moreover, inhibiting autophagy suppresses cellular senescence, suggesting that autophagy contributes to oxygen stress-induced cellular senescence.

Progress in the use of dental pulp stem cells in regenerative medicine

The field of tissue engineering is emerging as a multidisciplinary area with promising potential for regenerating new tissues and organs. This approach requires the involvement of three essential components: stem cells, scaffolds and growth factors. To date, dental pulp stem cells have received special attention because they represent a readily accessible source of stem cells. Their high plasticity and multipotential capacity to differentiate into a large array of tissues can be explained by its neural crest origin, which supports applications beyond the scope of oral tissues. Many isolation, culture and cryopreservation protocols have been proposed that are known to affect cell phenotype, proliferation rate and differentiation capacity. The clinical applications of therapies based on dental pulp stem cells demand the development of new biomaterials suitable for regenerative purposes that can act as scaffolds to handle, carry and implant stem cells into patients. Currently, the development of xeno-free culture media is emerging as a means of standardization to improve safe and reproducibility. The present review aims to describe the current knowledge of dental pulp stem cells, considering in depth the key aspects related to the characterization, establishment, maintenance and cryopreservation of primary cultures and their involvement in the multilineage differentiation potential. The main clinical applications for these stem cells and their combination with several biomaterials is also covered.

Recent Progress in Stem Cell Modification for Cardiac Regeneration

During the past decades, stem cell-based therapy has acquired a promising role in regenerative medicine. The application of novel cell therapeutics for the treatment of cardiovascular diseases could potentially achieve the ambitious aim of effective cardiac regeneration. Despite the highly positive results from preclinical studies, data from phase I/II clinical trials are inconsistent and the improvement of cardiac remodeling and heart performance was found to be quite limited. The major issues which cardiac stem cell therapy is facing include inefficient cell delivery to the site of injury, accompanied by low cell retention and weak effectiveness of remaining stem cells in tissue regeneration. According to preclinical and clinical studies, various stem cells (adult stem cells, embryonic stem cells, and induced pluripotent stem cells) represent the most promising cell types so far. Beside the selection of the appropriate cell type, researchers have developed several strategies to produce “second-generation” stem cell products with improved regenerative capacity. Genetic and nongenetic modifications, chemical and physical preconditioning, and the application of biomaterials were found to significantly enhance the regenerative capacity of transplanted stem cells. In this review, we will give an overview of the recent developments in stem cell engineering with the goal to facilitate stem cell delivery and to promote their cardiac regenerative activity.

The Immunomodulatory Effects of Mesenchymal Stem Cell Polarization within the Tumor Microenvironment Niche

Mesenchymal stem cells (MSCs) represent a promising tool for cell therapy, particularly for their antitumor effects. This cell population can be isolated from multiple tissue sources and also display an innate ability to home to areas of inflammation, such as tumors. Upon entry into the tumor microenvironment niche, MSCs promote or inhibit tumor progression by various mechanisms, largely through the release of soluble factors. These factors can be immunomodulatory by activating or inhibiting both the adaptive and innate immune responses. The mechanisms by which MSCs modulate the immune response are not well understood. Because of this, the relationship between MSCs and immune cells within the tumor microenvironment niche continues to be an active area of research in order to help explain the apparent contradictory findings currently available in the literature. The ongoing research aims to enhance the potential of MSCs in future therapeutic applications.

Preservation and stability of cell therapy products: recommendations from an expert workshop

If the field of regenerative medicine is to deliver therapies, rapid expansion and delivery over considerable distances to large numbers of patients is needed. This will demand efficient stabilization and shipment of cell products. However, cryopreservation science is poorly understood by life-scientists in general and in recent decades only limited progress has been made in the technology of preservation and storage of cells. Rapid translation of new developments to a broader range of cell types will be vital, as will assuring a deeper knowledge of the fundamental cell biology relating to successful preservation and recovery of cell cultures. This report presents expert consensus on these and other issues which need to be addressed for more efficient delivery of cell therapies.