Hypoxia increases Sca-1/CD44 co-expression in murine mesenchymal stem cells and enhances their adipogenic differentiation potential

TANGO6 regulates cell proliferation via COPI vesicle-mediated RPB2 nuclear entry

Coat protein complex I (COPI) vesicles mediate the retrograde transfer of cargo between Golgi cisternae and from the Golgi to the endoplasmic reticulum (ER). However, their roles in the cell cycle and proliferation are unclear. This study shows that TANGO6 associates with COPI vesicles via two transmembrane domains. The TANGO6 N- and C-terminal cytoplasmic fragments capture RNA polymerase II subunit B (RPB) 2 in the cis-Golgi during the G1 phase. COPI-docked TANGO6 carries RPB2 to the ER and then to the nucleus. Functional disruption of TANGO6 hinders the nuclear entry of RPB2, which accumulates in the cytoplasm, causing cell cycle arrest in the G1 phase. The conditional depletion or overexpression of TANGO6 in mouse hematopoietic stem cells results in compromised or expanded hematopoiesis. Our study results demonstrate that COPI vesicle-associated TANGO6 plays a role in the regulation of cell cycle progression by directing the nuclear transfer of RPB2, making it a potential target for promoting or arresting cell expansion.

Hypoxia inducible factor-1α related mechanism and TCM intervention in process of early fracture healing

As a common clinical disease, fracture is often accompanied by pain, swelling, bleeding as well as other symptoms and has a high disability rate, even threatening life, seriously endangering patients' physical and psychological health and quality of life. Medical practitioners take many strategies for the treatment of fracture healing, including Traditional Chinese Medicine (TCM). In the early stage of fracture healing, the local fracture is often in a state of hypoxia, accompanied by the expression of hypoxia inducible factor-1α (HIF-1α), which is beneficial to wound healing. Through literature mining, we thought that hypoxia, HIF-1α and downstream factors affected the mechanism of fracture healing, as well as dominated this process. Therefore, we reviewed the local characteristics and related signaling pathways involved in the fracture healing process and summarized the intervention of TCM on these mechanisms, in order to inspirit the new strategy for fracture healing, as well as elaborate on the possible principles of TCM in treating fractures based on the HIF molecular mechanism.

Tendon tissue engineering: An overview of biologics to promote tendon healing and repair

Tendons are dense connective tissues with a hierarchical polarized structure that respond to and adapt to the transmission of muscle contraction forces to the skeleton, enabling motion and maintaining posture. Tendon injuries, also known as tendinopathies, are becoming more common as populations age and participation in sports/leisure activities increases. The tendon has a poor ability to self-heal and regenerate given its intrinsic, constrained vascular supply and exposure to frequent, severe loading. There is a lack of understanding of the underlying pathophysiology, and it is not surprising that disorder-targeted medicines have only been partially effective at best. Recent tissue engineering approaches have emerged as a potential tool to drive tendon regeneration and healing. In this review, we investigated the physiochemical factors involved in tendon ontogeny and discussed their potential application in vitro to reproduce functional and self-renewing tendon tissue. We sought to understand whether stem cells are capable of forming tendons, how they can be directed towards the tenogenic lineage, and how their growth is regulated and monitored during the entire differentiation path. Finally, we showed recent developments in tendon tissue engineering, specifically the use of mesenchymal stem cells (MSCs), which can differentiate into tendon cells, as well as the potential role of extracellular vesicles (EVs) in tendon regeneration and their potential for use in accelerating the healing response after injury.

Discrepancies on the Role of Oxygen Gradient and Culture Condition on Mesenchymal Stem Cell Fate

Over the past few years, mesenchymal stem (or stromal) cells (MSCs) have garnered enormous interest due to their therapeutic value especially for their multilineage differentiation potential leading to regenerative medicine applications. MSCs undergo physiological changes upon in vitro expansion resulting in expression of different receptors, thereby inducing high variabilities in therapeutic efficacy. Therefore, understanding the biochemical cues that influence the native local signals on differentiation or proliferation of these cells is very important. There have been several reports that in vitro culture of MSCs in low oxygen gradient (or hypoxic conditions) upregulates the stemness markers and promotes cell proliferation in an undifferentiated state, as hypoxia mimics the conditions the progenitor cells experience within the tissue. However, different studies report different oxygen gradients and culture conditions causing ambiguity in their interpretation of the results. In this progress report, it is aimed to summarize recent studies in the field with specific focus on conflicting results reported during the application of hypoxic conditions for improving the proliferation or differentiation of MSCs. Further, it is tried to decipher the factors that can affect characteristics of MSC under hypoxia and suggest a few techniques that could be combined with hypoxic cell culture to better recapitulate the MSC tissue niche.

Therapeutic Use of Mesenchymal Stromal Cells: The Need for Inclusive Characterization Guidelines to Accommodate All Tissue Sources and Species

Following their discovery over 50 years ago, mesenchymal stromal cells (MSCs) have become one of the most studied cellular therapeutic products by both academia and industry due to their regenerative potential and immunomodulatory properties. The promise of MSCs as a therapeutic modality has been demonstrated by preclinical data yet has not translated to consistent, successful clinical trial results in humans. Despite the disparities across the field, MSC shareholders are unified under one common goal-to use MSCs as a therapeutic modality to improve the quality of life for those suffering from a malady in which the standard of care is suboptimal or no longer effective. Currently, there is no Food and Drug Administration (FDA)-approved MSC therapy on the market in the United States although several MSC products have been granted regulatory approval in other countries. In this review, we intend to identify hurdles that are impeding therapeutic progress and discuss strategies that may aid in accomplishing this universal goal of widespread therapeutic use.

Determinants of stem cell lineage differentiation toward chondrogenesis versus adipogenesis

Adult stem cells, also termed as somatic stem cells, are undifferentiated cells, detected among differentiated cells in a tissue or an organ. Adult stem cells can differentiate toward lineage specific cell types of the tissue or organ in which they reside. They also have the ability to differentiate into mature cells of mesenchymal tissues, such as cartilage, fat and bone. Despite the fact that the balance has been comprehensively scrutinized between adipogenesis and osteogenesis and between chondrogenesis and osteogenesis, few reviews discuss the relationship between chondrogenesis and adipogenesis. In this review, the developmental and transcriptional crosstalk of chondrogenic and adipogenic lineages are briefly explored, followed by elucidation of signaling pathways and external factors guiding lineage determination between chondrogenic and adipogenic differentiation. An in-depth understanding of overlap and discrepancy between these two mesenchymal tissues in lineage differentiation would benefit regeneration of high-quality cartilage tissues and adipose tissues for clinical applications.

Fatty pancreas: A possible risk factor for pancreatic cancer in animals and humans

Obesity, type 2 diabetes mellitus (T2DM) and aging are associated with pancreatic cancer risk, but the mechanisms of pancreatic cancer development caused by these factors are not clearly understood. Syrian golden hamsters are susceptible to N‐nitrosobis(2‐oxopropyl)amine (BOP)‐induced pancreatic carcinogenesis. Aging, BOP treatment and/or a high‐fat diet cause severe and scattered fatty infiltration (FI) of the pancreas with abnormal adipokine production and promote pancreatic ductal adenocarcinoma (PDAC) development. The KK‐A^y mouse, a T2DM model, also develops severe and scattered FI of the pancreas. Treatment with BOP induced significantly higher cell proliferation in the pancreatic ducts of KK‐A^y mice, but not in those of ICR and C57BL/6J mice, both of which are characterized by an absence of scattered FI. Thus, we hypothesized that severely scattered FI may be involved in the susceptibility to PDAC development. Indeed, severe pancreatic FI, or fatty pancreas, is observed in humans and is associated with age, body mass index (BMI) and DM, which are risk factors for pancreatic cancer. We analyzed the degree of FI in the non‐cancerous parts of PDAC and non‐PDAC patients who had undergone pancreatoduodenectomy by histopathology and demonstrated that the degree of pancreatic FI in PDAC cases is significantly higher than that in non‐PDAC controls. Moreover, the association with PDAC is positive, even after adjusting for BMI and the prevalence of DM. Accumulating evidence suggests that pancreatic FI is involved in PDAC development in animals and humans, and further investigations to clarify the genetic and environmental factors that cause pancreatic FI are warranted.

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.

Heterogeneity of adipose tissue in development and metabolic function

Adipose tissue is a central metabolic organ. Unlike other organs, adipose tissue is compartmentalized into individual depots and distributed throughout the body. These different adipose depots show major functional differences and risk associations for developing metabolic syndrome. Recent advances in lineage tracing demonstrate that individual adipose depots are composed of adipocytes that are derived from distinct precursor populations, giving rise to different populations of energy-storing white adipocytes. Moreover, distinct lineages of energy-dissipating brown and beige adipocytes exist in discrete depots or within white adipose tissue depots. In this Review, we discuss developmental and functional heterogeneity, as well as sexual dimorphism, between and within individual adipose tissue depots. We highlight current data relating to the differences between subcutaneous and visceral white adipose tissue in the development of metabolic dysfunction, with special emphasis on adipose tissue expansion and remodeling of the extracellular matrix. Moreover, we provide a detailed overview of adipose tissue development as well as the consensus and controversies relating to adult adipocyte precursor populations.

Microenvironmental Scenario of the Bone Marrow of Inorganic Arsenic-Exposed Experimental Mice

Exposure to arsenic on a regular basis, mainly through drinking water, agricultural pesticide, and sometimes therapeutic dose, results in various diseases of different tissues including the bone marrow hematopoietic system. Hematopoiesis is a dynamic process by which bone marrow (BM) hematopoietic stem/progenitor cells (HSPCs) generate a relatively constant pool of functionally mature blood cells by the support of microenvironmental components. The present study has been aimed to understand stem cell microenvironmental status during arsenic toxicity and the consequent reflection of dysregulation involving the hematopoietic machinery in experimental mice. Swiss albino mice were experimentally exposed to 10 μg arsenic trioxide/g body weight through oral gavage and 5 μg arsenic trioxide/g body weight intraperitoneally for a period of 30 days. Altered hemogram values in peripheral blood reflected the impaired hematopoiesis which was further validated by the reduced BM cellularity along with the deviated BM cell morphology as observed by scanning electron microscopy post arsenic exposure. The stromal cells were unable to establish a healthy matrix and the sustainability of hematopoietic progenitors was drastically affected in arsenic-exposed mouse groups, as observed in in vitro explant culture. The inability of stromal cells to establish supportive matrix was also explained by the decreased adherent colony formation in treated animals. Furthermore, the flow cytometric characterization of CXCR4⁺ and Sca-1⁺ CD44⁺ receptor expressions confirmed the dysregulation in the hematopoietic microenvironment. Thus, considering the importance of microenvironment in the maintenance of HSPC, it can be concluded that arsenic toxicity causes microenvironmental damage, leading to niche derangement and impaired hematopoiesis.

Tissue-Related Hypoxia Attenuates Proinflammatory Effects of Allogeneic PBMCs on Adipose-Derived Stromal Cells In Vitro

Human adipose tissue-stromal derived cells (ASCs) are considered a perspective tool for regenerative medicine. Depending on the application mode ASC/allogeneic immune cell interaction can occur in the systemic circulation under plenty high concentrations of O2 and in target tissues at lower O2 levels. Here we examined the effects of allogeneic PHA-stimulated peripheral blood mononuclear cells (PBMCs) on ASCs under ambient (20%) oxygen and "physiological" hypoxia (5% O2). As revealed with microarray analysis ASCs under 20% O2 were more affected by activated PBMCs, which was manifested in differential expression of more than 300 genes, whereas under 5% O2 only 140 genes were changed. Altered gene pattern was only partly overlapped at different O2 conditions. Under O2 ASCs retained their proliferative and differentiative capacities, mesenchymal phenotype, and intracellular organelle' state. ASCs were proinflammatory activated on transcription level that was confirmed by their ability to suppress activation and proliferation of mitogen-stimulated PBMCs. ASC/PBMCs interaction resulted in anti-inflammatory shift of paracrine mediators in conditioning medium with significant increase of immunosuppressive LIF level. Our data indicated that under both ambient and tissue-related O2 ASCs possessed immunosuppressive potential and maintained functional activity. Under "physiological" hypoxia ASCs were less susceptible to "priming" by allogeneic mitogen-activated PBMCs.

Effects of CoCl2 on multi-lineage differentiation of C3H/10T1/2 mesenchymal stem cells

Mesenchymal stem cells (MSCs) in the bone marrow and other somatic tissues reside in an environment with relative low oxygen tension. Cobalt chloride (CoCl₂) can mimic hypoxic conditions through transcriptional changes of some genes including hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF). This study evaluated the potential role of CoCl₂ preconditioning on multi-lineage differentiation of C3H/10T1/2, a murine MSC line to understand its possible molecular mechanisms in vitro. CoCl₂ treatment of MSCs markedly increased HIF-1α and VEGF mRNA, and protein expression of HIF-1α. Temporary preconditioning of MSCs with CoCl₂ induced up-regulation of osteogenic markers including alkaline phosphatase, osteocalcin, and type I collagen during osteogenic differentiation, followed by enhanced mineralization. CoCl₂ also increased chondrogenic markers including aggrecan, sox9, and type II collagen, and promoted chondrocyte differentiation. CoCl₂ suppressed the expression of adipogenic markers including PPARγ, aP2, and C/EBPα, and inhibited adipogenesis. Temporary preconditioning with CoCl₂ could affect the multi-lineage differentiation of MSCs.

In situ normoxia enhances survival and proliferation rate of human adipose tissue-derived stromal cells without increasing the risk of tumourigenesis

Adipose tissue-derived stromal cells (ASCs) natively reside in a relatively low-oxygen tension (i.e., hypoxic) microenvironment in human body. Low oxygen tension (i.e., in situ normoxia), has been known to enhance the growth and survival rate of ASCs, which, however, may lead to the risk of tumourigenesis. Here, we investigated the tumourigenic potential of ASCs under their physiological condition to ensure their safe use in regenerative therapy. Human ASCs isolated from subcutaneous fat were cultured in atmospheric O2 concentration (21% O2) or in situ normoxia (2% O2). We found that ASCs retained their surface markers, tri-lineage differentiation potential, and self-renewal properties under in situ normoxia without altering their morphology. In situ normoxia displayed a higher proliferation and viability of ASCs with less DNA damage as compared to atmospheric O2 concentration. Moreover, low oxygen tension significantly up-regulated VEGF and bFGF mRNA expression and protein secretion while reducing the expression level of tumour suppressor genes p16, p21, p53, and pRb. However, there were no significant differences in ASCs telomere length and their relative telomerase activity when cultured at different oxygen concentrations. Collectively, even with high proliferation and survival rate, ASCs have a low tendency of developing tumour under in situ normoxia. These results suggest 2% O2 as an ideal culture condition for expanding ASCs efficiently while maintaining their characteristics.

Biological differences between native and cultured mesenchymal stem cells: implications for therapies

We describe the current knowledge of the surface marker phenotype of native bone marrow mesenchymal stem/stromal cells (MSCs) in humans and in mouse models, highlighting similarities in the MSC marker "signature" between the two species. The chapter proceeds to discuss the published literature pertaining to native MSC topography and their interactions with hematopoietic stem cells and their progeny, as well as with blood vessels and nerve endings. Additionally, the chapter describes phenotypic and functional "drifts" that occur in MSC preparations as they are taken out of their native bone marrow microenvironment and induced to proliferate in vitro (in the presence of animal or human serum). We propose that the understanding of the biology of MSCs in their native niches in the bone marrow could lead to future developments in the treatment of hematological diseases such as multiple myeloma. Additionally, this knowledge would assist in the development of more "natural" MSC culture conditions, best preserving MSC functionality including their homing potential in order to optimize MSC transplantation in the context of graft-versus-host and other diseases.

Metabolic regulation of mesenchymal stem cell in expansion and therapeutic application

Human mesenchymal or stromal cells (hMSCs) isolated from various adult tissues are primary candidates in cell therapy and tissue regeneration. Despite promising results in preclinical studies, robust therapeutic responses to MSC treatment have not been reproducibly demonstrated in clinical trials. In the translation of MSC-based therapy to clinical application, studies of MSC metabolism have significant implication in optimizing bioprocessing conditions to obtain therapeutically competent hMSC population for clinical application. In addition, understanding the contribution of metabolic cues in directing hMSC fate also provides avenues to potentiate their therapeutic effects by modulating their metabolic properties. This review focuses on MSC metabolism and discusses their unique metabolic features in the context of common metabolic properties shared by stem cells. Recent advances in the fundamental understanding of MSC metabolic characteristics in relation to their in vivo origin and metabolic regulation during proliferation, lineage-specific differentiation, and exposure to in vivo ischemic conditions are summarized. Metabolic strategies in directing MSC fate to enhance their therapeutic potential in tissue engineering and regenerative medicine are discussed.

Effect of acute hypoxia on CXCR4 gene expression in C57BL/6 mouse bone marrow-derived mesenchymal stem cells

BACKGROUND

One of the most important stimuli in stem cell biology is oxygen. Chemokine receptor 4 (CXCR4) plays a crucial role in the migration and homing of stem cells. In this study, mesenchymal stem cells (MSCs) were exposed to 1% oxygen to investigate the effect of acute hypoxia on CXCR4 gene expression.

MATERIALS AND METHODS

MSCs were isolated from C57BL/6 mouse bone marrow and were identified and expanded in normoxic culture. Cells were incubated at 37°C under 1% hypoxic conditions for periods of 4, 8, 16, 24, and 48 h. After hypoxia preconditioning, the cells were placed in normoxic condition for 8 h to achieve cellular hypoxia-reoxygenation. To assess the level of CXCR4 gene expression, real-time quantitative reverse transcription-polymerase chain reaction was carried out for each group.

RESULTS

Data from statistical analysis illustrated that exposure of MSCs to acute hypoxic condition down-regulates CXCR4 expression with the maximum under-expression observed in 4 h (0.91 ± 0.107) and 8 h (50 ± 2.98) groups. Moreover, the relative gene expression of CXCR4 was decreased after hypoxia-reoxygenation by more than 80% in 4 h (0.136 ± 0.018) and 24 h (12.77 ± 0.707) groups.

CONCLUSION

The results suggest that CXCR4 expression in MSCs decreases upon acute hypoxic stress. Furthermore, hypoxia-reoxygenated MSCs showed decreased expression of CXCR4, compared to cells subjected to acute hypoxia. This difference could have resulted from the cells being compatible with low oxygen metabolism. In summary, before the therapeutic application of MSCs, it should be regarded as a necessity to optimize the oxygen concentration in these cells, as it is a critical factor in modulating CXCR4 expression.

Mesengenic differentiation: comparison of human and rat bone marrow mesenchymal stem cells

BACKGROUND AND OBJECTIVES

Cellular therapies using Mesenchymal Stem Cells (MSCs) represent a promising approach for the treatment of degenerative diseases, in particular for mesengenic tissue regeneration. However, before the approval of clinical trials in humans, in vitro studies must be performed aimed at investigating MSCs' biology and the mechanisms regulating their proliferation and differentiation abilities. Besides studies on human MSCs (hMSCs), MSCs derived from rodents have been the most used cellular type for in vitro studies. Nevertheless, the transfer of the results obtained using animal MSCs to hMSCs has been hindered by the limited knowledge regarding the similarities existing between cells of different origins. Aim of this paper is to highlight similarities and differences and to clarify the sometimes reported different results obtained using these cells.

METHODS AND RESULTS

We compare the differentiation ability into mesengenic lineages of rat and human MSCs cultured in their standard conditions. Our results describe in which way the source from which MSCs are derived affects their differentiation potential, depending on the mesengenic lineage considered. For osteogenic and chondrogenic lineages, the main difference between human and rat MSCs is represented by differentiation time, while for adipogenesis hMSCs have a greater differentiation potential.

CONCLUSIONS

These results on the one hand suggest to carefully evaluate the transfer of results obtained with animal MSCs, on the other hand they offer a clue to better apply MSCs into clinical practice.

Mesenchymal stem cells and hypoxia: where are we?

Multipotent mesenchymal stromal cells (MSCs) are involved in the organization and maintenance of tissue integrity. MSCs have also attracted attention as a promising tool for cell therapy and regenerative medicine. However, their usage is limited due to cell impairment induced by an extremely harsh microenvironment during transplantation ex vivo. The microenvironment of MSCs in tissue depots is characterized by rather low oxygen consumption, demonstrating that MSCs might be quite resistant to oxygen limitation. However, accumulated data revealed that the response of MSCs to hypoxic conditions is rather controversial, demonstrating both damaging and ameliorating effects. Here, we make an attempt to summarize recent knowledge on the survival of MSCs under low oxygen conditions of varying duration and severity and to elucidate the mechanisms of MSC resistance/sensitivity to hypoxic impact.

Impact of low oxygen tension on stemness, proliferation and differentiation potential of human adipose-derived stem cells

Adipose-derived stem cells (ASCs) have been found adapted to a specific niche with low oxygen tension (hypoxia) in the body. As an important component of this niche, oxygen tension has been known to play a critical role in the maintenance of stem cell characteristics. However, the effect of O2 tension on their functional properties has not been well determined. In this study, we investigated the effects of O2 tension on ASCs stemness, differentiation and proliferation ability. Human ASCs were cultured under normoxia (21% O2) and hypoxia (2% O2). We found that hypoxia increased ASC stemness marker expression and proliferation rate without altering their morphology and surface markers. Low oxygen tension further enhances the chondrogenic differentiation ability, but reduces both adipogenic and osteogenic differentiation potential. These results might be correlated with the increased expression of HIF-1α under hypoxia. Taken together, we suggest that growing ASCs under 2% O2 tension may be important in expanding ASCs effectively while maintaining their functional properties for clinical therapy, particularly for the treatment of cartilage defects.

Human bone marrow-derived mesenchymal stem cells display enhanced clonogenicity but impaired differentiation with hypoxic preconditioning

Stem cells are promising candidate cells for regenerative applications because they possess high proliferative capacity and the potential to differentiate into other cell types. Mesenchymal stem cells (MSCs) are easily sourced but do not retain their proliferative and multilineage differentiative capabilities after prolonged ex vivo propagation. We investigated the use of hypoxia as a preconditioning agent and in differentiating cultures to enhance MSC function. Culture in 5% ambient O(2) consistently enhanced clonogenic potential of primary MSCs from all donors tested. We determined that enhanced clonogenicity was attributable to increased proliferation, increased vascular endothelial growth factor secretion, and increased matrix turnover. Hypoxia did not impact the incidence of cell death. Application of hypoxia to osteogenic cultures resulted in enhanced total mineral deposition, although this effect was detected only in MSCs preconditioned in normoxic conditions. Osteogenesis-associated genes were upregulated in hypoxia, and alkaline phosphatase activity was enhanced. Adipogenic differentiation was inhibited by exposure to hypoxia during differentiation. Chondrogenesis in three-dimensional pellet cultures was inhibited by preconditioning with hypoxia. However, in cultures expanded under normoxia, hypoxia applied during subsequent pellet culture enhanced chondrogenesis. Whereas hypoxic preconditioning appears to be an excellent way to expand a highly clonogenic progenitor pool, our findings suggest that it may blunt the differentiation potential of MSCs, compromising their utility for regenerative tissue engineering. Exposure to hypoxia during differentiation (post-normoxic expansion), however, appears to result in a greater quantity of functional osteoblasts and chondrocytes and ultimately a larger quantity of high-quality differentiated tissue.

The alliance of mesenchymal stem cells, bone, and diabetes

Bone fragility has emerged as a new complication of diabetes. Several mechanisms in diabetes may influence bone homeostasis by impairing the action between osteoblasts, osteoclasts, and osteocytes and/or changing the structural properties of the bone tissue. Some of these mechanisms can potentially alter the fate of mesenchymal stem cells, the initial precursor of the osteoblast. In this review, we describe the main factors that impair bone health in diabetic patients and their clinical impact.

Effects of severe hypoxia on bone marrow mesenchymal stem cells differentiation potential

Background. The interests in mesenchymal stem cells (MSCs) and their application in cell therapy have resulted in a better understanding of the basic biology of these cells. Recently hypoxia has been indicated as crucial for complete chondrogenesis. We aimed at analyzing bone marrow MSCs (BM-MSCs) differentiation capacity under normoxic and severe hypoxic culture conditions. Methods. MSCs were characterized by flow cytometry and differentiated towards adipocytes, osteoblasts, and chondrocytes under normoxic or severe hypoxic conditions. The differentiations were confirmed comparing each treated point with a control point made of cells grown in DMEM and fetal bovine serum (FBS). Results. BM-MSCs from the donors displayed only few phenotypical differences in surface antigens expressions. Analyzing marker genes expression levels of the treated cells compared to their control point for each lineage showed a good differentiation in normoxic conditions and the absence of this differentiation capacity in severe hypoxic cultures. Conclusions. In our experimental conditions, severe hypoxia affects the in vitro differentiation potential of BM-MSCs. Adipogenic, osteogenic, and chondrogenic differentiations are absent in severe hypoxic conditions. Our work underlines that severe hypoxia slows cell differentiation by means of molecular mechanisms since a decrease in the expression of adipocyte-, osteoblast-, and chondrocyte-specific genes was observed.

Low ATP level is sufficient to maintain the uncommitted state of multipotent mesenchymal stem cells

BACKGROUND

Multipotent mesenchymal stromal cells (MMSCs) are minimally differentiated precursors with great potential to transdifferentiate. These cells are quite resistant to oxygen limitation, suggesting that a hypoxic milieu can be physiological for MMSCs.

METHODS

Human MMSCs isolated from adipose tissue were grown at various oxygen concentrations. Alteration in cell immunophenotype was determined by flow cytometry after staining with specific antibodies. Concentrations of glucose and lactate were determined using the Biocon colorimetric test. Cellular respiration was assessed using oxygen electrode. The modes of cell death were analyzed by flow cytometry after staining with Annexin V and propidium iodide.

RESULTS

We found that permanent oxygen deprivation attenuated cellular ATP levels in these cells, diminishing mitochondrial ATP production but stimulating glycolytic ATP production. At the same time, permanent hypoxia did not affect MMSCs' viability, stimulated their proliferation and reduced their capacity to differentiate. Further, permanent hypoxia decreased spontaneous cell death by MMSCs.

CONCLUSIONS

Under hypoxic conditions glycolysis provides sufficient energy to maintain MMSCs in an uncommitted state.

GENERAL SIGNIFICANCE

These findings are of interest not only for scientific reasons, but also in practical terms. Oxygen concentration makes an essential contribution to MMSC physiology and should be taken into account in the setting of protocols for cellular therapy.

Low oxygen tension maintains multipotency, whereas normoxia increases differentiation of mouse bone marrow stromal cells

Optimization of mesenchymal stem cells (MSC) culture conditions is of great importance for their more successful application in regenerative medicine. O₂ regulates various aspects of cellular biology and, in vivo, MSC are exposed to different O₂ concentrations spanning from very low tension in the bone marrow niche, to higher amounts in wounds. In our present work, we isolated mouse bone marrow stromal cells (BMSC) and showed that they contained a population meeting requirements for MSC definition. In order to establish the effect of low O₂ on cellular properties, we examined BSMC cultured under hypoxic (3% O₂) conditions. Our results demonstrate that 3% O₂ augmented proliferation of BMSC, as well as the formation of colonies in the colony-forming unit assay (CFU-A), the percentage of quiescent cells, and the expression of stemness markers Rex-1 and Oct-4, thereby suggesting an increase in the stemness of culture when exposed to hypoxia. In contrast, intrinsic differentiation processes were inhibited by 3% O₂. Overall yield of differentiation was dependent on the adjustment of O₂ tension to the specific stage of BMSC culture. Thus, we established a strategy for efficient BMSC in vitro differentiation using an initial phase of cell propagation at 3% O₂, followed by differentiation stage at 21% O₂. We also demonstrated that 3% O₂ affected BMSC differentiation in p53 and reactive oxygen species (ROS) independent pathways. Our findings can significantly contribute to the obtaining of high-quality MSC for effective cell therapy.

Adipose tissue oxygen tension: implications for chronic metabolic and inflammatory diseases

PURPOSE OF REVIEW

The present review aims to address the role of adipose tissue oxygen partial pressure (PO2) in the metabolic and endocrine derangements in conditions characterized by insulin resistance.

RECENT FINDINGS

The balance between adipose tissue oxygen supply and its metabolic rate seems to determine adipose tissue PO2. Studies in ob/ob and dietary-induced obese mice have provided evidence for adipose tissue hypoxia in obesity, which has been explained by insufficient adipose tissue angiogenesis during the massive and rapid weight gain in these animals. However, conflicting data have been reported in humans, showing both increased and decreased adipose tissue PO2 in obese compared with lean individuals. Both low and high adipose tissue PO2 may induce a proinflammatory phenotype in (pre)adipocytes, but most studies have been performed under rather extreme PO2 levels, not reflecting human adipose tissue physiology. Furthermore, adipose tissue PO2 may affect glucose and lipid metabolism as well as adipogenic differentiation, but many issues still need to be addressed.

SUMMARY

Adipose tissue hypoxia has been demonstrated in animal models of obesity, but findings in humans are controversial and require further investigation. Although adipose tissue PO2 seems to be involved in metabolic and endocrine derangements in human adipose tissue, future studies should investigate how low and high adipose tissue PO2 within the human physiological range (3-11% O2) relates to adipose tissue blood flow and oxygen consumption, cellular metabolic responses, and the inflammatory phenotype.

Oct4 and Nanog directly regulate Dnmt1 to maintain self-renewal and undifferentiated state in mesenchymal stem cells

The roles of Oct4 and Nanog in maintaining self-renewal and undifferentiated status of adult stem cells are unclear. Here, increase in Oct4 and Nanog expression along with increased proliferation and differentiation potential but decreased spontaneous differentiation were observed in early-passage (E), hypoxic culture (H), and p21 knockdown (p21KD) mesenchymal stem cells (MSCs) compared to late-passage (L), normoxic culture (N), and scrambled shRNA-overexpressed (Scr) MSCs. Knockdown of Oct4 and Nanog in E, H, and p21KD MSCs decreased proliferation and differentiation potential and enhanced spontaneous differentiation, whereas overexpression of Oct4 and Nanog in L, N, and Scr MSCs increased proliferation and differentiation potential and suppressed spontaneous differentiation. Oct4 and Nanog upregulate Dnmt1 through direct binding to its promoter, thereby leading to the repressed expression of p16 and p21 and genes associated with development and lineage differentiation. These data demonstrate the important roles of Oct4 and Nanog in maintaining MSC properties.

Pre-culturing human adipose tissue mesenchymal stem cells under hypoxia increases their adipogenic and osteogenic differentiation potentials

OBJECTIVES

Hypoxia is an important factor in many aspects of stem-cell biology including their viability, proliferation, differentiation and migration. We evaluated whether low oxygen level (2%) affected human adipose tissue mesenchymal stem-cell (hAT-MSC) phenotype, population growth, viability, apoptosis, necrosis and their adipogenic and osteogenic differentiation potential.

MATERIALS AND METHODS

hAT-MSCs from four human donors were cultured in growth medium under either normoxic or hypoxic conditions for 7 days and were then transferred to normoxic conditions to study their differentiation potential.

RESULTS

Hypoxia enhanced hAT-MSC expansion and viability, whereas expression of mesenchymal markers such as CD90, CD73 and endothelial progenitor cell marker CD34, remained unchanged. We also found that pre-culturing hAT-MSCs under hypoxia resulted in their enhanced ability to differentiate into adipocytes and osteocytes.

CONCLUSIONS

This protocol could be useful for maximizing hAT-MSC potential to differentiate in vitro into the adipogenic and osteogenic lineages, for use in plastic and reconstructive surgery, and in tissue engineering strategies.

The hypoxic microenvironment upgrades stem-like properties of ovarian cancer cells

Background

To study whether hypoxia influences the stem-like properties of ovarian cancer cells and their biological behavior under hypoxia.

Method

Ovarian cancer cell lines ES-2 and OVCAR-3 were cultivated in different oxygen tensions for proliferation, cell cycling and invasion analyses. The clonogenic potential of cells was examined by colony formation and sphere formation assays. Stem cell surface markers, SP and CD44^bright and CD44^dim cells were analyzed by flow cytometry. Protein expression of HIF-1α, HIF-2α, Ot3/4 and Sox2 were investigated by Western blotting.

Results

Both cell lines cultivated at hypoxic condition grew relatively slowly with extended G0/G1 phase. However, if the cells were pre-treated under 1% O₂ for 48 hrs before brought back to normoxia, the cells showed significantly higher proliferation rate with higher infiltration capability, and significant more colonies and spheres, in comparison to the cells always cultivated under normoxia. CD44^bright cells expressed significantly higher levels of Oct3/4 and Sox2 than the CD44^dim cells and formed significantly more clones and spheres examined in vitro. Hypoxic treatment of the cells resulted in stronger CD44 expression in both cell lines, and stronger CD133 expression in the OVCAR-3 cell line. In parallel with these findings, significantly increased number of side population (SP) cells and up-regulated expression of Oct3/4 and Sox2 in both ES-2 and OVCAR-3 cell lines were observed.

Conclusion

We conclude that ovarian cancer cells survive hypoxia by upgrading their stem-like properties through up-regulation of stemness-related factors and behave more aggressively when brought back to higher oxygen environment.

Hypoxia-mimetic agents inhibit proliferation and alter the morphology of human umbilical cord-derived mesenchymal stem cells

BACKGROUND

The therapeutic efficacy of human mesenchymal stem cells (hMSCs) for the treatment of hypoxic-ischemic diseases is closely related to level of hypoxia in the damaged tissues. To elucidate the potential therapeutic applications and limitations of hMSCs derived from human umbilical cords, the effects of hypoxia on the morphology and proliferation of hMSCs were analyzed.

RESULTS

After treatment with DFO and CoCl₂, hMSCs were elongated, and adjacent cells were no longer in close contact. In addition, vacuole-like structures were observed within the cytoplasm; the rough endoplasmic reticulum expanded, and expanded ridges were observed in mitochondria. In addition, DFO and CoCl₂ treatments for 48 h significantly inhibited hMSCs proliferation in a concentration-dependent manner (P < 0.05). This treatment also increased the number of cells in G0/G1 phase and decreased those in G2/S/M phase.

CONCLUSIONS

The hypoxia-mimetic agents, DFO and CoCl₂, alter umbilical cord-derived hMSCs morphology and inhibit their proliferation through influencing the cell cycle.

Current methods of adipogenic differentiation of mesenchymal stem cells

There has been a recent increase in our understanding in the isolation, culture, and differentiation of mesenchymal stem cells (MSCs). Concomitantly, the availability of MSCs has increased, with cells now commercially available, including human MSCs from adipose tissue and bone marrow. Despite an increased understanding of MSC biology and an increase in their availability, standardization of techniques for adipogenic differentiation of MSCs is lacking. The following review will explore the variability in adipogenic differentiation in vitro, specifically in 3T3-L1 and primary MSCs derived from both adipose tissue and bone marrow. A review of alternative methods of adipogenic induction is also presented, including the use of specific peroxisome proliferator-activated receptor-gamma agonists as well as bone morphogenetic proteins. Finally, we define a standard, commonly used adipogenic differentiation medium in the hopes that this will be adopted for the future standardization of laboratory techniques--however, we also highlight the essentially arbitrary nature of this decision. With the current, rapid pace of electronic publications, it becomes imperative for standardization of such basic techniques so that interlaboratory results may be easily compared and interpreted.

C/EBP-α and C/EBP-β-mediated adipogenesis of human mesenchymal stem cells (hMSCs) using PLGA nanoparticles complexed with poly(ethyleneimmine)

In this study, to drive efficient adipogenic differentiation, the adipogenic transcription factors C/EBP-α and C/EBP-β fused to green fluorescent protein (GFP) or red fluorescent protein (RFP) were complexed with poly-ethyleneimine (PEI) coupled with biodegradable PLGA nanospheres and delivered to human mesenchymal stem cell (hMSC). FACS analysis revealed that the transfection efficiency of C/EBP-α, C/EBP-β, or both genes complexed with PEI-coated PLGA nanospheres was 12.59%, 21.74%, and 28.96% of hMSCs. Expression and localization of C/EBP-α and C/EBP-β were confirmed by Western blotting and confocal laser microscopy. Overexpression of exogenous C/EBP-α and C/EBP-β significantly elevated adipogenic differentiation processes as indicated by RT-PCR, real-time PCR, Western blotting, histology, and immunofluorescence microscopy. During adipogenesis, PEI-coupled PLGA nanospheres complexed with C/EBP-α and C/EBP-β greatly increased the adipogenic capability of in vitro cultured cells, as well of in vivo transplanted cells. The expression of genes and proteins specific to adipogenic differentiation in hMSCs was significantly elevated compared to the controls.

Comparison of metabolite profiles in U87 glioma cells and mesenchymal stem cells

Gas chromatography-mass spectrometry (GC-MS) profiles were generated from U87 glioma cells and human mesenchymal stem cells (hMSC). 37 metabolites representing glycolysis intermediates, TCA cycle metabolites, amino acids and lipids were selected for a detailed analysis. The concentrations of these metabolites were compared and Pearson correlation coefficients were used to calculate the relationship between pairs of metabolites. Metabolite profiles and correlation patterns differ significantly between the two cell lines. These profiles can be considered as a signature of the underlying biochemical system and provide snap-shots of the metabolism in mesenchymal stem cells and tumor cells.