Hypoxia promotes proliferation and osteogenic differentiation potentials of human mesenchymal stem cells

Severe hypoxia exerts parallel and cell-specific regulation of gene expression and alternative splicing in human mesenchymal stem cells

BACKGROUND

The endosteum of the bone marrow provides a specialized hypoxic niche that may serve to preserve the integrity, pluripotency, longevity and stemness of resident mesenchymal stem cells (MSCs). To explore the molecular genetic consequences of such a niche we subjected human (h) MSCs to a pO2 of 4 mmHg and analyzed global gene expression and alternative splicing (AS) by genome-exon microarray and RT-qPCR, and phenotype by western blot and immunostaining.

RESULTS

Out of 446 genes differentially regulated by >2.5-fold, down-regulated genes outnumbered up-regulated genes by 243:203. Exon analyses revealed 60 hypoxia-regulated AS events with splice indices (SI) >1.0 from 53 genes and a correlation between high SI and degree of transcript regulation. Parallel analyses of a publicly available AS study on human umbilical vein endothelial cells (HUVECs) showed that there was a strong cell-specific component with only 11 genes commonly regulated in hMSCs and HUVECs and 17 common differentially spliced genes. Only 3 genes were differentially responsive to hypoxia at the gene (>2.0) and AS levels in both cell types. Functional assignments revealed unique profiles of gene expression with complex regulation of differentiation, extracellular matrix, intermediate filament and metabolic marker genes. Antioxidant genes, striated muscle genes and insulin/IGF-1 signaling intermediates were down-regulated. There was a coordinate induction of 9 out of 12 acidic keratins that along with other epithelial and cell adhesion markers implies a partial mesenchymal to epithelial transition.

CONCLUSIONS

We conclude that severe hypoxia confers a quiescent phenotype in hMSCs that is reflected by both the transcriptome profile and gene-specific changes of splicosome actions. The results reveal that severe hypoxia imposes markedly different patterns of gene regulation of MSCs compared with more moderate hypoxia. This is the first study to report hypoxia-regulation of AS in stem/progenitor cells and the first molecular genetic characterization of MSC in a hypoxia-induced quiescent immobile state.

Concise review: optimizing expansion of bone marrow mesenchymal stem/stromal cells for clinical applications

Bone marrow-derived mesenchymal stem/stromal cells (MSCs) have demonstrated success in the clinical treatment of hematopoietic pathologies and cardiovascular disease and are the focus of treating other diseases of the musculoskeletal, digestive, integumentary, and nervous systems. However, during the requisite two-dimensional (2D) expansion to achieve a clinically relevant number of cells, MSCs exhibit profound degeneration in progenitor potency. Proliferation, multilineage potential, and colony-forming efficiency are fundamental progenitor properties that are abrogated by extensive monolayer culture. To harness the robust therapeutic potential of MSCs, a consistent, rapid, and minimally detrimental expansion method is necessary. Alternative expansion efforts have exhibited promise in the ability to preserve MSC progenitor potency better than the 2D paradigm by mimicking features of the native bone marrow niche. MSCs have been successfully expanded when stimulated by growth factors, under reduced oxygen tension, and in three-dimensional bioreactors. MSC therapeutic value can be optimized for clinical applications by combining system inputs to tailor culture parameters for recapitulating the niche with probes that nondestructively monitor progenitor potency. The purpose of this review is to explore how modulations in the 2D paradigm affect MSC progenitor properties and to highlight recent efforts in alternative expansion techniques.

Preconditioning of mesenchymal stem cells by sevoflurane to improve their therapeutic potential

Background

Bone marrow mesenchymal stem cells (MSCs) have been found to produce beneficial effects on ischemia-reperfusion injury. However, most of the MSCs died when transplanted into the ischemic tissue, which severely limit their therapeutic potential.

Methods

Using an in vitro model of hypoxia and serum deprivation (H/SD), we investigated the hypothesis that sevoflurane preconditioning could protect MSCs against H/SD-induced apoptosis and improve their migration, proliferation, and therapeutic potential. The H/SD of MSCs and neuron-like PC12 cells were incubated in a serum-free medium and an oxygen concentration below 0.1% for 24 h. Sevoflurane preconditioning was performed through a 2-h incubation of MSCs in an airtight chamber filled with 2 vol% sevoflurane. Apoptosis of MSCs or neuron-like PC12 cells was assessed using Annexin V-FITC/propidium iodide (PI). Furthermore, the mitochondrial membrane potential was assessed using lipophilic cationic probe. The proliferation rate was evaluated through cell cycle analysis. Finally, HIF-1α, HIF-2α, VEGF and p-Akt/Akt levels were measured by western blot.

Results

Sevoflurane preconditioning minimized the MSCs apoptosis and loss of mitochondrial membrane potential. Furthermore, it increased the migration and expression of HIF-1α, HIF-2α, VEGF, and p-Akt/Akt, reduced by H/SD. In addition, neuron-like PC12 cells were more resistant to H/SD-induced apoptosis when they were co-cultured with sevoflurane preconditioning MSCs.

Conclusion

These findings suggest that sevoflurane preconditioning produces protective effects on survival and migration of MSCs against H/SD, as well as improving the therapeutic potential of MSCs. These beneficial effects might be mediated at least in part by upregulating HIF-1α, HIF-2α, VEGF, and p-Akt/Akt.

Effects of long-term hypoxia and pro-survival cocktail in bone marrow-derived stromal cell survival

The goal of this study was to determine whether a pro-survival cocktail (PSC, consisting of IGF-1, Bcl-XL, and Caspase-I Inhibitor) and long-term hypoxia (LTH) enhance survival and functional properties of bone marrow-derived stromal stem cells (BMSCs), in response to stress conditions. PSC-treated cells retained BMSC surface markers and protected cells from apoptosis under serum starvation and ischemic (1% O2 and 100 μM H2O2) conditions. LTH promoted osteogenesis, while suppressing adipogenesis. LTH alone did not result in an improvement in the apoptosis rate; however, PSC conferred significant protection regardless of the oxygenation status. One of the possible mechanisms of PSC protection was due to the elevated phospho-AKT in treated groups. PSC treatment or LTH did not alter migration toward stem cell-derived factor-1 alpha (SDF-1α) or fetal bovine serum, nor did they enhance cell motility during wound healing. There was no difference in the secreted cytokine profiles of BMSCs treated with PSC after stress when grown in normoxic or LTH. However, LTH did upregulate the vascular endothelial growth factor, hepatocyte growth factor, and SDF-1α, while it downregulated other anti- and proinflammatory cytokines and chemokines. We also observed a high degree of interdonor BMSC variability in response to pretreatment with PSC and LTH, confounding the functional results, underscoring the observation that not all donor-derived BMSCs will respond similarly.

Dopaminergic-like cells from epigenetically reprogrammed mesenchymal stem cells

A number of recent studies have examined the ability of stem cells derived from different sources to differentiate into dopamine-producing cells and ameliorate behavioural deficits in Parkinsonian models. Recently, using the approach of cell reprogramming by small cell-permeable biological active compounds that involved in the regulation of chromatin structure and function, and interfere with specific cell signalling pathways that promote neural differentiation we have been able to generate neural-like cells from human bone marrow (BM)-derived MSCs (hMSCs). Neurally induced hMSCs (NI-hMSCs) exhibited several neural properties and exerted beneficial therapeutic effect on tissue preservation and locomotor recovery in spinal cord injured rats. In this study, we aimed to determine whether hMSCs neuralized by this approach can generate dopaminergic (DA) neurons. Immunocytochemisty studies showed that approximately 50–60% of NI-hMSCs expressed early and late dopaminergic marker such as Nurr-1 and TH that was confirmed by Western blot. ELISA studies showed that NI-hMSCs also secreted neurotrophins and dopamine. Hypoxia preconditioning prior to neural induction increased hMSCs proliferation, viability, expression TH and the secretion level of dopamine induced by ATP. Taken together, these studies demonstrated that hMSCs neurally modified by this original approach can be differentiated towards DA-like neurons.

Extracellular vesicles derived from human bone marrow mesenchymal stem cells promote angiogenesis in a rat myocardial infarction model

Mesenchymal stem cells (MSCs) have been increasingly tested experimentally and clinically for cardiac repair. However, the underlying mechanisms remain controversial due to the poor viability and considerable death of the engrafted cells in the infracted myocardium. Recent reports have suggested that extracellular vesicles (EVs) released by MSCs have angiogenesis-promoting activity; however, the therapeutic effect of MSC-EVs on an ischemic heart is unclear. In the present study, we reported that MSCs could release a large quantity of EVs around 100 nm in diameter upon hypoxia stimulation though the majority of the cells had not experienced apoptosis. MSC-EVs could be promptly uptaken by human umbilical vein endothelial cells, and the internalization resulted in dose-dependent enhancement of in vitro proliferation, migration, and tube formation of endothelial cells. Using an acute myocardial infarction rat model, we found that intramyocardial injection of MSC-EVs markedly enhanced blood flow recovery, in accordance with reduced infarct size and preserved cardiac systolic and diastolic performance compared to those treated with PBS. These data suggest that like MSCs, MSC-EVs could also protect cardiac tissue from ischemic injury at least by means of promoting blood vessel formation, though further detailed investigations should be performed to define the functionality of MSC-EVs.

KEY MESSAGES

MSCs released extracellular vesicles (EVs) upon hypoxia stimulation. MSC-EVs were a mixture of microvesicles and exosomes. MSC-EVs could be promptly uptaken by human umbilical vein endothelial cells. MSC-EVs promoted neoangiogenesis in vitro and in vivo. MSC-EVs preserved cardiac performance in an AMI model.

Modulation of Human Cardiac Progenitors via Hypoxia-ERK Circuit Improves their Functional Bioactivities

Recent accumulating studies have reported that hypoxic preconditioning during ex vivo expansion enhanced the self-renewal or differentiation of various stem cells and provide an important strategy for the adequate modulation of oxygen in culture conditions, which might increase the functional bioactivity of these cells for cardiac regeneration. In this study, we proposed a novel priming protocol to increase the functional bioactivity of cardiac progenitor cells (CPCs) for the treatment of cardiac regeneration. Firstly, patient-derived c-kit⁺ CPCs isolated from the atrium of human hearts by enzymatic digestion and secondly, pivotal target molecules identifi ed their differentiation into specific cell lineages. We observed that hCPCs, in response to hypoxia, strongly activated ERK phosphorylation in ex vivo culture conditioning. Interestingly, pre-treatment with an ERK inhibitor, U0126, significantly enhanced cellular proliferation and tubular formation capacities of CPCs. Furthermore, we observed that hCPCs efficiently maintained the expression of the c-kit, a typical stem cell marker of CPCs, under both hypoxic conditioning and ERK inhibition. We also show that hCPCs, after preconditioning of both hypoxic and ERK inhibition, are capable of differentiating into smooth muscle cells (SMCs) and cardiomyocytes (CMs), but not endothelial cells (ECs), as demonstrated by the strong expression of α-SMA, Nkx2.5, and cTnT, respectively. From our results, we conclude that the functional bioactivity of patient-derived hCPCs and their ability to differentiate into SMCs and CMs can be effi ciently increased under specifically defined culture conditions such as shortterm hypoxic preconditioning and ERK inhibition.

Stem cell-based tissue engineering approaches for musculoskeletal regeneration

The field of regenerative medicine and tissue engineering is an ever evolving field that holds promise in treating numerous musculoskeletal diseases and injuries. An important impetus in the development of the field was the discovery and implementation of stem cells. The utilization of mesenchymal stem cells, and later embryonic and induced pluripotent stem cells, opens new arenas for tissue engineering and presents the potential of developing stem cell-based therapies for disease treatment. Multipotent and pluripotent stem cells can produce various lineage tissues, and allow for derivation of a tissue that may be comprised of multiple cell types. As the field grows, the combination of biomaterial scaffolds and bioreactors provides methods to create an environment for stem cells that better represent their microenvironment for new tissue formation. As technologies for the fabrication of biomaterial scaffolds advance, the ability of scaffolds to modulate stem cell behavior advances as well. The composition of scaffolds could be of natural or synthetic materials and could be tailored to enhance cell self-renewal and/or direct cell fates. In addition to biomaterial scaffolds, studies of tissue development and cellular microenvironments have determined other factors, such as growth factors and oxygen tension, that are crucial to the regulation of stem cell activity. The overarching goal of stem cell-based tissue engineering research is to precisely control differentiation of stem cells in culture. In this article, we review current developments in tissue engineering, focusing on several stem cell sources, induction factors including growth factors, oxygen tension, biomaterials, and mechanical stimulation, and the internal and external regulatory mechanisms that govern proliferation and differentiation.

Comparison of uncultured marrow mononuclear cells and culture-expanded mesenchymal stem cells in 3D collagen-chitosan microbeads for orthopedic tissue engineering

Stem cell-based therapies have shown promise in enhancing repair of bone and cartilage. Marrow-derived mesenchymal stem cells (MSC) are typically expanded in vitro to increase cell number, but this process is lengthy, costly, and there is a risk of contamination and altered cellular properties. Potential advantages of using fresh uncultured bone marrow mononuclear cells (BMMC) include heterotypic cell and paracrine interactions between MSC and other marrow-derived cells including hematopoietic, endothelial, and other progenitor cells. In the present study, we compared the osteogenic and chondrogenic potential of freshly isolated BMMC to that of cultured-expanded MSC, when encapsulated in three-dimensional (3D) collagen-chitosan microbeads. The effect of low and high oxygen tension on cell function and differentiation into orthopedic lineages was also examined. Freshly isolated rat BMMC (25 × 10(6) cells/mL, containing an estimated 5 × 10(4) MSC/mL) or purified and culture-expanded rat bone marrow-derived MSC (2 × 10(5) cells/mL) were added to a 65-35 wt% collagen-chitosan hydrogel mixture and fabricated into 3D microbeads by emulsification and thermal gelation. Microbeads were cultured in control MSC growth media in either 20% O2 (normoxia) or 5% O2 (hypoxia) for an initial 3 days, and then in control, osteogenic, or chondrogenic media for an additional 21 days. Microbead preparations were evaluated for viability, total DNA content, calcium deposition, and osteocalcin and sulfated glycosaminoglycan expression, and they were examined histologically. Hypoxia enhanced initial progenitor cell survival in fresh BMMC-microbeads, but it did not enhance osteogenic potential. Fresh uncultured BMMC-microbeads showed a similar degree of osteogenesis as culture-expanded MSC-microbeads, even though they initially contained only 1/10th the number of MSC. Chondrogenic differentiation was not strongly supported in any of the microbead formulations. This study demonstrates the microbead-based approach to culturing and delivering cells for tissue regeneration, and suggests that fresh BMMC may be an alternative to using culture-expanded MSC for bone tissue engineering.

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.

Hypoxic culture conditions as a solution for mesenchymal stem cell based regenerative therapy

Cell-based regenerative therapies, based on in vitro propagation of stem cells, offer tremendous hope to many individuals suffering from degenerative diseases that were previously deemed untreatable. Due to the self-renewal capacity, multilineage potential, and immunosuppressive property, mesenchymal stem cells (MSCs) are considered as an attractive source of stem cells for regenerative therapies. However, poor growth kinetics, early senescence, and genetic instability during in vitro expansion and poor engraftment after transplantation are considered to be among the major disadvantages of MSC-based regenerative therapies. A number of complex inter- and intracellular interactive signaling systems control growth, multiplication, and differentiation of MSCs in their niche. Common laboratory conditions for stem cell culture involve ambient O₂ concentration (20%) in contrast to their niche where they usually reside in 2–9% O₂. Notably, O₂ plays an important role in maintaining stem cell fate in terms of proliferation and differentiation, by regulating hypoxia-inducible factor-1 (HIF-1) mediated expression of different genes. This paper aims to describe and compare the role of normoxia (20% O₂) and hypoxia (2–9% O₂) on the biology of MSCs. Finally it is concluded that a hypoxic environment can greatly improve growth kinetics, genetic stability, and expression of chemokine receptors during in vitro expansion and eventually can increase efficiency of MSC-based regenerative therapies.

Modulation of physical environment makes placental mesenchymal stromal cells suitable for therapy

Low level of oxygen at the site of injury is likely to affect the viability and proliferation of the transplanted mesenchymal stromal cells (MSCs). Hence there is a need to understand the effect of the physical environment on transplanted stromal cells. Therefore, we have studied the effect of the duration of hypoxic exposure alone or in combination with normoxia on placenta derived mesenchymal stem cell (PDMSCs). PDMSCs and bone marrow MSCs (BMMSCs) were analysed under four different culture conditions, exposure to direct normoxia (N), direct hypoxia (H) and intermittent normoxia followed by hypoxia (NH) and intermittent hypoxia followed by normoxia (HN). The effect on morphology, proliferation, metabolic activity by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide) and viability by 7AAD (7-amino-actinomycin D) were assayed, along with markers for MSCs and HLADR. No change in morphology, marker expression or HLADR was detected in N, H, NH or HN. An increase in proliferation rate, decrease in population doubling-time (PDT) and a relative increase in metabolic activity was strongly noted in the order: NH, N/HN and H. No significant difference was observed in the viability between N, H, NH or HN. A similar pattern was also observed in BMMSCS, indicating comparable suitability of PDMSCs in therapeutic applications. Thus we conclude that intermittent exposure to normoxia prior to hypoxic exposure is a better option than direct exposure to hypoxia. This may have clinical relevance in that they probably mirror the in vivo scenario of systemic delivery (NH) of cells as opposed to local delivery (H), thereby suggesting that systemic delivery is better than local delivery.

Antioxidants cause rapid expansion of human adipose-derived mesenchymal stem cells via CDK and CDK inhibitor regulation

Background

Antioxidants have been shown to enhance the proliferation of adipose-derived mesenchymal stem cells (ADMSCs) in vitro, although the detailed mechanism(s) and potential side effects are not fully understood.

In this study, human ADMSCs cultured in ImF-A medium supplemented with antioxidants (N-acetyl-l-cysteine and ascorbic acid-2-phosphate) and fibroblast growth factor 2 (FGF-2) were compared with ADMSCs cultured with FGF-2 alone (ImF) or with FGF-2 under 5% pO₂ conditions (ImF-H).

Results

During log-phase growth, exposure to ImF-A resulted in a higher percentage of ADMSCs in the S phase of the cell cycle and a smaller percentage in G0/G1 phase. This resulted in a significantly reduced cell-doubling time and increased number of cells in the antioxidant-supplemented cultures compared with those supplemented with FGF-2 alone, an approximately 225% higher cell density after 7 days. Western blotting showed that the levels of the CDK inhibitors p21 and p27 decreased after ImF-A treatment, whereas CDK2, CDK4, and CDC2 levels clearly increased. In addition, ImF-A resulted in significant reduction in the expression of CD29, CD90, and CD105, whereas relative telomere length, osteogenesis, adipogenesis, and chondrogenesis were enhanced. The results were similar for ADMSCs treated with antioxidants and those under hypoxic conditions.

Conclusion

Antioxidant treatment promotes entry of ADMSCs into the S phase by suppressing cyclin-dependent kinase inhibitors and results in rapid cell proliferation similar to that observed under hypoxic conditions.

Hypoxia induces osteogenesis in rabbit adipose-derived stem cells overexpressing bone morphogenic protein-2

OBJECTIVE

Hypoxic culture potentiates mesenchymal stem cells (MSCs) to survive and secrete various growth factors. Genetically modified stem cells overexpressing bone morphogenic protein-2 (BMP-2) demonstrate strong osteogenic ability. Hence, we investigated the coeffect of hypoxic culture conditions and BMP-2 overexpression on the osteogenic ability of rabbit adipose-derived stem cells (rASCs) in vitro.

MATERIALS AND METHODS

Rabbit adipose-derived stem cells with or without adenoviral-BMP-2 transduction were cultured in hypoxic (1%) and normoxic (21%) conditions. Cell viability, attachment, and proliferation were compared. Real-time PCR amplification of osteogenic and angiogenic genes including alkaline phosphatase (ALP), osteocalcin (OCN), HIF-1α, and vascular endothelial growth factor (VEGF) was performed. Moreover, ALP activity, immunofluorescent staining of OCN, and mineralization assay by alizarin red S quantification and von Kossa staining were conducted.

RESULTS

Cells under hypoxic conditions attached better within 12 h and proliferated faster. While BMP-2 overexpression and hypoxic condition separately elevated the transcription of key osteogenic and angiogenic genes, a cooperative effect was observed to enhance the upregulation of osteogenic as well as angiogenic genes. Identical changes were observed in ALP activity, immunofluorescent staining of OCN, and mineralization assay.

CONCLUSIONS

Hypoxic culture can enhance the osteogenic ability of BMP-2 gene-modified rASCs, which provides a strategy to improve the osteogenesis of rASCs for in vivo bone regeneration.

Bone mineral density is associated with site-specific atherosclerosis in patients with severe peripheral artery disease

Recent studies have highlighted a significant association between the severity of atherosclerosis and bone mineral density (BMD) among healthy subjects, although its connection to angiographically determined peripheral artery disease (PAD) has never been investigated. We evaluated the connection between the angiographic severity and site specificity of peripheral atherosclerosis and osteoporosis among patients with chronic lower limb ischemia. In our cross-sectional study we investigated 172 patients with PAD. The anatomic sites of the lesions were analyzed. The severity of atherosclerosis was diagnosed using the Bollinger angiographic score (BS). BMD was measured at the lumbar spine (l-BMD) and at femoral (f-BMD) and radial (r-BMD) sites by dual-energy X-ray absorptiometry. Dyslipidemia, the level of vitamin D(3), and different bone turnover markers were also noted. Among PAD patients, regardless of the lesion site, we did not find any association between BMD and BS. Among patients with iliac disease, BS was associated with l-BMD (p = 0.038, r = -0.467) and with f-BMD (p = 0.002, r = -0.642). The level of r-BMD among patients with iliac disease was not associated with BS (p = 0.233, r = -0.306). We did not find any difference between the group of patients with and that without dyslipidemia and low or normal levels of vitamin D(3). Our results show a connection between the severity of atherosclerosis and osteoporosis among patients with PAD, specific to the site of the lesion. The findings regarding dyslipidemia, bone markers, and site specificity support the hypothesis that reduced blood flow is the key factor responsible for the inverse association of BMD with atherosclerosis.

Low oxygen tension enhances proliferation and maintains stemness of adipose tissue-derived stromal cells

Recent evidence indicates that low oxygen tension or hypoxia alters the characteristics of stem cells. The actions of hypoxia are mediated through the hypoxia-inducible factor, a critical mediator of the cellular response to hypoxia. Adipose tissue–derived stromal cells (ASCs) are one of the most promising cell sources for tissue engineering applications. This study investigated the effect of hypoxia on ASCs in terms of the ability to proliferate and differentiate. ASCs were extracted from mice and maintained under hypoxic atmosphere (2% O₂) for up to eight in vitro passages. The proliferation rate was examined as a growth curve, and the potency of differentiation was evaluated. To investigate the cell characteristics, we checked several stem-cell markers and growth factors. Compared with the normoxic state (20% O₂), hypoxia enhances proliferation with an approximately six- to sevenfold higher ASC expansion over 6 weeks. The expression of Oct3/4 and Nanog (stem-cell marker) and the amount of secreted growth factors were increased under the hypoxic condition. These results suggest that low oxygen tension enhances proliferation and maintains stemness of ASCs. Thus, this study emphasizes the profitability of hypoxic culture for expansion of ASCs and maintenance of their undifferentiated state for further therapeutic use.

The use of hypoxic cultured mesenchymal stem cell for oncolytic virus therapy

The safety of oncolytic viruses, such as conditionally replicative adenoviruses (CRAds), has been validated in clinical trials for cancer therapy. Their antitumor efficacy is limited by the presence of preexisting neutralizing antibodies (NAbs). Mesenchymal stem cells (MSCs) are attractive as a cellular vehicle to carry antitumor agents, not only because they are easily obtained and expanded to great numbers in vitro, but also because of their ability to migrate and engraft to tumors. MSCs expanded under hypoxic conditions decrease in replicative senescence and increase in proliferation capacity and differentiation potentials. However it remains to be clarified whether these hypoxic MSCs also are good carriers for the delivery of CRAds to tumor cells in the presence of NAbs. This study firstly demonstrated hypoxic MSCs with an increased ability to migrate toward tumors through the upregulation of chemokine receptors, such as CXCR4 and CX3CR1. It is then demonstrated that hypoxic MSCs has the capacity to carry CRAds, without inducing apoptosis, for up to one week. Using an in vitro coculture with human colon cancer cells and with intraperitoneally (i.p.) and subcutaneously (s.c.) developed human colon cancer xenografts, it is demonstrated that hypoxic MSCs are able to protect CRAds from attack by NAbs, thereby successfully delivering them to the target tumor cells. These results show that hypoxic MSCs can serve as cell carriers for CRAds and may help to develop new strategies against cancer.

[Prevalence of osteoporosis in patients with severe peripheral artery disease]

INTRODUCTION

Recent studies highlighted a significant association between bone mineral density and atherosclerosis. Cardiovascular disease is the main cause of death in Western countries, while the prevalence of osteoporosis reached 9% in Hungary.

AIM

The aim of this study was to investigate the prevalence of osteoporosis among patients with peripheral vascular disease.

METHODS

In a cross-sectional study bone mineral density using dual-energy X-ray absorptiometry in 172 patients with lower limb ischemia was investigated. According to previous medical history and blood tests, risk factors of atherosclerosis were also assessed and serum markers of bone turnover and other factors that could influence osteoporosis were evaluated.

RESULTS

Prior to bone mineral density screening, osteoporosis was known in 9% of patients. Based on osteodensitometric evaluation, 37% of the patients were diagnosed as having osteopenia and 31% as having osteoporosis. According to risk factors, different patient groups were created. Significantly more female than male patients had osteoporosis, while smoking, age and body mass index failed to affect the prevalence of osteoporosis.

CONCLUSION

These results suggest that patients with severe atherosclerosis need to be regularly screened and, if necessary, treated for osteoporosis.

A quantitative approach for understanding small-scale human mesenchymal stem cell culture - implications for large-scale bioprocess development

Human mesenchymal stem cell (hMSC) therapies have the potential to revolutionise the healthcare industry and replicate the success of the therapeutic protein industry; however, for this to be achieved there is a need to apply key bioprocessing engineering principles and adopt a quantitative approach for large-scale reproducible hMSC bioprocess development. Here we provide a quantitative analysis of the changes in concentration of glucose, lactate and ammonium with time during hMSC monolayer culture over 4 passages, under 100% and 20% dissolved oxgen (dO2 ), where either a 100%, 50% or 0% growth medium exchange was performed after 72h in culture. Yield coefficients, specific growth rates (h(-1) ) and doubling times (h) were calculated for all cases. The 100% dO2 flasks outperformed the 20% dO2 flasks with respect to cumulative cell number, with the latter consuming more glucose and producing more lactate and ammonium. Furthermore, the 100% and 50% medium exchange conditions resulted in similar cumulative cell numbers, whilst the 0% conditions were significantly lower. Cell immunophenotype and multipotency were not affected by the experimental culture conditions. This study demonstrates the importance of determining optimal culture conditions for hMSC expansion and highlights a potential cost savings from only making a 50% medium exchange, which may prove significant for large-scale bioprocessing.

Induction of Functional Mesenchymal Stem Cells from Rabbit Embryonic Stem Cells by Exposure to Severe Hypoxic Conditions

Embryonic stem cells (ESCs) have the potential to be used as an unlimited cell source for cell transplantation therapy, as well as for studying mechanisms of disease and early mammalian development. However, applications involving ESCs have been limited by the lack of reliable differentiation methods in many cases. Mesenchymal stem cells (MSCs) have also emerged as a promising cell source, but as suggested in recent studies, these cells display limited potential for proliferation and differentiation, thereby limiting their usefulness in the clinic and in the laboratory. Unfortunately, effective methods for induction of MSCs from pluripotent stem cells have not been established, and the development of such methods remains a major challenge facing stem cell biologists. Oxygen concentration is one of the most important factors regulating tissue development. It has profound effects on cell metabolism and physiology and can strongly influence stem cell fate. Here we demonstrate that severe low O2 concentrations (1%) can function as a selective pressure for removing undifferentiated pluripotent cells during the induction of MSCs from rabbit ESCs (rESCs) and that MSCs induced under severe hypoxic conditions function as normal MSCs; that is, they repopulate after cloning, express specific markers (vimentin, CD29, CD90, CD105, and CD140a) and differentiate into adipocytes, osteoblasts, and chondrocytes. Furthermore, we demonstrate that these cells can contribute to cartilage regeneration in an in vivo rabbit model for joint cartilage injury. These results support the notion that exposing ESCs to severe hypoxic conditions during differentiation can be used as a strategy for the preparation of functional MSCs from ESCs.

Mesenchymal stromal/stem cells markers in the human bone marrow

BACKGROUND AIMS

Mesenchymal stromal/stem cells (MSCs) can be isolated from human bone marrow (BM), expanded ex vivo and identified via numerous surface antigens. Despite the importance of these cells in regenerative therapy programs, it is unclear whether the cell membrane signature defining MSC preparations ex vivo is determined during culture or may reflect an in vivo counterpart. BM-MSC phenotype in vivo requires further investigation.

METHODS

To characterize cells in their natural BM environment, we performed multi-parametric immunohistochemistry on trabecular bone biopsy specimens from multiple donors and described cells by different morphology and micro-anatomic localization in relationship to a precise pattern of MSC antigen expression.

RESULTS

Microscopically examined high-power field marrow sections revealed an overlapping in vivo expression of antigens characterizing ex vivo expanded BM-MSCs, including CD10, CD73, CD140b, CD146, GD2 and CD271. Expanding this panel to proteins associated with pluripotency, such as Oct4, Nanog and SSEA-4, we were able to identify different cellular populations in the human trabecular bone and BM expressing different progenitor cell markers.

CONCLUSIONS

Targeting several multipotency and pluripotency markers, we found that the BM contains identifiable and distinct progenitor cells further justifying their introduction for a wide range of applications in regenerative medicine.

Hypoxia-induced secretion of TGF-β1 in mesenchymal stem cell promotes breast cancer cell progression

In solid tumors, a decreased oxygen and nutrient supply creates a hypoxic microenvironment in the central region. This hypoxic condition induces molecular responses of normal and cancer cells in the local area, including angiogenesis, metabolic changes, and metastasis. In addition, other cells including mesenchymal stem cells (MSCs) have been reported to be recruited into the hypoxic area of solid tumors. In our previous study, we found that hypoxic condition induces the secretion of growth factors and cytokines in MSCs, and here we demonstrate that elevated secretion of transforming growth factor-β1 (TGF-β1) by MSCs under hypoxia promotes the growth, motility, and invasive ability of breast cancer cells. It was found that TGF-β1 promoter activity was regulated by hypoxia, and the major hypoxia-regulated element was located between bp -1030 to -666 in front of the TGF-β1 promoter region. In ChIP assay, the results revealed that HIF-1 was bound to the hypoxia response element (HRE) of TGF-β1 promoter. Collectively, the results indicate that hypoxia microenvironment can enhance cancer cell growth through the paracrine effects of the MSCs by driving their TGF-β1 gene expression and secretion. Therefore, extra caution has to be exercised when considering hypoxia pretreatment of MSCs before cell transplantation into patients for therapeutic purposes, particularly in patients susceptible to tumor growth.

Microvesicles derived from human umbilical cord mesenchymal stem cells stimulated by hypoxia promote angiogenesis both in vitro and in vivo

Although mesenchymal stem cells (MSCs) have been increasingly trialed to treat a variety of diseases, the underlying mechanisms remain still elusive. In this study, human umbilical cord (UC)-derived MSCs were stimulated by hypoxia, and the membrane microvesicles (MVs) in the supernatants were collected by ultracentrifugation, observed under an electron microscope, and the origin was identified with the flow cytometric technique. The results showed that upon hypoxic stimulus, MSCs released a large quantity of MVs of ~100 nm in diameter. The MVs were phenotypically similar to the parent MSCs, except that the majority of them were negative for the receptor of platelet-derived growth factor. DiI-labeling assay revealed that MSC-MVs could be internalized into human UC endothelial cells (UC-ECs) within 8 h after they were added into the culture medium. Carboxyfluorescein succinimidyl ester-labeling technique and MTT test showed that MSC-MVs promoted the proliferation of UC-ECs in a dose-dependent manner. Further, MVs could enhance in vitro capillary network formation of UC-ECs in a Matrigel matrix. In a rat hindlimb ischemia model, both MSCs and MSC-MVs were shown to improve significantly the blood flow recovery compared with the control medium (P<0.0001), as assessed by laser Doppler imaging analysis. These data indicate that MV releasing is one of the major mechanisms underlying the effectiveness of MSC therapy by promoting angiogenesis.

Atmospheric oxygen inhibits growth and differentiation of marrow-derived mouse mesenchymal stem cells via a p53-dependent mechanism: implications for long-term culture expansion

Large scale expansion of human mesenchymal stem cells (MSCs) is routinely performed for clinical therapy. In contrast, developing protocols for large scale expansion of primary mouse MSCs has been more difficult due to unique aspects of rodent biology. Currently, established methods to isolate mouse MSCs select for rapidly dividing subpopulations that emerge from bone marrow cultures following long-term (months) expansion in atmospheric oxygen. Herein, we demonstrate that exposure to atmospheric oxygen rapidly induced p53, TOP2A, and BCL2-associated X protein (BAX) expression and mitochondrial reactive oxygen species (ROS) generation in primary mouse MSCs resulting in oxidative stress, reduced cell viability, and inhibition of cell proliferation. Alternatively, procurement and culture in 5% oxygen supported more prolific expansion of the CD45(-ve) /CD44(+ve) cell fraction in marrow, produced increased MSC yields following immunodepletion, and supported sustained MSC growth resulting in a 2,300-fold increase in cumulative cell yield by fourth passage. MSCs cultured in 5% oxygen also exhibited enhanced trilineage differentiation. The oxygen-induced stress response was dependent upon p53 since siRNA-mediated knockdown of p53 in wild-type cells or exposure of p53(-/-) MSCs to atmospheric oxygen failed to induce ROS generation, reduce viability, or arrest cell growth. These data indicate that long-term culture expansion of mouse MSCs in atmospheric oxygen selects for clones with absent or impaired p53 function, which allows cells to escape oxygen-induced growth inhibition. In contrast, expansion in 5% oxygen generates large numbers of primary mouse MSCs that retain sensitivity to atmospheric oxygen, and therefore a functional p53 protein, even after long-term expansion in vitro.

Bioreactors to influence stem cell fate: augmentation of mesenchymal stem cell signaling pathways via dynamic culture systems

BACKGROUND

Mesenchymal stem cells (MSCs) are a promising cell source for bone and cartilage tissue engineering as they can be easily isolated from the body and differentiated into osteoblasts and chondrocytes. A cell based tissue engineering strategy using MSCs often involves the culture of these cells on three-dimensional scaffolds; however the size of these scaffolds and the cell population they can support can be restricted in traditional static culture. Thus dynamic culture in bioreactor systems provides a promising means to culture and differentiate MSCs in vitro.

SCOPE OF REVIEW

This review seeks to characterize key MSC differentiation signaling pathways and provides evidence as to how dynamic culture is augmenting these pathways. Following an overview of dynamic culture systems, discussion will be provided on how these systems can effectively modify and maintain important culture parameters including oxygen content and shear stress. Literature is reviewed for both a highlight of key signaling pathways and evidence for regulation of these signaling pathways via dynamic culture systems.

MAJOR CONCLUSIONS

The ability to understand how these culture systems are affecting MSC signaling pathways could lead to a shear or oxygen regime to direct stem cell differentiation. In this way the efficacy of in vitro culture and differentiation of MSCs on three-dimensional scaffolds could be greatly increased.

GENERAL SIGNIFICANCE

Bioreactor systems have the ability to control many key differentiation stimuli including mechanical stress and oxygen content. The further integration of cell signaling investigations within dynamic culture systems will lead to a quicker realization of the promise of tissue engineering and regenerative medicine. This article is part of a Special Issue entitled Biochemistry of Stem Cells.

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.

Increased stemness and migration of human mesenchymal stem cells in hypoxia is associated with altered integrin expression

Human mesenchymal stem cells (hMSCs) are regularly cultured and characterised under normoxic (21% O(2)) conditions, although the physiological oxygen tension in the stem cell niche is known to be as low as 1-2%. Oxygen itself is an important signalling molecule, but the distinct impact on various stem cell characteristics is still unclear. Therefore, the aim of this study was to evaluate the influence of oxygen concentration on the hMSC subpopulation composition, cell morphology and migration on different surfaces (polystyrene, collagen I, fibronectin, laminin) as well as on the expression of integrin receptors. Bone marrow-derived hMSCs were cultured either in normoxic (21% O(2)) or hypoxic (2% O(2)) conditions. The hMSC subpopulations were assessed by aspect ratio and cell area. Hypoxia promoted a more homogeneous cell population with a significantly higher fraction of rapidly self-renewing cells which are believed to be the true stem cells. Under hypoxic conditions hMSC volume and height were significantly decreased on all surfaces as measured by white light confocal microscopy. Furthermore, low oxygen tension led to a significant increase in cell velocity and Euclidian distance on all matrixes, which was evaluated by time-lapse microscopy. With regard to cell-matrix contacts, expression of several integrin subunits was evaluated by semi-quantitative RT-PCR. Increased expression of the subunits α(1), α(3), α(5,) α(6), α(11), α(v), β(1) and β(3) was observed in hypoxic conditions, while α(2) was higher expressed in normoxic cultured hMSCs. Taken together, our results indicate that hypoxic conditions promote stemness and migration of hMSC along with altering their integrin expression.

Assessing statistical significance in causal graphs

Background

Causal graphs are an increasingly popular tool for the analysis of biological datasets. In particular, signed causal graphs--directed graphs whose edges additionally have a sign denoting upregulation or downregulation--can be used to model regulatory networks within a cell. Such models allow prediction of downstream effects of regulation of biological entities; conversely, they also enable inference of causative agents behind observed expression changes. However, due to their complex nature, signed causal graph models present special challenges with respect to assessing statistical significance. In this paper we frame and solve two fundamental computational problems that arise in practice when computing appropriate null distributions for hypothesis testing.

Results

First, we show how to compute a p-value for agreement between observed and model-predicted classifications of gene transcripts as upregulated, downregulated, or neither. Specifically, how likely are the classifications to agree to the same extent under the null distribution of the observed classification being randomized? This problem, which we call "Ternary Dot Product Distribution" owing to its mathematical form, can be viewed as a generalization of Fisher's exact test to ternary variables. We present two computationally efficient algorithms for computing the Ternary Dot Product Distribution and investigate its combinatorial structure analytically and numerically to establish computational complexity bounds.

Second, we develop an algorithm for efficiently performing random sampling of causal graphs. This enables p-value computation under a different, equally important null distribution obtained by randomizing the graph topology but keeping fixed its basic structure: connectedness and the positive and negative in- and out-degrees of each vertex. We provide an algorithm for sampling a graph from this distribution uniformly at random. We also highlight theoretical challenges unique to signed causal graphs; previous work on graph randomization has studied undirected graphs and directed but unsigned graphs.

Conclusion

We present algorithmic solutions to two statistical significance questions necessary to apply the causal graph methodology, a powerful tool for biological network analysis. The algorithms we present are both fast and provably correct. Our work may be of independent interest in non-biological contexts as well, as it generalizes mathematical results that have been studied extensively in other fields.