Hypoxia and stem cell-based engineering of mesenchymal tissues

Culture in 10% O2 enhances the production of active hormones in neuro-endocrine cells by up-regulating the expression of processing enzymes

To closely mimic physiological conditions, low oxygen cultures have been employed in stem cell and cancer research. Although in vivo oxygen concentrations in tissues are often much lower than ambient 21% O₂ (ranging from 3.6 to 12.8% O₂), most cell cultures are maintained at 21% O₂ To clarify the effects of the O₂ culture concentration on the regulated secretion of peptide hormones in neuro-endocrine cells, we examined the changes in the storage and release of peptide hormones in neuro-endocrine cell lines and endocrine tissues cultured in a relatively lower O₂ concentration. In both AtT-20 cells derived from the mouse anterior pituitary and freshly prepared mouse pituitaries cultured in 10% O₂ for 24 h, the storage and regulated secretion of the mature peptide hormone adrenocorticotropic hormone were significantly increased compared with those in cells and pituitaries cultured in ambient 21% O₂, whereas its precursor proopiomelanocortin was not increased in the cells and tissues after being cultured in 10% O₂ Simultaneously, the prohormone-processing enzymes PC1/3 and carboxypeptidase E were up-regulated in cells cultured in 10% O₂, thus facilitating the conversion of prohormones to their active form. Similarly, culturing the mouse β-cell line MIN6 and islet tissue in 10% O₂ also significantly increased the conversion of proinsulin into mature insulin, which was secreted in a regulated manner. These results suggest that culture under 10% O₂ is more optimal for endocrine tissues/cells to efficiently generate and secrete active peptide hormones than ambient 21% O₂.

Mesenchymal Stromal Cell Secretome: Influencing Therapeutic Potential by Cellular Pre-conditioning

Mesenchymal stromal cells (MSCs) are self-renewing, culture-expandable adult stem cells that have been isolated from a variety of tissues, and possess multipotent differentiation capacity, immunomodulatory properties, and are relatively non-immunogenic. Due to this unique set of characteristics, these cells have attracted great interest in the field of regenerative medicine and have been shown to possess pronounced therapeutic potential in many different pathologies. MSCs' mode of action involves a strong paracrine component resulting from the high levels of bioactive molecules they secrete in response to the local microenvironment. For this reason, MSCs' secretome is currently being explored in several clinical contexts, either using MSC-conditioned media (CM) or purified MSC-derived extracellular vesicles (EVs) to modulate tissue response to a wide array of injuries. Rather than being a constant mixture of molecular factors, MSCs' secretome is known to be dependent on the diverse stimuli present in the microenvironment that MSCs encounter. As such, the composition of the MSCs' secretome can be modulated by preconditioning the MSCs during in vitro culture. This manuscript reviews the existent literature on how preconditioning of MSCs affects the therapeutic potential of their secretome, focusing on MSCs' immunomodulatory and regenerative features, thereby providing new insights for the therapeutic use of MSCs' secretome.

Mesenchymal stem cell cultivation in electrospun scaffolds: mechanistic modeling for tissue engineering

Tissue engineering is a multidisciplinary field of research in which the cells, biomaterials, and processes can be optimized to develop a tissue substitute. Three-dimensional (3D) architectural features from electrospun scaffolds, such as porosity, tortuosity, fiber diameter, pore size, and interconnectivity have a great impact on cell behavior. Regarding tissue development in vitro, culture conditions such as pH, osmolality, temperature, nutrient, and metabolite concentrations dictate cell viability inside the constructs. The effect of different electrospun scaffold properties, bioreactor designs, mesenchymal stem cell culture parameters, and seeding techniques on cell behavior can be studied individually or combined with phenomenological modeling techniques. This work reviews the main culture and scaffold factors that affect tissue development in vitro regarding the culture of cells inside 3D matrices. The mathematical modeling of the relationship between these factors and cell behavior inside 3D constructs has also been critically reviewed, focusing on mesenchymal stem cell culture in electrospun scaffolds.

Demineralized Bone Scaffolds with Tunable Matrix Stiffness for Efficient Bone Integration

As a biophysical cue, matrix stiffness can decide the stem cell fate. However, most methods to construct three-dimensional (3D) scaffolds may change the 3D microstructure while altering their mechanical properties. In this study, demineralized bone matrix scaffolds with different compressive modulus (66.06 ± 27.83 MPa (high), 26.90 ± 13.16 MPa (medium), and 0.67 ± 0.14 MPa (low)) were constructed by controlling the decalcification duration (1 h, 12 h, and 5 days), respectively. The pore size and porosity have no significant difference between the scaffolds before and after decalcification. Cell experiments indicated that the low scaffolds could promote the osteogenic differentiation of bone marrow mesenchymal stem cells (MSCs) in vitro. Rat subcutaneous implantation experiments further demonstrated that the low scaffolds could efficiently improve the cell infiltration, deposition of collagen fibers, and positive osteocalcin and osteopontin expression of endogenous cells as well as angiogenesis. Finally, rabbit femoral condylar defect experiments proved that the low scaffolds could significantly promote the bone repair and integration and stromal cell derived factor-1α/CXC chemokine receptor signal pathway was essential for the stiffness-mediated bone repair. These investigations provided a novel method for fabricating 3D bone grafts with different stiffness, which is also of great significance for studying the effect of stiffness on the biological behavior of MSCs in three dimensions.

Regenerative medicine and 3D bioprinting for human space exploration and planet colonisation

3D printing also known as additive manufacturing (AM) is seen as one of the key enabling technologies for a large number of high-end industrial sectors including the automotive, aerospace and medical industry. Recent advances and breakthroughs in the last years have enabled 3D printing of biocompatible materials, cells and supporting components into complex 3D functional living tissues. 3D bioprinting is being applied to regenerative medicine, addressing the need for tissues and organs suitable for transplantation. Bioprinting implies additional complexities related to the sensitivities of living cells such as printing parameters and conditions, material selection, cell types etc. Despite these challenges, beating artificial heart cells, cartilage implants, skin repairs, functional kidney tissues have been printed successfully on Earth. The present paper addresses the possibility of performing regenerative medicine in space, which may guarantee sustainable life support on long term/long distance planetary exploration missions, opening to stable planet colonisation.

Exposure to tobacco smoke increases bone loss in spontaneously hypertensive rats

PURPOSE

To define if exposure to tobacco smoke (TS) could induce reduction of bone mass and impairment of bone architecture, features observed in osteoporosis in normotensive rats and the influence of TS exposure on the osteoporotic features exhibited in the spontaneously hypertensive (SH) rats.

METHODS

Normotensive Wistar Kyoto (WKY) and SH rats were exposed to filtered air or TS for 8 weeks, then their proximal femurs were extracted for micro-computed tomography (micro-CT) assessment, histological and immune-histological examinations to quantify the adverse influence of TS exposure on the bone mass and density, as well as bone architecture.

RESULTS

We found that TS exposure not only induced significant decreases in bone mineral density (BMD), bone volume (BV), cortical and trabecular thickness (Ct.Th and Tb.Th), trabecular surface area (Tb.Ar), expression of hypoxia-inducible factor-1α (HIF-1α) in the trabecular marrow, delayed ossification of cartilage, as well as statistical increases in trabecular separation (Tb.SP) and the number of trabecular marrow adipocytes in both WKY and SH rats, but also exacerbated multiple features of osteoporosis exhibited in SH rats, including decreased BMD, Ct.Th, Tb.Ar, HIF-1α expression, delayed cartilage ossification, and increased Tb.SP.

CONCLUSIONS

Our results show that TS exposure can reduce bone mass and impair bone architecture and exacerbate multiple features of osteoporosis exhibited in SH rats.

Expansion of Human Mesenchymal Stem Cells in a Fixed-Bed Bioreactor System Based on Non-Porous Glass Carrier – Part B: Modeling and Scale-up of the System

Human mesenchymal stem cells (hMSC) are a promising cell source for the manufacturing of cell therapy or tissue-engineered implants. In part A of this publication a fixed-bed bioreactor system based on non-porous borosilicate glass spheres and procedures for the automated expansion of hMSC with high yield and vitality was introduced. Part B of this study deals with the modeling of the process in order to transfer the bioreactor system from the laboratory to the production scale. Relevant model parameters were obtained by fitting them to the experimental data of hMSC-TERT cultivations in scales up to 300 cm3. Scale-up calculations were carried out exemplarily for a target cell number of twenty billion cells.

Physiological Hypoxia Enhances Stemness Preservation, Proliferation, and Bidifferentiation of Induced Hepatic Stem Cells

Induced hepatic stem cells (iHepSCs) have great potential as donors for liver cell therapy due to their self-renewal and bipotential differentiation properties. However, the efficiency of bidifferentiation and repopulation efficiency of iHepSCs is relatively low. Recent evidence shows that physiological hypoxia, a vital factor within stem cell “niche” microenvironment, plays key roles in regulating tissue stem cell biological behaviors including proliferation and differentiation. In this study, we found that physiological hypoxia (10% O₂) enhanced the stemness properties and promoted the proliferation ability of iHepSCs by accelerating G1/S transition via p53-p21 signaling pathway. In addition, short-term hypoxia preconditioning improved the efficiency of hepatic differentiation of iHepSCs, and long-term hypoxia promoted cholangiocytic differentiation but inhibited hepatic differentiation of iHepSCs. These results demonstrated the potential effects of hypoxia on stemness preservation, proliferation, and bidifferentiation of iHepSCs and promising perspective to explore appropriate culture conditions for therapeutic stem cells.

iTRAQ-Based Proteomic Analysis Exploring the Influence of Hypoxia on the Proteome of Dental Pulp Stem Cells under 3D Culture

Hypoxic preconditioning is commonly applied to enhance mesenchymal stem cells (MSCs) therapeutic effect before transplantation. Elucidating the effect of hypoxic preconditioning would be beneficial for improved application. However, the influence of hypoxia on dental tissue derived MSCs cultured in 3D was unknown. Thus, the present study is to investigate gene expression and proteome of dental pulp stem cells (DPSCs) after hypoxic preconditioning. DPSCs were isolated, cultured in a 3D system under the normoxic and hypoxic conditions. The gene expression was examined with reverse transcription polymerase chain reaction, and the proteome was analyzed using iTRAQ-based mass spectrometry. The expressions of HIF-1α, VEGFA, KDR at mRNA level was upregulated while BMP-2 was downregulated. Two thousand one hundred and fifteen proteins were identified and 57 proteins exhibited significant differences after hypoxic preconditioning (30 up-regulated, 27 down-regulated). Bioinformatic analysis revealed the majority of up-regulated proteins are involved in cellular process, angiogenesis, protein binding and transport, regulation of response to stimulus, metabolic processes, and immune response. Increased IL-6 and decreased TGF-1β protein expression under hypoxic condition were verified by ELISA. Hypoxic preconditioning partly affected the gene and protein expression in DPSCs under 3D culture and may enhance the efficacy of MSCs transplantation.

An Injectable Oxygen Release System to Augment Cell Survival and Promote Cardiac Repair Following Myocardial Infarction

Oxygen deficiency after myocardial infarction (MI) leads to massive cardiac cell death. Protection of cardiac cells and promotion of cardiac repair are key therapeutic goals. These goals may be achieved by re-introducing oxygen into the infarcted area. Yet current systemic oxygen delivery approaches cannot efficiently diffuse oxygen into the infarcted area that has extremely low blood flow. In this work, we developed a new oxygen delivery system that can be delivered specifically to the infarcted tissue, and continuously release oxygen to protect the cardiac cells. The system was based on a thermosensitive, injectable and fast gelation hydrogel, and oxygen releasing microspheres. The fast gelation hydrogel was used to increase microsphere retention in the heart tissue. The system was able to continuously release oxygen for 4 weeks. The released oxygen significantly increased survival of cardiac cells under the hypoxic condition (1% O₂) mimicking that of the infarcted hearts. It also reduced myofibroblast formation under hypoxic condition (1% O₂). After implanting into infarcted hearts for 4 weeks, the released oxygen significantly augmented cell survival, decreased macrophage density, reduced collagen deposition and myofibroblast density, and stimulated tissue angiogenesis, leading to a significant increase in cardiac function.

Transplantation of Rat Mesenchymal Stem Cells Overexpressing Hypoxia-Inducible Factor 2α Improves Blood Perfusion and Arteriogenesis in a Rat Hindlimb Ischemia Model

Mesenchymal stem cells (MSCs) have been increasingly tested in cell-based therapy to treat numerous diseases. Genetic modification to improve MSC behavior may enhance posttransplantation outcome. This study aims to test the potential therapeutic benefits of rat bone marrow MSCs overexpressing hypoxia-inducible factor 2α (rMSCs^HIF-2α) in a rat hindlimb ischemia model. PBS, rMSCs, or rMSCs^HIF-2α were injected into rat ischemic hindlimb. Compared with the injection of PBS or rMSCs, transplantation of rMSCs^HIF-2α significantly improved blood perfusion, increased the number of vessel branches in the muscle of the ischemic hindlimb, and improved the foot mobility of the ischemic hindlimb (all P < 0.05). rMSC^HIF-2α transplantation also markedly increased the expression of proangiogenic factors VEGF, bFGF, and SDF1 and Notch signaling proteins including DII4, NICD, Hey1, and Hes1, whereas it reduced the expression of proapoptotic factor Bax in the muscle of the ischemic hindlimb. Overexpression of HIF-2α did not affect rMSC stemness and proliferation under normoxia but significantly increased rMSC migration and tube formation in matrigel under hypoxia (all P < 0.05). RMSCs^HIF-2α stimulated endothelial cell invasion under hypoxia significantly (P < 0.05). Genetic modification of rMSCs via overexpression of HIF-2α improves posttransplantation outcomes in a rat hindlimb ischemia model possibly by stimulating proangiogenic growth factors and cytokines.

Embryonic body culturing in an all-glass microfluidic device with laser-processed 4 μm thick ultra-thin glass sheet filter

In this paper, we report the development and demonstration of a method to fabricate an all-glass microfluidic cell culturing device without circulation flow. On-chip microfluidic cell culturing is an indispensable technique for cellular replacement therapies and experimental cell biology. Polydimethylsiloxane (PDMS) have become a popular material for fabricating microfluidic cell culture devices because it is a transparent, biocompatible, deformable, easy-to-mold, and gas-permeable. However, PDMS is also a chemically and physically unstable material. For example, PDMS undergoes aging easily even in room temperature conditions. Therefore, it is difficult to control long term experimental culturing conditions. On the other hand, glass is expected to be stable not only in physically but also chemically even in the presence of organic solvents. However, cell culturing still requires substance exchanges such as gases and nutrients, and so on, which cannot be done in a closed space of a glass device without circulation flow that may influence cell behavior. Thus, we introduce a filter structure with micropores onto a glass device to improve permeability to the cell culture space. Normally, it is extremely difficult to fabricate a filter structure on a normal glass plate by using a conventional fabrication method. Here, we demonstrated a method for fabricating an all-glass microfluidic cell culturing device having filters structure. The function of this all-glass culturing device was confirmed by culturing HeLa, fibroblast and ES cells. Compared with the closed glass devices without a filter structure, the numbers of cells in our device increased and embryonic bodies (EBs) were formed. This method offers a new tool in microfluidic cell culture technology for biological analysis and it expands the field of microfluidic cell culture.

Mesenchymal Stem Cell Secretome: Toward Cell-Free Therapeutic Strategies in Regenerative Medicine

Earlier research primarily attributed the effects of mesenchymal stem cell (MSC) therapies to their capacity for local engrafting and differentiating into multiple tissue types. However, recent studies have revealed that implanted cells do not survive for long, and that the benefits of MSC therapy could be due to the vast array of bioactive factors they produce, which play an important role in the regulation of key biologic processes. Secretome derivatives, such as conditioned media or exosomes, may present considerable advantages over cells for manufacturing, storage, handling, product shelf life and their potential as a ready-to-go biologic product. Nevertheless, regulatory requirements for manufacturing and quality control will be necessary to establish the safety and efficacy profile of these products. Among MSCs, human uterine cervical stem cells (hUCESCs) may be a good candidate for obtaining secretome-derived products. hUCESCs are obtained by Pap cervical smear, which is a less invasive and painful method than those used for obtaining other MSCs (for example, from bone marrow or adipose tissue). Moreover, due to easy isolation and a high proliferative rate, it is possible to obtain large amounts of hUCESCs or secretome-derived products for research and clinical use.

Mesenchymal Stem Cell-based Therapy as a New Horizon for Kidney Injuries

Today, the prevalence of kidney diseases is increasing around the world, but there has still been no effective medical treatment. The therapeutic choices are confined to supportive cares and preventive strategies. Currently, mesenchymal stem cells (MSCs)-based cell therapy was proposed for the treatment of kidney injuries. However, after the transplantation of MSCs, they are exposed to masses of cytotoxic factors involving an inflammatory cytokine storm, a nutritionally-poor hypoxic environment and oxidative stresses that finally lead to minimize the efficacy of MSCs based cell therapy. Therefore, several innovative strategies were developed in order to potentiate MSCs to withstand the unfavorable microenvironments of the injured kidney tissues and improve their therapeutic potentials. This review aims to introduce MSCs as a new modality in the treatment of renal failure. Here, we discuss the clinical trials of MSCs-based therapy in kidney diseases as well as the in vivo studies dealing with MSCs application in kidney injuries mainly from the proliferation, differentiation, migration and survival points of view. The obstacles and challenges of this new modality in kidney injuries are also discussed.

Influence of oxygen levels on chondrogenesis of porcine mesenchymal stem cells cultured in polycaprolactone scaffolds

Chondrogenesis of mesenchymal stem cells (MSCs) is known to be regulated by a number of environmental factors, including local oxygen levels. The hypothesis of this study is that the response of MSCs to hypoxia is dependent on the physical and chemical characteristics of the substrate used. The objective of this study was to explore how different modifications to polycaprolactone (PCL) scaffolds influenced the response of MSCs to hypoxia. PCL, PCL-hyaluronic acid (HA), and PCL-Bioglass^® (BG) scaffolds were seeded with MSCs derived from bone marrow and cultured for 35 days under normoxic or low oxygen conditions, and the resulting biochemical properties of the MSC laden construct were assessed. Low oxygen tension has a positive effect over cell proliferation and macromolecules biosynthesis. Furthermore, hypoxia enhanced the distribution of collagen and glycosaminoglycans (GAGs) deposition through the scaffold. On the other hand, MSCs displayed certain material dependent responses to hypoxia. Low oxygen tension had a positive effect on cell proliferation in BG and HA scaffolds, but only a positive effect on GAGs synthesis in PCL and HA scaffolds. In conclusion, hypoxia increased cell viability and expression of chondrogenic markers but the cell response was modulated by the type of scaffold used. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1684-1691, 2017.

Application of human mesenchymal stem cells cultured in different oxygen concentrations for treatment of graft-versus-host disease in mice

Human mesenchymal stem cell (MSC) heterogeneity and problems associated with the ex vivo expansion of MSC are linked with the failure of MSC clinical trials. In this study, we compared the effect of MSCs cultured in different oxygen concentrations on GVHD in mice to elucidate whether hypoxia improves the immunosuppressive capacity of MSCs. Hypoxia increased the proliferative activity and the expression of several stemness and chemokine genes, such as KLF4, OCT4, C-MYC, CCL2, and CXCL10. Mice that received MSCs cultured in normoxia or hypoxia showed alleviated symptoms of GVHD and increased survival times. However, there was no significant difference in survival rates between mice that received MSCs cultured in normoxia and hypoxia. These data suggest that hypoxic culture is a useful method for maintaining and obtaining MSCs used for cell therapy and that the therapeutic potential of MSCs cultured in hypoxia warrants further investigation.

Strategies to Enhance Implantation and Survival of Stem Cells After Their Injection in Ischemic Neural Tissue

High post-transplantation cell mortality is the main limitation of various approaches that are aimed at improving regeneration of injured neural tissue by an injection of neural stem cells (NSCs) and mesenchymal stromal cells (MStroCs) in and/or around the lesion. Therefore, it is of paramount importance to identify efficient ways to increase cell transplant viability. We have previously proposed the "evolutionary stem cell paradigm," which explains the association between stem cell anaerobic/microaerophilic metabolic set-up and stem cell self-renewal and inhibition of differentiation. Applying these principles, we have identified the main critical point in the collection and preparation of these cells for experimental therapy: exposure of the cells to atmospheric O₂, that is, to oxygen concentrations that are several times higher than the physiologically relevant ones. In this way, the primitive anaerobic cells become either inactivated or adapted, through commitment and differentiation, to highly aerobic conditions (20%-21% O₂ in atmospheric air). This inadvertently compromises the cells' survival once they are transplanted into normal tissue, especially in the hypoxic/anoxic/ischemic environment, which is typical of central nervous system (CNS) lesions. In addition to the findings suggesting that stem cells can shift to glycolysis and can proliferate in anoxia, recent studies also propose that stem cells may be able to proliferate in completely anaerobic or ischemic conditions by relying on anaerobic mitochondrial respiration. In this systematic review, we propose strategies to enhance the survival of NSCs and MStroCs that are implanted in hypoxic/ischemic neural tissue by harnessing their anaerobic nature and maintaining as well as enhancing their anaerobic properties via appropriate ex vivo conditioning.

Bone marrow-derived mesenchymal stem cells ameliorate sodium nitrite-induced hypoxic brain injury in a rat model

Sodium nitrite (NaNO₂) is an inorganic salt used broadly in chemical industry. NaNO₂ is highly reactive with hemoglobin causing hypoxia. Mesenchymal stem cells (MSCs) are capable of differentiating into a variety of tissue specific cells and MSC therapy is a potential method for improving brain functions. This work aims to investigate the possible therapeutic role of bone marrow-derived MSCs against NaNO₂ induced hypoxic brain injury. Rats were divided into control group (treated for 3 or 6 weeks), hypoxic (HP) group (subcutaneous injection of 35 mg/kg NaNO₂ for 3 weeks to induce hypoxic brain injury), HP recovery groups N-2wR and N-3wR (treated with the same dose of NaNO₂ for 2 and 3 weeks respectively, followed by 4-week or 3-week self-recovery respectively), and MSCs treated groups N-2wSC and N-3wSC (treated with the same dose of NaNO₂ for 2 and 3 weeks respectively, followed by one injection of 2 × 10⁶ MSCs via the tail vein in combination with 4 week self-recovery or intravenous injection of NaNO₂ for 1 week in combination with 3 week self-recovery). The levels of neurotransmitters (norepinephrine, dopamine, serotonin), energy substances (adenosine monophosphate, adenosine diphosphate, adenosine triphosphate), and oxidative stress markers (malondialdehyde, nitric oxide, 8-hydroxy-2'-deoxyguanosine, glutathione reduced form, and oxidized glutathione) in the frontal cortex and midbrain were measured using high performance liquid chromatography. At the same time, hematoxylin-eosin staining was performed to observe the pathological change of the injured brain tissue. Compared with HP group, pathological change of brain tissue was milder, the levels of malondialdehyde, nitric oxide, oxidized glutathione, 8-hydroxy-2'-deoxyguanosine, norepinephrine, serotonin, glutathione reduced form, and adenosine triphosphate in the frontal cortex and midbrain were significantly decreased, and glutathione reduced form/oxidized glutathione and adenosine monophosphate/adenosine triphosphate ratio were significantly increased in the MSCs treated groups. These findings suggest that bone marrow-derived MSCs exhibit neuroprotective effects against NaNO₂-induced hypoxic brain injury through exerting anti-oxidative effects and providing energy to the brain.

Chinese herbal medicines promote hippocampal neuroproliferation, reduce stress hormone levels, inhibit apoptosis, and improve behavior in chronically stressed mice

ETHNOPHARMACOLOGICAL RELEVANCE

An efficacious antidepressant without unwanted side effects is need urgently at present. This study aimed to investigate whether treatment with four Chinese herbal medicines (CHMs), namely Radix Astragali, Saposhnikovia divaricate (SD), Eucommia ulmoides Oliv. bark (EU), and Corydalis yanhusuo W. T. Wang (C. yanhusuo), could reverse the effects of chronic mild stress (CMS) in a depression-like mouse model and the potential mechanism(s) of their action.

MATERIALS AND METHODS

In vitro study, the proliferation of NSCs was assessed using the MTS assay. In vivo study, chronic mild stress (CMS) was used in mice for 14 days to establish a depression-like mouse model. Plasma corticosterone levels were assessed by UPLC coupled to a triple-quadrupole mass spectrometer. The forced swim test (FST) was used to assess the effects of the four CHMs on depression. BrdU incorporation and TUNEL staining were used to assay hippocampal precursor cell proliferation rate and apoptosis.

RESULTS

The CHMs included Radix Astragali, EU, C. yanhusuo, and SD were shown to promote neuroproliferation in vitro. In vivo study, oral administration of these four CHMs for 14 days reversed the elevated plasma corticosterone levels, body weight loss, decrease in proliferation of hippocampal precursor cells; they also inhibited hippocampal cell apoptosis, and exhibited an antidepressant-like effect in a depression-like mouse model induced by CMS.

CONCLUSIONS

Our study indicates that each of these CHMs has the potential to ameliorate depression. The possible mechanisms of action include modulation of the HPA axis, reduction in stress hormone levels, inhibition of apoptosis, and promotion of hippocampal neuronal plasticity and neurogenesis.

The effects of hypoxia on the stemness properties of human dental pulp stem cells (DPSCs)

Recent studies have demonstrated that culture under hypoxia has beneficial effects on mesenchymal stem cells (MSCs). However, there are limitations to achieving a stable condition in conventional hypoxic CO₂ incubators. DPSCs are a unique type of MSCs which are promising in many regenerative therapies. In this study, we investigated the ideal hypoxic culture environment for DPSCs using a new system that can provide controlled O₂ environment. The effects of hypoxia (3%, 5%) on the stemness properties of DPSCs. Their morphology, proliferation rate, expression of stem cell markers, migration ability, mRNA expression of angiogenic/neurotrophic factors and immunomodulatory genes were evaluated and compared. Additionally, the effect of the discrete secretome on proliferation, migration, and neurogenic induction was assessed. Hypoxic DPSCs were found to be smaller in size and exhibited larger nuclei. 5% O₂ significantly increased the proliferation rate, migration ability, expression of stem cell markers (CXCR4 and G-CSFR), and expression of SOX2, VEGF, NGF, and BDNF genes of DPSCs. Moreover, secretome collected from 5%O₂ cultures displayed higher stimulatory effects on proliferation and migration of NIH3T3 cells and on neuronal differentiation of SH-SY5Y cells. These results demonstrate that 5%O₂ may be ideal for enhancing DPSCs growth, stem cell properties, and secretome trophic effect.

Preconditioning of mesenchymal stem cells with 2,4-dinitrophenol improves cardiac function in infarcted rats

AIMS

The aim of this study is to determine if preconditioning of bone marrow derived mesenchymal stem cells (MSCs) with 2,4-dinitrophenol (DNP) improves survival of transplanted stem cells in a rat model of myocardial infarction (MI), and to asses if this strategy has measurable impact on cardiac function.

MAIN METHODS

MSCs were preconditioned with DNP. In vitro cell adhesion assay and qRT-PCR were performed to analyze the expression of genes involved in cardiomyogenesis, cell adhesion and angiogenesis. MI was produced by occlusion of left anterior descending coronary artery. One million cells were transplanted by intramyocardial injection into the infarcted myocardium. Echocardiography was performed after two and four weeks of cellular transplantation. Hearts were harvested after four weeks and processed for histological analysis.

KEY FINDINGS

DNP treated MSCs adhered to the surface more (p<0.001) as compared to the normal MSCs. Gene expression levels were significantly upregulated in case of DNP treatment. The number of viable MSCs was more (p<0.001) in animals that received DNP treated MSCs, leading to significant improvement in cardiac function. Histological analysis revealed significant reduction in scar formation (p<0.001), maintenance of left ventricular wall thickness (p<0.001), and increased angiogenesis (p<0.01).

SIGNIFICANCE

The study evidenced for the first time that MSCs preconditioned with DNP improved cardiac function after transplantation. This can be attributed to improved survival, homing, adhesion, and cardiomyogenic and angiogenic differentiation of DNP treated MSCs in vivo.

Effects of hypoxia on osteogenic differentiation of mesenchymal stromal cells used as a cell therapy for avascular necrosis of the femoral head

BACKGROUND AIMS

Avascular necrosis of the femoral head (AVN) occurs as common result of various conditions or develops as a primary entity, with a high freqency in young adults. Because of its tendency toward osteoarthritis requiring total hip arthroplasty, alternative treatments are being advocated, including cell therapy with mesenchymal stromal cells (MSCs). Because osteonecrotic bone is a severely hypoxic tissue, with a 1-3% oxygen tension, the survival and function of multipotent cells is questionable.

METHODS

In this study, the proliferative, immunophenotypic and osteogenic properties of bone marrow (BM)-derived MSCs from a clinical series of patients with AVN were evaluated under in vitro conditions mimicking the hypoxic milieu of AVN to verify the rationale for cell therapy. MSCs retrieved from the iliac crest (BM-MSC) were isolated, expanded and induced to osteogenic differentiation under a 2% pO2 atmosphere (hypoxia) in comparison with the standard 21% pO2 (normoxia) that is routinely used in cell culture assays.

RESULTS

Both proliferation and colony-forming ability were significantly enhanced in hypoxia-exposed BM-MSCs compared with BM-MSCs under normoxia. The expression of bone-related genes, including alkaline phosphatase, Type I collagen, and osteocalcin was significantly increased under hypoxia. Moreover, mineral deposition after osteogenic induction was not hampered, but in some cases even enhanced under low oxygen tension.

CONCLUSIONS

These findings support autologous cell therapy as an effective treatment to stimulate bone healing in the hypoxic microenvironment of AVN.

Role of oxygen as a regulator of stem cell fate during the spontaneous repair of osteochondral defects

The complexity of the in vivo environment makes it is difficult to isolate the effects of specific cues on regulating cell fate during regenerative events such as osteochondral defect repair. The objective of this study was to develop a computational model to explore how joint specific environmental factors regulate mesenchymal stem cell (MSC) fate during osteochondral defect repair. To this end, the spontaneous repair process within an osteochondral defect was simulated using a tissue differentiation algorithm which assumed that MSC fate was regulated by local oxygen levels and substrate stiffness. The developed model was able to predict the main stages of tissue formation observed by a number of in vivo studies. Following this, a parametric study was conducted to better understand why interventions that modulate angiogenesis dramatically impact the outcome of osteochondral defect healing. In the simulations where angiogenesis was reduced, by week 12, the subchondral plate was predicted to remain below the native tidemark, although the chondral region was composed entirely of cartilage and fibrous tissue. In the simulations where angiogenesis was increased, more robust cell proliferation and cartilage formation were observed during the first 4 weeks, however, by week 12 the subchondral plate had advanced above the native tidemark although any remaining tissue was either hypertrophic cartilage or fibrous tissue. These results suggest that osteochondral defect repair could be enhanced by interventions where angiogenesis is promoted but confined to within the subchondral region of the defect. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1026-1036, 2016.

Hypercapnia slows down proliferation and apoptosis of human bone marrow promyeloblasts

Stem cells are being applied in increasingly diverse fields of research and therapy; as such, growing and culturing them in scalable quantities would be a huge advantage for all concerned. Gas mixtures containing 5 % CO2 are a typical concentration for the in vitro culturing of cells. The effect of varying the CO2 concentration on promyeloblast KG-1a cells was investigated in this paper. KG-1a cells are characterized by high expression of CD34 surface antigen, which is an important clinical surface marker for human hematopoietic stem cells (HSCs) transplantation. KG-1a cells were cultured in three CO2 concentrations (1, 5 and 15 %). Cells were batch-cultured and analyzed daily for viability, size, morphology, proliferation, and apoptosis using flow cytometry. No considerable differences were noted in KG-1a cell morphological properties at all three CO2 levels as they retained their myeloblast appearance. Calculated population doubling time increased with an increase in CO2 concentration. Enhanced cell proliferation was seen in cells cultured in hypercapnic conditions, in contrast to significantly decreased proliferation in hypocapnic populations. Flow cytometry analysis revealed that apoptosis was significantly (p = 0.0032) delayed in hypercapnic cultures, in parallel to accelerated apoptosis in hypocapnic ones. These results, which to the best of our knowledge are novel, suggest that elevated levels of CO2 are favored for the enhanced proliferation of bone marrow (BM) progenitor cells such as HSCs.

Low Oxygen Modulates Multiple Signaling Pathways, Increasing Self-Renewal, While Decreasing Differentiation, Senescence, and Apoptosis in Stromal MIAMI Cells

Human bone marrow multipotent mesenchymal stromal cell (hMSC) number decreases with aging. Subpopulations of hMSCs can differentiate into cells found in bone, vasculature, cartilage, gut, and other tissues and participate in their repair. Maintaining throughout adult life such cell subpopulations should help prevent or delay the onset of age-related degenerative conditions. Low oxygen tension, the physiological environment in progenitor cell-rich regions of the bone marrow microarchitecture, stimulates the self-renewal of marrow-isolated adult multilineage inducible (MIAMI) cells and expression of Sox2, Nanog, Oct4a nuclear accumulation, Notch intracellular domain, notch target genes, neuronal transcriptional repressor element 1 (RE1)-silencing transcription factor (REST), and hypoxia-inducible factor-1 alpha (HIF-1α), and additionally, by decreasing the expression of (i) the proapoptotic proteins, apoptosis-inducing factor (AIF) and Bak, and (ii) senescence-associated p53 expression and β-galactosidase activity. Furthermore, low oxygen increases canonical Wnt pathway signaling coreceptor Lrp5 expression, and PI3K/Akt pathway activation. Lrp5 inhibition decreases self-renewal marker Sox2 mRNA, Oct4a nuclear accumulation, and cell numbers. Wortmannin-mediated PI3K/Akt pathway inhibition leads to increased osteoblastic differentiation at both low and high oxygen tension. We demonstrate that low oxygen stimulates a complex signaling network involving PI3K/Akt, Notch, and canonical Wnt pathways, which mediate the observed increase in nuclear Oct4a and REST, with simultaneous decrease in p53, AIF, and Bak. Collectively, these pathway activations contribute to increased self-renewal with concomitant decreased differentiation, cell cycle arrest, apoptosis, and/or senescence in MIAMI cells. Importantly, the PI3K/Akt pathway plays a central mechanistic role in the oxygen tension-regulated self-renewal versus osteoblastic differentiation of progenitor cells.

Preconditioning in lowered oxygen enhances the therapeutic potential of human umbilical mesenchymal stem cells in a rat model of spinal cord injury

Human umbilical cord mesenchymal stem cells (UCMSCs) have recently been shown to hold great therapeutic potential for the treatment of spinal cord injury (SCI). However, the number of engrafted cells has been shown to decrease dramatically post-transplantation. Physioxia is known to enhance the paracrine properties and immune modulation of stem cells, a notion that has been applied in many clinical settings. We therefore hypothesized that preconditioning of UCMSCs in physioxic environment would enhance the regenerative properties of these cells in the treatment of rat SCI. UCMSCs were pretreated with either atmospheric normoxia (21% O2, N-UCMSC) or physioxia (5% O2, P-UCMSC). The MSCs were characterized using flow cytometry, immunocytochemistry, and real-time polymerase chain reaction. Furthermore, 10(5) N-UCMSC or P-UCMSC were injected into the injured spinal cord immediately after SCI, and locomotor function as well as cellular, molecular and pathological changes were compared between the groups. We found that N-UCMSC and P-UCMSC displayed similar surface protein expression. P-UCMSC grew faster, while physioxia up-regulated the expression of trophic and growth factors, including hepatocyte growth factor (HGF), brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor(VEGF), in UCMSCs. Compared to N-UCMSC, treatment with P-UCMSC was associated with marked changes in the SCI environment, with a significant increase in axonal preservation and a decrease in the number of caspase-3+ cells and ED-1+ macrophages. These changes were accompanied by improved functional recovery. Thus, the present study indicated that preculturing UCMSCs under 5% lowered oxygen physioxic conditions prior to transplantation improves their therapeutic potential for the treatment of SCI in rats.

Tissue engineering advances in spine surgery

Autograft, while currently the gold standard for bone grafting, has several significant disadvantages including limited supply, donor site pain, hematoma formation, nerve and vascular injury, and fracture. Bone allografts have their own disadvantages including reduced osteoinductive capability, lack of osteoprogenitor cells, immunogenicity and risk of disease transmission. Thus demand exists for tissue-engineered constructs that can produce viable bone while avoiding the complications associated with human tissue grafts. This review will focus on recent advancements in tissue-engineered bone graft substitutes utilizing nanoscale technology in spine surgery applications. An evaluation will be performed of bone graft substitutes, biomimetic 3D scaffolds, bone morphogenetic protein, mesenchymal stem cells and intervertebral disc regeneration strategies.

Reduced serum and hypoxic culture conditions enhance the osteogenic potential of human mesenchymal stem cells

Current protocols for inducing osteogenic differentiation in mesenchymal stem/stromal cells (MSCs) in culture for tissue engineering applications depend on the use of biochemical supplements. However, standard in vitro culture conditions expose cells to ambient oxygen concentrations and high levels of serum (21% O2, 10% FBS) that do not accurately recapitulate the physiological milieu. While we and others have examined MSC behavior under hypoxia, the synergistic effect of low serum levels, such as those present in ischemic injury sites, on osteogenic differentiation has not been clearly examined. We hypothesized that a concomitant reduction of serum and O2 would enhance in vitro osteogenic differentiation of MSCs by more accurately mimicking the fracture microenvironment. We show that serum deprivation, in conjunction with hypoxia, potentiates osteogenic differentiation in MSCs. These data demonstrate the role of serum levels in regulating osteogenesis and its importance in optimizing MSC differentiation strategies.

HIGHLIGHTS

Serum levels, in addition to hypoxia, have a significant effect on MSC osteogenic differentiation. Both naïve and osteogenically induced MSCs exhibit higher osteogenic markers in reduced serum. MSCs deposit the most calcium under 5% O2 in osteogenic media supplemented with 5% FBS. Standard culture conditions (21% O2, 10% FBS) may not be optimal for MSC osteogenic differentiation.

Heart valve regeneration: the need for systems approaches

Tissue-engineered heart valves are promising alternatives to address the limitations of current valve replacements, particularly for growing children. Current heart valve tissue engineering strategies involve the selection of biomaterial scaffolds, cell types, and often in vitro culture conditions aimed at regenerating a valve for implantation and subsequent maturation in vivo. However, identifying optimal combinations of cell sources, biomaterials, and/or bioreactor conditions to produce functional, durable valve tissue remains a challenge. Despite some short-term success in animal models, attempts to recapitulate aspects of the native heart valve environment based on 'best guesses' of a limited number of regulatory factors have not proven effective. Better outcomes for valve tissue regeneration will likely require a systems-level understanding of the relationships between multiple interacting regulatory factors and their effects on cell function and tissue formation. Until recently, conventional culture methods have not allowed for multiple design parameters to be considered at once. Emerging microtechnologies are well suited to systematically probe multiple inputs, in combination, in high throughput and with great precision. When combined with statistical and network systems analyses, these microtechnologies have excellent potential to define multivariate signal-response relationships and reveal key regulatory pathways for robust functional tissue regeneration.

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.

Cell-free scaffolds with different stiffness but same microstructure promote bone regeneration in rabbit large bone defect model

To promote bone healing, bone repair biomaterials are increasingly designed to incorporate growth factors. However, the impact of matrix mechanics of cell-free scaffold independent of microstructure on the osteogenic differentiation of endogenous osteoprogenitor cells orchestrating bone repair and regeneration remains not to be fully understood. In our recent study, three-dimensional (3D) scaffolds with different stiffness but same microstructure have been successfully fabricated by coating decellularized bone with collagen/hydroxyapatite (HA) mixture with different collagen rations. It has been demonstrated that the scaffold with optimal stiffness can induce the osteogenic differentiation of MSCs in vitro and in the subcutaneous tissue. The present in vivo study further investigated the repair efficiency of these scaffolds in a rabbit radius with a critical-sized segmental defect model and its potential mechanism. Micro-computed tomography (μ-CT), X-ray and histological analysis were carried out to evaluate the repair capacity of these scaffolds. The results demonstrated that the cell-free scaffold with optimal stiffness incorporation of endogenous osteoprogenitor cells significantly promoted the repair and reconstruction quality of mass bone defect. One of the crucial mechanisms was that hypoxia and stromal cell-derived factor-1α (SDF-1α) mediated mesenchymal stem cells (MSCs) migration by which matrix mechanics exerted influence on bone fracture healing. These findings suggested that only modulating the matrix stiffness of cell-free scaffold can be one of the most attractive strategies for promoting the progression of bone healing.

Chondrogenic potential and anti-senescence effect of hypoxia on canine adipose mesenchymal stem cells

Mesenchymal stem cells (MSCs) have the ability to differentiate into multi-lineage cells, which confers great promise for use in regenerative medicine. In this study, canine adipose MSCs (cAD-MSCs) were isolated from canine adipose tissue. These cells clearly represented stemness (Oct4, Sox2, and Nanog) and differentiation potential into the mesoderm (adipocytes, chondrocytes, and osteoblasts) at early passages. The aim of this study was to evaluate the effects of hypoxia on the differentiation potential into mesoderm, and the expression of anti-apoptotic genes associated with cell survival for the optimal culturing of MSCs. We observed that the proliferation of the cAD-MSCs meaningfully increased when cultured under hypoxic condition than in normoxic condition, during 7 consecutive passages. Also, we found that hypoxia strongly expressed anti-senescence related genes such as HDAC1 (histone deacetylase 1), DNMT1 (DNA (cytosine-5)-methyltransferase 1), Bcl-2 (inhibitor of apoptosis), TERT (telomerase reverse transcriptase), LDHA (lactate dehydrogenase A), SLC2A1 (glucose transporter), and DKC1 (telomere holoenzyme complex) and differentiation potential of cAD-MSCs into chondrocytes, than seen under the normoxic culture conditions. We also examined the multipotency of hypoxic conditioned MSCs using quantitative real-time RT-PCR. We found that the expression levels of stemness genes such as Oct-4, Nanog, and Sox-2 were increased in hypoxic condition when compared to the normoxic condition. Collectively, these results suggest that hypoxic conditions have the ability to induce proliferation of MSCs and augment their chondrogenic potential. This study suggests that cell proliferation of cAD-MSC under hypoxia could be beneficial, when considering these cells for cell therapies of canine bone diseases.

Hypoxia pretreatment of bone marrow-derived mesenchymal stem cells seeded in a collagen-chitosan sponge scaffold promotes skin wound healing in diabetic rats with hindlimb ischemia

Bone marrow-derived mesenchymal stem cells (BM-MSCs) have properties that make them promising for the treatment of chronic nonhealing wounds. The major challenge is ensuring an efficient, safe, and painless delivery of BM-MSCs. Tissue-engineered skin substitutes have considerable benefits in skin damage resulting from chronic nonhealing wounds. Here, we have constructed a three-dimensional biomimetic scaffold known as collagen-chitosan sponge scaffolds (CCSS) using the cross-linking and freeze-drying method. Scanning electron microscopy images showed that CCSS had an interconnected network pore configuration about 100 μm and exhibited a suitable swelling ratio for maintaining morphological stability and appropriate biodegradability to improve biostability using swelling and degradation assays. Furthermore, BM-MSCs were seeded in CCSS using the two-step seeding method to construct tissue-engineered skin substitutes. In addition, in this three-dimensional biomimetic CCSS, BM-MSCs secreted their own collagen and maintain favorable survival ability and viability. Importantly, BM-MSCs exhibited a significant upregulated expression of proangiogenesis factors, including HIF-1α, VEGF, and PDGF following hypoxia pretreatment. In vivo, hypoxia pretreatment of the skin substitute observably accelerated wound closure via the reduction of inflammation and enhanced angiogenesis in diabetic rats with hindlimb ischemia. Thus, hypoxia pretreatment of the skin substitutes can serve as ideal bioengineering skin substitutes to promote optimal diabetic skin wound healing.

Endothelial properties of third-trimester amniotic fluid stem cells cultured in hypoxia

Introduction

Endothelial dysfunction is found in different pathologies such as diabetes and renal and heart diseases, representing one of the major health problems. The reduced vasodilation of impaired endothelium starts a prothrombotic state associated with irregular blood flow. We aimed to explore the potential of amniotic fluid stem (AFS) cells as a source for regenerative medicine in this field; for the first time, we focused on third-trimester amniotic fluid AFS cells and compared them with the already-described AFS cells from the second trimester.

Methods

Cells from the two trimesters were cultured, selected and expanded in normoxia (20 % oxygen) and hypoxia (5 % oxygen). Cells were analysed to compare markers, proliferation rate and differentiation abilities. Endothelial potential was assessed not only in vitro—Matrigel tube formation assay, acetylated human low-density lipoprotein (AcLDL) uptake—but also in vivo (Matrigel plug with cell injection and two animal models). Specifically, for the latter, we used established protocols to assess the involvement of AFS cells in two different mouse models of endothelial dysfunction: (1) a chronic ischemia model with local injection of cells and (2) an electric carotid damage where cells were systemically injected.

Results

We isolated and expanded AFS cells from third-trimester amniotic fluid samples by using CD117 as a selection marker. Hypoxia enhanced the proliferation rate, the surface protein pattern was conserved between the trimesters and comparable differentiation was achieved after culture in both normoxia and hypoxia. Notably, the expression of early endothelial transcription factors and AngiomiRs was detected before and after induction. When in vivo, AFS cells from both trimesters expanded in hypoxia were able to rescue the surface blood flow when locally injected in mice after chronic ischemia damage, and importantly AFS cells at term of gestation possessed enhanced ability to fix carotid artery electric damage compared with AFS cells from the second trimester.

Conclusions

To the best of our knowledge, this is the first research work that fully characterizes AFS cells from the third trimester for regenerative medicine purposes. The results highlight how AFS cells, in particular at term of gestation and cultured in hypoxia, can be considered a promising source of stem cells possessing significant endothelial regenerative potential.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0204-0) contains supplementary material, which is available to authorized users.

In Vitro Evaluation of Scaffolds for the Delivery of Mesenchymal Stem Cells to Wounds

Mesenchymal stem cells (MSCs) have been shown to improve tissue regeneration in several preclinical and clinical trials. These cells have been used in combination with three-dimensional scaffolds as a promising approach in the field of regenerative medicine. We compare the behavior of human adipose-derived MSCs (AdMSCs) on four different biomaterials that are awaiting or have already received FDA approval to determine a suitable regenerative scaffold for delivering these cells to dermal wounds and increasing healing potential. AdMSCs were isolated, characterized, and seeded onto scaffolds based on chitosan, fibrin, bovine collagen, and decellularized porcine dermis. In vitro results demonstrated that the scaffolds strongly influence key parameters, such as seeding efficiency, cellular distribution, attachment, survival, metabolic activity, and paracrine release. Chick chorioallantoic membrane assays revealed that the scaffold composition similarly influences the angiogenic potential of AdMSCs in vivo. The wound healing potential of scaffolds increases by means of a synergistic relationship between AdMSCs and biomaterial resulting in the release of proangiogenic and cytokine factors, which is currently lacking when a scaffold alone is utilized. Furthermore, the methods used herein can be utilized to test other scaffold materials to increase their wound healing potential with AdMSCs.

Density-Dependent Metabolic Heterogeneity in Human Mesenchymal Stem Cells

Human mesenchymal stem cells (hMSCs) are intrinsically heterogeneous and comprise subpopulations that differ in their proliferation, multi-potency, and functional properties, which are commonly demonstrated by culturing hMSCs at different plating densities. The objective of this study was to investigate the metabolic profiles of different subpopulations of hMSC by testing the hypothesis that the clonogenic hMSC subpopulation, which is selectively enriched in clonal density (CD) and low density (LD) culture (10 and 100 cells per square centimeter, respectively), possesses a metabolic phenotype that differs from that of hMSC in medium- or high-density (MD: 1,000 and HD: 3,000 cells per square centimeter, respectively). Cells at CD and LD conditions exhibited elevated expression of CD146 and colony forming unit-fibroblast compared with cells at MD- or HD. Global metabolic profiles revealed by gas chromatography-mass spectrometry of cell extracts showed clear distinction between LD and HD cultures, and density-dependent differences in coupling of glycolysis to the TCA cycle. Metabolic inhibitors revealed density-dependent differences in glycolysis versus oxidative phosphorylation (OXPHOS) for ATP generation, in glutamine metabolism, in the dependence on the pentose phosphate pathway for maintaining cellular redox state, and sensitivity to exogenous reactive oxygen species. We also show that active OXPHOS is not required for proliferation in LD culture but that OXPHOS activity increases senescence in HD culture. Together, the results revealed heterogeneity in hMSC culture exists at the level of primary metabolism. The unique metabolic characteristics of the clonogenic subpopulation suggest a novel approach for optimizing in vitro expansion of hMSCs.

Do hypoxia/normoxia culturing conditions change the neuroregulatory profile of Wharton Jelly mesenchymal stem cell secretome?

Introduction

The use of human umbilical cord Wharton Jelly-derived mesenchymal stem cells (hWJ-MSCs) has been considered a new potential source for future safe applications in regenerative medicine. Indeed, the application of hWJ-MSCs into different animal models of disease, including those from the central nervous system, has shown remarkable therapeutic benefits mostly associated with their secretome. Conventionally, hWJ-MSCs are cultured and characterized under normoxic conditions (21 % oxygen tension), although the oxygen levels within tissues are typically much lower (hypoxic) than these standard culture conditions. Therefore, oxygen tension represents an important environmental factor that may affect the performance of mesenchymal stem cells in vivo. However, the impact of hypoxic conditions on distinct mesenchymal stem cell characteristics, such as the secretome, still remains unclear.

Methods

In the present study, we have examined the effects of normoxic (21 % O₂) and hypoxic (5 % O₂) conditions on the hWJ-MSC secretome. Subsequently, we address the impact of the distinct secretome in the neuronal cell survival and differentiation of human neural progenitor cells.

Results

The present data indicate that the hWJ-MSC secretome collected from normoxic and hypoxic conditions displayed similar effects in supporting neuronal differentiation of human neural progenitor cells in vitro. However, proteomic analysis revealed that the use of hypoxic preconditioning led to the upregulation of several proteins within the hWJ-MSC secretome.

Conclusions

Our results suggest that the optimization of parameters such as hypoxia may lead to the development of strategies that enhance the therapeutic effects of the secretome for future regenerative medicine studies and applications.

Extracellular Matrix can Recover the Downregulation of Adhesion Molecules after Cell Detachment and Enhance Endothelial Cell Engraftment

The low cell engraftment after transplantation limits the successful application of stem cell therapy and the exact pathway leading to acute donor cell death following transplantation is still unknown. Here we investigated if processes involved in cell preparation could initiate downregulation of adhesion-related survival signals, and further affect cell engraftment after transplantation. Human embryonic stem cell-derived endothelial cells (hESC-ECs) were suspended in PBS or Matrigel and kept at 4 °C. Quantitative RT-PCR analysis was used to test the adhesion and apoptosis genes’ expression of hESC-ECs. We demonstrated that cell detachment can cause downregulation of cell adhesion and extracellular matrix (ECM) molecules, but no obvious cell anoikis, a form of apoptosis after cell detachment, was observed. The downregulation of adhesion and ECM molecules could be regained in the presence of Matrigel. Finally, we transplanted hESC-ECs into a mouse myocardial ischemia model. When transplanted with Matrigel, the long-term engraftment of hESC-ECs was increased through promoting angiogenesis and inhibiting apoptosis, and this was confirmed by bioluminescence imaging. In conclusion, ECM could rescue the functional genes expression after cell detached from culture dish, and this finding highlights the importance of increasing stem cell engraftment by mimicking stem cell niches through ECM application.

Hypoxic preconditioning of mesenchymal stromal cells induces metabolic changes, enhances survival, and promotes cell retention in vivo

Mesenchymal stem cells/multipotent stromal cells (MSCs) are promising therapeutics for a variety of conditions. However, after transplantation, cell retention remains extremely challenging. Given that many hypoxic signals are transitory and that the therapeutic administration of MSCs is typically into tissues that are normally hypoxic, we studied the effect of hypoxic preconditioning (HP) prior to new exposure to hypoxia. We show that preincubation for 2 days or more in 1% oxygen reduces serum deprivation-mediated cell death, as observed by higher cell numbers and lower incorporation of EthD-III and Annexin V. Consistently, HP-MSCs expressed significantly lower levels of cytochrome c and heme oxygenase 1 as compared to controls. Most importantly, HP-MSCs showed enhanced survival in vivo after intramuscular injection into immune deficient NOD/SCID-IL2Rgamma(-/-) mice. Interestingly, HP-MSCs consume glucose and secrete lactate at a slower rate than controls, possibly promoting cell survival, as glucose remains available to the cells for longer periods of time. In addition, we compared the metabolome of HP-MSCs to controls, before and after hypoxia and serum deprivation, and identified several possible mediators for HP-mediated cell survival. Overall, our findings suggest that preincubation of MSCs for 2 days or more in hypoxia induces metabolic changes that yield higher retention after transplantation.

The effects of short-term hypoxia on human mesenchymal stem cell proliferation, viability and p16(INK4A) mRNA expression: Investigation using a simple hypoxic culture system with a deoxidizing agent

A hypoxic environment is thought to be important for the maintenance of stemness and suppressing cell senescence, in stem cells. Therefore, a hypoxic condition is induced during cell expansion and/or induction of intended differentiation. However, the induction of these conditions requires a specially equipped hypoxia chamber and expensive gas mixtures, which are expensive and space-consuming. Owing to these restrictions, appropriate hypoxic conditions cannot be provided during cell transportation, which is increasingly required for regenerative medicine. Hence, a simple and economical culture system is required. The purpose of this study was to investigate the effects of short-term hypoxic conditions on human mesenchymal stem cell (MSC) proliferation, viability, and senescence, utilizing the CulturePal system (CulturePal-Zero and CulturePal-Five), a novel and simple hypoxic culture system with a built-in deoxidizing agent. The O₂ concentration in the CulturePal-Zero was observed to reduce to <0.1% within 1 h, and to 5% within 24h in the CulturePal-Five system. Cell proliferation under these hypoxic conditions showed a sharp increase at 5% O₂ concentration, and no noticeable cell death was observed even at severe hypoxic conditions (<0.1% O₂) up to 72h. The p16^INK4A (cell senescence marker) mRNA expression was retained under hypoxic conditions up to 72h, but it was up-regulated under normoxic conditions. Interestingly, the p16^INK4A expression altered proportionately to the O₂ concentration. These results indicated that the short-term hypoxic condition, at an approximate O₂ concentration of 5%, would be suitable for promoting cell proliferation and repressing cell senescence, without aggravating the MSC viability. Therefore, the CulturePal systems may be suitable for providing an appropriate hypoxic condition in stem cell research and transportation.

In vitro augmentation of mesenchymal stem cells viability in stressful microenvironments : In vitro augmentation of mesenchymal stem cells viability

Mesenchymal stem cells (MSCs) are under intensive investigation for use in cell-based therapies because their differentiation abilities, immunomodulatory effects, and homing properties offer potential for significantly augmenting regenerative capacity of many tissues. Nevertheless, major impediments to their therapeutic application, such as low proliferation and survival rates remain as obstacles to broad clinical use of MSCs. Another major challenge to evolution of MSC-based therapies is functional degradation of these cells as a result of their exposure to oxidative stressors during isolation. Indeed, oxidative stress-mediated MSC depletion occurs due to inflammatory processes associated with chemotherapy, radiotherapy, and expression of pro-apoptotic factors, and the microenvironment of damaged tissue in patients receiving MSC therapy is typically therapeutic not favorable to their survival. For this reason, any strategies that enhance the viability and proliferative capacity of MSCs associated with their therapeutic use are of great value. Here, recent strategies used by various researchers to improve MSC allograft function are reviewed, with particular focus on in vitro conditioning of MSCs in preparation for clinical application. Preconditioning, genetic manipulation, and optimization of MSC culture conditions are some examples of the methodologies described in the present article, along with novel strategies such as treatment of MSCs with secretome and MSC-derived microvesicles. This topic material is likely to find value as a guide for both research and clinical use of MSC allografts and for improvement of the value that use of these cells brings to health care.

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.

Continuous hypoxia regulates the osteogenic potential of mesenchymal stem cells in a time-dependent manner

The effects of hypoxia on the osteogenic potential of mesenchymal stem cells (MSCs) have been previously reported. From these studies, possible factors affecting the association between hypoxia and the osteogenic differentiation of MSCs have been suggested, including hypoxia severity, cell origin and methods of induction. The effect of the duration of hypoxia, however, remains poorly understood. The aim of the present study was to investigate the effect of continuous hypoxia on the induced osteogenesis of MSCs. Rat MSCs were isolated and cultured in vitro. Once the cells had been cultured to passage three, they were switched to 1% oxygen and cultured either with or without osteogenic medium, while cells in the control groups were cultured under normoxia in corresponding conditions. Four osteogenic differentiation biomarkers, runt-related transcription factor 2, osteopontin, osteocalcin and alkaline phosphatase, were analyzed by quantitative polymerase chain reaction and western blotting at defined intervals throughout the culture period. In addition, Alizarin Red staining was used to assess changes in mineralization. The results showed that 1% hypoxia was able to enhance and accelerate the osteogenic ability of the MSCs during the initial phases of differentiation, and the protein expression of certain associated biomarkers was upregulated. However, continuous hypoxia was shown to impair osteogenesis in the latter stages of differentiation. These findings suggest that hypoxia can regulate the osteogenesis of MSCs in a time-dependent manner.