Effect of nitric oxide production and oxygen tension on progenitor preservation in ex vivo culture

Therapeutic targeting and HSC proliferation by small molecules and biologicals

Hematopoietic stem cells (HSCs) have considerably therapeutic value on autologous and allogeneic transplantation for many malignant/non-malignant hematological diseases, especially with improvement of gene therapy. However, acquirement of limited cell dose from HSC sources is the main handicap for successful transplantation. Therefore, many strategies based on the utilization of various cytokines, interaction of stromal cells, modulation of several extrinsic and intrinsic factors have been developed to promote ex vivo functional HSC expansion with high reconstitution ability until today. Besides all these strategies, small molecules become prominent with their ease of use and various advantages when they are translated to the clinic. In the last two decades, several small molecule compounds have been investigated in pre-clinical studies and, some of them were evaluated in different stages of clinical trials for their safety and efficiencies. In this chapter, we will present an overview of HSC biology, function, regulation and also, pharmacological HSC modulation with small molecules from pre-clinical and clinical perspectives.

Epigenetic Alterations under Oxidative Stress in Stem Cells

Epigenetic regulation of gene expression, including DNA methylation and histone modifications, provides finely tuned responses for cells that undergo cellular environment changes. Abundant evidences have demonstrated the detrimental role of oxidative stress in various human pathogenesis since oxidative stress results from the imbalance between reactive oxygen species (ROS) accumulation and antioxidant defense system. Stem cells can self-renew themselves and meanwhile have the potential to differentiate into many other cell types. As some studies have described the effects of oxidative stress on homeostasis and cell fate decision of stem cells, epigenetic alterations have emerged crucial for mediating the stem cell behaviours under oxidative stress. Here, we review recent findings on the oxidative effects on DNA and histone modifications in stem cells. We propose that epigenetic alterations and oxidative stress may influence each other in stem cells.

Nitric Oxide Mediation in Hydroxyurea and Nitric Oxide Metabolites' Inhibition of Erythroid Progenitor Growth

In several systems, hydroxyurea has been shown to trigger nitric oxide (NO) release or activation of NO synthase (NOS). To elucidate this duality in its pharmacological effects, during myelosuppression, we individually examined hydroxyurea's (NO releasing agent) and NO metabolites' (stable NO degradation products) effects on erythroid colony growth and NOS/NO levels in mice using NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO). Hydroxyurea and nitrite/nitrate decreased the bone marrow cellularity that was blocked by PTIO only for the NO metabolites. Hydroxyurea inhibition of colony-forming unit-erythroid (CFU-E) formation and reticulocytes was reversed by PTIO. Moreover, hydroxyurea, through a negative feedback mechanism, reduced inducible NOS (iNOS) expressing cells in CFU-E, also prevented by PTIO. Nitrate inhibition of burst-forming units-erythroid (BFU-E) colony growth was blocked by PTIO, but not in mature CFU-E. The presented results reveal that NO release and/or production mediates the hydroxyurea inhibition of mature erythroid colony growth and the frequency of iNOS immunoreactive CFU-E.

Nitric Oxide Synthase Dependency in Hydroxyurea Inhibition of Erythroid Progenitor Growth

Hydroxyurea (HU) causes nitric oxide (NO) bioactivation, acting as both a NO donor and a stimulator of NO synthase (NOS). To examine whether HU effects are NO mediated by chemical degradation or enzymatic induction, we studied human and mouse erythroid cells during proliferation, apoptosis, and differentiation. The HU and NO donor demonstrated persisted versus temporary inhibition of erythroid cell growth during differentiation, as observed by γ- and β-globin gene expression. HU decreased the percentage of erythroleukemic K562 cells in the G2/M phase that was reversed by N-nitro l-arginine methyl ester hydrochloride (L-NAME). Besides activation of endothelial NOS, HU significantly increased apoptosis of K562 cells, again demonstrating NOS dependence. Administration of HU to mice significantly inhibited colony-forming unit-erythroid (CFU-E), mediated by NOS. Moreover, burst-forming-units-erythroid (BFU-E) and CFU-E ex vivo growth was inhibited by the administration of nitrate or nitrite to mice. Chronic in vivo NOS inhibition with L-NAME protected the bone marrow cellularity despite HU treatment of mice. NO metabolites and HU reduced the frequency of NOS-positive cells from CFU-E and BFU-E colonies that was reverted by NOS inhibition. HU regulation of the G2/M phase, apoptosis, differentiation, cellularity, and NOS immunoreactive cells was NOS dependent. Inhalation of NO therapy as well as strategies to increase endogenous NO production could replace or enhance HU activity.

SENP3-Mediated PPARγ2 DeSUMOylation in BM-MSCs Potentiates Glucocorticoid-Induced Osteoporosis by Promoting Adipogenesis and Weakening Osteogenesis

Glucocorticoid-induced osteoporosis (GIOP) is the most common secondary osteoporosis and reduced bone formation was the main pathological change in GIOP. Our previous studies have shown that there was an imbalance between adipogenic and osteogenic differentiation in GIOP BM-MSCs and peroxisome proliferator-activated receptor γ2 (PPARγ2) played a vital role in this disorders. Here, we reported that there was an increase in ROS level and SENP3 expression in Dex-induced osteoporotic BM-MSCs, and enhanced adipogenesis and weakened osteogenesis in osteoporotic BM-MSCs might be caused by upregulated SENP3. Then we found that SENP3 de-SUMOylated PPARγ2 on K107 site to potentiate adipogenesis and weaken osteogenesis. These results may provide new strategy and target in the clinical diagnosis and treatment of GIOP.

Optimization of oxidative stress for mesenchymal stromal/stem cell engraftment, function and longevity

Mesenchymal stromal/stem cells (MSCs) are multipotent cells that possess great potential as a cellular therapeutic based on their ability to differentiate to different lineages and to modulate immune responses. However, their potential is limited by their low tissue abundance, and thus the need for robust ex vivo expansion prior to their application. This creates its own issues, namely replicative senescence, which could lead to reduced MSC functionality and negatively impact their engraftment. Ex vivo expansion and MSC aging are associated with greater oxidative stress. Therefore, there is great need to identify strategies to reduce oxidative stress in MSCs. This review summarizes the achievements made to date in addressing oxidative stress in MSCs and speculates about interesting avenues of future investigation to solve this critical problem.

Human Tonsil-Derived Mesenchymal Stromal Cells Maintain Proliferating and ROS-Regulatory Properties via Stanniocalcin-1

Mesenchymal stromal cells (MSCs) from various sources exhibit different potential for stemness and therapeutic abilities. Recently, we reported a unique MSCs from human palatine tonsil (TMSCs) and their superior proliferation capacity compared to MSCs from other sources. However, unique characteristics of each MSC are not yet precisely elucidated. We investigated the role of stanniocalcin-1 (STC1), an anti-oxidative hormone, in the functions of TMSCs. We found that STC1 was highly expressed in TMSC compared with MSCs from bone marrow or adipose tissue. The proliferation, senescence and differentiation of TMSCs were assessed after the inhibition of STC1 expression. STC1 inhibition resulted in a significant decrease in the proliferation of TMSCs and did not affect the differentiation potential. To reveal the anti-oxidative ability of STC1 in TMSCs themselves or against other cell types, the generation of mitochondrial reactive oxygen species (ROS) in TMSC or ROS-mediated production of interleukin (IL)-1β from macrophage-like cells were detected. Interestingly, the basal level of ROS generation in TMSCs was significantly elevated after STC1 inhibition. Moreover, down-regulation of STC1 impaired the inhibitory effect of TMSCs on IL-1β production in macrophages. Taken together, these findings indicate that STC1 is highly expressed in TMSCs and plays a critical role in proliferating and ROS-regulatory abilities.

Strategies for elevating hematopoietic stem cells expansion and engraftment capacity

Hematopoietic stem cells (HSCs) are a rare cell population in adult bone marrow, mobilized peripheral blood, and umbilical cord blood possessing self-renewal and differentiation capability into a full spectrum of blood cells. Bone marrow HSC transplantation has been considered as an ideal option for certain disorders treatment including hematologic diseases, leukemia, immunodeficiency, bone marrow failure syndrome, genetic defects such as thalassemia, sickle cell anemia, autoimmune disease, and certain solid cancers. Ex vivo proliferation of these cells prior to transplantation has been proposed as a potential solution against limited number of stem cells. In such culture process, MSCs have also been shown to exhibit high capacity for secretion of soluble mediators contributing to the principle biological and therapeutic activities of HSCs. In addition, endothelial cells have been introduced to bridge the blood and sub tissues in the bone marrow, as well as, HSCs regeneration induction and survival. Cell culture in the laboratory environment requires cell growth strict control to protect against contamination, symmetrical cell division and optimal conditions for maximum yield. In this regard, microfluidic systems provide culture and analysis capabilities in micro volume scales. Moreover, two-dimensional cultures cannot fully demonstrate extracellular matrix found in different tissues and organs as an abstract representation of three dimensional cell structure. Microfluidic systems can also strongly describe the effects of physical factors such as temperature and pressure on cell behavior.

c-Myc Inhibitor 10074-G5 Induces Murine and Human Hematopoietic Stem and Progenitor Cell Expansion and HDR Modulator Rad51 Expression

Background:

c-Myc plays a major role in the maintenance of glycolytic metabolism and hematopoietic stem cell (HSC) quiescence.

Objective:

Targeting modulators of HSC quiescence and metabolism could lead to HSC cell cycle entry with concomitant expansion.

Methods and Results:

Here we show that c-Myc inhibitor 10074-G5 treatment leads to 2-fold increase in murine LSKCD34low HSC compartment post 7 days. In addition, c-Myc inhibition increases CD34+ and CD133+ human HSC number. c-Myc inhibition leads to downregulation of glycolytic and cyclindependent kinase inhibitor (CDKI) gene expression ex vivo and in vivo. In addition, c-Myc inhibition upregulates major HDR modulator Rad51 expression in hematopoietic cells. Besides, c-Myc inhibition does not alter proliferation kinetics of endothelial cells, fibroblasts or adipose-derived mesenchymal stem cells, however, it limits bone marrow derived mesenchymal stem cell proliferation. We further demonstrate that a cocktail of c-Myc inhibitor 10074-G5 along with tauroursodeoxycholic acid (TUDCA) and i-NOS inhibitor L-NIL provides a robust HSC maintenance and expansion ex vivo as evident by induction of all stem cell antigens analyzed. Intriguingly, the cocktail of c-Myc inhibitor 10074-G5, TUDCA and L-NIL improves HDR related gene expression.

Conclusion:

These findings provide tools to improve ex vivo HSC maintenance and expansion, autologous HSC transplantation and gene editing through modulation of HSC glycolytic and HDR pathways.

Defining Physiological Normoxia for Improved Translation of Cell Physiology to Animal Models and Humans

The extensive oxygen gradient between the air we breathe (Po₂ ~21 kPa) and its ultimate distribution within mitochondria (as low as ~0.5-1 kPa) is testament to the efforts expended in limiting its inherent toxicity. It has long been recognized that cell culture undertaken under room air conditions falls short of replicating this protection in vitro. Despite this, difficulty in accurately determining the appropriate O₂ levels in which to culture cells, coupled with a lack of the technology to replicate and maintain a physiological O₂ environment in vitro, has hindered addressing this issue thus far. In this review, we aim to address the current understanding of tissue Po₂ distribution in vivo and summarize the attempts made to replicate these conditions in vitro. The state-of-the-art techniques employed to accurately determine O₂ levels, as well as the issues associated with reproducing physiological O₂ levels in vitro, are also critically reviewed. We aim to provide the framework for researchers to undertake cell culture under O₂ levels relevant to specific tissues and organs. We envisage that this review will facilitate a paradigm shift, enabling translation of findings under physiological conditions in vitro to disease pathology and the design of novel therapeutics.

Nitric oxide has contrasting age-dependent effects on the functionality of murine hematopoietic stem cells

Background

The success of hematopoietic stem cell (HSC) transplantation is dependent on the quality of the donor HSCs. Some sources of HSCs display reduced engraftment efficiency either because of inadequate number (e.g., fetal liver and cord blood), or age-related dysfunction (e.g. in older individuals). Therefore, use of pharmacological compounds to improve functionality of HSCs is a forefront research area in hematology.

Methods

Lineage negative (Lin⁻) cells isolated from murine bone marrow or sort-purified Lin⁻Sca-1⁺c-Kit⁺CD34⁻ (LSK-CD34⁻) were treated with a nitric oxide donor, sodium nitroprusside (SNP). The cells were subjected to various phenotypic and functional assays.

Results

We found that SNP treatment of Lin⁻ cells leads to an increase in the numbers of LSK-CD34⁺ cells in them. Using sort-purified LSK CD34⁻ HSCs, we show that this is related to acquisition of CD34 expression by LSK-CD34⁻ cells, rather than proliferation of LSK-CD34⁺ cells. Most importantly, this upregulated expression of CD34 had age-dependent contrasting effects on HSC functionality. Increased CD34 expression significantly improved the engraftment of juvenile HSCs (6–8 weeks); in sharp contrast, it reduced the engraftment of adult HSCs (10–12 weeks). The molecular mechanism behind this phenomenon involved nitric oxide (NO)-mediated differential induction of various transcription factors involved in commitment with regard to self-renewal in adult and juvenile HSCs, respectively. Preliminary experiments performed on cord blood-derived and mobilized peripheral blood-derived cells revealed that NO exerts age-dependent contrasting effects on human HSCs as well.

Conclusions

This study demonstrates novel age-dependent contrasting effects of NO on HSC functionality and suggests that HSC age may be an important parameter in screening of various compounds for their use in manipulation of HSCs.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0433-x) contains supplementary material, which is available to authorized users.

Effects of Oxidative Stress on Mesenchymal Stem Cell Biology

Mesenchymal stromal/stem cells (MSCs) are multipotent stem cells present in most fetal and adult tissues. Ex vivo culture-expanded MSCs are being investigated for tissue repair and immune modulation, but their full clinical potential is far from realization. Here we review the role of oxidative stress in MSC biology, as their longevity and functions are affected by oxidative stress. In general, increased reactive oxygen species (ROS) inhibit MSC proliferation, increase senescence, enhance adipogenic but reduce osteogenic differentiation, and inhibit MSC immunomodulation. Furthermore, aging, senescence, and oxidative stress reduce their ex vivo expansion, which is critical for their clinical applications. Modulation of sirtuin expression and activity may represent a method to reduce oxidative stress in MSCs. These findings have important implications in the clinical utility of MSCs for degenerative and immunological based conditions. Further study of oxidative stress in MSCs is imperative in order to enhance MSC ex vivo expansion and in vivo engraftment, function, and longevity.

Reliability of ROS and RNS detection in hematopoietic stem cells − potential issues with probes and target cell population

Many studies have provided evidence for the crucial role of the reactive oxygen species (ROS) and reactive nitrogen species (RNS) in the regulation of differentiation and/or self-renewal, and the balance between quiescence and proliferation of hematopoietic stem cells (HSCs). Several metabolic regulators have been implicated in the maintenance of HSC redox homeostasis; however, the mechanisms that are regulated by ROS and RNS, as well as their downstream signaling are still elusive. This is partially owing to a lack of suitable methods that allow unequivocal and specific detection of ROS and RNS. In this Opinion, we first discuss the limitations of the commonly used techniques for detection of ROS and RNS, and the problem of heterogeneity of the cell population used in redox studies, which, together, can result in inaccurate conclusions regarding the redox biology of HSCs. We then propose approaches that are based on single-cell analysis followed by a functional test to examine ROS and RNS levels specifically in HSCs, as well as methods that might be used in vivo to overcome these drawbacks, and provide a better understanding of ROS and RNS function in stem cells.

The role of Hibiscus sabdariffa L. (Roselle) in maintenance of ex vivo murine bone marrow-derived hematopoietic stem cells

Hematopoietic stem cells- (HSCs-) based therapy requires ex vivo expansion of HSCs prior to therapeutic use. However, ex vivo culture was reported to promote excessive production of reactive oxygen species (ROS), exposing HSCs to oxidative damage. Efforts to overcome this limitation include the use of antioxidants. In this study, the role of Hibiscus sabdariffa L. (Roselle) in maintenance of cultured murine bone marrow-derived HSCs was investigated. Aqueous extract of Roselle was added at varying concentrations (0–1000 ng/mL) for 24 hours to the freshly isolated murine bone marrow cells (BMCs) cultures. Effects of Roselle on cell viability, reactive oxygen species (ROS) production, glutathione (GSH) level, superoxide dismutase (SOD) activity, and DNA damage were investigated. Roselle enhanced the survival (P < 0.05) of BMCs at 500 and 1000 ng/mL, increased survival of Sca-1⁺ cells (HSCs) at 500 ng/mL, and maintained HSCs phenotype as shown from nonremarkable changes of surface marker antigen (Sca-1) expression in all experimental groups. Roselle increased (P < 0.05) the GSH level and SOD activity but the level of reactive oxygen species (ROS) was unaffected. Moreover, Roselle showed significant cellular genoprotective potency against H₂O₂-induced DNA damage. Conclusively, Roselle shows novel property as potential supplement and genoprotectant against oxidative damage to cultured HSCs.

Hemozoin inhibition and control of clinical malaria

Malaria has a negative impact on health and social and economic life of residents of endemic countries. The ultimate goals of designing new treatment for malaria are to prevent clinical infection, reduce morbidity, and decrease mortality. There are great advances in the understanding of the parasite-host interaction through studies by various scientists. In some of these studies, attempts were made to evaluate the roles of malaria pigment or toxins in the pathogenesis of malaria. Hemozoin is a key metabolite associated with severe malaria anemia (SMA), immunosuppression, and cytokine dysfunction. Targeting of this pigment may be necessary in the design of new therapeutic products against malaria. In this review, the roles of hemozoin in the morbidity and mortality of malaria are highlighted as an essential target in the quest for effective control of clinical malaria.

Mild hyperthermia promotes and accelerates development and maturation of erythroid cells

Hyperthermia treatment has at times been associated with increased platelet levels in humans. The heat shock protein HSP70, which can be induced by hyperthermia in megakaryocytes and erythrocytes, was recently shown to protect GATA-1 from degradation and to be required for erythroid differentiation. Based on these findings, we hypothesize that mild hyperthermia (MH), such as fever (39°C), could impact the differentiation of hematopoietic progenitors into erythrocytes and their subsequent maturation. Cell growth and erythroid differentiation increased dramatically in cord blood CD34(+) cell cultures incubated under MH. Erythroid maturation was also strongly promoted, which resulted in an increased proportion of hemoglobinized and enucleated erythroids. The rise in erythroid development was traced to a strong synergistic activity between MH and erythropoietin (EPO). The molecular basis for this potent synergy appears to originate from the capacity of MH to increase the basal activation of several signaling molecules downstream of the EPO receptor and the transcriptional activity of GATA-1. Moreover, the potent impact of MH on erythroid development was found be dependent on increased intracellular levels of reactive oxygen species. Thus, fever-like temperatures can promote the differentiation of progenitors along the erythroid lineage and accelerate their maturation through normal regulatory circuitry.

Low oxygen tension positively influences cardiomyocyte progenitor cell function

Previously we observed that cardiomyocyte progenitor cells (hCMPCs) isolated from the human heart differentiate spontaneously into cardiomyocytes and vascular cells when transplanted after myocardial infarction (MI) in the ischemic heart. After MI, deprivation of oxygen is the first major change in the cardiac environment. How cells handle hypoxia is highly cell type dependent. The effect of hypoxia on cardiac stem or progenitor cells remains to be elucidated. Here, we show for the first time that short- and long-term hypoxia have different effects on hCMPCs. Short-term hypoxia increased the migratory and invasive capacities of hCMPCs likely via mesenchymal transformation. Although long-term exposure to low oxygen levels did not induce differentiation of hCMPCs into mature cardiomyocytes or endothelial cells, it did increase their proliferation, stimulated the secretome of the cells which was shifted to a more anti-inflammatory profile and dampened the migration by altering matrix metalloproteinase (MMP) modulators. Interestingly, hypoxia greatly induced the expression of the extracellular matrix modulator thrombospondin-2 (TSP-2). Knockdown of TSP-2 resulted in increased proliferation, migration and MMP activity. In conclusion, short exposure to hypoxia increases migratory and invasive capacities of hCMPCs and prolonged exposure induces proliferation, an angiogenic secretion profile and dampens migration, likely controlled by TSP-2.

Effect of long-term culture of mouse embryonic stem cells under low oxygen concentration as well as on glycosaminoglycan hyaluronan on cell proliferation and differentiation

OBJECTIVES

Maintaining undifferentiated stem cells in defined conditions is of critical importance to improve their in vitro culture. We have evaluated the effects of culturing mouse stem (mES) cells under physiological oxygen concentration as well as by replacing fibroblast feeder layer (mEF) with gelatin or glycosaminoglycan hyaluronan (HA), on cell proliferation and differentiation.

MATERIALS AND METHODS

After 3 days culture or after long-term cell culture under different conditions, levels of apoptotic cell death were determined by cell cycle and TUNEL (TdT-mediated dUTP nick end labelling) assays and levels of cell proliferation by CFSE (5-(and-6)-carboxyfluorescein diacetate succinimidyl ester) labelling. We assessed spontaneous differentiation into cardiomyocytes and mRNA expression of pluripotency and differentiation biomarkers.

RESULTS

After 3 days culture under hypoxic conditions, levels of proliferation and apoptosis of mES cells were higher, in correlation with increase in intracellular reactive oxygen species. However, when cells were continuously grown for 1 month under those conditions, the level of apoptosis was, in all cases, under 4%. Hypoxia reduced spontaneous differentiation of mES into cardiomyocytes. Long-term culture on HA was more effective in maintaining the pluripotent state of the mES cells when compared to that on gelatin. Level of terminal differentiation was highest on mEF, intermediate on HA and lowest on gelatin.

CONCLUSIONS

Our data suggest that hypoxia is not necessary for maintaining pluripotency of mES cells and appeared to be detrimental during ES differentiation. Moreover, HA may offer a valuable alternative for long-term culture of mES cells in vitro.

Nitric oxide enhances Oct-4 expression in bone marrow stem cells and promotes endothelial differentiation

This study was designed to investigate the role of nitric oxide (NO) in bone marrow stem cells and their differentiation into endothelial cells in vitro. Adult mouse bone marrow multipotent progenitor cells (MAPCs) were used as the source of stem cells. Oct-4 expression (both mRNA and protein) was significantly increased by up to 68.0% in MAPCs when incubated with NO donors DETA-NONOate or sodium nitroprusside (SNP) in a concentration-dependant manner (n=3, P<0.05). However, the cell proliferation was dramatically decreased by over 3-folds when treated with DETA-NONOate or SNP for 48 h (n=3, P<0.05). When MAPCs were exposed to DETA-NONOate (100 microM) for the first 48 h during differentiation, the expression (both mRNA and protein) of vWF was significantly increased at day 14 in the differentiating cells. The effects of DETA-NONOate or SNP on cell proliferation, Oct-4 expression and endothelial differentiation of MAPCs were not affected by the guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one or cGMP analog 8-Br-cGMP. These data indicate that NO may regulate both the pluripotency and differentiation of MAPCs via a cGMP-independent mechanism.

Role of the plasma membrane ROS-generating NADPH oxidase in CD34+ progenitor cells preservation by hypoxia

Hypoxia favored the preservation of progenitor characteristics of hematopoietic stem and progenitor cells (HSPCs) in bone marrow. This work aimed at studying the role of reactive oxygen species (ROS)-generating NADPH oxidase system regulated by hypoxia in ex vivo cultures of cord blood CD34+ cells. The results showed that NADPH oxidase activity and ROS generation were reduced in hypoxia with respect to normal oxygen tension. Meanwhile the ROS generation was found to be inhibited by diphenyleneiodonium (the NADPH oxidase inhibitor), or N-acetylcysteine (the ROS scavenger). Accordingly NADPH oxidase mRNA and p67 protein levels decreased in hypoxia. The analysis of progenitor characteristics, including the proportion of cultured cells expressing the HSPCs marker CD34+CD38-, colony production ability of the colony-forming cells (CFCs), and the re-expansion capability of the cultured CD34+ cells, showed that either 5% pO(2) or reduced ROS favored preserving the characteristics of CD34+ progenitors, and promoted the expansion of CD34+CD38- cells as well. The above results demonstrated that hypoxia effectively maintained biological characteristics of CD34+ cells through keeping lower intracellular ROS levels by regulating NADPH oxidase.

Stressed stem cells: Temperature response in aged mesenchymal stem cells

Mesenchymal stem cells (MSCs) derived from young (6 week) and aged (56 week) Wistar rats were cultured at standard (37 degrees C) and reduced (32 degrees C) temperature and compared for age markers and stress levels. (ROS, NO, TBARS, carbonyls, lipofuscin, SOD, GPx, apoptosis, proteasome activity) and heat shock proteins (HSP27, -60, -70, -90). Aged MSCs display many of the stress markers associated with aging in other cell types, but results vary across marker categories and are temperature dependant. In young MSCs, culturing at reduced temperature had a generally beneficial effect: the anti-apoptotic heat shock proteins HSP 27, HSP70, and HSP90 were up-regulated; pro-apoptotic HSP60 was downregulated; SOD, GPx increased; and levels in ROS, NO, TBARS, carbonyl, and lipofuscin were diminished. Apoptosis was reduced, but also proteasome activity. In contrast, in aged MSCs, culturing at reduced temperature generally produced no 'beneficial' changes in these parameters, and can even have detrimental effects. Implications for tissue engineering and for stem cell gerontology are discussed. The results suggest that a 'hormesis' theory of stress response can be extended to MSCs, but that cooling cultivation temperature stress produces positive effects in young cells only.

Identification of CXCR4 as a new nitric oxide-regulated gene in human CD34+ cells

As an intracellular second messenger, nitric oxide (NO) is increasingly implicated in the control of transcriptional machinery and gene expression. Here, we show that cell surface expression of CXCR4 on CD34(+) cells was increased in a dose- and time-dependent manner in response to NO donors. Augmented surface expression was correlated with an increase in CXCR4 mRNA level. A specific NO scavenger prevented the elevation in CXCR4 mRNA caused by NO donors, suggesting a direct signaling action mediated by NO on CXCR4 transcription. NO treatment had no significant effect on CXCR4 mRNA stability. However, induction of CXCR4 mRNA by NO was still observed in conditions in which initiation of translation was inhibited, suggesting that the NO effect must be mediated by a pre-existing protein. CXCR4 mRNA induction did not involve cGMP (guanosine 3', 5'-cyclic monophosphate) generation but was most likely mediated via oxidation of intracellular protein thiols. Finally, CD34(+) cells pretreated with NO donors exhibited an increased chemotactic response. This study demonstrates that the NO pathway can modulate CXCR4 expression in human CD34(+) cells and suggests that NO may play a critical role in the trafficking of hematopoietic progenitors.

Endothelial Progenitor Cell Release into Circulation Is Triggered by Hyperoxia-Induced Increases in Bone Marrow Nitric Oxide

Endothelial progenitor cells (EPC) are known to contribute to wound healing, but the physiologic triggers for their mobilization are often insufficient to induce complete wound healing in the presence of severe ischemia. EPC trafficking is known to be regulated by hypoxic gradients and induced by vascular endothelial growth factor-mediated increases in bone marrow nitric oxide (NO). Hyperbaric oxygen (HBO) enhances wound healing, although the mechanisms for its therapeutic effects are incompletely understood. It is known that HBO increases nitric oxide levels in perivascular tissues via stimulation of nitric oxide synthase (NOS). Here we show that HBO increases bone marrow NO in vivo thereby increasing release of EPC into circulation. These effects are inhibited by pretreatment with the NOS inhibitor l-nitroarginine methyl ester (l-NAME). HBO-mediated mobilization of EPC is associated with increased lower limb spontaneous circulatory recovery after femoral ligation and enhanced closure of ischemic wounds, and these effects on limb perfusion and wound healing are also inhibited by l-NAME pretreatment. These data show that EPC mobilization into circulation is triggered by hyperoxia through induction of bone marrow NO with resulting enhancement in ischemic limb perfusion and wound healing.

Nitric oxide induces promyelocytic cell growth arrest and apoptosis through deactivation of Akt pathway

It is NO that mediates the inhibitory effect of IFN-gamma, MIP-1alpha and TNFalpha on hematopoiesis. However, the mechanism for NO effect on the hematopoietic system is likely to not clear. In the current work, we demonstrates that NO can directly suppress the colony formation of granulocyte/macrophage in vitro. Using a granulocyte/macrophage progenitor (GMP) model, HL-60 cell line, we show that NO inhibits the proliferation of HL-60 cells by inducing G0/G1 arrest and apoptosis in a dose- and time-dependent manner. Exposure of HL-60 cells to 1mM SNP for 2-48h results in marked decrease in Akt activation and Bad phosphorylation. Constitutively active Akt overexpression reduces NO-induced apoptosis and cell cycle arrest in HL-60 cells. A further investigation on apoptosis related protein shows that NO induces Bid cleavage and Bax expression but down-regulates the expression of Bcl-2 and Bcl-xL. We also demonstrate here that G0/G1 arrest is resulted from NO-induced disruption of cell cycle balance, which is mediated by up-regulation of p21(waf/cip1), p27(kip1) and down-regulation of cyclin D1, cyclin E. In brief, NO-induced apoptosis and G0/G1 arrest is mediated through regulation of apoptosis and cell cycle related protein, which may depend on Akt deactivation by NO, ultimately led to its inhibitory effect on hematopoiesis.

Effect of reduced culture temperature on antioxidant defences of mesenchymal stem cells

Mesenchymal stem cells (MSC) promise to be valuable therapeutic tools but, due to their low numbers, require considerable in vitro expansion before use. This leads to in vitro aging, the accumulation of intracellular oxidative damage, and subsequently a decreased potential for proliferation and differentiation. Optimised culture conditions might help to reduce oxidative damage in MSC in vitro, and therefore, as reduced temperature is known to reduce oxidative stress in other somatic cells, we have investigated the effect of reduced temperature on rat MSC viability, differentiation, and oxidative damage. Temperature reduction did not affect MSC viability but increased differentiation and reduced apoptosis. Oxidative-damage-related indices were improved; reactive oxide species, nitric oxide, thiobarbituric acid reactive substances, carbonyl, and lipofuscin levels were reduced and glutathione peroxidase and superoxide dimutase levels increased. Levels of antiapoptotic heat shock proteins (HSP-27, -70, and -90) were raised and levels of the proapoptotic HSP-60 reduced. These data demonstrate that culturing MSC at reduced temperature decreases the accumulation of oxidative damage and therefore would probably improve long-term viability and successful engraftment of MSC used for tissue engineering or cell therapeutic purposes.

Oxygen in the cultivation of stem cells

Cultivation of stem cells, like all cells in culture, is performed under conditions that cannot and do not replicate normal physiologic conditions. For example, direct exposure of cultured monolayer cells to serum contents is normally prevented in vivo by the vasculature. The heterogeneity of cells and signals between different cell types in an organ is certainly not captured when a single cell type is grown and studied in vitro. Gases, in particular, are not accounted for in routine tissue culture. Oxygen is fundamental for life and its concentration is an important signal for virtually all cellular processes. Nonetheless, oxygen is rarely taken into account in culturing stem and other cells. This review will summarize work that highlights the importance of considering oxygen conditions for culturing and manipulating stem cells. Emphasis is placed on major phenotypic changes in response to oxygen, recognizing that oxygen-mediated transcriptional and post-translational effects are enormously complex, and beyond the scope of this review. The review emphasizes that oxygen is an important signal in all major aspects of stem cell biology including proliferation and tumorigenesis, cell death and differentiation, self-renewal, and migration.

Regulating immunity to malaria

The optimal outcome of a malaria infection is that parasitized cells are killed and degraded without inducing significant pathology. Since much of the pathology of malaria infection can be immune-mediated, this implies that immune responses have to be carefully regulated. The mechanisms by which anti-malarial immune responses are believed to be regulated were discussed at the recent Malaria Immunology Workshop (Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland, USA; February 2005). Potential regulatory mechanisms include regulatory T cells, which have been shown to significantly modify cellular immune responses to various protozoan infections, including leishmania and malaria; neutralising antibodies to pro-inflammatory malarial toxins such as glycosylphosphatidylinositol and haemozoin; and self-regulating networks of effector molecules. Innate and adaptive immune responses are further moderated by the broader immunological environment, which is influenced by both the genetic background of the host and by co-infection with other pathogens. A detailed understanding of the interplay between these different immunoregulatory processes may facilitate the rationale design of vaccines and novel therapeutics.

Modification of the content of plasma protein carbonyl groups in donors after granulocyte colony stimulating factor-induced stem cell mobilization

Granulocyte-colony stimulating factor (G-CSF), the most established agent for the mobilization of stem cells in current clinical practice, could induce a condition of oxidative stress. Herein plasmatic levels of protein carbonyl groups (a biomarker of oxidative stress) were measured in a group of donors given recombinant human G-CSF (rHuG-CSF) at different times: (1) before starting rHuG-CSF administration, (2) on day 5 of rHuG-CSF administration, (3) on the same day immediately after the end of the first leukapheresis procedure and (4) one week after rHuG-CSF withdrawal. Plasma levels of protein carbonyl groups enhanced significantly in donors after 5 days of rHuG-CSF treatment and appeared further slightly increased following leukapheresis procedure; 7 days following rHuG-CSF withdrawal, they showed a tendency to normalization. These findings may contribute to better understand the oxidative reactions following rHuG-CSF treatment and leukapheresis.

Specific antibodies to mouse Sca-1- (Ly-6A/E) or Thy-1-positive haematopoietic progenitor cells induce formation of nitric oxide which inhibits subsequent colony formation

Mouse bone marrow cells were exposed to specific monoclonal antibodies, so that lineage positive (Lin+) cells could be removed with magnetic beads. The Lin- cells were cultured with Sca-1 or CD90 (Thy-1) monoclonal antibodies (MoAbs) in semi-solid medium for 7 d. We found that Sca-1 MoAb suppressed colony formation (20-30%), and the effect was largely abolished by N-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthase. Similar results were obtained with antibodies to CD90. The findings suggest that the unknown physiological ligands to Sca-1 and Thy-1 markers on haematopoietic progenitor cells can inhibit colony formation, with NO as a pivotal mediator. Primitive progenitors may be a primary target of this Sca-1 ligand, as the Sca-1+ cell population contains the major part of the multipotent haematopoietic stem cells.

Elevated nitric oxide production in children with malarial anemia: hemozoin-induced nitric oxide synthase type 2 transcripts and nitric oxide in blood mononuclear cells

Experiments outlined here investigate the role of nitric oxide (NO) in the pathogenesis of Plasmodium falciparum-induced malarial anemia (MA). The results show that ex vivo and in vitro NO synthase (NOS) activity in peripheral blood mononuclear cells (PBMCs) is significantly elevated in children with MA and inversely associated with hemoglobin levels. Additional experiments using PBMCs from non-malaria-exposed donors demonstrate that physiologic amounts of P. falciparum-derived hemozoin augment NOS type 2 (NOS2) transcripts and NO production. Results of these experiments illustrate that elevated NO production in children with MA is associated with decreased hemoglobin concentrations and that hemozoin can induce NOS2-derived NO formation in cultured blood mononuclear cells.

Macrophage overgrowth affects neighboring nonovergrown encapsulated islets

BACKGROUND

Encapsulation significantly prolongs islet graft survival in the absence of immunosuppression. However, encapsulated islet graft survival is limited to periods of several months. Part of the encapsulated islet graft is affected by a nonprogressive pericapsular overgrowth. To investigate whether macrophages on overgrown capsules affect neighboring nonovergrown encapsulated islets, encapsulated islets were studied during coculture.

MATERIALS AND METHODS

Encapsulated islet function, islet vitality, and islet cell replication were assessed, as well as the mRNA expression of Bcl-2, Bax, inducible nitric oxide synthase, and monocyte chemoattractant protein-1 in encapsulated islets after 48 h of culture together with microcapsules with macrophage overgrowth. Overgrown capsules were retrieved from the rat peritoneum, three weeks after implantation of an encapsulated islet graft.

RESULTS

Coculture was associated with inhibition of the stimulated insulin secretion, with decreased cell replication, and with increased cell necrosis, but not with apoptosis of encapsulated islet cells. mRNA expression levels in encapsulated islets after coculture were not different from controls, except for a decrease in Bax mRNA. We found a high level of nitrite, as an indicator of nitric oxide production, but not an increase in inducible nitric oxide synthase mRNA in islets. This, in combination with the absence of increase in monocyte chemoattractant protein-1 mRNA and the lack of apoptosis, indicates that neither interleukin-1beta nor tumor necrosis factor-alpha was responsible for the deleterious effects of coculture on encapsulated islets.

CONCLUSIONS

Nonovergrown encapsulated islets are affected by the overgrowth on encapsulated islets in their close proximity. This overgrowth contains macrophages that produce nitric oxide which, rather than cytokines, may be held responsible for the deleterious effect on the neighboring encapsulated islets.

Effects of the farnesyl transferase inhibitor R115777 on normal and leukemic hematopoiesis

Patients with acute myelogenous leukemia or myelodysplastic syndrome may respond to farnesyl transferase inhibitors (FTIs) with partial or complete response rates noted in about 30% of such patients. FTIs prevent the attachment of a lipid farnesyl moiety to dependent proteins prior to their insertion into the plasma membrane and thereby prevent activity of these prenylation-dependent proteins, but their mechanism of tumor suppression remains unknown. Many patients receiving FTIs do experience myelosuppression. In this work, the in vitro effects of the FTI, R115777 on normal and leukemic hematopoiesis have been examined as have its effects on apoptosis induction and cell cycle profile in both leukemic blasts and normal CD34+ cells. R115777 was inhibitory to normal CD34+ cell proliferation and to leukemic blast cells, but did not affect long-term culture initiating cell frequency nor NOD-SCID reconstituting capacity. No induction of apoptosis or cell cycle changes were noted in AML blasts. These data suggest that myelosuppression with R115777 occurs largely at the intermediate to late progenitor stage of hematopoiesis and that cyclic use might avoid long-term marrow suppression.

Flavonoid effects on normal and leukemic cells

Quercetin and flavopiridol, both flavonoids which influence oxidative milieu, proliferation, and apoptosis of various cell types, were examined for their effects on acute myelogenous leukemic cells and normal progenitors. Both quercetin and flavopiridol inhibited the growth and viability of various acute myelogenous leukemia (AML) cell lines and AML blasts isolated afresh from patients with AML of various subtypes. The effects on inhibition of proliferation and decreased viability were also significant in normal CD34+ cells isolated from normal marrow donors. In certain AML cases, the effects of flavopiridol appeared to be mediated through activation of caspase 3, offering one possible mechanism for the apoptosis evident after exposure to flavopiridol as measured by annexin V expression. These flavonoid compounds might find use in various therapeutic settings in AML.

Increased inducible nitric oxide synthase expression and nitric oxide concentration in patients with aplastic anemia

Nitric oxide (NO) is a biological mediator that is synthesized from L-arginine by the nitric oxide synthase (NOS) family. We investigated the expression of iNOS in bone marrow (BM) mononuclear cells (MNCs) using a reverse transcriptase polymerase chain reaction (RT-PCR) assay and the concentration of NO from BM serum by measuring the metabolite NO(2)(-) in 13 patients with aplastic anemia (AA) compared with 10 normal controls who were donors for allogeneic bone marrow transplantation (BMT). All samples of BM MNCs in patients with AA expressed iNOS mRNA, but iNOS was not expressed in patients who were treated successfully with allogeneic BMT. Normal control samples and samples from leukemia patients who had bone marrow aplasia after chemotherapy did not show significant iNOS expression. When we measured the density of bands for both iNOS and beta(2)-microglobin expressed as the iNOS/beta(2)-microglobin density ratio, there was a significant difference in the ratio between AA and normal controls (0.88+/-0.15 vs 0.26+/-0.05, P<0.001). The BM serum NO(2)(-) concentration in the patients with AA was significantly higher than that of normal controls (88.1+/-32.8 microM vs 48.8+/-8.6 microM, P=0.002). In addition, there was a significant correlation between the NO(2)(-) concentration and the calculated iNOS/beta(2)-microglobin density ratio (r=0.567, P=0.01). These findings suggest that upregulation of iNOS expression for local NO production may contribute in part to the pathogenesis of AA.

Hypoxia-inducible factor and the development of stem cells of the cardiovascular system

Decreased oxygen (O2) levels activate hypoxia-inducible factor (HIF-1) to induce genes involved in glycolysis, glucose transport, erythropoiesis, and angiogenesis. Mutations in various HIF-1 subunits have contributed to our understanding of the role hypoxia plays during early embryonic development in general and the cardiovascular system in particular. We propose that HIF-1 is important for the generation, proliferation, maintenance, and differentiation of the early cardiovascular system. Understanding aberrations in these hypoxic responses is important since they contribute to serious human disease such as ischemia and tumorigenesis. In this review we will focus on the critical role of O2 in regulating cardiovascular events during early embryonic development.

Regulation of the acute myeloid leukemia cell line OCI/AML-2 by endothelial nitric oxide synthase under the control of a vascular endothelial growth factor signaling system

It is generally accepted that the vascular endothelial growth factor (VEGF) signal system has no role in the maintenance of normal blood cell formation, although it obviously regulates the development of primitive hematopoiesis during an early stage of embryogenesis. The VEGF signaling pathway, however, might have some role in malignant hematopoiesis, since malignant hematopoietic cells, including acute myeloid leukemia (AML) cells, have been shown to express VEGF and its receptors. In endothelial cells, the VEGF/Flk-1/KDR signal system is a very important generator of nitric oxide (NO) through the activation of its downstream effectors phosphatidylinositol-3-OH-kinase (PI3-K), Akt kinase and endothelial NO synthase (eNOS). It is known that NO regulates hematopoiesis and modulates AML cell growth. The role of the VEGF signaling pathway in the control of AML cell growth through eNOS, however, has not been studied. By using the OCI/AML-2 cell line, which expresses VEGF receptor-2, ie Flk-1/KDR, eNOS and VEGF, as analyzed by flow cytometry, and produces VEGF into growth medium, as analyzed by ELISA, we showed that the Akt kinase and NOS activities in these cells were decreased by the inhibitors of VEGF, Flk-1/KDR and PI3-K, and NOS activity also by the direct inhibitor of NOS. The decreased NOS activity led to inhibition of clonogenic cell growth and, to some extent, induction of apoptosis. We also found that blast cells of bone marrow samples randomly taken from 14 AML patients uniformly expressed Flk-1/KDR and to varying degrees eNOS and VEGF, as analyzed by immunohistochemistry. We conclude that autocrine VEGF through Flk-1/KDR, by activating eNOS to produce NO through PI3-K/Akt kinase, maintains clonogenic cell growth in the OCI/AML-2 cell line. Since the patient samples did not express VEGF in all cases, it is possible that in vivo the regulatory connection between these two signal systems is also mediated via endocrine VEGF in addition to autocrine or paracrine VEGF.

Phase II study of combination human recombinant GM-CSF with intermediate-dose cytarabine and mitoxantrone chemotherapy in patients with high-risk myelodysplastic syndromes (RAEB, RAEBT, and CMML): an Eastern Cooperative Oncology Group Study

A Phase II study of GM-CSF with intermediate-dose cytarabine and mitoxantrone was conducted in patients with high-risk myelodysplastic syndrome. It was designed to evaluate if priming with growth factor could increase the efficiency of chemotherapy. In this older population only two of 10 patients achieved a bone marrow CR, including one patient whose leukemic blasts had an "S" phase increase of 2.55x at 48 hr. Unexpected hepatotoxicity was noted. This regimen cannot be recommended for this elderly population of patients.

Expression of hematopoietic growth factor receptors on early hematopoietic precursors: detection and regulation

Since the original isolation of colony-stimulating factors from human serum, conditioned medium of murine or human cell lines, or freshly isolated human mononuclear cells, a revolutionary explosion of ideas has occurred in our understanding of molecular controls of the hematopoietic stem cell self-renewal and differentiation. With the availability of techniques of molecular cloning in the early 1 980s, the first hematopoietically activated cytokines led to molecular clones expressed in bacteria, yeast, or mammalian cellular systems. There then followed a development of techniques leading to the molecular cloning and expression of many hematopoietic growth factors and their receptors, as well as the primary, secondary, and tertiary molecules in signal transduction into activation of specific genes for differentiation or self-renewal. The clinical use of these factors in the diagnosis, treatment, and incorporation into new cell therapies for a variety of diseases is a subject of current interest.