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

iNOS regulates hematopoietic stem and progenitor cells via mitochondrial signaling and is critical for bone marrow regeneration

Hematopoietic stem cells (HSCs) replenish blood cells under steady state and on demand, that exhibit therapeutic potential for Bone marrow failures and leukemia. Redox signaling plays key role in immune cells and hematopoiesis. However, the role of reactive nitrogen species in hematopoiesis remains unclear and requires further investigation. We investigated the significance of inducible nitric oxide synthase/nitric oxide (iNOS/NO) signaling in hematopoietic stem and progenitor cells (HSPCs) and hematopoiesis under steady-state and stress conditions. HSCs contain low levels of NO and iNOS under normal conditions, but these increase upon bone marrow stress. iNOS-deficient mice showed subtle changes in peripheral blood cells but significant alterations in HSPCs, including increased HSCs and multipotent progenitors. Surprisingly, iNOS-deficient mice displayed heightened susceptibility and delayed recovery of blood progeny following 5-Fluorouracil (5-FU) induced hematopoietic stress. Loss of quiescence and increased mitochondrial stress, indicated by elevated MitoSOX and MMPhi HSCs, were observed in iNOS-deficient mice. Furthermore, pharmacological approaches to mitigate mitochondrial stress rescued 5-FU-induced HSC death. Conversely, iNOS-NO signaling was required for demand-driven mitochondrial activity and proliferation during hematopoietic recovery, as iNOS-deficient mice and NO signaling inhibitors exhibit reduced mitochondrial activity. In conclusion, our study challenges the conventional view of iNOS-derived NO as a cytotoxic molecule and highlights its intriguing role in HSPCs. Together, our findings provide insights into the crucial role of the iNOS-NO-mitochondrial axis in regulating HSPCs and hematopoiesis.

Regulation of pleiotropic physiological roles of nitric oxide signaling

Nitric Oxide (NO) is a highly diffusible, ubiquitous signaling molecule and a free radical that is naturally synthesized by our body. The pleiotropic effects of NO in biological systems are due to its reactivity with different molecules, such as molecular oxygen (O₂), superoxide anion, DNA, lipids, and proteins. There are several contradictory findings in the literature pertaining to its role in oncology. NO is a Janus-faced molecule shown to have both tumor promoting and tumoricidal effects, which depend on its concentration, duration of exposure, and location. A high concentration is shown to have cytotoxic effects by triggering apoptosis, and at a low concentration, NO promotes angiogenesis, metastasis, and tumor progression. Upregulated NO synthesis has been implicated as a causal factor in several pathophysiological conditions including cancer. This dichotomous effect makes it highly challenging to discover its true potential in cancer biology. Understanding the mechanisms by which NO acts in different cancers helps to develop NO based therapeutic strategies for cancer treatment. This review addresses the physiological role of this molecule, with a focus on its bimodal action in various types of cancers.

Pharmacological Inhibition of p38 MAPK Rejuvenates Bone Marrow Derived-Mesenchymal Stromal Cells and Boosts their Hematopoietic Stem Cell-Supportive Ability

The therapeutic value of mesenchymal stromal cells (MSCs) for various regenerative medicine applications, including hematopoietic stem cell transplantations (HSCT), has been well-established. Owing to their small numbers in vivo, it becomes necessary to expand them in vitro, which leads to a gradual loss of their regenerative capacity. Stress-induced mitogen-activated protein kinase p38 (p38 MAPK) signaling has been shown to compromise the MSC functions. Therefore, we investigated whether pharmacological inhibition of p38 MAPK signaling rejuvenates the cultured MSCs and boosts their functionality. Indeed, we found that the ex vivo expanded MSCs show activated p38 MAPK signaling and exhibit increased oxidative stress. These MSCs show a decreased ability to secrete salutary niche factors, thereby compromising their ability to support hematopoietic stem cell (HSC) self-renewal, proliferation, and differentiation. We, therefore, attempted to rejuvenate the cultured MSCs by pharmacological inhibition of p38 MAPK - a strategy broadly known as "priming of MSCs". We demonstrate that priming of MSCs with a p-38 MAPK inhibitor, PD169316, boosts their niche-supportive functions via upregulation of various HSC-supportive transcription factors. These primed MSCs expand multipotent HSCs having superior homing and long-term reconstitution ability. These findings shed light on the significance of non-cell-autonomous mechanisms operative in the hematopoietic niche and point towards the possible use of pharmacological compounds for rejuvenation of ex vivo cultured MSCs. Such approaches could improve the outcome of regenerative therapies involving in vitro cultured MSCs.

Nitric Oxide in the Control of the in vitro Proliferation and Differentiation of Human Hematopoietic Stem and Progenitor Cells

Hematopoietic stem and progenitor cell (HSPC) transplantation is the best-studied cellular therapy and successful in vitro control of HSPCs has wide clinical implications. Nitric oxide (NO) is a central signaling molecule in vivo and has been implicated in HSPC mobilization to the blood stream in mice. The influence of NO on HSPC behavior in vitro is, however, largely obscure due to the variety of employed cell types, NO administration systems, and used concentration ranges in the literature. Additionally, most studies are based on murine cells, which do not necessarily mimic human HSPC behavior. Thus, the aim of the present study was the systematic, concentration-dependent evaluation of NO-mediated effects on human HSPC behavior in vitro. By culture in the presence of the long-term NO donor diethylenetriamine/nitric oxide adduct (DETA/NO) in a nontoxic concentration window, a biphasic role of NO in the regulation of HSPC behavior was identified: Low DETA/NO concentrations activated classical NO signaling, identified via increased intracellular cyclic guanosine monophosphate (cGMP) levels and proteinkinases G (PKG)-dependent vasodilator-stimulated phosphoprotein (VASP) phosphorylation and mediated a pro-proliferative response of HSPCs. In contrast, elevated NO concentrations slowed cell proliferation and induced HSPC differentiation. At high concentrations, s-nitrosylation levels were elevated, and myeloid differentiation was increased at the expense of lymphoid progenitors. Together, these findings hint at a central role of NO in regulating human HSPC behavior and stress the importance and the potential of the use of adequate NO concentrations for in vitro cultures of HSPCs, with possible implications for clinical application of in vitro expanded or differentiated HSPCs for cellular therapies.

Cryopreservation of mesenchymal stromal cell-derived extracellular vesicles using trehalose maintains their ability to expand hematopoietic stem cells in vitro

The multitude of clinical trials using mesenchymal stromal cells (MSCs) has underscored their significance as a promising cell source for regenerative therapies. Most studies have however shown that MSCs get entrapped into the microvasculature of lungs, liver and spleen. In addition to intercellular communication, MSCs exert their effects in a paracrine manner by secretion of extracellular vesicles (EVs). The therapeutic effects of MSC-derived EVs have been examined in several diseases such as hepatic failure, liver injury, hematopoiesis etc. Therefore, optimization of cryopreservation strategies for the long-term storage of functional EVs could help in the development of off-the-shelf biologics. The aim of this study was to develop an optimal cryopreservation strategy for the efficient storage of both types of EVs - Microvesicles (MVs) and exosomes, independently, and to further examine the effect of the cryopreserved EVs on the ex vivo expansion of HSCs. MVs and exosomes were separately cryopreserved at different temperatures using PBS or PBS supplemented with trehalose (pTRE), and these cryopreserved EVs were then assessed for their functionality after revival. We found that addition of trehalose during cryopreservation helped in maintaining the morphology and functionality of the EVs, as assessed by their HSC-supportive potential, ability to expand phenotypically defined HSCs and ability to maintain the chemotactic migration potential of the HSCs co-cultured with them. This strategy could prove to be beneficial for facilitating the use of EVs as cell-free ready-to-use biologics for the ex vivo expansion of HSCs and in regenerative medicine.

Viability and intracellular nitric oxide generation in the umbilical cord blood CD34+CD133- and CD34+CD133+ cell populations exposed to local anaesthetics

Local anesthetics (LAs) are capable of influencing cell viability in systemic immunity and may also modify metabolism of those present in umbilical cord blood (UCB) following obstetric neuraxial analgesia and anaesthesia. Data regarding UCB immature cells, important for the neonate and critical for putative UCB transplantations, are lacking. LAs are capable of stimulating intracellular nitric oxide (NO) in human neutrophils; no information is available concerning newly perpetuated cells and its potential association with viability. The study aimed at assessing the LAs influence on the cell viability and intracellular NO production by UCB CD34⁺CD133^– and CD34⁺ CD133⁺ cell populations. Mononuclear cells separated from UCB samples (n = 19) were incubated with bupivacaine (0.0005, 0.005, 1 mM), lidocaine (0.002, 0.02, 4 mM), and ropivacaine (0.0007, 0.007, 1.4 mM) for 4 h. Flow cytometry was applied for the assessment of cell viability and intracellular NO generation in CD34⁺CD133^– and CD34⁺CD133⁺ cell populations using annexinV/7-AAD and DAF-2DA stainings, respectively. CD34⁺CD133⁺ cells showed less pronounced late apoptosis and necrosis as compared to CD34⁺CD133-population. Intracellular NO generation was comparable between both cell populations studied. LAs neither influenced cell viability nor changed NO production in either population. LAs do not interfere with viability and intracellular NO generation in the UCB CD34⁺CD133^– and CD34⁺CD133⁺ cell populations.

Persistent stimulation with Mycobacterium tuberculosis antigen impairs the proliferation and transcriptional program of hematopoietic cells in bone marrow

Mycobacterium tuberculosis (M. tuberculosis) persistent infection might cause the dysfunction of hematopoiesis. To investigate whether M. tuberculosis persistent antigen stimulation impairs the proliferation and differentiation of hematopoietic stem and progenitor cells characterized as lineage^- c-Kit⁺ (LK cells), C57BL/6 mice were primed with Mycobacterium bovis Bacillus Calmette-Guérin (BCG) and boosted with a cocktail of M. tuberculosis antigens ESAT6, CFP10 and Mtb10.4-HspX (MH) along with adjuvant N, N'-dimethyl-N, N'-dioctadecylammonium bromide (DDA) plus polyinosinic-polycytidylic acid (Poly I:C) weekly for 12 or 22 weeks. The cytokine production by splenic T cells, proliferation of LK cells and transcriptional events during differentiation of bone marrow (BM) c-Kit⁺ cells were investigated. Meanwhile, the mice were treated with interleukin 2 (IL-2) and the therapeutic effects were analyzed. We found that antigen specific interferon-γ (IFN-γ) production by splenic CD4⁺ T cells increased following antigen stimulation for 12 weeks, but it declined after continuous stimulation for 22 weeks. The long-term exposure of mice to M. tuberculosis antigen compromised the proliferation of LK cells. Moreover, the expression of transcription factors in the c-Kit⁺ cells was adjusted, with up-regulation of IRF8 and Batf2 involved in myeloid differentiation and down-regulation of NOTCH1 and GATA2 participated in T-cell lineage commitment. The concentrations of IFN-γ in BM of the persistent antigen group were higher than that in sham control at the 12th week, while the concentrations of IL-2 in BM of the persistent antigen group were lower compared with the transient antigen stimulation control. Following IL-2 treatment, the concentrations of IL-2 in BM increased while IFN-γ got declined. IL-2 treatment could restore the expression levels of those transcription factors and the proliferating activity of LK cells impaired by persistent antigen stimulation. Our results indicate that M. tuberculosis antigen persistent stimulation decreases the proliferating activity of LK cells, promotes myelopoietic differentiation, and represses lymphopoietic differentiation as a consequence of elevated IFN-γ production. IL-2 supplementation contributes to maintaining the homeostasis of hemopoiesis.

Microvesicles Secreted by Nitric Oxide-Primed Mesenchymal Stromal Cells Boost the Engraftment Potential of Hematopoietic Stem Cells

Patients with leukemia, lymphoma, severe aplastic anemia, etc. are frequently the targets of bone marrow transplantation, the success of which critically depends on efficient engraftment by transplanted hematopoietic cells (HSCs). Ex vivo manipulation of HSCs to improve their engraftment ability becomes necessary when the number or quality of donor HSCs is a limiting factor. Due to their hematopoiesis-supportive ability, bone marrow-derived mesenchymal stromal cells (MSCs) have been traditionally used as feeder layers for ex vivo expansion of HSCs. MSCs form a special HSC-niche in vivo, implying that signaling mechanisms operative in them would affect HSC fate. We have recently demonstrated that AKT signaling prevailing in the MSCs affect the HSC functionality. Here we show that MSCs primed with nitric oxide donor, Sodium nitroprusside (SNP), significantly boost the engraftment potential of the HSCs co-cultured with them via intercellular transfer of microvesicles (MVs) harboring mRNAs encoding HSC-supportive genes. Our data suggest that these MVs could be used as HSC-priming agents to improve transplantation efficacy. Since both, nitric oxide donors and MSCs are already in clinical use; their application in clinical settings may be relatively straight forward. This approach could also be applied in regenerative medicine protocols. Stem Cells 2019;37:128-138.

Mesenchymal stromal cells enhance the hematopoietic stem cell-supportive activity of resveratrol

Aim: To examine the stromal cell-mediated effects of trans-resveratrol (TRV) on the fate of hematopoietic stem cells (HSCs). Materials & methods: Proliferation assay, cell cycle analysis, apoptosis assay, flow cytometry, western blot. Results: Using KG1a, we show that TRV has a dose-dependent effect on the proliferation of hematopoietic cells. Its stimulatory effect was significantly enhanced when the cells were cocultured with stromal cells. Addition of TRV in the coculture of murine bone marrow-derived HSCs and stromal cells led to a significant increase in the pool of long-term HSCs. We identify AKT and extracellular-signal-regulated kinase pathways as the players behind the mechanism of growth stimulatory action of TRV. Conclusion: Our findings may have implications in the ex vivo manipulation of HSCs for therapeutic purposes.

Regulation of Cellular Redox Signaling by Matricellular Proteins in Vascular Biology, Immunology, and Cancer

SIGNIFICANCE

In contrast to structural elements of the extracellular matrix, matricellular proteins appear transiently during development and injury responses, but their sustained expression can contribute to chronic disease. Through interactions with other matrix components and specific cell surface receptors, matricellular proteins regulate multiple signaling pathways, including those mediated by reactive oxygen and nitrogen species and H2S. Dysregulation of matricellular proteins contributes to the pathogenesis of vascular diseases and cancer. Defining the molecular mechanisms and receptors involved is revealing new therapeutic opportunities. Recent Advances: Thrombospondin-1 (TSP1) regulates NO, H2S, and superoxide production and signaling in several cell types. The TSP1 receptor CD47 plays a central role in inhibition of NO signaling, but other TSP1 receptors also modulate redox signaling. The matricellular protein CCN1 engages some of the same receptors to regulate redox signaling, and ADAMTS1 regulates NO signaling in Marfan syndrome. In addition to mediating matricellular protein signaling, redox signaling is emerging as an important pathway that controls the expression of several matricellular proteins.

CRITICAL ISSUES

Redox signaling remains unexplored for many matricellular proteins. Their interactions with multiple cellular receptors remains an obstacle to defining signaling mechanisms, but improved transgenic models could overcome this barrier.

FUTURE DIRECTIONS

Therapeutics targeting the TSP1 receptor CD47 may have beneficial effects for treating cardiovascular disease and cancer and have recently entered clinical trials. Biomarkers are needed to assess their effects on redox signaling in patients and to evaluate how these contribute to their therapeutic efficacy and potential side effects. Antioxid. Redox Signal. 27, 874-911.