Pleiotropic effects of prostaglandin E2 in hematopoiesis; prostaglandin E2 and other eicosanoids regulate hematopoietic stem and progenitor cell function

Disruption of the PGE2 synthesis / response pathway restrains atherogenesis in programmed cell death-1 (Pd-1) deficient hyperlipidemic mice

Immune checkpoint inhibitors (ICIs) that target programmed cell death 1 (PD-1) have revolutionized cancer treatment by enabling the restoration of suppressed T-cell cytotoxic responses. However, resistance to single-agent ICIs limits their clinical utility. Combinatorial strategies enhance their antitumor effects, but may also enhance the risk of immune related adverse effects of ICIs. Prostaglandin (PG) E2, formed by the sequential action of the cyclooxygenase (COX) and microsomal PGE synthase (mPGES-1) enzymes, acting via its E prostanoid (EP) receptors, EPr2 and EPr4, promotes lymphocyte exhaustion, revealing an additional target for ICIs. Thus, COX inhibitors and EPr4 antagonists are currently being combined with ICIs potentially to enhance antitumor efficacy in clinical trials. However, given the cardiovascular (CV) toxicity of COX inhibitors, such combinations may increase the risk particularly of CV AEs. Here, we compared the impact of distinct approaches to disruption of the PGE2 synthesis /response pathway - global or myeloid cell specific depletion of mPges-1 or global depletion of Epr4 - on the accelerated atherogenesis in Pd-1 deficient hyperlipidemic (Ldlr-/-) mice. All strategies restrained the atherogenesis. While depletion of mPGES-1 suppresses PGE2 biosynthesis, reflected by its major urinary metabolite, PGE2 biosynthesis was increased in mice lacking EPr4, consistent with enhanced expression of aortic Cox-1 and mPges-1. Deletions of mPges-1 and Epr4 differed in their effects on immune cell populations in atherosclerotic plaques; the former reduced neutrophil infiltration, while the latter restrained macrophages and increased the infiltration of T-cells. Consistent with these findings, chemotaxis by bone-marrow derived macrophages from Epr4-/- mice was impaired. Epr4 depletion also resulted in extramedullary lymphoid hematopoiesis and inhibition of lipoprotein lipase activity (LPL) with coincident spelenomegaly, leukocytosis and dyslipidemia. Targeting either mPGES-1 or EPr4 may restrain lymphocyte exhaustion while mitigating CV irAEs consequent to PD-1 blockade.

Pharmacokinetics and Biodistribution of 16,16 dimethyl Prostaglandin E2 in Non-Irradiated and Irradiated Mice and Non-Irradiated Non-Human Primates

Exposure to high-dose ionizing radiation can lead to life-threatening injuries and mortality. Bone marrow is the most sensitive organ to radiation damage, resulting in the hematopoietic acute radiation syndrome (H-ARS) with the potential sequelae of infection, hemorrhage, anemia, and death if untreated. The development of medical countermeasures (MCMs) to protect or mitigate radiation injury is a medical necessity. In our well-established murine model of H-ARS we have demonstrated that the prostaglandin E2 (PGE2) analog 16,16 dimethyl-PGE2 (dmPGE2) has survival efficacy as both a radioprotectant and radiomitigator. The purpose of this study was to investigate the pharmacokinetics (PK) and biodistribution of dmPGE2 when used as a radioprotector in irradiated and non-irradiated inbred C57BL/6J mice, PK in irradiated and non-irradiated Jackson Diversity Outbred (JDO) mice, and the PK profile of dmPGE2 in non-irradiated non-human primates (NHPs). The C57BL/6J and JDO mice each received a single subcutaneous (SC) dose of 35 ug of dmPGE2 and were randomized to either receive radiation 30 min later or remain non-irradiated. Plasma and tissue PK profiles were established. The NHP were dosed with 0.1 mg/kg by SC administration and the PK profile in plasma was established. The concentration time profiles were analyzed by standard non-compartmental analysis and the metrics of AUC0-Inf, AUC60-480 (AUC from 60-480 min), Cmax, and t1/2 were evaluated. AUC60-480 represents the postirradiation time frame and was used to assess radiation effect. Overall, AUC0-Inf, Cmax, and t1/2 were numerically similar between strains (C57BL/6J and JDO) when combined, regardless of exposure status (AUC0-Inf: 112.50 ng·h/ml and 114.48 ng·h/ml, Cmax: 44.53 ng/ml and 63.96 ng/ml; t1/2: 1.8 h and 1.1 h, respectively). PK metrics were numerically lower in irradiated C57BL/6J mice than in non-irradiated mice [irradiation ratio: irradiated values/non-irradiated values = 0.71 for AUC60-480 (i.e., 29% lower), and 0.6 for t1/2]. In JDO mice, the radiation ratio was 0.53 for AUC60-480 (i.e., 47% lower), and 1.7 h for t1/2. The AUC0-Inf, Cmax, and t1/2 of the NHPs were 29.20 ng·h/ml, 7.68 ng/ml, and 3.26 h, respectively. Despite the numerical differences seen between irradiated and non-irradiated groups in PK parameters, the effect of radiation on PK can be considered minimal based on current data. The biodistribution in C57BL/6J mice showed that dmPGE2 per gram of tissue was highest in the lungs, regardless of exposure status. The radiation ratio for the different tissue AUC60-480 in C57BL/6J mice ranged between 0.5-1.1 (50% lower to 10% higher). Spleen, liver and bone marrow showed close to twice lower exposures after irradiation, whereas heart had a 10% higher exposure. Based on the clearance values from mice and NHP, the estimated allometric scaling coefficient was 0.81 (95% CI: 0.75, 0.86). While slightly higher than the current literature estimates of 0.75, this scaling coefficient can be considered a reasonable estimate and can be used to scale dmPGE2 dosing from animals to humans for future trials.

The Role of COX-2 and PGE2 in the Regulation of Immunomodulation and Other Functions of Mesenchymal Stromal Cells

The ability of MSCs to modulate the inflammatory environment is well recognized, but understanding the molecular mechanisms responsible for these properties is still far from complete. Prostaglandin E2 (PGE2), a product of the cyclooxygenase 2 (COX-2) pathway, is indicated as one of the key mediators in the immunomodulatory effect of MSCs. Due to the pleiotropic effect of this molecule, determining its role in particular intercellular interactions and aspects of cell functioning is very difficult. In this article, the authors attempt to summarize the previous observations regarding the role of PGE2 and COX-2 in the immunomodulatory properties and other vital functions of MSCs. So far, the most consistent results relate to the inhibitory effect of MSC-derived PGE2 on the early maturation of dendritic cells, suppressive effect on the proliferation of activated lymphocytes, and stimulatory effect on the differentiation of macrophages into M2 phenotype. Additionally, COX-2/PGE2 plays an important role in maintaining the basic life functions of MSCs, such as the ability to proliferate, migrate and differentiate, and it also positively affects the formation of niches that are conducive to both hematopoiesis and carcinogenesis.

Upregulation of SIRT1 Contributes to dmPGE2-dependent Radioprotection of Hematopoietic Stem Cells

Exposure to potentially lethal high-dose ionizing radiation results in bone marrow suppression, known as the hematopoietic acute radiation syndrome (H-ARS), which can lead to pancytopenia and possible death from hemorrhage or infection. Medical countermeasures to protect from or mitigate the effects of radiation exposure are an ongoing medical need. We recently reported that 16,16 dimethyl prostaglandin E₂ (dmPGE₂) given prior to lethal irradiation protects hematopoietic stem (HSCs) and progenitor (HPCs) cells and accelerates hematopoietic recovery by attenuating mitochondrial compromise, DNA damage, apoptosis, and senescence. However, molecular mechanisms responsible for the radioprotective effects of dmPGE₂ on HSCs are not well understood. In this report, we identify a crucial role for the NAD⁺-dependent histone deacetylase Sirtuin 1 (Sirt1) downstream of PKA and CREB in dmPGE₂-dependent radioprotection of hematopoietic cells. We found that dmPGE₂ increases Sirt1 expression and activity in hematopoietic cells including HSCs and pharmacologic and genetic suppression of Sirt1 attenuates the radioprotective effects of dmPGE₂ on HSC and HPC function and its ability to reduce DNA damage, apoptosis, and senescence and stimulate autophagy in HSCs. DmPGE₂-mediated enhancement of Sirt1 activity in irradiated mice is accompanied by epigenetic downregulation of p53 activation and inhibition of H3K9 and H4K16 acetylation at the promoters of the genes involved in DNA repair, apoptosis, and autophagy, including p53, Ku70, Ku80, LC3b, ATG7, and NF-κB. These studies expand our understanding of intracellular events that are induced by IR but prevented/attenuated by dmPGE₂ and suggest that modulation of Sirt1 activity may facilitate hematopoietic recovery following hematopoietic stress. Graphical Abstract.

Hematopoietic Stem Cell Mobilization: Current Collection Approaches, Stem Cell Heterogeneity, and a Proposed New Method for Stem Cell Transplant Conditioning

Hematopoietic stem cells naturally traffic out of their bone marrow niches into the peripheral blood. This natural trafficking process can be enhanced with numerous pharmacologic agents - a process termed "mobilization" - and the mobilized stem cells can be collected for transplantation. We review the current state of mobilization with an update on recent clinical trials and new biologic mechanisms regulating stem cell trafficking. We propose that hematopoietic mobilization can be used to answer questions regarding hematopoietic stem cell heterogeneity, can be used for non-toxic conditioning of patients receiving stem cell transplants, and can enhance gene editing and gene therapy strategies to cure genetic diseases.

Prostaglandin E2 Regulates Bipotent Monocyte-Dendritic Progenitor Cell Lineage-Commitment

The factors/mechanisms regulating multipotent or bipotent hematopoietic progenitor cells lineage-commitment are not well understood. In this study, we found that prostaglandin E₂ (PGE₂) is a crucial physiological regulator of lineage choice for the bipotential monocyte-dendritic progenitor cell (MDP). Inhibition of endogenous PGE₂ biosynthesis in mice by the dual cyclooxygenase inhibitor, indomethacin, enhances bone marrow and spleen monocyte (MO) differentiation and reduces dendritic cell (DC) differentiation. Ex vivo treatment of purified MDP with indomethacin preferentially increases MO development at the expense of DC generation, whereas addition of exogenous PGE₂ reverses the indomethacin-mediated alteration in MDP differentiation potential. Treatment of MDP with selective EP receptor agonists demonstrated that EP1 signaling promotes MDP differentiation into DC at the expense of MO generation. Conversely, EP1 receptor knockout mice showed reduced DC and increased MO differentiation. Mechanistic studies revealed that PGE₂ increases expression of the tyrosine kinase receptor Flt3 on MDP and increases the DC-lineage-related transcription factor PU.1, while reducing expression of M-CSFR and the MO-lineage-related transcription factor MafB. These data indicate that PGE₂-EP1 signaling plays a critical role in MDP lineage commitment and DC and MO differentiation.

Prostaglandin E2 Enhances Aged Hematopoietic Stem Cell Function

Aging of hematopoiesis is associated with increased frequency and clonality of hematopoietic stem cells (HSCs), along with functional compromise and myeloid bias, with donor age being a significant variable in survival after HSC transplantation. No clinical methods currently exist to enhance aged HSC function, and little is known regarding how aging affects molecular responses of HSCs to biological stimuli. Exposure of HSCs from young fish, mice, nonhuman primates, and humans to 16,16-dimethyl prostaglandin E₂ (dmPGE₂) enhances transplantation, but the effect of dmPGE₂ on aged HSCs is unknown. Here we show that ex vivo pulse of bone marrow cells from young adult (3 mo) and aged (25 mo) mice with dmPGE₂ prior to serial competitive transplantation significantly enhanced long-term repopulation from aged grafts in primary and secondary transplantation (27 % increase in chimerism) to a similar degree as young grafts (21 % increase in chimerism; both p < 0.05). RNA sequencing of phenotypically-isolated HSCs indicated that the molecular responses to dmPGE₂ are similar in young and old, including CREB1 activation and increased cell survival and homeostasis. Common genes within these pathways identified likely key mediators of HSC enhancement by dmPGE₂ and age-related signaling differences. HSC expression of the PGE₂ receptor EP4, implicated in HSC function, increased with age in both mRNA and surface protein. This work suggests that aging does not alter the major dmPGE₂ response pathways in HSCs which mediate enhancement of both young and old HSC function, with significant implications for expanding the therapeutic potential of elderly HSC transplantation.

Optimizing and Profiling Prostaglandin E2 as a Medical Countermeasure for the Hematopoietic Acute Radiation Syndrome

Identification of medical countermeasures (MCM) to mitigate radiation damage and/or protect first responders is a compelling unmet medical need. The prostaglandin E2 (PGE2) analog, 16,16 dimethyl-PGE2 (dmPGE2), has shown efficacy as a radioprotectant and radiomitigator that can enhance hematopoiesis and ameliorate intestinal mucosal cell damage. In this study, we optimized the time of administration of dmPGE2 for protection and mitigation against mortality from the hematopoietic acute radiation syndrome (H-ARS) in young adult mice, evaluated its activity in pediatric and geriatric populations, and investigated potential mechanisms of action. Windows of 30-day survival efficacy for single administration of dmPGE2 were defined as within 3 h prior to and 6-30 h after total-body γ irradiation (TBI). Radioprotective and radio-mitigating efficacy was also observed in 2-year-old geriatric mice and 6-week-old pediatric mice. PGE2 receptor agonist studies suggest that signaling through EP4 is primarily responsible for the radioprotective effects. DmPGE2 administration prior to TBI attenuated the drop in red blood cells and platelets, accelerated recovery of all peripheral blood cell types, and resulted in higher hematopoietic and mesenchymal stem cells in survivor bone marrow. Multiplex analysis of bone marrow cytokines together with RNA sequencing of hematopoietic stem cells indicated a pro-hematopoiesis cytokine milieu induced by dmPGE2, with IL-6 and G-CSF strongly implicated in dmPGE2-mediated radioprotective activity. In summary, we have identified windows of administration for significant radio-mitigation and radioprotection by dmPGE2 in H-ARS, demonstrated survival efficacy in special populations, and gained insight into radioprotective mechanisms, information useful towards development of dmPGE2 as a MCM for first responders, military personnel, and civilians facing radiation threats.

Epo receptor signaling in macrophages alters the splenic niche to promote erythroid differentiation

Anemic stress induces stress erythropoiesis, which rapidly generates new erythrocytes to restore tissue oxygenation. Stress erythropoiesis is best understood in mice where it is extramedullary and occurs primarily in the spleen. However, both human and mouse stress erythropoiesis use signals and progenitor cells that are distinct from steady-state erythropoiesis. Immature stress erythroid progenitors (SEPs) are derived from short-term hematopoietic stem cells. Although the SEPs are capable of self-renewal, they are erythroid restricted. Inflammation and anemic stress induce the rapid proliferation of SEPs, but they do not differentiate until serum erythropoietin (Epo) levels increase. Here we show that rather than directly regulating SEPs, Epo promotes this transition from proliferation to differentiation by acting on macrophages in the splenic niche. During the proliferative stage, macrophages produce canonical Wnt ligands that promote proliferation and inhibit differentiation. Epo/Stat5-dependent signaling induces the production of bioactive lipid mediators in macrophages. Increased production of prostaglandin J2 (PGJ2) activates peroxisome proliferator-activated receptor γ (PPARγ)-dependent repression of Wnt expression, whereas increased production of prostaglandin E2 (PGE2) promotes the differentiation of SEPs.

A Single Radioprotective Dose of Prostaglandin E2 Blocks Irradiation-Induced Apoptotic Signaling and Early Cycling of Hematopoietic Stem Cells

Ionizing radiation exposure results in acute and delayed bone marrow suppression. Treatment of mice with 16,16-dimethyl prostaglandin E₂ (dmPGE₂) prior to lethal ionizing radiation (IR) facilitates survival, but the cellular and molecular mechanisms are unclear. In this study we show that dmPGE₂ attenuates loss and enhances recovery of bone marrow cellularity, corresponding to a less severe hematopoietic stem cell nadir, and significantly preserves long-term repopulation capacity and progenitor cell function. Mechanistically, dmPGE₂ suppressed hematopoietic stem cell (HSC) proliferation through 24 h post IR, which correlated with fewer DNA double-strand breaks and attenuation of apoptosis, mitochondrial compromise, oxidative stress, and senescence. RNA sequencing of HSCs at 1 h and 24 h post IR identified a predominant interference with IR-induced p53-downstream gene expression at 1 h, and confirmed the suppression of IR-induced cell-cycle genes at 24 h. These data identify mechanisms of dmPGE₂ radioprotection and its potential role as a medical countermeasure against radiation exposure.

Brief Story on Prostaglandins, Inhibitors of their Synthesis, Hematopoiesis, and Acute Radiation Syndrome

Prostaglandins and inhibitors of their synthesis (cyclooxygenase (COX) inhibitors, non-steroidal anti-inflammatory drugs) were shown to play a significant role in the regulation of hematopoiesis. Partly due to their hematopoiesis-modulating effects, both prostaglandins and COX inhibitors were reported to act positively in radiation-exposed mammalian organisms at various pre- and post-irradiation therapeutical settings. Experimental efforts were targeted at finding pharmacological procedures leading to optimization of therapeutical outcomes by minimizing undesirable side effects of the treatments. Progress in these efforts was obtained after discovery of selective inhibitors of inducible selective cyclooxygenase-2 (COX-2) inhibitors. Recent studies have been able to suggest the possibility to find combined therapeutical approaches utilizing joint administration of prostaglandins and inhibitors of their synthesis at optimized timing and dosing of the drugs which could be incorporated into the therapy of patients with acute radiation syndrome.

Prostaglandin regulation of T cell biology

Prostaglandins (PG) are pleiotropic bioactive lipids involved in the control of many physiological processes, including key roles in regulating inflammation. This links PG to the modulation of the quality and magnitude of immune responses. T cells, as a core part of the immune system, respond readily to inflammatory cues from their environment, and express a diverse array of PG receptors that contribute to their function and phenotype. Here we put in context our knowledge about how PG affect T cell biology, and review advances that bring light into how specific T cell functions that have been newly discovered are modulated through PG. We will also comment on drugs that target PG metabolism and sensing, their effect on T cell function during disease, and we will finally discuss how we can design new approaches that modulate PG in order to maximize desired therapeutic T cell effects.

An ARC-Regulated IL1β/Cox-2/PGE2/β-Catenin/ARC Circuit Controls Leukemia-Microenvironment Interactions and Confers Drug Resistance in AML

The apoptosis repressor with caspase recruitment domain (ARC) protein is a strong independent adverse prognostic marker in acute myeloid leukemia (AML). We previously reported that ARC regulates leukemia-microenvironment interactions through the NFκB/IL1β signaling network. Malignant cells have been reported to release IL1β, which induces PGE2 synthesis in mesenchymal stromal cells (MSC), in turn activating β-catenin signaling and inducing the cancer stem cell phenotype. Although Cox-2 and its enzymatic product PGE2 play major roles in inflammation and cancer, the regulation and role of PGE2 in AML are largely unknown. Here, we report that AML-MSC cocultures greatly increase Cox-2 expression in MSC and PGE2 production in an ARC/IL1β-dependent manner. PGE2 induced the expression of β-catenin, which regulated ARC and augmented chemoresistance in AML cells; inhibition of β-catenin decreased ARC and sensitized AML cells to chemotherapy. NOD/SCIDIL2RγNull-3/GM/SF mice transplanted with ARC-knockdown AML cells had significantly lower leukemia burden, lower serum levels of IL1β/PGE2, and lower tissue human ARC and β-catenin levels, prolonged survival, and increased sensitivity to chemotherapy than controls. Collectively, we present a new mechanism of action of antiapoptotic ARC by which ARC regulates PGE2 production in the tumor microenvironment and microenvironment-mediated chemoresistance in AML.Significance: The antiapoptotic protein ARC promotes AML aggressiveness by enabling detrimental cross-talk with bone marrow mesenchymal stromal cells.

Identification of mutations in the prostaglandin transporter gene SLCO2A1 and phenotypic comparison between two subtypes of primary hypertrophic osteoarthropathy (PHO): A single-center study

Primary hypertrophic osteoarthropathy (PHO) is an inherited disease characterized by digital clubbing, periostosis, and pachydermia. Based on two causative genes, hydroxyprostaglandin dehydrogenase (HPGD) and solute carrier organic anion transporter family member 2A1 (SLCO2A1), PHO is categorized into two subtypes: hypertrophic osteoarthropathy, primary, autosomal recessive 1 (PHOAR1) and hypertrophic osteoarthropathy, primary, autosomal recessive 2 (PHOAR2). In this study, we summarized the clinical manifestations and analyzed SLCO2A1 gene in 23 PHOAR2 patients in our center. As a result, 18 patients displayed complete phenotypes of PHO with digital clubbing, periostosis, and pachydermia. 29 mutations were found in total, and 22 of them were novel mutations including 13 missense, three nonsense, four deletion, one frame-shift and one splicing site mutations. Compared with nine PHOAR1 patients we previously reported, PHO patients with SLCO2A1 mutations were all male and presented with a later onset age. Peptic ulcers and myelofibrosis occurred only in PHOAR2 patients. The urinary level of prostaglandin E2 metabolite (PGEM) is significantly higher in PHOAR2 patients than that in PHOAR1 group. In conclusion, this study was the largest cohort to date to summarize PHOAR2 patients and to assess the phenotypic difference between two subtypes of PHO. The difference of urinary PGEM concentration between two subtypes is helpful for the differential diagnosis of PHO.

UV Irradiation of Skin Enhances Glycolytic Flux and Reduces Migration Capabilities in Bone Marrow-Differentiated Dendritic Cells

A systemic immunosuppression follows UV irradiation of the skin of humans and mice. In this study, dendritic cells (DCs) differentiating from the bone marrow (BM) of UV-irradiated mice had a reduced ability to migrate toward the chemokine (C-C motif) ligand 21. Fewer DCs also accumulated in the peritoneal cavity of UV-chimeric mice (ie, mice transplanted with BM from UV-irradiated mice) after injection of an inflammatory stimulus into that site. We hypothesized that different metabolic states underpin altered DC motility. Compared with DCs from the BM of nonirradiated mice, those from UV-irradiated mice produced more lactate, consumed more glucose, and had greater glycolytic flux in a bioenergetics stress test. Greater expression of 3-hydroxyanthranilate 3,4-dioxygenase was identified as a potential contributor to increased glycolysis. Inhibition of 3-hydroxyanthranilate 3,4-dioxygenase by 6-chloro-dl-tryptophan prevented both increased lactate production and reduced migration toward chemokine (C-C motif) ligand 21 by DCs differentiated from BM of UV-irradiated mice. UV-induced prostaglandin E₂ has been implicated as an intermediary in the effects of UV radiation on BM cells. DCs differentiating from BM cells pulsed in vitro for 2 hours with dimethyl prostaglandin E₂ were functionally similar to those from the BM of UV-irradiated mice. Reduced migration of DCs to lymph nodes associated with increased glycolytic flux may contribute to their reduced ability to initiate new immune responses in UV-irradiated mice.

Prostaglandin E2 promotes human CD34+ cells homing through EP2 and EP4 in vitro

Recently, certain studies have demonstrated in vitro that prostaglandin E2 (PGE2) promotes human cluster of differentiation (CD)34⁺ cell homing. However, the sub-type receptors activated by PGE2 are unknown, as the PGE2 receptor EP1-4 subtypes (EP1-4) are expressed on the membrane of human CD34⁺ cells. Based on the above, the present study aimed to screen the receptor subtype activity by PGE2 to promote human CD34⁺ cell homing. It was observed that human CD34⁺ cells expressed the four PGE2 sub-receptors, particularly EP2 and 4. PGE2 increased EP2 and 4 mRNA expression significantly, while EP1 and 3 mRNA exhibited no significant alteration. PGE2, EP2 agonist (EP2A), and EP4A upregulated C-X-C chemokine receptor 4 mRNA and protein expression in human CD34⁺ cells, and promoted stromal cell-derived factor 1α (SDF-1α) expression in bone marrow mesenchymal stem cells (BMMSCs). These phenomena were inhibited by the associated receptor antagonists. PGE2, EP2A, and EP4A facilitated human CD34⁺ cell migration towards SDF-1α and BMMSCs. The results of the present study suggested that PGE2 promoted human CD34⁺ cell homing through EP2 and 4 receptors in vitro.

Eicosanoids: Emerging contributors in stem cell-mediated wound healing

Eicosanoids are bioactive lipid products primarily derived from the oxidation of arachidonic acid (AA). The individual contributions of eicosanoids and stem cells to wound healing have been of great interest. This review focuses on how stem cells work in concert with eicosanoids to create a beneficial environment in the wound bed and in the promotion of wound healing. Stem cells contribute to wound healing through modulating inflammation, differentiating into skin cells or endothelial cells, and exerting paracrine effects by releasing various potent growth factors. Eicosanoids have been shown to stimulate proliferation, migration, homing, and differentiation of stem cells, all of which contribute to the process of wound healing. Increasing evidence has shown that eicosanoids improve wound healing through increasing stem cell densities, stimulating differentiation, and enhancing the angiogenic properties of stem cells. Chronic wounds have become a major problem in health care. Therefore, research regarding the effects of stem cells and eicosanoids in the promotion wound healing is of great importance.

Tetrandrine identified in a small molecule screen to activate mesenchymal stem cells for enhanced immunomodulation

Pre-treatment or priming of mesenchymal stem cells (MSC) prior to transplantation can significantly augment the immunosuppressive effect of MSC-based therapies. In this study, we screened a library of 1402 FDA-approved bioactive compounds to prime MSC. We identified tetrandrine as a potential hit that activates the secretion of prostaglandin E2 (PGE2), a potent immunosuppressive agent, by MSC. Tetrandrine increased MSC PGE2 secretion through the NF-κB/COX-2 signaling pathway. When co-cultured with mouse macrophages (RAW264.7), tetrandrine-primed MSC attenuated the level of TNF-α secreted by RAW264.7. Furthermore, systemic transplantation of primed MSC into a mouse ear skin inflammation model significantly reduced the level of TNF-α in the inflamed ear, compared to unprimed cells. Screening of small molecules to pre-condition cells prior to transplantation represents a promising strategy to boost the therapeutic potential of cell therapy.

Reduced immune responses in chimeric mice engrafted with bone marrow cells from mice with airways inflammation

OBJECTIVE

During respiratory inflammation, it is generally assumed that dendritic cells differentiating from the bone marrow are immunogenic rather than immunoregulatory. Using chimeric mice, the outcomes of airways inflammation on bone marrow progenitor cells were studied.

METHODS

Immune responses were analyzed in chimeric mice engrafted for >16 weeks with bone marrow cells from mice with experimental allergic airways disease (EAAD).

RESULTS

Responses to sensitization and challenge with the allergen causing inflammation in the bone marrow-donor mice were significantly reduced in the chimeric mice engrafted with bone marrow cells from mice with EAAD (EAAD-chimeric). Responses to intranasal LPS and topical fluorescein isothiocyanate (non-specific challenges) were significantly attenuated. Fewer activated dendritic cells from the airways and skin of the EAAD-chimeric mice could be tracked to the draining lymph nodes, and may contribute to the significantly reduced antigen/chemical-induced hypertrophy in the draining nodes, and the reduced immune responses to sensitizing allergens. Dendritic cells differentiating in vitro from the bone marrow of >16 weeks reconstituted EAAD-chimeric mice retained an ability to poorly prime immune responses when transferred into naïve mice.

CONCLUSIONS

Dendritic cells developing from bone marrow progenitors during airways inflammation are altered such that daughter cells have reduced antigen priming capabilities.

Microarray Analysis of Gene Expression Reveals that Cyclo-oxygenase-2 Gene Therapy Up-regulates Hematopoiesis and Down-regulates Inflammation During Endochondral Bone Fracture Healing

BACKGROUND

Cyclo-oxygenase-2 (Cox-2) is an inflammatory mediator that is necessary for the tissue repair, including bone fracture healing. Although the application of Cox-2 gene therapy to a murine closed femoral fracture has accelerated bony union, but the beneficial effect was not observed until the endochondral stage of bone repair that is well after the inflammatory stage normally subsides.

METHODS

To identify the molecular pathways through which Cox-2 regulates fracture healing, we examined gene expression profile in fracture tissues in response to Cox-2 gene therapy during the endochondral bone repair phase. Cox-2 gene therapy was applied to the closed murine femur fracture model. Microarray analysis was performed at 10 days post-fracture to examine global gene expression profile in the fracture tissues during the endochondral bone repair phase. The entire repertoire of significantly expressed genes was examined by gene set enrichment analysis, and the most up-regulated individual genes were evaluated further.

RESULTS

The genes that normally promote inflammation were under-represented in the microarray analysis, and the expression of several inflammatory chemokines was significantly down-regulated. There was an up-regulation of two key transcription factor genes that regulate hematopoiesis and erythropoiesis. More surprisingly, there was no significant up-regulation in the genes that are normally involved in angiogenesis or bone formation. However, the expression of two tissue remodeling genes was up-regulated.

CONCLUSIONS

The down-regulation of the inflammatory genes in response to Cox-2 gene therapy was unexpected, given the pro-inflammatory role of prostaglandins. Cox-2 gene therapy could promote bony union through hematopoietic precursor proliferation during endochondral bone repair and thereby enhances subsequently fracture callus remodeling that leads to bony union of the fracture gap.

Prostaglandin E2 enhances long-term repopulation but does not permanently alter inherent stem cell competitiveness

Hematopoietic stem cell (HSC) transplantation is a lifesaving therapy for malignant and nonmalignant hematologic diseases and metabolic disorders. Although successful, hematopoietic transplantation can be hindered by inadequate stem cell number or poor engrafting efficiency. To overcome these deficits, we and others have previously reported the HSC-enhancing ability of a short-term exposure of prostaglandin E2 (PGE2); this strategy has now progressed to phase 1 clinical trials in double cord blood transplantation. To further analyze the short- and long-term effects of HSC exposure to PGE2, we followed the repopulation kinetics of PGE2-treated hematopoietic grafts through 5 serial transplantations and compared inherent long-term competitiveness in a HSC head-to-head secondary transplantation model. Treatment with PGE2 did not result in a long-term increase in HSC competitiveness, lineage bias, or enhanced proliferative potential, demonstrating that pulse exposure to PGE2 results in transient increases in HSC homing and engraftment potential.

Innate immunity derived factors as external modulators of the CXCL12-CXCR4 axis and their role in stem cell homing and mobilization

The α-chemokine CXCL12 (stromal derived factor-1; SDF-1) and its corresponding G_αI protein-coupled CXCR4 receptor axis play an important role in retention of hematopoietic stem progenitor cells (HSPCs) in bone marrow (BM) stem cell niches. CXCL12 has also been identified as a strong chemoattractant for HSPCs and implicated both in homing of HSPCs to BM after transplantation and in egress of these cells from BM into peripheral blood (PB). However, since CXCL12, as a peptide, is highly susceptible to degradation by proteolytic enzymes, its real biological availability in biological fluids may be somewhat limited. In this review, we will present data demonstrating that the CXCL12-CXCR4 axis is positively modulated by innate immunity-derived several external factors, ensuring that even low (near threshold) doses of CXCL12 still exert a robust chemotactic influence on HSPCs.

Recovery from hematopoietic injury by modulating prostaglandin E(2) signaling post-irradiation

While high dose total body irradiation (TBI) is used therapeutically, the proliferation of nuclear weapons, increasing use of nuclear power, and worldwide radical terrorism underscore the need to develop countermeasures to a radiological mass casualty event. The hematopoietic syndrome of the acute radiation syndrome (HS-ARS) results from severe compromise to the hematopoietic system, including lymphocytopenia, neutropenia, thrombocytopenia, and possible death from infection and/or hemorrhage. Given adequate time to recover, expand, and appropriately differentiate, bone marrow hematopoietic stem cells (HSC) and progenitor cells (HPC) may overcome HS-ARS and restore homeostasis of the hematopoietic system. Prostaglandin E(2) (PGE(2)) has been shown to have pleiotropic effects on hematopoiesis, acting to inhibit apoptosis and promote self-renewal of HSC, while inhibiting HPC proliferation. We assessed the radio-mitigating potential of modulating PGE(2) signaling in a mouse model of HS-ARS. Treatment with the PGE(2) analog 16,16 dimethyl PGE(2) (dmPGE(2)) 6h post-irradiation or inhibition of PGE(2) synthesis via delayed administration of the non-steroidal anti-inflammatory drug (NSAID) Meloxicam resulted in increased survival of lethally irradiated mice. Both early dmPGE(2) and delayed Meloxicam treatment were associated with increased HPC activity 35days following irradiation, demonstrating enhanced recovery of hematopoiesis. Our results define two different treatment modalities that are highly effective and safe to administer, and can be readily available.

An emerging link in stem cell mobilization between activation of the complement cascade and the chemotactic gradient of sphingosine-1-phosphate

Under steady-state conditions, hematopoietic stem/progenitor cells (HSPCs) egress from bone marrow (BM) and enter peripheral blood (PB) where they circulate at low levels. Their number in PB, however, increases significantly in several stress situations related to infection, organ/tissue damage, or strenuous exercise. Pharmacologically mediated enforced egress of HSPCs from the BM microenvironment into PB is called "mobilization", and this phenomenon has been exploited in hematological transplantology as a means to obtain HSPCs for hematopoietic reconstitution. In this review we will present the accumulated evidence that innate immunity, including the complement cascade and the granulocyte/monocyte lineage, and the PB plasma level of the bioactive lipid sphingosine-1-phosphate (S1P) together orchestrate this evolutionarily conserved mechanism that directs trafficking of HSPCs.

Prostaglandin transporter mutations cause pachydermoperiostosis with myelofibrosis

Pachydermoperiostosis, or primary hypertrophic osteoarthropathy (PHO), is an inherited multisystem disorder, whose features closely mimic the reactive osteoarthropathy that commonly accompanies neoplastic and inflammatory pathologies. We previously described deficiency of the prostaglandin-degrading enzyme 15-hydroxyprostaglandin dehydrogenase (HPGD) as a cause of this condition, implicating elevated circulating prostaglandin E(2) (PGE(2)) as causative of PHO, and perhaps also as the principal mediator of secondary HO. However, PHO is genetically heterogeneous. Here, we use whole-exome sequencing to identify recessive mutations of the prostaglandin transporter SLCO2A1, in individuals lacking HPGD mutations. We performed exome sequencing of four probands with severe PHO, followed by conventional mutation analysis of SLCO2A1 in nine others. Biallelic SLCO2A1 mutations were identified in 12 of the 13 families. Affected individuals had elevated urinary PGE(2), but unlike HPGD-deficient patients, also excreted considerable quantities of the PGE(2) metabolite, PGE-M. Clinical differences between the two groups were also identified, notably that SLCO2A1-deficient individuals have a high frequency of severe anemia due to myelofibrosis. These findings reinforce the key role of systemic or local prostaglandin excess as the stimulus to HO. They also suggest that the induction or maintenance of hematopoietic stem cells by prostaglandin may depend upon transporter activity.