Prostaglandin E2 promotes endothelial differentiation from bone marrow-derived cells through AMPK activation

The Impact of Modern Anti-Diabetic Treatment on Endothelial Progenitor Cells

Diabetes is one of the leading chronic diseases globally with a significant impact on mortality. This condition is associated with chronic microvascular and macrovascular complications caused by vascular damage. Recently, endothelial progenitor cells (EPCs) raised interest due to their regenerative properties. EPCs are mononuclear cells that are derived from different tissues. Circulating EPCs contribute to regenerating the vessel's intima and restoring vascular function. The ability of EPCs to repair vascular damage depends on their number and functionality. Diabetic patients have a decreased circulating EPC count and impaired EPC function. This may at least partially explain the increased risk of diabetic complications, including the increased cardiovascular risk in these patients. Recent studies have confirmed that many currently available drugs with proven cardiovascular benefits have beneficial effects on EPC count and function. Among these drugs are also medications used to treat different types of diabetes. This manuscript aims to critically review currently available evidence about the ways anti-diabetic treatment affects EPC biology and to provide a broader context considering cardiovascular complications. The therapies that will be discussed include lifestyle adjustments, metformin, sulphonylureas, gut glucosidase inhibitors, thiazolidinediones, dipeptidyl peptidase 4 inhibitors, glucagon-like peptide 1 receptor analogs, sodium-glucose transporter 2 inhibitors, and insulin.

Evaluation of the Antioxidant and Antiangiogenic Activity of a Pomegranate Extract in BPH-1 Prostate Epithelial Cells

Benign prostatic hypertrophy (BPH) is a noncancerous enlargement of the prostate gland that develops from hyper-proliferation of the stromal and epithelium region. Activation of pathways involving inflammation and oxidative stress can contribute to cell proliferation in BPH and tumorigenesis. Agricultural-waste-derived extracts have drawn the attention of researchers as they represent a valid and sustainable way to exploit waste production. Indeed, such extracts are rich in bioactive compounds and can provide health-promoting effects. In particular, extracts obtained from pomegranate wastes and by-products have been shown to exert antioxidant and anti-inflammatory effects. This study focused on the evaluation of the anti-angiogenic effects and chemopreventive action of a pomegranate extract (PWE) in cellular models of BPH. In our experimental conditions, we observed that PWE was able to significantly (p < 0.001) reduce the proliferation and migration rates (up to 60%), together with the clonogenic capacity of BPH-1 cells concomitantly with the reduction in inflammatory cytokines (e.g., IL-6, PGE2) and pro-angiogenic factor (VEGF-ADMA) release. Additionally, we demonstrated the ability of PWE in reducing angiogenesis in an in vitro model of BPH consisting in transferring BPH-1-cell-conditioned media to human endothelial H5V cells. Indeed, PWE was able to reduce tube formation in H5V cells through VEGF level reduction even at low concentrations. Overall, we confirmed that inhibition of angiogenesis may be an alternative therapeutic option to prevent neovascularization in prostate tissue with BPH and its transformation into malignant prostate cancer.

Immune Function of Endothelial Cells: Evolutionary Aspects, Molecular Biology and Role in Atherogenesis

Atherosclerosis is one of the key problems of modern medicine, which is due to the high prevalence of atherosclerotic cardiovascular diseases and their significant share in the structure of morbidity and mortality in many countries. Atherogenesis is a complex chain of events that proceeds over many years in the vascular wall with the participation of various cells. Endothelial cells are key participants in vascular function. They demonstrate involvement in the regulation of vascular hemodynamics, metabolism, and innate immunity, which act as leading links in the pathogenesis of atherosclerosis. These endothelial functions have close connections and deep evolutionary roots, a better understanding of which will improve the prospects of early diagnosis and effective treatment.

Notch-activated mesenchymal stromal/stem cells enhance the protective effect against acetaminophen-induced acute liver injury by activating AMPK/SIRT1 pathway

Background

Notch signaling plays important roles in regulating innate immunity. However, little is known about the role of Notch in mesenchymal stromal/stem cell (MSC)-mediated immunomodulation during liver inflammatory response.

Methods

Notch activation in human umbilical cord-derived MSCs was performed by a tissue culture plate coated with Notch ligand, recombinant human Jagged1 (JAG1). Mice were given intravenous injection of Notch-activated MSCs after acetaminophen (APAP)-induced acute liver injury. Liver tissues were collected and analyzed by histology and immunohistochemistry.

Results

MSC administration reduced APAP-induced hepatocellular damage, as manifested by decreased serum ALT levels, intrahepatic macrophage/neutrophil infiltration, hepatocellular apoptosis and proinflammatory mediators. The anti-inflammatory activity and therapeutic effects of MSCs were greatly enhanced by Notch activation via its ligand JAG1. However, Notch2 disruption in MSCs markedly diminished the protective effect of MSCs against APAP-induced acute liver injury, even in the presence of JAG1 pretreatment. Strikingly, Notch-activated MSCs promoted AMP-activated protein kinase (AMPKα) phosphorylation, increased the sirtuins 1 (SIRT1) deacetylase expression, but downregulated spliced X-box-binding protein 1 (XBP1s) expression and consequently reduced NLR family pyrin domain-containing 3 (NLRP3) inflammasome activation. Furthermore, SIRT1 disruption or XBP1s overexpression in macrophages exacerbated APAP-triggered liver inflammation and augmented NLRP3/caspase-1 activity in MSC-administrated mice. Mechanistic studies further demonstrated that JAG1-pretreated MSCs activated Notch2/COX2/PGE2 signaling, which in turn induced macrophage AMPK/SIRT1 activation, leading to XBP1s deacetylation and inhibition of NLRP3 activity.

Conclusions

Activation of Notch2 is required for the ability of MSCs to reduce the severity of APAP-induced liver damage in mice. Our findings underscore a novel molecular insights into MSCs-mediated immunomodulation by activating Notch2/COX2/AMPK/SIRT1 pathway and thus provide a new strategy for the treatment of liver inflammatory diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02999-6.

Improved osteogenic differentiation by extremely low electromagnetic field exposure: possible application for bone engineering

Human periodontal ligament mesenchymal stem cells (hPDLSCs) are a promising cell type model for regenerative medicine applications due to their anti-inflammatory, immunomodulatory and non-tumorigenic potentials. Extremely low-frequency electromagnetic fields (ELF-EMF) are reported to affect biological properties such as cell proliferation and differentiation and modulate gene expression profile. In this study, we investigated the effects of an intermittent ELF-EMF exposure (6 h/day) for the standard differentiation period (28 days) and for 10 days in hPDLSCs in the presence or not of osteogenic differentiation medium (OM). We evaluated cell proliferation, de novo calcium deposition and osteogenic differentiation marker expression in sham and ELF-EMF-exposed cells. After ELF-EMF exposure, compared with sham-exposed, an increase in cell proliferation rate (p < 0.001) and de novo calcium deposition (p < 0.001) was observed after 10 days of exposure. Real-time PCR and Western blot results showed that COL1A1 and RUNX-2 gene expression and COL1A1, RUNX-2 and OPN protein expression were upregulated respectively in the cells exposed to ELF-EMF exposure along with or without OM for 10 days. Altogether, these results suggested that the promotion of osteogenic differentiation is more efficient in ELF-EMF-exposed hPDLSCs. Moreover, our analyses indicated that there is an early induction of hPDLSC differentiation after ELF-EMF application.

Salvianolic Acid B Suppresses ER Stress-Induced NLRP3 Inflammasome and Pyroptosis via the AMPK/FoxO4 and Syndecan-4/Rac1 Signaling Pathways in Human Endothelial Progenitor Cells

Mounting evidence demonstrates uncontrolled endoplasmic reticulum (ER) stress responses can activate the inflammasome, which generally results in endothelial dysfunction, a major pathogenetic factor of chronic inflammatory diseases such as atherosclerosis. Salvianolic acid B (SalB), produced by Radix Salviae, exerts antioxidative and anti-inflammatory activities in multiple cell types. However, SalB's effects on ER stress-related inflammasome and endothelial dysfunction remain unknown. Here, we showed SalB substantially abrogated ER stress-induced cell death and reduction in capillary tube formation, with declined intracellular reactive oxygen species (ROS) amounts and restored mitochondrial membrane potential (MMP), as well as increased expression of HO-1 and SOD2 in bone marrow-derived endothelial progenitor cells (BM-EPCs). ER stress suppression by CHOP or caspase-4 siRNA transfection attenuated the protective effect of SalB. Additionally, SalB alleviated ER stress-mediated pyroptotic cell death via the suppression of TXNIP/NLRP3 inflammasome, as evidenced by reduced cleavage of caspase-1 and interleukin- (IL-) 1β and IL-18 secretion levels. Furthermore, this study provided a mechanistic basis that AMPK/FoxO4/KLF2 and Syndecan-4/Rac1/ATF2 signaling pathway modulation by SalB substantially prevented BM-EPCs damage associated with ER stress by decreasing intracellular ROS amounts and inducing NLRP3-dependent pyroptosis. In summary, our findings identify that ER stress triggered mitochondrial ROS release and NLRP3 generation in BM-EPCs, while SalB inhibits NLRP3 inflammasome-mediated pyroptotic cell death by regulating the AMPK/FoxO4/KLF2 and Syndecan-4/Rac1/ATF2 pathways. The current findings reveal SalB as a potential new candidate for the treatment of atherosclerotic heart disease.

The sustained PGE2 release matrix improves neovascularization and skeletal muscle regeneration in a hindlimb ischemia model

BACKGROUND

The promising therapeutic strategy for the treatment of peripheral artery disease (PAD) is to restore blood supply and promote regeneration of skeletal muscle regeneration. Increasing evidence revealed that prostaglandin E₂ (PGE₂), a lipid signaling molecule, has significant therapeutic potential for tissue repair and regeneration. Though PGE₂ has been well reported in tissue regeneration, the application of PGE₂ is hampered by its short half-life in vivo and the lack of a viable system for sustained release of PGE₂.

RESULTS

In this study, we designed and synthesized a new PGE₂ release matrix by chemically bonding PGE₂ to collagen. Our results revealed that the PGE₂ matrix effectively extends the half-life of PGE₂ in vitro and in vivo. Moreover, the PGE₂ matrix markedly improved neovascularization by increasing angiogenesis, as confirmed by bioluminescence imaging (BLI). Furthermore, the PGE₂ matrix exhibits superior therapeutic efficacy in the hindlimb ischemia model through the activation of MyoD1-mediated muscle stem cells, which is consistent with accelerated structural recovery of skeletal muscle, as evidenced by histological analysis.

CONCLUSIONS

Our findings highlight the chemical bonding strategy of chemical bonding PGE₂ to collagen for sustained release and may facilitate the development of PGE₂-based therapies to significantly improve tissue regeneration.

An Mg-MOFs based multifunctional medicine for the treatment of osteoporotic pain

Bone pain is the primary problem for patients with osteoporosis. Ketoprofen is clinically used to treat osteoporotic pain, while long-term oral administration of ketoprofen can cause some side effects. In addition, osteoporosis is also accompanied by bone mass loss and inflammation. In this study, we designed a multifunctional drug (Ket@Mg-MOF-74) adopted Mg-MOF-74 to load ketoprofen to treat osteoporotic pain, bone loss and inflammation comprehensively. Mg-MOF-74 was prepared, and the physicochemical characterization proved that it had excellent physical and chemical stability. Ket@Mg-MOF-74 was synthesized by post-synthetic modification method and a high loading rate of ketoprofen was confirmed. Drug release and ion release experiments indicated Ket@Mg-MOF-74 had a good controlled release of ketoprofen and Mg in solution. Cell experiments in vitro proved the compound drug could significantly reduce the expression of pain-related genes of cyclooxygenase 2 (COX2), obviously up-regulated the expression of osteogenic cytokines and remarkably down-regulated the secretion of pro-inflammatory factors. Therefore, Ket@Mg-MOF-74 is believed a promising painkiller for osteoporotic bone pain, with the function of anti-inflammatory and promoting bone formation.

Role of oxylipins generated from dietary PUFAs in the modulation of endothelial cell function

Oxylipins, which are circulating bioactive lipids generated from polyunsaturated fatty acids (PUFAs) by cyclooxygenase, lipooxygenase and cytochrome P450 enzymes, have diverse effects on endothelial cells. Although studies of the effects of oxylipins on endothelial cell function are accumulating, a review that provides a comprehensive compilation of current knowledge and recent advances in the context of vascular homeostasis is lacking. This is the first compilation of the various in vitro, ex vivo and in vivo reports to examine the effects and potential mechanisms of action of oxylipins on endothelial cells. The aggregate data indicate docosahexaenoic acid-derived oxylipins consistently show beneficial effects related to key endothelial cell functions, whereas oxylipins derived from other PUFAs exhibit both positive and negative effects. Furthermore, information is lacking for certain oxylipin classes, such as those derived from α-linolenic acid, which suggests additional studies are required to achieve a full understanding of how oxylipins affect endothelial cells.

Endothelial cell prostaglandin E2 receptor EP4 is essential for blood pressure homeostasis

Prostaglandin E2 and its cognate EP1-4 receptors play important roles in blood pressure (BP) regulation. Herein, we show that endothelial cell-specific (EC-specific) EP4 gene-knockout mice (EC-EP4-/-) exhibited elevated, while EC-specific EP4-overexpression mice (EC-hEP4OE) displayed reduced, BP levels compared with the control mice under both basal and high-salt diet-fed conditions. The altered BP was completely abolished by treatment with l-NG-nitro-l-arginine methyl ester (l-NAME), a competitive inhibitor of endothelial nitric oxide synthase (eNOS). The mesenteric arteries of the EC-EP4-/- mice showed increased vasoconstrictive response to angiotensin II and reduced vasorelaxant response to acetylcholine, both of which were eliminated by l-NAME. Furthermore, EP4 activation significantly reduced BP levels in hypertensive rats. Mechanistically, EP4 deletion markedly decreased NO contents in blood vessels via reducing eNOS phosphorylation at Ser1177. EP4 enhanced NO production mainly through the AMPK pathway in cultured ECs. Collectively, our findings demonstrate that endothelial EP4 is essential for BP homeostasis.

Dual Roles of the AMP-Activated Protein Kinase Pathway in Angiogenesis

Angiogenesis plays important roles in development, stress response, wound healing, tumorigenesis and cancer progression, diabetic retinopathy, and age-related macular degeneration. It is a complex event engaging many signaling pathways including vascular endothelial growth factor (VEGF), Notch, transforming growth factor-beta/bone morphogenetic proteins (TGF-β/BMPs), and other cytokines and growth factors. Almost all of them eventually funnel to two crucial molecules, VEGF and hypoxia-inducing factor-1 alpha (HIF-1α) whose expressions could change under both physiological and pathological conditions. Hypoxic conditions stabilize HIF-1α, while it is upregulated by many oncogenic factors under normaxia. HIF-1α is a critical transcription activator for VEGF. Recent studies have shown that intracellular metabolic state participates in regulation of sprouting angiogenesis, which may involve AMP-activated protein kinase (AMPK). Indeed, AMPK has been shown to exert both positive and negative effects on angiogenesis. On the one hand, activation of AMPK mediates stress responses to facilitate autophagy which stabilizes HIF-1α, leading to increased expression of VEGF. On the other hand, AMPK could attenuate angiogenesis induced by tumor-promoting and pro-metastatic factors, such as the phosphoinositide 3-kinase /protein kinase B (Akt)/mammalian target of rapamycin (PI3K/Akt/mTOR), hepatic growth factor (HGF), and TGF-β/BMP signaling pathways. Thus, this review will summarize research progresses on these two opposite effects and discuss the mechanisms behind the discrepant findings.

Dopamine receptor antagonists induce differentiation of PC-3 human prostate cancer cell-derived cancer stem cell-like cells

BACKGROUND

The objective of this study was to determine whether PC-3 human prostate cancer cell-derived cancer stem cells (CSC)-like cells grown in a regular cell culture plate not coated with a matrix molecule might be useful for finding differentiation-inducing agents that could alter properties of prostate CSC.

METHODS

Monolayer cells prepared from sphere culture of PC-3 cells were characterized for the presence of pluripotency and tumorigenicity. They were then applied to screen a compound library to find compounds that could induce morphology changes of cells. Mechanisms of action of compounds selected from the chemical library that induced the loss of pluripotency of cells were also investigated.

RESULTS

C5A cells prepared from PC-3 cell-derived sphere culture expressed pluripotency markers such as Oct4, Sox2, and Klf4. C5A cells were highly proliferative. They were invasive in vitro and tumorigenic in vivo. Some dopamine receptor antagonists such as thioridazine caused reduction of pluripotency markers and tumorigenicity. Thioridazine, unlike promazine, inhibited phosphorylation of AMPK in a dose dependent manner. BML-275, an AMPK inhibitor, also induced differentiation of C5A cells as seen with thioridazine whereas A769663, an AMPK activator, blocked its differentiation-inducing ability. Transfection of C5A cells with siRNAs of dopamine receptor subtypes revealed that knockdown of DRD2 or DRD4 induced morphology changes of C5A cells.

CONCLUSIONS

Some dopamine receptor antagonists such as thioridazine can induce differentiation of CSC-like cells by inhibiting phosphorylation of AMPK. Binding to DRD2 or DRD4 might have mediated the action of thioridazine involved in the differentiation of CSC-like cells.

Endothelial Cells: From Dysfunction Mechanism to Pharmacological Effect in Cardiovascular Disease

Endothelial cells (ECs) are the innermost layer of blood vessels that play important roles in homeostasis and vascular function. However, recent evidence suggests that the onset of inflammation and the production of reactive oxygen species impair the function of ECs and are a main factor in the development of cardiovascular disease (CVD). In this study, we investigated the effects of inflammatory markers, oxidative stress, and treatment on ECs in CVD patients. This review article is based on the material obtained from PubMed up to 2018. The key search terms used were "Cardiovascular Disease," "Endothelial Cell Dysfunction," "Inflammation," "Treatment," and "Oxidative Stress." The generation of reactive oxygen species (ROS) as well as reduced nitric oxide (NO) production by ECs impairs the function of blood vessels. Therefore, treatment of CVD patients leads to the expression of transcription factors activating anti-oxidant mechanisms and NO production. In contrast, NO production by inflammatory agents can cause ECs repair due to differentiation of endothelial progenitor cells (EPCs). Therefore, identifying the molecular pathways leading to the differentiation of EPCs through mediation of factors induced by inflammatory factors can be effective in regenerative medicine for ECs repair.

The role of endothelial colony forming cells in kidney cancer's pathogenesis, and in resistance to anti-VEGFR agents and mTOR inhibitors: A speculative review

Renal cell carcinoma (RCC) is highly dependent on angiogenesis, due to the overactivation of the VHL/HIF/VEGF/VEGFRs axis; this justifies the marked sensitivity of this neoplasm to antiangiogenic agents which, however, ultimately fail to control tumor growth. RCC also frequently shows alterations in the mTOR signaling pathway, and mTOR inhibitors have shown a similar pattern of initial activity/late failure as pure antiangiogenic agents. Understanding mechanisms of resistance to these agents would be key to improve the outcome of our patients. Circulating endothelial cells are a family of mainly bone marrow-derived progenitors, which have been postulated to be responsible of the reactivation of angiogenesis in different tumors. In this review, we shall discuss the complex nature and function of these cells, the evidence pro and contra their contribution to tumor vascularization, especially as far as RCC is concerned, and their possible role in determining resistance to presently available treatments.

Ghrelin Stimulates Endothelial Cells Angiogenesis through Extracellular Regulated Protein Kinases (ERK) Signaling Pathway

Adipose tissue is hyper-vascularized. Vessels in adipose tissue not only supply nutrients and oxygen to nourish adipocytes, but also provide cytokines that regulate mass and function of adipose tissue. Understanding the fundamental mechanisms how vessels modulate adipocyte functions would provide new therapeutic options for treatment of metabolic disease and obesity. In recent years, researches about ghrelin are focused on glucose and lipid metabolism, but its effect on vascular function remains uncharacterized. In the present study, ghrelin receptor gene deletion mice (Ghsr^-/- mice) were used to study ghrelin-regulated vascular metabolism in white adipose tissue. Ghsr^-/- mice demonstrated lower food intake, lower body weight, and resistance to high-fat diet-induced obesity. The number of vessels in white adipose tissue was decreased in Ghsr^-/- mice when compared with wild type mice fed with high-fat diet. To further define ghrelin effects in vitro, we used endothelial progenitor cells from wild type and Ghsr^-/- mice as well as human umbilical vein endothelial cells in our experiments. We found that ghrelin stimulated endothelial cells angiogenesis and migration through the MEK-ERK signaling pathway. [d-Lys3]-GHRP-6 and PD98059 could reverse the effects of ghrelin on endothelial cells. Our study indicates that ghrelin activates its receptor on endothelial cells to promote angiogenesis and migration via a mechanism involving the extracellular regulated protein kinases (ERK) signaling pathway.

Aspirin Suppresses PGE2 and Activates AMP Kinase to Inhibit Melanoma Cell Motility, Pigmentation, and Selective Tumor Growth In Vivo

There are conflicting epidemiologic data on whether chronic aspirin (ASA) use may reduce melanoma risk in humans. Potential anticancer effects of ASA may be mediated by its ability to suppress prostaglandin E₂ (PGE₂) production and activate 5'-adenosine monophosphate-activated protein kinase (AMPK). We investigated the inhibitory effects of ASA in a panel of melanoma and transformed melanocyte cell lines, and on tumor growth in a preclinical model. ASA and the COX-2 inhibitor celecoxib did not affect melanoma cell viability, but significantly reduced colony formation, cell motility, and pigmentation (melanin production) in vitro at concentrations of 1 mmol/L and 20 μmol/L, respectively. ASA-mediated inhibition of cell migration and pigmentation was rescued by exogenous PGE₂ or Compound C, which inhibits AMPK activation. Levels of tyrosinase, MITF, and p-ERK were unaffected by ASA exposure. Following a single oral dose of 0.4 mg ASA to NOD/SCID mice, salicylate was detected in plasma and skin at 4 hours and PGE₂ levels were reduced up to 24 hours. Some human melanoma tumors xenografted into NOD/SCID mice were sensitive to chronic daily ASA administration, exhibiting reduced growth and proliferation. ASA-treated mice bearing sensitive and resistant tumors exhibited both decreased PGE₂ in plasma and tumors and increased phosphorylated AMPK in tumors. We conclude that ASA inhibits colony formation, cell motility, and pigmentation through suppression of PGE₂ and activation of AMPK and reduces growth of some melanoma tumors in vivo This preclinical model could be used for further tumor and biomarker studies to support future melanoma chemoprevention trials in humans. Cancer Prev Res; 11(10); 629-42. ©2018 AACR.

Inositol Polyphosphate Multikinase Inhibits Angiogenesis via Inositol Pentakisphosphate-Induced HIF-1α Degradation

RATIONALE

Inositol polyphosphate multikinase (IPMK) and its major product inositol pentakisphosphate (IP5) regulate a variety of cellular functions, but their role in vascular biology remains unexplored.

OBJECTIVE

We have investigated the role of IPMK in regulating angiogenesis.

METHODS AND RESULTS

Deletion of IPMK in fibroblasts induces angiogenesis in both in vitro and in vivo models. IPMK deletion elicits a substantial increase of VEGF (vascular endothelial growth factor), which mediates the regulation of angiogenesis by IPMK. The regulation of VEGF by IPMK requires its catalytic activity. IPMK is predominantly nuclear and regulates gene transcription. However, IPMK does not apparently serve as a transcription factor for VEGF. HIF (hypoxia-inducible factor)-1α is a major determinant of angiogenesis and induces VEGF transcription. IPMK deletion elicits a major enrichment of HIF-1α protein and thus VEGF. HIF-1α is constitutively ubiquitinated by pVHL (von Hippel-Lindau protein) followed by proteasomal degradation under normal conditions. However, HIF-1α is not recognized and ubiquitinated by pVHL in IPMK KO (knockout) cells. IP5 reinstates the interaction of HIF-1α and pVHL. HIF-1α prolyl hydroxylation, which is prerequisite for pVHL recognition, is interrupted in IPMK-deleted cells. IP5 promotes HIF-1α prolyl hydroxylation and thus pVHL-dependent degradation of HIF-1α. Deletion of IPMK in mouse brain increases HIF-1α/VEGF levels and vascularization. The increased VEGF in IPMK KO disrupts blood-brain barrier and enhances brain blood vessel permeability.

CONCLUSIONS

IPMK, via its product IP5, negatively regulates angiogenesis by inhibiting VEGF expression. IP5 acts by enhancing HIF-1α hydroxylation and thus pVHL-dependent degradation of HIF-1α.

Neuronal migration is mediated by inositol hexakisphosphate kinase 1 via α-actinin and focal adhesion kinase

Inositol hexakisphosphate kinase 1 (IP6K1), which generates 5-diphosphoinositol pentakisphosphate (5-IP7), physiologically mediates numerous functions. We report that IP6K1 deletion leads to brain malformation and abnormalities of neuronal migration. IP6K1 physiologically associates with α-actinin and localizes to focal adhesions. IP6K1 deletion disrupts α-actinin's intracellular localization and function. The IP6K1 deleted cells display substantial decreases of stress fiber formation and impaired cell migration and spreading. Regulation of α-actinin by IP6K1 requires its kinase activity. Deletion of IP6K1 abolishes α-actinin tyrosine phosphorylation, which is known to be regulated by focal adhesion kinase (FAK). FAK phosphorylation is substantially decreased in IP6K1 deleted cells. 5-IP7, a product of IP6K1, promotes FAK autophosphorylation. Pharmacologic inhibition of IP6K by TNP [N2-(m-Trifluorobenzyl), N6-(p-nitrobenzyl)purine] recapitulates the phenotype of IP6K1 deletion. These findings establish that IP6K1 physiologically regulates neuronal migration by binding to α-actinin and influencing phosphorylation of both FAK and α-actinin through its product 5-IP7.

An EP4 Receptor Agonist Inhibits Cardiac Fibrosis Through Activation of PKA Signaling in Hypertrophied Heart

Cardiac fibrosis is a pathological feature of myocardium of failing heart and plays causative roles in arrhythmia and cardiac dysfunction, but its regulatory mechanisms remain largely elusive. In this study, we investigated the effects of the novel EP4 receptor agonist ONO-0260164 on cardiac fibrosis in hypertrophied heart and explored the regulatory mechanisms in cardiac fibroblasts.In a mouse model of cardiac hypertrophy generated by transverse aortic constriction (TAC), ONO-0260164 treatment significantly prevented systolic dysfunction and progression of myocardial fibrosis at 5 weeks after TAC. In cultured neonatal rat cardiac fibroblasts, transforming growth factor-β1 (TGF-β1) induced upregulation of collagen type 1, alpha 1 (Col1a1) and type 3, alpha 1 (Col3a1), which was inhibited by ONO-0260164 treatment. ONO-0260164 activated protein kinase A (PKA) in the presence of TGF-β1 in the cardiac fibroblasts. PKA activation suppressed an increase in collagen expression induced by TGF-β1, indicating the important inhibitory roles of PKA activation in TGF-β1mediated collagen induction.We have demonstrated for the first time the antifibrotic effects of the novel EP4 agonist ONO-0260164 in vivo and in vitro, and the important role of PKA activation in the effects.

Doxorubicin resistant cancer cells activate myeloid-derived suppressor cells by releasing PGE2

Chemotherapies often induce drug-resistance in cancer cells and simultaneously stimulate proliferation and activation of Myeloid-Derived Suppressor Cells (MDSCs) to inhibit anti-tumor T cells, thus result in poor prognosis of patients with breast cancers. To date, the mechanism underlying the expansion of MDSCs in response to chemotherapies is poorly understood. In the present study, we used in vitro cell culture and in vivo animal studies to demonstrate that doxorubicin-resistant breast cancer cells secret significantly more prostaglandin E₂ (PGE₂) than their parental doxorubicin-sensitive cells. The secreted PGE₂ can stimulate expansion and polymerization of MDSCs by directly target to its receptors, EP2/EP4, on the surface of MDSCs, which consequently triggers production of miR-10a through activating PKA signaling. More importantly, activated MDSCs can inhibit CD4⁺CD25⁻ T cells as evidenced by reduced proliferation and IFN-γ release. In order to determine the molecular pathway that involves miR-10a mediated activation of MDSCs, biochemical and pharmacological studies were carried out. We found that miR-10a can activate AMPK signaling to promote expansion and activation of MDSCs. Thus, these results reveal, for the first time, a novel role of PGE₂/miR-10a/AMPK signaling axis in chemotherapy-induced immune resistance, which might be targeted for treatment of chemotherapy resistant tumors.

Possible involvement of AMP-activated protein kinase in PGE1-induced synthesis of osteoprotegerin in osteoblasts

AMP-activated protein kinase (AMPK) is firmly established as a central regulator of cellular energy homeostasis. We have previously reported that prostaglandin E₁ (PGE₁) stimulates the synthesis of osteoprotegerin through p38 mitogen-activated protein (MAP) kinase and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) in osteoblast-like MC3T3-E1 cells. The present study investigated the involvement of AMPK in PGE₁-induced osteoprotegerin synthesis in MC3T3-E1 cells. The levels of osteoprotegerin were measured using an enzyme-linked immunosorbent assay, while the phosphorylation of AMPK, acetyl-CoA carboxylase, p38 MAP kinase and SAPK/JNK were analyzed by western blotting. In addition, the mRNA expression levels of osteoprotegerin were determined by a reverse transcription-quantitative polymerase chain reaction. It was revealed that PGE₁ significantly induced the phosphorylation of the α and β subunits of AMPK in a time-dependent manner (P<0.05). In addition, acetyl-CoA carboxylase, a direct substrate of AMPK, was significantly phosphorylated by PGE₁ (P<0.05). Compound C, an AMPK inhibitor, was revealed to suppress the phosphorylation of acetyl-CoA carboxylase, which significantly reduced the release and mRNA expression levels of PGE₁-stimulated osteoprotegerin (P<0.05). However, the PGE₁-induced phosphorylation of p38 MAP kinase and SAPK/JNK were not affected by compound C. The results of the present study indicated that AMPK may positively regulate PGE₁-stimulated osteoprotegerin synthesis in osteoblasts; thus providing novel insight into the regulatory mechanisms underlying bone metabolism.

Regulation by AMP-activated protein kinase of PGE2-induced osteoprotegerin synthesis in osteoblasts

Adenosine monophosphate-activated protein kinase (AMPK) is currently recognized to act as a key sensing enzyme in the regulation of cellular energy homeostasis. It has been previously demonstrated that prostaglandin E2 (PGE2) stimulates the synthesis of osteoprotegerin (OPG) through the activation of p38 mitogen-activated protein (MAP) kinase, p44/p42 MAP kinase and stress-activated protein kinase/c‑Jun N‑terminal kinase (SAPK/JNK) in osteoblast‑like MC3T3‑E1 cells. In the present study, it was investigated whether AMPK is implicated in the PGE2‑induced OPG synthesis in MC3T3‑E1 cells. PGE2 was observed to induce the phosphorylation of AMPKα (Thr‑172) and AMPKβ (Ser‑108) in a time‑dependent manner. PGE2 additionally induced the phosphorylation of acetyl‑coenzyme A (CoA) carboxylase, a direct substrate of AMPK. Compound C, an inhibitor of AMPK, which attenuated the phosphorylation of acetyl‑CoA carboxylase, significantly suppressed the PGE2‑stimulated OPG release and the mRNA expression level. Compound C failed to affect the PGE2‑stimulated phosphorylation of p38 MAP kinase or p44/p42 MAP kinase. On the contrary, the phosphorylation of SAPK/JNK was markedly attenuated by compound C. The results of the current study suggest that AMPK acts as a positive regulator in PGE2-stimulated OPG synthesis via SAPK/JNK signaling in osteoblasts.

Role of Polyunsaturated Fatty Acids and Their Metabolites on Stem Cell Proliferation and Differentiation

The nervous system is highly enriched with long-chain polyunsaturated fatty acids (PUFAs). Essential fatty acids, namely, ω-6 (n - 6) and ω-3 (n - 3) PUFA, and their metabolites are critical components of cell structure and function and could therefore influence stem cell fate. The available supporting experimental data reveal that n - 6 and n - 3 PUFA and their metabolites can act through multiple mechanisms to promote the proliferation and differentiation of various stem cell types. PUFAs and their mediators regulate several processes within the brain, such as neurotransmission, cell survival and neuroinflammation, and thereby mood and cognition. PUFA levels and the signaling pathways that they regulate are altered in various neurological disorders, including Alzheimer's disease and major depression. Therefore, elucidating the role of PUFAs and their metabolites in stem cell fate regulation is important for stem cell biology as well as stem cell therapy. PUFA-based interventions to generate a positive environment for stem cell proliferation or differentiation might be a promising and practical approach to controlling stem cell fate for clinical applications.

Prostaglandin E2/cyclooxygenase pathway in human skeletal muscle: influence of muscle fiber type and age

Prostaglandin E2 (PGE2) produced by the cyclooxygenase (COX) pathway regulates skeletal muscle protein turnover and exercise training adaptations. The purpose of this study was twofold: 1) define the PGE2/COX pathway enzymes and receptors in human skeletal muscle, with a focus on type I and II muscle fibers; and 2) examine the influence of aging on this pathway. Muscle biopsies were obtained from the soleus (primarily type I fibers) and vastus lateralis (proportionally more type II fibers than soleus) of young men and women (n = 8; 26 ± 2 yr), and from the vastus lateralis of young (n = 8; 25 ± 1 yr) and old (n = 12; 79 ± 2 yr) men and women. PGE2/COX pathway proteins [COX enzymes (COX-1 and COX-2), PGE2 synthases (cPGES, mPGES-1, and mPGES-2), and PGE2 receptors (EP1, EP2, EP3, and EP4)] were quantified via Western blot. COX-1, cPGES, mPGES-2, and all four PGE2 receptors were detected in all skeletal muscle samples examined. COX-1 (P < 0.1) and mPGES-2 were ∼20% higher, while EP3 was 99% higher and EP4 57% lower in soleus compared with vastus lateralis (P < 0.05). Aging did not change the level of skeletal muscle COX-1, while cPGES increased 45% and EP1 (P < 0.1), EP3, and EP4 decreased ∼33% (P < 0.05). In summary, PGE2 production capacity and receptor levels are different in human skeletal muscles with markedly different type I and II muscle fiber composition. In aging skeletal muscle, PGE2 production capacity is elevated and receptor levels are downregulated. These findings have implications for understanding the regulation of skeletal muscle adaptations to exercise and aging by the PGE2/COX pathway and related inhibitors.

Inositol Hexakisphosphate Kinase-3 Regulates the Morphology and Synapse Formation of Cerebellar Purkinje Cells via Spectrin/Adducin

The inositol hexakisphosphate kinases (IP6Ks) are the principal enzymes that generate inositol pyrophosphates. There are three IP6Ks (IP6K1, 2, and 3). Functions of IP6K1 and IP6K2 have been substantially delineated, but little is known of IP6K3's role in normal physiology, especially in the brain. To elucidate functions of IP6K3, we generated mice with targeted deletion of IP6K3. We demonstrate that IP6K3 is highly concentrated in the brain in cerebellar Purkinje cells. IP6K3 physiologically binds to the cytoskeletal proteins adducin and spectrin, whose mutual interactions are perturbed in IP6K3-null mutants. Consequently, IP6K3 knock-out cerebella manifest abnormalities in Purkinje cell structure and synapse number, and the mutant mice display deficits in motor learning and coordination. Thus, IP6K3 is a major determinant of cytoskeletal disposition and function of cerebellar Purkinje cells.

SIGNIFICANCE STATEMENT

We identified and cloned a family of three inositol hexakisphosphate kinases (IP6Ks) that generate the inositol pyrophosphates, most notably 5-diphosphoinositol pentakisphosphate (IP7). Of these, IP6K3 has been least characterized. In the present study we generated IP6K3 knock-out mice and show that IP6K3 is highly expressed in cerebellar Purkinje cells. IP6K3-deleted mice display defects of motor learning and coordination. IP6K3-null mice manifest aberrations of Purkinje cells with a diminished number of synapses. IP6K3 interacts with the cytoskeletal proteins spectrin and adducin whose altered disposition in IP6K3 knock-out mice may mediate phenotypic features of the mutant mice. These findings afford molecular/cytoskeletal mechanisms by which the inositol polyphosphate system impacts brain function.

Expanding roles for AMPK in skeletal muscle plasticity

Skeletal muscle possesses a remarkable plasticity and responds to environmental and physiological challenges by changing its phenotype in terms of size, composition, and metabolic properties. Muscle fibers rapidly adapt to drastic changes in energy demands during exercise through fine-tuning of the balance between catabolic and anabolic processes. One major sensor of energy demand in exercising muscle is AMP-activated protein kinase (AMPK). Recent advances have shed new light on the relevance of AMPK both as a multitask gatekeeper and as an energy regulator in skeletal muscle. Here we summarize recent findings on the function of AMPK in skeletal muscle adaptation to contraction and highlight its role in the regulation of energy metabolism and the control of skeletal muscle regeneration post-injury.

Cell-based screening identifies the active ingredients from Traditional Chinese Medicine formula Shixiao San as the inhibitors of atherosclerotic endothelial dysfunction

In this study, we performed a phenotypic screening in human endothelial cells exposed to oxidized low density lipoprotein (an in vitro model of atherosclerotic endothelial dysfunction) to identify the effective compounds in Shixiao San. After investigating the suitability and reliability of the cell-based screening method using atorvastatin as the positive control drug, this method was applied in screening Shixiao San and its extracts. The treatment of n-butanol fraction on endothelial cells exhibited stronger healing effects against oxidized low density lipoprotein-induced insult when compared with other fractions. Cell viability, the level of nitric oxide, endothelial nitric oxide synthase and endothelin-1 were measured, respectively. The assays revealed n-butanol fraction significantly elevated the survival ratio of impaired cells in culture. In parallel, n-butanol fraction exhibited the highest inhibition of inflammation. The generation of prostaglandin-2 and adhesion molecule (soluble intercellular adhesion molecule-1) was obviously declined. Furthermore, n-butanol fraction suppressed the production of reactive oxygen species and malondialdehyde, and restored the activity of superoxide dismutase. Compounds identification of the n-butanol fraction was carried out by ultra high liquid chromatography coupled to quadrupole time-of-flight tandem mass spectrometry. The active ingredients including quercetin-3-O-(2G-α-l-rhamnosyl)-rutinoside, quercetin-3-O-neohesperidoside, isorhamnetin-3-O-neohesperidoside and isorhamnetin-3-O-rutinoside revealed the ability of anti-atherosclerosis after exposing on endothelial cells. The current work illustrated the pharmacology effect of Shixiao San and clearly indicated the major active components in Shixiao San. More importantly, the proposed cell-based screening method might be particularly suitable for fast evaluating the anti-atherosclerosis efficacy of Traditional Chinese Medicines and screening out the interesting ingredients of Traditional Chinese Medicines.

Concise review: Regulation of stem cell proliferation and differentiation by essential fatty acids and their metabolites

Stem cell therapy holds great promise for regenerative medicine and the treatment of numerous diseases. A key issue of stem cell therapy is the control of stem cell fate, but safe and practical methods are limited. Essential fatty acids, namely ω-6 (n-6) and ω-3 (n-3) polyunsaturated fatty acids (PUFA), and their metabolites are critical components of cell structure and function, and could therefore influence stem cell fate. The available evidence demonstrates that n-6 and n-3 PUFA and their metabolites can act through multiple mechanisms to promote the proliferation and differentiation of various stem cell types. Therefore, elucidating the role of PUFA and their metabolites in stem cell fate regulation is both a challenge and an opportunity for stem cell biology as well as stem cell therapy. PUFA-based interventions to create a favorable environment for stem cell proliferation or differentiation may thus be a promising and practical approach to controlling stem cell fate for clinical applications.

Angiogenesis in the primate ovulatory follicle is stimulated by luteinizing hormone via prostaglandin E2

Rapid angiogenesis occurs as the ovulatory follicle is transformed into the corpus luteum. To determine if luteinizing hormone (LH)-stimulated prostaglandin E2 (PGE2) regulates angiogenesis in the ovulatory follicle, cynomolgus macaques received gonadotropins to stimulate multiple follicular development and chorionic gonadotropin (hCG) substituted for the LH surge to initiate ovulatory events. Before hCG, vascular endothelial cells were present in the perifollicular stroma but not amongst granulosa cells. Endothelial cells entered the granulosa cell layer 24-36 h after hCG, concomitant with the rise in follicular PGE2 and prior to ovulation, which occurs about 40 h after hCG. Intrafollicular administration of the PG synthesis inhibitor indomethacin was coupled with PGE2 replacement to demonstrate that indomethacin blocked and PGE2 restored follicular angiogenesis in a single, naturally developed monkey follicle in vivo. Intrafollicular administration of indomethacin plus an agonist selective for a single PGE2 receptor showed that PTGER1 and PTGER2 agonists most effectively stimulated angiogenesis within the granulosa cell layer. Endothelial cell tracing and three-dimensional reconstruction indicated that these capillary networks form via branching angiogenesis. To further explore how PGE2 mediates follicular angiogenesis, monkey ovarian microvascular endothelial cells (mOMECs) were isolated from ovulatory follicles. The mOMECs expressed all four PGE2 receptors in vitro. PGE2 and all PTGER agonists increased mOMEC migration. PTGER1 and PTGER2 agonists promoted sprout formation while the PTGER3 agonist inhibited sprouting in vitro. While PTGER1 and PTGER2 likely promote the formation of new capillaries, each PGE2 receptor may mediate aspects of PGE2's actions and, therefore, LH's ability to regulate angiogenesis in the primate ovulatory follicle.

Curcumin inhibits EMMPRIN and MMP-9 expression through AMPK-MAPK and PKC signaling in PMA induced macrophages

In coronary arteries, plaque disruption, the major acute clinical manifestations of atherosclerosis, leads to a subsequent cardiac event, such as acute myocardial infarction (AMI) and unstable angina pectoris (UA). Numerous reports have shown that high expression of MMP-9 (matrix metalloproteinase-9), MMP-13 (matrix metalloproteinase-13) and EMMPRIN (extracellular matrix metalloproteinase induce) in monocyte/macrophage results in the plaque progression and destabilization. Curcumin exerts well-known anti-inflammatory and antioxidant effects and probably has a protective role in the atherosclerosis. The purpose of our study was to investigate the molecular mechanisms by which curcumin affects MMP-9, MMP13 and EMMPRIN in PMA (phorbol 12-myristate 13-acetate) induced macrophages. Human monocytic cells (THP-1 cells) were pretreated with curcumin or compound C for 1 h, and then induced by PMA for 48 h. Total RNA and proteins were collected for real-time PCR and Western blot analysis, respectively. In the present study, the exposure to curcumin resulted in attenuated JNK, p38, and ERK activation and decreased expression of MMP-9, MMP-13 and EMMPRIN in PMA induced macrophages. Moreover, we demonstrated that AMPK (AMP-activated protein kinase) and PKC (Protein Kinase C) was activated by PMA during monocyte/macrophage differentiation. Furthermore, curcumin reversed PMA stimulated PKC activation and suppressed the chronic activation of AMPK, which in turn reduced the expression of MMP-9, MMP-13 and EMMPRIN. Therefore, it is suggested that curcumin by inhibiting AMPK-MAPK (mitogen activated protein kinase) and PKC pathway may led to down-regulated EMMPRIN, MMP-9 and MMP-13 expression in PMA-induced THP-1 cells.

Role of AMP-activated protein kinase in regulating hypoxic survival and proliferation of mesenchymal stem cells

AIMS

Mesenchymal stem cells (MSCs) are widely used for cell therapy, particularly for the treatment of ischaemic heart disease. Mechanisms underlying control of their metabolism and proliferation capacity, critical elements for their survival and differentiation, have not been fully characterized. AMP-activated protein kinase (AMPK) is a key regulator known to metabolically protect cardiomyocytes against ischaemic injuries and, more generally, to inhibit cell proliferation. We hypothesized that AMPK plays a role in control of MSC metabolism and proliferation.

METHODS AND RESULTS

MSCs isolated from murine bone marrow exclusively expressed the AMPKα1 catalytic subunit. In contrast to cardiomyocytes, a chronic exposure of MSCs to hypoxia failed to induce cell death despite the absence of AMPK activation. This hypoxic tolerance was the consequence of a preference of MSC towards glycolytic metabolism independently of oxygen availability and AMPK signalling. On the other hand, A-769662, a well-characterized AMPK activator, was able to induce a robust and sustained AMPK activation. We showed that A-769662-induced AMPK activation inhibited MSC proliferation. Proliferation was not arrested in MSCs derived from AMPKα1-knockout mice, providing genetic evidence that AMPK is essential for this process. Among AMPK downstream targets proposed to regulate cell proliferation, we showed that neither the p70 ribosomal S6 protein kinase/eukaryotic elongation factor 2-dependent protein synthesis pathway nor p21 was involved, whereas p27 expression was increased by A-769662. Silencing p27 expression partially prevented the A-769662-dependent inhibition of MSC proliferation.

CONCLUSION

MSCs resist hypoxia independently of AMPK whereas chronic AMPK activation inhibits MSC proliferation, p27 being involved in this regulation.

Transcription factor Krüppel-like factor 2 plays a vital role in endothelial colony forming cells differentiation

AIMS

Endothelial colony forming cells (ECFCs) participate in post-natal vasculogenesis. We previously reported that vascular endothelial growth factor (VEGF) promotes human ECFC differentiation through AMP-activated protein kinase (AMPK) activation. However, the mechanisms underlying transcriptional regulation of ECFC differentiation still remain largely elusive. Here, we investigated the role of transcription factor Krüppel-like factor 2 (KLF2) in the regulation of ECFC function.

METHODS AND RESULTS

Human ECFCs were isolated from cord blood and cultured. Treatment with VEGF significantly increased endothelial markers in ECFCs and their capacity for migration and tube formation. The mRNA and protein levels of KLF2 were also significantly up-regulated. This up-regulation was abrogated by AMPK inhibition or by knockdown of KLF2 with siRNA. Furthermore, adenovirus-mediated overexpression of KLF2 promoted ECFC differentiation by enhancing expression of endothelial cell markers, reducing expression of progenitor cell markers, and increasing the capacity for tube formation in vitro, indicating the important role of KLF2 in ECFC-mediated angiogenesis. Histone deacetylase 5 (HDAC5) was phosphorylated by AMPK activity induced by VEGF and the AMPK agonist AICAR (5-amino-1-β-D-ribofuranosyl-imidazole-4-carboxamide). In vivo angiogenesis assay revealed that overexpression of KLF2 in bone-marrow-derived pro-angiogenic progenitor cells promoted vessel formation when the cells were implanted in C57BL/6 mice.

CONCLUSION

Up-regulation of KLF2 by AMPK activation constitutes a novel mechanism of ECFC differentiation, and may have therapeutic value in the treatment of ischaemic heart disease.

Prostaglandin E2 promotes cellular recovery from established nephrotoxic serum nephritis in mice, prosurvival, and regenerative effects on glomerular cells

We postulated that prostaglandin E2 (PGE2), which exhibits regulatory functions to control immune-mediated inflammation, fibrosis, oxidative stress, and tissue/cellular regeneration, has the potential to improve the course of nephritis. Therefore, the therapeutic potential of prostanoid on established nephritis in mice was evaluated focusing on its role on renal cellular recovery, with emphasis on its cytoprotecting and growth-promoting effects. Acute nephritis was induced in mice by single injection of nephrotoxic serum (NTS), followed by PGE2 administration with severity of nephritis evaluated over time. Mice injected with PGE2 recovered promptly with normalization of blood urea nitrogen and urine protein levels and histology. Recovery was observed with dosing of prostanoid at day 1, as well as day 4. With the use of selective EP1-4 receptor agonists, EP3 receptor has been identified as important in mediating beneficial effects of PGE2 in our system. PGE2 normalized glomerular cell losses during nephrotoxic serum-induced nephritis, restored synaptopodin distribution and F-actin filaments arrangement in glomeruli. In cell culture, PGE2 reduced nephrotoxim serum (NTS)-induced apoptosis of glomerular cells and promoted cell reproliferation after NTS-mediated injury. In conclusion, PGE2 treatment promotes resolution of glomerular inflammation. Consistent with this observation, the regenerative and cytoprotective effects of prostanoid on glomerular cells in culture were observed, suggesting that PGE2 may be beneficial in the treatment of glomerulonephritis.

Multifaceted roles of PGE2 in inflammation and cancer

Prostaglandin E(2) (PGE(2)) is a bioactive lipid that elicits a wide range of biological effects associated with inflammation and cancer. PGE(2) exerts diverse effects on cell proliferation, apoptosis, angiogenesis, inflammation, and immune surveillance. This review concentrates primarily on gastrointestinal cancers, where the actions of PGE(2) are most prominent, most likely due to the constant exposure to dietary and environmental insults and the intrinsic role of PGE(2) in tissue homeostasis. A discussion of recent efforts to elucidate the complex and interconnected pathways that link PGE(2) signaling with inflammation and cancer is provided, supported by the abundant literature showing a protective effect of NSAIDs and the therapeutic efficacy of targeting mPGES-1 or EP receptors for cancer prevention. However, suppressing PGE(2) formation as a means of providing chemoprotection against all cancers may not ultimately be tenable, undoubtedly the situation for patients with inflammatory bowel disease. Future studies to fully understand the complex role of PGE(2) in both inflammation and cancer will be required to develop novel strategies for cancer prevention that are both effective and safe.

Immunosuppressive activity enhances central carbon metabolism and bioenergetics in myeloid-derived suppressor cells in vitro models

Background

The tumor microenvironment contains a vast array of pro- and anti-inflammatory cytokines that alter myelopoiesis and lead to the maturation of immunosuppressive cells known as myeloid-derived suppressor cells (MDSCs). Incubating bone marrow (BM) precursors with a combination of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-6 (IL-6) generated a tumor-infiltrating MDSC-like population that impaired anti-tumor specific T-cell functions. This in vitro experimental approach was used to simulate MDSC maturation, and the cellular metabolic response was then monitored. A complementary experimental model that inhibited L-arginine (L-Arg) metabolizing enzymes in MSC-1 cells, an immortalized cell line derived from primary MDSCs, was used to study the metabolic events related to immunosuppression.

Results

Exposure of BM cells to GM-CSF and IL-6 activated, within 24 h, L-Arg metabolizing enzymes which are responsible for the MDSCs immunosuppressive potential. This was accompanied by an increased uptake of L-glutamine (L-Gln) and glucose, the latter being metabolized by anaerobic glycolysis. The up-regulation of nutrient uptake lead to the accumulation of TCA cycle intermediates and lactate as well as the endogenous synthesis of L-Arg and the production of energy-rich nucleotides. Moreover, inhibition of L-Arg metabolism in MSC-1 cells down-regulated central carbon metabolism activity, including glycolysis, glutaminolysis and TCA cycle activity, and led to a deterioration of cell bioenergetic status. The simultaneous increase of cell specific concentrations of ATP and a decrease in ATP-to-ADP ratio in BM-derived MDSCs suggested cells were metabolically active during maturation. Moreover, AMP-activated protein kinase (AMPK) was activated during MDSC maturation in GM-CSF and IL-6–treated cultures, as revealed by the continuous increase of AMP-to-ATP ratios and the phosphorylation of AMPK. Likewise, AMPK activity was decreased in MSC-1 cells when L-Arg metabolizing enzymes were inhibited. Finally, inhibition of AMPK activity by the specific inhibitor Compound C (Comp-C) resulted in the inhibition of L-Arg metabolizing enzyme activity and abolished MDSCs immunosuppressive activity.

Conclusions

We anticipate that the inhibition of AMPK and the control of metabolic fluxes may be considered as a novel therapeutic target for the recovery of the immunosurveillance process in cancer-bearing hosts.