Sergey Ryzhov

Differential Expression of Adenosine Receptors in Human Endothelial Cells: Role of A2B Receptors in Angiogenic Factor Regulation

Adenosine has been reported to stimulate or inhibit the release of angiogenic factors depending on the cell type examined. To test the hypothesis that differential expression of adenosine receptor subtypes contributes to endothelial cell heterogeneity, we studied microvascular (HMEC-1) and umbilical vein (HUVEC) human endothelial cells. Based on mRNA level and stimulation of adenylate cyclase, we found that HUVECs preferentially express A2A adenosine receptors and HMEC-1 preferentially express A2B receptors. Neither cells expressed A1 or A3 receptors. The nonselective adenosine agonist 5′-N-ethylcarboxamidoadenosine (NECA) increased expression of interleukin-8 (IL-8), basic fibroblast growth factor (bFGF), and vascular endothelial growth factor (VEGF) in HMEC-1, but had no effect in HUVECs. In contrast, the selective A2A agonist 2-p-(2-carboxyethyl)phenylethylamino-NECA (CGS 21680) had no effect on expression of these angiogenic factors. Cotransfection of each type of adenosine receptors with a luciferase reporter in HMEC-1 showed that A2B receptors, but not A1, A2A, or A3, activated IL-8 and VEGF promoters. These effects were mimicked by constitutively active &agr;Gq, &agr;G12, and &agr;G13, but not &agr;Gs or &agr;Gi1-3. Furthermore, stimulation of phospholipase C indicated coupling of A2B receptors to Gq proteins in HMEC-1. Thus, differential expression of adenosine receptor subtypes contributes to functional heterogeneity of human endothelial cells. A2B receptors, predominantly expressed in human microvascular cells, modulate expression of angiogenic factors via coupling to Gq, and possibly via G12/13.

Adenosine receptors in regulation of dendritic cell differentiation and function.

Differentiation of functional dendritic cells (DCs) critically depends on the microenvironment. DCs differentiate in hypoxic tumor sites and inflamed or damaged tissue. Because local concentrations of adenosine reach high physiologically relevant levels in these conditions, we assessed the expression of adenosine receptors and the effect of their activation on differentiation of human monocytes and mouse peritoneal macrophages and hematopoietic progenitor cells (HPCs) into myeloid DCs. Stimulation of adenosine receptors skews DC differentiation toward a distinct cell population characterized by expression of both DC and monocyte/macrophage cell surface markers. Pharmacologic analysis and experiments with cells from A(2B) adenosine receptor knockout mice identified A(2B) receptor as the mediator of adenosine effects on DCs. Unlike normal myeloid DCs, adenosine-differentiated DCs have impaired allostimulatory activity and express high levels of angiogenic, pro-inflammatory, immune suppressor, and tolerogenic factors, including VEGF, IL-8, IL-6, IL-10, COX-2, TGF-beta, and IDO. They promoted tumor growth if injected into tumors implanted in mice. Using adenosine desaminase knockout animals, we showed that DCs with proangiogenic phenotype are highly abundant under conditions associated with elevated levels of extracellular adenosine in vivo. Adenosine signaling through A(2B) receptor is an important factor of aberrant DC differentiation and generation of tolerogenic, angiogenic, and proinflammatory cells.

Mast Cell–Mediated Stimulation of Angiogenesis Cooperative Interaction Between A2B and A3 Adenosine Receptors

Abstract— Adenosine is released during tissue injury, ischemia and tumor growth, and promotes angiogenesis. Because mast cells accumulate in the proximity of new blood vessel development, we examined if they may contribute to adenosine-induced angiogenesis. We found that HMC-1 human mast cells express A2A, A2B, and A3 adenosine receptors. The adenosine agonist NECA (100 &mgr;mol/L) increased interleukin-8 (IL-8), vascular endothelial growth factor (VEGF), and angiopoietin-2 mRNA expression. NECA-induced secretion of IL-8 and VEGF was verified by ELISA. A2B receptors mediate VEGF and IL-8 secretion because neither CGS21680 (selective A2A agonist) nor IB-MECA (selective A3 agonist) produced this effect, and it was inhibited by the selective A2B antagonist IPDX but not by the selective A2A antagonist SCH58261 or the selective A3 antagonist MRS1191. In contrast, the selective A3 agonist IB-MECA (EC50 1 nmol/L) stimulated angiopoietin-2 expression. Conditioned media from NECA-activated HMC-1 stimulated human umbilical vein endothelial cell proliferation and migration, and induced capillary tube formation. Capillary formation induced by mast cell–conditioned media was maximal if both HMC-1 A2B and A3 receptors were activated, whereas activation of A2B receptor alone was less effective. Thus, adenosine A2B and A3 receptors act in a functional cooperative fashion to promote angiogenesis by a paracrine mechanism involving the differential expression and secretion of angiogenic factors from human mast cells.

Adenosine-Activated Mast Cells Induce IgE Synthesis by B Lymphocytes: An A2B-Mediated Process Involving Th2 Cytokines IL-4 and IL-13 with Implications for Asthma

Adenosine provokes bronchoconstriction in asthmatics through acute activation of mast cells, but its potential role in chronic inflammation has not been adequately characterized. We hypothesized that adenosine up-regulates Th2 cytokines in mast cells, thus promoting IgE synthesis by B lymphocytes. We tested this hypothesis in human mast cells (HMC-1) expressing A2A, A2B, and A3 adenosine receptors. The adenosine analog 5′-N-ethylcarboxamidoadenosine (NECA) (10 μM) increased mRNA expression of IL-1β, IL-3, IL-4, IL-8, and IL-13, but not IL-2 and IFN-γ. Up-regulation of IL-4 and IL-13 was verified using RT-PCR and ELISA; 10 μM NECA increased IL-13 concentrations in HMC-1 conditioned medium 28-fold, from 7.6 ± 0.3 to 215 ± 4 pg/ml, and increased IL-4 concentrations 6-fold, from 19.2 ± 0.1 to 117 ± 2 pg/ml. This effect was mediated by A2B receptors because neither the selective A2A agonist 2-p-(2-carboxyethyl)phenethylamino-NECA nor the selective A3 agonist N6-(3-iodobenzyl)-N-methyl-5′-carbamoyladenosine reproduced it, and the selective A2B antagonist 3-isobutyl-8-pyrrolidinoxanthine prevented it. Constitutive expression of CD40 ligand on HMC-1 surface was not altered by NECA. Human B lymphocytes cocultured for 12 days with NECA-stimulated HMC-1 produced 870 ± 33 pg IgE per 106 B cells, whereas lymphocytes cocultured with nonstimulated HMC-1, or cultured alone in the absence or in the presence of NECA, produced no IgE. Thus, we demonstrated induction of IgE synthesis by the interaction between adenosine-stimulated mast cells and B lymphocytes, and suggest that this mechanism is involved in the amplification of the allergic inflammatory responses associated with asthma.

Conditional Knockout of Macrophage PPARγIncreases Atherosclerosis in C57BL/6 and Low-Density Lipoprotein Receptor–Deficient Mice

Objective—Peroxisome proliferator-activated receptor gamma (PPARγ) is highly expressed in macrophage-derived foam cells of atherosclerotic lesions, and its expression may have a dramatic impact on atherosclerosis. Methods and Results—To investigate the contribution of macrophage PPARγ expression on atherogenesis in vivo, we generated macrophage-specific PPARγ knockout (MacPPARγKO) mice. C57BL/6 and low-density lipoprotein (LDL) receptor–deficient (LDLR−/−) mice were reconstituted with MacPPARγKO or wild-type marrow and challenged with an atherogenic diet. No differences were found in serum lipids between recipients reconstituted with MacPPARγKO and wild-type marrow. In contrast, both C57BL/6 and LDLR−/− mice transplanted with MacPPARγKO marrow had significantly larger atherosclerotic lesions than control recipients. In addition, MacPPARγKO→LDLR−/− mice had higher numbers of macrophages in atherosclerotic lesions compared with controls. Peritoneal macrophages isolated from the MacPPARγKO mice had decreased uptake of oxidized but not acetylated LDL and showed no changes in either cholesterol efflux or inflammatory cytokine expression. Macrophages from MacPPARγKO mice had increased levels of migration and CC chemokine receptor 2 (CCR2) expression compared with wild-type macrophages. Conclusion—Thus, macrophage PPARγ deficiency increases atherosclerosis under conditions of mild and severe hypercholesterolemia, indicating an antiatherogenic role for PPARγ, which may be caused, at least in part, by modulation of CCR2 expression and monocyte recruitment.

Hypoxia Modulates Adenosine Receptors in Human Endothelial and Smooth Muscle Cells Toward an A2B Angiogenic Phenotype

We previously reported that adenosine A2B receptor activation stimulates angiogenesis. Because hypoxia is a potent stimulus for the release of both adenosine and angiogenic factors, we tested the hypothesis that hypoxia alters the expression of adenosine receptors toward an “angiogenic” phenotype. We used human umbilical vein endothelial cells (HUVECs) and bronchial smooth muscle cells (BSMCs) because, under normoxic conditions, adenosine does not release vascular endothelial growth factor (VEGF). HUVECs expressed a characteristic A2A phenotype (the selective A2A agonist CGS21680 was as potent as the nonselective agonist 5′-N-ethylcarboxamidoadenosine [NECA] in generating cAMP). Hypoxia (4.6% O2, 3 hours) decreased A2A mRNA from 1.56±0.3% to 0.16±0.01% of &bgr;-actin expression but increased A2B mRNA from 0.08±0.01% to 0.27±0.05%. Consistent with changes in receptor expression, CGS21680 failed to increase cAMP in hypoxic HUVECs, whereas NECA remained active (A2B phenotype), and NECA increased VEGF release from 9.5±1.0 to 14.2±1.2 pg/mL (P<0.05), indicating that increased A2B receptors were functionally coupled to upregulation of VEGF. Hypoxia had similar effects on BSMCs, increasing A2B mRNA by 2.4±0.3-fold, from 0.42±0.04% to 1.00±0.13% of &bgr;-actin. Whereas NECA had no effect on VEGF release in normoxic BSMCs, it increased VEGF release in hypoxic BSMCs, from 74.6±9.6 to 188.3±16.7 pg/mL (P<0.01), and a selective A2B antagonist, CVT-6694, inhibited this increase. A2B receptors activated a VEGF reporter made unresponsive to hypoxia by mutating its hypoxia-inducible factor-1 (HIF-1) binding element, indicating a mechanism independent of HIF-1. In conclusion, hypoxia modulates the expression of adenosine receptors in human endothelial and smooth muscle cells toward an A2B“angiogenic” phenotype.

Experimental myocardial infarction triggers canonical Wnt signaling and endothelial-to-mesenchymal transition

SUMMARY Despite available therapies, myocardial infarction (MI) remains a leading cause of death worldwide. Better understanding of the molecular and cellular mechanisms that regulate cardiac repair should help to improve the clinical outcome of MI patients. Using the reporter mouse line TOPGAL, we show that canonical (β-catenin-dependent) Wnt signaling is induced 4 days after experimental MI in subepicardial endothelial cells and perivascular smooth muscle actin (SMA)-positive (SMA+) cells. At 1 week after ischemic injury, a large number of canonical-Wnt-positive cells accumulated in the infarct area during granulation tissue formation. Coincidently with canonical Wnt activation, endothelial-to-mesenchymal transition (EndMT) was also triggered after MI. Using cell lineage tracing, we show that a significant portion of the canonical-Wnt-marked SMA+ mesenchymal cells is derived from endothelial cells. Canonical Wnt signaling induces mesenchymal characteristics in cultured endothelial cells, suggesting a direct role in EndMT. In conclusion, our study demonstrates that canonical Wnt activation and EndMT are molecular and cellular responses to MI and that canonical Wnt signaling activity is a characteristic property of EndMT-derived mesenchymal cells that take part in cardiac tissue repair after MI. These findings could lead to new strategies to improve the course of cardiac repair by temporal and cell-type-specific manipulation of canonical Wnt signaling.

Adenosinergic Regulation of the Expansion and Immunosuppressive Activity of CD11b+Gr1+ Cells

Extracellular adenosine and purine nucleotides are elevated in many pathological situations associated with the expansion of CD11b+Gr1+ myeloid-derived suppressor cells (MDSCs). Therefore, we tested whether adenosinergic pathways play a role in MDSC expansion and functions. We found that A2B adenosine receptors on hematopoietic cells play an important role in accumulation of intratumoral CD11b+Gr1high cells in a mouse Lewis lung carcinoma model in vivo and demonstrated that these receptors promote preferential expansion of the granulocytic CD11b+Gr1high subset of MDSCs in vitro. Flow cytometry analysis of MDSCs generated from mouse hematopoietic progenitor cells revealed that the CD11b+Gr-1high subset had the highest levels of CD73 (ecto-5′-nucleotidase) expression (Δmean fluorescence intensity [MFI] of 118.5 ± 16.8), followed by CD11b+Gr-1int (ΔMFI of 57.9 ± 6.8) and CD11b+Gr-1−/low (ΔMFI of 12.4 ± 1.0) subsets. Even lower levels of CD73 expression were found on Lewis lung carcinoma tumor cells (ΔMFI of 3.2 ± 0.2). The high levels of CD73 expression in granulocytic CD11b+Gr-1high cells correlated with high levels of ecto-5′-nucleotidase enzymatic activity. We further demonstrated that the ability of granulocytic MDSCs to suppress CD3/CD28-induced T cell proliferation was significantly facilitated in the presence of the ecto-5′-nucleotidase substrate 5′-AMP. We propose that generation of adenosine by CD73 expressed at high levels on granulocytic MDSCs may promote their expansion and facilitate their immunosuppressive activity.

Effect of A2B Adenosine Receptor Gene Ablation on Adenosine-Dependent Regulation of Proinflammatory Cytokines

Pharmacological studies suggest that A2B adenosine receptors mediate proinflammatory effects of adenosine. This concept was recently challenged by the finding that A2B adenosine receptor knockout (A2BKO) mice had moderate inflammation due to elevated basal plasma tumor necrosis factor (TNF)-α and an exaggerated response to lipopolysaccharide (LPS) challenge. However, it is unclear whether this phenomenon actually reflects the loss of putative taming of proinflammatory cytokine production via activation of A2B receptors by endogenous adenosine. In this report, we examined adenosine receptor-dependent regulation of interleukin (IL)-6 and TNF-α blood plasma levels in A2BKO and wild-type mice in vivo and their release from peritoneal macrophages ex vivo. Stimulation of adenosine receptors with 5′-N-ethylcarboxamidoadenosine (NECA) up-regulated IL-6 and suppressed LPS-induced TNF-α in wild-type mice. The selective A2B antagonists 3-isobutyl-8-pyrrolidinoxanthine and 8-[4-[((4-cyanophenyl)carbamoylmethyl)oxy]phenyl]-1,3-di(n-propyl)xanthine (MRS 1754) inhibited NECA-induced IL-6 release but not the suppression of LPS-induced TNF-α secretion from macrophages. Genetic ablation of A2B receptors abrogated NECA-induced increases in IL-6 release from mouse peritoneal macrophages and dramatically reduced the ability of NECA to raise IL-6 plasma levels in vivo. In contrast, the absence of A2B adenosine receptors did not affect NECA-induced suppression of LPS-activated TNF-α release in macrophages, nor did it reduce the ability of NECA to suppress LPS-induced increase in TNF-α plasma levels in vivo. Thus, our results indicate that stimulation of A2B receptors up-regulates the proinflammatory cytokine IL-6 and argue against the recently suggested anti-inflammatory role of A2B receptors in suppression of LPS-stimulated TNF-α production by adenosine.

RAS/MAPK Activation Is Associated with Reduced Tumor-Infiltrating Lymphocytes in Triple-Negative Breast Cancer: Therapeutic Cooperation Between MEK and PD-1/PD-L1 Immune Checkpoint Inhibitors

Purpose: Tumor-infiltrating lymphocytes (TIL) in the residual disease (RD) of triple-negative breast cancers (TNBC) after neoadjuvant chemotherapy (NAC) are associated with improved survival, but insight into tumor cell-autonomous molecular pathways affecting these features are lacking. Experimental Design: We analyzed TILs in the RD of clinically and molecularly characterized TNBCs after NAC and explored therapeutic strategies targeting combinations of MEK inhibitors with PD-1/PD-L1–targeted immunotherapy in mouse models of breast cancer. Results: Presence of TILs in the RD was significantly associated with improved prognosis. Genetic or transcriptomic alterations in Ras–MAPK signaling were significantly correlated with lower TILs. MEK inhibition upregulated cell surface MHC expression and PD-L1 in TNBC cells both in vivo and in vitro. Moreover, combined MEK and PD-L1/PD-1 inhibition enhanced antitumor immune responses in mouse models of breast cancer. Conclusions: These data suggest the possibility that Ras–MAPK pathway activation promotes immune-evasion in TNBC, and support clinical trials combining MEK- and PD-L1–targeted therapies. Furthermore, Ras/MAPK activation and MHC expression may be predictive biomarkers of response to immune checkpoint inhibitors. Clin Cancer Res; 22(6); 1499–509. ©2015 AACR.