Tuere Wilder

Requirements for T Lymphocyte Migration in Explanted Lymph Nodes

Although the requirements for T lymphocyte homing to lymph nodes (LNs) are well studied, much less is known about the requirements for T lymphocyte locomotion within LNs. Imaging of murine T lymphocyte migration in explanted LNs using two-photon laser-scanning fluorescence microscopy provides an opportunity to systematically study these requirements. We have developed a closed system for imaging an intact LN with controlled temperature, oxygenation, and perfusion rate. Naive T lymphocyte locomotion in the deep paracortex of the LN required a perfusion rate of >13 μm/s and a partial pressure of O2 (pO2) of >7.4%. Naive T lymphocyte locomotion in the subcapsular region was 38% slower and had higher turning angles and arrest coefficients than naive T lymphocytes in the deep paracortex. T lymphocyte activation decreased the requirement for pO2, but also decreased the speed of locomotion in the deep paracortex. Although CCR7−/− naive T cells displayed a small reduction in locomotion, systemic treatment with pertussis toxin reduced naive T lymphocyte speed by 59%, indicating a contribution of Gαi-mediated signaling, but involvement of other G protein-coupled receptors besides CCR7. Receptor knockouts or pharmacological inhibition in the adenosine, PG/lipoxygenase, lysophosphatidylcholine, and sphingosine-1-phosphate pathways did not individually alter naive T cell migration. These data implicate pO2, tissue architecture, and G-protein coupled receptor signaling in regulation of naive T lymphocyte migration in explanted LNs.

Ecto-5′-nucleotidase (CD73) -mediated extracellular adenosine production plays a critical role in hepatic fibrosis

Adenosine is a potent endogenous regulator of tissue repair that is released from injured cells and tissues. Hepatic fibrosis results from chronic hepatic injury, and we have previously reported that endogenously generated adenosine, acting at A2A receptors, plays a role in toxin‐induced hepatic fibrosis. Adenosine may form intracellularly and then be transported to the extracellular space or it may form extracellularly from adenine nucleotides released from injured cells. Because ecto‐5′‐ nucleotidase (CD73) catalyzes the terminal step in extracellular adenosine formation from AMP, we determined whether CD73 plays a role in the development of hepatic fibrosis. Mice were treated overnight with PBS, CCl4, ethanol, or thioacetamide (TAA);their livers were harvested, and slices were incubated in medium for 20 h before adenosine concentration in the supernatant was measured by HPLC. Hepatic fibrosis was induced by CCl4 or TAA treatment in CD73 knockout (CD73KO and C57BL/6 background) and C57BL/6 control mice [wild‐type (WT)] mice and quantified by digital analysis of picrosirius red stained slides and hydroxyproline content. mRNA expression was quantified by real‐time polymerase chain reaction, and protein was quantified by Western blot or enzyme‐linked immunosorbent assay. Livers from WT mice treated with CCl4, ethanol, and TAA released 2‐ to 3‐fold higher levels of adenosine than livers from comparably treated CD73KO mice. CD73KO mice were protected from fibrosis with significantly less collagen content in the livers of CD73KO than WT mice after treatment with either CCl4 or TAA. There were far fewer αa‐smooth muscle actin positive hepatic stellate cells in CCl4‐treated KO mice than that in WT mice. After CCl4 treatment, the mRNA level of A1, A2A, A2B, and A3 adenosine receptors, tumor necrosis factor‐α, interleukin (IL) ‐1β, IL‐13rα1, matrix metalloproteinase (MMP)‐2, MMP‐14, tissue inhibitor of metalloproteinase (TIMP) ‐1, and TIMP‐2, and IL‐13 level increased markedly in both CD73KO and WT mice, but Col1α1, Col3α1, and transforming growth factor‐β1 mRNA increased much more in WT mice than that in KO mice. Moreover, IL‐13rα2, MMP‐13 mRNA, and MMP‐13 protein were higher in KO mice than that in WT mice. These results indicate that adenosine, formed extracellularly from adenine nucleotides, plays a major role in the patho genesis of hepatic fibrosis and that inhibition of aden osine production or blockade of adenosine receptors may help prevent hepatic fibrosis.—Peng, Z., Fernandez, P., Wilder, T., Yee, H., Chiriboga, L., Chan, E. S. L., Cronstein, B. N. Ecto‐5′‐ nucleotidase (CD73) ‐mediated extracellular adenosine production plays a critical role in hepatic fibrosis. FASEB J. 22, 2263–2272 (2008)

Pharmacological Blockade of A2A Receptors Prevents Dermal Fibrosis in a Model of Elevated Tissue Adenosine

Adenosine is a potent modulator of inflammation and tissue repair. We have recently reported that activation of adenosine A(2A) receptors promotes collagen synthesis by human dermal fibroblasts and that blockade or deletion of this receptor in mice protects against bleomycin-induced dermal fibrosis, a murine model of scleroderma. Adenosine deaminase (ADA) is the principal catabolic enzyme for adenosine in vivo, and its deficiency leads to the spontaneous development of pulmonary fibrosis in mice. The aim of this study was to characterize further the contributions of endogenous adenosine and adenosine A(2A) receptors to skin fibrosis. Taking advantage of genetically modified ADA-deficient mice, we herein report a direct fibrogenic effect of adenosine on the skin, in which increased collagen deposition is accompanied by increased levels of key mediators of fibrosis, including transforming growth factor beta1, connective tissue growth factor, and interleukin-13. Pharmacological treatment of ADA-deficient mice with the A(2A) receptor antagonist ZM-241385 prevented the development of dermal fibrosis in this model of elevated tissue adenosine, by reducing dermal collagen content and expression of profibrotic cytokines and growth factors. These data confirm a fibrogenic role for adenosine in the skin and reveal A(2A) receptor antagonists as novel therapeutic agents for the modulation of dermal fibrotic disorders.

Adenosine A2A Receptor Activation Prevents Wear Particle-Induced Osteolysis

An adenosine A2A receptor agonist prevents osteolysis caused by polymeric wear particles in mouse calvaria. Agonist Abates Bone Destruction Surgeons perform tens of thousands of total hip replacements per year in the United States. Despite the prevalence of hip implants, they often loosen over time, making the patient return to the surgeon for a revision procedure, typically involving implant removal. Prosthesis loosening has been associated with a breakdown of the implant materials into tiny wear particles, which leads to inflammation in the joint and destruction of the bone (“pitting”) via the small signaling molecule adenosine. Mediero and colleagues have now found that by stimulating the adenosine A2A receptor (A2AR), they can prevent wear particle–induced bone damage and inflammation at the implant site. To simulate wear particle exposure, the authors injected mice with ultrahigh–molecular weight polyethylene (UHMWPE) particles. After 2 weeks, these mouse calvaria showed pitting and increased porosity compared to particle-free mice. Giving the mice CGS21680, an adenosine A2AR agonist, at the same time as the wear particles reduced bone destruction and inflammation. Mechanism was confirmed in A2AR knockout mice, where the agonist had no effect on bone pitting. CGS21680 also inhibited differentiation of human-derived osteoclast precursor cells (from the bone marrow of four patients) into osteoclasts—the cell type that chews up bone. This suggests that the agonist will have a similar effect on human cells and could be used to prevent wear particle–induced damage in people, although only future clinical trials will confirm this. The authors indicate that this agonist could be included in bone cement or as a coating on prostheses to exert its bone-protective effects over time and thus prevent painful revision procedures. Prosthesis loosening, associated with wear particle–induced inflammation and osteoclast-mediated bone destruction, is a common cause for joint implant failure, leading to revision surgery. Adenosine A2A receptors (A2ARs) mediate potent anti-inflammatory effects in many tissues and prevent osteoclast differentiation. We tested the hypothesis that an A2AR agonist could reduce osteoclast-mediated bone resorption in a murine calvaria model of wear particle–induced bone resorption. C57BL/6 and A2AR knockout (A2AR KO) mice received ultrahigh–molecular weight polyethylene particles and were treated daily with either saline or the A2AR agonist CGS21680. After 2 weeks, micro-computed tomography of calvaria demonstrated that CGS21680 reduced particle-induced bone pitting and porosity in a dose-dependent manner, increasing cortical bone and bone volume compared to control mice. Histological examination demonstrated diminished inflammation after treatment with CGS21680. In A2AR KO mice, CGS21680 did not affect osteoclast-mediated bone resorption or inflammation. Levels of bone resorption markers receptor activator of nuclear factor κB (RANK), RANK ligand, cathepsin K, CD163, and osteopontin were reduced after CGS21680 treatment, together with a reduction in osteoclasts. Secretion of interleukin-1β (IL-1β) and tumor necrosis factor–α was significantly decreased, whereas IL-10 was markedly increased in bone by CGS21680. These results in mice suggest that site-specific delivery of an adenosine A2AR agonist could enhance implant survival, delaying or eliminating the need for revision arthroplastic surgery.

Adenosine A2A Receptor Ligation Inhibits Osteoclast Formation

Adenosine is generated in increased concentrations at sites of injury/hypoxia and mediates a variety of physiological and pharmacological effects via G protein-coupled receptors (A(1), A(2A), A(2B), and A(3)). Because all adenosine receptors are expressed on osteoclasts, we determined the role of A(2A) receptor in the regulation of osteoclast differentiation. Differentiation and bone resorption were studied as the macrophage colony-stimulating factor-1-receptor activator of NF-κB ligand formation of multinucleated tartrate-resistant acid phosphatase (TRAP)-positive cells from primary murine bone marrow-derived precursors. A(2A) receptor and osteoclast marker expression levels were studied by RT-PCR. Cytokine secretion was assayed by enzyme-linked immunosorbent assay. In vivo examination of A(2A) knockout (KO)/control bones was determined by TRAP staining, micro-computed tomography, and electron microscopy. The A(2A) receptor agonist, CGS21680, inhibited osteoclast differentiation and function (half maximal inhibitory concentration, 50 nmol/L), increased the percentage of immature osteoclast precursors, and decreased IL-1β and tumor necrosis factor-α secretion, an effect that was reversed by the A(2A) antagonist, ZM241385. Cathepsin K and osteopontin mRNA expression increased in control and ZM241385-pretreated osteoclasts, and this was blocked by CGS21680. Micro-computed tomography of A(2A)KO mouse femurs showed a significantly decreased bone volume/trabecular bone volume ratio, decreased trabecular number, and increased trabecular space. A(2A)KO femurs showed an increased TRAP-positive osteoclast. Electron microscopy in A(2A)KO femurs showed marked osteoclast membrane folding and increased bone resorption. Thus, adenosine, acting via the A(2A) receptor, inhibits macrophage colony-stimulating factor-1-receptor activator of NF-κB ligand-stimulated osteoclast differentiation and may regulate bone turnover under conditions in which adenosine levels are elevated.

Adenosine is required for sustained inflammasome activation via the A2A receptor and the HIF-1α pathway

Inflammasome pathways are important in chronic diseases, but it is not known how the signalling is sustained after initiation. Inflammasome activation is dependent on stimuli such as LPS and ATP that provide two distinct signals resulting in rapid production of IL-1β, with lack of response to repeat stimulation. Here we report that adenosine is a key regulator of inflammasome activity, increasing the duration of the inflammatory response via the A2A receptor. Adenosine does not replace signals provided by stimuli such as LPS or ATP, but sustains inflammasome activity via a cAMP/PKA/CREB/HIF-1α pathway. In the setting of lack of IL-1β responses after previous exposure to LPS, adenosine can supersede this tolerogenic state and drive IL-1β production. These data reveal that inflammasome activity is sustained, after initial activation, by A2A receptor-mediated signalling.

Adenosine regulates bone metabolism via A1, A2A, and A2B receptors in bone marrow cells from normal humans and patients with multiple myeloma

Multiple myeloma (MM) is characterized by osteolytic bone lesions with uncoupled bone remodeling. In this study, we examined the effects of adenosine and its receptors (A1R, A2AR, A2BR, and A3R) on osteoblast and osteoclast differentiation of cells derived from patients with MM and healthy control subjects. Mesenchymal stem cells and bone marrow‐derived mononuclear cells were isolated from bone marrow and differentiated into osteoblasts and osteoclasts, respectively. A1R antagonist rolofylline and A2BR agonist BAY60‐6583 inhibit osteoclast differentiation of cells from patients with MM in a dose‐dependent manner, as shown by TRAP staining (IC50: 10 and ~10 nM, respectively). BAY60‐6583 and dipyridamole, a nucleoside transport inhibitor, stimulate osteoblast differentiation of cells from patients with MM, as measured by ALP activity at d 14 and Alizarin Red staining at d 21 (by 1.57±0.03‐ and 1.71±0.45‐fold, respectively), which can be blocked by A2BR antagonist MRS1754. Consistently, real‐time PCR showed a significant increase of mRNA of osteocalcin and osterix at d 14. The effect of adenosine and its receptors is consistent in patients with MM and healthy subjects, suggesting an intrinsic mechanism that is important in both MM bone metabolism and normal physiology. Furthermore, the effect of dipyridamole on osteoblast differentiation is diminished in both A2BR‐ and CD39‐knockout mice. These results indicate that adenosine receptors may be useful targets for the treatment of MM‐induced bone disease.—He, W., Mazumder, A., Wilder, T., Cronstein. B. N. Adenosine regulates bone metabolism via A1, A2A, and A2B receptors in bone marrow cells from normal humans and patients with multiple myeloma. FASEB J. 27, 3446–3454 (2013). www.fasebj.org

Direct or indirect stimulation of adenosine A2A receptors enhances bone regeneration as well as bone morphogenetic protein-2

Promoting bone regeneration and repair of bone defects is a need that has not been well met to date. We have previously found that adenosine, acting via receptors (A2AR) promotes wound healing and inhibits inflammatory osteolysis and hypothesized that A2AR might be a novel target to promote bone regeneration. Therefore, we determined whether direct A2AR stimulation or increasing endogenous adenosine concentrations via purine transport blockade with dipyridamole regulates bone formation. We determined whether coverage of a 3 mm trephine defect in a mouse skull with a collagen scaffold soaked in saline, bone morphogenetic protein‐2 (BMP‐2; 200 ng), 1 μM CGS21680 (A2AR agonist, EC50 = 160 nM), or 1 μM dipyridamole (EC50 = 32 nM) promoted bone regeneration. Microcomputed tomography examination demonstrated that CGS21680 and dipyridamole markedly enhanced bone regeneration as well as BMP‐2 8 wk after surgery (60 ± 2%, 79 ± 2%, and 75 ± 1% bone regeneration, respectively, vs. 32 ± 2% in control, P < 0.001). Blockade by a selective A2AR antagonist (ZM241385, 1 μM) or deletion of A2AR abrogated the effect of CGS21680 and dipyridamole on bone regeneration. Both CGS21680 and dipyridamole treatment increased alkaline phosphatase‐positive osteoblasts and diminished tartrate resistance acid phosphatase‐positive osteoclasts in the defects. In vivo imaging with a fluorescent dye for new bone formation revealed a strong fluorescent signal in treated animals that was equivalent to BMP‐2. In conclusion, stimulation of A2AR by specific agonists or by increasing endogenous adenosine levels stimulates new bone formation as well as BMP‐2 and represents a novel approach to stimulating bone regeneration.—Mediero, A., Wilder, T., Perez‐Aso, M., Cronstein, B. N. Direct or indirect stimulation of adenosine A2A receptors enhances bone regeneration as well as bone morphogenetic protein‐2. FASEB J. 29, 1577‐1590 (2015). www.fasebj.org

Bone regeneration in critical bone defects using three-dimensionally printed β-tricalcium phosphate/hydroxyapatite scaffolds is enhanced by coating scaffolds with either dipyridamole or BMP-2

Bone defects resulting from trauma or infection need timely and effective treatments to restore damaged bone. Using specialized three-dimensional (3D) printing technology we have created custom 3D scaffolds of hydroxyapatite (HA)/beta-tri-calcium phosphate (β-TCP) to promote bone repair. To further enhance bone regeneration we have coated the scaffolds with dipyridamole, an agent that increases local adenosine levels by blocking cellular uptake of adenosine. Nearly 15% HA:85% β-TCP scaffolds were designed using Robocad software, fabricated using a 3D Robocasting system, and sintered at 1100°C for 4 h. Scaffolds were coated with BMP-2 (200 ng mL-1 ), dypiridamole 100 µM or saline and implanted in C57B6 and adenosine A2A receptor knockout (A2AKO) mice with 3 mm cranial critical bone defects for 2-8 weeks. Dipyridamole release from scaffold was assayed spectrophotometrically. MicroCT and histological analysis were performed. Micro-computed tomography (microCT) showed significant bone formation and remodeling in HA/β-TCP-dipyridamole and HA/β-TCP-BMP-2 scaffolds when compared to scaffolds immersed in vehicle at 2, 4, and 8 weeks (n = 5 per group; p ≤ 0.05, p ≤ 0.05, and p ≤ 0.01, respectively). Histological analysis showed increased bone formation and a trend toward increased remodeling in HA/β-TCP- dipyridamole and HA/β-TCP-BMP-2 scaffolds. Coating scaffolds with dipyridamole did not enhance bone regeneration in A2AKO mice. In conclusion, scaffolds printed with HA/β-TCP promote bone regeneration in critical bone defects and coating these scaffolds with agents that stimulate A2A receptors and growth factors can further enhance bone regeneration. These coated scaffolds may be very useful for treating critical bone defects due to trauma, infection or other causes.

Apremilast, a novel phosphodiesterase 4 (PDE4) inhibitor, regulates inflammation through multiple cAMP downstream effectors

IntroductionThis work was undertaken to delineate intracellular signaling pathways for the PDE4 inhibitor apremilast and to examine interactions between apremilast, methotrexate and adenosine A2A receptors (A2AR).MethodsAfter apremilast and LPS incubation, intracellular cAMP, TNF-α, IL-10, IL-6 and IL-1α were measured in the Raw264.7 monocytic murine cell line. PKA, Epac1/2 (signaling intermediates for cAMP) and A2AR knockdowns were performed by shRNA transfection and interactions with A2AR and A2BR, as well as with methotrexate were tested in vitro and in the murine air pouch model. Statistical differences were determined using one or two-way ANOVA or Student’s t test. The alpha nominal level was set at 0.05 in all cases. A P value of < 0.05 was considered significant.ResultsIn vitro, apremilast increased intracellular cAMP and inhibited TNF-α release (IC50=104nM) and the specific A2AR-agonist CGS21680 (1μM) increased apremilast potency (IC50=25nM). In this cell line, apremilast increased IL-10 production. PKA, Epac1 and Epac2 knockdowns prevented TNF-α inhibition and IL-10 stimulation by apremilast. In the murine air pouch model, both apremilast and MTX significantly inhibited leukocyte infiltration, while apremilast, but not MTX, significantly inhibited TNF-α release. The addition of MTX (1 mg/kg) to apremilast (5 mg/kg) yielded no more inhibition of leukocyte infiltration or TNF-α release than with apremilast alone.ConclusionsThe immunoregulatory effects of apremilast appear to be mediated by cAMP through the downstream effectors PKA, Epac1, and Epac2. A2AR agonism potentiated TNF-α inhibition by apremilast, consistent with the cAMP-elevating effects of that receptor. Because the A2AR is also involved in the anti-inflammatory effects of MTX, the mechanism of action of both drugs involves cAMP-dependent pathways and is therefore partially overlapping in nature.