A(1) and A(3) adenosine receptors inhibit LPS-induced hypoxia-inducible factor-1 accumulation in murine astrocytes.

Adenosine (Ado) exerts neuroprotective and anti-inflammatory functions by acting through four receptor subtypes A1, A2A, A2B and A3. Astrocytes are one of its targets in the central nervous system. Hypoxia-inducible factor-1 (HIF-1), a master regulator of oxygen homeostasis, is induced after hypoxia, ischemia and inflammation and plays an important role in brain injury. HIF-1 is expressed by astrocytes, however the regulatory role played by Ado on HIF-1α modulation induced by inflammatory and hypoxic conditions has not been investigated. Primary murine astrocytes were activated with lipopolysaccharide (LPS) with or without Ado, Ado receptor agonists, antagonists and receptor silencing, before exposure to normoxia or hypoxia. HIF-1α accumulation and downstream genes regulation were determined. Ado inhibited LPS-increased HIF-1α accumulation under both normoxic and hypoxic conditions, through activation of A1 and A3 receptors. In cells incubated with the blockers of p44/42 MAPK and Akt, LPS-induced HIF-1α accumulation was significantly decreased in normoxia and hypoxia, suggesting the involvement of p44/42 MAPK and Akt in this effect and Ado inhibited kinases phosphorylation. A series of angiogenesis and metabolism related genes were modulated by hypoxia in an HIF-1 dependent way, but not further increased by LPS, with the exception of GLUT-1 and hexochinase II that were elevated by LPS only in normoxia and inhibited by Ado receptors. Instead, genes involved in inflammation, like inducible nitric-oxide synthase (iNOS) and A2B receptors, were increased by LPS in normoxia, strongly stimulated by LPS in concert with hypoxia and inhibited by Ado, through A1 and A3 receptor subtypes. In conclusion A1 and A3 receptors reduce the LPS-mediated HIF-1α accumulation in murine astrocytes, resulting in a downregulation of genes involved in inflammation and hypoxic injury, like iNOS and A2B receptors, in both normoxic and hypoxic conditions.

Gessi S ，Merighi S ，Stefanelli A ，Fazzi D ，Varani K ，Borea PA ... -  《-》

The role of the adenosinergic system in lung fibrosis.

Adenosine (ADO) is a retaliatory metabolite that is expressed in conditions of injury or stress. During these conditions ATP is released at the extracellular level and is metabolized to adenosine. For this reason, adenosine is defined as a "danger signal" for cells and organs, in addition to its important role as homeostatic regulator. Its physiological functions are mediated through interaction with four specific transmembrane receptors called ADORA1, ADORA2A, ADORA2B and ADORA3. In the lungs of mice and humans all four adenosine receptors are expressed with different roles, having pro- and anti-inflammatory roles, determining bronchoconstriction and regulating lung inflammation and airway remodeling. Adenosine receptors can also promote differentiation of lung fibroblasts into myofibroblasts, typical of the fibrotic event. This last function suggests a potential involvement of adenosine in the fibrotic lung disease processes, which are characterized by different degrees of inflammation and fibrosis. Idiopathic pulmonary fibrosis (IPF) is the pathology with the highest degree of fibrosis and is of unknown etiology and burdened by lack of effective treatments in humans.

Della Latta V ，Cabiati M ，Rocchiccioli S ，Del Ry S ，Morales MA ... -  《-》

A(2a) and a(2b) adenosine receptors affect HIF-1α signaling in activated primary microglial cells.

Microglia are central nervous system (CNS)-resident immune cells, that play a crucial role in neuroinflammation. Hypoxia-inducible factor-1 (HIF-1), the main transcription factor of hypoxia-inducible genes, is also involved in the immune response, being regulated in normoxia by inflammatory mediators. Adenosine is an ubiquitous nucleoside that has an influence on many immune properties of microglia through interaction with four receptor subtypes. The aim of this study was to investigate whether adenosine may affect microglia functions by acting on HIF-1α modulation. Primary murine microglia were activated with lipopolysaccharide (LPS) with or without adenosine, adenosine receptor agonists and antagonists and HIF-1α accumulation and downstream genes regulation were determined. Adenosine increased LPS-induced HIF-1α accumulation leading to an increase in HIF-1α target genes involved in cell metabolism [glucose transporter-1 (GLUT-1)] and pathogens killing [inducible nitric-oxide synthase (iNOS)] but did not induce HIF-1α dependent genes related to angiogenesis [vascular endothelial growth factor (VEGF)] and inflammation [tumor necrosis factor-α (TNF-α)]. The stimulatory effect of adenosine on HIF-1α and its target genes was essentially exerted by activation of A2A through p44/42 and A2B subtypes via p38 mitogen-activated protein kinases (MAPKs) and Akt phosphorylation. Furthermore the nucleoside raised VEGF and decreased TNF-α levels, by activating A2B subtypes. In conclusion adenosine increases GLUT-1 and iNOS gene expression in a HIF-1α-dependent way, through A2A and A2B receptors, suggesting their role in the regulation of microglial cells function following injury. However, inhibition of TNF-α adds an important anti-inflammatory effect only for the A2B subtype. GLIA 2015;63:1933-1952.

Merighi S ，Borea PA ，Stefanelli A ，Bencivenni S ，Castillo CA ，Varani K ，Gessi S ... -  《-》

Functional expression of adenosine A2A and A3 receptors in the mouse dendritic cell line XS-106.

Dickenson JM ，Reeder S ，Rees B ，Alexander S ，Kendall D ... -  《EUROPEAN JOURNAL OF PHARMACOLOGY》

Suppression of inflammation response by a novel A₃ adenosine receptor agonist thio-Cl-IB-MECA through inhibition of Akt and NF-κB signaling.

Adenosine, a purine nucleoside, is released from metabolically active cells into extracellular space and plays an important role in various pathophysiological processes. Adenosine regulates many biological responses including inflammation by the interaction with their receptors such as A₁, A(2A), A(2B), and A₃. Especially, A₃ adenosine receptor (A₃AR) is considered to be expressed in macrophage cells. To the end, A₃AR agonists have been reported to have an anti-inflammatory activity. In our continuous efforts to develop new anti-inflammatory agents, we found a novel adenosine analog, 2-chloro-N⁶-(3-iodobenzyl)-4'-thioadenosine-5'-N-methyluronamide (thio-Cl-IB-MECA), was a potent human A₃AR agonist. The study was designed to investigate whether thio-Cl-IB-MECA has an anti-inflammatory potential in mouse macrophage RAW 264.7 cells and mouse sepsis model in vivo. Thio-Cl-IB-MECA exhibited an effective anti-inflammatory activity. The expression of pro-inflammatory biomarkers including inducible nitric oxide synthase (iNOS), interleukin-1β (IL-1β), and tumor necrosis factor (TNF-α) was suppressed by the treatment of thio-Cl-IB-MECA in the protein and mRNA levels in lipopolysaccharide (LPS)-stimulated mouse macrophage RAW 264.7 cells. Further examination revealed that thio-Cl-IB-MECA inhibited LPS-induced phosphatidylinositol 3-kinase (PI3 kinase)/Akt activation, NF-kB binding activity, and β-catenin expression. In addition, in in vivo LPS-induced mouse endotoxemia model, thio-Cl-IB-MECA exerted the increase of survival rate compared to vehicle-treated mouse. The analysis of the protein levels of iNOS, IL-1β, and TNF-α was also suppressed by the compound-treated groups in lung tissues. These results suggest that thio-Cl-IB-MECA might have an anti-inflammatory activity through the inhibition of pro-inflammatory cytokine expression by modulating PI3K/Akt and NF-κB signaling pathways.

Lee HS ，Chung HJ ，Lee HW ，Jeong LS ，Lee SK ... -  《-》