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 ... -  《-》

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 ... -  《-》

Adenosine modulates HIF-1{alpha}, VEGF, IL-8, and foam cell formation in a human model of hypoxic foam cells.

Gessi S ，Fogli E ，Sacchetto V ，Merighi S ，Varani K ，Preti D ，Leung E ，Maclennan S ，Borea PA ... -  《-》

Synergistic up-regulation of vascular endothelial growth factor (VEGF) expression in macrophages by adenosine A2A receptor agonists and endotoxin involves transcriptional regulation via the hypoxia response element in the VEGF promoter.

Ramanathan M ，Pinhal-Enfield G ，Hao I ，Leibovich SJ ... -  《MOLECULAR BIOLOGY OF THE CELL》

Caffeine inhibits adenosine-induced accumulation of hypoxia-inducible factor-1alpha, vascular endothelial growth factor, and interleukin-8 expression in hypoxic human colon cancer cells.

Merighi S ，Benini A ，Mirandola P ，Gessi S ，Varani K ，Simioni C ，Leung E ，Maclennan S ，Baraldi PG ，Borea PA ... -  《MOLECULAR PHARMACOLOGY》