A2B adenosine receptor dampens hypoxia-induced vascular leak

Abstract

IntroductionPrevious studies have implicated extracellular nucleotide metabolites, predominantly adenosine, as triggers of endogenous protective mechanisms in a number of acute injury models. [1][2][3][4][5][6][7] Extracellular adenosine is derived primarily through phosphohydrolysis of adenosine 5Ј-monophosphate (AMP). Ecto-5Ј-nucleotidase (CD73), a ubiquitously expressed ectoenzyme, is the pacemaker of this reaction. 8 Studies on the role of CD73 in tissue-injury showed that cd73 Ϫ/Ϫ mice develop profound vascular leakage and pulmonary edema upon hypoxia exposure. 8 Once generated into the extracellular space, adenosine can signal through any of 4 G-protein coupled adenosine-receptors (ARs: A1AR/A2AAR/A2BAR/A3AR). All of these receptors are expressed on vascular endothelia 9 and have been implicated in tissue-protection in different models of injury. [1][2][3]7,[10][11][12][13][14][15][16][17][18] Changes in vascular barrier function closely coincide with tissue injury of many etiologies, and result in fluid loss, edema, and organ dysfunction. [19][20][21] The predominant barrier (ϳ90%) to movement of macromolecules across a blood vessel wall is presented by the vascular endothelium. 20,22 Under physiologic conditions, macromolecules such as albumin (molecular weight ϳ70 kD) can cross the endothelial monolayer via a paracellular route (eg, by passing between adjacent endothelia) with some contribution of transcellular passage. 23,24 Endothelial barrier function correlates inversely with the size of molecules that can gain entry into tissues and differs between tissues of different origins. Endothelial permeability is highly regulated and may increase markedly upon exposure to inflammatory stimuli (eg, lipopolysaccharide, bacteria, bacterial compounds, prostaglandins, reactive oxygen species, leukotrienes) or adverse conditions such as ischemia or hypoxia. 18,20,[25][26][27][28][29] Given that activation of ARs can lead to an elevation of intracellular cAMP, and that elevated cAMP in endothelia promotes barrier function, 20,30 we considered the possibility of endothelial AR-signaling to regulate vascular permeability. In contrast to previous studies that found tissue protection during hypoxia or inflammation through signaling pathways involving the A2AAR, 1,3,7,31,32 the present studies conclude that the A2BAR is central to the control of vascular leak in hypoxia. Methods Cell cultureHuman microvascular endothelial cells (HMEC)-1 were cultured as described previously. 9,18 For preparation of experimental HMEC-1 monolayers, confluent endothelial cells were seeded at approximately less than 10 5 cells/cm 2 onto either permeable polycarbonate inserts or 100-mm Petri dishes. Endothelial cell purity was assessed by phase microscopic "cobblestone" appearance and uptake of fluorescent acetylated low-density lipoprotein. Stable repression of AR expression by siRNAWith the help of the siRNA Wizard (www.sirnawizard.com; InvivoGen, San Diego, CA) the following primer sequences were chosen within the coding region of the g...

CD73-Dependent Generation of Adenosine and Endothelial Adora2b Signaling Attenuate Diabetic Nephropathy

“…As first step, we induced diabetic nephropathy in previously described Adora2b 2/2 mice. 23,[28][29][30][31][48][49][50][51] Similar to the preceding studies in Cd73 2/2 mice, we observed a more severe degree of diabetic nephropathy in Adora2b 2/2 mice without differences regarding systolic BP and blood glucose levels (Supplemental Figure 4, A and B), but a more severe degree of body weight loss ( Figure 5A), increased kidney weight (Figure 5B), and elevated urine (Figure 5C) and drinking ( Figure 5D) volumes. Determination of the GFR showed a more severe hyperfiltration in Adora2b 2/2 mice compared with diabetic control mice ( Figure 5E).…”

“…We had shown in several previous studies that this compound has pharmacologic effects in wild-type or Adora2a 2/2 mice, but not in Adora2b 2/2 mice. 24,31,50,51 For the purpose of our studies, we administered BAY 60-6583 via osmotic pump (0.3 mg per mouse per hour). Indeed, we observed that continuous BAY 60-6583 treatment had no effect on systolic BP or blood glucose levels (Supplemental Figure 6, A and B) but was associated with an attenuated wasting syndrome after STZ treatment ( Figure 8, A-D).…”

Anti-inflammatory effects of purine nucleosides, adenosine and inosine, in a mouse model of pleurisy: evidence for the role of adenosine A2 receptors

“…In this same study, the pivotal role of the A 2B in attenuating hypoxia-induced increases in vascular leak, mainly in the lungs, was also observed with selective agonists or antagonists of adenosine A 2B receptor in mice or in vitro treatment with siRNA-targeting adenosine A 2B receptor. Furthermore, additional studies suggested a critical role of HIF-1 in the transcriptional induction of the adenosine A 2B receptor during hypoxia [51]. Recently, an interesting study conducted by the same group extended the data described above and revealed an adenosine A 2B receptor-dependent lung protection to ventilation-induced lung injury and LPS-induced lung injury, related to a decrease in pulmonary inflammation, increase in alveolar fluid clearance, reduction in pulmonary edema, and maintenance of capillary-alveolar barrier-a mechanism that involves adenosine A 2B receptor expression with elevation of pulmonary cAMP levels [52].…”

Physiological roles of A1 and A2A adenosine receptors in regulating heart rate, body temperature, and locomotion as revealed using knockout mice and caffeine

“…It is also virtually equipotent with caffeine on most studied isoforms of PDE (45) and less potent than other caffeine metabolites such as theophylline or paraxanthine. The more specific A 2B antagonist PSB1115 (11,12,22,48) had no effect on HR, suggesting that induced PDE inhibition may be important. We also did not observe any changes in Temp following long-term oral caffeine ingestion.…”

“…In the present study, we have examined caffeine effects in mice that lack either A 1 R or A 2A R or both. We also examined effects of the selective A 2B R antagonists, enprofylline (20,39) and 1-propyl-8-psulfophenylxanthine (PSB1115) (11,22,48). The parameters we examined were heart rate (HR), body temperature (Temp), locomotor activity (LA), and oxygen consumption (O 2 C) since they could be examined in awake animals and for prolonged periods of time.…”