BackgroundAdenosine levels rise during inflammation and modulate inflammatory responses by engaging with four different G protein-coupled receptors. It is suggested that adenosine exhibits pro-inflammatory effects through its A1 receptor (A1R), and anti-inflammatory effects through A2A receptor (A2AR). Therefore, understanding of the mechanisms that govern adenosine receptor regulation may advance treatment of various inflammatory disorders. We previously reported that peak A1R expression during leukocyte recruitment, is followed by a peak in A2AR during inflammation resolution.Principal FindingsHere, we examined whether A1R activation sequentially induces A2AR expression and by this reverses inflammation. The effect of adenosine on A1R mediated A2AR expression was examined in peritoneal macrophages (PMΦ) and primary peritoneal mesothelial cells (PMC) in vitro. Induction of A2AR was inhibited by pertussis toxin (PTX) and partly dependent on A2AR stimulation. Administration of A1R agonists to healthy mice reduced A1R expression and induced A2AR production in PMC. Mice that were preconditioned with A1R agonists 24 hours before E. coli inoculation exhibited decreased TNFα and IL-6 sera levels and reduced leukocytes recruitment. Preconditioning was blocked by pretreatment with A1R antagonist, as well as, or by late treatment with A2AR antagonist, and was absent in A2AR−/− mice.ConclusionsOur data suggest that preconditioning by an A1R-agonist promotes the resolution of inflammation by inducing the production of A2AR. Future implications may include early treatment during inflammatory disorders or pretreatment before anticipated high risk inflammatory events, such as invasive surgery and organ transplantation.
Loss of function of the peritoneal membrane is associated with peritonitis. Adenosine levels in sites of inflammation were shown to increase and exhibit immunoregulatory effects. Our aim was to elucidate the regulatory role of adenosine during peritonitis and to test the involvement of peritoneal mesothelial cells (PMC) in adenosine regulation. In a mice model of Escherichia coli peritonitis, the adenosine A(2A) receptor (A(2A)R) agonist (CGS21680) prevented leukocyte recruitment and reduced tumor necrosis factor alpha (TNF-alpha) and interleukin-6 (IL-6) levels. Peritonitis induced the elevation of adenosine with a peak at 24 h. Analysis of adenosine receptor levels on peritoneum showed that A(1) receptor (A(1)R) protein levels peak at 12 h after inoculation and then return to baseline at 24 h, whereas high affinity A(2A)R protein levels peak at 24 h concomitantly with the peak of adenosine concentration. Low affinity A(2B) receptor (A(2B)R) levels elevated slowly, remaining elevated up to 48 h. In human PMC (HPMC), the early cytokines, IL-1-alpha, and TNF-alpha upregulated the A(2B) and A(2A) receptors. However, interferon-gamma (IFN-gamma) upregulated the A(2B)R and decreased A(2A)R levels. Treatment with the A(2A)R agonist reduced IL-1-dependent IL-6 secretion from HPMC. In conclusion, the kinetics of adenosine receptors suggest that at early stage of peritonitis, the A(1)R dominates, and later its dominance is replaced by the G stimulatory (Gs) protein-coupled A(2A)R that suppresses inflammation. Early proinflammatory cytokines are an inducer of the A(2A)R and this receptor reduces their production and leukocyte recruitment. Future treatment with adenosine agonists should be considered for attenuating the damage to mesothelium during the course of acute peritonitis.
Death-associated protein kinase (DAPk) is a tumor suppressor thought to inhibit cancer by promoting apoptosis and autophagy. Because cancer progression is linked to inflammation, we investigated the in vivo functions of DAPk in lung responses to various acute and chronic inflammatory stimuli. Lungs of DAPk knockout (KO) mice secreted higher concentrations of IL-6 and keratinocyte chemoattractant (or chemokine [C-X-C motif] ligand 1) in response to transient intranasal administrations of the Toll-like receptor-4 (TLR4) agonist LPS. In addition, DAPk-null macrophages and neutrophils were hyperresponsive to ex vivo stimulation with LPS. DAPk-null neutrophils were also hyperresponsive to activation via Fc receptor and Toll-like receptor-3, indicating that the suppressive functions of this kinase are not restricted to TLR4 pathways. Even after the reconstitution of DAPk-null lungs with DAPk-expressing leukocytes by transplanting wild-type (WT) bone marrow into lethally irradiated DAPk KO mice, the chimeric mice remained hypersensitive to both acute and chronic LPS challenges, as well as to tobacco smoke exposure. DAPk-null lungs reconstituted with WT leukocytes exhibited elevated neutrophil content and augmented cytokine secretion in the bronchoalveolar space, as well as enhanced epithelial cell injury in response to both acute and chronic inflammatory conditions. These results suggest that DAPk attenuates a variety of inflammatory responses, both in lung leukocytes and in lung epithelial cells. The DAPk-mediated suppression of lung inflammation and airway injury may contribute to the tumor-suppressor functions of this kinase in epithelial carcinogenesis.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.