Adenosine A_2Areceptor activation protects CD4⁺T lymphocytes against activation‐induced cell death

Abstract

Activation-induced cell death (AICD) is initiated by T-cell receptor (TCR) restimulation of already activated and expanded peripheral T cells and is mediated through Fas/Fas ligand (FasL) interactions. Adenosine is a purine nucleoside signaling molecule, and its immunomodulatory effects are mediated by 4 G-protein-coupled receptors: A(1), A(2A), A(2B), and A(3). In this study, we investigated the role of A(2A) receptors in regulating CD4(+) T lymphocyte AICD. Our results showed that the selective A(2A) receptor agonist CGS21680 (EC(50)=15.2-32.6 nM) rescued mouse CD4(+) hybridomas and human Jurkat cells from AICD and that this effect was reversed by the selective A(2A) receptor antagonist ZM241385 (EC(50)=2.3 nM). CGS21680 decreased phosphatidylserine exposure on the membrane, as well as the cleavage of caspase-3, caspase-8 and poly(ADP-ribose) polymerase indicating that A(2A) receptor stimulation blocks the extrinsic apoptotic pathway. In addition, CGS21680 attenuated both Fas and FasL mRNA expression. This decrease in FasL expression was associated with decreased activation of the transcription factor systems NF-kappaB, NF-ATp, early growth response (Egr)-1, and Egr-3. The antiapoptotic effect of A(2A) receptor stimulation was mediated by protein kinase A. Together, these results demonstrate that A(2A) receptor activation suppresses the AICD of peripheral T cells.

Antiproliferative effects of selective adenosine receptor agonists and antagonists on human lymphocytes: evidence for receptor-independent mechanisms

“…The results obtained from real-time PCR analysis showed expression for all four AR subtypes in the investigated cells, consistent with previous reports [22][23][24]39]. The adenosine A 2A receptor mRNA expression level was higher in PBL than in Jurkat T cells and was further upregulated after stimulation of the cells with PHA, as previously reported [40,41]. The levels for A 1 AR mRNA did not change upon cell stimulation, while mRNA for the A 2B and A 3 ARs appeared to be somewhat downregulated upon PHA stimulation.…”

“…It should, however, be kept in mind that mRNA expression levels are not always well correlated with the protein levels expressed on the cell surface. The high expression levels of adenosine A 2A receptors in native PBL and their upregulation after stimulation of the cells have previously been reported [40,41]. These results underscore the importance of this receptor subtype as a mediator of antiinflammatory effects triggering the emergency downregulation of overactive immune cells [43].…”

Hypoxia-Inducible Factor-2α Limits Natural Killer T Cell Cytotoxicity in Renal Ischemia/Reperfusion Injury

“…Moreover, given the fact that tissue inflammation/destruction is always accompanied by prolonged local hypoxia, our results also suggest that hypoxia/HIF-2a/ adora2a axis may serve as a molecular "brake" system to control undue inflammation through its effect on NKT cells. It was reported 27,28 that adora2a activation in T cells could inhibit their FasL expression and cytotoxicity. However, no reports correlated adora2a activation with FasL inhibition in NKT cells.…”

“…27,28 To determine whether adora2a was behind FasL upregulation in HIF-2a 2/2 NKT cells and the role of HIF-2a in adora2a expression, WT and Mx1-HIF-2a 2/2 mice were placed in airtight chambers under normoxic (21% oxygen) or hypoxic conditions (10% oxygen). As shown in Figure 8, A and B, adora2a was constitutively expressed in thymocytes but not splenocytes.…”

Monitoring cell proliferation in vitro with different cellular fluorescent dyes

“…After cell labelling, both CD8+ and CD4+ enriched T-cell populations respond to ConA [6]. Some T cells after activation induce physiological apoptotic process [7]. Although commonly used in diagnoses, the cell tracer CSFE [8][9][10][11] emits fluorescence in the range frequently used for antibody labelling; therefore, it may be inconvenient in some studies.…”