Search

Myocardial infarction (MI) activates the epicardium to form epicardial stromal cells (EpiSC) that reside in the epicardial hypoxic microenvironment. Paracrine factors secreted by EpiSC were shown to modulate the injury response of the post-MI heart and improve cardiac function. We have previously reported that the expression of the angiogenic cytokines vascular endothelial growth factor A (VEGFA) and IL-6 is strongly upregulated in EpiSC by adenosine acting via the A 2B receptor (A 2B R). Since tissue hypoxia is well known to be a potent stimulus for the generation of extracellular adenosine, the present study explored the crosstalk of A 2B R activation and hypoxia-hypoxia-inducible factor 1 alpha (HIF-1α) signaling in cultured EpiSC, isolated from rat hearts 5 days after MI. We found substantial nuclear accumulation of HIF-1α after A 2B R activation even in the absence of hypoxia. This normoxic HIF-1α induction was PKC-dependent and involved upregulation of HIF-1α mRNA expression. While the influence of hypoxia on adenosine generation and A 2B R signaling was only minor, hypoxia and A 2B R activation cumulatively increased VEGFA expression. Normoxic A 2B R activation triggered an HIF-1α-associated cell-protective metabolic switch and reduced oxygen consumption. HIF-1α targets and negative regulators PHD2 and PHD3 were only weakly induced by A 2B R signaling, which may result in a sustained HIF-1α activity. The A 2B R-mediated normoxic HIF-1α induction was also observed in cardiac fibroblasts from healthy mouse hearts, suggesting that this mechanism is also functional in other A 2B R-expressing cell types. Altogether, we identified A 2B R-mediated HIF-1α induction as novel aspect in the HIF-1α-adenosine crosstalk, which modulates EpiSC activity and can amplify HIF-1α-mediated cardioprotection., (© 2021 The Authors. The FASEB Journal published by Wiley Periodicals LLC on behalf of Federation of American Societies for Experimental Biology.)

Background: T cells are required for proper healing after myocardial infarction. The mechanism of their beneficial action, however, is unknown. The proinflammatory danger signal ATP, released from damaged cells, is degraded by the ectonucleotidases CD39 and CD73 to the anti-inflammatory mediator adenosine. Here, we investigate the contribution of CD73-derived adenosine produced by T cells to cardiac remodeling after ischemia/reperfusion and define its mechanism of action., Methods: Myocardial ischemia (50 minutes followed by reperfusion) was induced in global CD73 -/- and CD4-CD73 - /- mice. Tissue injury, T-cell purinergic signaling, cytokines, and cardiac function (magnetic resonance tomography at 9.4 T over 4 weeks) were analyzed., Results: Changes in functional parameters of CD4-CD73 -/- mice were identical to those in global CD73 knockouts (KOs). T cells infiltrating the injured heart significantly upregulated at the gene (quantitative polymerase chain reaction) and protein (enzymatic activity) levels critical transporters and enzymes (connexin43, connexin37, pannexin-1, equilibrative nucleoside transporter 1, CD39, CD73, ecto-nucleotide pyrophosphatase/phosphodiesterases 1 and 3, CD157, CD38) for the accelerated release and hydrolysis of ATP, cAMP, AMP, and NAD to adenosine. It is surprising that a lack of CD39 on T cells (from CD39 -/- mice) did not alter ATP hydrolysis and very likely involves pyrophosphatases (ecto-nucleotide pyrophosphatase/phosphodiesterases 1 and 3). Circulating T cells predominantly expressed A 2a receptor (A 2a R) transcripts. After myocardial infarction, A 2b receptor (A 2b R) transcription was induced in both T cells and myeloid cells in the heart. Thus, A 2a R and A 2b R signaling may contribute to myocardial responses after myocardial infarction. In the case of T cells, this was associated with an accelerated secretion of proinflammatory and profibrotic cytokines (interleukin-2, interferon-γ, and interleukin-17) when CD73 was lacking. Cytokine production by T cells from peripheral lymph nodes was inhibited by A 2a R activation (CGS-21680). The A 2b R agonist BAY 60-6583 showed off-target effects. The adenosine receptor agonist NECA inhibited interferon-γ and stimulated interleukin-6 production, each of which was antagonized by a specific A 2b R antagonist (PSB-603)., Conclusions: This work demonstrates that CD73 on T cells plays a crucial role in the cardiac wound healing process after myocardial infarction. The underlying mechanism involves a profound increase in the hydrolysis of ATP/NAD and AMP, resulting primarily from the upregulation of pyrophosphatases and CD73. We also define A 2b R/A 2a R-mediated autacoid feedback inhibition of proinflammatory/profibrotic cytokines by T cell-derived CD73., (© 2017 American Heart Association, Inc.)

Myocardial infarction (MI) activates the epicardium to form epicardial stromal cells (EpiSC) that reside in the epicardial hypoxic microenvironment. Paracrine factors secreted by EpiSC were shown to modulate the injury response of the post‐MI heart and improve cardiac function. We have previously reported that the expression of the angiogenic cytokines vascular endothelial growth factor A (VEGFA) and IL‐6 is strongly upregulated in EpiSC by adenosine acting via the A2B receptor (A2BR). Since tissue hypoxia is well known to be a potent stimulus for the generation of extracellular adenosine, the present study explored the crosstalk of A2BR activation and hypoxia‐hypoxia‐inducible factor 1 alpha (HIF‐1α) signaling in cultured EpiSC, isolated from rat hearts 5 days after MI. We found substantial nuclear accumulation of HIF‐1α after A2BR activation even in the absence of hypoxia. This normoxic HIF‐1α induction was PKC‐dependent and involved upregulation of HIF‐1α mRNA expression. While the influence of hypoxia on adenosine generation and A2BR signaling was only minor, hypoxia and A2BR activation cumulatively increased VEGFA expression. Normoxic A2BR activation triggered an HIF‐1α‐associated cell‐protective metabolic switch and reduced oxygen consumption. HIF‐1α targets and negative regulators PHD2 and PHD3 were only weakly induced by A2BR signaling, which may result in a sustained HIF‐1α activity. The A2BR‐mediated normoxic HIF‐1α induction was also observed in cardiac fibroblasts from healthy mouse hearts, suggesting that this mechanism is also functional in other A2BR‐expressing cell types. Altogether, we identified A2BR‐mediated HIF‐1α induction as novel aspect in the HIF‐1α‐adenosine crosstalk, which modulates EpiSC activity and can amplify HIF‐1α‐mediated cardioprotection. [ABSTRACT FROM AUTHOR]