The Stimulatory Adenosine Receptor ADORA2B Regulates Serotonin (5-HT) Synthesis and Release in Oxygen-Depleted EC Cells in Inflammatory Bowel Disease

Abstract

ObjectiveWe recently demonstrated that hypoxia, a key feature of IBD, increases enterochromaffin (EC) cell 5-HT secretion, which is also physiologically regulated by the ADORA2B mechanoreceptor. Since hypoxia is associated with increased extracellular adenosine, we wanted to examine whether this nucleotide amplifies HIF-1α-mediated 5-HT secretion.DesignThe effects of hypoxia were studied on IBD mucosa, isolated IBD-EC cells, isolated normal EC cells and the EC cell tumor derived cell line KRJ-1. Hypoxia (0.5% O2) was compared to NECA (adenosine agonist), MRS1754 (ADORA2B receptor antagonist) and SCH442146 (ADORA2A antagonist) on HIF signaling and 5-HT secretion. Antisense approaches were used to mechanistically evaluate EC cells in vitro. PCR and western blot were used to analyze transcript and protein levels of HIF-1α signaling and neuroendocrine cell function. An animal model of colitis was evaluated to confirm hypoxia:adenosine signaling in vivo.ResultsHIF-1α is upregulated in IBD mucosa and IBD-EC cells, the majority (∼90%) of which express an activated phenotype in situ. Hypoxia stimulated 5-HT release maximally at 30 mins, an effect amplified by NECA and selectively inhibited by MRS1754, through phosphorylation of TPH-1 and activation of VMAT-1. Transient transfection with Renilla luciferase under hypoxia transcriptional response element (HRE) control identified that ADORA2B activated HIF-1α signaling under hypoxic conditions. Additional signaling pathways associated with hypoxia:adenosine included MAP kinase and CREB. Antisense approaches mechanistically confirmed that ADORA2B signaling was linked to these pathways and 5-HT release under hypoxic conditions. Hypoxia:adenosine activation which could be reversed by 5′-ASA treatment was confirmed in a TNBS-model.ConclusionHypoxia induced 5-HT synthesis and secretion is amplified by ADORA2B signaling via MAPK/CREB and TPH-1 activation. Targeting ADORA2s may decrease EC cell 5-HT production and secretion in IBD.

Adenosine A2b receptor promotes progression of human oral cancer

“…Our data showed that the immunoexpression of ADORA2B was correlated with HIF-1α expression in primary OSCCs (Additional file 1 ). HIF-1α is a common transcription factor induced by ADORA2B activation in inflammatory bowel disease and urologic diseases [ 37 , 38 ]. Based on these findings, we observed the expression status of HIF-1α in the ADORA2B knockdown cells.…”

Serotonin—Its Synthesis and Roles in the Healthy and the Critically Ill

“…The opposite is true for increased SERT in platelet membranes, resulting in higher reuptake and reduced serotonin levels in the bloodstream [ 29 ]. Altered motility causing hypoxia in patients with IBD was shown to induce serotonin synthesis by stimulating adenosine receptors, leading to diarrhea [ 30 ].…”

Potential for Developing Purinergic Drugs for Gastrointestinal Diseases

“…Activation of A 2B AR via MAPK/CREB and TPH-1 signaling amplifies the effect of hypoxia in human EC cells. 129 Overall, effects of adenosine in IBD are very complex, and much more work needs to be done, but targeting this pathway in EC cells is of potential interest as a therapeutic target in IBD.…”