Feed-Forward Inhibition of CD73 and Upregulation of Adenosine Deaminase Contribute to the Loss of Adenosine Neuromodulation in Postinflammatory Ileitis

Abstract

Purinergic signalling is remarkably plastic during gastrointestinal inflammation. Thus, selective drugs targeting the “purinome” may be helpful for inflammatory gastrointestinal diseases. The myenteric neuromuscular transmission of healthy individuals is fine-tuned and controlled by adenosine acting on A2A excitatory receptors. Here, we investigated the neuromodulatory role of adenosine in TNBS-inflamed longitudinal muscle-myenteric plexus of the rat ileum. Seven-day postinflammation ileitis lacks adenosine neuromodulation, which may contribute to acceleration of gastrointestinal transit. The loss of adenosine neuromodulation results from deficient accumulation of the nucleoside at the myenteric synapse despite the fact that the increases in ATP release were observed. Disparity between ATP outflow and adenosine deficit in postinflammatory ileitis is ascribed to feed-forward inhibition of ecto-5′-nucleotidase/CD73 by high extracellular ATP and/or ADP. Redistribution of NTPDase2, but not of NTPDase3, from ganglion cell bodies to myenteric nerve terminals leads to preferential ADP accumulation from released ATP, thus contributing to the prolonged inhibition of muscle-bound ecto-5′-nucleotidase/CD73 and to the delay of adenosine formation at the inflamed neuromuscular synapse. On the other hand, depression of endogenous adenosine accumulation may also occur due to enhancement of adenosine deaminase activity. Both membrane-bound and soluble forms of ecto-5′-nucleotidase/CD73 and adenosine deaminase were detected in the inflamed myenteric plexus. These findings provide novel therapeutic targets for inflammatory gut motility disorders.

Involvement of the P2X7 Purinergic Receptor in Colonic Motor Dysfunction Associated with Bowel Inflammation in Rats

“…In line with the concept of an enhancement of extracellular ATP during inflammation [29] , we observed also increased concentrations of ATP in the incubation media of colonic preparations from DNBS-treated rats both under resting conditions and after electrical stimulation. Consistently with the results by Vieira et al [15] , our ATP levels were in the range of picomolar concentration. Even though P2X7 receptors require micromolar concentrations of ATP to be activated, current knowledge suggests that ATP levels found in tissue incubation media do not likely reflect the actual ATP concentrations available for receptor activation in purinergic receptor biophase [30] , [31] .…”

“…The evaluation of ATP release was performed as previously reported by Vieira et al . [15] . Briefly, the experiments were performed in organ baths containing standard Krebs solution at 37°C, bubbled with 95% O 2 +5% CO 2 in the absence or in the presence of apyrase (10 U/ml) [16] .…”

Regulation of the T Cell Response by CD39

“…In this context, CD39 inhibition is likely to be more effective than only targeting CD73 (91), because of its effects not only in arresting the generation of immunosuppressive adenosine, but also in promoting the accumulation of immunostimulatory eATP (92), as well as indirectly leading to the feed forward inhibition of CD73 (93). …”

Impairment of ATP hydrolysis decreases adenosine A1 receptor tonus favoring cholinergic nerve hyperactivity in the obstructed human urinary bladder

“…After equilibrium, the preparations were incubated with 30 μM of ATP or AMP (zero time). Samples of 75 μL were collected from the organ bath at different times up to 45 min for HPLC (with UV detection) analysis (LaChrome Elite; Merck, Germany) of the variation of substrate disappearance and product formation [21,22,26]. The stoichiometry of ATP and AMP conversion into their metabolites was kept unaltered (30 μM).…”