Impact of Disrupting Adenosine A3 Receptors (A3-/-AR) on Colonic Motility or Progression of Colitis in the Mouse

Background: Pharmacological studies suggest that adenosine A(3)AR influences motility and colitis. Functional A(3)(-/-)AR knockout mice were used to prove whether A(3)AR activation is involved in modulating either motility or colitis. Methods: A(3)AR was probed by polymerase chain reaction (PCR) genotyping, Western blot, and immunochemistry. Motility was assessed in vivo by artificial bead-expulsion, stool-frequency, and FITC-dextran transit. Colitis was induced with dextran sodium sulfate (DSS) in A(3)(-/-)AR or wildtype (WT) age- and sex-matched controls. Progression of colitis was evaluated by histopathology, changes in myeloperoxidase (MPO), colon length, CD4(+)-cells, weight-loss, diarrhea, and the guaiac test. Results: Goat anti-hu-A(3) antiserum identified a 66 kDa immunogenic band in colon. A(3)AR-immunoreactivity is expressed in SYN+-nerve varicosities, s-100(+)-glia, and crypt cells, but not 5-HT+ (EC), CD4(+) (T), tryptase(+) (MC), or muscle cells. A(3)AR immunoreactivity in myenteric ganglia of distal colon >> proximal colon by a ratio of 2:1. Intestinal transit and bead expulsion were accelerated in A(3)(-/-)AR mice compared to WT; stool retention was lower by 40%-60% and stool frequency by 67%. DSS downregulated A(3)AR in epithelia. DSS histopathology scores indicated less mucosal damage in A(3)(-/-)AR mice than WT. A(3)(-/-)AR phenotype protected against DSS-induced weight loss, neutrophil (MPO), or CD4(+)-T cell infiltration, colon shortening, change in splenic weight, diarrhea, or occult-fecal blood. Conclusions: Functional disruption of A(3)AR in A(3)(-/-)AR mice alters intestinal motility. We postulate that ongoing release of adenosine and activation of presynaptic-inhibitory A(3)AR can slow down transit and inhibit the defecation reflex. A(3)AR may be involved in gliotransmission. In separate studies, A(3)(-/-)AR protects against DSS colitis, consistent with a novel hypothesis that A(3)AR activation contributes to development of colitis.