Adenylyl cyclase 6 is involved in the hyposecretory status of experimental colitis

One of the cardinal symptoms of intestinal inflammation is diarrhea. Acute intestinal inflammation is associated with inhibition of ion absorption and increased secretion, along with fluid leakage due to epithelial injury and changes in permeability. However, in the chronic situation, a downregulation of both absorptive and secretory transport has been reported. We investigated how experimental colitis reduces cAMP levels in intestinal epithelial cells through modulation of adenylyl cyclases (AC). Primary colonic epithelial cells obtained from rats with trinitrobenzenesulfonic acid colitis and non-colitic controls were analyzed for AC expression by RT-qPCR and Western blot, following a preliminary microarray analysis. AC6 and AC5 were found to be expressed in colonocytes, and downregulated by inflammation, with the former exhibiting considerably higher mRNA levels in both cases. To test the hypothesis that inflammatory cytokines may account for this effect, Caco 2 cells were treated with IL-1β, TNF-α, or IFN-γ. All three cytokines inhibited forskolin evoked short-circuit currents in Ussing chambers and lowered intracellular cAMP, but failed to alter AC6 mRNA levels. AC5/AC6 expression was however inhibited in mouse jejunal organoids treated with IFN-γ and TNF-α, but not IL-1β. Gene knockdown of AC6 resulted in a significant decrease of ion secretion in T84 cells. We conclude that the disturbances in ion secretion observed in rat TNBS colitis are associated with low intracellular levels of cAMP in the epithelium, which may be explained in part by the downregulation of AC5/AC6 expression by proinflammatory cytokines.