Opposing Roles of Akt isoforms in intestinal epithelial integrity, inflammation and cell renewal: therapeutic implications or Inflammatory Bowel Disease.

Background Akt1 and Akt2 genetic deficiency in mice have a role in inflammatory bowel disease development, but the mechanism of action is not yet fully understood. Methods Akt (Protein Kinase B) isoform-specific inhibitors were assayed in mouse colon organoids and in a mouse model of colitis induced by dextran sulfate sodium. Mice were monitored in real time for clinical signs including colonoscopy. Inflammation and colon structure were analyzed using immunohistochemistry and PCR. Permeability was assessed through transepithelial electrical resistance assays, and the expression of tight junction protein and βCatenin was analyzed using western blot and immunofluorescence in various epithelial cell lines with specific overexpression or inhibition of Akt isoforms. Results In the mouse model of IBD (Inflammatory Bowel Disease) induced by dextran sulfate sodium, the inhibition of Akt2 strongly ameliorates disease with animals exhibiting healthy-like crypts, tight colon epithelial cells expressing tight junction proteins, and presenting an anti-inflammatory M2 macrophage phenotype. Conversely, treatment with Akt1 inhibitors exacerbated histological damage, with disorganized tight junction proteins, reduced Lgr5+ expression, and promoted a more pro-inflammatory environment, further favoring disease development. Akt1 was expressed in healthy colon whereas Akt2 expression was associated with diseased epithelia. Mouse intestinal organoids treated ex vivo with Akt1 inhibitors exhibited disassembled and disorganized structures that mimic the histological features of IBD. Notably, overexpression of Akt1 or chemical inhibition of Akt2 on intestinal epithelial cells, had similar effects increasing the permeability of the epithelial barrier and affecting the expression and/or intracellular localization of tight junction proteins. In contrast, inhibition of Akt1 or overexpression of Akt2 showed opposite results. Overexpression of Akt1 or inhibition of Akt2 also promoted activation of βCatenin and Lgr5. Conclusions The results suggest that a balance between Akt1 and Akt2 regulates the functionality of the intestinal epithelial barrier, cell renewal and inflammation which affects the development of the disease. Thus, Akt2 inhibition can be considered as a new therapy for inflammatory bowel disease.