Activation of 5-Hydroxytryptamine 4 Receptor Improves Colonic Barrier Function by Triggering Mucin 2 Production in a Mouse Model of Type 1 Diabetes.

Diabetes leads to intestinal barrier dysfunction. 5-Hydroxytryptamine 4 receptor (5-HTR) is distributed in the colonic mucosa, but little is known about the role of its activation in diabetes-evoked colonic barrier dysfunction. This study investigates whether activation of 5-HTRs on goblet cells (GCs) protects the colon from commensal bacterial translocation in diabetic mice. Expression of 5-HTR detected inside the colonic epithelium by RNAscope in situ hybridization was further observed within the mucin 2 (MUC2)-immunoreactive GCs. In diabetic mice, neither 5-HTR transcription nor protein levels were altered compared with those in nondiabetic mice. Bacterial translocation was characterized by 16S rRNA RNAscope in situ hybridization and manifested in both crypts and lamina propria of the colon in diabetic mice. Mucin production and MUC2 expression were significantly decreased in diabetic mice. Furthermore, the loss of mitochondrial cristae of GCs and the down-regulation of mitofilin, the core protein maintaining mitochondrial homeostasis, were observed in diabetic mice. Long-term treatment with 5-HTR agonist in diabetic mice not only prevented bacterial penetration of the whole colonic mucosa but also promoted mucin production and MUC2 expression. Markedly, 5-HTR agonist also restored the mitochondrial cristae of GCs and up-regulated mitofilin. However, co-administration of 5-HTR antagonist abolished the effects of 5-HTR agonist on diabetic mice. These findings indicate that 5-HTR in colonic mucosa is an effective target for the treatment of diabetes-induced colonic mucous barrier dysfunction.