5-Hydroxytryptamine 4 Receptor Agonist Attenuates Diabetic Enteric Neuropathy through Inhibition of the Receptor-Interacting Protein Kinase 3 Pathway

Necroptosis, considered as a form of programmed cell death, contributes to the neural loss. The 5-hydroxytryptamine 4 receptor (5-HT4R) is involved in neurogenesis in the enteric nervous system. However, it is unclear whether the activation of 5-HT4R can alleviate diabetic enteric neuropathy by inhibiting receptor-interacting protein kinase 3 (RIPK3)–mediated necroptosis. This study aimed to explore the beneficial effects of 5-HT4R agonist on enteric neuropathy in a mouse model of diabetes and the mechanisms underlying these effects. Diabetes developed neural loss in the colon of mice. 5-HT4Rs localized in submucosal and myenteric plexuses were confirmed. Administration of 5-HT4R agonist attenuated diabetes-induced colonic hypomotility and neural loss of the colon in mice. Remarkably, RIPK3, phosphorylated RIPK3, and its downstream target mixed lineage kinase domain-like protein (MLKL), two key proteins regulating necroptosis, were significantly up-regulated in the colon of diabetic mice. Treatment with 5-HT4R agonist appeared to inhibit diabetes-induced elevation of RIPK3, phosphorylated RIPK3, and MLKL in the colon of mice. Diabetes-induced up-regulation of MLKL in both the mucosa and the muscularis of the colon was prevented by RIPK3 deletion. Moreover, diabetes-evoked neural loss and delayed colonic transit were significantly inhibited by RIPK3 removal. These findings suggest that activation of 5-HT4Rs could potentially provide a protective effect against diabetic enteric neuropathy by suppressing RIPK3-mediated necroptosis.