Objective: Post-transplantation diabetes mellitus (PTDM) is a key factor affecting the prognosis of transplant patients, with a prevalence of 10-40%. As a mainstream immunosuppressant, tacrolimus (TAC) is closely associated with the development of PTDM with impaired β-cell function. Our previous study indicated that L-Histidine (L-His), a metabolite of gut microbiota, can improve insulin resistance by inducing inflammation, oxidative stress, and other mechanisms. Therefore, an in-depth Investigation of the glucose metabolism regulatory pathway and molecular mechanism of L-His in the presence of TAC will provide novel insight for unraveling the pathogenesis of PTDM and offer a new therapeutic strategy for transplantation.
Methods: We constructed a TAC-induced islet dysfunction cell model and a diabetic mouse model. When L-His was delivered, we collected the cell, the mouse serum, and tissue samples. Insulin secretion was assessed by ELISA, and the histomorphology of islets by H&E staining. RNA and protein in the samples were extracted, gene expression was detected by real-time PCR, and protein expression levels were analyzed by Western Blot. Meanwhile, immunohistochemistry and immunofluorescence were used to assess the effects of TAC and L-His on pancreatic islets, insulin secretion-related signaling pathways to evaluate their molecular mechanisms.
Results: TAC treatment significantly inhibited the insulin secretion of pancreatic β-cells both in vitro and in vivo (P<0.01) and led to histopathological alterations in the pancreas. However, L-His could alleviate the impaired islet function by stimulating the insulin responses under high glucose. Meanwhile, it could restore the normal morphology of pancreatic islets and significantly enhance insulin secretion (P<0.001). Both Western Blot analysis and real-time PCR showed that TAC induced a significant decrease in the IRS-2 and p-mTOR expression (P≤0.05), while L-His treatment significantly up-regulated IRS-2, p-mTOR, p-Akt, and FOXO1 expression (P≤0.05), suggesting that the IRS-2/Akt/mTOR/FOXO1 pathway is involved in the L-His-stimulated insulin secretion, and counteracts the toxicity of TAC on islets.
Conclusion: L-His may significantly ameliorate pancreatic β-cell dysfunction induced by TAC by regulating the IRS-2/Akt/mTOR/FOXO1 signaling pathway. These findings provide a new potential drug for the treatment of PTDM.