METTL3‐Activated IDO1‐Kynurenine Pathway in Insulin‐Producing Cells Enhances Graft Survival and Attenuates Endogenous Islet Apoptosis in Diabetic Mice
TL;DR
It is shown that METTL3 overexpression is associated with IDO1 upregulation and elevated systemic Kyn levels, which suggest that the METTL3‐IDO1‐Kyn pathway may be a potential target for improving cell replacement therapy for diabetes.
Abstract
Insulin‐producing cells (IPCs) derived from human amniotic epithelial stem cells (hAECs) represent a promising strategy for cell replacement therapy for diabetes. However, poor graft survival and immune rejection remain major obstacles to clinical application. Our previous work established that METTL3 overexpression enhances IPCs induction efficiency and maturation, yet whether it improves in vivo transplantation efficacy and the associated mechanisms remain unexplored. WT‐IPCs and Mettl3‐OE‐IPCs were transplanted beneath the renal capsule of streptozotocin‐induced type 1 diabetic mice. Blood glucose, serum C‐peptide, in vivo GFP fluorescence imaging, and histology were used to assess graft survival. Untargeted metabolomics of intestinal contents identified differential metabolites. Western blot, RT‐qPCR, immunofluorescence, and ELISA examined associations among METTL3, IDO1, and kynurenine (Kyn) in vitro. A four‐group rescue experiment (WT‐IPCs, WT‐IPCs+Kyn, Mettl3‐OE‐IPCs, Mettl3‐OE‐IPCs+1‐MT) evaluated the causal contribution of Kyn. Immunofluorescence and immunohistochemistry assessed endogenous islet apoptosis and local immune infiltration. Mettl3‐OE‐IPCs transplantation significantly improved glycemic control and prolonged graft survival compared with the WT‐IPCs group. Endogenous islets in the Mettl3‐OE‐IPCs group showed elevated insulin expression, reduced BAX, and increased Bcl‐2. Serum C‐peptide levels were also higher in this group. Untargeted metabolomics identified Kyn as the significantly enriched metabolite in the intestinal contents of the Mettl3‐OE‐IPCs group. Serum Kyn levels were markedly elevated (p < 0.0001). In vitro, METTL3 overexpression was associated with IDO1 upregulation at mRNA and protein levels and increased Kyn secretion. Rescue experiments showed that Kyn supplementation conferred comparable glycemic benefits and islet apoptosis suppression to the Mettl3‐OE‐IPCs group; IDO1 inhibition with 1‐MT substantially attenuated these advantages (IPGTT AUC, p < 0.0001). Immune profiling revealed splenic CD25+CD4+ T cell expansion and reduced transplant side renal CD8+ T cell infiltration in Kyn‐treated and the Mettl3‐OE‐IPCs group; both effects were abrogated by 1‐MT. This study shows that METTL3 overexpression is associated with IDO1 upregulation and elevated systemic Kyn levels. These changes are accompanied by improved graft survival and reduced endogenous islet apoptosis. Rescue experiments show that Kyn is both sufficient and necessary for these effects. These findings suggest that the METTL3‐IDO1‐Kyn pathway may be a potential target for improving cell replacement therapy for diabetes.