METTL3-overexpressing IPCs enhance graft survival, attenuate islet apoptosis in diabetic mice via IDO1-Kynurenine.

Cell replacement therapy using insulin-producing cells (IPCs) derived from human amniotic epithelial stem cells (hAECs) offers a promising avenue for treating diabetes, particularly type 1. However, significant challenges persist, including poor graft survival and immune rejection, which hinder clinical translation. Current standard-of-care often fails to restore endogenous beta-cell function or prevent immune-mediated destruction. Understanding mechanisms that enhance IPC viability and function post-transplantation is crucial. Previous work indicated that METTL3 overexpression improves IPC induction and maturation, but its impact on in vivo graft efficacy and underlying mechanisms remained unclear.

Researchers transplanted either WT-IPCs or Mettl3-OE-IPCs (METTL3-overexpressing IPCs) beneath the renal capsule of streptozotocin-induced type 1 diabetic mice. Graft survival and function were assessed using blood glucose, serum C-peptide levels, in vivo GFP fluorescence imaging, and histology. Untargeted metabolomics of intestinal contents identified differential metabolites. Associations among METTL3, IDO1, and kynurenine (Kyn) were examined in vitro via Western blot, RT-qPCR, immunofluorescence, and ELISA. A four-group rescue experiment (WT-IPCs, WT-IPCs+Kyn, Mettl3-OE-IPCs, Mettl3-OE-IPCs+1-MT) further evaluated Kyn's causal contribution. Endogenous islet apoptosis and local immune infiltration were assessed by immunofluorescence and immunohistochemistry.

Transplantation of Mettl3-OE-IPCs significantly improved glycemic control and prolonged graft survival compared to the WT-IPCs group. Endogenous islets in the Mettl3-OE-IPCs group exhibited elevated insulin expression, reduced BAX, and increased Bcl-2, indicating attenuated apoptosis. Serum C-peptide levels were also higher in this group. Untargeted metabolomics identified Kynurenine (Kyn) as a significantly enriched metabolite in the intestinal contents of the Mettl3-OE-IPCs group, with serum Kyn levels markedly elevated (p < 0.0001). In vitro, METTL3 overexpression was associated with IDO1 upregulation at both mRNA and protein levels, leading to increased Kyn secretion. > Rescue experiments demonstrated that Kyn supplementation conferred comparable glycemic benefits and islet apoptosis suppression to the Mettl3-OE-IPCs group, while IDO1 inhibition with 1-MT substantially attenuated these advantages, confirming Kyn's causal role.