Transcriptionally mature and immature β-cells co-exist within the adult islet. How such diversity contributes to insulin release remains poorly understood. Here we show that subtle differences in β-cell maturity, defined using PDX1 and MAFA expression, contribute to islet operation. Functional mapping of rodent and human islets containing proportionally more PDX1HIGH and MAFAHIGH β-cells reveals defects in metabolism, ionic fluxes and insulin secretion. At the transcriptomic level, the presence of increased numbers of PDX1HIGH and MAFAHIGH β-cells leads to dysregulation of gene pathways involved in metabolic processes. Using a chemogenetic disruption strategy, differences in PDX1 and MAFA expression are shown to depend on islet Ca2+ signaling patterns. During metabolic stress, islet function can be restored by redressing the balance between PDX1 and MAFA levels across the β-cell population. Thus, preserving heterogeneity in PDX1 and MAFA expression, and more widely in β-cell maturity, might be important for the maintenance of islet function.

Transcriptionally mature and immature β-cells co-exist within the adult islet. How such diversity contributes to insulin release remains poorly understood. Here we show that differences in β-cell maturity, defined using PDX1 and MAFA expression, are required for proper islet operation. Functional mapping of rodent and human islets containing proportionally more mature β-cells revealed defects in metabolism, ionic fluxes and insulin secretion. At the transcriptomic level, the presence of increased numbers of mature β-cells led to dysregulation of gene pathways involved in metabolic processes. Using a chemogenetic disruption strategy, the islet signalling network was found to contribute to differences in maturity across β-cells. During metabolic stress, islet function could be restored by redressing the balance between immature and mature β-cells. Thus, preserving a balance between immature and mature β-cells might be important for islet engineering efforts and more broadly the treatment of type 1 and type 2 diabetes.

Xenografts of organ cultured fetal pig pancreas in prediabetic NOD mice can survive for prolonged periods (>20 weeks) in recipients treated with anti‐T cell monoclonal antibodies (MAb) directed against host CD4 and CD3 cell surface molecules. Anti‐CD4 MAb treatment alone is only partly effective and xenograft rejection occurs over a period of many weeks. In diabetic recipients, by contrast, recurrence of autoimmune disease in isografts is rapid (<28 days) despite similar depletion of CD4+ve T cells. In spontaneously diabetic NOD mice immunosuppressed with anti‐CD3 and anti‐CD4 MAbs xenograft function occurs and the recipient's blood glucose levels fall into the pig range. Organ cultured fetal pig pancreas transplanted into cynomolgus monkeys is rapidly but not hyperacutely rejected when azathioprine‐cyclosporin A‐prednisolone immunosuppression is used. Anti‐T‐cell MAb treatment is now being studied in this primate model.

Atrogin-1 and MuRF1 are highly expressed in multiple conditions of skeletal muscle atrophy. The PI3K/Akt/FoxO signaling pathway is well known to regulate Atrogin-1 and MuRF1 gene expressions. However, Akt activation also activates the mammalian target of rapamycin complex 1 (mTORC1) which induces skeletal muscle hypertrophy. Whether mTORC1-dependent signaling has a role in regulating Atrogin-1 and/or MuRF1 gene and protein expression is currently unclear. In this study, we showed that activation of insulin-mediated Akt signaling suppresses both Atrogin-1 and MuRF1 protein contents and that inhibition of Akt increases both Atrogin-1 and MuRF1 protein contents in C2C12 myotubes. Interestingly, inhibition of mTORC1 using a specific mTORC1 inhibitor, rapamycin, increased Atrogin-1, but not MuRF1, protein content. Furthermore, activation of AMP-activated protein kinase (AMPK), a negative regulator of the mTORC1 signaling pathway, also showed distinct time-dependent changes between Atrogin-1 and MuRF1 protein contents, suggesting differential regulatory mechanisms between Atrogin-1 and MuRF1 protein content. To further explore the downstream of mTORC1 signaling, we employed a specific S6K1 inhibitor, PF-4708671. We found that Atrogin-1 protein content was dose-dependently increased with PF-4708671 treatment, whereas MuRF1 protein content was decreased at 50 μM of PF-4708671 treatment. However, MuRF1 protein content was unexpectedly increased when treated with PF-4708671 for a longer period. Overall, our results indicate that Atrogin-1 and MuRF1 protein contents are regulated by different mechanisms, the downstream of Akt, and that Atrogin-1 protein content can be regulated by rapamycin-sensitive mTOR-S6K1 dependent signaling pathway.