Type 1 (T1D) and type 2 (T2D) diabetes share pathophysiological characteristics, yet mechanistic links have remained elusive. T1D results from autoimmune destruction of pancreatic beta cells, whereas beta cell failure inT2D is delayed and progressive. Here we find a new genetic component of diabetes susceptibility in T1D non-obese diabetic (NOD) mice, identifying immune-independent beta cell fragility. Genetic variation in Xrcc4 and Glis3 alters the response of NOD beta cells to unfolded protein stress, enhancing the apoptotic and senescent fates. The same transcriptional relationships were observed in human islets, demonstrating the role of beta cell fragility in genetic predisposition to diabetes.

SummaryIn humans, maximal expression of T helper 1 cytokines coincide with the nocturnal nadir of plasma cortisol, whereas T helper 2 cytokine responses are dominant during day-time. The pro-inflammatory cytokine, macrophage migration inhibitory factor counter-regulates glucocorticoid-mediated immune suppression. To determine the relationship between cortisol and macrophage migration inhibitory factor, healthy volunteers had blood drawn hourly for 24 h for measurement of plasma cortisol and basal-and stimulated-macrophage migration inhibitory factor. Similar to cortisol, macrophage migration inhibitory factor peaked during the late morning whereas interferon-γ, tumour necrosis factor-α, interleukin-1 and interleukin-12 demonstrated a nocturnal peak. After oral cortisone, plasma macrophage migration inhibitory factor rose 2-4-fold, whereas the other cytokines decreased. There was no correlation between cortisol during the insulin tolerance test and plasma macrophage migration inhibitory factor. The late morning peak of macrophage migration inhibitory factor, by antagonizing cortisol-mediated pro-inflammatory cytokine suppression may prolong the duration of early morning inflammation. These observations explain the beneficial role of macrophage migration inhibitory factor neutralization in models of inflammatory arthritis.

Fas ligand (FasL), a type 2 membrane protein belonging to the TNF family, plays an important role in the induction of cell death. Ligation of Fas receptors by FasL results in apoptosis of the Fas‐expressing cell. Autoimmune diabetes results from β cell destruction by islet‐reactive T cells, a process that involves β cell apoptosis. This raises the question of whether the FasL‐Fas pathway plays a major role in β cell death. To address this issue it is important to know whether β cells express Fas and/or FasL and, if so, whether induction of these molecules leads to β cell death. In fact, both Fas and FasL have been demonstrated to be expressed by β cells in response to cytokine stimulation, although there remains an argument in the literature as to whether β cells truly express FasL. This is largely because FasL expression has only been demonstrable by immunohistochemistry and not by flow cytometry. Transgenic NOD mice with β cells expressing a FasL transgene develop an accelerated form of diabetes. We show here that β cells from FasL transgenic NOD mice are more susceptible to cytokine‐induced apoptosis than wild‐type β cells, consistent with the hypothesis that if β cells express FasL then Fas‐FasL interaction on the β cell surface is able to mediate β cell self‐death in the absence of T cells. Interventions that block the Fas‐FasL pathway may be useful, therefore, in the prevention or treatment of type 1 diabetes.