Apoptosis in autoimmune diabetes: the fate of beta-cells in the cleft between life and death

Partners in Crime: Beta-Cells and Autoimmune Responses Complicit in Type 1 Diabetes Pathogenesis

Type 1 diabetes (T1D) is an autoimmune disease characterized by autoreactive T cell-mediated destruction of insulin-producing pancreatic beta-cells. Loss of beta-cells leads to insulin insufficiency and hyperglycemia, with patients eventually requiring lifelong insulin therapy to maintain normal glycemic control. Since T1D has been historically defined as a disease of immune system dysregulation, there has been little focus on the state and response of beta-cells and how they may also contribute to their own demise. Major hurdles to identifying a cure for T1D include a limited understanding of disease etiology and how functional and transcriptional beta-cell heterogeneity may be involved in disease progression. Recent studies indicate that the beta-cell response is not simply a passive aspect of T1D pathogenesis, but rather an interplay between the beta-cell and the immune system actively contributing to disease. Here, we comprehensively review the current literature describing beta-cell vulnerability, heterogeneity, and contributions to pathophysiology of T1D, how these responses are influenced by autoimmunity, and describe pathways that can potentially be exploited to delay T1D.

Neutralization Versus Reinforcement of Proinflammatory Cytokines to Arrest Autoimmunity in Type 1 Diabetes

As physiological pathways of intercellular communication produced by all cells, cytokines are involved in the pathogenesis of inflammatory insulitis as well as pivotal mediators of immune homeostasis. Proinflammatory cytokines including interleukins, interferons, transforming growth factor-β, tumor necrosis factor-α, and nitric oxide promote destructive insulitis in type 1 diabetes through amplification of the autoimmune reaction, direct toxicity to β-cells, and sensitization of islets to apoptosis. The concept that neutralization of cytokines may be of therapeutic benefit has been tested in few clinical studies, which fell short of inducing sustained remission or achieving disease arrest. Therapeutic failure is explained by the redundant activities of individual cytokines and their combinations, which are rather dispensable in the process of destructive insulitis because other cytolytic pathways efficiently compensate their deficiency. Proinflammatory cytokines are less redundant in regulation of the inflammatory reaction, displaying protective effects through restriction of effector cell activity, reinforcement of suppressor cell function, and participation in islet recovery from injury. Our analysis suggests that the role of cytokines in immune homeostasis overrides their contribution to β-cell death and may be used as potent immunomodulatory agents for therapeutic purposes rather than neutralized.

IGF2: an endocrine hormone to improve islet transplant survival

In the week following pancreatic islet transplantation, up to 50% of transplanted islets are lost due to apoptotic cell death triggered by hypoxic and pro-inflammatory cytokine-mediated cell stress. Thus, therapeutic approaches designed to protect islet cells from apoptosis could significantly improve islet transplant success. IGF2 is an anti-apoptotic endocrine protein that inhibits apoptotic cell death through the mitochondrial (intrinsic pathway) or via antagonising activation of pro-inflammatory cytokine signalling (extrinsic pathway), in doing so IGF2 has emerged as a promising therapeutic molecule to improve islet survival in the immediate post-transplant period. The development of novel biomaterials coated with IGF2 is a promising strategy to achieve this. This review examines the mechanisms mediating islet cell apoptosis in the peri- and post-transplant period and aims to identify the utility of IGF2 to promote islet survival and enhance long-term insulin independence rates within the setting of clinical islet transplantation.

Hyperglycemia, oxidative and nitrosative stress affect antiviral, inflammatory and apoptotic signaling of cultured thymocytes

A high prevalence of various infectious diseases is reported in diabetic patients, which may suggest impaired innate immunity against different pathogen-associated molecular patterns. This study investigated the effects of hyperglycemia, oxidative stress (H(2)O(2)), nitric oxide (NO) and peroxynitrite (ONOO(-)) on the modulation of antiviral (MDA-5, IRF-3 and phospho-IRF-3), inflammatory (NF-kappaB) and pro/anti-apoptotic molecules (Bax and Bcl-2) in BALB/c mice thymocytes. Each of the experimental conditions, except the weakest NO concentration, resulted in down-regulation of MDA-5, IRF-3 and phospho-IRF-3. In contrast, each of the experimental conditions elicited up-regulation of NF-kappaB, Bcl-2 and Bax. These results suggest that hyperglycemia, oxidative and nitrosative stress may contribute to the reduced immunity of the host by altering the MDA-5/IRF-3/phosphoIRF-3 axis, as well as contributing to the mechanisms of inflammatory reaction via increased NF-kappaB, and to augmented turnover rate of thymocyte cells via Bcl2/Bax up-regulation.

Prevention and management of hyperglycemia after pancreas transplantation

PURPOSE OF REVIEW

Pancreas transplantation is considered the optimal therapy for patients with insulin-dependent diabetes. Successful pancreas transplantation achieves euglycemia and allows freedom from insulin therapy. Long-term allograft success may be limited by the development of impaired glucose metabolism. The objectives of the present review are to summarize the possible reasons for endocrine pancreatic dysfunction and to focus on its prevention and management and emphasize the role of immunosuppression.

RECENT FINDINGS

The diabetogenic effects of current immunosuppressive agents have been well established. Regimens without corticosteroids and calcineurin-inhibitor minimization or avoidance have been promoted. Recent studies have revisited the pathogenesis of type I and type II diabetes and demonstrated common pathways, including apoptosis induction, for the exhaustion and destruction of the pancreatic islets.

SUMMARY

The immunosuppressive regimens in pancreatic transplantation should be designed and appropriately modified according to the graft immunological and metabolic conditions. New molecules that are able to preserve islet function and maintain optimal insulin secretion should be considered for pancreas transplant recipients.