Inflammatory Cytokines Rewire the Proinsulin Interaction Network in Human Islets

Differentiation of Pancreatic Beta Cells: Dual Acting of Inflammatory Factors

In the past decades, scientists have made outstanding efforts to treat diabetes. However, diabetes treatment is still far from satisfactory due to the complex nature of the disease and the challenges encountered in resolving it. Inflammatory factors are key regulators of the immune system's response to pathological insults, organ neogenesis, rejuvenation of novel cells to replace injured cells and overwhelming disease conditions. Currently, the available treatments for type 1 diabetes include daily insulin injection, pancreatic beta cell or tissue transplantation, and gene therapy. Cell therapy, exploiting differentiation, and reprogramming various types of cells to generate pancreatic insulin-producing cells are novel approaches for the treatment of type 1 diabetes. A better understanding of the inflammatory pathways offers valuable and improved therapeutic options to provide more advanced and better treatments for diabetes. In this review, we investigated different types of inflammatory factors that participate in the pathogenesis of type 1 diabetes, their possible dual impacts on the differentiation, reprogramming, and fusion of other stem cell lines into pancreatic insulin-producing beta cells, and the possibility of applying these factors to improve the treatment of this disease.

NOD mice have distinct metabolic and immunologic profiles when compared with genetically similar MHC-matched ICR mice

Nonobese diabetic (NOD) mice are the most commonly used rodent model to study mechanisms relevant to the autoimmunity and immunology of type 1 diabetes. Although many different strains of mice have been used as controls for studies comparing nondiabetic lines to the NOD strain, we hypothesized that the parental strain that gave rise to the NOD line might be one of the best options. Therefore, we compared female ICR and NOD mice, which are matched at key major histocompatibility complex (MHC) loci, to understand their metabolic and immunologic similarities and differences. Several novel observations emerged: 1) NOD mice have greater circulating proinsulin when compared with ICR mice. 2) NOD mice display CD3+ and IBA1+ cell infiltration into and near pancreatic islets before hyperglycemia. 3) NOD mice show increased expression of the Il1b and Cxcl11 genes in islets when compared with islets from age-matched ICR mice. 4) NOD mice have a greater abundance of STAT1 and ICAM-1 protein in islets when compared with ICR mice. These data show that ICR mice, which are genetically similar to NOD mice, do not retain the same immunologic outcomes. Thus, ICR mice are an excellent choice as a genetically similar and MHC-matched control for NOD mice in studies designed to understand mechanisms relevant to autoimmune-mediated diabetes onset as well as novel therapeutic interventions.NEW & NOTEWORTHY Nonobese diabetic (NOD) mice have more proinsulin in circulation and STAT1 protein in islets compared with the major histocompatibility complex (MHC)-matched ICR line. NOD mice also display greater expression of cytokines and chemokines in pancreatic islets consistent with immune cell infiltration before hyperglycemia when compared with age-matched ICR mice. Thus, ICR mice represent an excellent control for autoimmunity and inflammation studies using the NOD line of mice.

Unveiling nanoscale optical signatures of cytokine-induced β-cell dysfunction

Pro-inflammatory cytokines contribute to β-cell failure in both Type-1 and Type-2 Diabetes. Data collected so far allowed to dissect the genomic, transcriptomic, proteomic and biochemical landscape underlying cytokine-induced β-cell progression through dysfunction. Yet, no report thus far complemented such molecular information with the direct optical nanoscopy of the β-cell subcellular environment. Here we tackle this issue in Insulinoma 1E (INS-1E) β-cells by label-free fluorescence lifetime imaging microscopy (FLIM) and fluorescence-based super resolution imaging by expansion microscopy (ExM). It is found that 24-h exposure to IL-1β and IFN-γ is associated with a neat modification of the FLIM signature of cell autofluorescence due to the increase of either enzyme-bound NAD(P)H molecules and of oxidized lipid species. At the same time, ExM-based direct imaging unveils neat alteration of mitochondrial morphology (i.e. ~ 80% increase of mitochondrial circularity), marked degranulation (i.e. ~ 40% loss of insulin granules, with mis-localization of the surviving pool), appearance of F-actin-positive membrane blebs and an hitherto unknown extensive fragmentation of the microtubules network (e.g. ~ 37% reduction in the number of branches). Reported observations provide an optical-microscopy framework to interpret the amount of molecular information collected so far on β-cell dysfunction and pave the way to future ex-vivo and in-vivo investigations.

Synchronized proinsulin trafficking reveals delayed Golgi export accompanies β-cell secretory dysfunction in rodent models of hyperglycemia

The pancreatic islet β-cell's preference for release of newly synthesized insulin requires careful coordination of insulin exocytosis with sufficient insulin granule production to ensure that insulin stores exceed peripheral demands for glucose homeostasis. Thus, the cellular mechanisms regulating insulin granule production are critical to maintaining β-cell function. In this report, we utilized the synchronous protein trafficking system, RUSH, in primary β-cells to evaluate proinsulin transit through the secretory pathway leading to insulin granule formation. We demonstrate that the trafficking, processing, and secretion of the proinsulin RUSH reporter, proCpepRUSH, are consistent with current models of insulin maturation and release. Using both a rodent dietary and genetic model of hyperglycemia and β-cell dysfunction, we show that proinsulin trafficking is impeded at the Golgi and coincides with the decreased appearance of nascent insulin granules at the plasma membrane. Ultrastructural analysis of β-cells from diabetic leptin receptor deficient mice revealed gross morphological changes in Golgi structure, including shortened and swollen cisternae, and partial Golgi vesiculation, which are consistent with defects in secretory protein export. Collectively, this work highlights the utility of the proCpepRUSH reporter in studying proinsulin trafficking dynamics and suggests that altered Golgi export function contributes to β-cell secretory defects in the pathogenesis of Type 2 diabetes.