Islet Amyloid in Patients With Diabetes Due to Exocrine Pancreatic Disorders, Type 2 Diabetes, and Nondiabetic Patients.

BACKGROUND: Amyloid deposits are a typical finding in pancreatic islets from patients with type 2 diabetes. Whether this is linked to the pathogenesis of type 2 diabetes is currently unknown. Therefore, we compared the occurrence of islet amyloid in patients with type 2 diabetes, diabetes secondary to pancreatic disorders, and nondiabetic individuals. PATIENTS AND METHODS: Pancreatic tissue from 15 nondiabetic patients, 22 patients with type 2 diabetes, and 11 patients with diabetes due to exocrine pancreatic disorders (chronic pancreatitis, pancreatic carcinoma) were stained for insulin, amyloid, and apoptosis. ß-cell area, amyloid deposits, and ß-cell apoptosis were quantified by morphometric analysis. RESULTS: The proportion of islets containing amyloid deposits was significantly higher in both type 2 diabetes and diabetes due to exocrine pancreatic disorders than in healthy subjects. Islets with both amyloid and apoptosis were observed more frequently in type 2 diabetes and significantly more so in diabetes due to exocrine pancreatic disorders. In both diabetic groups, apoptotic ß-cells were found significantly more frequently in islets with more prominent amyloid deposits. CONCLUSIONS: The occurrence of amyloid deposits in both type 2 diabetes and diabetes secondary to exocrine pancreatic disorders suggests that islet amyloid formation is a common feature of diabetes mellitus of different etiologies and may be associated with a loss of pancreatic ß-cells.

Activation of the HIF1α/PFKFB3 stress response pathway in beta cells in type 1 diabetes.

AIMS/HYPOTHESIS: The conserved hypoxia inducible factor 1 α (HIF1α) injury-response pro-survival pathway has recently been implicated in early beta cell dysfunction but slow beta cell loss in type 2 diabetes. We hypothesised that the unexplained prolonged prediabetes phase in type 1 diabetes may also be, in part, due to activation of the HIF1α signalling pathway. METHODS: RNA sequencing (RNA-Seq) data from human islets with type 1 diabetes or after cytokine exposure in vitro was evaluated for activation of HIF1α targets. This was corroborated by immunostaining human pancreases from individuals with type 1 diabetes for 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3), the key effector of HIF1α-mediated metabolic remodelling, and by western blotting of islets and INS-1 832/13 cells exposed to cytokines implicated in type 1 diabetes. RESULTS: HIF1α signalling is activated (p = 4.5 × 10-9) in islets from individuals with type 1 diabetes, and in human islets exposed in vitro to cytokines implicated in type 1 diabetes (p = 1.1 × 10-14). Expression of PFKFB3 is increased fivefold (p < 0.01) in beta cells in type 1 diabetes and in human and rat islets exposed to cytokines that induced increased lactate production. HIF1α attenuates cytokine-induced cell death in beta cells. CONCLUSIONS/INTERPRETATION: The conserved pro-survival HIF1α-mediated injury-response signalling is activated in beta cells in type 1 diabetes and likely contributes to the relatively slow rate of beta cell loss at the expense of early defective glucose-induced insulin secretion.

IAPP toxicity activates HIF1α/PFKFB3 signaling delaying ß-cell loss at the expense of ß-cell function.

The islet in type 2 diabetes (T2D) is characterized by amyloid deposits derived from islet amyloid polypeptide (IAPP), a protein co-expressed with insulin by ß-cells. In common with amyloidogenic proteins implicated in neurodegeneration, human IAPP (hIAPP) forms membrane permeant toxic oligomers implicated in misfolded protein stress. Here, we establish that hIAPP misfolded protein stress activates HIF1α/PFKFB3 signaling, this increases glycolysis disengaged from oxidative phosphorylation with mitochondrial fragmentation and perinuclear clustering, considered a protective posture against increased cytosolic Ca2+ characteristic of toxic oligomer stress. In contrast to tissues with the capacity to regenerate, ß-cells in adult humans are minimally replicative, and therefore fail to execute the second pro-regenerative phase of the HIF1α/PFKFB3 injury pathway. Instead, ß-cells in T2D remain trapped in the pro-survival first phase of the HIF1α injury repair response with metabolism and the mitochondrial network adapted to slow the rate of cell attrition at the expense of ß-cell function.

Cell cycle-related metabolism and mitochondrial dynamics in a replication-competent pancreatic beta-cell line.

Cell replication is a fundamental attribute of growth and repair in multicellular organisms. Pancreatic beta-cells in adults rarely enter cell cycle, hindering the capacity for regeneration in diabetes. Efforts to drive beta-cells into cell cycle have so far largely focused on regulatory molecules such as cyclins and cyclin-dependent kinases (CDKs). Investigations in cancer biology have uncovered that adaptive changes in metabolism, the mitochondrial network, and cellular Ca2+ are critical for permitting cells to progress through the cell cycle. Here, we investigated these parameters in the replication-competent beta-cell line INS 832/13. Cell cycle synchronization of this line permitted evaluation of cell metabolism, mitochondrial network, and cellular Ca2+ compartmentalization at key cell cycle stages. The mitochondrial network is interconnected and filamentous at G1/S but fragments during the S and G2/M phases, presumably to permit sorting to daughter cells. Pyruvate anaplerosis peaks at G1/S, consistent with generation of biomass for daughter cells, whereas mitochondrial Ca2+ and respiration increase during S and G2/M, consistent with increased energy requirements for DNA and lipid synthesis. This synchronization approach may be of value to investigators performing live cell imaging of Ca2+ or mitochondrial dynamics commonly undertaken in INS cell lines because without synchrony widely disparate data from cell to cell would be expected depending on position within cell cycle. Our findings also offer insight into why replicating beta-cells are relatively nonfunctional secreting insulin in response to glucose. They also provide guidance on metabolic requirements of beta-cells for the transition through the cell cycle that may complement the efforts currently restricted to manipulating cell cycle to drive beta-cells through cell cycle.

Islet inflammation and ductal proliferation may be linked to increased pancreatitis risk in type 2 diabetes.

Pancreatitis is more frequent in type 2 diabetes mellitus (T2DM), although the underlying cause is unknown. We tested the hypothesis that ongoing ß cell stress and apoptosis in T2DM induces ductal tree proliferation, particularly the pancreatic duct gland (PDG) compartment, and thus potentially obstructs exocrine outflow, a well-established cause of pancreatitis. PDG replication was increased 2-fold in human pancreas from individuals with T2DM, and was associated with increased pancreatic intraepithelial neoplasia (PanIN), lesions associated with pancreatic inflammation and with the potential to obstruct pancreatic outflow. Increased PDG replication in the prediabetic human-IAPP-transgenic (HIP) rat model of T2DM was concordant with increased ß cell stress but preceded metabolic derangement. Moreover, the most abundantly expressed chemokines released by the islets in response to ß cell stress in T2DM, CXCL1, -4, and -10, induced proliferation in human pancreatic ductal epithelium. Also, the diabetes medications reported as potential modifiers for the risk of pancreatitis in T2DM modulated PDG proliferation accordingly. We conclude that chronic stimulation and proliferation of the PDG compartment in response to islet inflammation in T2DM is a potentially novel mechanism that serves as a link to the increased risk for pancreatitis in T2DM and may potentially be modified by currently available diabetes therapy.

Endogenous hyperinsulinaemia in insulinoma patients is not associated with changes in beta-cell area and turnover in the tumor-adjacent pancreas.

INTRODUCTION: Insulin therapy has been suggested to preserve beta-cell mass in patients with diabetes through the mechanisms of beta-cell rest as well as direct effects on beta-cell proliferation. However, data about the effects of hyperinsulinism on beta-cell mass and turnover in humans are sparse. PATIENTS AND METHODS: Pancreatic tissue specimens from five patients with pancreatic insulinomas and ten non-diabetic control subjects were examined. Pancreatic sections were stained for insulin, Ki67 (replication) and TUNEL (apoptosis), and quantitative morphometric analyses were performed. RESULTS: Fractional beta-cell area was 1.11%±0.67% in the tumor-free pancreatic tissue of the insulinoma patients and 0.78%±0.26% in the control group (p=0.19). There also were no differences in islet size (p=0.62) or beta-cell nuclear diameter (p=0.20). Beta-cell replication and apoptosis were infrequently detected, without any measurable differences between the groups. There were also no differences in percentage of duct cells expressing insulin (p=0.47), a surrogate marker for islet neogenesis. CONCLUSIONS: Beta-cell area and turnover are not significantly altered in the proximity of intra-pancreatic insulinomas. Future in vivo studies, ideally employing larger animal models, are warranted to further evaluate the impact of exogenous insulin on beta-cell turnover.