Topologically selective islet vulnerability and self-sustained downregulation of markers for β-cell maturity in streptozotocin-induced diabetes

Mouse models of Streptozotocin (STZ) induced diabetes represent the most widely used preclinical diabetes research systems. We applied state of the art optical imaging schemes, spanning from single islet resolution to the whole organ, providing a first longitudinal, 3D-spatial and quantitative account of β-cell mass (BCM) dynamics and islet longevity in STZ-treated mice. We demonstrate that STZ-induced β-cell destruction predominantly affects large islets in the pancreatic core. Further, we show that hyperglycemic STZ-treated mice still harbor a large pool of remaining β-cells but display pancreas-wide downregulation of glucose transporter type 2 (GLUT2). Islet gene expression studies confirmed this downregulation and revealed impaired β-cell maturity. Reversing hyperglycemia by islet transplantation partially restored the expression of markers for islet function, but not BCM. Jointly our results indicate that STZ-induced hyperglycemia results from β-cell dysfunction rather than β-cell ablation and that hyperglycemia in itself sustains a negative feedback loop restraining islet function recovery.

Pharmacologic activation of the mitochondrial phosphoenolpyruvate cycle enhances islet function in vivo

SummaryThe mitochondrial GTP (mtGTP)-dependent phosphoenolpyruvate (PEP) cycle is an anaplerotic-cataplerotic mitochondrial shuttle utilizing mitochondrial PEPCK (PCK2) and pyruvate kinase (PK). PEP cycling stimulates insulin secretion via OxPhos-independent lowering of ADP by PK. We assess in vivo whether islet PCK2 is necessary for glucose sensing and if speeding the PEP cycle via pharmacological PK activators amplifies insulin secretion. Pck2-/- mice had severely impaired insulin secretion during islet perifusion, oral glucose tolerance tests and hyperglycemic clamps. Acute and chronic pharmacologic PK activator therapy improved islet insulin secretion from normal, high-fat diet (HFD) fed, or Zucker diabetic fatty (ZDF) rats, and glucolipotoxic or diabetic humans. A similar improvement in insulin secretion was observed in regular chow and HFD rats in vivo. Insulin secretion and cytosolic Ca2+ during PK activation were dependent on PCK2. These data provide a preclinical rationale for strategies, such as PK activation, that target the PEP cycle to improve glucose homeostasis.HighlightsLoss of mitochondrial phosphoenolpyruvate (PEP) impairs insulin release in vivo.Pyruvate kinase (PK) activators stimulate beta-cells in preclinical diabetes models.PEP cycling in vivo depends on PK and mitochondrial PEPCK (PCK2) for insulin release.Acute and 3-week oral PK activator amplifies insulin release during hyperglycemia.eTOC BlurbAbudukadier et al. show that small molecule pyruvate kinase activation in vivo and in vitro increases insulin secretion in rodent and human models of diabetes. The phosphoenolpyruvate (PEP) cycling mechanism and its amplification are dependent on mitochondrial PEPCK (PCK2).

Changes of Platelet Function and Blood Clotting in Diabetes Mellitus

SummaryWe investigated some aspects of blood clotting and of platelet functions in 48 diabetics (12 affected by preclinical diabetes, 15 by clinical diabetes, 21 with complications of diabetes, peripheral vascular disease, ischaemic heart disease or diabetic nephropathy with or without hypertension) in 35 age matched controls and in 7 prediabetics.Blood clotting has been investigated by gel-chromatography of fibrin soluble complexes, by factor VIIICOAG two stage assay, by factor VIIIAGN electroimmunodiffusion assay and by factor VIIIvWF assay. Platelet functions have been investigated by the determination of circulating platelet aggregates associated with megathrombocytes count, by the malondial- dehyde formation after thrombin and after arachidonic acid. In order to clarify some mechanisms responsible for platelet aggregating plasmatic activity (PAPA) has been investigated by plasmaplatelet cross-matches.Our results indicate early changes of platelet functions in diabetics, already demonstrable in preclinical diabetes. Platelets are hyperaggregable and produce increased amounts of malondialdehyde after stimulation by thrombin and arachidonic acid, thus suggesting an increased activity of the intraplatelet endoperoxide-thromboxane forming metabolic pathway. An increased concentration of fibrin soluble complexes can be shown in clinical and complicated diabetes whereas in preclinical diabetes the fibrogen complexes concentration is within the normal range.Factor VIIIvWF results significantly increased in all groups of diabetics, and even in the subjects with prediabetes. Factor VHICoag and Factor VIIIAGN, besides factor VIIIvWF, were significantly increased in clinical and in complicated diabetes. The increased concentration of factor VIIICOAG and of soluble fibrinogen complexes suggest the existence of a hypercoagulable condition in patients with clinical and above all with complicated diabetes.In these patients a platelet aggregating plasmatic activity can be frequently found. The indication is that platelet hyperaggregation in diabetes is due to various mechanisms. In preclinical diabetes and in some patients with clinical diabetes platelet hyperaggregability is mainly due to a primary platelet hypersensitivity whereas in complicated diabetes, specially when hypercoagulability occurs, platelet hyperaggregation is due to a plasmatic factor related to blood clotting activation.