Insulin secretion in pancreatic beta-cells is regulated by cortical complexes that are enriched at the sites of adhesion to extracellular matrix facing the vasculature. Many components of these... Show moreInsulin secretion in pancreatic beta-cells is regulated by cortical complexes that are enriched at the sites of adhesion to extracellular matrix facing the vasculature. Many components of these complexes, including bassoon, RIM, ELKS and liprins, are shared with neuronal synapses. Here, we show that insulin secretion sites also contain the non-neuronal proteins LL5 beta (also known as PHLDB2) and KANK1, which, in migrating cells, organize exocytotic machinery in the vicinity of integrin-based adhesions. Depletion of LL5 beta or focal adhesion disassembly triggered by myosin II inhibition perturbed the clustering of secretory complexes and attenuated the first wave of insulin release. Although previous analyses in vitro and in neurons have suggested that secretory machinery might assemble through liquid-liquid phase separation, analysis of endogenously labeled ELKS in pancreatic islets indicated that its dynamics is inconsistent with such a scenario. Instead, fluorescence recovery after photobleaching and single-molecule imaging showed that ELKS turnover is driven by binding and unbinding to low-mobility scaffolds. Both the scaffold movements and ELKS exchangewere stimulated by glucose treatment. Our findings help to explain how integrin-based adhesions control spatial organization of glucose-stimulated insulin release. Show less
Extensive literature links the dopamine receptor D2 to insulin resistance and diabetes mellitus type 2. However, many aspects of the functional relationship remain unclear. In this thesis we... Show moreExtensive literature links the dopamine receptor D2 to insulin resistance and diabetes mellitus type 2. However, many aspects of the functional relationship remain unclear. In this thesis we focused on unraveling the characteristics of the interplay between dopamine D2 receptors and glucose metabolism as well as understanding the underlying mechanism(s). We evaluated the impact of DRD2 agonistic and antagonistic drugs on glucose and insulin metabolism in healthy volunteers, mice and INS-1E cells and we assessed dopaminergic parameters under different metabolic conditions. Our results show that altered dopaminergic parameters associated with obesity are due to mechanisms other than diet composition. But, changes in dopaminergic signaling may set the stage for metabolic corollaries of high fat feeding and may be involved in the beneficial impact of calorie restriction. We also demonstrate that inhibiting DRD2 activation may affect glucose homeostasis independent of body weight alterations. The underlying mechanisms include a reduction in physical activity and a direct effect on insulin sensitivity. In addition we provide evidence that inhibition of insulin secretion may, paradoxically, underlie the beneficial impact of DRD2 activation on glucose metabolism. We believe these findings may offer new ideas for strategies to prevent of treat diabetes mellitus type 2. Show less
