The pancreatic beta cell: an intricate relation between anatomical structure, the signalling mechanism of glucose-induced insulin secretion, the low antioxidative defence, the high vulnerability and sensitivity to diabetic stress

Abstract

AbstractThe biosynthesis of insulin takes place in the insulin-producing beta cells that are organized in the form of islets of Langerhans together with a few other islet cell types in the pancreas organ. The signal for glucose-induced insulin secretion is generated in two pathways in the mitochondrial metabolism of the pancreatic beta cells. These pathways are also known as the triggering pathway and the amplifying pathway. Glucokinase, the low-affinity glucose-phosphorylating enzyme in beta cell glycolysis acts as the signal-generating enzyme in this process. ATP ultimately generated is the crucial second messenger in this process. Insulin-producing pancreatic beta cells are badly protected against oxidative stress resulting in a particular vulnerability of this islet cell type due to low expression of H2O2-inactivating enzymes in various subcellular locations, specifically in the cytosol, mitochondria, peroxisomes and endoplasmic reticulum. This is in contrast to the glucagon-producing alpha cells and other islet cell types in the islets that are well equipped with these H2O2-inactivating enzymes. On the other hand the membranes of the pancreatic beta cells are well protected against lipid peroxidation and ferroptosis through high level expression of glutathione peroxidase 4 (GPx4) and this again is at variance from the situation in the non-beta cells of the islets with a low expression level of GPx4. The weak antioxidative defence equipment of the pancreatic beta cells, in particular in states of disease, is very dangerous because the resulting particular vulnerability endangers the functionality of the beta cells, making people prone to the development of a diabetic metabolic state.