Autophagy in human type 2 diabetes pancreatic beta cells

Abstract

Aims/hypothesis Beta cell loss contributes to type 2 diabetes, with increased apoptosis representing an underlying mechanism. Autophagy, i.e. the physiological degradation of damaged organelles and proteins, may, if altered, be associated with a distinct form of cell death. We studied several features of autophagy in beta cells from type 2 diabetic patients and assessed the role of metabolic perturbation and pharmacological intervention. Methods Pancreatic samples were obtained from organ donors and isolated islets prepared both by collagenase digestion and density gradient centrifugation. Beta cell morphology and morphometry were studied by electron microscopy. Gene expression studies were performed by quantitative RT-PCR. Results Using electron microscopy, we observed more dead beta cells in diabetic (2.24±0.53%) than control (0.66± 0.52%) samples (p < 0.01). Massive vacuole overload (suggesting altered autophagy) was associated with 1.18± 0.54% dead beta cells in type 2 diabetic samples and with 0.36±0.26% in control samples (p<0.05). Density volume of autophagic vacuoles and autophagosomes was significantly higher in diabetic beta cells. Unchanged gene expression of beclin-1 and ATG1 (also known as ULK1), and reduced transcription of LAMP2 and cathepsin B and D was observed in type 2 diabetic islets. Exposure of nondiabetic islets to increased NEFA concentration led to a marked increase of vacuole accumulation, together with enhanced beta cell death, which was associated with decreased LAMP2 expression. Metformin ameliorated autophagy alterations in diabetic beta cells and beta cells exposed to NEFA, a process associated with normalisation of LAMP2 expression. Conclusions/interpretation Beta cells in human type 2 diabetes have signs of altered autophagy, which may contribute to loss of beta cell mass. To preserve beta cell mass in diabetic patients, it may be necessary to target multiple cell-death pathways.

Autophagy in adipose tissue and the beta cell: implications for obesity and diabetes

“…hyperglycaemia, elevated NEFA and human islet amyloid polypeptide [hIAPP], and inflammation) affects autophagy and its impact on beta cell function also remains controversial. Several studies have shown that NEFA inhibit the expression of lysosome enzymes [78], lysosomal acidification and autophagic flux [81]. Similarly, the amyloidogenic peptide hIAPP has been found to inhibit autophagy [82].…”

“…As an example, Danon disease (OMIM: 300257) results from lysosome-associated membrane protein-2 (LAMP-2) deficiency, which disrupts the maturation of autophagosomes and their fusion with lysosomes, hence impairing autophagy [86]. This results in autophagic vacuole accumulation in various tissues, including liver, pancreas, muscle and heart [87], resembling the findings in human diabetic islets [78]. Without monitoring the autophagic flux, these findings could be erroneously interpreted as stimulation of autophagy.…”

“…In Zucker diabetic fatty rats and in insulinoma cells, hyperglycaemia and oxidative stress led to the accumulation of polyubiquitinated protein aggregates that were degraded by autophagy [77]. Importantly, beta cells of human type 2 diabetic patients showed a massive overload of autophagic vacuoles that associated with beta cell death, without nuclear condensation, which was referred to as autophagy-associated cell death [78]. However, these morphological changes do not imply that beta cell death resulted from 'hyperactive' autophagy.…”

High Glucose Condition Induces Autophagy in Endothelial Progenitor Cells Contributing to Angiogenic Impairment

“…20) The exact role and the regulation of autophagy in diabetes are still controversial. 21) While it is reported that autophagic cell death was enhanced in type-2 diabetes pancreatic beta cells, 22) most studies claimed that impaired autophagy was associated with the accumulation of dysfunctional or damaged cellular components, contributing to cellular dysfunction. 20) In our present study, we reported the increased autophagy in hyper-glycemic environment.…”

Glucagon-Like Peptide-1 Protects Human Islets against Cytokine-Mediated β-Cell Dysfunction and Death: A Proteomic Study of the Pathways Involved

“…29,30 Cells were considered dead on the basis of the following criteria: loss of plasma membrane integrity, fragmentation into discrete bodies, engulfment of cell corpse, or its fragments by an adjacent cell. The presence of marked chromatin condensation or blebs was considered to be a sign of apoptosis.…”