Autophagy in human type 2 diabetes pancreatic beta cells

Department of Experimental Pathology, University of Pisa, Pisa, Italy.
Diabetologia (Impact Factor: 6.67). 04/2009; 52(6):1083-6. DOI: 10.1007/s00125-009-1347-2
Source: PubMed


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.
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.
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 non-diabetic 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.
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.

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Available from: Marco Bugliani, Apr 23, 2014
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    • "In mammalian animal models of diabetes and in human diabetic patients, upregulation of Pc1/3 (Pcsk1) expression and GLP-1 production in α cells was observed together with increased glucagon secretion (Nie et al., 2000; Thyssen et al., 2006; Marchetti et al., 2012). Furthermore, GLP-1 production in α cells is associated with β cell compensation and regeneration in response to β cell injury (Kilimnik et al., 2010; Hansen et al., 2011; Donath and Burcelin, 2013). "
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    ABSTRACT: The interconversion of cell lineages via transdifferentiation is an adaptive mode of tissue regeneration and an appealing therapeutic target. However, its clinical exploitation is contingent upon the discovery of contextual regulators of cell fate acquisition and maintenance. In murine models of diabetes, glucagon-secreting alpha cells transdifferentiate into insulin-secreting beta cells following targeted beta cell depletion, regenerating the form and function of the pancreatic islet. However, the molecular triggers of this mode of regeneration are unknown. Here, using lineage-tracing assays in a transgenic zebrafish model of beta cell ablation, we demonstrate conserved plasticity of alpha cells during islet regeneration. In addition, we show that glucagon expression is upregulated after injury. Through gene knockdown and rescue approaches, we also find that peptides derived from the glucagon gene are necessary for alpha-to-beta cell fate switching. Importantly, whereas beta cell neogenesis was stimulated by glucose, alpha-to-beta cell conversion was not, suggesting that transdifferentiation is not mediated by glucagon/GLP-1 control of hepatic glucose production. Overall, this study supports the hypothesis that alpha cells are an endogenous reservoir of potential new beta cells. It further reveals that glucagon plays an important role in maintaining endocrine cell homeostasis through feedback mechanisms that govern cell fate stability. © 2015. Published by The Company of Biologists Ltd.
    Development 04/2015; 142(8):1407-17. DOI:10.1242/dev.117911 · 6.46 Impact Factor
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    • "Volume densities were calculated according to the formula: volume density = Pi/Pt, where Pi is the number of points within the subcellular component and Pt is the total number of points; values are expressed as ml/100 ml tissue (ml%). By electron microscopy analysis, morphological evidence of marked chromatin condensation and/or the presence of blebs were considered as signs of apoptosis (Masini et al., 2009). "
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    ABSTRACT: Pancreatic α cells are exposed to metabolic stress during the evolution of type 2 diabetes (T2D), but it remains unclear whether this affects their survival. We used electron microscopy to search for markers of apoptosis and endoplasmic reticulum (ER) stress in α and β cells in islets from T2D or non-diabetic individuals. There was a significant increase in apoptotic β cells (from 0.4% in control to 6.0% in T2D), but no α cell apoptosis. We observed, however, similar ER stress in α and β cells from T2D patients. Human islets or fluorescence-activated cell sorting (FACS)-purified rat β and α cells exposed in vitro to the saturated free fatty acid palmitate showed a similar response as the T2D islets, i.e. both cell types showed signs of ER stress but only β cells progressed to apoptosis. Mechanistic experiments indicate that this α cell resistance to palmitate-induced apoptosis is explained, at least in part, by abundant expression of the anti-apoptotic protein Bcl2l1 (also known as Bcl-xL).
    03/2015; 62(5). DOI:10.1016/j.ebiom.2015.03.012
    • "It should be noted that most of the obese, insulin-resistant humans do not become diabetic, implying additional mechanisms for the pathogenesis of type 2 diabetes mellitus. Indeed, dysfunction of the beta-cells with regard to insulin secretion and biosynthesis and a reduction of beta-cell mass were demonstrated in patients suffering from type 2 diabetes or impaired glucose tolerance (Butler et al., 2003; Kahn et al., 2009; Marchetti et al., 2012; Weir and Bonner-Weir, 2013) (Figure 1). Hence, the targets of an optimal anti-diabetic therapy are the attenuation of the inflammation of metabolic tissues and insulin resistance and the restoration or at least the amelioration of beta-cell function and mass to ultimately prevent the development of micro-and macrovascular complications. "
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