Masini M, Bugliani M, Lupi R, del Guerra S, Boggi U, Filipponi F, Marselli L, Masiello P, Marchetti P
Department of Experimental Pathology, University of Pisa, Pisa, Italy.
Diabetologia. 2009 Jun;52(6):1083-6. doi: 10.1007/s00125-009-1347-2. Epub 2009 Apr 15.
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.
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.
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.
目的/假设：β细胞丢失导致2型糖尿病，细胞凋亡增加是其潜在机制。自噬，即受损细胞器和蛋白质的生理性降解，如果发生改变，可能与一种独特的细胞死亡形式有关。我们研究了2型糖尿病患者β细胞自噬的几个特征，并评估了代谢紊乱和药物干预的作用。
从器官捐献者获取胰腺样本，通过胶原酶消化和密度梯度离心制备分离的胰岛。通过电子显微镜研究β细胞形态和形态计量学。通过定量RT-PCR进行基因表达研究。
使用电子显微镜，我们观察到糖尿病样本（2.24±0.53%）中死亡的β细胞比对照样本（0.66±0.52%）更多（p<0.01）。大量液泡过载（提示自噬改变）与2型糖尿病样本中1.18±0.54%的死亡β细胞相关，而对照样本中为0.36±0.26%（p<0.05）。糖尿病β细胞中自噬泡和自噬体的密度体积显著更高。在2型糖尿病胰岛中观察到beclin-1和ATG1（也称为ULK1）的基因表达未改变，而LAMP2、组织蛋白酶B和D的转录减少。将非糖尿病胰岛暴露于升高的NEFA浓度会导致液泡积累显著增加，同时β细胞死亡增加，这与LAMP2表达降低有关。二甲双胍改善了糖尿病β细胞和暴露于NEFA的β细胞中的自噬改变，这一过程与LAMP2表达正常化相关。
结论/解读：人类2型糖尿病中的β细胞有自噬改变的迹象，这可能导致β细胞数量减少。为了在糖尿病患者中保留β细胞数量，可能有必要针对多种细胞死亡途径。
