Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the Eberhard Karls University of Tuebingen (IDM), Tuebingen, Germany.
German Center for Diabetes Research (DZD), Tuebingen, Germany.
Diabetologia. 2017 Nov;60(11):2240-2251. doi: 10.1007/s00125-017-4385-1. Epub 2017 Aug 8.
AIMS/HYPOTHESIS: Obesity-linked ectopic fat accumulation is associated with the development of type 2 diabetes. Whether pancreatic and liver steatosis impairs insulin secretion is controversial. We examined the crosstalk of human pancreatic fat cells with islets and the role of diabetogenic factors, i.e. palmitate and fetuin-A, a hepatokine released from fatty liver.
Human pancreatic resections were immunohistochemically stained for insulin, glucagon, somatostatin and the macrophage/monocyte marker CD68. Pancreatic adipocytes were identified by Oil Red O and adiponectin staining. Primary pancreatic pre-adipocytes and differentiated adipocytes were co-cultured with human islets isolated from organ donors and the metabolic crosstalk between fatty liver and fatty pancreas was mimicked by the addition of palmitate and fetuin-A. Insulin secretion was evaluated by ELISA and RIA. Cytokine expression and secretion were assessed by RT-PCR and multiplex assay, respectively. Subcellular distribution of proteins was examined by confocal microscopy and protein phosphorylation by western blotting.
In human pancreatic parenchyma, highly differentiated adipocytes were detected in the proximity of islets with normal architecture and hormone distribution. Infiltration of adipocytes was associated with an increased number of CD68-positive cells within islets. In isolated primary pancreatic pre-adipocytes and differentiated adipocytes, palmitate and fetuin-A induced IL6, CXCL8 and CCL2 mRNA expression. Cytokine production was toll-like receptor 4 (TLR4)-dependent and further accentuated in pre-adipocytes when co-cultured with islets. In islets, IL6 and CXCL8 mRNA levels were also increased by fetuin-A and palmitate. Only in macrophages within the isolated islets, palmitate and fetuin-A stimulated the production of the cytotoxic cytokine IL-1β. Palmitate, but not fetuin-A, exerted pro-apoptotic effects in islet cells. Instead, fetuin-A impaired glucose-induced insulin secretion in a TLR4-independent, but c-Jun N-terminal kinase- and Ca-dependent, manner.
CONCLUSIONS/INTERPRETATION: These results provide the first evidence that fetuin-A-mediated metabolic crosstalk of fatty liver with islets may contribute to obesity-linked glucose blindness of beta cells, while fatty pancreas may exacerbate local inflammation.
目的/假设：肥胖相关的异位脂肪积累与 2 型糖尿病的发展有关。胰腺和肝脏脂肪变性是否会损害胰岛素分泌仍存在争议。我们研究了人胰腺脂肪细胞与胰岛的串扰以及糖尿病相关因子（即棕榈酸和胎球蛋白 A，一种来自脂肪肝的肝细胞因子）的作用。
用人胰腺切片进行胰岛素、胰高血糖素、生长抑素和巨噬细胞/单核细胞标志物 CD68 的免疫组织化学染色。用油红 O 和脂联素染色鉴定胰腺脂肪细胞。将原代胰腺前脂肪细胞和分化的脂肪细胞与从器官供体中分离的人胰岛共培养，并通过添加棕榈酸和胎球蛋白 A 模拟脂肪肝和胰腺脂肪变性之间的代谢串扰。通过 ELISA 和 RIA 评估胰岛素分泌。通过 RT-PCR 和多重分析分别评估细胞因子的表达和分泌。通过共聚焦显微镜检查蛋白质的亚细胞分布，并通过 Western blot 检查蛋白质磷酸化。
在人胰腺实质中，在结构和激素分布正常的胰岛附近检测到高度分化的脂肪细胞。脂肪细胞的浸润与胰岛内 CD68 阳性细胞数量的增加有关。在分离的原代胰腺前脂肪细胞和分化的脂肪细胞中，棕榈酸和胎球蛋白 A 诱导了 IL6、CXCL8 和 CCL2 的 mRNA 表达。细胞因子的产生依赖于 Toll 样受体 4（TLR4），并且当与胰岛共培养时，在前脂肪细胞中进一步加重。在胰岛中，胎球蛋白 A 和棕榈酸也增加了 IL6 和 CXCL8 的 mRNA 水平。只有在分离的胰岛中的巨噬细胞中，棕榈酸和胎球蛋白 A 才能刺激细胞毒性细胞因子 IL-1β的产生。棕榈酸，但不是胎球蛋白 A，对胰岛细胞具有促凋亡作用。相反，胎球蛋白 A 以 TLR4 非依赖性、但 c-Jun N-末端激酶和 Ca 依赖性的方式损害葡萄糖诱导的胰岛素分泌。
结论/解释：这些结果首次提供了证据，表明脂肪肝与胰岛之间的胎球蛋白 A 介导的代谢串扰可能导致与肥胖相关的β细胞葡萄糖盲，而胰腺脂肪变性可能会加剧局部炎症。
