Aims/hypothesis

Normal cellular prion protein (PrP^C) is a conserved mammalian glycoprotein found on the outer plasma membrane leaflet through a glycophosphatidylinositol anchor. Although PrP^C is expressed by a wide range of tissues throughout the body, the complete repertoire of its functions has not been fully determined. The misfolded pathogenic isoform PrP^Sc (the scrapie form of PrP) is a causative agent of neurodegenerative prion diseases. The aim of this study is to evaluate PrP^C localisation, expression and trafficking in pancreases from organ donors with and without type 1 diabetes and to infer PrP^C function through studies on interacting protein partners.

Methods

In order to evaluate localisation and trafficking of PrP^C in the human pancreas, 12 non-diabetic, 12 type 1 diabetic and 12 autoantibody-positive organ donor tissue samples were analysed using immunofluorescence analysis. Furthermore, total RNA was isolated from 29 non-diabetic, 29 type 1 diabetic and 24 autoantibody-positive donors to estimate PrP^C expression in the human pancreas. Additionally, we performed PrP^C-specific immunoblot analysis on total pancreatic protein from non-diabetic and type 1 diabetic organ donors to test whether changes in PrP^C mRNA levels leads to a concomitant increase in PrP^C protein levels in human pancreases.

Results

In non-diabetic and type 1 diabetic pancreases (the latter displaying both insulin-positive [INS(+)] and -negative [INS(−)] islets), we found PrP^C in islets co-registering with beta cells in all INS(+) islets and, strikingly, unexpected activation of PrP^C in alpha cells within diabetic INS(−) islets. We found PrP^C localised to the plasma membrane and endoplasmic reticulum (ER) but not the Golgi, defining two cellular pools and an unconventional protein trafficking mechanism bypassing the Golgi. We demonstrate PrP^C co-registration with established protein partners, neural cell adhesion molecule 1 (NCAM1) and stress-inducible phosphoprotein 1 (STI1; encoded by STIP1) on the plasma membrane and ER, respectively, linking PrP^C function with cyto-protection, signalling, differentiation and morphogenesis. We demonstrate that both PRNP (encoding PrP^C) and STIP1 gene expression are dramatically altered in type 1 diabetic and autoantibody-positive pancreases.

Conclusions/interpretation

As the first study to address PrP^C expression in non-diabetic and type 1 diabetic human pancreas, we provide new insights for PrP^C in the pathogenesis of type 1 diabetes. We evaluated the cell-type specific expression of PrP^C in the human pancreas and discovered possible connections with potential interacting proteins that we speculate might address mechanisms relevant to the role of PrP^C in the human pancreas.

Graphical abstract

中文翻译：

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在 1 型糖尿病中改变朊病毒蛋白 PrPC 的细胞定位和表达，以及非常规的蛋白质运输

目标/假设

正常细胞朊病毒蛋白 (PrP ^C ) 是通过糖磷脂酰肌醇锚在外质膜小叶上发现的一种保守的哺乳动物糖蛋白。尽管 PrP ^C在全身的多种组织中都有表达，但其功能的完整组成部分尚未完全确定。错误折叠的致病异构体 PrP ^Sc（朊病毒的搔痒症形式）是神经退行性朊病毒疾病的病原体。本研究的目的是评估 PrP ^C在患有和未患有 1 型糖尿病的器官捐赠者的胰腺中的定位、表达和运输，并通过对相互作用的蛋白质伙伴的研究来推断 PrP ^{C的功能。}

方法

为了评估人类胰腺中 PrP ^C的定位和运输，使用免疫荧光分析对 12 个非糖尿病患者、12 个 1 型糖尿病患者和 12 个自身抗体阳性器官供体组织样本进行了分析。此外，从 29 名非糖尿病患者、29 名 1 型糖尿病患者和 24 名自身抗体阳性供体中分离出总 RNA，以估计人胰腺中 PrP ^C的表达。此外，我们对来自非糖尿病和 1 型糖尿病器官供体的总胰腺蛋白进行了 PrP ^{C特异性免疫印迹分析，以测试 PrP C} mRNA 水平的变化是否导致人类胰腺中 PrP ^{C蛋白水平的伴随增加。}

结果

在非糖尿病和 1 型糖尿病胰腺（后者显示胰岛素阳性 [INS(+)] 和阴性 [INS(-)] 胰岛）中，我们发现胰岛中的 PrP ^C与所有 INS 中的 β 细胞共同注册(+) 胰岛，令人惊讶的是，糖尿病 INS(-) 胰岛内 α 细胞中 PrP ^{C的意外激活。}我们发现 PrP ^C定位于质膜和内质网 (ER) 而不是高尔基体，定义了两个细胞池和绕过高尔基体的非常规蛋白质运输机制。我们证明了 PrP ^C与已建立的蛋白质伙伴、神经细胞粘附分子 1 (NCAM1) 和应激诱导磷蛋白 1 (STI1; 由STIP1编码) 分别在质膜和 ER 上，将 PrP ^C功能与细胞保护、信号传导、分化和形态发生联系起来。我们证明PRNP（编码 PrP ^C）和STIP1基因表达在 1 型糖尿病和自身抗体阳性胰腺中发生显着改变。

结论/解释

作为第一个解决 PrP ^C在非糖尿病和 1 型糖尿病人胰腺中表达的研究，我们为 PrP ^C在 1 型糖尿病发病机制中的作用提供了新的见解。^{我们评估了人类胰腺中 PrP C}的细胞类型特异性表达，并发现了与潜在相互作用蛋白的可能联系，我们推测这些蛋白可能涉及与人类胰腺中 PrP ^C的作用相关的机制。

图形概要