AIMS/HYPOTHESIS Peptide hormones are first synthesised as larger, inactive precursors that are converted to their active forms by endopeptidase cleavage and post-translational modifications, such as amidation. Recent, large-scale genome-wide studies have suggested that two coding variants of the amidating enzyme, peptidylglycine α-amidating monooxygenase (PAM), are associated with impaired insulin secretion and increased type 2 diabetes risk. We aimed to elucidate the role of PAM in modulating beta cell peptide amidation, beta cell function and the development of diabetes. METHODS PAM transcript and protein levels were analysed in mouse islets following induction of endoplasmic reticulum (ER) or cytokine stress, and PAM expression patterns were examined in human islets. To study whether haploinsufficiency of PAM accelerates the development of diabetes, Pam+/- and Pam+/+ mice were fed a low-fat diet (LFD) or high-fat diet (HFD) and glucose homeostasis was assessed. Since aggregates of the PAM substrate human islet amyloid polypeptide (hIAPP) lead to islet inflammation and beta cell failure, we also investigated whether PAM haploinsufficiency accelerated hIAPP-induced diabetes and islet amyloid formation in Pam+/- and Pam+/+ mice with beta cell expression of hIAPP. RESULTS Immunostaining revealed high expression of PAM in alpha, beta and delta cells in human pancreatic islets. Pam mRNA and PAM protein expression were reduced in mouse islets following administration of an HFD, and in isolated islets following induction of ER stress with thapsigargin, or cytokine stress with IL-1β, IFN-γ and TFN-α. Despite Pam+/- only having 50% PAM expression and enzyme activity as compared with Pam+/+ mice, glucose tolerance and body mass composition were comparable in the two models. After 24 weeks of HFD, both Pam+/- and Pam+/+ mice had insulin resistance and impaired glucose tolerance, but no differences in glucose tolerance, insulin sensitivity or plasma insulin levels were observed in PAM haploinsufficient mice. Islet amyloid formation and beta cell function were also similar in Pam+/- and Pam+/+ mice with beta cell expression of hIAPP. CONCLUSIONS/INTERPRETATION Haploinsufficiency of PAM in mice does not accelerate the development of diet-induced obesity or hIAPP transgene-induced diabetes.

中文翻译：

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PAM单倍剂量不足不能加速饮食和人类IAPP诱导的小鼠糖尿病的发展。

目的/假设：首先将肽激素合成为较大的无活性前体，这些前体通过内肽酶裂解和翻译后修饰（例如酰胺化）转变成其活性形式。最近的大规模全基因组研究表明，酰胺化酶的两个编码变体肽基甘氨酸α-酰胺化单加氧酶（PAM）与胰岛素分泌受损和2型糖尿病风险增加有关。我们旨在阐明PAM在调节β细胞肽酰胺化，β细胞功能和糖尿病发展中的作用。方法分析内质网（ER）或细胞因子应激后小鼠胰岛中PAM的转录本和蛋白质水平，并检测人胰岛中PAM的表达模式。为了研究单倍剂量不足的PAM是否能促进糖尿病的发生，对Pam +/-和Pam + / +小鼠进行了低脂饮食（LFD）或高脂饮食（HFD）喂养，并评估了葡萄糖的体内稳态。由于PAM底物人胰岛淀粉样多肽（hIAPP）的聚集导致胰岛炎症和β细胞衰竭，我们还研究了PAM单倍剂量不足是否会加速具有β细胞表达的Pam +/-和Pam + / +小鼠中的hIAPP诱导的糖尿病和胰岛淀粉样蛋白形成的hIAPP。结果免疫染色显示PAM在人胰岛的alpha，β和delta细胞中高表达。施用HFD后，小鼠胰岛中的Pam mRNA和PAM蛋白表达降低；用毒胡萝卜素诱导ER应激，或用IL-1β，IFN-γ和TFN-α诱导细胞因子应激后，分离的胰岛中Pam mRNA和PAM蛋白表达降低。尽管与Pam + / +小鼠相比，Pam +/-仅具有50％的PAM表达和酶活性，但在这两个模型中，葡萄糖耐量和体重组成相当。HFD 24周后，Pam +/-和Pam + / +小鼠均具有胰岛素抵抗和葡萄糖耐量受损，但在PAM单倍剂量不足的小鼠中未观察到葡萄糖耐量，胰岛素敏感性或血浆胰岛素水平的差异。在具有hIAPPβ细胞表达的Pam +/-和Pam + / +小鼠中，胰岛淀粉样蛋白的形成和β细胞功能也相似。结论/解释小鼠中PAM的单倍剂量不足不能促进饮食诱导的肥胖症或hIAPP转基因诱导的糖尿病的发展。HFD 24周后，Pam +/-和Pam + / +小鼠均具有胰岛素抵抗和葡萄糖耐量受损，但在PAM单倍剂量不足的小鼠中未观察到葡萄糖耐量，胰岛素敏感性或血浆胰岛素水平的差异。在具有hIAPPβ细胞表达的Pam +/-和Pam + / +小鼠中，胰岛淀粉样蛋白的形成和β细胞功能也相似。结论/解释小鼠中PAM的单倍剂量不足不能促进饮食诱导的肥胖症或hIAPP转基因诱导的糖尿病的发展。HFD 24周后，Pam +/-和Pam + / +小鼠均具有胰岛素抵抗和葡萄糖耐量受损，但在PAM单倍剂量不足的小鼠中未观察到葡萄糖耐量，胰岛素敏感性或血浆胰岛素水平的差异。在具有hIAPPβ细胞表达的Pam +/-和Pam + / +小鼠中，胰岛淀粉样蛋白的形成和β细胞功能也相似。结论/解释小鼠中PAM的单倍剂量不足不能促进饮食诱导的肥胖症或hIAPP转基因诱导的糖尿病的发展。在具有hIAPPβ细胞表达的Pam +/-和Pam + / +小鼠中，胰岛淀粉样蛋白的形成和β细胞功能也相似。结论/解释小鼠中PAM的单倍剂量不足不能促进饮食诱导的肥胖症或hIAPP转基因诱导的糖尿病的发展。在具有hIAPPβ细胞表达的Pam +/-和Pam + / +小鼠中，胰岛淀粉样蛋白的形成和β细胞功能也相似。结论/解释小鼠中PAM的单倍剂量不足不能促进饮食诱导的肥胖症或hIAPP转基因诱导的糖尿病的发展。