Department of Surgery, University of British Columbia and BC Children's Hospital Research Institute, 950 West 28th Avenue, Vancouver, BC, V5Z 4H4, Canada.
Department of Neuroscience, University of Connecticut Health Center, Farmington, CT, USA.
Diabetologia. 2020 Mar;63(3):561-576. doi: 10.1007/s00125-019-05060-z. Epub 2020 Jan 27.
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.
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.
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.
目的/假设：肽激素最初被合成成为较大的、无活性的前体，然后通过内肽酶切割和翻译后修饰（如酰胺化）转化为其活性形式。最近，大规模全基因组研究表明，酰胺化酶肽基甘氨酸 α-酰胺化单加氧酶（PAM）的两个编码变异体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。
在诱导内质网（ER）或细胞因子应激后，分析小鼠胰岛中 PAM 的转录物和蛋白质水平，并检查人胰岛中的 PAM 表达模式。为了研究 PAM 单倍不足是否会加速糖尿病的发展，Pam 和 Pam 小鼠分别喂食低脂饮食（LFD）或高脂饮食（HFD），并评估葡萄糖稳态。由于 PAM 底物人胰岛淀粉样多肽（hIAPP）的聚集体导致胰岛炎症和β细胞衰竭，我们还研究了 PAM 单倍不足是否会加速 Pam 和 Pam 小鼠β细胞表达 hIAPP 时 hIAPP 诱导的糖尿病和胰岛淀粉样形成。
免疫染色显示 PAM 在人胰腺胰岛的α、β和δ细胞中高表达。在给予 HFD 后，小鼠胰岛中 Pam mRNA 和 PAM 蛋白表达减少，用他普西醇诱导 ER 应激或用白细胞介素 1β（IL-1β）、干扰素 γ（IFN-γ）和转化生长因子-β（TNF-α）诱导细胞因子应激后，分离的胰岛中 PAM 蛋白表达也减少。尽管 Pam 小鼠的 PAM 表达和酶活性仅为 Pam 小鼠的 50%，但在两种模型中，葡萄糖耐量和体重组成均无差异。在 HFD 喂养 24 周后，Pam 和 Pam 小鼠均出现胰岛素抵抗和葡萄糖耐量受损，但在 PAM 单倍不足小鼠中，葡萄糖耐量、胰岛素敏感性或血浆胰岛素水平均无差异。Pam 和 Pam 小鼠β细胞表达 hIAPP 时，胰岛淀粉样形成和β细胞功能也相似。
结论/解释：在小鼠中 PAM 的单倍不足不会加速饮食诱导的肥胖或 hIAPP 转基因诱导的糖尿病的发展。
