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.
Haploinsufficiency of PAM in mice does not accelerate the development of diet-induced obesity or hIAPP transgene-induced diabetes.
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The datasets generated and analysed during the current study are available from the corresponding author upon request.
Human islet amyloid polypeptide
- hIAPP Tg/0:
hIAPP transgenic mice
Islet amyloid polypeptide
Peptidyl-α-hydroxyglycine α-amidating lyase
Peptidylglycine α-amidating monooxygenase
Peptidylglycine α-hydroxylating monooxygenase
Thyrotropin releasing hormone
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We thank G. Soukhatcheva, D. Dai, M. Komba and K. Zhu (Department of Surgery, University of British Columbia, Vancouver, BC, Canada) for the assistance with mouse metabolic tests and islet isolation. We also wish to acknowledge K. Zhu and J. Wang (BC Children’s Hospital Research Institute, Vancouver, BC, Canada) for help with microscope image acquisition.
This work was supported by grants from the Canadian Institutes of Health Research (PJT - 153156) and JDRF (3-SRA-2014-39-Q-R) (to CBV), a grant from the National Institutes of Health DK-32949 (to BAE and REM) and a postdoctoral fellowship from JDRF International 3-PDF-2017-373-A-N (to Y-CC).
The authors declare that there is no duality of interest associated with this manuscript.
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Chen, Y., Mains, R.E., Eipper, B.A. et al. PAM haploinsufficiency does not accelerate the development of diet- and human IAPP-induced diabetes in mice. Diabetologia 63, 561–576 (2020). https://doi.org/10.1007/s00125-019-05060-z
- Glucose homeostasis
- Insulin secretion