25-OR: Investigating a Candidate Causal Allele in Type 2 Diabetes Susceptibility Gene PAM as a Cause of Neonatal Diabetes Mellitus

Autor: Mahesh M. Umapathysivam, Anne Raimondo, Shahana Sengupta, Markku Laakso, Peter S. Chines, Anna L. Gloyn, Anne Clark, Hanna Huopio, Antje Grotz, Lori L. Bonnycastle, Amy J. Swift, Benoit Hastoy, Francis S. Collins
Rok vydání: 2019
Předmět:
Zdroj: Diabetes. 68
ISSN: 1939-327X
0012-1797
Popis: Peptidylglycine α-amidating monooxygenase (PAM) catalyses the amidation of glycine-extended peptides, thereby maximising their biological potency. We recently showed that coding alleles in PAM mediate type 2 diabetes (T2D) risk through alterations to PAM protein activity and expression in the β cell. Identifying alleles along a continuum of functional severity informs on the relationship between protein perturbation and clinical effect. We hypothesised that rare, loss of function PAM alleles could cause severe β cell dysfunction presenting as neonatal diabetes. Sequencing of 15 probands presenting with diabetes at ≤ 6 months of age and their unaffected immediate family, identified a novel de novo nonsynonymous coding variant (p.R36S) in PAM in a single proband. We investigated the impact of the variant allele on amidating activity, protein stability and localisation as a measure of PAM function and the consequences on β cell viability. Recombinant R36S-PAM exhibited normal amidating activity in vitro which was consistent with PAM activity measured in patient serum (WT: 391pmol/μl/hr vs. R36S: 305pmol/μl/hr). In human β cells (EndoC-βh1) the secreted luminal R36S-PAM isoform displayed reduced protein expression (-78%, p=0.004) compared to WT-PAM, which could be rescued by inhibiting the proteosomal pathway (+120% of WT); whilst the non-secreted membrane-integral isoform was retained in the endoplasmic reticulum (ER). We observed that overexpression of R36S-PAM elevated levels of ER stress (p-IRE1: +196%, p=0.02; CHOP: +114%, p=0.051) and pro-apoptotic markers (ASK1: +145%, caspase-3: +154%) compared with WT-PAM. We have identified a novel, de novo coding variant, in a gene with a proven role in T2D risk, in a single patient with neonatal diabetes. Functional studies provide evidence for protein mislocalisation and instability and support a role for this allele in ER stress and β cell dysfunction consistent with neonatal diabetes pathogenesis. Disclosure S. Sengupta: None. L.L. Bonnycastle: None. B. Hastoy: None. A. Grotz: None. M.M. Umapathysivam: None. A. Raimondo: None. A. Swift: None. P.S. Chines: None. A. Clark: None. H. Huopio: None. F.S. Collins: None. M. Laakso: None. A.L. Gloyn: Consultant; Spouse/Partner; Eli Lilly and Company, Merck & Co., Inc. Consultant; Self; Merck & Co., Inc. Consultant; Spouse/Partner; Novo Nordisk A/S, Pfizer Inc. Research Support; Self; Novo Nordisk A/S. Speaker's Bureau; Self; Novo Nordisk A/S. Other Relationship; Self; Diabetes UK, European Foundation for the Study of Diabetes. Funding UK Wellcome Trust
Databáze: OpenAIRE
Externí odkaz: