Insulin resistance uncoupled from dyslipidemia due to C-terminal PIK3R1 mutations
Isabel Huang-Doran, Patsy Tomlinson, Felicity Payne, Alexandra Gast, Alison Sleigh, William Bottomley, Julie Harris, Allan Daly, Nuno Rocha, Simon Rudge, Jonathan Clark, Albert Kwok, Stefano Romeo, Emma McCann, Barbara Müksch, Mehul Dattani, Stefano Zucchini, Michael Wakelam, Lazaros C. Foukas, David B. Savage, Rinki Murphy, Stephen O’Rahilly, Inês Barroso, Robert K. Semple
Isabel Huang-Doran, Patsy Tomlinson, Felicity Payne, Alexandra Gast, Alison Sleigh, William Bottomley, Julie Harris, Allan Daly, Nuno Rocha, Simon Rudge, Jonathan Clark, Albert Kwok, Stefano Romeo, Emma McCann, Barbara Müksch, Mehul Dattani, Stefano Zucchini, Michael Wakelam, Lazaros C. Foukas, David B. Savage, Rinki Murphy, Stephen O’Rahilly, Inês Barroso, Robert K. Semple
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Research Article Endocrinology Metabolism

Insulin resistance uncoupled from dyslipidemia due to C-terminal PIK3R1 mutations

Abstract

Obesity-related insulin resistance is associated with fatty liver, dyslipidemia, and low plasma adiponectin. Insulin resistance due to insulin receptor (INSR) dysfunction is associated with none of these, but when due to dysfunction of the downstream kinase AKT2 phenocopies obesity-related insulin resistance. We report 5 patients with SHORT syndrome and C-terminal mutations in PIK3R1, encoding the p85α/p55α/p50α subunits of PI3K, which act between INSR and AKT in insulin signaling. Four of 5 patients had extreme insulin resistance without dyslipidemia or hepatic steatosis. In 3 of these 4, plasma adiponectin was preserved, as in insulin receptor dysfunction. The fourth patient and her healthy mother had low plasma adiponectin associated with a potentially novel mutation, p.Asp231Ala, in adiponectin itself. Cells studied from one patient with the p.Tyr657X PIK3R1 mutation expressed abundant truncated PIK3R1 products and showed severely reduced insulin-stimulated association of mutant but not WT p85α with IRS1, but normal downstream signaling. In 3T3-L1 preadipocytes, mutant p85α overexpression attenuated insulin-induced AKT phosphorylation and adipocyte differentiation. Thus, PIK3R1 C-terminal mutations impair insulin signaling only in some cellular contexts and produce a subphenotype of insulin resistance resembling INSR dysfunction but unlike AKT2 dysfunction, implicating PI3K in the pathogenesis of key components of the metabolic syndrome.

Authors

Isabel Huang-Doran, Patsy Tomlinson, Felicity Payne, Alexandra Gast, Alison Sleigh, William Bottomley, Julie Harris, Allan Daly, Nuno Rocha, Simon Rudge, Jonathan Clark, Albert Kwok, Stefano Romeo, Emma McCann, Barbara Müksch, Mehul Dattani, Stefano Zucchini, Michael Wakelam, Lazaros C. Foukas, David B. Savage, Rinki Murphy, Stephen O’Rahilly, Inês Barroso, Robert K. Semple

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Figure 5

A dominant negative mutation in ADIPOQ.

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A dominant negative mutation in ADIPOQ. (A) Domain structure of adipone...
(A) Domain structure of adiponectin, with the approximate site of the p.Asp231Ala (D231A) substitution indicated. SP, signal peptide. (B) Genomic DNA sequence from P1 and her parents showing the D231A mutation in ADIPOQ. (C) Western blot of adiponectin in serum from P1, insulin-resistant controls with mutations in INSR or AKT2, and insulin-sensitive controls (IS), after non-denaturing, non-reducing SDS-PAGE. Representative of 3 independent experiments. Low- (LMW), medium- (MMW), and high-molecular-weight (HMW) adiponectin complexes are indicated. F, female; M, male. (D) Secretion of low-molecular-weight adiponectin complexes into the culture medium of HEK293-T cells transfected with 1 μg or 2 μg WT or mutant ADIPOQ or cotransfected with 1 μg WT and 1 μg mutant ADIPOQ, determined by non-denaturing, non-reducing SDS-PAGE, followed by Western blotting of adiponectin. Representative blot with quantified data from 3 independent experiments (n = 2 in each experiment), normalized to intensity of the 1 μg WT sample. Dot plot displays mean ± SEM. ***P < 0.005; 1-way ANOVA. EV, empty vector.