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 3

Downstream insulin signaling in patient cells expressing truncated p85α.

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Downstream insulin signaling in patient cells expressing truncated p85α....
(A) Western blot of total p85 (p85α/β) in phosphotyrosine immunoprecipitates or total lysates from dermal fibroblasts from P1 and healthy controls (C1–C3) treated with PBS or 100 nM insulin. Representative blots with quantified data from 3 independent experiments normalized to mean baseline intensity (dot plot displays mean ± SEM). Lane order in image of lysate blot adjusted to reflect that of the immunoprecipitate blot. (B) Western blot of total p85 (p85α/β) in phospho-IRS1 immunoprecipitates from patient and control fibroblasts after treatment with PBS or insulin. Representative blot with quantified data from three independent experiments normalized to mean baseline intensity across control cell lines. (C) Phosphatidylinositol-3,4,5-trisphosphate (PIP3) levels in dermal fibroblasts from P1 and healthy controls (C1–C5) stimulated with PBS or insulin, as determined by liquid chromatography mass spectroscopy. PIP3 area ratios were normalized to that of an internal standard. Dot plot displays median of 2 samples, each quantified in duplicate. Representative of 3 independent experiments. (D) Western blot of phosphorylated AKT1/2 (Ser473/474) and ERK1/2 (Thr202/Tyr204) in dermal fibroblasts from P1 and healthy controls (C1, C2) after stimulation with a range of insulin doses. Representative blots with quantified data from 3 independent experiments normalized to the highest intensity signal in each experiment and a calnexin loading control. Data represent mean ± SEM.