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 4

Insulin signaling and adipocyte differentiation in 3T3-L1 preadipocyte models of SHORT syndrome.

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Insulin signaling and adipocyte differentiation in 3T3-L1 preadipocyte m...
(A) Total p85 and p110α expression in preadipocyte lysates 72 hours after treatment with or without doxycycline (DOX) to induce expression of WT or mutant p85α. β Actin was assessed as a loading control. (B) Lipid accumulation, assessed by Oil red O staining on day 10 of an adipocyte differentiation protocol. Doxycycline was added at the time points indicated to inducibly overexpress full-length or truncated p85α. (C) Insulin-induced phosphorylation of AKT at Ser473/474 and Thr308 in preadipocytes infected with WT and mutant p85α lentivirus, with or without doxycycline treatment, after stimulation with 1, 10, or 100 nM insulin for 10 minutes. Representative of 3 independent experiments. (D) Quantification of AKT phosphorylation, showing pooled data from 3 independent experiments. –DOX and +DOX groups were compared using multiple t tests, with correction for multiple comparisons using the Holm-Šidák method, with α = 0.05. Data represent mean ± SEM; *P < 0.05.