Abstract Increased insulin receptor substrate 2 expression is associated with steatohepatitis and altered lipid metabolism in obese subjects Objective: The aim of this study was to evaluate whether dysregulation of molecules involved in FOXO1 dependent insulin signalling in the liver is associated with de novo lipogenesis (DNL) and altered lipid metabolism in severely obese subjects. Design: Observational retrospective study. Subjects: We considered 71 obese subjects (age 20-68 years; BMI>40 kg/m2 or BMI>35 kg/m2 in the presence of metabolic complications) classified into three groups according to liver histology: normal liver (n=12), simple steatosis (n=27), and non-alcoholic steatohepatitis (NASH; n=32). Key nodes in insulin signalling and gene expression of molecules implicated in insulin dependent glucoregulatory pathway and DNL were evaluated by quantitative real-time PCR and Western blotting. Results: Patients with steatosis had decreased phosphorylation of the insulin kinase AKT1, mediating insulin receptor signalling, and the transcription factor FOXO1, which was therefore more active mediating insulin resistance at transcriptional level. Despite no changes in insulin receptor substrate (IRS)1 mRNA levels, the mRNA and protein levels of the FOXO1 target IRS2 increased progressively with the severity of steatosis from normal liver to NASH. IRS2 expression was correlated with the severity of steatosis, dyslipidemia, and liver damage. In patients with NASH, upregulation of IRS2 was associated with preserved activation of AKT2, mediating the stimulating effect of insulin on DNL, and over-expression of its target sterol regulatory element binding protein 1c (SREBP1c), inducing DNL at transcriptional level. Both FOXO1 and SREBP1c overexpression converged on upregulation of glucokinase, providing substrates for DNL, in NASH patients. Conclusion: Differential regulation of IRS1 and IRS2 and of their downstream effectors AKT1 and AKT2 is consistent with upregulation of FOXO1 and may justify the paradoxical state of insulin resistance relative to the glucoregulatory pathway and augmented insulin sensitivity of the liporegulatory pathway typical of steatosis and the metabolic syndrome in obese patients.
Design: Studio retrospettivo osservazionale. Soggetti: Abbiamo considerato 71 soggetti obesi (età compresa tra 20 e 68 anni; BMI>40 kg/m2 or BMI>35 kg/m2 in presenza di complicazioni metaboliche) classificati in tre gruppi secondo l’istologia epatica: controlli (n=12), steatosi semplice(n=27), e steatoepatite non alcolica (NASH; n=32). Abbiamo valutato i punti chiave del signalling insulinico e l’espressione genica delle molecole implicate nel pathway glucoregolatorio e nella DNL insulino dipendenti mediante PCR quantitativa real-time e Western blotting. RIASSUNTO 5 Risultati: I pazienti con steatosi semplice mostrano una ridotta fosforilazione della chinasi AKT1, responsabile della trasduzione del signalling insulinico, con conseguente sostenuta attività del fattore di trascrizione FOXO1 che media l’insulino resistenza a livello trascrizionale. Nonostante nessuna variazione significativa dell’espressione di insulin receptor substrate 1 (IRS1), i livelli proteici e di mRNA di IRS2, target di FOXO1, aumentano progressivamente con la severità della steatosi dai controlli alla NASH. L’espressione di IRS2 è correlata con la severità della steatosi, l’insulino resistenza e la dislipidemia. Nei pazienti con NASH, l’upregolazione di IRS2 è associata alla preservata attività di AKT2, che è il mediatore gli effetti stimolanti di insulina sulla DNL, e all’overespressione del suo target sterol regulatory element binding protein 1c (SREBP1c), che induce DNL a livello trascrizionale. L’overespressione sia di FOXO1 che di SREBP1c convergono sull’upregolazione della glucochinasi, che fornisce substrati alla DNL, nei pazienti con NASH. Conclusioni: La regolazione differenziale di IRS1 e IRS2 e dei loro effettori a valle AKT1 e AKT2 è coerente con l’upregolazione di FOXO1 e potrebbe giustificare lo stato paradossale di insulino resistenza a carico del pathway glucoregolatorio e l’aumentata insulino sensibilità di quello liporegolatorio tipico della steatosi e della dislipidemia in pazienti obesi con sindrome metabolica.
UN¿AUMENTATA ESPRESSIONE DEL SUBSTRATO DEL RECETTORE DELL¿INSULINA 2 (IRS-2) È ASSOCIATA ALLA STEATOEPATITE E AL DISMETABOLISMO LIPIDICO IN PAZIENTI AFFETTI DA OBESITÀ GRAVE / R. Rametta ; tutor: S.R. Fargion ; coordinatore: M. Cattaneo. UNIVERSITA' DEGLI STUDI DI MILANO, 2013 Mar 25. 25. ciclo, Anno Accademico 2012. [10.13130/rametta-raffaela_phd2013-03-25].
UN¿AUMENTATA ESPRESSIONE DEL SUBSTRATO DEL RECETTORE DELL¿INSULINA 2 (IRS-2) È ASSOCIATA ALLA STEATOEPATITE E AL DISMETABOLISMO LIPIDICO IN PAZIENTI AFFETTI DA OBESITÀ GRAVE.
R. Rametta
2013
Abstract
Abstract Increased insulin receptor substrate 2 expression is associated with steatohepatitis and altered lipid metabolism in obese subjects Objective: The aim of this study was to evaluate whether dysregulation of molecules involved in FOXO1 dependent insulin signalling in the liver is associated with de novo lipogenesis (DNL) and altered lipid metabolism in severely obese subjects. Design: Observational retrospective study. Subjects: We considered 71 obese subjects (age 20-68 years; BMI>40 kg/m2 or BMI>35 kg/m2 in the presence of metabolic complications) classified into three groups according to liver histology: normal liver (n=12), simple steatosis (n=27), and non-alcoholic steatohepatitis (NASH; n=32). Key nodes in insulin signalling and gene expression of molecules implicated in insulin dependent glucoregulatory pathway and DNL were evaluated by quantitative real-time PCR and Western blotting. Results: Patients with steatosis had decreased phosphorylation of the insulin kinase AKT1, mediating insulin receptor signalling, and the transcription factor FOXO1, which was therefore more active mediating insulin resistance at transcriptional level. Despite no changes in insulin receptor substrate (IRS)1 mRNA levels, the mRNA and protein levels of the FOXO1 target IRS2 increased progressively with the severity of steatosis from normal liver to NASH. IRS2 expression was correlated with the severity of steatosis, dyslipidemia, and liver damage. In patients with NASH, upregulation of IRS2 was associated with preserved activation of AKT2, mediating the stimulating effect of insulin on DNL, and over-expression of its target sterol regulatory element binding protein 1c (SREBP1c), inducing DNL at transcriptional level. Both FOXO1 and SREBP1c overexpression converged on upregulation of glucokinase, providing substrates for DNL, in NASH patients. Conclusion: Differential regulation of IRS1 and IRS2 and of their downstream effectors AKT1 and AKT2 is consistent with upregulation of FOXO1 and may justify the paradoxical state of insulin resistance relative to the glucoregulatory pathway and augmented insulin sensitivity of the liporegulatory pathway typical of steatosis and the metabolic syndrome in obese patients.File | Dimensione | Formato | |
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