Fatty Aldehyde Dehydrogenase Demozay, Damien; Rocchi, Stéphane; Mas, Jean-Christophe ...
The Journal of biological chemistry,
February 2004, Letnik:
279, Številka:
8
Journal Article
Recenzirano
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Phosphatidylinositol 3-kinase signaling regulates the expression of several genes involved in lipid and glucose homeostasis; deregulation of these genes may contribute to insulin resistance and ...progression toward type 2 diabetes. By employing RNA arbitrarily primed-PCR to search for novel phosphatidylinositol 3-kinase-regulated genes in response to insulin in isolated rat adipocytes, we identified fatty aldehyde dehydrogenase (FALDH), a key component of the detoxification pathway of aldehydes arising from lipid peroxidation events. Among these latter events are oxidative stresses associated with insulin resistance and diabetes. Upon insulin injection, FALDH mRNA expression increased in rat liver and white adipose tissue and was impaired in two models of insulin-resistant mice, db/db and high fat diet mice. FALDH mRNA levels were 4-fold decreased in streptozotocin-treated rats, suggesting that FALDH deregulation occurs both in hyperinsulinemic insulin-resistant state and hypoinsulinemic type 1 diabetes models. Moreover, insulin treatment increases FALDH activity in hepatocytes, and expression of FALDH was augmented during adipocyte differentiation. Considering the detoxifying role of FALDH, its deregulation in insulin-resistant and type 1 diabetic models may contribute to the lipid-derived oxidative stress. To assess the role of FALDH in the detoxification of oxidized lipid species, we evaluated the production of reactive oxygen species in normal versus FALDH-overexpressing adipocytes. Ectopic expression of FALDH significantly decreased reactive oxygen species production in cells treated by 4-hydroxynonenal, the major lipid peroxidation product, suggesting that FALDH protects against oxidative stress associated with lipid peroxidation. Taken together, our observations illustrate the importance of FALDH in insulin action and its deregulation in states associated with altered insulin signaling.
OBJECTIVE--Appropriate regulation of insulin receptor substrate 2 (IRS-2) expression in pancreatic beta-cells is essential to adequately compensate for insulin resistance. In liver, basal IRS-2 ...expression is controlled via a temporal negative feedback of sterol regulatory element-binding protein 1 (SREBP-1) to antagonize transcription factors forkhead box class 0 (FoxO)1/ FoxO3a at an insulin response element (IRE) on the IRS-2 promoter. The purpose of the study was to examine if a similar mechanism controlled IRS-2 expression in beta-cells. RESEARCH DESIGN AND METHODS--IRS-2 mRNA and protein expression, as well as IRS-2 gene promoter activity, were examined in isolated rat islets. Specific transcription factor association with the IRE on the IRS-2 promoter was examined by chromatin immunoprecipitation (CHIP) assay, and their nuclear translocation was examined by immunofluorescence. A direct in vivo effect of insulin on control of IRS-2 expression in liver and pancreatic islets was also investigated. RESULTS--In IRS-2 promoter-reporter assays conducted in isolated islets, removal of the IRE decreased basal IRS-2 promoter activity in beta-cells up to 80%. Activation of IRS signaling in isolated rat islets by insulin/IGF-I (used as an experimental in vitro tool) or downstream constitutive activation of protein kinase B (PKB) significantly decreased IRS-2 expression. In contrast, inhibition of phosphatidylinositol 3-kinase (PI3K) or PKB significantly increased IRS-2 levels in beta-cells. ChIP assays indicated that transcription factors FoxO1 and FoxO3a associated with the IRE on the IRS-2 promoter in beta-cells in a PI3K/PKB-dependent manner, whereas others, such as SREBP-1, the transcription factor binding to immunoglobulin heavy chain enhancer 3', and the aryl hydrocarbon receptor nuclear translocator (ARNT), did not. However, only FoxO3a, not FoxO1, was capable of driving IRS-2 promoter activity via the IRE in beta-cells. In vivo studies showed insulin was able to suppress IRS-2 expression via activation of SREBP-1 in the liver, but this mechanism was not apparent in pancreatic islets from the same animal. CONCLUSIONS--The molecular mechanism for feedback control of IRS signaling to decrease IRS-2 expression in liver and beta-cells is quite distinct, with a predominant role played by FoxO3a in beta-cells. Diabetes 60:2883-2891, 2011
OBJECTIVE--Insulin receptor substrate-2 (IRS-2) plays an essential role in pancreatic islet β-cells by promoting growth and survival. IRS-2 turnover is rapid in primary β-cells, but its expression is ...highly regulated at the transcriptional level, especially by glucose. The aim was to investigate the molecular mechanism on how glucose regulates IRS-2 gene expression in β-cells. RESEARCH DESIGN AND METHODS--Rat islets were exposed to inhibitom or subjected to adenoviral vector-mediated gene manipulations and then to glucose-induced IRS-2 expression analyzed by real-time PCR and immunoblotting. Transcription factor nuclear factor of activated T cells (NFAT) interaction with IRS-2 promoter was analyzed by chromatin immunoprecipitation assay and glucose-induced NFAT translocation by immanohistochemistry. RESULTS--Glucose-induced IRS-2 expression occurred in pancreatic islet p-cells in vivo but not in liver. Modulating rat islet p-cell Ca.sup.2+ influx with nifedipine or depolarization demonstrated that glucose-induced IRS-2 gene expression was dependent on a rise in intracellular calcium concentration derived from extracellular sources. Calcineurin inhibitom (FK506, cyclosporin A, and a peptide calcineurin inhibitor CAIN) abolished glucose-induced IRS-2 mRNA and protein levels, whereas expression of a constitutively active calcineurin increased them. Specific inhibition of NFAT with the peptide inhibitor VIV1T prevented a glucose-induced IRS-2 transcription. NFATc1 translocation to the nucleus in response to glucose and association of NFATc1 to conserved NFAT binding sites in the IRS-2 promoter were demonstrated. CONCLUSIONS--The mechanism behind glucose-induced transcriptional control of IRS-2 gene expression specific to the islet β-cell is mediated by the Ca.sup.2+/calcineurin/NFAT pathway. This insight into the IRS-2 regulation could provide novel therapeutic means in type 2 diabetes to maintain an adequate functional mass. Diabetes 60:2892-2902, 2011
OBJECTIVE--Insulin receptor substrate-2 (IRS-2) plays an essential role in pancreatic islet beta-cells by promoting growth and survival. IRS-2 turnover is rapid in primary beta-cells, but its ...expression is highly regulated at the transcriptional level, especially by glucose. The aim was to investigate the molecular mechanism on how glucose regulates IRS-2 gene expression in beta-cells. RESEARCH DESIGN AND METHODS--Rat islets were exposed to inhibitom or subjected to adenoviral vector-mediated gene manipulations and then to glucose-induced IRS-2 expression analyzed by real-time PCR and immunoblotting. Transcription factor nuclear factor of activated T cells (NFAT) interaction with IRS-2 promoter was analyzed by chromatin immunoprecipitation assay and glucose-induced NFAT translocation by immanohistochemistry. RESULTS--Glucose-induced IRS-2 expression occurred in pancreatic islet p-cells in vivo but not in liver. Modulating rat islet p-cell Ca.sup.2+ influx with nifedipine or depolarization demonstrated that glucose-induced IRS-2 gene expression was dependent on a rise in intracellular calcium concentration derived from extracellular sources. Calcineurin inhibitom (FK506, cyclosporin A, and a peptide calcineurin inhibitor CAIN) abolished glucose-induced IRS-2 mRNA and protein levels, whereas expression of a constitutively active calcineurin increased them. Specific inhibition of NFAT with the peptide inhibitor VIV1T prevented a glucose-induced IRS-2 transcription. NFATc1 translocation to the nucleus in response to glucose and association of NFATc1 to conserved NFAT binding sites in the IRS-2 promoter were demonstrated. CONCLUSIONS--The mechanism behind glucose-induced transcriptional control of IRS-2 gene expression specific to the islet beta-cell is mediated by the Ca.sup.2+/calcineurin/NFAT pathway. This insight into the IRS-2 regulation could provide novel therapeutic means in type 2 diabetes to maintain an adequate functional mass. Diabetes 60:2892-2902, 2011
Phosphatidylinositol 3-kinase signaling regulates the expression of several genes involved in lipid and glucose homeostasis; deregulation of these genes may contribute to insulin resistance and ...progression toward type 2 diabetes. By employing RNA arbitrarily primed-PCR to search for novel phosphatidylinositol 3-kinase-regulated genes in response to insulin in isolated rat adipocytes, we identified fatty aldehyde dehydrogenase (FALDH), a key component of the detoxification pathway of aldehydes arising from lipid peroxidation events. Among these latter events are oxidative stresses associated with insulin resistance and diabetes. Upon insulin injection, FALDH mRNA expression increased in rat liver and white adipose tissue and was impaired in two models of insulin-resistant mice, db/db and high fat diet mice. FALDH mRNA levels were 4-fold decreased in streptozotocin-treated rats, suggesting that FALDH deregulation occurs both in hyperinsulinemic insulin-resistant state and hypoinsulinemic type 1 diabetes models. Moreover, insulin treatment increases FALDH activity in hepatocytes, and expression of FALDH was augmented during adipocyte differentiation. Considering the detoxifying role of FALDH, its deregulation in insulin-resistant and type 1 diabetic models may contribute to the lipid-derived oxidative stress. To assess the role of FALDH in the detoxification of oxidized lipid species, we evaluated the production of reactive oxygen species in normal versus FALDH-overexpressing adipocytes. Ectopic expression of FALDH significantly decreased reactive oxygen species production in cells treated by 4-hydroxynonenal, the major lipid peroxidation product, suggesting that FALDH protects against oxidative stress associated with lipid peroxidation. Taken together, our observations illustrate the importance of FALDH in insulin action and its deregulation in states associated with altered insulin signaling.
Insulin receptor substrate-2 (IRS-2) plays an essential role in pancreatic islet beta-cells by promoting growth and survival. IRS-2 turnover is rapid in primary beta-cells, but its expression is ...highly regulated at the transcriptional level, especially by glucose. The aim was to investigate the molecular mechanism on how glucose regulates IRS-2 gene expression in beta-cells. Rat islets were exposed to inhibitors or subjected to adenoviral vector-mediated gene manipulations and then to glucose-induced IRS-2 expression analyzed by real-time PCR and immunoblotting. Transcription factor nuclear factor of activated T cells (NFAT) interaction with IRS-2 promoter was analyzed by chromatin immunoprecipitation assay and glucose-induced NFAT translocation by immunohistochemistry. Glucose-induced IRS-2 expression occurred in pancreatic islet beta-cells in vivo but not in liver. Modulating rat islet beta-cell Ca(2+) influx with nifedipine or depolarization demonstrated that glucose-induced IRS-2 gene expression was dependent on a rise in intracellular calcium concentration derived from extracellular sources. Calcineurin inhibitors (FK506, cyclosporin A, and a peptide calcineurin inhibitor CAIN) abolished glucose-induced IRS-2 mRNA and protein levels, whereas expression of a constitutively active calcineurin increased them. Specific inhibition of NFAT with the peptide inhibitor VIVIT prevented a glucose-induced IRS-2 transcription. NFATc1 translocation to the nucleus in response to glucose and association of NFATc1 to conserved NFAT binding sites in the IRS-2 promoter were demonstrated. The mechanism behind glucose-induced transcriptional control of IRS-2 gene expression specific to the islet beta-cell is mediated by the Ca(2+)/calcineurin/NFAT pathway. This insight into the IRS-2 regulation could provide novel therapeutic means in type 2 diabetes to maintain an adequate functional mass.
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