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E4orf1 induction in adipose tissue promotes insulin-independent signaling in the adipocyte.

Kusminski CM, Gallardo-Montejano VI, Wang ZV, Hegde V, Bickel PE, Dhurandhar NV, Scherer PE - Mol Metab (2015)

Bottom Line: At the whole body level, this leads to reduced body-weight gain under a high fat diet challenge.Nevertheless, they are protected from diet-induced hepatic steatosis.The resulting systemic phenotype is complex, yet highlights the powerful nature of manipulating selective branches of the insulin signaling network within the adipocyte.

View Article: PubMed Central - PubMed

Affiliation: Touchstone Diabetes Center, Department of Internal Medicine, The University of Texas Southwestern Medical Center, Dallas, TX, USA.

ABSTRACT

Background/purpose: Type 2 diabetes remains a worldwide epidemic with major pathophysiological changes as a result of chronic insulin resistance. Insulin regulates numerous biochemical pathways related to carbohydrate and lipid metabolism.

Methods: We have generated a novel mouse model that allows us to constitutively activate, in an inducible fashion, the distal branch of the insulin signaling transduction pathway specifically in adipocytes.

Results: Using the adenoviral 36 E4orf1 protein, we chronically stimulate locally the Ras-ERK-MAPK signaling pathway. At the whole body level, this leads to reduced body-weight gain under a high fat diet challenge. Despite overlapping glucose tolerance curves, there is a reduced requirement for insulin action under these conditions. The mice further exhibit reduced circulating adiponectin levels that ultimately lead to impaired lipid clearance, and inflamed and fibrotic white adipose tissues. Nevertheless, they are protected from diet-induced hepatic steatosis. As we observe constitutively elevated p-Akt levels in the adipocytes, even under conditions of low insulin levels, this pinpoints enhanced Ras-ERK-MAPK signaling in transgenic adipocytes as a potential alternative route to bypass proximal insulin signaling events.

Conclusion: We conclude that E4orf1 expression in the adipocyte leads to enhanced baseline activation of the distal insulin signaling node, yet impaired insulin receptor stimulation in the presence of insulin, with important implications for the regulation of adiponectin secretion. The resulting systemic phenotype is complex, yet highlights the powerful nature of manipulating selective branches of the insulin signaling network within the adipocyte.

No MeSH data available.


Related in: MedlinePlus

Adipose-tissue-specific induction of E4orf1 promotes fasting-induced lipolysis and lowering of adiponectin levels. (A) Representative Western blots showing E4orf1 protein expression levels (top panel) and β-actin (bottom panel) in subcutaneous white adipose tissue (sWAT), gonadal WAT (gWAT) and brown adipose tissue (BAT) derived from wild-type (WT) mice versus adipose tissue-specific E4orf1 transgenic (E4orf1-Tg) mice fed doxycycline (Dox)-chow (600 mg/kg Dox) for one-week. (B) Food-intake (g/day/body-weight gain [g]) of WT mice versus E4orf1-Tg mice following two-weeks of Dox-chow (600 mg/kg) feeding, (n = 5 per group). (C) Ad libitum and 24 h fasted circulating triglycerides (TAG), free fatty acid (FFA), glycerol and adiponectin levels in male C57/Bl6 WT mice versus E4orf1-Tg mice post two-weeks Dox-chow (600 mg/kg) feeding, (n = 5 per group). (Student's t-test, *P < 0.05; **P < 0.01; ***P < 0.001).
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fig1: Adipose-tissue-specific induction of E4orf1 promotes fasting-induced lipolysis and lowering of adiponectin levels. (A) Representative Western blots showing E4orf1 protein expression levels (top panel) and β-actin (bottom panel) in subcutaneous white adipose tissue (sWAT), gonadal WAT (gWAT) and brown adipose tissue (BAT) derived from wild-type (WT) mice versus adipose tissue-specific E4orf1 transgenic (E4orf1-Tg) mice fed doxycycline (Dox)-chow (600 mg/kg Dox) for one-week. (B) Food-intake (g/day/body-weight gain [g]) of WT mice versus E4orf1-Tg mice following two-weeks of Dox-chow (600 mg/kg) feeding, (n = 5 per group). (C) Ad libitum and 24 h fasted circulating triglycerides (TAG), free fatty acid (FFA), glycerol and adiponectin levels in male C57/Bl6 WT mice versus E4orf1-Tg mice post two-weeks Dox-chow (600 mg/kg) feeding, (n = 5 per group). (Student's t-test, *P < 0.05; **P < 0.01; ***P < 0.001).

Mentions: To induce E4orf1 specifically in adipose tissue (AT), we generated a mouse in which the expression of E4orf1 is driven by a tetracycline-inducible promoter element (a tet-responsive element, or TRE). We refer to this mouse as the TRE-E4orf1 mouse. For this promoter element to be operational, the presence of the ‘Tet-on’ transcription factor rtTA is required. We provide this factor in an adipocyte-specific manner through a mouse that harbors the rtTA component under the control of the adiponectin promoter [24]. Upon crossing TRE-E4orf1 mice with adiponectin-rtTA mice, followed by administration of doxycycline (Dox) to the resulting pups (the “E4orf1-Tg mice”), we achieve induction of E4orf1 expression specifically within adipose tissues. Our in vivo system of E4orf1 overexpression is inducible, highly specific and titratable; with the latter achieved through alterations in Dox concentrations. Initial observations revealed that following one-week of Dox-chow (600 mg/kg Dox) feeding, we efficiently induce E4orf1 protein in transgenic subcutaneous white adipose tissue (sWAT), gonadal WAT (gWAT), mesenteric WAT (mWAT) and brown adipose tissue (BAT); with the highest degree of E4orf1 induction evident in BAT (Figure 1A). No induction of E4orf1 protein is observed in the liver, therefore highlighting the specificity of E4orf1 protein overexpression exclusively to adipose tissues.


E4orf1 induction in adipose tissue promotes insulin-independent signaling in the adipocyte.

Kusminski CM, Gallardo-Montejano VI, Wang ZV, Hegde V, Bickel PE, Dhurandhar NV, Scherer PE - Mol Metab (2015)

Adipose-tissue-specific induction of E4orf1 promotes fasting-induced lipolysis and lowering of adiponectin levels. (A) Representative Western blots showing E4orf1 protein expression levels (top panel) and β-actin (bottom panel) in subcutaneous white adipose tissue (sWAT), gonadal WAT (gWAT) and brown adipose tissue (BAT) derived from wild-type (WT) mice versus adipose tissue-specific E4orf1 transgenic (E4orf1-Tg) mice fed doxycycline (Dox)-chow (600 mg/kg Dox) for one-week. (B) Food-intake (g/day/body-weight gain [g]) of WT mice versus E4orf1-Tg mice following two-weeks of Dox-chow (600 mg/kg) feeding, (n = 5 per group). (C) Ad libitum and 24 h fasted circulating triglycerides (TAG), free fatty acid (FFA), glycerol and adiponectin levels in male C57/Bl6 WT mice versus E4orf1-Tg mice post two-weeks Dox-chow (600 mg/kg) feeding, (n = 5 per group). (Student's t-test, *P < 0.05; **P < 0.01; ***P < 0.001).
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fig1: Adipose-tissue-specific induction of E4orf1 promotes fasting-induced lipolysis and lowering of adiponectin levels. (A) Representative Western blots showing E4orf1 protein expression levels (top panel) and β-actin (bottom panel) in subcutaneous white adipose tissue (sWAT), gonadal WAT (gWAT) and brown adipose tissue (BAT) derived from wild-type (WT) mice versus adipose tissue-specific E4orf1 transgenic (E4orf1-Tg) mice fed doxycycline (Dox)-chow (600 mg/kg Dox) for one-week. (B) Food-intake (g/day/body-weight gain [g]) of WT mice versus E4orf1-Tg mice following two-weeks of Dox-chow (600 mg/kg) feeding, (n = 5 per group). (C) Ad libitum and 24 h fasted circulating triglycerides (TAG), free fatty acid (FFA), glycerol and adiponectin levels in male C57/Bl6 WT mice versus E4orf1-Tg mice post two-weeks Dox-chow (600 mg/kg) feeding, (n = 5 per group). (Student's t-test, *P < 0.05; **P < 0.01; ***P < 0.001).
Mentions: To induce E4orf1 specifically in adipose tissue (AT), we generated a mouse in which the expression of E4orf1 is driven by a tetracycline-inducible promoter element (a tet-responsive element, or TRE). We refer to this mouse as the TRE-E4orf1 mouse. For this promoter element to be operational, the presence of the ‘Tet-on’ transcription factor rtTA is required. We provide this factor in an adipocyte-specific manner through a mouse that harbors the rtTA component under the control of the adiponectin promoter [24]. Upon crossing TRE-E4orf1 mice with adiponectin-rtTA mice, followed by administration of doxycycline (Dox) to the resulting pups (the “E4orf1-Tg mice”), we achieve induction of E4orf1 expression specifically within adipose tissues. Our in vivo system of E4orf1 overexpression is inducible, highly specific and titratable; with the latter achieved through alterations in Dox concentrations. Initial observations revealed that following one-week of Dox-chow (600 mg/kg Dox) feeding, we efficiently induce E4orf1 protein in transgenic subcutaneous white adipose tissue (sWAT), gonadal WAT (gWAT), mesenteric WAT (mWAT) and brown adipose tissue (BAT); with the highest degree of E4orf1 induction evident in BAT (Figure 1A). No induction of E4orf1 protein is observed in the liver, therefore highlighting the specificity of E4orf1 protein overexpression exclusively to adipose tissues.

Bottom Line: At the whole body level, this leads to reduced body-weight gain under a high fat diet challenge.Nevertheless, they are protected from diet-induced hepatic steatosis.The resulting systemic phenotype is complex, yet highlights the powerful nature of manipulating selective branches of the insulin signaling network within the adipocyte.

View Article: PubMed Central - PubMed

Affiliation: Touchstone Diabetes Center, Department of Internal Medicine, The University of Texas Southwestern Medical Center, Dallas, TX, USA.

ABSTRACT

Background/purpose: Type 2 diabetes remains a worldwide epidemic with major pathophysiological changes as a result of chronic insulin resistance. Insulin regulates numerous biochemical pathways related to carbohydrate and lipid metabolism.

Methods: We have generated a novel mouse model that allows us to constitutively activate, in an inducible fashion, the distal branch of the insulin signaling transduction pathway specifically in adipocytes.

Results: Using the adenoviral 36 E4orf1 protein, we chronically stimulate locally the Ras-ERK-MAPK signaling pathway. At the whole body level, this leads to reduced body-weight gain under a high fat diet challenge. Despite overlapping glucose tolerance curves, there is a reduced requirement for insulin action under these conditions. The mice further exhibit reduced circulating adiponectin levels that ultimately lead to impaired lipid clearance, and inflamed and fibrotic white adipose tissues. Nevertheless, they are protected from diet-induced hepatic steatosis. As we observe constitutively elevated p-Akt levels in the adipocytes, even under conditions of low insulin levels, this pinpoints enhanced Ras-ERK-MAPK signaling in transgenic adipocytes as a potential alternative route to bypass proximal insulin signaling events.

Conclusion: We conclude that E4orf1 expression in the adipocyte leads to enhanced baseline activation of the distal insulin signaling node, yet impaired insulin receptor stimulation in the presence of insulin, with important implications for the regulation of adiponectin secretion. The resulting systemic phenotype is complex, yet highlights the powerful nature of manipulating selective branches of the insulin signaling network within the adipocyte.

No MeSH data available.


Related in: MedlinePlus