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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

E4orf1 induction promotes whitening of BAT. (A) Real-time qPCR data showing BAT marker gene expression levels (Ucp1, Pgc1α, Prdm16, Cidea and Otop1) in BAT derived from WT mice versus E4orf1-Tg mice following three-weeks of Dox-HFD (600 mg/kg) feeding. (Student's t-test, **P < 0.01; ***P < 0.001). (B) Representative images of BAT derived from WT mice versus E4orf1-Tg mice that underwent H&E staining (top panel), Trichrome staining (second panel), Mac2 IHC (third panel) and Ucp1 IHC (fourth panel). Scale bar: 32 μm.
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fig5: E4orf1 induction promotes whitening of BAT. (A) Real-time qPCR data showing BAT marker gene expression levels (Ucp1, Pgc1α, Prdm16, Cidea and Otop1) in BAT derived from WT mice versus E4orf1-Tg mice following three-weeks of Dox-HFD (600 mg/kg) feeding. (Student's t-test, **P < 0.01; ***P < 0.001). (B) Representative images of BAT derived from WT mice versus E4orf1-Tg mice that underwent H&E staining (top panel), Trichrome staining (second panel), Mac2 IHC (third panel) and Ucp1 IHC (fourth panel). Scale bar: 32 μm.

Mentions: The highest degree of E4orf1 induction is achieved in the BAT depot (Figure 1A). As such, we wanted to assess whether E4orf1 induction alters the transcriptional browning signature program in BAT. Interestingly, following two weeks of Dox-HFD feeding, gene markers of browning (Ucp1, Pgc1α, Cidea, Otop1 and Prdm16) were significantly down-regulated in E4orf1-Tg BAT compared to WT BAT (Figure 5A). Visually, the BAT depot in E4orf1-Tg mice appeared to have whitened in color, such that very little true BAT was evident. By utilizing Illumina microarrays, we identified significantly altered gene clusters in BAT derived from E4orf1-Tg mice that underwent two weeks of Dox-HFD feeding. Supplementary Table 3 highlights a significant suppression in the angiogenic marker Vegf-B in E4orf1-Tg BAT. Conversely, a significant up-regulation in several markers of fibrosis and ECM remodeling genes (Tgfbi, Tgf-βr1, Smad3/4 and many matrix metallopeptidases [MMPs]) was apparent in E4orf1-Tg BAT (Supplementary Table 3). Similar to sWAT, numerous collagens were also markedly up-regulated in E4orf1-Tg BAT (Supplementary Table 3), suggesting unhealthy fibrotic AT. In line with the gene expression data, histological examination through H&E staining revealed markedly disorganized and enlarged lipid-laden adipocytes in E4orf1-Tg BAT (Figure 5B). Further, consistent with the gene expression data (Supplementary Table 3), trichrome staining revealed enhanced tissue fibrosis in E4orf1-Tg BAT (Figure 5B). E4orf1-Tg BAT also displayed enhanced Mac2-positive staining (Figure 5B), indicating inflamed and unhealthy AT, similar to that observed for E4orf1-Tg sWAT (Figure 2E). However, despite the gene expression data highlighting a marked reduction in the browning signature program in E4orf1-Tg BAT (Figure 5A), Ucp1 IHC showed no striking differences in Ucp1-positive staining between WT BAT and E4orf1-Tg BAT (Figure 5B). This suggests that even though mRNA levels are reduced, UCP1 protein levels are maintained, either through enhance translational efficacy or a prolonged half-life for UCP1 protein.


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)

E4orf1 induction promotes whitening of BAT. (A) Real-time qPCR data showing BAT marker gene expression levels (Ucp1, Pgc1α, Prdm16, Cidea and Otop1) in BAT derived from WT mice versus E4orf1-Tg mice following three-weeks of Dox-HFD (600 mg/kg) feeding. (Student's t-test, **P < 0.01; ***P < 0.001). (B) Representative images of BAT derived from WT mice versus E4orf1-Tg mice that underwent H&E staining (top panel), Trichrome staining (second panel), Mac2 IHC (third panel) and Ucp1 IHC (fourth panel). Scale bar: 32 μm.
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fig5: E4orf1 induction promotes whitening of BAT. (A) Real-time qPCR data showing BAT marker gene expression levels (Ucp1, Pgc1α, Prdm16, Cidea and Otop1) in BAT derived from WT mice versus E4orf1-Tg mice following three-weeks of Dox-HFD (600 mg/kg) feeding. (Student's t-test, **P < 0.01; ***P < 0.001). (B) Representative images of BAT derived from WT mice versus E4orf1-Tg mice that underwent H&E staining (top panel), Trichrome staining (second panel), Mac2 IHC (third panel) and Ucp1 IHC (fourth panel). Scale bar: 32 μm.
Mentions: The highest degree of E4orf1 induction is achieved in the BAT depot (Figure 1A). As such, we wanted to assess whether E4orf1 induction alters the transcriptional browning signature program in BAT. Interestingly, following two weeks of Dox-HFD feeding, gene markers of browning (Ucp1, Pgc1α, Cidea, Otop1 and Prdm16) were significantly down-regulated in E4orf1-Tg BAT compared to WT BAT (Figure 5A). Visually, the BAT depot in E4orf1-Tg mice appeared to have whitened in color, such that very little true BAT was evident. By utilizing Illumina microarrays, we identified significantly altered gene clusters in BAT derived from E4orf1-Tg mice that underwent two weeks of Dox-HFD feeding. Supplementary Table 3 highlights a significant suppression in the angiogenic marker Vegf-B in E4orf1-Tg BAT. Conversely, a significant up-regulation in several markers of fibrosis and ECM remodeling genes (Tgfbi, Tgf-βr1, Smad3/4 and many matrix metallopeptidases [MMPs]) was apparent in E4orf1-Tg BAT (Supplementary Table 3). Similar to sWAT, numerous collagens were also markedly up-regulated in E4orf1-Tg BAT (Supplementary Table 3), suggesting unhealthy fibrotic AT. In line with the gene expression data, histological examination through H&E staining revealed markedly disorganized and enlarged lipid-laden adipocytes in E4orf1-Tg BAT (Figure 5B). Further, consistent with the gene expression data (Supplementary Table 3), trichrome staining revealed enhanced tissue fibrosis in E4orf1-Tg BAT (Figure 5B). E4orf1-Tg BAT also displayed enhanced Mac2-positive staining (Figure 5B), indicating inflamed and unhealthy AT, similar to that observed for E4orf1-Tg sWAT (Figure 2E). However, despite the gene expression data highlighting a marked reduction in the browning signature program in E4orf1-Tg BAT (Figure 5A), Ucp1 IHC showed no striking differences in Ucp1-positive staining between WT BAT and E4orf1-Tg BAT (Figure 5B). This suggests that even though mRNA levels are reduced, UCP1 protein levels are maintained, either through enhance translational efficacy or a prolonged half-life for UCP1 protein.

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