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Endothelial NO/cGMP/VASP signaling attenuates Kupffer cell activation and hepatic insulin resistance induced by high-fat feeding.

Tateya S, Rizzo NO, Handa P, Cheng AM, Morgan-Stevenson V, Daum G, Clowes AW, Morton GJ, Schwartz MW, Kim F - Diabetes (2011)

Bottom Line: We sought to determine whether reduced endothelial nitric oxide (NO) signaling contributes to the effect of high-fat feeding to increase hepatic inflammatory signaling and if so, whether this effect 1) involves activation of Kupffer cells and 2) is ameliorated by increased NO signaling.Targeted deletion of vasodilator-stimulated phosphoprotein (VASP), a key downstream target of endothelially derived NO, similarly predisposes to hepatic and Kupffer cell inflammation and abrogates the protective effect of NO signaling in both macrophages and hepatocytes studied in a cell culture model.Our findings also identify the NO/VASP pathway as a novel potential target for the treatment of obesity-associated liver insulin resistance.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, University of Washington, Seattle, Washington, USA.

ABSTRACT

Objective: Proinflammatory activation of Kupffer cells is implicated in the effect of high-fat feeding to cause liver insulin resistance. We sought to determine whether reduced endothelial nitric oxide (NO) signaling contributes to the effect of high-fat feeding to increase hepatic inflammatory signaling and if so, whether this effect 1) involves activation of Kupffer cells and 2) is ameliorated by increased NO signaling.

Research design and methods: Effect of NO/cGMP signaling on hepatic inflammation and on isolated Kupffer cells was examined in C57BL/6 mice, eNos(-/-) mice, and Vasp(-/-) mice fed a low-fat or high-fat diet.

Results: We show that high-fat feeding induces proinflammatory activation of Kupffer cells in wild-type mice coincident with reduced liver endothelial nitric oxide synthase activity and NO content while, conversely, enhancement of signaling downstream of endogenous NO by phosphodiesterase-5 inhibition protects against high fat-induced inflammation in Kupffer cells. Furthermore, proinflammatory activation of Kupffer cells is evident in eNos(-/-) mice even on a low-fat diet. Targeted deletion of vasodilator-stimulated phosphoprotein (VASP), a key downstream target of endothelially derived NO, similarly predisposes to hepatic and Kupffer cell inflammation and abrogates the protective effect of NO signaling in both macrophages and hepatocytes studied in a cell culture model.

Conclusions: These results collectively imply a physiological role for endothelial NO to limit obesity-associated inflammation and insulin resistance in hepatocytes and support a model in which Kupffer cell activation during high-fat feeding is dependent on reduced NO signaling. Our findings also identify the NO/VASP pathway as a novel potential target for the treatment of obesity-associated liver insulin resistance.

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Effect of daily sildenafil during high-fat (HF) feeding on liver NF-κB and hepatic insulin signaling. Six-week-old male C57BL/6 mice were maintained on either a low-fat (LF; 10% saturated fat) or HF (60% saturated fat) diet for 8 weeks, and for the last 2 weeks of the diet, study mice received 30 mg/kg per day oral sildenafil (n = 8) or vehicle (n = 8). A: IκB-α phosphorylation in liver lysates. B: IL-6 mRNA levels. C: Inflammatory markers from isolated Kupffer cells by quantitative RT-PCR (n = 5). *P < 0.05. D: Hepatic insulin (Ins) signaling at the level of Akt phosphorylation (n = 5). *P < 0.05. E: Hepatic triglyceride (TG) content (n = 5). *P < 0.05. ctl, control; veh, vehicle. IB, immunoblot; kD, kilodalton.
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Figure 3: Effect of daily sildenafil during high-fat (HF) feeding on liver NF-κB and hepatic insulin signaling. Six-week-old male C57BL/6 mice were maintained on either a low-fat (LF; 10% saturated fat) or HF (60% saturated fat) diet for 8 weeks, and for the last 2 weeks of the diet, study mice received 30 mg/kg per day oral sildenafil (n = 8) or vehicle (n = 8). A: IκB-α phosphorylation in liver lysates. B: IL-6 mRNA levels. C: Inflammatory markers from isolated Kupffer cells by quantitative RT-PCR (n = 5). *P < 0.05. D: Hepatic insulin (Ins) signaling at the level of Akt phosphorylation (n = 5). *P < 0.05. E: Hepatic triglyceride (TG) content (n = 5). *P < 0.05. ctl, control; veh, vehicle. IB, immunoblot; kD, kilodalton.

Mentions: Because increased NO/cGMP levels are associated with reduced NF-κB signaling, we next sought to determine whether increased NO/cGMP signaling would restore hepatic insulin signaling in an in vivo model. Adult male C57BL/6 mice were fed either a low-fat or a high-fat diet for 8 weeks to cause obesity, liver inflammation, and insulin resistance (15). During the final 2 weeks of the high-fat feeding protocol, mice on each diet received daily oral administration of either vehicle or the phosphodiesterase-5 (PDE-5) inhibitor sildenafil at a dose (30 mg/kg per day) that did not affect weight gain on either diet compared with the vehicle control group (15). In response to 8 weeks of high-fat feeding, liver IκB-α phosphorylation and IL-6 mRNA content in vehicle-treated mice were increased compared with those in low fat–fed mice, whereas in sildenafil-treated mice these inflammatory responses to high-fat feeding were not observed (Fig. 3A and B). In addition, a similar anti-inflammatory effect was seen in an analysis of Kupffer cells, in which expression of mRNA encoding TNF-α, iNOS, and CD11c was each reduced compared with Kupffer cells isolated from vehicle-treated controls (Fig. 3C).


Endothelial NO/cGMP/VASP signaling attenuates Kupffer cell activation and hepatic insulin resistance induced by high-fat feeding.

Tateya S, Rizzo NO, Handa P, Cheng AM, Morgan-Stevenson V, Daum G, Clowes AW, Morton GJ, Schwartz MW, Kim F - Diabetes (2011)

Effect of daily sildenafil during high-fat (HF) feeding on liver NF-κB and hepatic insulin signaling. Six-week-old male C57BL/6 mice were maintained on either a low-fat (LF; 10% saturated fat) or HF (60% saturated fat) diet for 8 weeks, and for the last 2 weeks of the diet, study mice received 30 mg/kg per day oral sildenafil (n = 8) or vehicle (n = 8). A: IκB-α phosphorylation in liver lysates. B: IL-6 mRNA levels. C: Inflammatory markers from isolated Kupffer cells by quantitative RT-PCR (n = 5). *P < 0.05. D: Hepatic insulin (Ins) signaling at the level of Akt phosphorylation (n = 5). *P < 0.05. E: Hepatic triglyceride (TG) content (n = 5). *P < 0.05. ctl, control; veh, vehicle. IB, immunoblot; kD, kilodalton.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC3198085&req=5

Figure 3: Effect of daily sildenafil during high-fat (HF) feeding on liver NF-κB and hepatic insulin signaling. Six-week-old male C57BL/6 mice were maintained on either a low-fat (LF; 10% saturated fat) or HF (60% saturated fat) diet for 8 weeks, and for the last 2 weeks of the diet, study mice received 30 mg/kg per day oral sildenafil (n = 8) or vehicle (n = 8). A: IκB-α phosphorylation in liver lysates. B: IL-6 mRNA levels. C: Inflammatory markers from isolated Kupffer cells by quantitative RT-PCR (n = 5). *P < 0.05. D: Hepatic insulin (Ins) signaling at the level of Akt phosphorylation (n = 5). *P < 0.05. E: Hepatic triglyceride (TG) content (n = 5). *P < 0.05. ctl, control; veh, vehicle. IB, immunoblot; kD, kilodalton.
Mentions: Because increased NO/cGMP levels are associated with reduced NF-κB signaling, we next sought to determine whether increased NO/cGMP signaling would restore hepatic insulin signaling in an in vivo model. Adult male C57BL/6 mice were fed either a low-fat or a high-fat diet for 8 weeks to cause obesity, liver inflammation, and insulin resistance (15). During the final 2 weeks of the high-fat feeding protocol, mice on each diet received daily oral administration of either vehicle or the phosphodiesterase-5 (PDE-5) inhibitor sildenafil at a dose (30 mg/kg per day) that did not affect weight gain on either diet compared with the vehicle control group (15). In response to 8 weeks of high-fat feeding, liver IκB-α phosphorylation and IL-6 mRNA content in vehicle-treated mice were increased compared with those in low fat–fed mice, whereas in sildenafil-treated mice these inflammatory responses to high-fat feeding were not observed (Fig. 3A and B). In addition, a similar anti-inflammatory effect was seen in an analysis of Kupffer cells, in which expression of mRNA encoding TNF-α, iNOS, and CD11c was each reduced compared with Kupffer cells isolated from vehicle-treated controls (Fig. 3C).

Bottom Line: We sought to determine whether reduced endothelial nitric oxide (NO) signaling contributes to the effect of high-fat feeding to increase hepatic inflammatory signaling and if so, whether this effect 1) involves activation of Kupffer cells and 2) is ameliorated by increased NO signaling.Targeted deletion of vasodilator-stimulated phosphoprotein (VASP), a key downstream target of endothelially derived NO, similarly predisposes to hepatic and Kupffer cell inflammation and abrogates the protective effect of NO signaling in both macrophages and hepatocytes studied in a cell culture model.Our findings also identify the NO/VASP pathway as a novel potential target for the treatment of obesity-associated liver insulin resistance.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, University of Washington, Seattle, Washington, USA.

ABSTRACT

Objective: Proinflammatory activation of Kupffer cells is implicated in the effect of high-fat feeding to cause liver insulin resistance. We sought to determine whether reduced endothelial nitric oxide (NO) signaling contributes to the effect of high-fat feeding to increase hepatic inflammatory signaling and if so, whether this effect 1) involves activation of Kupffer cells and 2) is ameliorated by increased NO signaling.

Research design and methods: Effect of NO/cGMP signaling on hepatic inflammation and on isolated Kupffer cells was examined in C57BL/6 mice, eNos(-/-) mice, and Vasp(-/-) mice fed a low-fat or high-fat diet.

Results: We show that high-fat feeding induces proinflammatory activation of Kupffer cells in wild-type mice coincident with reduced liver endothelial nitric oxide synthase activity and NO content while, conversely, enhancement of signaling downstream of endogenous NO by phosphodiesterase-5 inhibition protects against high fat-induced inflammation in Kupffer cells. Furthermore, proinflammatory activation of Kupffer cells is evident in eNos(-/-) mice even on a low-fat diet. Targeted deletion of vasodilator-stimulated phosphoprotein (VASP), a key downstream target of endothelially derived NO, similarly predisposes to hepatic and Kupffer cell inflammation and abrogates the protective effect of NO signaling in both macrophages and hepatocytes studied in a cell culture model.

Conclusions: These results collectively imply a physiological role for endothelial NO to limit obesity-associated inflammation and insulin resistance in hepatocytes and support a model in which Kupffer cell activation during high-fat feeding is dependent on reduced NO signaling. Our findings also identify the NO/VASP pathway as a novel potential target for the treatment of obesity-associated liver insulin resistance.

Show MeSH
Related in: MedlinePlus