Inhibition of protein kinase Cepsilon prevents hepatic insulin resistance in nonalcoholic fatty liver disease - PubMed (original) (raw)

. 2007 Mar;117(3):739-45.

doi: 10.1172/JCI30400. Epub 2007 Feb 22.

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Inhibition of protein kinase Cepsilon prevents hepatic insulin resistance in nonalcoholic fatty liver disease

Varman T Samuel et al. J Clin Invest. 2007 Mar.

Abstract

Nonalcoholic fatty liver disease is strongly associated with hepatic insulin resistance and type 2 diabetes mellitus, but the molecular signals linking hepatic fat accumulation to hepatic insulin resistance are unknown. Three days of high-fat feeding in rats results specifically in hepatic steatosis and hepatic insulin resistance. In this setting, PKCepsilon, but not other isoforms of PKC, is activated. To determine whether PKCepsilon plays a causal role in the pathogenesis of hepatic insulin resistance, we treated rats with an antisense oligonucleotide against PKCepsilon and subjected them to 3 days of high-fat feeding. Knocking down PKCepsilon expression protects rats from fat-induced hepatic insulin resistance and reverses fat-induced defects in hepatic insulin signaling. Furthermore, we show that PKCepsilon associates with the insulin receptor in vivo and impairs insulin receptor kinase activity both in vivo and in vitro. These data support the hypothesis that PKCepsilon plays a critical role in mediating fat-induced hepatic insulin resistance and represents a novel therapeutic target for type 2 diabetes.

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Figures

Figure 1

Figure 1. PKCε ASO is effective and well tolerated.

(A) The amount of PKC_ε mRNA was determined by quantitative RT-PCR after 4 weeks of treatment with saline, a control ASO, and a specific ASO against PKCε (PKCε ASO). Data are expressed as relative to expression in saline. #P < 0.01 versus saline; Χ_P < 0.001 versus control; ‡P < 0.01 versus control. (B) PKCε ASO specifically decreases PKCε protein levels in liver and epididymal white adipose tissue (WAT), but not in gastrocnemius. (C) Weight gain over 4 weeks of ASO therapy. Surgery was performed on rats between days 15 and 20.

Figure 2

Figure 2. PKCε ASO reduces fasting concentration of insulin without changes in plasma glucose, intrahepatic triglyceride, or DAG.

(A) Fasting plasma glucose. (B) Fasting plasma insulin. **P < 0.001 versus saline; ‡P < 0.01 versus control ASO. (C) Hepatic triglyceride content. (D) Intrahepatic total DAG.

Figure 3

Figure 3. PKCε ASO therapy results in improved hepatic insulin sensitivity and insulin-stimulated adipose glucose uptake.

(A) Basal rate of endogenous glucose production. (B) Percentage suppression of endogenous glucose production during hyperinsulinemic-euglycemic clamping. *P < 0.05 versus saline; ‡P < 0.01 versus control ASO. (C) Rate of insulin-stimulated whole-body glucose uptake. **P < 0.001 versus saline. (D) Soleus 14C-2-deoxyglucose (2-DOG) uptake. (E) Gastrocnemius 2-DOG uptake. (F) Epididymal white adipose tissue (WAT) 2-DOG uptake. *P < 0.05 versus saline. (G) Suppression of plasma fatty acid concentration during hyperinsulinemic-euglycemic clamping. *P < 0.05 versus saline.

Figure 4

Figure 4. PKCε ASO therapy improves hepatic insulin signaling and preserves insulin receptor kinase activity.

Insulin receptor (IR) tyrosine phosphorylation, IRS2 tyrosine phosphorylation, and AKT2 activity were assessed in the basal, fasted state, and after 20 minutes of hyperinsulinemic-euglycemic clamping. (A) Insulin receptor tyrosine phosphorylation. (B) IRS2 tyrosine phosphorylation. *P < 0.05 versus saline; †P < 0.05 versus control ASO. (C) AKT2 activity. †P < 0.05 versus control ASO. (D) Immunoprecipitation of the insulin receptor also precipitates PKCε and vice versa. (E) Incubation of active insulin receptor kinase with increasing molar ratios of PKCε results in a dose-dependent decrease in insulin receptor kinase activity. (F) Activity of lecithin-purified insulin receptor kinase from rats fed a normal low-fat diet and high-fat-fed (HFF) rats treated with saline, control ASO, and PKCε ASO. #P < 0.01 versus HFF/saline; Χ_P_ < 0.001 versus HFF.

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