Figure 1. Hepatic JNK contributes to diet-induced obesity and insulin resistance.

(A) The liver, adipose tissue (epididymal), and skeletal muscle (gastrocnemius) of L^WT, L^Δ1, L^Δ2 and L^Δ1,2 mice were examined by immunoblot analysis by probing with antibodies to JNK and GAPDH.

(B) Genomic DNA isolated from the liver of L^WT, L^Δ1, L^Δ2 and L^Δ1,2 mice was examined by PCR analysis to detect Jnk and ΔJnk alleles.

(C) Liver extracts prepared from mice fed a chow diet or a HFD (16 wk) and starved overnight were examined by immunoblot (IB) analysis by probing with antibodies to αTubulin and JNK. In vitro protein kinase assays (KA) with the substrates GST-cJun and [γ-³²P]ATP were performed to measure JNK activity. The amount of cJun and phosphorylated cJun (p-cJun) were detected by staining with Coomassie blue and Phosphorimager (Applied Biosystems) analysis, respectively.

(D) The fat and lean mass of chow-fed and HFD-fed (16 weeks) mice were measured by ¹H-MRS analysis (mean ± SEM; n = 8 ~ 10). Significant differences between L^WT and L^Δ1,2 mice were detected (**, p < 0.01, ***, p < 0.001).

(E,F) Glucose (GTT) and insulin (ITT) tolerance tests were performed on mice fed (16 wk) a HFD (mean ± SEM; n = 35 ~ 50; **, p < 0.01; ***, p < 0.001).

(G) Pyruvate (PTT) tolerance tests were performed on mice fed (16 wk) a HFD (mean ± SEM; n = 20 ~ 30; *, ***, p < 0.001).

(H–K) Insulin sensitivity was measured using hyperinsulinemic-euglycemic clamps with conscious L^WT and L^Δ1,2 mice fed a chow diet or HFD. The hepatic glucose production (HGP) during the clamp, hepatic insulin action (expressed as insulin-mediated percent suppression of basal HGP), glucose infusion rate, and glycogen plus lipid synthesis (mean ± SEM for 6 ~ 8 experiments) are presented. Statistically significant differences between L^WT and L^Δ1,2 mice are indicated (* p < 0.05).

(L–N) Chow-fed or HFD-fed L^WT and L^Δ1,2 mice were starved overnight and then administered insulin (1.5U/kg body mass) by intraperitoneal injection. Liver, epididymal adipose tissue, and gastrocnemius muscle extracts (prepared 15 mins post-injection) were examined (upper panels) by multiplexed ELISA for pS⁴⁷³-AKT and AKT (mean ± SEM; n = 5 ~ 6; *, p < 0.05). Representative extracts were also examined by immunoblot analysis using antibodies to AKT, phospho-AKT (pSer⁴⁷³ and pThr³⁰⁸) and GAPDH (lower panels).

See also Figures S1 & S2.