Fig. 1.

Short-term brain ER stress causes systemic insulin resistance. (A–E) C57BL/6 mice received daily third-ventricle injections of TG at the doses of 0.3, 0.6, or 1.0 μg/d for 3 consecutive d. Vehicle injection was used as negative control and is labeled as 0 in the bar graphs. Mice were fasted overnight before receiving the final injection on day 3 and were examined at 2 h postinjection for GTT (A and B), ITT (C and D), or plasma insulin levels (E). Area under the curve (AUC) data for GTT (B) and ITT (D) were calculated. ITT data are presented as the percentages of time-course blood glucose levels over the baseline level (C) and the percentage changes of AUC over the control (vehicle injection) group (D). *P < 0.05; **P < 0.01; n = 8–9 mice per group. (F–H) Mice injected with TG (1.0 μg/d) or vehicle for 3 consecutive d were anesthetized and challenged with insulin (INS) (5.0 units/kg) or saline for 3 min via the inferior vena cava. Liver samples were rapidly harvested and analyzed for insulin signaling with immunoprecipitation (IP) and Western blots. (G) Tyrosine phosphorylation (p-Tyr) of IRβ and IRS2, the binding of p85 to IRS2, and phosphorylated Akt (p-Akt) were quantitatively normalized by the total protein levels (Total) of IRβ, IRS2, p85, and Akt, respectively. β-actin (β-act) was used as an internal control. (H) Liver tissues were harvested from mice that received 3-d TG vs. vehicle treatment and analyzed for mRNA levels of gluconeogenic enzymes pepck and g6pase with real-time RT-PCR. *P < 0.05; **P < 0.01; n = 4–6 mice per group; AU, arbitrary unit. (Error bars reflect mean ± SEM.)