Central Apolipoprotein A-IV Stimulates Thermogenesis in Brown Adipose Tissue

Abstract

Stimulation of thermogenesis in brown adipose tissue (BAT) could have far-reaching health benefits in combatting obesity and obesity-related complications. Apolipoprotein A-IV (ApoA-IV), produced by the gut and the brain in the presence of dietary lipids, is a well-known short-term satiating protein. While our previous studies have demonstrated reduced diet-induced thermogenesis in ApoA-IV-deficient mice, it is unclear whether this reduction is due to a loss of peripheral or central effects of ApoA-IV. We hypothesized that central administration of ApoA-IV stimulates BAT thermogenesis and that sympathetic and sensory innervation is necessary for this action. To test this hypothesis, mice with unilateral denervation of interscapular BAT received central injections of recombinant ApoA-IV protein or artificial cerebrospinal fluid (CSF). The effects of central ApoA-IV on BAT temperature and thermogenesis in mice with unilateral denervation of the intrascapular BAT were monitored using transponder probe implantation, qPCR, and immunoblots. Relative to CSF, central administration of ApoA-IV significantly increased temperature and UCP expression in BAT. However, all of these effects were significantly attenuated or prevented in mice with unilateral denervation. Together, these results clearly demonstrate that ApoA-IV regulates BAT thermogenesis centrally, and this effect is mediated through sympathetic and sensory nerves.

Keywords: brown adipose tissue; thermogenesis; third ventricle; unilateral denervation.

Figure 1

The effects of ApoA-IV on BAT temperature and UCP1 protein levels. BAT temperature was measured every 5 min for up to 40 min in mice following administration of either ApoA-IV at two different doses or CSF (A). The mice received central administration of either CSF (1 µL) or ApoA-IV (12 µg) into the third ventricle, and BAT was collected at 40 min post-injection. UCP1 protein in BAT was measured by immunoblot analysis (B). Data are expressed as the means ± SEM for 7–8 mice per group. * Represents a significant difference relative to the corresponding CSF-treated BAT (p < 0.5).

Figure 2

Lipolytic and thermogenic gene expression in adipose tissues. Levels of Ampkα1 and Ampkα2 (A), Atgl and Hsl (B), Cpt1 (C), and Ucp1 and Ucp3 (D) gene expression were measured by qRT-PCR. Mice received central administration of either CSF (1 µL) or ApoA-IV (12 µg in 1 µL) into the third ventricle, and BAT was collected at 40 min post-injection. Data are expressed as the means ± SEM for 6–7 mice per group. * Represents a significant difference relative to CSF-treated controls (p < 0.05).

Figure 3

Levels of tyrosine hydroxylase (TH) and calcitonin gene-related peptide (CGRP) in innervated and denervated BAT. The TH (A) and CGRP (B) proteins were measured by immunoblot analyses. Mice with unilateral denervation of BAT received central administration of either CSF (1 µL) or ApoA-IV (12 µg in 1 µL) into the third ventricle, and BAT was collected at 40 min post-injection. Data are expressed as the means ± SEM for 10–11 mice per group. * Represents a significant difference relative to CSF-treated BAT (p < 0.05).

Figure 4

The effect of ApoA-IV on BAT temperature and UCP1 protein levels in mice with unilateral denervation of BAT. BAT temperature in intact and denervated BAT was measured every 5 min for up to 40 min in mice following administration of either ApoA-IV (n = 6–7/dose group) or CSF (A). Mice with unilateral denervation of BAT received central administration of either CSF (1 µL) or ApoA-IV (12 µg) into the third ventricle and BAT was collected at 40 min post-injection. UCP1 in BAT was measured by immunoblot analysis (B). Data are expressed as the means ± SEM for 5–6 mice per group. * Represents a significant difference relative to CSF-treated BAT (p < 0.05).

Figure 5

Lipolytic and thermogenic gene expression in intact and denervated BAT. Levels of Ampkα1 and Ampkα2 (A), Atgl and Hsl (B), Cpt1 (C), and Ucp1 and Ucp3 (D) gene expression in intact and denervated BAT were measured by qRT-PCR. Mice with unilateral denervation of BAT received central administration of either CSF (1 µL) or ApoA-IV (12 µg) into the third ventricle, and BAT was collected at 40 min post-injection. Data are expressed as the means ± SEM for 6–8 mice per group. * Represents a significant difference relative to CSF-treated controls (p < 0.05).

Figure 5

Lipolytic and thermogenic gene expression in intact and denervated BAT. Levels of Ampkα1 and Ampkα2 (A), Atgl and Hsl (B), Cpt1 (C), and Ucp1 and Ucp3 (D) gene expression in intact and denervated BAT were measured by qRT-PCR. Mice with unilateral denervation of BAT received central administration of either CSF (1 µL) or ApoA-IV (12 µg) into the third ventricle, and BAT was collected at 40 min post-injection. Data are expressed as the means ± SEM for 6–8 mice per group. * Represents a significant difference relative to CSF-treated controls (p < 0.05).