Vascular rarefaction mediates whitening of brown fat in obesity
Ippei Shimizu, … , Sonomi Maruyama, Kenneth Walsh
Ippei Shimizu, … , Sonomi Maruyama, Kenneth Walsh
Published April 8, 2014
Citation Information: J Clin Invest. 2014;124(5):2099-2112. https://doi.org/10.1172/JCI71643.
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Research Article Endocrinology

Vascular rarefaction mediates whitening of brown fat in obesity

Abstract

Brown adipose tissue (BAT) is a highly vascularized organ with abundant mitochondria that produce heat through uncoupled respiration. Obesity is associated with a reduction of BAT function; however, it is unknown how obesity promotes dysfunctional BAT. Here, using a murine model of diet-induced obesity, we determined that obesity causes capillary rarefaction and functional hypoxia in BAT, leading to a BAT “whitening” phenotype that is characterized by mitochondrial dysfunction, lipid droplet accumulation, and decreased expression of Vegfa. Targeted deletion of Vegfa in adipose tissue of nonobese mice resulted in BAT whitening, supporting a role for decreased vascularity in obesity-associated BAT. Conversely, introduction of VEGF-A specifically into BAT of obese mice restored vascularity, ameliorated brown adipocyte dysfunction, and improved insulin sensitivity. The capillary rarefaction in BAT that was brought about by obesity or Vegfa ablation diminished β-adrenergic signaling, increased mitochondrial ROS production, and promoted mitophagy. These data indicate that overnutrition leads to the development of a hypoxic state in BAT, causing it to whiten through mitochondrial dysfunction and loss. Furthermore, these results link obesity-associated BAT whitening to impaired systemic glucose metabolism.

Authors

Ippei Shimizu, Tamar Aprahamian, Ryosuke Kikuchi, Ayako Shimizu, Kyriakos N. Papanicolaou, Susan MacLauchlan, Sonomi Maruyama, Kenneth Walsh

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Figure 4

VEGF-A–mediated regulation of mitochondrial ROS production and autophagic responses in the BAT of obese mice.

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VEGF-A–mediated regulation of mitochondrial ROS production and autophagi...
(A and B) FACS analysis for mitochondrial ROS (MitoSOX; A) and membrane potential (MitoRed with or without CCCP treatment; B) using isolated mitochondria extracted from BAT. (C) Western blot analysis of LC3A/B expression in BAT. The right graph indicates the quantification of LC3A/B-II expression relative to GAPDH-loading control (n = 3). (D and F) Immunofluorescent staining showing mitochondrial membrane protein Tom20 (green) colocalizing with autophagosomal membrane protein LC3 (red) in BAT of mice fed NC or HFHS diet with (F) or without (D) the injection of ad-vegfa or a control adenoviral vector (Con). Representative photomicrograph observed at ×3000 magnification. Scale bar: 3 μm. Merged areas are indicated by white arrows. The graph at right quantifies the number of puncta double stained with Tom20 and LC3 measured on 10 random fields and observed at ×3000 magnification (n = 3). (E and G) Real-time PCR expression of Bnip3 and Map1lc3b in BAT of mice (n = 3–6). (H–J) Western blot analysis of PINK1 (H), Parkin (I), and ubiquitin-conjugated protein (J) expression in isolated mitochondria extracted from BAT of mice. The graphs at right indicate the quantification relative to the expression of the Cox IV loading control (n = 3). In J, the level of ubiquitination is compared with the 25 kDa protein between the groups. Data were analyzed by 2-tailed Student’s t test (C–E and H–J) or ANOVA (F and G). *P < 0.05; **P < 0.01. All values represent the mean ± SEM.