How brown is brown fat that we can see?

Troglitazone activates TRPV1 and causes deacetylation of PPARγ in 3T3-L1 cells

Published research suggests that activation of transient receptor potential vanilloid subfamily 1 (TRPV1) enhances the expression and deacetylation of peroxisome proliferator-activated receptor gamma (PPARγ) to cause browning of white adipose tissue. Here, we show that TRPV1 activation by capsaicin significantly prevents high fat diet-induced obesity in mice. This is associated with an increase in the expression and deacetylation of PPARγ in the epididymal fat of these mice. Consistent with the TRPV1 activation in vivo, overexpression of TRPV1 enhanced the PPARγ and other thermogenic genes in cultured 3T3-L1 preadipocytes. To determine the interaction between TRPV1 and PPARγ signaling, we analyzed the effect of Troglitazone (Trog; a thiazolidinedione derivative and an agonist of PAARγ) treatment on cultured 3T3-L1 cells. Trog enhanced the expression of TRPV1, PPARγ and thermogenic proteins in undifferentiated 3T3-L1 cells but not in differentiated cells. Acute application of Trog stimulated a robust Ca²⁺ influx into 3T3-L1 cells and TRPV1 inhibition by capsazepine prevented this. More interestingly, Trog or capsaicin treatment caused the deacetylation of PPARγ in 3T3-L1 cells and inhibition of TRPV1 or Sirtuin 1 - prevented this. Our data suggest a novel effect of Trog to induce PPARγ deacetylation by activating TRPV1. This research has a significant implication on the role of TRPV1 and PPARγ signaling in the browning of white adipose tissue.

Multiscale Imaging of Brown Adipose Tissue in Living Mice/Rats with Fluorescent Polymer Dots

Brown adipose tissue (BAT) has been identified as a promising target for the treatment of obesity, diabetes, and relevant metabolism disorders because of the adaptive thermogenesis ability of this tissue. Visualizing BAT may provide an essential tool for pathology study, drug screening, and efficacy evaluation. Owing to limitations of current nuclear and magnetic resonance imaging approaches for BAT detection, fluorescence imaging has advantages in large-scale preclinical research on small animals. Here, fast BAT imaging in mice is conducted based on polymer dots as fluorescent probes. As early as 5 min after the intravenous injection of polymer dots, extensive fluorescence is detected in the interscapular BAT and axillar BAT. In addition, axillar and inguinal white adipose tissues (WAT) are recognized. The real-time in vivo behavior of polymer dots in rodents is monitored using the probe-based confocal laser endomicroscopy imaging, and the preferred accumulation in BAT over WAT is confirmed by histological assays. Moreover, the whole study is conducted without a low temperature or pharmaceutical stimulation. The imaging efficacy is verified at the cellular, histological, and whole-body levels, and the present results indicate that fluorescent polymer dots may be a promising tool for the visualization of BAT in living subjects.

Neck circumference is associated with carotid intimal-media thickness but not with coronary artery calcium: Results from The ELSA-Brasil

BACKGROUND AND AIMS

It is uncertain whether neck circumference can be a risk indicator for subclinical atherosclerosis. We aimed to investigate their relationships measured by coronary artery calcium (CAC) and common carotid intima-media thickness (cc-IMT) with neck circumference in ELSA-Brasil.

METHODS AND RESULTS

In cross-sectional and sex-specific analyses of 2266 women (50.6 ± 8.4 yrs) and 1886 men (50.7 ± 9.0 yrs) with both cc-IMT and CAC, free from previous cardiovascular disease at baseline, we built logistic models using diverse cut-off points for CAC score (0 vs > 0, < 100 vs ≥ 100, < 400 vs ≥ 400 Agatston units) and cc-IMT (< 75 th percentile vs ≥ 75 th; <90th percentile vs ≥ 90 th) as dependent variables, after which adjustments for age and traditional cardiovascular risk factors were made. Mean neck circumference was 33.6 (± 2.4 cm) for women and 38.8 (± 2.6 cm) for men. In fully adjusted models including sociodemographic, cardiovascular risk factors and body-mass index and waist circumference, for each 1 standard deviation increase in neck circumference we found an odds ratio (OR, 95% CI) for IMT above the 75th percentile of (1.52, 1.16; 1.99) for women and (1.66, 1.28; 2.14) for men, and above the 90th cc-IMT percentile [1.66 (1.19; 2.32) for men but not for women [1.21 (0.80; 1.82)]. We found no association between neck circumference and CAC using different cut-off points (p > 0.05 for all).

CONCLUSION

Neck circumference was significantly and independently associated with cc-IMT but not with CAC in women and men, indicating a possible effect of perivascular fat tissue on atherosclerosis.