Intraindividual difference between supraclavicular and subcutaneous proton density fat fraction is associated with cold-induced thermogenesis.

Background: Brown adipose tissue (BAT) activity is triggered by cold exposure resulting in an increased resting energy expenditure, called cold-induced non-shivering thermogenesis (CIT). Magnetic resonance (MR)-based proton density fat fraction (PDFF) of the supraclavicular fossa has been proposed as a surrogate marker of human BAT. The present study investigates supraclavicular PDFF in relation to CIT. Methods: For this prospective cross-sectional study 39 adults were recruited, from a cross-sectional study, exploring energy expenditure after cold exposure compared to thermoneutral conditions. Participants underwent additional MR examination of neck, pelvis, and abdomen. Supraclavicular and subcutaneous gluteal adipose tissue depots were segmented semi-automatically. Mean PDFF was assessed for each compartment and the delta PDFF was calculated as the difference of both. Correlation analysis of supraclavicular PDFF to CIT was performed for the whole cohort and subgroups, sorted by body mass index (BMI) and body fat percentage. Results: Median age of participants (61.5% female) was 27 years. BMI ranged from 19.0 to 38.5 kg/m2, with body fat percentages from 4.6% to 45.3%. Median supraclavicular PDFF of 82.5% and median gluteal PDFF of 91.1%, were significantly different (P<0.0001). Median delta PDFF was 8.8% (3.9-21.9%). Mean CIT was 4.7%±9.0%. No statistically significant correlation of supraclavicular PDFF and CIT was found in the whole cohort and in most of the observed subgroups. Just the subgroup with normal body fat percentage revealed significant correlations between supraclavicular PDFF and CIT (rho =-0.59; P=0.003). Delta PDFF was significantly associated with CIT (rho =0.36; P=0.026). Conclusions: PDFF is influenced by adiposity. Therefore, if supraclavicular PDFF is used as approach to indirectly assess BAT presence, body composition should be considered. Delta PDFF, as the difference between gluteal and supraclavicular PDFF, may be a marker of CIT.

Gender Differences in the Response to Short-term Cold Exposure in Young Adults.

CONTEXT: Cold exposure (CE) has been shown to enhance energy expenditure by activating brown adipose tissue thermogenesis and metabolism in humans. However, it remains to be elucidated if there are gender-specific differences in cold-induced thermogenesis and metabolism. OBJECTIVE: To study the impact of mild CE on resting energy expenditure (REE) and metabolism in males compared with females. SETTING: A cross-sectional study. PARTICIPANTS: 117 healthy young Caucasians participated in this study (58 males). Mean age was 25.1 ± 3.6 years and mean body mass index 22.3 ± 1.7 kg/m2. INTERVENTION: Participants underwent a short-term CE using water perfused mattresses to activate nonshivering thermogenesis. MAIN OUTCOME MEASURES: REE was assessed before and 2 hours after CE followed by blood sampling. Selected metabolites and hormones were measured. Skin temperatures were monitored at various sites throughout the experiment. RESULTS: Participants showed a significant increase in REE after CE (6.5%, P < .001). This increase did not differ between genders (P = .908). However, there were differences between males and females in changes of plasma glucose (-5.1% versus -7.4%, P = .024), leptin (-14.3% versus -30.1%, P < .001) and adiponectin (5.4% versus 12.8%, P = .018) after CE. We observed a significant decrease of the supraclavicular skin temperature in men (-0.3%, P = .034), but not in women (0.3%, P = .326)(P = .019 between genders). CONCLUSIONS: We did not observe a difference in the thermogenic response, measured as change of REE, to CE in women compared with men. However, we found that some metabolic and hormonal changes were more pronounced in women than in men suggesting a gender-specific response to cold.

PUX10 Is a Lipid Droplet-Localized Scaffold Protein That Interacts with CELL DIVISION CYCLE48 and Is Involved in the Degradation of Lipid Droplet Proteins.

The number of known proteins associated with plant lipid droplets (LDs) is small compared with other organelles. Many aspects of LD biosynthesis and degradation are unknown, and identifying and characterizing candidate LD proteins could help elucidate these processes. Here, we analyzed the proteome of LD-enriched fractions isolated from tobacco (Nicotiana tabacum) pollen tubes. Proteins that were highly enriched in comparison with the total or cytosolic fraction were further tested for LD localization via transient expression in pollen tubes. One of these proteins, PLANT UBX DOMAIN-CONTAINING PROTEIN10 (PUX10), is a member of the plant UBX domain-containing (PUX) protein family. This protein localizes to LDs via a unique hydrophobic polypeptide sequence and can recruit the AAA-type ATPase CELL DIVISION CYCLE48 (CDC48) protein via its UBX domain. PUX10 is conserved in Arabidopsis thaliana and expressed in embryos, pollen tubes, and seedlings. In pux10 knockout mutants in Arabidopsis, LD size is significantly increased. Proteomic analysis of pux10 mutants revealed a delayed degradation of known LD proteins, some of which possessed ubiquitination sites. We propose that PUX10 is involved in a protein degradation pathway at LDs, mediating an interaction between polyubiquitinated proteins targeted for degradation and downstream effectors such as CDC48.