An obesogenic diet impairs uncoupled substrate oxidation and promotes whitening of the brown adipose tissue in rats

Liraglutide induced browning of visceral white adipose through regulation of miRNAs in high-fat-diet-induced obese mice

OBJECTIVE

Obesity is characterized by excessive accumulation of white adipose tissue (WAT). Conversely, brown adipose tissue is protective against obesity. We recently reported liraglutide, a glucagon-like peptide-1 receptor agonist (GLP-1RA), could inhibit high-fat-diet-induced obesity by browning of WAT. However, the molecular mechanism involved is not well defined. Hence, we aimed to explore whether GLP-1RA could promote brown remodeling in WAT by regulating miRNAs.

METHODS

After the obesity model was successfully constructed, C57BL/6J mice were treated with liraglutide (200 μg/kg/d) or equivoluminal saline subcutaneously for 12 weeks. Then, the deposition of abdominal fat was measured by CT scanning. At the end of the treatments, glucose and insulin tolerance in mice were assessed. Serum lipid levels were monitored and epididymal WAT (eWAT) were collected for analysis. Quantitative real-time PCR and western blot analyses were conducted to evaluate the expression of genes and miRNAs associated with white fat browning.

RESULTS

Liraglutide significantly reduced body weight and visceral fat mass. Levels of lipid profile were also improved. Liraglutide upregulated the expression of browning-related genes in eWAT. Meanwhile, the expression level of miRNAs (miR-196a and miR-378a) positively associated with the browning of WAT were increased, while the expression of miR-155, miR-199a, and miR-382 negatively related with browning of WAT were decreased.

CONCLUSION

Our findings suggest that liraglutide could promote brown remodeling of visceral WAT by bi-regulating miRNAs; this might be one of the mechanisms underlying its effect on weight loss.

Neural circuits of long-term thermoregulatory adaptations to cold temperatures and metabolic demands

The mammalian brain controls heat generation and heat loss mechanisms that regulate body temperature and energy metabolism. Thermoeffectors include brown adipose tissue, cutaneous blood flow and skeletal muscle, and metabolic energy sources include white adipose tissue. Neural and metabolic pathways modulating the activity and functional plasticity of these mechanisms contribute not only to the optimization of function during acute challenges, such as ambient temperature changes, infection and stress, but also to longitudinal adaptations to environmental and internal changes. Exposure of humans to repeated and seasonal cold ambient conditions leads to adaptations in thermoeffectors such as habituation of cutaneous vasoconstriction and shivering. In animals that undergo hibernation and torpor, neurally regulated metabolic and thermoregulatory adaptations enable survival during periods of significant reduction in metabolic rate. In addition, changes in diet can activate accessory neural pathways that alter thermoeffector activity. This knowledge may be harnessed for therapeutic purposes, including treatments for obesity and improved means of therapeutic hypothermia.

Intestinal epithelial adaptations to vertical sleeve gastrectomy defined at single-cell resolution

The gut plays a key role in regulating metabolic health. Dietary factors disrupt intestinal physiology and contribute to obesity and diabetes, whereas bariatric procedures such as vertical sleeve gastrectomy (VSG) cause gut adaptations that induce robust metabolic improvements. However, our understanding of these adaptations at the cellular and molecular levels remains limited. In a validated murine model, we leverage single-cell transcriptomics to determine how VSG impacts different cell lineages of the small intestinal epithelium. We define cell type-specific genes and pathways that VSG rescues from high-fat diet perturbation and characterize additional rescue-independent changes brought about by VSG. We show that Paneth cells have increased expression of the gut peptide Reg3g after VSG. We also find that VSG restores pathways pertaining to mitochondrial respiration and cellular metabolism, especially within crypt-based cells. Overall, our study provides unprecedented molecular resolution of VSG's therapeutic effects on the gut epithelium.

Changes in brown adipose tissue induced by resveratrol and its analogue pterostilbene in rats fed with a high-fat high-fructose diet

Natural bioactive compounds have attracted a great deal of attention since some of them can act as thermogenesis activators. In recent years, special interest has been placed on resveratrol and its analogue pterostilbene, a dimethylether derivative that shows higher bioavailability. The aim of the present study is to compare the effects of resveratrol and its derivative pterostilbene on the thermogenic capacity of interscapular brown adipose tissue (iBAT) in rats under a high-fat high-fructose diet. Rats were divided into four experimental groups: control, high-fat high-fructose diet (HFHF) and HFHF diet supplemented with 30 mg/kg body weight/day of pterostilbene (PT30) or resveratrol (RSV30), for eight weeks. Weights of adipose tissues, iBAT triglycerides, carnitine palmitoyltransferase 1A (CPT1A) and citrate synthase (CS) activities, protein levels of uncoupling protein 1 (UCP1), sirtuins (SIRT1 and 3), AMP-activated protein kinase (AMPK), glucose transporter (GLUT4), fatty acid synthase (FAS), nuclear respiratory factor (NRF1), hormone-sensitive lipase (HSL), adipose triglyceride lipase (ATGL), CD36 and FATP1 fatty acid transporters, peroxisome proliferator-activated receptor gamma coactivator 1 (PGC1) activation and the batokines EPDR1 and NRG4 were assessed in iBAT. The results show that some key proteins related to thermogenesis were modified by either pterostilbene or resveratrol, although the lack of effects on other crucial proteins of the thermogenic machinery suggest that these compounds were not able to stimulate this process in iBAT. Overall, these data suggest that the effects of stilbenes on brown adipose tissue thermogenic capacity depend on the metabolic status, and more precisely on the presence or absence of obesity, although further studies are needed to confirm this hypothesis.

The Crosstalk between Gut Microbiota and White Adipose Tissue Mitochondria in Obesity

Adipose tissue (AT) dysregulation is a key process in the pathophysiology of obesity and its cardiometabolic complications, but even if a growing body of evidence has been collected over recent decades, the underlying molecular basis of adiposopathy remains to be fully understood. In this context, mitochondria, the intracellular organelles that orchestrate energy production and undergo highly dynamic adaptive changes in response to changing environments, have emerged as crucial regulators of both white (WAT) and brown adipose tissue (BAT) metabolism and function. Given that the gut microbiota and its metabolites are able to regulate host metabolism, adipogenesis, WAT inflammation, and thermogenesis, we hypothesize that their frequently observed dysregulation in obesity could affect AT metabolism by exerting direct and indirect effects on AT mitochondria. By collecting and revising the current evidence on the connections between gut microbiota and AT mitochondria in obesity, we gained insights into the molecular biology of their hitherto largely unexplored crosstalk, tracing how gut microbiota may regulate AT mitochondrial function.