Leptin as an Antitorpor Hormone: An Explanation for the Increased Metabolic Efficiency and Cold Sensitivity of ob/ob Mice?

Alleviation of lipid metabolic dysfunction through regulation of intestinal bacteriophages and bacteria by green tea polyphenols in Ob/Ob mice

Green tea polyphenols (GTP) have been shown to ameliorate lipid metabolic disorders by regulating intestinal bacteria. Given the significant role of intestinal bacteriophages in shaping the gut microbiota, this study investigates GTP's influence on gut bacteriophage-bacteria interactions and lipid metabolism using metagenomics and metabonomics. The research results indicated that GTP significantly reduced body weight, serum triglycerides, leptin, insulin resistance, interleukin-6, and TNF-α levels while increasing adiponectin in ob/ob mice fed high-fat diet, aiding intestinal repair. GTP improved gut health by decreasing Enterobacter, Siphoviridae and Enterobacteria_phage_sfv, increasing Bifidobacterium and intestinal metabolites SCFA and hippuric acid. Correlation analysis showed negative correlations between Enterobacter sp. 50,588,862 and Enterobacteria_phages, Shigella_phages with 4-hydroxyphenylpyruvate and hippuric acid. Bifidobacterium choerinum and Bifidobacterium sp. AGR2158 were positively correlated with fatty acids and bile acids. In conclusion, GTP reduced fat accumulation and inflammation, enhanced gut barrier function in obese mice, closely associated with changes in the gut bacteriophage community.

Leptin Resistance Does Not Facilitate Migratory Fattening in Ruby-Throated Hummingbirds (Archilochus Colubris)

In mammals, leptin is an important energy homeostasis hormone produced by adipose tissue. Circulating leptin concentrations correlate positively with fat mass and act in a negative feedback fashion to inhibit food intake and increase energy expenditure, thereby preventing fat gain. For some species, leptin resistance is advantageous during times of year where fat gain is necessary (e.g., prior to hibernation). While the function of leptin in birds remains controversial, seasonal leptin resistance may similarly benefit migratory species. Here, we used the ruby-throated hummingbird (Archilochus colubris) to test the hypothesis that leptin resistance promotes fattening prior to migration. We predicted that during the migratory fattening period, leptin levels should correlate positively with fat mass but should not inhibit food intake or increase energy expenditure, resulting in fattening. We tracked the body (fat) mass, the concentration of leptin-like protein in the urine, and the food intake of 12 captive hummingbirds from August 2021 to January 2022. In a subset of hummingbirds, we also quantified voluntary physical activity as a proxy for energy expenditure. We found remarkable age-related variation in fattening strategies, with juveniles doubling their body fat by mid-September and adults exhibiting only a 50% increase. Changes in fat mass were strongly associated with increased food intake and reduced voluntary activity. However, we found no correlation between leptin-like protein concentration and fat mass, food intake, or voluntary activity. Since increased torpor use has been shown to accelerate migratory fattening in ruby-throated hummingbirds, we also hypothesized that leptin is a mediator of torpor use. In an experimental manipulation of circulating leptin, however, we found no change in torpor use, body fat, or food intake. Overall, our findings suggest that leptin may not act as an adipostat in hummingbirds, nor does leptin resistance regulate how hummingbirds fatten prior to migration.

Brown adipose tissue: can it keep us slim? A discussion of the evidence for and against the existence of diet-induced thermogenesis in mice and men

The issue under discussion here is whether a decrease in the degree of UCP1 activity (and brown adipose tissue activity in general) could be a cause of obesity in humans. This possibility principally requires the existence of the phenomenon of diet-induced thermogenesis. Obesity could be a consequence of a reduced functionality of diet-induced thermogenesis. Experiments in mice indicate that diet-induced thermogenesis exists and is dependent on the presence of UCP1 and thus of brown adipose tissue activity. Accordingly, many (but not all) experiments indicate that in the absence of UCP1, mice become obese. Whether similar mechanisms exist in humans is still unknown. A series of studies have indicated a correlation between obesity and low brown adipose tissue activity, but it may be so that the obesity itself may influence the estimates of brown adipose tissue activity (generally glucose uptake), partly explaining the relationship. Estimates of brown adipose tissue catabolizing activity would seem to indicate that it may possess a capacity sufficient to help maintain body weight, and obesity would thus be aggravated in its absence. This article is part of a discussion meeting issue 'Causes of obesity: theories, conjectures and evidence (Part II)'.

Roles of leptin on energy balance and thermoregulation in Eothenomys miletus

Leptin is a hormone mainly synthesized and secreted by white adipose tissue (WAT), which regulates various physiological processes. To investigate the role of leptin in energy balance and thermoregulation in Eothenomys miletus, voles were randomly divided into leptin-injected and PBS-injected groups and placed at 25°C ± 1°C with a photoperiod of 12 L:12 D. They were housed under laboratory conditions for 28 days and compared in terms of body mass, food intake, water intake, core body temperature, interscapular skin temperature, resting metabolic rate (RMR), nonshivering thermogenesis (NST), liver and brown adipose tissue (BAT) thermogenic activity, and serum hormone levels. The results showed that leptin injection decreased body mass, body fat, food intake, and water intake. But it had no significant effect on carcass protein. Leptin injection increased core body temperature, interscapular skin temperature, resting metabolic rate, non-shivering thermogenesis, mitochondrial protein content and cytochrome C oxidase (COX) activity in liver and brown adipose tissue, uncoupling protein 1 (UCP1) content and thyroxin 5'-deiodinase (T45'-DII) activity in brown adipose tissue significantly. Serum leptin, triiodothyronine (T3), thyrotropin-releasing hormone (TRH) and corticotropin-releasing hormone (CRH) concentrations were also increased significantly. Correlation analysis showed that serum leptin levels were positively correlated with core body temperature, body mass loss, uncoupling protein 1 content, thyroxin 5'-deiodinase activity, nonshivering thermogenesis, and negatively correlated with food intake; thyroxin 5'-deiodinase and triiodothyronine levels were positively correlated, suggesting that thyroxin 5'-deiodinase may play an important role in leptin-induced thermogenesis in brown adipose tissue. In conclusion, our study shows that exogenous leptin is involved in the regulation of energy metabolism and thermoregulation in E. miletus, and thyroid hormone may play an important role in the process of leptin regulating energy balance in E. miletus.