High-energy diets produce different effects on fatty acid synthesis in brown adipose tissue, white adipose tissue and liver in the rat
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Fatty acid synthesis
Although brown adipose tissue in infants and young children is important for regulation of energy expenditure, there has been considerable debate on whether brown adipose tissue normally exists in adult humans and has physiologic relevance in this population. In the last decade, radiologic studies in adults have identified areas of adipose tissue with high 18F-fluorodeoxyglucose (18F-FDG) uptake, putatively identified as brown fat. This radiologic study assessed the presence of physiologically significant brown adipose tissue among 1972 adult patients who had 3640 consecutive 18F-FDG positron-emission tomographic and computed tomographic whole-body scans between 2003 and 2006. Brown adipose tissue was defined as areas of tissue that were more than 4 mm in diameter, had the CT density of adipose tissue, and had maximal standardized uptake values of 18F-FDG of at least 2.0 gm per mL. A sample of 204 date-matched patients without brown adipose tissue served as the control group. Using these criteria, positron-emission tomographic and computed tomographic scans identified brown adipose tissue in 106 of the 1972 patients (5.4%). The most common location for substantial amounts of brown adipose tissue was the region extending from the anterior neck to supraclavicular region. Immunohistochemical staining for uncoupling protein 1 in this region confirmed the identity of immunopositive, multilocular adipocytes as brown adipose tissue. More brown adipose tissue was detected in women (7.5% {lsqb;76/1013{rsqb;) than in men (3.1% {lsqb;30/959{rsqb;); the female:male ratio was 2.4:1.0 (P < 0.001). The mass and activity of brown adipose tissue was also greater in women than in men. The probability of having substantial brown adipose tissue decreased with increasing age (<50–>64) (P < 0.001), short-term or long-term use of beta-blockers (P < 0.001), increasing mean outdoor temperature at the time of the scan (P < 0.02), and increasing tissue and increasing body mass index among patients in the top third for age (>64 years) (P for trend = 0.007). These findings show that functional brown adipose tissue is prevalent in adult humans, and significantly more frequently in women. The inverse correlation of body mass index with the amount of brown adipose tissue, especially in older patients, suggests to the investigators a possible role of brown adipose tissue in protecting against obesity.
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Adipose tissue exist in two different forms which can be distinguished with the free eye by their color: white adipose tissue and brown adipose tissue. Both have a highly differing fine structure. Furthermore, their location differs significantly. White adipose tissue is found in the subcutaneous tissue where it exists mainly as single adipocytes or in the peritoneal cavity where it forms a compact tissue. The adipocytes of the white adipose tissue contain a single lipid droplet and therefore are referred to as univacuolar (or unilocular) adipocytes. Since the size of the lipid droplet can vary considerably, white adipocytes may measure between 40 and 120μm.
Adipose tissue macrophages
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Brown and beige adipose tissues dissipate energy in the form of heat via mitochondrial uncoupling protein 1, defending against hypothermia and potentially obesity. The latter has prompted renewed interest in understanding the processes involved in browning to realize the potential therapeutic benefits. To characterize the temporal profile of cold-induced changes and browning of brown and white adipose tissues in mice.Male C57BL/6J mice were singly housed in conventional cages under cold exposure (4 °C) for 1, 2, 3, 4, 5 and 7 days. Food intake and body weight were measured daily. Interscapular brown adipose tissue (iBAT), inguinal subcutaneous (sWAT) and epididymal white adipose tissue (eWAT) were harvested for histological, immunohistochemical, gene and protein expression analysis.Upon cold exposure, food intake increased, whilst body weight and adipocyte size were found to be transiently reduced. iBAT mass was found to be increased, whilst sWAT and eWAT were found to be transiently decreased. A combination of morphological, genetic (Ucp-1, Pgc-1α and Elov13) and biochemical (UCP-1, PPARγ and aP2) analyses demonstrated the depot-specific remodelling in response to cold exposure.Our results demonstrate the differential responses to cold-induced changes across discrete BAT and WAT depots and support the notion that the effects of short-term cold exposure are achieved by expansion, activation and increasing thermogenic capacity of iBAT, as well as browning of sWAT and, to a lesser extent, eWAT.
Thermogenin
Browning
PRDM16
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Fatty acid synthesis
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Fatty acid synthesis was measured in vivo with 3H2O in interscapular brown adipose tissue of lean and genetically obese (ob/ob) mice. At 26 days of age, before the development of hyperphagia, synthesis in brown adipose tissue was higher in the obese than in the lean mice; synthesis was also elevated in the liver, white adipose tissue and carcass of the obese mice. At 8 weeks of age, when hyperphagia was well established, synthesis remained elevated in all tissues of the obese mice, with the exception of brown adipose tissue. Elevated synthesis rates were not apparent in brown adipose tissue of the obese mice at 14 days of age, nor at 35 days of age. These results demonstrate that brown adipose tissue in ob/ob mice has a transitory hyperlipogenesis at, and just after, weaning on to a low-fat/high-carbohydrate diet. Once hyperphagia has developed, by week 5 of life, brown adipose tissue is the only major lipogenic tissue in the obese mice not to exhibit elevated rates of fatty acid synthesis; this suggests that insulin resistance develops much more rapidly in brown adipose tissue than in other lipogenic tissues of the ob/ob mouse.
Fatty acid synthesis
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Fat tissue, called adipose tissue, is our energy storage and it plays a vital role in the growing process. Did you know that we have three different types of adipose tissue that can convert into each other during our lives? The white adipose tissue stores fat from the foods we eat. The brown adipose tissue is responsible for heat production. And lastly, the beige adipose tissue is a form that is halfway between these two. The white and brown adipose tissues are very important to the body’s functioning. But, if we eat a lot of sugar and fat, the metabolism and functions of these tissues change, which can result in diseases like obesity and diabetes. Nowadays, scientists are studying the possibility of turning white adipose tissue into brown adipose tissue, in an attempt to prevent and reverse some of these diseases.
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Morphology
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