Brown adipose tissue is a type of fat that burns calories rather than stores them.
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"In humans, brown adipose tissue likely explains about 1% or 2% of energy expenditure in cold situations, and shivering explains far more, so it's an exaggeration," he said.
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A study published in the Journal of Clinical Endocrinology & Metabolism found that participants who slept in bedrooms cooled to 66°F for a month doubled the amount of brown adipose tissue they burned.
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According to research by the International Journal of Obesity, a cold body's thermoreceptors activate Brown adipose tissue (BAT), known as "good fat," which in turn burns white fat, "bad fat," to produce heat.
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Although more research is needed to determine why -- and how -- this correlation even exists, the study posed one hypothesis that involves the way cooler temperatures can activate a type of body fat called brown fat, or brown adipose tissue.
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In a study published Monday, researchers at the University of Nottingham said that coffee may help stimulate our brown fat reserves, also known as brown adipose tissue, which play a key role in how quickly we can burn calories.
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Activation cascade of thermogenin in cells of brown adipose tissue Non-shivering thermogenesis occurs in brown adipose tissue (brown fat)Stuart Ira Fox. Human Physiology. Twelfth Edition. McGraw Hill. 2011. p. 667.
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Thermogenin is a 33 kDa protein first discovered in 1973. Thermogenin is primarily found in brown adipose tissue, or brown fat, and is responsible for non-shivering thermogenesis. Brown adipose tissue is found in mammals, and is at its highest levels in early life and in hibernating animals. In humans, brown adipose tissue is present at birth and decreases with age.
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Brown adipose tissue (BAT) oxidizes chemical energy to produce heat. This heat energy can act as a defense against hypothermia and obesity. PRDM16 is highly enriched in brown adipose cells as compared to white adipose cells, and plays a role in these thermogenic processes in brown adipose tissue. PRDM16 activates brown fat cell identity and can control the determination of brown adipose fate.
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PR domain containing 16, also known as PRDM16, is a protein which in humans is encoded by the PRDM16 gene. PRDM16 acts as a transcription coregulator that controls the development of brown adipocytes in brown adipose tissue. Previously, this coregulator was believed to be present only in brown adipose tissue, but more recent studies have shown that PRDM16 is highly expressed in subcutaneous white adipose tissue as well.
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In mice, highest mRNA expression levels of ANGPTL4 are found in white and brown adipose tissue, followed by liver, kidney, muscle and intestine. Human ANGPTL4 is most highly expressed in liver.
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Researchers in the 1960s investigating brown adipose tissue, found that in addition to producing more heat than typical of other tissues, brown adipose tissue seemed to short circuit, or uncouple, respiration coupling . Uncoupling protein 1 was discovered in 1978 by David Nicholls, Vibeke Bernson, and Gillian Heaton and shown to be the protein responsible for this uncoupling effect. UCP1 was later purified for the first time in 1980 and was first cloned in 1988. Uncoupling protein two (UCP2), a homolog of UCP1, was identified in 1997.
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Far from being hormonally inert, adipose tissue has, in recent years, been recognized as a major endocrine organ, as it produces hormones such as leptin, estrogen, resistin, and cytokine (especially TNFα). The two types of adipose tissue are white adipose tissue (WAT), which stores energy, and brown adipose tissue (BAT), which generates body heat. The formation of adipose tissue appears to be controlled in part by the adipose gene. Adipose tissue – more specifically brown adipose tissue – was first identified by the Swiss naturalist Conrad Gessner in 1551.
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The protein encoded by this gene is a member of the fibroblast growth factor (FGF) family. FGF family members possess broad mitogenic and cell survival activities, and are involved in a variety of biological processes, including embryonic development, cell growth, morphogenesis, tissue repair, tumor growth and invasion. The rat homolog is predominantly expressed in embryonic brown adipose tissue and has significant mitogenic activity, which suggests a role in proliferation of embryonic brown adipose tissue. Mutations in this gene have been found associated to cases of X-linked recessive metacarpal 4/5 fusion.
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Leptin is produced primarily in the adipocytes of white adipose tissue. It also is produced by brown adipose tissue, placenta (syncytiotrophoblasts), ovaries, skeletal muscle, stomach (the lower part of the fundic glands), mammary epithelial cells, bone marrow,gastric chief cells and P/D1 cells.
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Proceedings of the National Academy of Sciences, 117:18169-18171. Its distribution at high altitudes across the Andean plateau has led to plasticity in its non-shivering thermogenosis in order to cope with the low temperatures. This thermal acclimation relies on brown adipose tissue and is often induced by ingestion.
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The ablation of VEGFR1 by chemical and genetic means has also recently been found to augment the conversion of white adipose tissue to brown adipose tissue as well as increase brown adipose angiogenesis in mice. Functional genetic variation in FLT1 (rs9582036) has been found to affect non-small cell lung cancer survival.
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The two superficial depots are the paired inguinal depots, which are found anterior to the upper segment of the hind limbs (underneath the skin) and the subscapular depots, paired medial mixtures of brown adipose tissue adjacent to regions of white adipose tissue, which are found under the skin between the dorsal crests of the scapulae. The layer of brown adipose tissue in this depot is often covered by a "frosting" of white adipose tissue; sometimes these two types of fat (brown and white) are hard to distinguish. The inguinal depots enclose the inguinal group of lymph nodes. Minor depots include the pericardial, which surrounds the heart, and the paired popliteal depots, between the major muscles behind the knees, each containing one large lymph node.
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Unexpectedly, overexpression of SREBP-1c in HepG2 cells could also inhibit the endogenous FGF21 transcription by reducing FGF21 promoter activity. SREBP-1c has also been shown to upregulate in a tissue specific manner the expression of PGC1alpha expression in brown adipose tissue. Nur77 is suggested to inhibit LXR and downstream SREBP-1c expression modulating hepatic lipid metabolism.
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Mice that lack functional Cidea have higher metabolic rates, higher lipolysis in brown adipose tissue and higher core body temperatures when subjected to cold. These mice are also resistant to diet-induced obesity and diabetes. This suggests that in mice this gene product plays a role in thermogenesis and lipolysis. Two alternative transcripts encoding different isoforms have been identified.
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Distribution of white adipose tissue in the human body. White adipose tissue (WAT) or white fat is one of the two types of adipose tissue found in mammals. The other kind is brown adipose tissue. In healthy, non-overweight humans, white adipose tissue composes as much as 20% of the body weight in men and 25% in women.
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The human body has two methods of thermogenesis, which produces heat to raise the core body temperature. The first is shivering, which occurs in an unclothed person when the ambient air temperature is under 25 °C (77 °F). It is limited by the amount of glycogen available in the body. The second is non-shivering, which occurs in brown adipose tissue.
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Thermogenin (called uncoupling protein by its discoverers and now known as uncoupling protein 1, or UCP1) is an uncoupling protein found in the mitochondria of brown adipose tissue (BAT). It is used to generate heat by non-shivering thermogenesis, and makes a quantitatively important contribution to countering heat loss in babies which would otherwise occur due to their high surface area-volume ratio.
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The western rock elephant shrew or western rock sengi (Elephantulus rupestris) is a species of elephant shrew in the family Macroscelididae. It is found in Namibia, South Africa, possibly Angola, and possibly Botswana. Its natural habitats are subtropical or tropical dry shrubland and rocky areas. Smaller members of western rock elephant shrew possess functional brown adipose tissue, which changes in thermogenic capacity depending on the season.
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Perilipin 4, also known as S3-12, is a protein that in humans is encoded by the PLIN4 gene on chromosome 19. It is highly expressed in white adipose tissue, with lower expression in heart, skeletal muscle, and brown adipose tissue. PLIN4 coats lipid droplets in adipocytes to protect them from lipases. The PLIN4 gene may be associated with insulin resistance and obesity risk.
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Scientists observed the thermogenic activity in brown adipose tissue, which eventually led to the discovery of UCP1, initially known as "Uncoupling Protein". The brown tissue revealed elevated levels of mitochondria respiration and another respiration not coupled to ATP synthesis, which symbolized strong thermogenic activity. UCP1 was the protein discovered responsible for activating a proton pathway that was not coupled to ADP phosphorylation (ordinarily done through ATP Synthase).
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It is this distinction that often makes the term "poikilotherm" more useful than the vernacular "cold- blooded", which is sometimes used to refer to ectotherms more generally. Poikilothermic animals include types of vertebrate animals, specifically some fish, amphibians, and reptiles, as well as many invertebrate animals. The naked mole-ratDaly, T.J.M., Williams, L.A. and Buffenstein, R., (1997). Catecholaminergic innervation of interscapular brown adipose tissue in the naked mole-rat (Heterocephalus glaber).
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White adipose tissue (WAT) primarily stores excess energy in the form of triglycerides. Recent research has shown that PRDM16 is present in subcutaneous white adipose tissue. The activity of PRDM16 in white adipose tissue leads to the production of brown fat-like adipocytes within white adipose tissue, called beige cells (also called brite cells). These beige cells have a brown adipose tissue-like phenotype and actions, including thermogenic processes seen in BAT.
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In the periphery, it is highly expressed in platelets and many cell types of the cardiovascular system, in fibroblasts, and in neurons of the peripheral nervous system. Additionally, 5-HT2A mRNA expression has been observed in human monocytes. Whole-body distribution of the 5-HT2A/2C receptor agonist, [11C]Cimbi-36 show uptake in several internal organs and brown adipose tissue (BAT), but it is not clear if this represents specific 5-HT2A receptor binding.
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Thyroid hormone synthesis, with the end-product of triiodothyroninе seen at bottom right. T3 is the more metabolically active hormone produced from T4. T4 is deiodinated by three deiodinase enzymes to produce the more-active triiodothyronine: # Type I present in liver, kidney, thyroid, and (to a lesser extent) pituitary; it accounts for 80% of the deiodination of T4. # Type II present in CNS, pituitary, brown adipose tissue, and heart vessel, which is predominantly intracellular.
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Daily torpor, on the other hand, is not seasonally dependent and can be an important part of energy conservation at any time of year. Torpor is a well-controlled thermoregulatory process and not, as previously thought, the result of switching off thermoregulation. Marsupial torpor differs from non-marsupial mammalian (eutherian) torpor in the characteristics of arousal. Eutherian arousal relies on a heat-producing brown adipose tissue as a mechanism to accelerate rewarming.
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Research identified dysregulated responses of ILC2s in adipose tissue as a factor in the development of obesity in mice since ILC2s also play important role in energy homeostasis. Methionine-enkephalin peptides produced by ILC2s act directly on adipocytes to upregulate UCP1 and promote emergence of beige adipocytes in white adipose tissue. Beige and brown adipose tissue are specialized in thermogenesis. The process of beiging leads to increased energy expenditure and decreased adiposity.
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ERRα has wide tissue distribution but it is most highly expressed in tissues that preferentially use fatty acids as energy sources such as kidney, heart, brown adipose tissue, cerebellum, intestine, and skeletal muscle. Recently, ERRα has been detected in normal adrenal cortex tissues, in which its expression is possibly related to adrenal development, with a possible role in fetal adrenal function, in DHEAS production in adrenarche, and also in steroid production of post-adrenarche/adult life.
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Expression of PPAR-alpha is highest in tissues that oxidize fatty acids at a rapid rate. In rodents, highest mRNA expression levels of PPAR-alpha are found in liver and brown adipose tissue, followed by heart and kidney. Lower PPAR-alpha expression levels are found in small and large intestine, skeletal muscle and adrenal gland. Human PPAR-alpha seems to be expressed more equally among various tissues, with high expression in liver, intestine, heart, and kidney.
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Whole-body knockout of Kmt2d in mice results in early embryonic lethality. Targeted knockout of Kmt2d in precursors cells of brown adipocytes and myocytes results in decreases in brown adipose tissue and muscle mass in mice, indicating that KMT2D is required for adipose and muscle tissue development. In the hearts of mice, a single copy of the Kmt2d gene is sufficient for normal heart development. Complete loss of Kmt2d in cardiac precursors and myocardium leads to severe cardiac defects and early embryonic lethality.
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However, during the adaptation to reproductively inhibitory photoperiods, the levels of T3 decrease due to peri-hypothalamic DIO3 expression that catabolizes T4 and T3 into receptor inactive amines . Deiodinase 2 also plays a significant role in thermogenesis in brown adipose tissue (BAT). In response to sympathetic stimulation, dropping temperature, or overfeeding BAT, D2 increases oxidation of fatty acids and uncouples oxidative phosphorylation via uncoupling protein, causing mitochondrial heat production. D2 increases during cold stress in BAT and increases intracellular T3 levels.
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Ricquier specializes in the physiology and biochemistry of mitochondria, adipose tissue and thermogenic mechanisms. He is an expert on brown adipose tissue. His work has contribué́ to identify a family of proteins involved in mitochondrial respiration, ATP yield, heat production and mitochondrial control of the level of cellular oxygenated free radicals. Ricquier described in 1976 a mitochondrial membrane protein specific for brown adipocytes, later named UCP (uncoupling protein) and identified by David Nicholls as the protein responsible for heat energy dissipation.
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Adipocytes, also known as lipocytes and fat cells, are the cells that primarily compose adipose tissue, specialized in storing energy as fat. Adipocytes are derived from mesenchymal stem cells which give rise to adipocytes through adipogenesis. In cell culture, adipocytes can also form osteoblasts, myocytes and other cell types. There are two types of adipose tissue, white adipose tissue (WAT) and brown adipose tissue (BAT), which are also known as white and brown fat, respectively, and comprise two types of fat cells.
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Three sirtuins, SIRT3, SIRT4 and SIRT5, are located in mitochondria and have been implicated in regulating metabolic processes. Endogenous SIRT3 is a soluble protein located in the mitochondrial matrix. Overexpression of SIRT3 in cultured cells increases respiration and decreases the production of reactive oxygen species. Fasting increases SIRT3 expression in white and brown adipose tissue (WAT and BAT, respectively) and overexpression of SIRT3 in HIB1B brown adipocytes increases the expression of PGC-1α and UCP1, suggesting a role for SIRT3 in adaptive thermogenesis BAT.
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GPR3 activates adenylate cyclase in the absence of ligand. GPR3 is expressed in mammalian oocytes where it maintains meiotic arrest and is thought to be a communication link between oocytes and the surrounding somatic tissue. It has been proposed that sphingosine 1-phosphate (S1P) and sphingosylphosphorylcholine (SPC) are GPR3 ligands, however this result was not confirmed in a β-arrestin recruitment assay. Mice lacking GPR3 were found to develop late-onset obesity owing to decreased UCP-1 expression in brown adipose tissue and reduced thermogenic capacity.
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In addition to shivering, some hibernating animals also produce body heat by non-shivering thermogenesis to avoid freezing. Non- shivering thermogenesis is a regulated process in which the proton gradient generated by electron transport in mitochondria is used to produce heat instead of ATP in brown adipose tissue. Animals that hibernate include bats, ground squirrels and other rodents, mouse lemurs, the European hedgehog and other insectivores, monotremes and marsupials. Although hibernation is almost exclusively seen in mammals, some birds, such as the common poorwill, may hibernate.
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A 1.8m southern black racer basking in the Inverness, Florida sunshine on a cool morning. Ectotherms rely largely on external heat sources such as sunlight to achieve their optimal body temperature for various bodily activities. Accordingly, they depend on ambient conditions to reach operational body temperatures. In contrast, endothermic animals maintain nearly constant high operational body temperatures largely by reliance on internal heat produced by metabolically active organs (liver, kidney, heart, brain, muscle) or even by specialized heat producing organs like brown adipose tissue (BAT).
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This reflux releases free energy produced during the generation of the oxidized forms of the electron carriers (NAD+ and Q). The free energy is used to drive ATP synthesis, catalyzed by the F1 component of the complex. Coupling with oxidative phosphorylation is a key step for ATP production. However, in specific cases, uncoupling the two processes may be biologically useful. The uncoupling protein, thermogenin—present in the inner mitochondrial membrane of brown adipose tissue—provides for an alternative flow of protons back to the inner mitochondrial matrix.
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A 2011 publication suggested that selection for the expansion of skeletal muscle, rather than the evolution of flight, was the driving force for the emergence of this clade. Muscles became larger in prospectively endothermic saurians, according to this hypothesis, as a response to the loss of the vertebrate mitochondrial uncoupling protein, UCP1, which is thermogenic. In mammals, UCP1 functions within brown adipose tissue to protect newborns against hypothermia. In modern birds, skeletal muscle serves a similar function and is presumed to have done so in their ancestors.
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AdPLA has been characterized in Group XVI as a separate subgroup of the PLA2 family for its distinct properties from other known PLA2s. It bears similarity to its PLA2 family in phospholipase activity and calcium dependence. Unlike other PLA2 enzymes, AdPLA is expressed predominantly in adipose tissue at higher levels than in the rest of the body, more so in white adipose tissue (WAT) than brown adipose tissue (BAT). Its primary enzymatic function is to catalyze the preferential hydrolysis of phosphatidylcholines at the sn-2 position, generating free fatty acids.
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TRPV2 in mus musculus is also activated by hypo-osmolarity and cell stretching, indicating that TRPV2 plays a role in mechanotransduction in mice as well. In experiments with knockout mice (TRPV2KO mice), it was found that TRPV2 is expressed in brown adipocytes and in brown adipose tissue (BAT). It can be concluded that TRPV2 plays a role in BAT thermogenesis in mice, since it was found that a lack of TRPV2 impairs this thermogenesis in BAT; given these results, this could be a target for human obesity therapy.
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Neural top–down control of physiology concerns the direct regulation by the brain of physiological functions (in addition to smooth muscle and glandular ones). Cellular functions include the immune system’s production of T-lymphocytes and antibodies, and nonimmune related homeostatic functions such as liver gluconeogenesis, sodium reabsorption, osmoregulation, and brown adipose tissue nonshivering thermogenesis. This regulation occurs through the sympathetic and parasympathetic system (the autonomic nervous system), and their direct innervation of body organs and tissues that starts in the brainstem. There is also a noninnervation hormonal control through the hypothalamus and pituitary (HPA).
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Perilipin 5 is a protein often found in the adipose tissue, especially in those with high oxidative stress, including the heart, liver, skeletal muscle and brown adipose tissue (BAT). The perilipin family contributes to the creation of lipid droplets and it also plays a pivotal role in determining what the lipid droplet's function is within the cell. In addition, perilipin 5 regulates the activation of hepatic stellate cell, implicated in fibrosis, which is the creation of new tissue to repair the one damaged. The 3D structure of Perilipin 5 on humans.
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Expression of D3 contributes to the development of the brain, skin, liver, bone, ovary, testis, intestine, and brown adipose tissue. Introductory observations of D3-deficient mice indicate growth retardation and even some neonatal death. Due to its ability to activate or inactivate thyroid hormone, Dio3 coding of D3 could be a target for therapeutic intervention in insulin-related illness such as diabetes. In addition, an abnormal amount of Dio3 related to insufficient thyroid hormone levels could be responsible for the disruption of brain development in conjunction with alcohol exposure.
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Far from hormonally inert, adipose tissue has in recent years been recognized as a major endocrine organ[1], as it produces hormones such as leptin, resistin, and the cytokine TNFα. Moreover, adipose tissue can affect other organ systems of the body and may lead to disease. Obesity or being overweight in humans and most animals does not depend on body weight but on the amount of body fat – to be specific, adipose tissue. Two types of adipose tissue exist: white adipose tissue (WAT) and brown adipose tissue (BAT).
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Brown fat cell Brown fat or brown adipose tissue (BAT) is a specialized form of adipose tissue important for adaptive thermogenesis in humans and other mammals. BAT can generate heat by "uncoupling" the respiratory chain of oxidative phosphorylation within mitochondria through tissue-specific expression of uncoupling protein 1 (UCP1). BAT is primarily located around the neck and large blood vessels of the thorax, where may effectively act in heat exchange. BAT is robustly activated upon cold exposure by the release of catecholamines from sympathetic nerves that results in UCP1 activation.
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UCP1-mediated heat generation in brown fat uncouples the respiratory chain, allowing for fast substrate oxidation with a low rate of ATP production. UCP1 is related to other mitochondrial metabolite transporters such as the adenine nucleotide translocator, a proton channel in the mitochondrial inner membrane that permits the translocation of protons from the mitochondrial intermembrane space to the mitochondrial matrix. UCP1 is restricted to brown adipose tissue, where it provides a mechanism for the enormous heat-generating capacity of the tissue. UCP1 is activated in the brown fat cell by fatty acids and inhibited by nucleotides.
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Acyl-coenzyme A thioesterase 11 also known as StAR-related lipid transfer protein 14 (STARD14) is an enzyme that in humans is encoded by the ACOT11 gene. This gene encodes a protein with acyl-CoA thioesterase activity towards medium (C12) and long-chain (C18) fatty acyl-CoA substrates which relies on its StAR-related lipid transfer domain. Expression of a similar murine protein in brown adipose tissue is induced by cold exposure and repressed by warmth. Expression of the mouse protein has been associated with obesity, with higher expression found in obesity-resistant mice compared with obesity-prone mice.
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MAT has qualities of both white and brown fat. Subcutaneous white fat contain excess energy, indicating a clear evolutionary advantage during times of scarcity. WAT is also the source of adipokines and inflammatory markers which have both positive (e.g., adiponectin) and negative effects on metabolic and cardiovascular endpoints. Visceral abdominal fat (VAT) is a distinct type of WAT that is "proportionally associated with negative metabolic and cardiovascular morbidity", regenerates cortisol, and recently has been tied to decreased bone formation Both types of WAT substantially differ from brown adipose tissue (BAT) as by a group of proteins that help BAT’s thermogenic role.
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Having isolated antibodies specific to this protein, he demonstrated brown adipocytes in neonates and adult patients and demonstrated that the sympathetic nervous system controls the development of brown adipose tissue and the synthesis of DCS in animals and humans. With Fréderic Bouillaud, in 1984 and in collaboration with Jean Weissenbach at the Pasteur Institute, he isolated and sequenced the complementary DNA of the UCP and the UCP gene from rodents and humans. He then analyzed the mechanisms of control of the tissue-specific transcription of the UCP gene. In addition, he studied the functional organization of this membrane protein.
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Endothermic animals mostly use internal heat production through metabolic active organs and tissues (liver, kidney, heart, brain, muscle) or specialized heat producing tissues like brown adipose tissue (BAT). In general, endotherms therefore have higher metabolic rates than ectotherms at a given body mass. As a consequence they would also need higher food intake rates, which may limit abundance of endotherms more than ectotherms. Because ectotherms depend on environmental conditions for body temperature regulation, they typically are more sluggish at night and in the morning when they emerge from their shelters to heat up in the first sunlight.
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3 São Paulo April 2008. DOI and within this framework established a strong and active laboratory, which explored many areas, such as neural regulation of fatty acids and glucose, the effects of fasting and feeding on metabolism of brown adipose tissue and liver functions, the protein metabolism in skeletal muscle, the interactions of dietary protein and glucose in glycolysis in adipose tissue, exposure to cold and drugs, as well as the role and function of gluconeogenesis in strictly carnivorous animals, such as vultures. He published more than a hundred papers in noted international journals, particularly in the American Journal of Physiology. He was one of the most cited Brazilian biomedical researchers.
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Cytokines, such as interleukin-1 can be synthesized and released by neurons. Bartfai's group showed interleukin-1, then called the endogenous pyrogen, is released from the adrenal medulla and brain and demonstrated that the endogenous pyrogen can control body temperature by acting at receptors and hyperpolarizing hypothalamic gabaergic interneurons that control thermogenesis in brown adipose tissue, and thus core body temperature and the fever response., Bartfai has published two books with Graham Lees, Ph.D., on drug discovery and development: "Drug Discovery: from bedside to Wall Street" and "The Future of Drug Discovery: who decides which diseases to treat?", which are both also published in Japanese and Mandarin.
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Gessner is credited with a number of the first descriptions of species in Europe, both animals such as the brown rat (Rattus norvegicus), guinea pig (Cavia porcellus) and turkey (Meleagris), as well as plants such as the tulip (Tulipa gesneriana). He first saw a tulip in April 1559, growing in the garden of the magistrate Johann Heinrich Herwart at Augsberg, and called it Tulipa turcarum, the Turkish tulip. He is also credited with being the first person to describe brown adipose tissue, in 1551, in 1565 the first to document the pencil, and in 1563 among the first Europeans to write about the effects of tobacco.
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Attempts to simulate this process pharmacologically have so far been unsuccessful. Techniques to manipulate the differentiation of "brown fat" could become a mechanism for weight loss therapy in the future, encouraging the growth of tissue with this specialized metabolism without inducing it in other organs. Until recently, brown adipose tissue was thought to be primarily limited to infants in humans, but new evidence has now overturned that belief. Metabolically active tissue with temperature responses similar to brown adipose was first reported in the neck and trunk of some human adults in 2007, and the presence of brown adipose in human adults was later verified histologically in the same anatomical regions.
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Specific dynamic action (SDA), also known as thermic effect of food (TEF) or dietary induced thermogenesis (DIT), is the amount of energy expenditure above the basal metabolic rate due to the cost of processing food for use and storage. Heat production by brown adipose tissue which is activated after consumption of a meal is an additional component of dietary induced thermogenesis. The thermic effect of food is one of the components of metabolism along with resting metabolic rate and the exercise component. A commonly used estimate of the thermic effect of food is about 10% of one's caloric intake, though the effect varies substantially for different food components.
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Monounsaturated fatty acids, the products of SCD-1 catalyzed reactions, can serve as substrates for the synthesis of various kinds of lipids, including phospholipids, triglycerides, and can also be used as mediators in signal transduction and differentiation. Because MUFAs are heavily utilized in cellular processes, variation in SCD activity in mammals is expected to influence physiological variables, including cellular differentiation, insulin sensitivity, metabolic syndrome, atherosclerosis, cancer, and obesity. SCD-1 deficiency results in reduced adiposity, increased insulin sensitivity, and resistance to diet-induced obesity. Under non-fasting conditions, SCD-1 mRNA is highly expressed in white adipose tissue, brown adipose tissue, and the Harderian gland.
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An endotherm (from Greek ἔνδον endon "within" and θέρμη thermē "heat") is an organism that maintains its body at a metabolically favorable temperature, largely by the use of heat set free by its internal bodily functions instead of relying almost purely on ambient heat. Such internally generated heat is mainly an incidental product of the animal's routine metabolism, but under conditions of excessive cold or low activity an endotherm might apply special mechanisms adapted specifically to heat production. Examples include special- function muscular exertion such as shivering, and uncoupled oxidative metabolism such as within brown adipose tissue. Only birds and mammals are extant universally endothermic groups of animals.
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ERRα regulates genes involved in mitochondrial biogenesis, gluconeogenesis, oxidative phosphorylation, and fatty acid metabolism, and brown adipose tissue thermogenesis. It was recently identified as an important regulator of the mammalian circadian clock, and its output pathways at both transcriptional and physiological levels regulated the expression of transcription factors involved in metabolic homeostasis. It has been demonstrated that ERRα is required for the maintenance of diurnal cholesterol, glucose, insulin, bile acid, and trygliceride levels as well as locomotor rhythms in mice. ERRα is related to mitochondrial function but studies involving ERRα knockout mice suggested that this receptor, while dispensable for basal cellular function, is definitely necessary to provide the levels of energy necessary to respond to physiological and pathological insults in diverse tissues, the lack of that nuclear receptor leading to impaired fat metabolism and absorption.
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For example, if glycolysis and gluconeogenesis were to be active at the same time, glucose would be converted to pyruvate by glycolysis and then converted back to glucose by gluconeogenesis, with an overall consumption of ATP. Futile cycles may have a role in metabolic regulation, where a futile cycle would be a system oscillating between two states and very sensitive to small changes in the activity of any of the enzymes involved. The cycle does generate heat, and may be used to maintain thermal homeostasis, for example in the brown adipose tissue of young mammals, or to generate heat rapidly, for example in insect flight muscles and in hibernating animals during periodical arousal from torpor. It has been reported that the glucose metabolism substrate cycle is not a futile cycle but a regulatory process.
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MR is expressed in many tissues, such as the kidney, colon, heart, central nervous system (hippocampus), brown adipose tissue and sweat glands. In epithelial tissues, its activation leads to the expression of proteins regulating ionic and water transports (mainly the epithelial sodium channel or ENaC, Na+/K+ pump, serum and glucocorticoid induced kinase or SGK1) resulting in the reabsorption of sodium, and as a consequence an increase in extracellular volume, increase in blood pressure, and an excretion of potassium to maintain a normal salt concentration in the body. The receptor is activated by mineralocorticoids such as aldosterone and its precursor deoxycorticosterone as well as glucocorticoids, like cortisol. In intact animals, the mineralocorticoid receptor is "protected" from glucocorticoids by co-localization of an enzyme, corticosteroid 11-beta-dehydrogenase isozyme 2 (a.k.a.
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Irisin (fibronectin type III domain- containing protein 5 or FNDC5), a recently described myokine hormone produced and secreted by acutely exercising skeletal muscles, is thought to bind white adipose tissue cells via undetermined receptors. Irisin has been reported to promote a brown adipose tissue-like phenotype upon white adipose tissue by increasing cellular mitochondrial density and expression of uncoupling protein-1, thereby increasing adipose tissue energy expenditure via thermogenesis. This is considered important, because excess visceral adipose tissue in particular distorts the whole body energy homeostasis, increases the risk of cardiovascular disease and raises exposure to a milieu of adipose tissue-secreted hormones (adipokines) that promote inflammation and cellular aging. The authors enquired whether the favorable impact of irisin on white adipose tissue might be associated with maintenance of telomere length, a well-established genetic marker in the aging process.
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A study of captive shrews found, though they were primarily nocturnal, the degree of nocturnality changed with the season; that is, during the colder winter, the shrews exhibited more out-of-burrow activity earlier in the evening, but were active later in the night during the summer. This seasonal pattern was due to solar radiation and changing daily temperatures, and it allows the shrews to minimize the energy needed for thermoregulation. Other winter adaptations include the creation of a lined nest which aids the shrew in conserving heat, the caching of food in case of prey shortages, foraging below the leaf litter or snow where the temperature is milder, and decreasing activity levels during cold periods. Along with these behavioral adaptations, the northern short- tailed shrew increases its ability to generate body heat during the winter by nonshivering thermogenesis in brown adipose tissue.
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