Uncoupling protein-3 expression in skeletal muscle and free fatty acids in obesity.
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Adult↗
Biomedical subjects
P Muzzin
Publications and source records attributed to P Muzzin.
Genomic structure of uncoupling protein-3 (UCP3) and its assignment to chromosome 11q13.
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Carrier Proteins↗
Uncoupling protein-3 expression in rodent skeletal muscle is modulated by food intake but not by changes in environmental temperature.
A new member of the uncoupling protein (UCP) family called UCP3 has recently been cloned and shown to be highly expressed in skeletal muscle of rodents and humans. In the present study, UCP3 was overexpressed in C2C12 myoblasts where it acts as an uncoupling protein. Changes in UCP3 mRNA expression were examined in rodent muscles under conditions known to modulate thermogenesis in brown adipose tissue. In skeletal muscle, UCP3 expression did not change in response to 48 h of cold exposure (6 degrees C), whereas it was decreased by 81% or increased 5.6-fold by 1 week of 50% food restriction or fasting, respectively. It was also decreased by 36% in soleus muscle of obese (fa/fa) as compared with lean Zucker rats. The unexpected rise of UCP3 mRNA level induced by fasting did not change in vitro muscle basal heat production rate but decreased by 31% the capacity to produce heat in response to the uncoupler carbonylcyanide p-trifluoromethoxyphenylhydrazone. This decrease may reflect underlying uncoupling by UCP3. Up-regulation of UCP3 mRNA after a 24-h fast was still observed in mice exposed at thermoneutrality. These results show that the increase in UCP3 expression induced by fasting is associated with the maintenance of thermogenesis measured in muscle in vitro and is not modulated by environmental temperature. The notion that UCP3 expression is modulated by food intake is of importance to better understand the pathophysiology of obesity in humans.
Animals↗
Metabolic response to various beta-adrenoceptor agonists in beta3-adrenoceptor knockout mice: evidence for a new beta-adrenergic receptor in brown adipose tissue.
The beta3-adrenoceptor plays an important role in the adrenergic response of brown and white adipose tissues (BAT and WAT). In this study, in vitro metabolic responses to beta-adrenoceptor stimulation were compared in adipose tissues of beta3-adrenoceptor knockout and wild type mice. The measured parameters were BAT fragment oxygen uptake (MO2) and isolated white adipocyte lipolysis. In BAT of wild type mice (-)-norepinephrine maximally stimulated MO2 4.1+/-0.8 fold. Similar maximal stimulations were obtained with beta1-, beta2- or beta3-adrenoceptor selective agonists (dobutamine 5.1+/-0.3, terbutaline 5.3+/-0.3 and CL 316,243 4.8+/-0.9 fold, respectively); in BAT of beta3-adrenoceptor knockout mice, the beta1- and beta2-responses were fully conserved. In BAT of wild type mice, the beta1/beta2-antagonist and beta3-partial agonist CGP 12177 elicited a maximal MO2 response (4.7+/-0.4 fold). In beta3-adrenoceptor knockout BAT, this response was fully conserved despite an absence of response to CL 316,243. This unexpected result suggests that an atypical beta-adrenoceptor, distinct from the beta1-, beta2- and beta3-subtypes and referred to as a putative beta4-adrenoceptor is present in BAT and that it can mediate in vitro a maximal MO2 stimulation. In isolated white adipocytes of wild type mice, (-)-epinephrine maximally stimulated lipolysis 12.1+/-2.6 fold. Similar maximal stimulations were obtained with beta1-, beta2- or beta3-adrenoceptor selective agonists (TO509 12+/-2, procaterol 11+/-3, CL 316,243 11+/-3 fold, respectively) or with CGP 12177 (7.1+/-1.5 fold). In isolated white adipocytes of beta3-adrenoceptor knockout mice, the lipolytic responses to (-)epinephrine, to the beta1-, beta2-, beta3-adrenoceptor selective agonists and to CGP 12177 were almost or totally depressed, whereas those to ACTH, forskolin and dibutyryl cyclic AMP were conserved.
Adipose Tissue↗
Effect of endurance training on mRNA expression of uncoupling proteins 1, 2, and 3 in the rat.
Endurance exercise training has been shown to decrease diet-induced thermogenesis (DIT) in rats and humans. In rodents, most thermogenesis is thought to occur in brown adipose tissue via activation of the uncoupling protein-1 (UCP1) and in skeletal muscle. Since the level of UCP1 mRNA in rat BAT was reported to be unmodified by exercise training, the newly described uncoupling proteins UCP2 and UCP3 could be responsible for the decreased DIT in trained rats. UCP3 mRNA levels in endurance-trained rats were found to be reduced by 76% and 59% in tibialis anterior and soleus muscles, respectively. UCP2 mRNA levels were also decreased in tibialis anterior and in heart by 54% and 41%, respectively. Neither white adipose tissue UCP2 nor brown adipose tissue UCP1, UCP2, and UCP3 mRNA levels were modified. The results of this study show that a need for a higher metabolic efficiency is associated with decreased mRNA expression of the uncoupling proteins in skeletal and heart muscles, which would decrease energy dissipation in these tissues. The down-regulation of UCP3 and UCP2 expressions might also contribute to the rapid weight gain known to occur when exercise training ceased.
3-Hydroxyacyl CoA Dehydrogenases↗
The uncoupling proteins, a review.
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Adipose Tissue, Brown↗
Chronic central leptin infusion enhances insulin-stimulated glucose metabolism and favors the expression of uncoupling proteins.
Continuous (4 days) intracerebroventricular leptin infusion (12 microg/day) was performed in lean rats, and its hormonometabolic effects were determined. Intracerebroventricular leptin administration did not result in leakage of the hormone into the peripheral circulation. Thus, its effects were elicited by its presence within the central nervous system. Intracerebroventricular leptin infusion produced marked decreases in food intake and body weight gain relative to vehicle-infused fed ad libitum rats. Because decreases in food intake alter hormonometabolic homeostasis, additional control rats pair-fed to the amount of food consumed by leptin-infused ones were included in the study. Intracerebroventricular leptin-infused and vehicle-infused pair-fed rats were characterized, relative to vehicle-infused ad libitum-fed animals, by decreases in body weight and insulinemia and by increases in insulin-stimulated overall glucose utilization and muscle and brown adipose tissue glucose utilization index. Brown adipose tissue uncoupling protein (UCP)1, UCP2, and UCP3 mRNA levels were markedly decreased in pair-fed animals relative to those of fed ad libitum control animals, as were liver and white adipose tissue UCP2 and muscle UCP3 mRNA levels. In marked contrast, intracerebroventricular leptin administration was accompanied by the maintenance of high UCP1, UCP2, and UCP3 expression in all these tissues. Thus, despite analogies between leptin's effects and those of pair-feeding with regard to glucose handling, their respective underlying mechanisms differ. While leptin maintains or favors energy-dissipating mechanisms (UCP1, UCP2, and UCP3), the latter are markedly depressed in pair-fed rats. This effect of leptin may prevent subsequent excessive storage processes, thereby maintaining normal body homeostasis.
Adipose Tissue, Brown↗
Tissue-dependent upregulation of rat uncoupling protein-2 expression in response to fasting or cold.
The control of uncoupling protein-2 (UCP2) mRNA expression in rat brown adipose tissue (BAT), heart and skeletal muscles was examined. Cold exposure (48 h) increased UCP2 mRNA in BAT, heart and soleus muscle by 2.4-, 4.3- and 2.6-fold, respectively. Fasting (48 h) had no effect on UCP2 mRNA expression neither in BAT nor in heart, but markedly increased it in skeletal muscles. While the upregulation of UCP2 mRNA in response to cold exposure is in line with a putative uncoupling role for this protein in thermoregulatory thermogenesis, the unexpected upregulation of UCP2 in skeletal muscles in response to fasting seems inconsistent with its role as an uncoupling protein involved in dietary regulation of thermogenesis.
Adipose Tissue, Brown↗
Uncoupling protein-3: a new member of the mitochondrial carrier family with tissue-specific expression.
Brown adipose tissue (BAT) and skeletal muscle are important sites of nonshivering thermogenesis. The uncoupling protein-1 (UCP1) is the main effector of nonshivering thermogenesis in BAT and the recently described ubiquitous UCP2 [1] has been implicated in energy balance. In an attempt to better understand the biochemical events underlying nonshivering thermogenesis in muscle, we screened a human skeletal muscle cDNA library and isolated three clones: UCP2, UCP3L and UCP3S. The novel UCP3 was 57% and 73% identical to human UCP1 and UCP2, respectively, highly skeletal muscle-specific and its expression was unaffected by cold acclimation. This new member of the UCP family is a candidate protein for the modulation of the respiratory control in skeletal muscle.
Adipose Tissue↗
Hepatic insulin gene expression as treatment for type 1 diabetes mellitus in rats.
Type 1 diabetes mellitus is caused by a lack of insulin that results from the autoimmune destruction of the pancreatic beta-cells. Severe diabetes, if not controlled by periodic insulin injections, can lead to ketoacidosis and death. We have previously shown that sustained low level production of insulin in the liver of diabetic rats prevented their death from complications of diabetes. To test the hypothesis that there is a window of serum insulin concentrations that can prevent ketoacidosis without significant risk of hypoglycemia secondary to hyperinsulinemia, rats were infused with various doses of a recombinant retrovirus encoding an engineered rat preproinsulin-1 gene. The gene was engineered to allow processing into mature insulin by the protease furin. At the lower doses tested, fatal ketoacidosis was prevented, but the rats exhibited nonfasting hyperglycemia. At intermediate doses, which resulted in serum insulin concentrations of 1.6 mg/ml, the rats achieved near-normoglycemia and no serum ketones. These rats did not exhibit hypoglycemia even during a 24-h fast. At high virus doses, the animals achieved nonfasting normoglycemia but exhibited hypoglycemia during the fast. In conclusion, we have defined a therapeutic window of hepatic insulin expression that provides protection against ketoacidosis without significant risk of hypoglycemia. This window of sustained hepatic insulin expression might permit its development into a novel treatment modality for the prevention of ketoacidosis in patients with severe insulin-dependent diabetes mellitus.
Animals↗
Correction of obesity and diabetes in genetically obese mice by leptin gene therapy.
The ob/ob mouse is genetically deficient in leptin and exhibits both an obese and a mild non-insulin-dependent diabetic phenotype. To test the hypothesis that correction of the obese phenotype by leptin gene therapy will lead to the spontaneous correction of the diabetic phenotype, the ob/ob mouse was treated with a recombinant adenovirus expressing the mouse leptin cDNA. Treatment resulted in dramatic reductions in both food intake and body weight, as well as the normalization of serum insulin levels and glucose tolerance. The subsequent diminishment in serum leptin levels resulted in the rapid resumption of food intake and a gradual gain of body weight, which correlated with the gradual return of hyperinsulinemia and insulin resistance. These results not only demonstrated that the obese and diabetic phenotypes in the adult ob/ob mice are corrected by leptin gene treatment but also provide confirming evidence that body weight control may be critical in the long-term management of non-insulin-dependent diabetes mellitus in obese patients.
Adenoviridae↗
Adrenoceptor heterogeneity in human white adipocytes differentiated in culture as assessed by cytosolic free calcium measurements.
Changes in intracellular calcium concentration [Ca2+]i in response to norepinephrine (NE) and to various adrenergic agonists were monitored by dual excitation microfluorimetry in single human adipocytes differentiated in culture and loaded with fura-2 acetoxymethyl ester (fura-2 AM). The addition of NE elicited increases in [Ca2+]i that were depending on the cell, (1) either rapid (time to peak: 9 +/- 3 s), large, and transient; or (2) slow (time to peak: 125 +/- 8 s), small, and sustained. The rapid and large [Ca+]i response, which was inhibited by 90% by the alpha 1-antagonist prazosin and only by 20% by the non-specific beta antagonist (-)-propranolol, was considered to be mediated by the alpha 1-adrenoceptor. In fact, an alpha 1A-adrenoceptor was found to be expressed in human white adipose tissue. Consecutive additions of beta-agonists specific for each subtype of alpha-adrenoceptor enabled the characterization of four cell populations with different response patterns: 47% of the cells had alpha 1- and beta 1-, beta 2- and beta 3-induced [Ca2+]i responses; 29% had only beta 1-, beta 2-, beta 3-responses; 14% had alpha 1- and beta 3-responses, and 10% had only an alpha 1-response. Taken together, these results show that in differentiated human adipocytes: (1) alpha 1- and beta-adrenergic stimulations induce [Ca2+]i increases with different kinetics and amplitudes; (2) there is a beta 3-adrenergic response similar to the beta 1- or beta 2-adrenergic responses; and (3) there is a marked adrenoceptor heterogeneity.
Adipocytes↗
Respective degree of expression of beta 1-, beta 2- and beta 3-adrenoceptors in human brown and white adipose tissues.
1. The possible existence of a beta 3-adrenoceptor in human brown and white adipose tissues was investigated by mRNA expression and binding studies. 2. The relative amounts of beta 1-, beta 2- and beta 3-adrenoceptor mRNA, as determined by total RNA Northern blot analysis in newborn brown adipose tissue, were 28, 63 and 9% respectively of the total beta-adrenoceptor mRNA. 3. The beta 1/beta 2-adrenoceptors of human brown adipose tissue plasma membranes were characterized using [3H]-CGP 12177 as a ligand. Their Kd and Bmax values were 1.9 nM and 156 fmol mg-1 of membrane proteins, respectively. The beta 3-adrenoceptor was characterized by use of the new specific radioligand [3H]-SB 206606. The binding of this ligand was stereospecifically displaced by the active R,R- or the inactive S,S-enantiomer of BRL 37344 up to a concentration of about 10 microM. The Kd and Bmax values of the brown adipose tissue membrane beta 3-adrenoceptors were 87 nM and 167 fmol mg-1 of proteins, respectively. A low affinity [3H]-CGP 12177 binding site population was also detected in these membranes. 4. In human omental white adipose tissue, no beta 3-adrenoceptor mRNA could be detected in total RNA Northern blots and the beta 1-and beta 2-adrenoceptor mRNAs represented 9 and 91%, respectively of the total beta-adrenoceptor mRNA, and no specific binding of [3H]-SB 206606 could be measured.
Adipose Tissue↗
Analysis of CA repeat polymorphisms places three human gene loci on the 8p linkage map.
The gene loci for luteinizing hormone-releasing hormone (LHRH), the beta-3 adrenergic receptor (ADRB3), and heregulin (HGL) have been assigned to the short arm of human chromosome 8, but the positions of these loci on the human genetic linkage map have not been previously reported. We have isolated simple tandem repeat polymorphisms (STRPs) for these loci. These STRPs enabled us to determine the genetic map locations for these genes.
Base Sequence↗
Modulation of obese gene expression in rat brown and white adipose tissues.
The ob gene mRNA expression in rat brown adipose tissue (BAT) and epididymal white adipose tissue (WAT) was measured on Northern blots hybridized with a rat ob gene probe. The level of ob gene mRNA in BAT was about 40% of that in WAT. Fasting (36 h) or semi-starvation (10 days) decreased the ob gene mRNA level in both tissues by 62-68%, and cold exposure at 6 degrees C (24 h) decreased it in BAT (-84%) but not in WAT. Acute administration of the beta 3-adrenergic agonist Ro 16-8714 decreased the ob gene mRNA level in BAT (-51%) and WAT (-28%) of lean Zucker rats and only in BAT (-74%) of obese falfa rats. This study demonstrates that, in the rat, the ob gene is not only expressed in WAT but also in BAT, and suggests that in these two tissues, the modulation of the ob gene expression might be more closely associated with known alterations in cell lipid content than with changes in sympathetic activity.
Adipose Tissue↗
Control of beta 3-adrenergic receptor gene expression in brown adipocytes in culture.
Brown adipose tissue is a mammalian thermogenic tissue. Its ability to dissipate energy as heat is due to a unique mitochondrial protein, uncoupling protein (UCP). Activation and expression of UCP is under control of the sympathetic nervous system acting through beta -adrenergic receptors (AR). In this study we used Siberian hamster brown adipocytes differentiated in vitro to investigate the expression of the fat specific beta 3-AR. Binding studies using the new labelled beta 3 adrenergic ligand [3H]SB 206606 showed a density of beta 3-AR in brown adipocyte plasma membranes comparable to that measured in vivo. beta 3-AR mRNA expression was very high in mature brown adipocytes and was started to be expressed during differentiation before UCP mRNA. Its half-life was approximately 50 min. Treatment of cells with non-specific beta adrenergic agonists, specific beta 3-adrenergic agonists, and dibutyryl cyclic AMP resulted in a marked down regulation of beta 3-AR mRNA level within several hours.
Adipose Tissue, Brown↗
Expression of beta 1- and beta 3-adrenergic-receptor messages and adenylate cyclase beta-adrenergic response in bovine perirenal adipose tissue during its transformation from brown into white fat.
Possible modifications of the beta-adrenergic effector system during the development of bovine perirenal brown adipose tissue (BAT) in utero and its transformation into white-like adipose tissue after birth were studied. The parameters assessed were the level of expression of beta 1-, beta 2- and beta 3-adrenergic receptor (AR) mRNAs and the response of the plasma-membrane adenylate cyclase to (-)-isoprenaline and to the beta 3-agonist BRL 37344. The beta 3-AR mRNA was found to be expressed very early in utero, i.e. before the third month of foetal life. Then it increased dramatically (9-fold) between month 6 of foetal life and birth. A high beta 3-AR mRNA level was maintained after birth up to an age of 3 months. After conversion of BAT into white-like adipose tissue, i.e. in the adult bovine, the beta 3-AR mRNA expression became small or not detectable, and the beta 1-AR mRNA, which was expressed much less than the beta 3-AR mRNA in foetal life, became predominant. A response of the adenylate cyclase to (-)-isoprenaline was observed in foetal life (3.1-fold stimulation). It decreased after birth (1.8-fold stimulation) and then remained constant until adulthood. A response to BRL 37344 was also observed in foetal life (1.8-fold stimulation). It was maintained after birth, but disappeared in the adult. A possible relationship between the beta-AR expression and the adenylate cyclase response to (-)-isoprenaline on the one hand and the uncoupling-protein expression on the other is discussed. The bovine might represent a good model to understand the transition from brown to white fat in the human.
Adenylyl Cyclases↗
Characterization of a new, highly specific, beta 3-adrenergic receptor radioligand, [3H]SB 206606.
The RR-enantiomer of the beta 3-adrenergic receptor agonist BRL 37344 was tritiated to yield a high specific activity compound, [3H]SB 206606. This new, potentially specific, beta 3-adrenergic receptor ligand was characterized by binding studies using membranes from both Chinese hamster ovary K1 cells transfected with the rat beta 3-adrenergic receptor and rat interscapular brown adipose tissue, where beta 1-, beta 2-, and beta 3-adrenergic receptor subtypes are known to coexist. [3H]SB 206606 was found to bind to a single population of binding sites in both preparations. The Kd values for [3H]SB 206606 binding to membranes from Chinese hamster ovary K1 cells and brown adipose tissue were quite comparable (58 and 38 nM, respectively). At 37 degrees, the time courses of association and dissociation of [3H]SB 206606 with membranes of brown adipose tissue were quite short. At 4 degrees, the T1/2 were found to be 13 and 40 min, respectively. The Ki values for various beta-adrenergic agonists and antagonists in brown adipose tissue membranes were similar to those obtained in Chinese hamster ovary K1 cell membranes with both [3H]SB 206606 and [125I]iodocyanopindolol. The order of binding affinity was BRL 37344 >> (-)-isoproterenol = (-)-norepinephrine > (-)-epinephrine = (+)-isoproterenol. The similarity of the Kd values and of the Ki values for various beta-adrenergic agonists and antagonists in both systems tested indicates that, in a complex membrane system, [3H]SB 206606 binds selectively to the beta 3-adrenergic receptor. The affinity of [3H]SB 206606 is 76 times higher for the beta 3-adrenergic receptor than for the beta 1/beta 2-adrenergic receptors, thus allowing, under controlled conditions, measurement of interactions only with the beta 3-adrenergic receptor in complex membrane systems.
Adipose Tissue, Brown↗