Upregulation of uncoupling proteins by oral administration of capsiate, a nonpungent capsaicin analog.

Capsiate is a nonpungent capsaicin analog, a recently identified principle of the nonpungent red pepper cultivar CH-19 Sweet. In the present study, we report that 2-wk treatment of capsiate increased metabolic rate and promoted fat oxidation at rest, suggesting that capsiate may prevent obesity. To explain these effects, at least in part, we examined uncoupling proteins (UCPs) and thyroid hormones. UCPs and thyroid hormones play important roles in energy expenditure, the maintenance of body weight, and thermoregulation. Two-week treatment of capsiate increased the levels of UCP1 protein and mRNA in brown adipose tissue and UCP2 mRNA in white adipose tissue. This dose of capsiate did not change serum triiodothyronine or thyroxine levels. A single dose of capsiate temporarily raised both UCP1 mRNA in brown adipose tissue and UCP3 mRNA in skeletal muscle. These results suggest that UCP1 and UCP2 may contribute to the promotion of energy metabolism by capsiate, but that thyroid hormones do not.     

Tissue-specific expression of the uncoupling protein family in streptozotocin-induced diabetic rats

The vulnerability of streptozotocin (STZ)-induced diabetic rats to cold stress has been established. One of the elements controlling body temperature is thermogenesis, in which uncoupling protein (UCP) is known to play an important role. We have examined UCP2 and UCP3 expressions in brown adipose tissue (BAT), white adipose tissue (WAT), and skeletal muscle (MSL) during the acute and chronic phases of STZ-induced diabetes in rats. The long-term effect and the effect of insulin treatment thereafter were also unexplored previously and are examined in this study. In the acute phase of diabetes (2.5 days after STZ injection), UCP2 gene expression in BAT, WAT, and MSL, and UCP3 expression in the muscle were significantly increased. In the chronic phase of diabetes (21 days after STZ injection), UCP2 and UCP3 expression in the MSL were restored to the control levels without insulin supplementation. UCP2 in BAT and WAT remained high in the chronic phase, whereas UCP3 expression in BAT and WAT, which did not change in the acute phase, was significantly decreased. Insulin supplementation restored UCP2 expression in BAT and WAT, but over-corrected UCP3 in WAT above the control and did not affect UCP3 expression in BAT. Insulin supplementation depressed UCP3 expression in the MSL below control. These results indicate that the effects of STZ-induced diabetes on UCPs gene expression are tissue-specific as well as dependent on the duration of diabetes.     

Increased uncoupling protein-2 and -3 gene expressions in skeletal muscle of STZ-induced diabetic rats

Streptozotocin (STZ)-induced diabetic animals are vulnerable to cold stress. Uncoupling proteins (UCPs) play an important role in regulating thermogenesis. We investigated the gene expressions of UCPs in brown adipose tissue (BAT), white adipose tissue (WAT), liver and gastrocnemius muscle of STZ-diabetic rats using Northern blot. UCP-1, -2 and -3 mRNA expressions in BAT were all remarkably lower in STZ-diabetic rats than those in control rats. Both UCP-2 and -3 gene expressions in gastrocnemius muscle were substantially elevated in STZ-diabetic rats and insulin treatment restored UCP gene expressions to normal levels. These results suggest that in STZ-diabetic rats, the overexpression of UCP-2 and UCP-3 in skeletal muscle provides a defense against hypothermogenesis caused by decreased UCPs in BAT.     

禁食及胰岛素水平对大鼠解偶联蛋白-1、2、3基因表达的影响

 为探讨禁食和胰岛素对解偶联蛋白 - 1、2、3基因 (UCP1 ,2 ,3)表达的影响 ,应用 RT- PCR方法观察了在不同禁食时间和应用胰岛素条件下大鼠白色脂肪组织、棕色脂肪组织和骨骼肌中 UCP1 ,2 ,3m RNA水平的变化 .UCP1基因只在大鼠棕色脂肪组织中表达 .UCP2 ,3基因在三种组织中均有表达 ,在白色脂肪组织中以 UCP2表达为主 ;在骨骼肌中以 UCP3表达为主 .过夜禁食使棕色脂肪组织 UCP1 ,3m RNA水平明显下降 (P<0 .0 1 ) ;UCP2 m RNA水平在三种组织中均呈上升反应 ,以白色脂肪组织中表现最为明显 (P<0 .0 5) ;而对白色脂肪组织和骨骼肌中 UCP3基因表达无明显影响 .禁食时间延长至 48h,除棕色脂肪组织中 UCP2 ,3基因有明显下降外 ,各组织中UCPs基因表达基本调节至正常或高于对照组水平 .胰岛素对 UCPs基因表达水平有一定的上调作用 ,这一作用对棕色脂肪组织 UCPs各基因及骨骼肌中 UCP3基因表现得尤为明显 (P<0 .0 5) .大鼠 UCPs基因表达有一定的组织特异性 ;禁食时间对三种组织中 UCPs各成员基因表达的影响有时相上的区别 ;胰岛素可以调 UCPs各成员基因的表达 .结果反映了 UCPs各成员在能量代谢调节上的不同作用 ,这为理解膳食 -产热与体重调节的关系 ,及其能量代谢平衡与疾病关系提供了实验依据     

Energy metabolism of adipose tissue--physiological aspects and target in obesity treatment

Body fat content is controlled, at least in part, by energy charge of adipocytes. In vitro studies indicated that lipogenesis as well as lipolysis depend on cellular ATP levels. Respiratory uncoupling may, through the depression of ATP synthesis, control lipid metabolism of adipose cells. Expression of some uncoupling proteins (UCP2 and UCP5) as well as other protonophoric transporters can be detected in the adipose tissue. Expression of other UCPs (UCP1 and UCP3) can be induced by pharmacological treatments that reduce adiposity. A negative correlation between the accumulation of fat and the expression of UCP2 in adipocytes was also found. Ectopic expression of UCP1 in the white fat of aP2-Ucp1 transgenic mice mitigated obesity induced by genetic or dietary factors. In these mice, changes in lipid metabolism of adipocytes were associated with the depression of intracellular energy charge. Recent data show that AMP-activated protein kinase may be involved in the complex changes elicited by respiratory uncoupling in adipocytes. Changes in energy metabolism of adipose tissue may mediate effects of treatments directed against adiposity, dyslipidemia, and insulin resistance.     

Acute central infusion of leptin modulates fatty acid mobilization by affecting lipolysis and mRNA expression for uncoupling proteins

Chronic administration of leptin has been shown to reduce adiposity through energy intake and expenditure. The present study aims to examine how acute central infusion of leptin regulates peripheral lipid metabolism, as assessed by markers indicative of their mobilization and utilization. A bolus infusion of 1 microg/rat leptin into the third cerebroventricle increased the expression of mRNA for hormone-sensitive lipase (HSL), an indicator of lipolysis, in white adipose tissue (WAT). This was accompanied by elevation of plasma levels of glycerol, but not of free fatty acids, as compared to the saline control (P < 0.03). The same treatment with leptin decreased plasma insulin levels but did not affect the plasma glucose level (P < 0.05 for insulin). Among the major regulators of the transportation or utilization of energy substrates, leptin treatment increased expression of mRNA for uncoupling protein 1 (UCP1) in brown adipose tissue (BAT), UCP2 in WAT, and UCP3 in quadriceps skeletal muscle, but not those for fatty acid-binding protein in WAT, carnitine phosphate transferase-1, a marker for beta oxidation of fatty acids in muscle, nor glucose transporter 4 in WAT and muscle (P < 0.01 for HSL, P < 0.05 for UCP1, and P < 0.005 for UCP2 and UCP3). These results indicate that, even in a single bolus, leptin may regulate the mobilization and/or utilization of energy substrates such as fatty acids by affecting lipolytic activity in WAT and by increasing the expression of UCPs in BAT, WAT, and muscle.     

Changes in UCP mRNA expression levels in brown adipose tissue and skeletal muscle after feeding a high-energy diet and relationships with leptin, glucose and PPARgamma

Brown adipose tissue and skeletal muscle are known to be important sites for nonshivering thermogenesis. In this context, it is accepted that uncoupling proteins (UCPs) are involved in such process, but little is known about the physiological regulation of these proteins as affected by the intake of a high-energy (cafeteria) diet inducing fat deposition. In this study, the UCP messenger RNA (mRNA) expression in interscapular brown adipose tissue (iBAT) and skeletal muscle was assessed to evaluate the influence of a dietary manipulation on energy homeostasis regulation. We report a statistically significant increase in mRNA levels of iBAT UCP1 and UCP3 and a statistical marginal rise in skeletal muscle UCP3 mRNA expression after feeding a high-energy diet, whereas no changes in UCP2 expression were found in either tissue. Furthermore, significant positive associations between iBAT UCP1 and UCP3 mRNA levels with serum leptin were found. Although the expression of the beta(3) adrenoceptor (beta(3)AR) was about 50% in the lean controls compared with the obese group in iBAT, no statistically significant changes were observed concerning peroxisome proliferator-activated receptor gamma2 (PPARgamma2) mRNA levels in muscle or iBAT. We conclude that feeding a diet inducing weight and fat gain produces different outcomes on iBAT and skeletal muscle UCP mRNA expression, revealing a tissue-dependent response for the three UCPs. Results suggest that the regulation of UCP expression in both tissues under these specific dietary conditions may be related to leptin circulating levels.     

Intrauterine food restriction alters the expression of uncoupling proteins in brown adipose tissue of rat newborns

A previous study from our laboratory showed that maternal food restriction (MFR) delays thermoregulation in newborn rats. In neonates brown adipose tissue (BAT) is essential for thermogenesis due to the presence of uncoupling proteins (UCPs). The aim of this study was to evaluate the influence of MFR on the UCPs mRNA and protein expression in BAT and skeletal muscle (SM) of the newborn rat. Female Wistar EPM-1 control rats (CON) received chow ad libitum during pregnancy, whereas food-restricted dams (RES) received 50% of the amount ingested by CON. Fifteen hours after birth, the litters were weighed and sacrificed. Blood was collected for hormonal analysis. BAT and SM were used for determination of UCPs mRNA and protein expression, and Ca²⁺-ATPase sarcoplasmic reticulum (SERCA1). RES pups showed a significant reduction in body weight and fat content at birth. MFR caused a significant increase in the expression of UCP1 and UCP2 in BAT, without changes in UCP3 and SERCA1 expression in BAT and SM. No differences between groups were found for leptin, T4 and glucose levels. RES pups showed increased insulin and decreased T3 levels. The delay in development of thermoregulation previously described in RES animals appears not to result from impairment in thermogenesis, but from an increase in heat loss, since MFR caused low birth weight in pups, leading to greater surface/volume ratio. The higher expression of UCP1 and UCP2 in BAT suggests a compensatory mechanism to increased thermogenesis.     

Up-regulation of uterine UCP2 and UCP3 in pregnant rats.

Pregnancy produces profound changes in hormone dynamics, thermoregulation and energy metabolism. Uncoupling proteins (UCPs) have been identified in a variety of tissues and UCP1 is known to play important roles in energy homeostasis, while the regulation of UCP2 and UCP3 is still unclear. The present study aimed to investigate the effects of the changes during pregnancy on UCP gene expression in the uterus, as well as in brown adipose tissue (BAT), white adipose tissue (WAT), soleus muscle (Muscle), and liver, throughout the estrus and metestrus periods, at early, middle and late stages in pregnancy, and during post-gestational stages. The expression of uterine UCP2 and UCP3 were up-regulated by 3.2- and 1. 5-fold, respectively, during the late stage of pregnancy with an increase of WAT leptin mRNA expression and exogenous administration of leptin resulted in induction of the uterine UCP2 and UCP3 levels. Contrary to uterine UCPs, UCP1 mRNA expression in BAT was down-regulated by 0.5-fold and there were no remarkable changes in WAT or liver UCP2, or Muscle UCP3 expression throughout the periods. These results indicate that UCP gene expressions during pregnancy are regulated tissue-dependently, and up-regulation of uterine UCP2 and UCP3 mRNA may be due to increased leptin levels.     

Adipose tumor necrosis factor-alpha is reduced during onset of insulin resistance in Sprague-Dawley rats

Overexpression of mRNA for tumor necrosis factor-alpha (TNF-alpha) has been observed in adipose tissue in several rodent models of insulin resistance. The purpose of the present study was to examine the expression of TNF-alpha protein during the onset of insulin resistance in maturing Sprague-Dawley (S-D) rats. Compared to 2 months, rats aged 5 and 12 months were glucose intolerant and fasting glucose was elevated at 12 months (p < 0.05). Compared to 2 months, insulin concentrations following glucose loading were elevated at 5 months (p < 0.05) and also at 12 months, but to a lesser degree. In isolated strips of soleus muscle, insulin-stimulated glucose transport was reduced by 38% and 59% between 2 and 5 months and between 2 and 12 months, respectively (p < 0.05), with no changes in basal transport. Insulin resistance was associated with decreased content of TNF-alpha protein in visceral and subcutaneous fat. TNF-alpha protein content was also decreased in tibialis anterior muscle, but was unchanged in soleus and red gastrocnemius muscles. Liver was the only tissue examined that showed an increase in TNF-alpha protein content. In vitro secretion of TNF-alpha protein was markedly reduced in explants of visceral and subcutaneous fat from mature, insulin-resistant animals, but TNF-alpha bioactivity in subcutaneous fat was maintained with age. These results indicate that the onset of insulin resistance in mature S-D rats is associated with reduced adipose expression of TNF-alpha. Our findings do not support the adipose-endocrine model of TNF-alpha in insulin resistance. Our findings do support a paracrine role for TNF-alpha or for a reduction in endogenous TNF-alpha inhibitors in insulin resistance.     

Short-term, increasing dietary protein and fat moderately affect energy expenditure, substrate oxidation and uncoupling protein gene expression in rats

Macronutrient composition of diets can influence body-weight development and energy balance. We studied the short-term effects of high-protein (HP) and/or high-fat (HF) diets on energy expenditure (EE) and uncoupling protein (UCP1-3) gene expression. Adult male rats were fed ad libitum with diets containing different protein-fat ratios: adequate protein-normal fat (AP-NF): 20% casein, 5% fat; adequate protein-high fat (AP-HF): 20% casein, 17% fat; high protein-normal fat (HP-NF): 60% casein, 5% fat; high protein-high fat (HP-HF): 60% casein, 17% fat. Wheat starch was used for adjustment of energy content. After 4 days, overnight EE and oxygen consumption, as measured by indirect calorimetry, were higher and body-weight gain was lower in rats fed with HP diets as compared with rats fed diets with adequate protein content (P<.05). Exchanging carbohydrates by protein increased fat oxidation in HF diet fed groups. The UCP1 mRNA expression in brown adipose tissue was not significantly different in HP diet fed groups as compared with AP diet fed groups. Expression of different homologues of UCPs positively correlated with nighttime oxygen consumption and EE. Moreover, dietary protein and fat distinctly influenced liver UCP2 and skeletal muscle UCP3 mRNA expressions. These findings demonstrated that a 4-day ad libitum high dietary protein exposure influences energy balance in rats. A function of UCPs in energy balance and dissipating food energy was suggested. Future experiments are focused on the regulation of UCP gene expression by dietary protein, which could be important for body-weight management.     

Effects of the presence, absence, and overexpression of uncoupling protein-3 on adiposity and fuel metabolism in congenic mice

Uncoupling protein-3 (UCP3) is a poorly understood mitochondrial inner membrane protein expressed predominantly in skeletal muscle. The aim of this study was to examine the effects of the absence or constitutive physiological overexpression of UCP3 on whole body energy metabolism, glucose tolerance, and muscle triglyceride content. Congenic male UCP3 knockout mice (Ucp3-/-), wild-type, and transgenic UCP3 overexpressing (UCP3Tg) mice were fed a 10% fat diet for 4 or 8 mo after they were weaned. UCP3Tg mice had lower body weights and were less metabolically efficient than wild-type or Ucp3-/- mice, but they were not hyperphagic. UCP3Tg mice had smaller epididymal white adipose tissue and brown adipose tissue (BAT) depots; however, there were no differences in muscle weights. Glucose and insulin tolerance tests revealed that both UCP3Tg and Ucp3-/- mice were protected from development of impaired glucose tolerance and were more sensitive to insulin. 2-Deoxy-D-[1-3H]glucose tracer studies showed increased uptake of glucose into BAT and increased storage of liver glycogen in Ucp3-/- mice. Assessments of intramuscular triglyceride (IMTG) revealed decreases in quadriceps of UCP3Tg mice compared with wild-type and Ucp3-/- mice. When challenged with a 45% fat diet, Ucp3-/- mice showed increased accumulation of IMTG compared with wild-type mice, which in turn had greater IMTG than UCP3Tg mice. Results are consistent with a role for UCP3 in preventing accumulation of triglyceride in both adipose tissue and muscle.     

UCP2, UCP3, avUCP, what do they do when proton transport is not stimulated? Possible relevance to pyruvate and glutamine metabolism

Uncoupling proteins (UCPs) are specialized members of the mitochondrial transporter family. They allow passive proton transport through the mitochondrial inner membrane. This activity leads to uncoupling of mitochondrial respiration and to energy waste, which is well documented with UCP1 in brown adipose tissue. The uncoupling activity of the new UCPs (discovered after 1997), such as UCP2 and UCP3 in mammals or avUCP in birds, is more difficult to characterize. However, extensive data support the idea that the new UCPs are involved in the control of reactive oxygen species (ROS) generation. This fits with the hypothesis that mild uncoupling caused by the UCPs prevents ROS production. Activators and inhibitors regulate the proton transport activity of the UCPs. In the absence of activators of proton transport, the UCP allows the permeation of other ions. We suggest that this activity has physiological significance and, for example, UCP3 expressed in glycolytic muscle fibres may be a passive pyruvate transporter ensuring equilibrium between glycolysis and oxidative phosphorylation. Induction of UCP2 expression by glutamine strengthens the proposal that new UCPs could act to determine the choice of mitochondrial substrate. This would obviously have an impact on mitochondrial bioenergetics and ROS production.     

Obesity in Insulin Receptor Substrate‐2–Deficient Mice: Disrupted Control of Arcuate Nucleus Neuropeptides

Objectives : Disturbances in insulin signaling have been shown to induce obesity and/or hyperphagia in brain insulin receptor or insulin receptor substrate‐2 (IRS‐2) knockout (KO) mice. This study aimed to examine the central and peripheral mechanisms underlying the phenotype in IRS‐2 KO mice. Research Methods and Procedures : We measured the histological characterization of adipose tissues, mRNA levels of pro‐opiomelanocortin, agouti‐related protein, and neuropeptide Y in the hypothalamus and uncoupling proteins (UCPs) in peripheral tissues of IRS‐2 KO mice. Results : Female IRS‐2 KO mice showed increased daily food intake. Body weight and adiposity were increased in both sexes, although these differences were more pronounced in female than in male IRS‐2 KO mice. Both male and female IRS‐2 KO mice showed decreased UCP1 mRNA expression in brown adipose tissue with defective thermoregulation, and UCP2 mRNA expression was increased in the white adipose tissue of female knockout mice. Furthermore, arcuate nucleus mRNA expression of pro‐opiomelanocortin, was decreased in both male and female IRS‐2 KO mice, whereas expression of agouti‐related protein and neuropeptide Y were increased in female IRS‐2 KO mice. Discussion : In IRS‐2 KO mice, disrupted control of hypothalamic neuropeptide levels and UCP mRNA expression may contribute to the development of obesity.     

Association of resistin with visceral fat and muscle insulin resistance

Maturing Sprague-Dawley (S-D) rats develop obesity and skeletal muscle insulin resistance. To investigate the relationship between fat mass and insulin responses, we performed surgical removal of the epididymal and retroperitoneal depots of visceral adipose tissue (VF) or sham surgery (SHAM) in male rats aged 4 months. At sacrifice, 30 days later, the mass of visceral fat was 48% lower (p<0.05) in VF- compared to SHAM, while subcutaneous fat was essentially unchanged. VF- animals displayed increased insulin responses in isolated strips of skeletal muscle. Insulin-stimulated glucose transport was increased 28% in soleus muscle (p<0.05), with a trend toward a 31% increase in extensor digitorum longus muscle (p=0.058). Glucose tolerance was not significantly affected by surgical fat removal. In VF- animals, serum resistin was reduced 26% (p<0.05) and serum adiponectin was reduced 30% (p<0.05), with trends for reductions in IL-4 (58% reduction, p=0.084) and IL-6 (56% reduction, p=0.123). TNF-alpha, leptin and free fatty acids (NEFAs) were unchanged. We conclude that in maturing S-D rats, increased visceral adiposity leads to an increase in systemic release in resistin and possibly interleukins. Elevation of circulating cytokines may play a role in the development of muscle insulin resistance.     

Potential roles for uncoupling proteins in HIV lipodystrophy

The 'HIV lipodystrophy syndrome' consists of several distinct components, including lipoatrophy (pathological subcutaneous fat loss), lipohypertrophy (abdominal/visceral adiposity), and metabolic complications including insulin resistance and dyslipidemia. Lipoatrophy appears to represent an adipose tissue-specific form of mitochondrial toxicity associated strongly with stavudine NRTI therapy, whilst the 'metabolic syndrome' phenotype is associated with HIV protease inhibitor therapy. In this context, the role of uncoupling proteins (UCPs) in modulating resting energy expenditure in response to elevated fatty acid flux associated with the 'metabolic syndrome' is supported by clinical data as well as findings of elevated adipose tissue UCP expression. The role of UCPs in this syndrome therefore exemplifies the multifactorial nature of these antiretroviral therapy complications.     

Effect of resistance exercise training on expression of Hsp70 and inflammatory cytokines in skeletal muscle and adipose tissue of STZ-induced diabetic rats

Impairment of adipose tissue and skeletal muscles accrued following type 1 diabetes is associated with protein misfolding and loss of adipose mass and skeletal muscle atrophy. Resistance training can maintain muscle mass by changing both inflammatory cytokines and stress factors in adipose tissue and skeletal muscle. The purpose of this study was to determine the effects of a 5-week ladder climbing resistance training program on the expression of Hsp70 and inflammatory cytokines in adipose tissue and fast-twitch flexor hallucis longus (FHL) and slow-twitch soleus muscles in healthy and streptozotocin-induced diabetic rats. Induction of diabetes reduced body mass, while resistance training preserved FHL muscle weight in diabetic rats without any changes in body mass. Diabetes increased Hsp70 protein content in skeletal muscles, adipose tissue, and serum. Hsp70 protein levels were decreased in normal and diabetic rats by resistance training in the FHL, but not soleus muscle. Furthermore, resistance training decreased inflammatory cytokines in FHL skeletal muscle. On the other hand, Hsp70 and inflammatory cytokine protein levels were increased by training in adipose tissue. Also, significant positive correlations between inflammatory cytokines in adipose tissue and skeletal muscles with Hsp70 protein levels were observed. In conclusion, we found that in diabetic rats, resistance training decreased inflammatory cytokines and Hsp70 protein levels in fast skeletal muscle, increased adipose tissue inflammatory cytokines and Hsp70, and preserved FHL muscle mass. These results suggest that resistance training can maintain skeletal muscle mass in diabetes by changing inflammatory cytokines and stress factors such as Hsp70 in skeletal muscle and adipose tissue.     

Identification and characterization of uncoupling protein 4 in fat body and muscle mitochondria from the cockroach <Emphasis Type="Italic">Gromphadorhina cocquereliana</Emphasis>

We have identified and characterized an uncoupling protein in mitochondria isolated from leg muscle and from fat body, an insect analogue tissue of mammalian liver and adipose tissue, of the cockroach Gromphadorhina coquereliana (GcUCP). This is the first functional characterization of UCP activity in isolated insect mitochondria. Bioenergetic studies clearly indicate UCP function in both insect tissues. In resting (non-phosphorylating) mitochondria, cockroach GcUCP activity was stimulated by the addition of micromolar concentrations of palmitic acid and inhibited by the purine nucleotide GTP. Moreover, in phosphorylating mitochondria, GcUCP activity was able to divert energy from oxidative phosphorylation. Functional studies indicate a higher activity of GcUCP-mediated uncoupling in cockroach muscle mitochondria compared to fat body mitochondria. GcUCP activation by palmitic acid resulted in a decrease in superoxide anion production, suggesting that protection against mitochondrial oxidative stress may be a physiological role of UCPs in insects. GcUCP protein was immunodetected using antibodies raised against human UCP4 as a single band of around 36 kDa. GcUCP protein expression in cockroach muscle mitochondria was significantly higher compared to mitochondria isolated from fat body. LC-MS/MS analyses revealed 100% sequence identities for peptides obtained from GcUCP to UCP4 isoforms from D. melanogaster (the highest homology), human, rat or other insect mitochondria. Therefore, it can be proposed that cockroach GcUCP corresponds to the UCP4 isoforms of other animals.     

Effects of aging and denervation on the expression of uncoupling proteins in slow- and fast-twitch muscles of rats

We investigated the effects of aging and denervation on the gene expression of uncoupling proteins (UCPs) in slow-twitch soleus and fast-twitch gastrocnemius muscles. In a comparison between the control limbs of 6- and 24-month-old rats, the mRNA levels of UCP3, heart-type fatty acid binding protein (HFABP), and glucose transporter-4 (GLUT4) were considerably lower in the gastrocnemius muscles of the older rats, whereas no significant differences in the mRNA levels of those genes as well as UCP2 and cytochrome oxidase subunit IV (COX-IV) were observed in the soleus muscles of young and old rats. The UCP3 and COX-IV protein levels were also reduced considerably in the aged gastrocnemius muscles with atrophy. Denervation of the sciatic nerve caused an increase in UCP3 mRNA levels in both muscles, but the regulation of other genes contrasted between the two types of skeletal muscles. In spite of the increased mRNA level, a remarkable reduction in UCP3 protein was found in the denervated gastrocnemius muscles. These results indicate that the effects of aging and denervation on the gene expression of UCPs, HFABP, GLUT4, and COX-IV are different between the muscle types. The reduction in the mitochondrial UCP3 and COX proteins in aged fast-twitch muscles may have a negative effect on energy metabolism and thermogenesis in old animals.