Renewed selection for heat loss in mice: direct responses and correlated responses in feed intake, body weight, litter size, and conception rate

Divergent selection in mice was renewed in 3 independent replicates for high (MH) and low (ML) heat loss. An unselected control (MC) was maintained in all replicates. Heat loss was measured for individual male mice for 15 h, overnight in direct calorimeters. After 16 initial generations of selection followed by 26 generations of relaxed selection, divergent selection resumed for 9 generations. The realized selection applied was very close to the maximum possible selection according to the criteria and protocol. Selection differentials were greater for high than for low selection due to greater variation in the MH line. When corrected for SD, standardized selection differentials were similar for MH and ML selection. Unintended selection in MC was negligible. Realized heritability for divergence was 0.14 +/- 0.01, which was considerably less than that realized during the initial generations of selection (0.28 +/- 0.03). Realized heritabilities for MH selection (0.16 +/- 0.05) and for ML selection (0.07 +/- 0.06) were less, especially for ML selection, than were observed in the earlier generations. The difference in heat loss between MH and ML males was 55.7% of the MC mean at generation 51, compared with a difference of 53.6% in generation 15; this difference had decreased to 34.4% at the end of the relaxed selection (generation 42). For feed intake between 8 and 11 wk, MH and ML males differed by 34.0% of the MC mean by the end of the selection process. Body weight at 12 wk for MH and ML males was less than for MC males. Litter size response was positively related to the heat loss response. Conception rate was poorer in MH matings than in MC and ML matings.     

Locomotor activity, core body temperature, and circadian rhythms in mice selected for high or low heat loss

Daily locomotor activity, core body temperature, and their circadian rhythms were measured in lines of mice selected for high (MH) or low (ML) heat loss and unselected controls (MC). Lines were created by selecting for 16 generations in each of three replicates. Collection of locomotor activity and core temperature data spanned Generations 20 and 21 for a total of 352 mice. Physical activity and core body temperature data were accumulated using implanted transmitters and continuous automated collection. Measurement for each animal was for 3 d. Activity was recorded for each half hour and then averaged for the day; temperature was averaged daily; circadian rhythm was expressed in 12-h (light vs dark) or 6-h periods as well as by fitting cyclic models. Activity means were transformed to log base 2 to lessen heterogeneity of variance within lines. Heat loss for a 15-h period beginning at 1630 and feed intake for 7 d were measured on 74 additional mice in order to estimate the relationship between locomotor activity and heat loss or feed intake. Selection lines were different (P < 0.01) for both locomotor activity and core body temperature. Differences were due to selection (MH-ML, P < 0.01), and there was no evidence of asymmetry of response (P > 0.38). Retransformed from log base 2 to the scale of measurement, mean activity counts were 308, 210, and 150 for MH, MC, and ML, respectively. Mean core temperatures were 37.2, 36.9, and 36.7 degrees C for MH, MC, and ML (P < 0.01), respectively. Females had greater physical activity (P < 0.01) and body temperature (P < 0.01) than males. There was no evidence of a sex x selection criterion interaction for either activity or temperature (P > 0.20). Overall phenotypic correlation between body temperature and log base 2 activity was 0.43 (P < 0.01). Periods during the day were different for both 12- and 6-h analyses (P < 0.01), but there were no period x selection criterion interactions (P > 0.1) for physical activity or body temperature. More sensitive cyclic models revealed significant (P < 0.01) 24-, 12-, 8-, and 6-h cycles that differed (P < 0.01) among lines. Estimated differences between MH and ML mice in feed intake and heat loss due to locomotor activity were 36 and 11.5%, respectively. Variation in activity thus contributed to variation in feed intake.     

Comparison of feed energy costs of maintenance, lean deposition, and fat deposition in three lines of mice selected for heat loss

Three replications of mouse selection populations for high heat loss (MH), low heat loss (ML), and a nonselected control (MC) were used to estimate the feed energy costs of maintenance and gain and to test whether selection had changed these costs. At 21 and 49 d of age, mice were weighed and subjected to dual x-ray densitometry measurement for prediction of body composition. At 21 d, mice were randomly assigned to an ad libitum, an 80% of ad libitum, or a 60% of ad libitum feeding group for 28-d collection of individual feed intake. Data were analyzed using 3 approaches. The first approach was an attempt to partition energy intake between costs for maintenance, fat deposition, and lean deposition for each replicate, sex, and line by multiple regression of feed intake on the sum of daily metabolic weight (kg(0.75)), fat gain, and lean gain. Approach II was a less restrictive attempt to partition energy intake between costs for maintenance and total gain for each replicate, sex, and line by multiple regression of feed intake on the sum of daily metabolic weight and total gain. Approach III used multiple regression on the entire data set with pooled regressions on fat and lean gains, and subclass regressions for maintenance. Contrasts were conducted to test the effect of selection (MH - ML) and asymmetry of selection [(MH + ML)/2 - MC] for the various energy costs. In approach I, there were no differences between lines for costs of maintenance, fat deposition, or protein deposition, but we question our ability to estimate these accurately. In approach II, selection changed both cost of maintenance (P = 0.03) and gain (P = 0.05); MH mice had greater per unit costs than ML mice for both. Asymmetry of the selection response was found in approach II for the cost of maintenance (P = 0.06). In approach III, the effect of selection (P < 0.01) contributed to differences in the maintenance cost, but asymmetry of selection (P > 0.17) was not evident. Sex effects were found for the cost of fat deposition (P = 0.02) in approach I and the cost of gain (P = 0.001) in approach II; females had a greater cost per unit than males. When costs per unit of fat and per unit of lean gain were assumed to be the same for both sexes (approach III), females had a somewhat greater estimate for maintenance cost (P = 0.10). We conclude that selection for heat loss has changed the costs for maintenance per unit size but probably not the costs for gain.     

Performance of mouse lines divergently selected for heat loss when exposed to different environmental temperatures. I. Reproductive performance, pup survival, and metabolic hormones

Mouse populations differing in metabolic rate have been developed through selection for high (MH) and low (ML) heat loss, along with the unselected controls (MC). Objectives of the study were to compare the MH, ML, and MC lines for reproductive performance, pup survival, and metabolic hormones when reared at 12, 22, and 31 degrees C, and to search for line x environment interactions. Conception and litter size were recorded on the parent generation mice introduced to the environments at 11 wk of age and bred after a 3-wk acclimatization period. Survival of pups (preweaning to 3 wk; postweaning from 3 to 9 wk of age) was measured with continuous exposure in the designated environment from birth to the time of measurement. Corticosterone, triiodothyronine (T3), and thyroxine (T4) serum concentrations were measured on the parent generation after producing litters and on the pup generation at 9 wk. No line x environment interaction was detected for conception rate, preweaning mortality, postweaning survival, pup weaning weight, or body temperature. There were no differences in conception rate among lines and environments. Environments affected survival of pups, but there were no line differences. Rectal body temperatures were greater for MH than ML mice, and MC mice were intermediate; body temperature of mice did not differ among the environments. Lines differed significantly in litter size only in the 22 degrees C environment. No significant line differences were found for serum corticosterone or serum T3 or T4. Line x environment interaction was detected only for litter size and for serum corticosterone concentration in dams. Contrary to the other two lines, ML dam performance relative to MH and MC was not affected negatively by either of the thermal environments. Results from this study do not raise concern that selection to decrease maintenance requirements will produce livestock with any greater liability to cope and perform under an array of environmental temperatures.     

Correlated responses in maternal performance following divergent selection for heat loss in mice

Divergent selection in mice was applied in 3 independent replicates for high (maintenance high; MH) and low (maintenance low; ML) heat loss for 16 generations. An unselected control (maintenance control; MC) was also maintained in all replicates. Selection ceased for 26 generations; heat-loss measurement and selection resumed at generation 42. Lactation performance, dam weight, dam feed intake, and efficiency of production of pup weight were recorded or calculated for MH and ML dams in all 3 replicates at generation 46 or 47 with the objective of determining whether selection for heat loss has created correlated responses in maternal performance. One-half of the dams reared their own litters, and one-half reared cross-fostered (across lines) litters. Between 10 and 12 litters were used from each replicate-line-rearing class. Litter size was recorded, and litters were standardized to 8 pups within 24 h of birth. For cross fostering, MH litters were matched to ML litters born within 24 h of each other, and MH-ML litter pairs were cross-fostered at 3 d of age. A weigh-suckle-weigh protocol was used to obtain milk production estimates over a 2-h suckling period at 6, 9, 12, and 15 d. Dam (plus litter) feed intake was also recorded at these times and was calculated as the disappearance of feed over 3-d intervals. Dams of the MH selection tended (P < 0.11) to have greater litter size than those of the ML selection; litter size of MC dams was intermediate. Line of dam affected milk production (P = 0.04) and dam feed intake (P < 0.03) as MH dams produced more milk and consumed more feed than ML dams. Average milk production for the 2-h measurement period was 1.70 +/- 0.07 and 1.41 +/- 0.07 g, and average 3-d feed consumption was 50.8 +/- 1.2 and 45.2 +/- 1.2 g for MH and ML dams, respectively. Cross-fostering had no effect (P > 0.86) on milk production. Line of dam tended to affect 21-d litter weight (P = 0.15) with litters reared by MH dams weighing more than those reared by ML dams, but there was no difference (P > 0.86) in 21-d dam weights. Efficiency of producing litter weight (litter 15-d weight: dam plus litter feed intake from d 6 to 15) was greater (0.49 vs. 0.46, SE = 0.009; P = 0.03) for ML than for MH dams. Selection for reduced heat loss (lower maintenance feed intake in the ML line) resulted in reduced milk production and feed intake in dams and greater efficiency of litter weight production.     

Performance of mouse lines divergently selected for heat loss when exposed to different environmental temperatures. II. Feed intake, growth, fatness, and body organs

Mouse populations differing in metabolic rate have been developed through selection for high (MH) and low (ML) heat loss, along with the unselected controls (MC). Objectives of the study were to compare the MH, ML, and MC lines for feed intake, growth, body fatness, and organ weights when reared at 12, 22, and 31 degrees C, and investigate potential line x environment interactions. Feed intake was recorded weekly from 3 to 9 wk of age, and BW at 3, 6, and 9 wk of age. Body fat percent and organ weights were measured at 9 wk of age. No line x environment interactions were detected for any of the traits measured. The MH mice consumed more feed than ML mice from 5 to 9 wk of age. Between 8 and 9 wk of age, MH mice consumed 13% more feed than the ML mice, but they were relatively leaner (14.45 vs. 16.32% body fat); MC mice were intermediate for both traits. Mice in the cold environment consumed the greatest amount of feed, and those in the hot environment consumed the least. Males consumed more feed than females, and the difference was greater in the cold than in the hot environment. No differences in BW were found between the lines. Mice in the 22 degrees C environment were heavier than their age-matched counterparts in the other two environments, and males were heavier than females at all ages. Relative to BW, the three lines had similar tail length, body length, and liver weight. Mice in the cold environment had heavier spleens and livers than those in the hot environment but relatively shorter bodies and tails; the normal environment was intermediate for these traits. Results from this study indicate that selection to decrease maintenance requirements did not produce mice with any less ability to grow and perform under an array of environmental temperatures.     

Brown adipose tissue development and metabolism in ruminants

We conducted several experiments to better understand the relationship between brown adipose tissue (BAT) metabolism and thermogenesis. In Exp. 1, we examined perirenal (brown) and sternum s.c. adipose tissue in 14 Wagyu x Angus neonates infused with norepinephrine (NE). Perirenal adipocytes contained numerous large mitochondria with well-differentiated cristae; sternum s.c. adipocytes contained a few, small mitochondria, with poorly developed cristae. Lipogenesis from acetate was high in BAT but barely detectable in sternum s.c. adipose tissue. In Exp. 2, we compared perirenal and tailhead adipose tissues between NE-infused Angus (n = 6) and Brahman (n = 7) newborn calves. Brahman BAT contained two-to-three times as many total beta-receptors as Angus BAT. The mitochondrial UCP1:28S rRNA ratio was greater in Brahman BAT than in BAT from Angus calves. Lipogenesis from acetate and glucose again was high, but lipogenesis from palmitate was barely detectable. Tail-head s.c. adipose tissue from both breed types contained adipocytes with distinct brown adipocyte morphology. In Exp. 3, three fetuses of each breed type were taken at 96, 48, 24, 14, and 6 d before expected parturition, and at parturition. Lipogenesis from acetate and glucose in vitro decreased 97% during the last 96 d of gestation in both breed types, whereas the UCP1 gene expression tripled during gestation in both breed types. At birth, palmitate esterification was twice as high in Angus than in Brahman BAT and was at least 100-fold higher than in BAT from NE-infused calves from Exp. 2. Uncoupling protein-1 mRNA was readily detectable in tailhead s.c. adipose tissue in all fetal samples. In Exp. 4, male Brahman and Angus calves (n = 5 to 7 per group) were assigned to 1) newborn treatment (15 h of age), 2) 48 h of warm exposure (22 degrees C) starting at 15 h of age, or 3) 48 h of cold exposure (4 degrees C) starting at 15 h of age. Brahman BAT adipocytes shrank with cold exposure, whereas Angus BAT adipocytes did not. Similarly, BAT from neonatal lambs (Exp. 5; n = 6 per group) was depleted of lipid in response to cold exposure, although UCP1 gene expression persisted. In Exp. 4, NE stimulated lipogenesis from palmitate in BAT incubated in vitro. Lipogenesis from palmitate was higher in Angus than in Brahman BAT, and increased with both warm and cold exposure. These studies suggest that BAT from Brahman calves may be exhausted of lipid shortly after birth during times of cold exposure.     

解偶联蛋白与动物的冷适应

动物的脂肪组织为棕色脂肪组织(brow n ad ipose tissue,BAT)和白色脂肪组织(w h ite ad ipose tissue,W AT)。棕色脂肪组织中含有大量线粒体,是哺乳动物非颤抖产热的主要器官,对动物的体温控制和能量平衡调节起重要作用,位于线粒体内膜的解偶联蛋白(uncoup ling prote in,UCP)的含量和活性是决定其功能的关键因素。作者综述了UCP的结构、UCP基因的多态性及其与肥胖的关系、影响UCPmRNA表达的因素,并对UCP进行了讨论与展望。     

Ontogenic development of brown adipose tissue in Angus and Brahman fetal calves

Brahman calves experience greater neonatal mortality than Angus calves if cold-stressed. To establish a developmental basis for this, three fetuses of each breed type were taken at 96, 48, 24, 14, and 6 d before expected parturition, and at parturition. Overall fetal BW tended (P = 0.08) to be greater for Angus than for Brahman fetuses. There was no difference between breed types in total brown adipose tissue (BAT) mass or grams of BAT/kg BW. Brown adipocyte density decreased 56%, whereas lipogenesis from acetate and glucose in vitro decreased 97% during the last 96 d of gestation in both breed types. Glycerolipid synthesis from palmitate declined by 85% during the last trimester but still contributed 98% to total lipid synthesis at birth. The fetal age x breed interaction was significant for lipogenesis from glucose (P = 0.05) and palmitate (P = 0.005); rates were higher at 96 d before birth in Brahman BAT but declined to similar rates by birth. Uncoupling protein-1 (UCP1) mRNA tripled during gestation in both breed types (P = 0.002), whereas mitochondrial cross-sectional area did not change (P = 0.14) during gestation. Neither the breed nor the age x breed effect was significant (P > or = 0.24) for UCP1 mRNA concentration or mitochondrial cross-sectional area. In both breed types, a marked decrease in BAT UCP1 mRNA between 24 and 14 d prepartum was associated with a similar reduction in lipogenesis from palmitate and a noticeable change in BAT mitochondrial morphology, as the mitochondria became more elongated and the cristae became more elaborate. Uncoupling protein-1 mRNA initially was elevated in Angus tailhead s.c. adipose tissue, but was barely detectable by birth, and tended to be greater overall (P = 0.09) in Angus than in Brahman BAT. If uncoupling protein activity in s.c. adipose tissue persists after birth, then s.c. adipose tissue may contribute more to thermogenesis in Angus newborn calves than in Brahman calves. In contrast, we did not observe differences in ontogenic development of perirenal BAT that could explain the documented differences in thermogenic capacity between Angus and Brahman newborn calves.     

冷刺激小鼠脂肪组织差异表达长链非编码RNA的初步研究

脂肪组织主要有白色脂肪组织(WAT)和褐色脂肪组织(BAT)两种类型;WAT储存能量,BAT通过特异性表达解耦联蛋白1(uncoupling protein 1,UCP1)消耗能量产热。与BAT不同,WAT具有很强的可塑性,在寒冷刺激下,呈现褐色脂肪表型、获得褐色脂肪的产热活性("褐色化")。根据对冷刺激组(6℃)和对照组(28℃)小鼠的肩胛区褐色脂肪组织(iBAT)和皮下白色脂肪组织(sWAT)的RNA转录组测序分析结果,初步筛选出1个差异明显的长链非编码RNA (lncRNA-6030408B16Rik)。通过qRT-PCR检测lncRNA-6030408B16Rik在野生型小鼠的脾脏、肌肉、肾脏、十二指肠、大脑、肝脏、sWAT和iBAT中的表达;24只雄性C57BL/6野生型小鼠随机分成冷刺激组(6℃)和对照组(28℃),两组小鼠分别在6和28℃环境下处理10 d,分别采集两组的iBAT和sWAT;并分离出生1 d的野生型小鼠褐色前脂肪细胞,诱导分化后,收集0、1、3、5 d的细胞,检测UCP1基因和lncRNA-6030408B16Rik在分化过程中的时空表达。qRT-PCR结果显示iBAT和sWAT中lncRNA-6030408B16Rik的表达量均明显高于其他组织;与对照组相比,冷刺激组iBAT中lncRNA-6030408B16Rik的表达量极显著上调(P<0.01),冷刺激组sWAT中lncRNA-6030408B16Rik的表达量显著上调(P<0.05);前脂肪细胞诱导分化的过程中,lncRNA-6030408B16Rik的表达量呈先上调后下调的趋势。lncRNA-6030408B16Rik在脂肪组织中特异性高表达。lncRNA-6030408B16Rik可能对白色脂肪组织"褐色化"及褐色前脂肪细胞的分化具有重要的调控作用。     

Metabolism and morphology of brown adipose tissue from Brahman and Angus newborn calves

The objective of this study was to compare adipocyte morphology and lipogenesis between breed types (Angus vs Brahman) in brown adipose tissue (BAT) and white adipose tissue (WAT) from newborn calves. The Brahman calves (n = 7) were born during the fall season, whereas the Angus calves were born in fall (n = 6) or the following spring (n = 4). At parturition, Brahman cows were lighter than fall Angus cows, but were heavier than spring Angus cows (P < .05). Birth weights and perirenal BAT weights were greater in spring-born, but not in fall-born Angus calves, than in Brahman calves (P < .05). Fall-born Angus BAT contained 63% more (P < .05) adipocytes/100 mg tissue and contained a greater proportion (P < .05) of adipocytes with mean diameters of 40 to 50 microm, and fewer adipocytes with diameters of 60 microm or greater, than Brahman BAT. Brahman BAT contained two-to-three times as many beta-receptors as Angus BAT (P < .05), although the dissociation constant (Kd) was not different between breed types. Mitochondria in Brahman BAT were primarily spherical, whereas Angus BAT mitochondria were elongated, and mitochondrial cross-sectional area tended (P = .08) to be greater in Brahman BAT than in Angus BAT. The mitochondrial uncoupling protein (UCP) mRNA concentration (per 10(6) cells) was greater in Brahman BAT than in BAT from fall-born Angus calves. Lipogenesis from acetate was greater in Angus BAT than in Brahman BAT (P < .05), and glucose and palmitate contributed a greater proportion of carbon to lipogenesis in Brahman BAT than in Angus BAT. These differences in lipogenesis between breed types were not observed in s.c. WAT. The WAT from both breed types contained adipocytes with distinct brown adipocyte morphology, suggesting an involution of BAT to WAT in utero. We conclude that differences in UCP gene expression cannot cause the greater peak thermogenesis of Angus calves; however, differences between breed types in lipid metabolism and(or) mitochondrial morphology may contribute to this phenomenon.     

Molecular and histological evidence of brown adipose tissue in adult cats

Brown adipose tissue (BAT) can influence glucose, lipid, and energy metabolism in rodents. Active BAT is now known to be present in adult humans, and interventions targeting BAT are being investigated for the treatment of human obesity and disorders of glucose and lipid metabolism. Domestic cats, like humans, are at increasing risk for obesity and diabetes but little is known about the presence and role of BAT in adult cats. The purpose of this study was to determine if brown adipocytes, identifiable by histological features and molecular markers, were present in the fat depots of adult cats. Adipose tissue samples from intrascapular, perirenal, and subcutaneous depots of eleven 8–12 year old cats (6 lean, 5 obese), were analyzed by real-time PCR for brown adipocyte markers uncoupling protein 1 (UCP1) and Type II iodothyronine 5′deiodinase (D2), by histological examination and by immunohistochemistry for UCP1.UCP1 mRNA was detectable in interscapular and subcutaneous depots in all cats, and in the perirenal depot in 10/11 cats. D2 mRNA was detectable in all depots from all cats. Multilocular adipocytes were identified in the interscapular depots of 4/11 cats and these were positive for UCP1 immunoreactivity. The results demonstrate that UCP1-expressing brown adipocytes are present in multiple depots of adult lean and long-term obese cats, even at 8–12 years of age. It is possible that dietary components or pharmacological agents that influence brown fat activity could exert a relevant biological effect in cats.     

日粮鱼油对高脂日粮饲喂小鼠发情周期和机体产热的影响

本研究旨在探讨鱼油对高脂日粮饲喂小鼠发情周期和机体代谢产热的影响。试验选用36只4周龄C57BL/6 J雌性小鼠,随机分成3组（n=12）：对照组、高脂组和高脂+鱼油组。对照组饲喂标准啮齿动物饲料（AIN-93G）,高脂组和高脂+鱼油组分别饲喂高脂日粮（脂肪提供60%能量）和添加5%鱼油（等能替代猪油）的高脂日粮。试验期间,对小鼠体组成（12周龄）、整体代谢（16周龄）、褐色脂肪温度（18周龄）、体核温度（直肠温度,18周龄）和发情周期（20周龄）等进行检测。试验结束后,眼球采血分离血清,检测促卵泡激素（follicle-stimulating hormone,FSH）和雌二醇（estradiol,E2）的水平。此外,采集皮下脂肪、腹部脂肪和肩胛间褐色脂肪,称重并使用Western blot检测脂肪组织中产热相关基因的蛋白表达（UCP1、Cyto C）,使用实时荧光定量PCR检测褐色脂肪组织中产热基因的mRNA表达（UCP1, PRDM16,PGC1α,Cidea,Elovl3）。结果显示,与对照组相比,高脂日粮显著增加了小鼠的体脂含量（12周龄）及皮下和腹部脂肪的沉积量（21周龄）（P<0.05）,而添加鱼油显著降低了高脂饮食引起的体脂含量增加（P<0.05）。另外,高脂日粮导致小鼠的发情周期紊乱,伴随着周期延长、发情期缩短,以及血清中FSH和E2的水平降低（P<0.05）,而添加鱼油可缓解高脂日粮导致的小鼠发情周期紊乱,提高血清中FSH和E2的水平（P<0.05）。同时,添加鱼油可增加高脂饲喂小鼠肩胛间褐色脂肪（interscapular brown adipose tissue,iBAT）和腹股沟白色脂肪（inguinal white adipose tissue,iWAT）中产热相关基因的表达（P<0.05）,进而促进iBAT激活/产热和iWAT褐色化。结果提示,日粮鱼油可缓解高脂日粮导致的发情周期紊乱,可能与BAT激活和WAT褐色化造成的机体代谢产热增强有关。     

Beta 3-adrenergic agonist up-regulates uncoupling proteins 2 and 3 in skeletal muscle of the mouse

Chronic stimulation of the beta3-adrenergic receptor (AR) in obese animals resulted in a reduced adiposity associated with an increased expression of thermogenic uncoupling protein (UCP)1 in adipose tissues. In this study, the mRNA expression of newly cloned UCP isoforms (UCP2 and UCP3) were examined in obese yellow KK and C57BL control mice. UCP2 mRNA was found in all tissues examined, with higher levels in adipose tissues and skeletal muscle of the obese mice. UCP3 mRNA was expressed in skeletal muscle, heart and brown adipose tissue similarly in the two mouse strains. Daily injection of a selective beta3-adrenergic agonist, CL316,243 (0.1 mg/kg), for 10 days resulted in a marked reduction of white fat pad weight and 1.8-4.8-fold increase in the mRNA levels of UCP2 and UCP3 in skeletal muscle of obese mice. No noticeable change in the UCP2 and 3 mRNA levels was found in brown and white adipose tissues. It was also found that CL316,243 injection produced a marked and sustained elevation of the plasma free fatty acid level. These results, together with our previous findings of the fatty acid-induced UCP expression in a myocyte cell line in vitro, suggest that the beta3-AR agonist-induced UCP expression in skeletal muscle may be mediated through the elevated plasma free fatty acids. It was also suggested that anti-obesity effect of beta3-AR agonists is attributable to increased thermogenesis not only by UCP1 but also by UCP2 and UCP3.     

Molecular cloning and tissue distribution of uncoupling protein 1 (UCP1) in plateau pika (Ochotona dauurica)

Uncoupling protein 1 (UCP1) is present exclusively in brown adipose tissue, and contributes to body temperature control during cold exposure. We cloned UCP1 cDNA of plateau pika (Ochotona dauurica), a small, non-hibernating, diurnal lagomorph that inhabits in relatively cold climates and at high altitudes in Mongolia and in northern China. The nucleotide sequence of pika UCP1 was highly homologous to UCP1 of other species, and the deduced amino acid sequence had some common domains for UCP, including six mitochondrial carrier protein motifs and a putative purine-nucleotide binding site. RT-PCR and Western blot analyses revealed that both UCP1 mRNA and protein were expressed exclusively in the interscapular adipose tissue. These results suggest that pika UCP1 contributes to heat production in brown adipose tissue, as do those in other species.     

Pathology of congenital generalized lipodystrophy in Agpat2-/- mice

Congenital generalized lipodystrophy (CGL) comprises a heterogeneous group of rare diseases associated with partial or total loss of adipose tissue. Of these, autosomal recessive Berardinelli-Seip congenital lipodystrophy (BSCL) is characterized by the absence of metabolically active subcutaneous and visceral adipose tissues. Metabolic abnormalities associated with lipodystrophy include insulin resistance, hypertriglyceridemia, hepatic steatosis, and diabetes. One form of BSCL has been linked to genetic mutations affecting the lipid biosynthetic enzyme 1-acyl-sn-glycerol 3-phosphate O-acyltransferase 2 (AGPAT2), which is highly expressed in adipose tissue. Precisely how AGPAT2 deficiency causes lipodystrophy remains unresolved, but possible mechanisms include impaired lipogenesis (triglyceride synthesis and storage), blocked adipogenesis (differentiation of preadipocytes to adipocytes), or apoptosis/necrosis of adipocytes. Agpat2(-/-) mice share important pathophysiologic features of CGL previously reported in humans. However, the small white adipose tissue (WAT) depots consisting largely of amoeboid adipocytes with microvesiculated basophilic cytoplasm showed that adipogenesis with deficient lipogenesis was present in all usual locations. Although well-defined lobules of brown adipose tissue (BAT) were present, massive necrosis resulted in early ablation of BAT. Although necrotic or apoptotic adipocytes were not detected in WAT of 10-day-old Agpat2(-/-), the absence of adipocytes in aged mice indicates that these cells must undergo necrosis/apoptosis at some point. Another significant finding in aged lipodystrophic mice was massive pancreatic islet hypertrophy in the face of chronic hyperglycemia, which suggests that glucotoxicity is insufficient by itself to cause β-cell loss and that adipocyte-derived factors help regulate total β-cell mass.     

The response of adipose tissues to Mycoplasma pulmonis and Sendai virus infection in C57BL/6 and DBA/2 mice

Adipose tissues in mammals are categorized into white and brown adipose tissues in which cellular morphology, cell functions, and tissue distribution are different. White adipose tissue (WAT) plays a major role in energy reservation, while brown adipose tissue (BAT) mainly relates to the thermoregulation of the body. One interesting function of adipose tissue is the response to the infection, especially the pathogens that cause pneumonia. We have previously reported that DBA/2 (D2) mice are susceptible to pathogens causing pneumonia, Mycoplasma (M.) pulmonis and Sendai virus (SeV), whereas C57BL/6 (B6) mice are resistant to them. Furthermore, morphological alteration of mediastinal fat tissue (MFT) was seen after infection of M. pulmonis in D2 mice but not in B6 mice. In this study, we aimed to exhibit the difference in adipose tissue response in other areas, including interscapular brown adipose tissue (iBAT), inguinal white adipose tissue (ingWAT), and perigonadal WAT (perigoWAT) between resistant strain, B6 and susceptible strain, D2 after challenging them with M. pulmonis and SeV. Compared with B6 mice, D2 mice showed an increase in fat-associated lymphoid cluster in MFT, an increase in BAT in both iBAT and ingWAT after M. pulmonis and SeV infection. The results of this study indicate that pneumonia caused by M. pulmonis and SeV infection induces browning of adipocyte, suggesting that BAT plays a role in pathogen infection and inflammation.     

苏尼特羔羊褐色脂肪鉴定及特征研究

哺乳动物脂肪组织主要可以分为白色脂肪组织和褐色脂肪组织,无论细胞形态还是功能,褐色脂肪与白色脂肪都有较大差别。褐色脂肪在哺乳动物产热以及能量平衡方面发挥着重要作用。为探究绵羊褐色脂肪分布特点,本研究采集了出生1、7和30 d苏尼特羊的肾周、颈部、背部、尾部、胸部、腹股沟和心包脂肪,通过HE染色、透射电镜和免疫组织化学鉴定脂肪组织类型,并通过实时荧光定量PCR和Western blot探究苏尼特羔羊不同日龄以及不同部位褐色脂肪的特点。结果发现,苏尼特羔羊体内存在两种不同类型的脂肪细胞,多室小脂滴的褐色脂肪细胞和空泡状脂滴的白色脂肪细胞。褐色脂肪细胞内有嵴的线粒体较多,并检测到褐色脂肪组织特异性蛋白UCP1的表达。而白色脂肪细胞内很少有带规则嵴的线粒体,不表达UCP1。出生1和7 d时褐色脂肪细胞数量及UCP1表达无显著差异,但出生30 d时明显下降。本研究通过形态学观察和标记基因以及蛋白检测鉴定了苏尼特羔羊的褐色脂肪和白色脂肪,证明了肾周脂肪和尾部脂肪分别是褐色脂肪以及白色脂肪的主要来源部位。出生1和7 d时苏尼特羔羊体内褐色脂肪较多,出生30 d时褐色脂肪的表型变化较大,呈现下降的趋势。本文探究了苏尼特羔羊褐色脂肪的特点,为反刍动物褐色脂肪研究提供了一定的基础。     

PRDM16——控制BAT和WAT发育的分子开关

棕色脂肪组织通过大量表达解偶联蛋白-1(UCP-1)以加强线粒体呼吸作用的解偶联,使能量以热量形式散失,从而抵御肥胖和相关疾病.研究发现,PRDM16是调节棕色脂肪细胞形成的关键转录因子,是控制棕色和白色脂肪细胞特异基因表达程序的分子开关,其机制是C末端结合蛋白和过氧化物酶体增殖剂活性受体γ辅助激活子1 (PPARγ-coactivator-1α and β,PGC-1α/β) 竞争性结合PRDM16,分别形成PRDM16/CtBPs和PRDM16/PGC-1s转录复合物,前者可激活棕色脂肪特异基因的表达,后者则抑制白色脂肪特异基因的表达.论文通过对PRDM16的结构、功能及其作用机制的介绍,有助于研究者了解棕色脂肪组织发育的调控系统,为肥胖和相关疾病的治疗提供新思路.