亮氨酸调节动物骨骼肌蛋白质分解的研究进展

随着对亮氨酸调节试验动物(如鼠)生理功能研究的深入,学者们发现,亮氨酸对于骨骼肌蛋白质沉积的影响不仅是其可以提高骨骼肌蛋白质的合成,还由于其可以减少骨骼肌蛋白质的分解,而这一过程中,亮氨酸对于骨骼肌细胞内蛋白质降解的多条途径都存在抑制作用。本文综述了亮氨酸对动物(如鼠)骨骼肌及其细胞内蛋白质分解的调节作用,并分析讨论了这一过程当中亮氨酸的相关作用机制。     

亮氨酸对绵羊机体蛋白质合成的影响

本试验通过在饲粮中添加不同水平的过瘤胃保护性亮氨酸,采用大剂量一次性灌注法来测定亮氨酸对绵羊机体蛋白质合成的影响.试验选取绵羊12只,随机分为4组,分别饲喂添加0(对照组)、0.5、1.0和1.5 g/d的瘤胃保护性亮氨酸的饲粮.15 d后,在绵羊颈静脉大剂量一次性灌注L-d5苯丙氨酸并且采集血样及皮肤组织样,90 min后屠宰,取背最长肌、股二头肌和肝脏样品,经前处理后,通过气-质联用仪来测定各组织蛋白质合成率(FSR)及蛋白质合成量.结果表明:瘤胃保护性亮氨酸对绵羊骨骼肌FSR的影响显著(P＜0.05),对肝脏FSR则影响不显著(P＞0.05);瘤胃保护性亮氨酸对绵羊骨骼肌及肝脏组织的蛋白质合成量显著增加(P＜0.05),以1.0 g/d添加组效果最好.     

瘦素及其受体对肌肉组织蛋白质代谢的调节

近年来,体内外试验研究表明,瘦素的短期或长期处理能够调节哺乳动物骨骼肌和肌细胞内蛋白质的代谢,而这主要是由于瘦素可以调节肌细胞内与蛋白质代谢相关的信号通路(如胰岛素相关信号通路和丝裂原活化蛋白激酶信号通路)的活性.因此,本文综述了瘦素及其受体在动物体内肌肉组织蛋白质代谢过程中的调节作用,并分析讨论了这一过程中瘦素的可能...     

日粮中添加亮氨酸对生长大鼠血浆瘦素水平和骨骼肌蛋白质代谢的影响

试验旨在探讨添加亮氨酸的日粮对生长大鼠生长性能、骨骼肌蛋白质代谢和瘦素分泌的影响。试验选用24只4周龄雄性Sprague-Dawley大鼠作为试验动物,分别饲喂添加3%L-亮氨酸的试验日粮和添加2.04%L-丙氨酸的对照日粮,试验期为12 d。试验第12天,所有大鼠大剂量一次性腹腔注射L-[ring-2H5]苯丙氨酸注射液。结果表明:日粮添加亮氨酸对大鼠生长性能没有显著影响(P>0.05);试验组大鼠血浆中瘦素浓度显著高于对照组(P<0.01)。持续饲喂试验日粮的大鼠腓肠肌和比目鱼肌的蛋白质分解均显著低于对照组大鼠(P<0.01),但仅腓肠肌蛋白质合成显著高于对照组(P<0.01)。总之,长期饲喂添加L-亮氨酸的日粮可以提高生长大鼠血浆中瘦素浓度,并可显著调节生长大鼠骨骼肌蛋白质代谢。     

亮氨酸对κ-酪蛋白合成的影响及相关信号通路的研究

本研究旨在探讨其他氨基酸缺乏条件下补充亮氨酸对奶牛乳腺上皮细胞κ-酪蛋白基因表达和蛋白合成以及细胞增殖的影响,并从mRNA水平探究mTOR信号通路介导的蛋白质合成的重要性。处理组1在对照组(稀释100倍的培养基)的基础上补充亮氨酸,处理组2在处理组1的基础上添加mTOR信号通路上游抑制剂,分别采用RT-qPCR技术和ELISA法测定基因的相对表达量和蛋白合成量,CCK-8法测定细胞增殖。结果表明:亮氨酸显著促进了κ-酪蛋白基因表达和蛋白合成(P<0.05),而添加抑制剂极显著降低了这种作用(P<0.01);各处理对蛋白质合成信号通路相关基因mTOR、S6K1、4EBP1、eIF4E、eEF2相对表达量均有一定影响;抑制剂能显著抑制细胞增殖(P<0.05)。结果提示,补充亮氨酸能显著促进κ-酪蛋白的合成,这可能与mTOR信号通路介导蛋白质合成有关,此外,mTOR信号通路也可调控奶牛乳腺上皮细胞的增殖。     

谷氨酰胺、精氨酸和亮氨酸在肠道中的信号传导(一)

动植物蛋白中谷氨酰胺和亮氨酸含量丰富且较稳定,而食物和动物体液中精氨酸含量差异较大。除在蛋白质合成中起作用外,这三种氨基酸可独自激活信号传导通路以促进蛋白质的合成,并可能抑制肠上皮细胞自噬介导的蛋白质降解。此外,谷氨酰胺和精氨酸可分别激活有丝分裂原活化蛋白激酶通路和哺乳动物雷帕霉素靶蛋白(mTOR)/p70(s6)激酶通路,从而加强粘膜细胞的迁移和修复。利用一氧化氮依赖型cGMP的信号级联,精氨酸可调节肠道多种生理活动,这有利于细胞的生存和维持动态平衡。动物体内外试验显示,谷氨酰胺和精氨酸可促进细胞增殖,并可针对养分损失、氧化损伤、应激和免疫应激来发挥不同的细胞保护作用。此外,一氧化氮存在时亮氨酸可加强肠道细胞的迁移。因此,通过细胞信号传导机制,精氨酸、谷氨酰胺和亮氨酸在肠道的生长发育和功能完善过程中发挥了关键作用。     

谷氨酰胺对草鱼肠道L-亮氨酸、L-脯氨酸吸收及肠道蛋白质合成的影响

利用肠道离体灌注模型和同位素示踪技术,研究谷氨酰胺对草鱼肠道L-亮氨酸和L-脯氨酸吸收量、肠道组织游离亮氨酸和脯氨酸量、以及对肠道蛋白质合成量的影响。结果表明:谷氨酰胺能够显著增加草鱼肠道对两种氨基酸的吸收量,显著增加肠道组织游离亮氨酸和脯氨酸量,并显著增加肠道蛋白质的合成量;将1.0mmol/L组与5.0mmol/L组谷氨酰胺的试验结果相互比较,无论是肠道吸收总量还是肠道组织游离氨基酸、新蛋白质合成量均没有显著差异;草鱼肠道在吸收亮氨酸和脯氨酸的同时,能够利用吸收的亮氨酸和脯氨酸和肠道蛋白质周转的氨基酸合成新的蛋白质,蛋白质合成量随着亮氨酸和脯氨酸浓度增加呈线性增加关系。本文结果表明,谷氨酰胺能够显著增加草鱼肠道对亮氨酸和脯氨酸的吸收量、能够显著增加肠道蛋白质的合成代谢。     

亮氨酸的代谢及营养生理作用研究进展

面对保护环境和降低成本的双重压力,低蛋白日粮配方技术已经成为动物营养学的研究热点之一。国内外对低蛋白日粮添加赖氨酸、蛋氨酸、苏氨酸和精氨酸等合成氨基酸的应用效果及其作用机制已经进行了大量研究,但亮氨酸在低蛋白日粮中的应用却没有引起足够的重视。大量文献表明:亮氨酸可以促进氮储留,增加亮氨酸-tRNA的水平,从而促进蛋白质的合成。总结了近年关于亮氨酸的     

雏鸡组织中的蛋白质更新与日龄的关系

在禽类研究中,与家禽体内蛋白质代谢有关的研究报道很少.在80年代,日龄对雏鸡蛋白质代谢的影响主要是针对鸡的整个胴体来作分析的,那时着重讨论了整个胴体的蛋白质合成(以每天克计算)增长情况,而不是蛋白质合成率.例如:每天合成和分解的蛋白质比例(以每天百分率计算),当时获得的结果与从哺乳动物中获得的结果是一致的.然而,在各个不同组织中是否都是如此,仍是个未知数.因此,我们通过测量肝脏和按照组织化学特性选择不同类型的骨骼肌(胸大肌、前背阔肌和缝匠肌)来研究商品代肉仔鸡早期(2、3、4周龄)发育过程中的体内组织蛋白质的更新情况.     

畜禽支链氨基酸的营养

亮氨酸、异亮氨酸和缬氨酸是畜禽体内不能合成而必须从饲料中获取的必需氨基酸 ,因其分子组成中都含有支链而又称之为支链氨基酸(ＢＣＡＡ)。近年来研究表明 ,支链氨基酸对动物有特殊的营养作用 ,如影响蛋白质的合成和分解、增强免疫防护作用、调节母畜泌乳等 ,现就畜禽支链氨基酸的营养作一综述。1　支链氨基酸的营养与拮抗1 1　促进蛋白质合成并抑制其分解　支链氨基酸具有促进氮储留和蛋白质合成的作用 (Ｋｉｓｈｉ等 ,1 980 )。亮氨酸可增加亮氨酸 -ｔＲＮＡ的水平 ,从而促进蛋白质的合成。也有人认为 ,支链氨基酸是通过促进多肽链合成…     

Differential regulation of protein synthesis in skeletal muscle and liver of neonatal pigs by leucine through an mTORC1-dependent pathway

Neonatal growth is characterized by a high protein synthesis rate that is largely due to an enhanced sensitivity to the postprandial rise in insulin and amino acids, especially leucine. The mechanism of leucine’s action in vivo is not well understood. In this study, we investigated the effect of leucine infusion on protein synthesis in skeletal muscle and liver of neonatal pigs. To evaluate the mode of action of leucine, we used rapamycin, an inhibitor of mammalian target of rapamycin (mTOR) complex-1 (mTORC1). Overnight-fasted 7-day-old piglets were treated with rapamycin for 1 hour and then infused with leucine (400 μmol·kg -1 ·h -1 ) for 1 hour. Leucine infusion increased the rate of protein synthesis, and ribosomal protein S6 kinase 1 (S6K1) and eukaryotic initiation factor (eIF) 4E-binding protein-1 (4E-BP1) phosphorylation in gastrocnemius and masseter muscles (P < 0.05), but not in the liver. The leucine-induced stimulation of protein synthesis and S6K1 and 4E-BP1 phosphorylation were completely blocked by rapamycin, suggesting that leucine action is by an mTORC1-dependent mechanism. Neither leucine nor rapamycin had any effect on the activation of the upstream mTORC1 regulators, AMP-activated protein kinase and protein kinase B, in skeletal muscle or liver. The activation of eIF2a and elongation factor 2 was not affected by leucine or rapamycin, indicating that these two pathways are not limiting steps of leucine-induced protein synthesis. These results suggest that leucine stimulates muscle protein synthesis in neonatal pigs by inducing the activation of mTORC1 and its downstream pathway leading to mRNA translation.     

Resorption and incorporation of radioactive-labeled amino acids during administration of various protein carriers in rats. 3. Uptake of radioactivity by blood plasma, liver and muscular tissue and incorporation into tissue proteins after intragastric administration of 14C-leucine and 3H-glycine]

Growing male rats received diets of varying biological value (protein sources: powdered whole egg (V); fish meal (F); yeast (H); gelatine (G); protein-free diet (e)) for a 14-day feeding period. Subsequently, 14C leucine and 3H glycine were administered intragastrically. The level of uptake of 14C and 3H radioactivity into blood plasma, liver and muscular tissue and the rate of incorporation of the radioactive tracers into the proteins of these tissues was examined. A negative correlation was found to exist between the incorporation of radioactivity into liver proteins and the biological value of dietary proteins, the former being mainly dependent on the level of incorporation into the liver. For muscular proteins the rate of incorporation decreases with the decreasing biological value of the dietary proteins. This may be attributed to the fact that with poor protein nutrition the rate of protein synthesis in the skeletal muscles is also reduced. Comparative studies on the specific 14C radioactivity from free leucine made in the group on the protein-free diet and in the group receiving the whole egg diet showed that the leucine pool of the skeletal muscles was markedly redueced in animals fed a protein-deficient diet while the leucine pool in the liver remained comparatively constant.     

The leucine metabolite 3-hydroxy-3-methylbutyrate (HMB) modifies protein turnover in muscles of laboratory rats and domestic chickens in vitro

This study was conducted to assess the in vitro effects of leucine and 3-hydroxy-3-methylbutyrate (HMB) on protein synthesis and degradation in isolated rat and chick muscles. Isolated muscles — extensor digitorum longus (EDL) and soleus (S) in rats and EDL and tibialis anterior (TA) in chicks — were taken out intact and incubated in Krebs—Henseleit buffer with [¹⁴C]phenylalanine. Protein synthesis was then determined by measuring [¹⁴C]phenylalanine incorporation into protein and protein breakdown was estimated by net release of tyrosine from muscle proteins. In all muscles investigated leucine stimulated protein synthesis (average 20%; p < 0.05 versus control) but only slightly reduced proteolysis (average 8%, NS). In contrast, HMB had no significant effect on protein synthesis but consistently decreased protein degradation in the range from −29% (p < 0.01 versus control) in rat extensor digitorus longus to −5% (NS) in rat soleus muscles. HMB appeared to suppress protein degradation more in white muscle fibres than in red muscle fibres (at least in the rat). These data support observations in humans indicating that HMB decreases muscle proteolysis. It is suggested that metabolism of leucine to HMB could be responsible for the reported suppressive effects of leucine on protein breakdown.     

Leucine‐induced promotion of post‐absorptive EAA utilization and hepatic gluconeogenesis contributes to protein synthesis in skeletal muscle of dairy calves

The high rate of protein synthesis in skeletal muscle of dairy calves can benefit their first lactation even lifetime milk yield. Since the rate of protein synthesis is relatively low in the post‐absorptive state, the aim of this research was to determine whether leucine supplementation could increase the post‐absorptive essential amino acid (EAA) utilization and protein synthesis in the skeletal muscle. Ten male neonatal dairy calves (38 ± 3 kg) were randomly assigned to either the control (CON, no leucine supplementation, n = 5) or supplementation with 1.435 g leucine/L milk (LEU, n = 5). Results showed that leucine significantly increased the length and protein concentration in longissimus dorsi (LD) muscle, whereas it decreased creatinine concentration and glutamic‐oxalacetic transaminase (GOT) activity. Compared to the control group, leucine supplementation also reduced the glutamic‐pyruvic transaminase (GPT) activity. Supplementation of leucine improved the phosphorylation of mammalian target of rapamycin (mTOR), eukaryotic initiation factor 4E‐binding protein 1 (4EBP1) and substrates ribosomal protein S6 kinase 1 (p70S6K). Supplementation of leucine resulted in increased concentrations of glucose, methionine, threonine, histidine and EAAs and decreased concentration of arginine in serum. Liver glucose concentration was higher and pyranic acid was lower in LEU compared to CON. In conclusion, leucine supplementation can promote post‐absorptive EAA utilization and hepatic gluconeogenesis, which contributes to protein synthesis in skeletal muscle of dairy calves.     

Triennial Growth Symposium: leucine acts as a nutrient signal to stimulate protein synthesis in neonatal pigs

The postprandial increases in AA and insulin independently stimulate protein synthesis in skeletal muscle of piglets. Leucine is an important mediator of the response to AA. We have shown that the postprandial increase in leucine, but not isoleucine or valine, acutely stimulates muscle protein synthesis in piglets. Leucine increases muscle protein synthesis by modulating the activation of mammalian target of rapamycin (mTOR) complex 1 and signaling components of translation initiation. Leucine increases the phosphorylation of mTOR, 70-kDa ribosomal protein S6 kinase-1, eukaryotic initiation factor (eIF) 4E-binding protein-1, and eIF4G; decreases eIF2α phosphorylation; and increases the association of eIF4E with eIF4G. However, leucine does not affect the upstream activators of mTOR, that is, protein kinase B, adenosine monophosphate-activated protein kinase, and tuberous sclerosis complex 1/2, or the activation of translation elongation regulator, eukaryotic elongation factor 2. The action of leucine can be replicated by α-ketoisocaproate but not by norleucine. Interference by rapamycin with the raptor-mTOR interaction blocks leucine-induced muscle protein synthesis. The acute leucine-induced stimulation of muscle protein synthesis is not maintained for prolonged periods, despite continued activation of mTOR signaling, because circulating AA fall as they are utilized for protein synthesis. However, when circulating AA concentrations are maintained, the leucine-induced stimulation of muscle protein synthesis is maintained for prolonged periods. Thus, leucine acts as a nutrient signal to stimulate translation initiation, but whether this translates into a prolonged increase in protein synthesis depends on the sustained availability of all AA.     

支链氨基酸调控机体糖代谢的研究进展

支链氨基酸是体内最丰富的必需氨基酸,包括亮氨酸﹑异亮氨酸和缬氨酸。支链氨基酸具有促进蛋白质合成、提高机体免疫力和促进胚胎发育等生理功能。支链氨基酸在机体糖代谢调节中发挥着重要作用,其可以通过调控机体胰岛素的分泌﹑胰岛素的敏感性以及葡萄糖转运载体的表达和易位等方式调控糖代谢。本文对支链氨基酸在体内的代谢途径及其调控机体糖代谢的途径进行综述。     

Effects of zeranol on protein turnover in L6 myotubes

Protein synthesis and degradation were measured in cultures of L6 myotubes to determine the direct anabolic activity of zeranol on muscle. Zeranol, dexamethasone, insulin and zeranol-dexamethasone combination, at various concentrations from 10(-8) to 10(-6) M, were added to cultures at either 18 hr prior to or at the beginning of a 6 hr synthesis or degradation measuring period. Protein synthesis was measured by determining the incorporation of radioactivity into trichloraoacetic acid precipitable cell protein following incubation with [3H] leucine. Protein synthesis was expressed as cpm incorporated in 6 hr per mg protein. Protein degradation was measured by a pulse-chase procedure using [3H] leucine. Protein degradation was expressed as the percent labeled protein degraded in 6 hr. Results from the study indicate that zeranol did not stimulate protein synthesis or inhibit proteolysis (P greater than .01). Stimulation of proteolysis observed with 10(-8) M dexamethasone was 13% and 18% (P less than .01) at the 6 hr and 24 hr incubation period, respectively. Dexamethasone-stimulated protein degradation was not altered appreciably by zeranol. In contrast, 10(-6) M insulin significantly (P less than .01) stimulated protein synthesis (16%) and inhibited protein degradation (15%). These results suggest that the anabolic action of zeranol does not occur by directly regulating muscle protein synthesis or degradation, or by altering the glucocorticoid-induced catabolic response in muscle.     

Regulation of protein degradation pathways by amino acids and insulin in skeletal muscle of neonatal pigs

Background： The rapid gain in lean mass in neonates requires greater rates of protein synthesis than degradation. We previously delineated the molecular mechanisms by which insulin and amino acids, especially leucine, modulate skeletal muscle protein synthesis and how this changes with development. In the current study, we identified mechanisms involved in protein degradation regulation. In experiment 1,6- and 26-d-old pigs were studied during 1） euinsulinemic-euglycemic-euaminoacidemic, 2） euinsulinemic-euglycemiohyperaminoacidemic, and 3） hyperinsulinemic-euglycemic-euaminoacidemic clamps for 2 h. In experiment 2, 5-d-old pigs were studied during 1） euinsulinemic-euglycemic-euaminoacidemic-euleucinemic, 2） euinsulinemic-euglycemic-hypoaminoacidemic- hyperleucinemic, and 3） euinsulinemic-euglycemic-euaminoacidemic-hyperleucinemic clamps for 24 h. We determined in muscle indices of ubiquitin-proteasome, i.e., atrogin-1 （MAFbx） and muscle RING-finger protein-1 （MuRF1） and autophagy-lysosome systems, i.e., unc51-1ike kinase 1 （UKL1）, microtubule-associated protein light chain 3 （LC3）, and lysosomal-associated membrane protein 2 （Lamp-2）. For comparison, we measured ribosomal protein 56 （rpS6） and eukaryotic initiation factor 4E （elF4E） activation, components of translation initiation. Results： Abundance of atrogin-1, but not MuRF1, was greater in 26- than 6-d-old pigs and was not affected by insulin, amino acids, or leucine. Abundance of ULK1 and LC3 was higher in younger pigs and not affected by treatment. The LC3-11/LC3-1 ratio was reduced and ULK1 phosphorylation increased by insulin, amino acids, and leucine. These responses were more profound in younger pigs. Abundance of Lamp-2 was not affected by treatment or development. Abundance of elF4E, but not rpS6, was higher in 6- than 26-d-old-pigs but unaffected by treatment. Phosphorylation of elF4E was not affected by treatment, however, insulin, amino acids, and leucine stimulated rpS6 phosphorylation, and the response     

In ovo injection of branched‐chain amino acids: Embryonic development,hatchability and hatching quality of turkey poults

In this study, the influence of a branched‐chain amino acid blend (BCAA composed of 3 l ‐leucine:1 l ‐valine:2 l ‐isoleucine) injected into the amniotic fluid was evaluated for embryonic growth, yolk‐sac (YS) utilization and development of gastrointestinal tract (GIT) and skeletal muscles of turkey embryos from day 24 of incubation (24E) to hatching, together with hatchability, poult quality and liver L* (lightness), a* (redness) and b* (yellowness) values at hatch. At day 22 of incubation, embryonated eggs (n = 240) were assigned to three treatments, that is, eggs were not injected (control, NC) or injected with 1.5 ml sterile solution with 0.9% salt (SA) or 0.2% BCAA blend (BCAAb). These solutions were injected manually into the amniotic fluid of the embryonated eggs. To determine weights and lengths (where appropriate) of the studied organs and tissues, four embryonated eggs and poults per treatment were selected at 24E and at hatch. While the BCAAb decreased the YS and embryo weight, hatchability and the liver L* value, it increased the weight and quality of poults and the weights of breast and thigh muscles at hatch. In conclusion, the in ovo feeding of the BCAA blend negatively affected hatchability but positively affected hatching weight and poult quality by improving development of skeletal muscles and by regulating energy metabolism.