畜牧兽医学报  2022, Vol. 53 Issue (8): 2586-2597. DOI: 10.11843/j.issn.0366-6964.2022.08.017    PDF    
日粮添加不同水平芦丁对热应激小鼠睾丸组织的影响
刘慧娟, 庄苏, 张佳琦, 周斌斌, 熊玮, 王恬, 王超     
南京农业大学动物科技学院, 南京 210095
摘要:本试验旨在探讨日粮添加不同水平芦丁对缓解热应激小鼠睾丸组织损伤的影响。将30只5周龄体重相近(20~22 g)的ICR系雄性小鼠随机分为5组,各组小鼠分别饲喂基础日粮添加0(CON组)、0(HS组)、250(HS+R250)、500(HS+R500)和1 000(HS+R1000)mg·kg-1芦丁的日粮,饲养10 d后,除对照组(CON)外,所有小鼠在每天10:00至14:00之间置于42℃恒温箱中连续处理8 d后屠宰取样分析。结果显示:1)与CON组相比,HS组小鼠睾丸指数无显著变化(P>0.05),而日粮添加250 mg·kg-1芦丁显著提高热应激小鼠睾丸指数(P<0.05);小鼠睾丸组织切片结果显示,与CON组相比,HS组小鼠生精小管直径和横截面积显著降低(P<0.05),生精细胞脱落比率显著增加(P<0.05);与HS组相比,HS+R250组小鼠生精小管横截面积显著增加(P<0.05),生精细胞脱落比率显著降低(P<0.05),HS+R500组生精细胞脱落比率也显著降低(P<0.05),HS+R1000组小鼠生精小管直径显著增加(P<0.05);小鼠睾丸指数、生精小管直径及生精小管脱落比率在芦丁处理组与CON组之间无显著差异(P>0.05),但HS+R250组小鼠睾丸生精小管横截面积显著高于CON组(P<0.05)。2)与CON组相比,HS组小鼠睾丸组织丙二醛(MDA)含量显著升高(P<0.05),总抗氧化能力(T-AOC)与还原型谷胱甘肽(GSH)含量以及血红素酶-1(HO-1)mRNA的表达量均显著降低(P<0.05);日粮添加250 mg·kg-1芦丁显著降低热应激小鼠睾丸组织中MDA含量(P<0.05),提高T-AOC与GSH含量(P<0.05),并增强核因子E2相关因子2(Nrf2)、HO-1和谷胱甘肽过氧化物酶(GSH-Px)mRNA的表达量(P<0.05),而添加500和1 000 mg·kg-1芦丁也显著提高了GSH含量(P<0.05);与CON组相比,除HS+R250组Nrf2 mRNA表达量显著高于CON组(P<0.05)外,芦丁组热应激小鼠睾丸组织抗氧化相应基因与酶活指标均无显著性变化(P>0.05)。3)热应激小鼠睾丸中核因子-κB(NF-κB)、TOLL样受体4(TLR-4)和Bax的mRNA表达量显著增加(P<0.05),而Bcl-2表达量显著降低(P<0.05);日粮添加250 mg·kg-1芦丁显著降低NF-κBTLR-4、髓样分化因子88(MyD88)、白细胞介素-Ⅰβ(IL-1β)和Bax mRNA表达量(P<0.05),增强Bcl-2的表达水平(P<0.05);添加500 mg·kg-1芦丁显著降低NF-κBTLR-4表达量(P<0.05),而1 000 mg·kg-1芦丁能够显著增加Bcl-2的表达(P<0.05);小鼠睾丸组织中免疫和增值凋亡相关基因的表达量在添加芦丁组及CON组之间无显著性差异(P>0.05)。结果提示,日粮添加适宜剂量芦丁具有改善热应激小鼠睾丸组织形态及功能的效果,其机制可能与芦丁通过Nrf2信号通路缓解氧化应激,通过TLR-4/NF-κB信号通路抑制炎症反应及调控Bax/Bcl-2 mRNA的表达密切相关。本试验条件下日粮添加250 mg·kg-1芦丁的效果较好。
关键词热应激    小鼠    睾丸    芦丁    氧化应激    炎症    组织损伤    
Effects of Dietary Supplementation of Different Levels of Rutin on Testicular Tissue in Mice under Heat Stress
LIU Huijuan, ZHUANG Su, ZHANG Jiaqi, ZHOU Binbin, XIONG Wei, WANG Tian, WANG Chao     
College of Animal Science and Technology, Nanjing Agricultural University, Nanjing 210095, China
Abstract: The purpose of this experiment was to explore the effects of dietary supplementation of different levels of rutin on alleviating testicular tissue damage in heat-stressed mice. Thirty 5-week-old male mice of ICR strain with similar body weight (20-22 g) were randomly divided into 5 groups. Mice in each group were fed basal diet supplemented with 0 (CON group), 0 (HS group), 250 (HS+R250), 500 (HS+R500) and 1 000 (HS+R1000) mg·kg-1 rutin for 10 days, respectively. Except for control group (CON), all mice were treated in an incubator at 42℃ between 10:00 and 14:00 every day for 8 consecutive days, and then slaughtered for sampling and analysis. The results showed as follows: 1) Compared with CON group, the testis index of mice in HS group had no significant change (P > 0.05), but dietary 250 mg·kg-1 rutin significantly increased the testis index of mice under heat stress (P < 0.05). The results of mouse testicular tissue sections showed that compared with the CON group, the cross-sectional area and diameter of the seminiferous tubules in the HS group were significantly reduced (P < 0.05), and the rate of spermatogenic cell shedding was significantly increased (P < 0.05). Compared with the HS group, the cross-sectional area of the seminiferous tubules in the HS+R250 group was significantly increased (P < 0.05), the rate of spermatogenic cells shedding was significantly reduced (P < 0.05), while the rate of spermatogenic cell shedding in the HS+R500 group was significantly reduced (P < 0.05), and the diameter of the seminiferous tubules in the HS+R1000 group was significantly increased (P < 0.05); There was no significant difference in testis index, seminiferous tubule diameter and seminiferous tubule shedding ratio between the rutin-treated groups and the CON group (P > 0.05), however, the cross-sectional area of the seminiferous tubules in the HS+R250 group was significantly higher than that in the CON group (P < 0.05). 2) Compared with CON group, malondialdehyde (MDA) content in testis tissue of HS group increased significantly (P < 0.05), while total antioxidant capacity (T-AOC), glutathione (GSH) content and the mRNA expression of hemolytic enzyme 1 (HO-1) in testis tissue of mice were significantly decreased (P < 0.05). The supplementation of 250 mg·kg-1 rutin significantly decreased the MDA content (P < 0.05), increased the T-AOC and GSH content in testis of heat-stressed mice (P < 0.05), and enhanced nuclear factor E2 related factors 2 (Nrf2), HO-1 and glutathione peroxidase (GSH-Px) mRNA expression (P < 0.05), while the supplementation of 500 and 1 000 mg·kg-1 rutin also significantly increased the GSH content (P < 0.05); Compared with the CON group, except that the Nrf2 mRNA expression in the HS+R250 group was significantly higher than that in the CON group (P < 0.05), there were no significant changes in the antioxidant genes and enzyme activity indexes in the testis tissue of the heat-stressed mice in the rutin groups. (P > 0.05). 3) The mRNA expression levels of nuclear factor -κB (NF-κB), Toll-like receptor 4 (TLR-4) and Bax in testis of heat-stressed mice were significantly increased (P < 0.05), while the expression level of Bcl-2 was significantly decreased (P < 0.05). Dietary supplementation of 250 mg·kg-1 rutin significantly reduced the mRNA expression of NF-κB, TLR-4, myeloid differentiation factor 88 (MyD88), interleukin-Ⅰβ (IL-1β) and Bax (P < 0.05), enhanced the expression level of Bcl-2 (P < 0.05); Adding 500 mg·kg-1 rutin to the diet significantly reduced the expression of NF-κB and TLR-4 (P < 0.05), while adding 1 000 mg·kg-1 rutin significantly increased the expression of Bcl-2 (P < 0.05). There was no significant difference in the expression of immune and proliferation apoptosis-related genes in mouse testis between the rutin groups and the CON group (P > 0.05). These results suggest that dietary supplementation with appropriate dose of rutin can improve the morphology and function of testis in heat-stress mice, and the mechanism may be closely related to the relief of oxidative stress through Nrf2 signaling pathway, the inhibition of inflammatory response through TLR-4/NF-κB signaling pathway and the regulation of Bax/Bcl-2 mRNA expression. The effect of dietary 250 mg·kg-1 rutin was better under the experimental conditions.
Key words: heat stress    mice    testis    rutin    oxidative stress    inflammation    tissue damage    

在高度集约化、规模化养殖模式下,热应激是影响动物生产的重要因素之一,特别是在我国南方地区,热应激可导致动物采食量与免疫力下降,严重影响动物生长发育和繁殖性能[1-2]。热应激的作用机制与氧化应激密切相关,它诱导机体组织中活性氧(ROS)过量聚积,导致氧化与抗氧化状态失衡,脂质、蛋白质和核酸氧化,进而引起组织损伤,影响动物健康与生长[3]。当机体组织中核因子E2相关因子2(Nrf2)被激活后可上调下游抗氧化酶基因的表达,提高抗氧化酶活性,有助于提高机体抗氧化能力,缓解机体热应激[4]。热应激诱发氧化应激是造成畜禽机体损伤的关键因素,氧化应激是由于机体抗氧化调节失衡,导致氧化中间产物过多,体内自由基物质大量堆积从而引起机体氧化损伤[5-6]。在畜牧生产中,热应激对雄性动物生殖系统的影响更加突出,有研究指出,热应激可引起小鼠睾丸组织损伤,造成生精细胞凋亡[7]。因此,热应激已成为动物生产过程中所面临的重要挑战之一[8-9],寻找缓解动物热应激的新型安全高效抗氧化剂已迫在眉睫。芦丁(rutin)又称芸香甙,是主要来源于芸香叶的一种黄酮类化合物,广泛存在于多种药用植物和食物中,为淡黄色或淡绿色针状结晶或结晶性粉末[10],它具有抗氧化、抗炎、抗病毒等多种生物学功能[11-13]。研究证明,日粮添加芦丁可改善肥胖诱导的小鼠睾丸细胞结构异常、精子数量下降现象,缓解小鼠睾丸损伤[14-15],同时还具有提高睾丸生精功能的潜力[16]。因此推测,日粮添加芦丁是一种潜在的缓解由热应激诱导的睾丸组织功能障碍的营养调控方式。所以,本试验在构建了热应激小鼠模型基础上,进一步从组织形态、抗氧化、炎症、增殖凋亡等方面系统评估日粮添加芦丁对热应激小鼠睾丸组织的影响,并初步探讨其潜在的作用机制。

1 材料与方法 1.1 实验动物及设计

将30只5周龄体重相近ICR系雄性小鼠(20~22 g,购于苏州大学)随机分为5组,各组小鼠分别饲喂基础日粮添加0(CON组)、0(HS组)、250(HS+ R250)、500(HS+R500)和1 000 mg·kg-1(HS+R1000)芦丁的日粮(芦丁购自上海阿拉丁生物科技股份有限公司,纯度95%),于清洁级动物房(温度控制在(22±2)℃,相对湿度为55%~60%)饲养10 d后,除对照组外,所有小鼠在每天10:00至14:00之间禁食并置于42 ℃恒温箱中连续处理8 d,具体方法参照以往报道[17-18]进行。饲养试验结束后称重、腹腔注射5%水合氯醛(按体重计算用量,每10 g体重0.1 mL)麻醉后,眼球采血,脱颈致死,取睾丸称重,并将左侧睾丸置于4%多聚甲醛中固定,右侧睾丸置冻存管内,液氮迅速冷冻后置于-80 ℃低温冰柜储存备用。

1.2 测定指标与方法

1.2.1 睾丸指数   睾丸指数=睾丸重(g)/空腹活体重(kg)

1.2.2 睾丸形态组织观察   睾丸组织于4%多聚甲醛中固定48 h后,通过酒精、二甲苯处理,石蜡包埋、切片、伊红和苏木精(HE)染色后置于显微镜(ECLIPSE 80i型,尼康日本)下观察,采用Image J软件参照Li等[18-19]的研究报道测定生精小管直径、横截面积以及生精细胞脱落比率。

1.2.3 睾丸组织抗氧化酶活测定   取睾丸组织样本(约100 mg),按1∶9 (质量g/体积mL)的比例加入预冷的生理盐水,冰水浴条件下匀浆,3 000 r·min-1离心15 min,取上清采用南京建成生物工程研究所(中国,南京)提供的试剂盒测定总蛋白(A045-3-1)、还原型谷胱甘肽(GSH,A006-1-1)与丙二醛(MDA,A003-1-1)含量,同时测定总超氧化物歧化酶(T-SOD,A001-1-1)活性和总抗氧化能力(T-AOC,A015-1-2)。

1.2.4 mRNA相对表达量测定   从-80 ℃冰箱中取0.1 g左右的睾丸组织样品,使用TRIzol试剂(TaKaRa,大连)提取总RNA,通过qRT-PCR检测目的基因mRNA表达,具体操作参照Zhang等[20]进行。以β-actin作为内参基因,使用2-ΔΔCT方法计算各基因mRNA的相对表达量[21],引物序列见表 1

表 1 qRT-PCR引物序列 Table 1 Primer sequences used for quantitative real-time PCR
1.3 据统计与分析

试验数据经Excel 2019初步整理后,使用IBM SPSS Statistics 22.0软件进行统计分析。采用单因素方差分析处理组间差异,并用Tukey法进行多重比较, 采用多项式中的线性和二次分析对不同浓度芦丁的效果进行分析。结果以“平均值±标准误”表示,P<0.05表示差异显著。

2 结果 2.1 日粮添加不同剂量芦丁对热应激小鼠睾丸指数的影响

图 1所示,HS组小鼠睾丸指数与CON组无显著差异(P>0.05),与HS组相比,HS+R250组小鼠睾丸指数显著增加(P<0.05),添加芦丁组与CON组相比小鼠睾丸指数无显著差异(P>0.05)。

CON. 未经高温处理的对照组;HS. 热应激组;HS+R250. 日粮添加250 mg·kg-1芦丁的热应激处理组;HS+R500. 日粮添加500 mg·kg-1芦丁的热应激处理组;HS+R1000. 日粮添加1 000 mg·kg-1芦丁的热应激处理组。柱上不同小写字母表示差异显著(P<0.05),下同 CON. Control group without high temperature treatment; HS. Heat stress group; HS+R250. Heat stress treatment group supplemented with 250 mg·kg-1 rutin; HS+R500. Heat stress treatment group supplemented with 500 mg·kg-1 rutin; HS+R1000. Heat stress treatment group supplemented with 1 000 mg·kg-1 rutin. Different lowercase letters on the column indicate significant difference (P < 0.05), the same as below 图 1 不同剂量芦丁对热应激小鼠睾丸指数的影响 Fig. 1 Effects of different doses of rutin on testis index of heat-stressed mice
2.2 日粮添加不同剂量芦丁对热应激小鼠睾丸形态的影响

图 2可知,与CON组相比,HS组小鼠生精小管横截面积和生精小管直径显著降低(P<0.05),生精细胞脱落比率显著增加(P<0.05);与HS组相比,HS+R250组小鼠生精小管横截面积显著增加(P<0.05),生精细胞脱落比率显著降低(P<0.05),生精小管直径无显著性差异(P>0.05),而HS+R500组生精细胞脱落比率显著降低(P<0.05),HS+R1000组小鼠生精小管直径显著增加(P<0.05);芦丁处理组小鼠睾丸生精小管直径及生精小管脱落比率与CON组无显著差异(P>0.05),但HS+R250组小鼠睾丸生精小管横截面积显著高于CON组(P<0.05)。

A. HE染色的小鼠睾丸组织,下排图为相应上图矩形框内结构的放大,黑色箭头指示的是生精细胞脱落情况;B. 生精小管横截面积; C. 生精小管直径; D. 生精细胞脱落比率 A. HE stained mouse testicular tissue, the lower line of pictures are the enlargement of the structure in the corresponding rectangular box above, and the black arrow indicates the spermatogenic cells shed; B. Spermatogenic tubule cross-sectional area; C. Diameter of spermatogenic tubule; D. Spermatogenic cell shedding rate 图 2 不同剂量芦丁对热应激小鼠睾丸组织形态的影响(HE染色) Fig. 2 The effect of different doses of rutin on the morphology of heat-stressed mice testis (HE staining)
2.3 日粮添加不同剂量芦丁对热应激小鼠睾丸抗氧化功能的影响

表 2所示,HS组小鼠睾丸中MDA含量较CON组显著增加(P<0.05),T-AOC活性与GSH含量显著降低(P<0.05),T-SOD活性无显著性差异(P>0.05);与HS组相比,HS+R250组MDA含量显著降低(P<0.05),T-AOC与GSH含量显著增加(P<0.05),HS+R500和HS+R1000组小鼠睾丸组织GSH含量显著高于HS组(P<0.05),而芦丁处理热应激小鼠睾丸组织中MDA、GSH含量以及T-AOC和T-SOD活性与CON组相比均无显著性差异(P>0.05)。

表 2 不同剂量芦丁对热应激小鼠睾丸抗氧化功能的影响 Table 2 Effects of different doses of rutin on the anti-oxidant function in the testis of heat-stressed mice
2.4 日粮添加不同剂量芦丁对热应激小鼠睾丸抗氧化相关基因表达的影响

图 3可知,HS组小鼠睾丸中HO-1 mRNA的表达量与CON组相比显著降低(P<0.05);与HS组相比,HS+R250组Nrf2、HO-1、GSH-Px基因的相对表达量显著增加(P<0.05),HS+R500组Nrf2表达量显著升高(P<0.05),HS+R1000组Nrf2表达量无显著性差异(P<0.05)。与CON组相比,HS+R250组Nrf2 mRNA表达量显著增加(P<0.05),SOD2与NQO1 mRNA表达量在各组之间均无显著性差异(P>0.05)。

图 3 不同剂量芦丁对热应激小鼠睾丸抗氧化相关基因表达的影响 Fig. 3 The effect of different doses of rutin on the expression of antioxidant-related genes in the testis of heat-stressed mice
2.5 日粮添加不同剂量芦丁对热应激小鼠睾丸炎症相关基因表达的影响

图 4可知,与CON组相比,HS组小鼠睾丸NF-κBTLR-4表达量显著增加(P<0.05),MyD88、IL-1βTNF-αIFN-γ mRNA表达量无显著性差异(P>0.05);与HS组相比,HS+R250组NF-κBTLR-4、MyD88与IL-1β mRNA表达量显著降低(P<0.05),HS+R500组NF-κBTLR-4的mRNA表达量显著下降(P<0.05),HS+R1000组中NF-κB mRNA的表达量也显著低于HS组(P>0.05);日粮添加250~1 000 mg·kg-1芦丁处理热应激小鼠睾丸组织中炎症相关基因表达量与CON组之间未见显著差异(P>0.05)。

图 4 不同剂量芦丁对热应激小鼠睾丸炎症相关基因表达的影响 Fig. 4 Effects of different doses of rutin on the expression of inflammation-related genes in the testis of heat-stressed mice
2.6 日粮添加不同剂量芦丁对热应激小鼠睾丸增殖与凋亡基因表达的影响

图 5可知,与CON组相比,HS组Bax基因的相对表达量显著增加(P<0.05),Bcl-2表达量显著降低(P<0.05);与HS组相比,HS+R250组Bax mRNA表达量显著降低(P<0.05),Bcl-2表达量显著升高(P<0.05),HS+R1000组Bcl-2 mRNA表达量也显著高于HS组(P<0.05),HS+R500组无显著性变化(P>0.05);日粮添加250~1 000 mg·kg-1芦丁处理热应激小鼠睾丸组织中增殖与凋亡相关基因表达量与CON组之间未见显著差异(P>0.05)。

图 5 不同剂量芦丁对热应激小鼠睾丸增殖与凋亡基因表达的影响 Fig. 5 Effects of different doses of rutin on testis proliferation and apoptosis genes expression in heat-stressed mice
3 讨论 3.1 日粮添加芦丁对热应激小鼠睾丸指数及睾丸形态的影响

睾丸是具有高度增殖能力的组织,大多数哺乳动物的睾丸位于低于体温2~ 8 ℃的阴囊内,对温度非常敏感[22-23]。温度过高(如42 ℃)可使睾丸温度升高,导致睾丸组织形态异常,抑制精子发生,影响精子成熟与存活[24-25]。睾丸组织形态是反映睾丸组织功能与生殖能力的重要指标之一。吴璟等[26]研究发现,将ICR小鼠下腹部连续7 d置于43 ℃恒温水浴锅中热应激处理15 min后可显著降低小鼠睾丸系数,减少生精细胞数量,使小鼠睾丸生精上皮空泡变性及萎缩,从而改变睾丸形态,导致小鼠睾丸组织损伤诱导氧化应激。而本试验结果显示,HS组小鼠置于42 ℃恒温箱中(4 h·d-1)连续热处理8 d后睾丸指数与正常组无明显变化,这可能与热处理的方式和时间有关;但本试验中热处理小鼠睾丸组织生精小管直径和横截面积显著降低,生精细胞脱落比率显著增加,提示高温处理可改变小鼠睾丸形态,引起睾丸组织损伤。Mehfooz等[15]研究发现,日粮添加芦丁对束缚应激引起的小鼠睾丸损伤、细胞凋亡以及精子形态具有一定的保护作用。在本试验中日粮添加250 mg·kg-1芦丁可使热应激小鼠睾丸指数和生精小管横截面积显著提高,添加1 000 mg·kg-1芦丁显著增加了热应激小鼠生精小管直径,且添加250和500 mg·kg-1芦丁均可显著降低热应激小鼠生精细胞脱落比率,提示芦丁可改变小鼠睾丸形态缓解睾丸损伤,这可能与芦丁具有较好的抗氧化能力,缓解动物氧化应激和促进睾丸生精功能密切相关[13, 16],而添加1 000 mg·kg-1芦丁对热应激小鼠生精细胞脱落比率无显著性差异,提示芦丁添加量过高对机体可能会产生一定的负面影响,但长期添加高剂量芦丁对机体的影响及作用机制尚有待进一步研究。

3.2 日粮添加芦丁对热应激小鼠睾丸抗氧化功能的影响

抗氧化酶是一种存在于细胞环境中的蛋白质,它能通过调控抗氧化酶活性及数量来清除体内自由基[27]。GSH作为一种内源性活性肽,能够清除或中和体内过氧化物质和自由基,缓解机体氧化应激[28]。研究表明,日粮添加芦丁对大鼠睾丸免受缺血再灌注损伤具有保护作用,这可能与芦丁可提高超氧化物歧化酶和过氧化氢酶的活性[29]并增强GSH含量缓解氧化应激反应有关[16]。与之相似,本试验发现日粮中添加250、500和1 000 mg·kg-1芦丁均能显著提高热应激小鼠睾丸组织中GSH含量,发挥其抗氧化功能。此外,日粮添加250 mg·kg-1的芦丁可显著提高HS组小鼠睾丸组织T-AOC活性,显著降低MDA含量。MDA是机体内评价脂质氧化损伤的重要指标[30],故本试验结果提示,日粮添加250 mg·kg-1能够有效抑制小鼠睾丸脂质过氧化,缓解氧化应激。在本试验中日粮添加250、500和1 000 mg·kg-1芦丁均未对睾丸组织中T-SOD活性产生显著性影响,但韩雨薇等[31]研究发现,对蛛网膜下腔出血(SAH)大鼠给药50 mg·kg-1芦丁后可通过增加T-SOD与GSH-Px活性缓解SAH大鼠氧化应激反应,此两者结果不同的原因可能与芦丁处理的剂量、方式或检测组织不同有关。

Nrf2是一个与抗氧化功能密切相关的重要转录因子,可通过调节相关抗氧化基因表达影响抗氧化防御系统,如HO-1[32]HO-1作为一种抗氧化酶在应激状态下能够保持机体细胞稳定性[33],表达上调时可有助于增强机体抗氧化功能,缓解组织氧化损伤[34]。本研究发现,热应激小鼠睾丸组织中HO-1 mRNA的表达量显著降低,而日粮添加250 mg·kg-1芦丁可提高热应激小鼠睾丸Nrf2 mRNA表达量,上调HO-1和GSH-Px mRNA的表达,且HO-1表达水平与对照组小鼠无显著性差异。因此推测,日粮添加芦丁缓解热应激诱导的小鼠睾丸氧化损伤功能可能与Nrf2/HO-1信号通路有关,这与王斌等[35]研究发现灌胃芦丁(每天100 mg·kg-1)可通过Nrf2/HO-1信号通路缓解小鼠肾氧化应激损伤的结果一致。芦丁是从植物中提取的一种天然黄酮类物质,多被认为是一种安全性物质,但天然类物质也可对机体造成不良影响[36]。Féres等[37]发现,添加2 000 mg·kg-1芸香苷(dimorphandra mollis,芦丁含量为(76±3)%)可对机体产生一定毒副作用。本研究也发现与250 mg·kg-1芦丁组相比,日粮添加1 000 mg·kg-1芦丁显著降低了睾丸组织中Nrf2 mRNA表达量,提示日粮添加高剂量芦丁并未线性提高其抗氧化功能,这可能与高剂量芦丁可对机体产生一定副作用有关[37-38],但其具体机制尚需要进一步研究。

3.3 日粮添加芦丁对热应激小鼠睾丸炎症因子相关基因表达的影响

热应激可以导致炎症因子增加、抗炎因子下降,从而诱导炎症反应发生[39]NF-κB介导的信号通路参与体内多种反应,TLR-4可激活NF-κB通路介导下游炎症因子表达[40]。有研究表明,TLR-4/NF-κB信号通路与抗炎免疫机制密切相关,被认为是经典的炎症相关信号通路[41]MyD88是一种髓样蛋白分子,处于TLR-4信号通路的下游,参与TLR-4基因所介导的炎症信号转导[42]TLR-4通过MyD88途径使NF-κB信号通路被激活, 合成并释放TNF-αIL-1β等相关促炎症因子,完成炎症反应信号的传递[43]。本试验结果表明,热应激导致小鼠睾丸组织中TLR-4/NF-κB信号通路被激活,MyD88和IL-1β基因表达显著增强,这与巩栋梁[44]研究发现, 热应激状态下猪肠道组织中TLR-4/NF-κB信号通路被激活后上调IL-6等相关促炎症因子表达,从而导致机体炎症反应的结果一致。大量研究表明,芦丁在增强机体免疫的同时也可抑制多个促炎因子基因表达[45-46],并对大鼠肾组织具有较强的抗炎作用[47-48]。Yeh等[49]研究表明, 芦丁能显著抑制NF-κB表达,降低IL-1βTNF-αIL-6等多种促炎症因子的水平,具有较强的抗炎作用。本试验结果显示,日粮添加250、500和1 000 mg·kg-1芦丁均显著抑制了小鼠睾丸组织NF-κB mRNA的表达量,同时添加250和500 mg·kg-1芦丁可使TLR-4表达量显著降低,且当添加剂量为250 mg·kg-1时,HS组小鼠睾丸中MyD88与IL-1β mRNA表达量也显著下降,故推测热应激小鼠日粮中添加250 mg·kg-1芦丁可能通过抑制TLR-4/NF-κB信号通路下调相关炎症因子的表达发挥抗炎作用。

3.4 日粮添加芦丁对热应激小鼠睾丸增殖与凋亡基因表达的影响

Bcl-2是一个重要细胞凋亡基因,能够抑制细胞凋亡、参与细胞增殖调控,在组织器官生长发育及正常功能发挥方面具有重要作用[50-51]BaxBcl-2的同源基因,当Bax表达过量可自身结合成同源二聚体, 促进凋亡发生[52]。何萌萌等[22]研究发现,大鼠在43 ℃环境中水浴20 min可引起睾丸生精细胞凋亡,导致生殖障碍。口服75和150 mg·kg-1芦丁可抑制小鼠肾炎症和细胞凋亡[53]。本试验结果显示,连续热处理8 d(42 ℃,4 h·d-1)后使小鼠睾丸组织中Bax基因表达量显著增加,而日粮添加250 mg·kg-1芦丁显著抑制热应激小鼠睾丸Bax mRNA的表达;添加250和1 000 mg·kg-1芦丁显著增加Bcl-2 mRNA的表达量,这与添加250 mg·kg-1芦丁可降低热应激小鼠睾丸生精细胞脱落比率的结果相吻合,提示日粮添加适宜剂量芦丁对改善热应激小鼠睾丸组织损伤及抑制细胞凋亡具有重要作用。

4 结论

本试验结果提示,日粮添加适宜剂量芦丁具有改善热应激小鼠睾丸组织形态及功能的效果,其机制可能与芦丁通过Nrf2信号通路缓解氧化应激,通过TLR-4/NF-κB信号通路抑制炎症反应及调控Bax/Bcl-2 mRNA表达密切相关。本试验条件下日粮添加250 mg·kg-1芦丁效果较好。

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(编辑   范子娟)