李曉玲 劉媛 宋莉敏 董靜
[摘要]目的探討2型糖尿病進程中nesfatin`-1在小鼠下丘腦室旁核和視上核中的表達。方法將雄性昆明小鼠隨機分為對照組(普通飲食喂養(yǎng))、高脂飲食組和糖尿病組。糖尿病組小鼠腹腔注射鏈脲佐菌素,并給予高脂飲食喂養(yǎng)誘導2型糖尿病模型。比較3組小鼠血糖水平、穩(wěn)態(tài)模型的胰島素抵抗指數(shù)(HOMA`-IR)及攝食量。分別于造模成功后的2、4、6、8、10、12周,采用免疫熒光組織化學技術(shù)檢測各組小鼠下丘腦室旁核和視上核組織中nesfatin`-1表達。結(jié)果糖尿病組小鼠血糖較高脂飲食組和對照組明顯增高,且出現(xiàn)明顯的胰島素抵抗,同時攝食量增多。糖尿病組小鼠室旁核和視上核nesfatin`-1陽性神經(jīng)元數(shù)量在造模后前6周逐漸增加,后6周逐漸降低,總體nesfatin`-1表達水平低于高脂飲食組和對照組。結(jié)論2型糖尿病小鼠下丘腦室旁核和視上核中的nesfatin`-1表達水平降低,其表達變化呈前期上升、后期下降的趨勢。
[關(guān)鍵詞]nesfatin`-1;糖尿病,2型;下丘腦室旁核;視上核;小鼠
[ABSTRACT]ObjectiveTo investigate the expression of nesfain`-1 in the hypothalamic paraventricular nucleus (PVN) and the supraoptic nucleus (SON) in mice during the course of type 2 diabetes. MethodsMale Kunming mice were randomly divi`-ded into control group with a normal diet, high`-fat diet group, and diabetes group. The mice in the diabetes group were given intrape`-ritoneal injection of streptozotocin and a high`-fat diet to induce diabetes. The three groups were compared in terms of the level of blood glucose, homeostasis model assessment of insulin resistance (HOMA`-IR), and food intake. At 2,4,6,8,10, and 12 weeks after the model was successfully established, immunofluorescence assay was used to measure the expression of nesfatin`-1 in the PVN and the SON. ResultsCompared with the high`-fat diet group and the control group, the diabetes group had significantly higher blood glucose level, HOMA`-IR, and food intake. In the diabetes group, there was a gradual increase in the number of nesfatin`-1`-positive neurons in the PVN and the SON during the first 6 weeks, followed by a gradual reduction in the next 6 weeks, and the diabetes group generally had lower expression of nesfatin`-1 than the high`-fat diet group and the control group. ConclusionThere is a reduction in the expression of nesfatin`-1 in the hypothalamic PVN and the SON in mice with type 2 diabetes, and the expression of nesfatin`-1 increases in the early stage and then decreases in the late stage.
[KEY WORDS]nesfatin`-1; diabetes mellitus, type 2; paraventricular hypothalamic nucleus; supraoptic nucleus; mice
2型糖尿病表現(xiàn)為代謝功能障礙。高脂血癥以及高糖血癥是影響2型糖尿病病人許多組織器官(包括心臟、肝臟、腎臟和眼血管內(nèi)皮等)并發(fā)癥的觸發(fā)因素[1`-2]。Nesfatin`-1作為一種厭食肽,通過中樞機制參與能量穩(wěn)態(tài)的調(diào)節(jié)。有研究結(jié)果表明,2型糖尿病病人的血漿nesfatin`-1水平升高,并與體質(zhì)量指數(shù)(BMI)、血漿胰島素水平和穩(wěn)態(tài)模型的胰島素抵抗指數(shù)(HOMA`-IR)有關(guān)[3]。最近的研究結(jié)果揭示了nesfatin`-1在體內(nèi)葡萄糖平衡中的抗高糖血癥作用[4]。中樞nesfatin`-1在標準飲食和高脂飲食的大鼠中均能夠顯著抑制肝臟磷酸烯醇丙酮酸羧激酶(PEPCK)表達水平,而且 nesfatin`-1在高糖血癥條件下可增加β細胞的胰島素釋放。外周nesfatin`-1可通過激活2型糖尿病小鼠的AMP`-ACC途徑參與脂肪代謝調(diào)節(jié)[5]。但nesfatin`-1在2型糖尿病進程中是否有變化及其所起的作用目前尚不清楚,本研究旨在進一步探討2型糖尿病進程中小鼠中樞核團室旁核(PVN)和視上核(SON)nesfatin`-1的表達變化,為糖脂代謝下丘腦調(diào)節(jié)機制的深入研究提供實驗依據(jù)。現(xiàn)將結(jié)果報告如下。
1材料和方法
1.1動物及分組
實驗所用3周齡雄性昆明小鼠90只,均由青島市藥品檢驗所提供。將小鼠隨機分為對照組(Con組)、高脂飲食組(HFD組)以及糖尿病組(DM組)。Con組小鼠喂普通鼠糧,HFD組和DM組小鼠喂高脂食物(59%普通鼠糧,20%糖,18%豬油和3%蛋黃)。小鼠飼養(yǎng)于標準動物房,室溫(23±2)℃,濕度50%~60%,7:00—19:00進行光照,嚴格12 h晝夜循環(huán),自由飲水和進食。處理小鼠的規(guī)程經(jīng)青島大學動物保護和使用委員會認證。本研究符合國立衛(wèi)生研究院《實驗室護理與使用指南》的指導方針。
1.2主要試劑
小鼠胰島素ELISA試劑盒(R&D Systems),兔抗鼠nesfatin`-1抗體購于美國 Phoenix公司,熒光標記的山羊抗兔IgG購于北京中杉金橋公司,鏈脲佐菌素(STZ)購于Sigma公司,生理鹽水(NS)購于青島大學校醫(yī)院,水合氯醛購于天津市瑞金特化學品有限公司。
1.32型糖尿病小鼠模型構(gòu)建
在6和9周齡時,DM組的小鼠進行兩次低劑量STZ(100 mg/kg,將STZ溶解于pH值為4.5的0.1 mol/L檸檬酸鹽緩沖液中)腹腔注射,Con組和HFD組僅注射等劑量的緩沖液。在11周齡末進行空腹血糖以及空腹血漿胰島素水平檢測,空腹血糖水平高于12 mmol/L且HOMA`-IR異常增高,則認為2型糖尿病造模成功[6]。
1.4小鼠血糖水平、胰島素抵抗和攝食量測定
于造模成功后2、4、6、8、10、12周末,從小鼠尾靜脈采血,用德國貝朗倍佳血糖儀測定空腹血糖水平,用ELISA試劑盒測定空腹血漿胰島素水平。通過以下公式計算HOMA`-IR[7]:HOMA`-IR=空腹血漿胰島素(mU/L)×空腹血糖(mmol/L)/22.5。每周周日19:00開始測12 h累積攝食量。
1.5免疫熒光法檢測小鼠下丘腦核團nesfatin`-1陽性神經(jīng)元表達
于造模成功后2、4、6、8、10、12周末尾靜脈取血后,腹腔注射80 g/L水合氯醛0.4 g/kg麻醉小鼠,進行心臟灌注,迅速斷頭取腦置40 g/L多聚甲醛溶液中固定,于4 ℃冰箱中固定24 h后,再用300 g/L蔗糖溶液脫水24 h。根據(jù)小鼠大腦立體定位圖譜分別切取下丘腦PVN和SON進行冷凍切片(切片厚度為10~15 μm),將切片置于載玻片上。切好的腦片置于60 ℃溫箱中烤片4 h,用PBST溶液浸泡20 min,置于修復液內(nèi),用微波爐95 ℃中火修復抗原10 min,待自然冷卻后以PBST溶液洗3次,每次7 min。用小牛血清室溫封閉2 h,兔抗鼠nesfatin`-1抗體(1∶500)4 ℃孵育腦片12 h,以PBST溶液沖洗3次,用熒光標記的山羊抗兔IgG(1∶100)室溫避光孵育2 h,以PBST溶液洗片后用封片液(PBST和甘油體積比為1∶1)封片固定腦片,在熒光顯微鏡下觀察nesfatin`-1的表達。采用Image`-Pro Plus 6.0軟件進行陽性神經(jīng)元計數(shù)。
1.6統(tǒng)計學分析
實驗所得計量數(shù)據(jù)以±s表示,使用SPSS 20.0軟件、采用析因設(shè)計的方差分析進行顯著性檢驗,以P<0.05為差異有統(tǒng)計學意義。
2結(jié)果
2.12型糖尿病小鼠血糖水平、胰島素抵抗和攝食量改變
造模成功后小鼠攝食量持續(xù)增加,并且顯著高于HFD和Con組小鼠(F=5.151~101.225,P<0.01)。見圖1。小鼠血糖水平組別的主效應(yīng)有統(tǒng)計學意義(F=155.922,P<0.01),DM組小鼠不同時間的血糖水平均顯著高于HFD組和Con組(F=14.435~253.832,P<0.01);時間的主效應(yīng)也有統(tǒng)計學意義(F=2.844,P<0.05),DM組小鼠造模成功后2周的血糖水平低于4、6、8、10、12周(F=2.578,P<0.05);兩因素間的交互效應(yīng)無統(tǒng)計學意義(P>0.05)。見表1。小鼠胰島素抵抗水平組別的主效應(yīng)有統(tǒng)計學意義(F=142.257,P<0.01),DM組小鼠各時間的HOMA`-IR較HFD和Con組明顯增加(F=6.905~150.941,P<0.05);時間的主效應(yīng)也有統(tǒng)計學意義(F=3.546,P<0.05),DM組小鼠造模成功后4周的HOMA`-IR較其他時間明顯增高(F=5.122,P<0.05);兩因素間的交互效應(yīng)有統(tǒng)計學意義(F=3.899,P<0.01)。見表2。
2.22型糖尿病小鼠下丘腦PVN和SON中nesfatin`-1陽性神經(jīng)元表達
免疫熒光檢測顯示,小鼠PVN中nesfatin`-1表達水平組別的主效應(yīng)有統(tǒng)計學意義(F=64.747,P<0.01),DM組小鼠各時間nesfatin`-1陽性神經(jīng)元的數(shù)量明顯少于HFD組和Con組(F=4.917~30.321,P<0.05);時間的主效應(yīng)沒有統(tǒng)計學意義(P>0.05),但DM組小鼠nesfatin`-1陽性神經(jīng)元的數(shù)量在造模成功后前6周呈上升趨勢,之后呈下降趨勢;兩因素間的交互效應(yīng)沒有統(tǒng)計學意義(P>0.05)。SON中陽性nesfatin`-1神經(jīng)元數(shù)量的變化呈現(xiàn)出與PVN大致相同的趨勢。小鼠PVN中nesfatin`-1表達水平組別的主效應(yīng)有統(tǒng)計學意義(F=29.622,P<0.01),DM組小鼠各時間nesfatin`-1陽性神經(jīng)元的數(shù)量明顯少于HFD組和Con組(F=5.185~31.538,P<0.05);時間的主效應(yīng)無統(tǒng)計學意義(P>0.05);兩因素間的交互效應(yīng)無統(tǒng)計學意義(P>0.05)。見圖2。
3討論
Nesfatin`-1是由前體蛋白核苷結(jié)合蛋白2水解產(chǎn)生的含有82個氨基酸的多肽[8],可產(chǎn)生厭食的效應(yīng)[9]。Nesfatin`-1誘導的攝食抑制可能是通過抑制促食欲神經(jīng)元來介導的[10]。Nesfatin`-1分布于中樞神經(jīng)系統(tǒng)如PVN和SON等,以及外周如胃黏膜、胰腺、脂肪組織等[11]。在下丘腦和內(nèi)分泌器官中的廣泛分布意味著nesfatin`-1在能量穩(wěn)態(tài)和代謝調(diào)節(jié)中起關(guān)鍵作用。有研究結(jié)果表明,nesfatin`-1可影響PVN中大部分不同亞群神經(jīng)元的興奮性,作為上游調(diào)節(jié)因子,能激活PVN縮宮素神經(jīng)元的黑素皮質(zhì)素通路,從而揭示了厭食性縮宮素的神經(jīng)通路[12]。PVN和SON中的nesfatin`-1神經(jīng)元可在餐后調(diào)節(jié)攝食行為,在能量穩(wěn)態(tài)中起重要作用[13]。已有研究表明,nesfatin`-1能夠增加能量消耗[14],并誘導動物心血管改變,升高血壓[15`-17],增加胰島素敏感性[18]。
Nesfatin`-1作為一種厭食肽,通過中樞機制參與能量穩(wěn)態(tài)的調(diào)節(jié)[19`-20]。Nesfatin`-1可在大腦中發(fā)揮上調(diào)胰島素敏感性的作用[18],并能增加β細胞胰島素的釋放,從而降低升高的血糖[21]。Nesfatin`-1也被發(fā)現(xiàn)可抑制中樞神經(jīng)系統(tǒng)調(diào)節(jié)的食物攝入[8]。Nesfatin`-1在肥胖動物中的表達增加,并且隨著攝食和饑餓狀態(tài)的不同而改變[22]。2型糖尿病常發(fā)生于肥胖人群[23],胰島素功能障礙[24]、飲食失調(diào)[25]和炎癥[26]等因素也可引發(fā)2型糖尿病。2型糖尿病通常與葡萄糖代謝改變、胰島素抵抗、空腹血糖異常和葡萄糖耐量降低有關(guān)。本研究中糖尿病模型小鼠攝食量增加,體質(zhì)量下降,表現(xiàn)為明顯的胰島素抵抗。有研究提出,糖尿病性多食是由循環(huán)nesfatin`-1水平降低引起的[27]。還有研究表明,nesfatin`-1可以刺激脂質(zhì)代謝表現(xiàn)出抗炎作用[5]。目前總體來說,nesfatin`-1是肥胖(機體能量代謝)[28]、糖尿?。ㄆ咸烟谴x)[29]和抑郁癥[30]等的極為重要的肽激素。
有研究顯示,血漿nesfatin`-1水平在2型糖尿病病人中升高[3,31],與BMI、血漿胰島素和HOMA`-IR有關(guān);并且發(fā)現(xiàn)只有新診斷的2型糖尿病病人的循環(huán)nesfatin`-1水平增加。但是也有研究顯示,糖尿病病人的nesfatin`-1水平較低[27,32],認為結(jié)果不一致是由病人的BMI和胰島素抵抗的差異引起的。本研究比較了糖尿病小鼠與高脂飲食及正常飲食小鼠下丘腦核團nesfatin`-1的表達水平,結(jié)果顯示,與HFD組和Con組相比,DM組小鼠PVN和SON中nesfatin`-1的表達水平顯著降低,表明nesfatin`-1在2型糖尿病的發(fā)展中起重要作用。本研究還觀察到,在2型糖尿病病程進展過程中,PVN和SON中nesfatin`-1的表達量呈早期逐漸升高后期逐漸降低的趨勢。這可能是由于糖尿病早期血糖升高,營養(yǎng)物質(zhì)相對充足,無需攝入食物來供能,表現(xiàn)為代償性nesfatin`-1水平升高;但在糖尿病的后期,隨著胰島素抵抗的加重,細胞缺乏足夠的能量,刺激攝食中樞,引起攝食的增加,nesfatin`-1水平降低。這與循環(huán)中nesfatin`-1水平與2型糖尿病關(guān)系的Meta分析結(jié)果相一致[33],即接受抗糖尿病治療或疾病持續(xù)時間長的2型糖尿病病人循環(huán)nesfatin`-1水平較低,早期2型糖尿病與nesfatin`-1水平升高相關(guān),可能是由于血糖和食物攝入的補償機制。
中樞神經(jīng)系統(tǒng)可以通過下丘腦`-垂體`-腎上腺皮質(zhì)軸來調(diào)控外周器官功能活動,近年來,下丘腦對內(nèi)臟功能的調(diào)節(jié)一直受到關(guān)注。有文獻報道,下丘腦nesfatin`-1活性是由ERK信號傳導介導的,ERK進而調(diào)節(jié)自主神經(jīng)系統(tǒng)[34]。先前的研究發(fā)現(xiàn),許多不同的下丘腦細胞內(nèi)信號,如AMPK、mTOR等通過介導nesfatin`-1影響交感神經(jīng)系統(tǒng)[18]。但中樞nesfatin`-1到底如何改善體內(nèi)代謝紊亂目前仍不是非常明確,還需進一步探討nesfatin`-1是否通過交感神經(jīng)調(diào)節(jié)外周代謝以及如何調(diào)節(jié)。
綜上所述,STZ和高能量攝食誘導的2型糖尿病小鼠下丘腦PVN和SON中的nesfatin`-1表達降低,nesfatin`-1的表達變化呈前期上升、后期下降的趨勢。表明nesfatin`-1在2型糖尿病的進程中發(fā)揮了重要作用,有望成為抗糖尿病治療的新靶標。本文結(jié)果為糖脂代謝的神經(jīng)調(diào)節(jié)研究提供了依據(jù)。
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