盧榮華孫君君梁旭方聶國(guó)興楊 峰

(1. 河南師范大學(xué)水產(chǎn)學(xué)院, 新鄉(xiāng) 453007; 2. 華中農(nóng)業(yè)大學(xué)水產(chǎn)學(xué)院, 武漢 430070)

魚(yú)類(lèi)leptin的生物學(xué)特性及功能

盧榮華1孫君君1梁旭方2聶國(guó)興1楊 峰1

(1. 河南師范大學(xué)水產(chǎn)學(xué)院, 新鄉(xiāng) 453007; 2. 華中農(nóng)業(yè)大學(xué)水產(chǎn)學(xué)院, 武漢 430070)

瘦素(Leptin)是肥胖基因(Obese gene)的產(chǎn)物, 屬于I型細(xì)胞因子。在哺乳動(dòng)物中, leptin主要由脂肪細(xì)胞合成與分泌, 是調(diào)控?cái)z食、能量代謝、骨骼發(fā)育、甲狀腺功能以及繁殖等生理過(guò)程的重要激素。目前, 多種硬骨魚(yú)類(lèi)的leptin基因已被克隆, 其功能也已得到初步研究。研究認(rèn)為, 魚(yú)類(lèi)leptin的主要合成部位在肝臟, 其在氨基酸序列上與哺乳動(dòng)物存在很大差異, 但蛋白質(zhì)結(jié)構(gòu)高度保守; 功能方面, leptin可調(diào)節(jié)魚(yú)類(lèi)的攝食、葡萄糖和脂肪代謝以及繁殖等生命活動(dòng)過(guò)程。本文就魚(yú)類(lèi)leptin及其受體的特征結(jié)構(gòu)、組織分布、表達(dá)調(diào)控及功能研究進(jìn)展進(jìn)行簡(jiǎn)要綜述。

Leptin; 魚(yú)類(lèi); 生物學(xué)特性; 食欲調(diào)節(jié); 能量代謝

1994年, Zhang等[1]首次分離出哺乳動(dòng)物的肥胖基因(Obese gene), 瘦素(Leptin)即是肥胖基因的產(chǎn)物, 該名字起源于希臘語(yǔ)leptos意為“瘦的”, 其得名是由于研究發(fā)現(xiàn)缺失leptin會(huì)造成哺乳動(dòng)物的肥胖。哺乳動(dòng)物leptin由脂肪組織分泌, 已證明其在糖脂代謝[2,3]、生殖[4,5]、免疫[6]、能量消耗[7]以及攝食中發(fā)揮重要作用, 被認(rèn)為是機(jī)體的一種飽食因子[8—10]。與對(duì)陸生動(dòng)物leptin的深入研究相比, 魚(yú)類(lèi)leptin雖然也已引起學(xué)者們的關(guān)注, 但相關(guān)功能研究尚開(kāi)展的不多。

1 Leptin及Leptin受體的結(jié)構(gòu)與同源性分析

1.1 Leptin的結(jié)構(gòu), 拷貝數(shù)及同源性分析

Johnson等[11]首次通過(guò)鼠leptin抗體在藍(lán)綠鱗鰓太陽(yáng)魚(yú)(Lepomis macrochirus)、虹鱒(Oncorhynchus mykiss)、大口黑鱸(Pomonix annularis)和斑點(diǎn)叉尾鲴(Ictalurus punctatus)中檢測(cè)到其血液、腦、心、肝中均存在leptin。日本學(xué)者Kurokawa等[12]通過(guò)基因組同線性方法從紅鰭東方鲀(Takifugu rubripes)等變溫動(dòng)物中首次鑒定并分離出肥胖基因。隨后, 包括日本青 鳉(Oryzias latipes)[12,13]、鯉(Cyprinus carpio)[14]、斑馬魚(yú)(Danio rerio)[15]、大麻哈魚(yú)(Oncorhynchus keta)[16]、虹鱒[16]、草魚(yú)(Ctenopharyngodon idella)[17]、北極鮭(Salvelinus alpinus)[18]、大西洋鮭(Salmo salar)[19]、 鱸 (Morone saxatilis)[20]、 黃 顙 魚(yú)(Pelteobagrus fulvidraco)[21]和大黃魚(yú)[22]等魚(yú)類(lèi)以及非洲爪蟾(Xenopus laevis)[23]、熱帶爪蟾(Xenopus tropicalis)[12,23]、寬虎紋鈍口螈(Ambystoma tigrinum)[24]等兩棲動(dòng)物的leptin基因也被先后分離, 并在鯉[14]、草魚(yú)[17]、虹鱒[16,25]和 青 鳉(Oryzias latipes)[26]等部分物種中進(jìn)行了相對(duì)深入的研究。

在非洲爪蟾和目前已知的多數(shù)魚(yú)類(lèi)中, 肥胖基因由3個(gè)外顯子和2個(gè)內(nèi)含子組成, 與人類(lèi)的肥胖基因結(jié)構(gòu)相似[1], 且內(nèi)含子的相對(duì)位置高度保守[12,16,17,23,27]。然而, 寬虎紋鈍口螈[24]、鯉[14]和鱖(Siniperca chuatsi)的肥胖基因只含有 2個(gè)外顯子和 1個(gè)內(nèi)含子(第 2個(gè)內(nèi)含子), 它們的第1個(gè)內(nèi)含子在進(jìn)化過(guò)程中已丟失[13,15,23,24,27—29]?；蚪M同線性分析表明, 人、小鼠、熱帶爪蟾、河鲀 和斑馬魚(yú)等的leptin基因在基因組中的線性排列非常相似[12,14,16,17,23,24,27], 表明它們起源相同。

在人和小鼠等哺乳動(dòng)物以及非洲爪蟾的基因組中, 肥胖基因僅有一個(gè)拷貝, 編碼一種蛋白產(chǎn)物。然而最近的研究發(fā)現(xiàn), 在斑馬魚(yú)、日本青 鳉和石斑魚(yú)(Epinephelus coioides)的基因組中存在2個(gè)肥胖基因拷貝, 編碼兩種不同的產(chǎn)物(分別命名為leptin-A型和leptin-B型)[13,15,30]。斑馬魚(yú)的leptin-A和leptin-B僅含有24%的氨基酸同源性, 表明它們屬于兩種不同的leptin亞型。因此魚(yú)類(lèi)可能普遍存在兩種leptin亞型[13,15]。盡管先前的研究發(fā)現(xiàn)鯉中也存在兩種leptin轉(zhuǎn)錄本, 然而它們之間的氨基酸同源性高達(dá)84%,系統(tǒng)樹(shù)分析發(fā)現(xiàn)它們同聚于leptin-A進(jìn)化分枝, 表明它們很可能同屬于leptin-A型, 這可能是由鯉(四倍體)在～16Mya發(fā)生的基因組加倍引起。系統(tǒng)樹(shù)分析和氨基酸同源性分析顯示, 目前分離得到的魚(yú)類(lèi)leptin絕大部分屬于leptin-A型, 包括綠河豚(Tetraodon nigroviridis)[12]、虹鱒[16]、北極紅點(diǎn)鮭(Salvelinus alpinus)[18]、鰱(Hypophthalmichthys molitrix)和草魚(yú)[17]等, 在鯉及其他大部分魚(yú)類(lèi)中很可能還存在leptin-B型[15]。兩種leptin亞型在魚(yú)類(lèi)中的出現(xiàn)以及它們組織表達(dá)的差異, 可能賦予leptin新的功能。最新的研究發(fā)現(xiàn), 某些種類(lèi)如大西洋鮭的leptin甚至出現(xiàn)了多達(dá)四個(gè)亞型同源物(LepA1, LepA2, LepB1/B2)[31]。

Leptin的蛋白序列在哺乳動(dòng)物中高度保守, 魚(yú)類(lèi)及其他變溫動(dòng)物leptin與哺乳動(dòng)物leptin的氨基酸同源性卻很低(如河 鲀 、斑馬魚(yú)、虹鱒和非洲爪蟾 leptin等與人leptin的氨基酸同源性分別為13.2%、22%、21.4%和35.0%)[12,14,16,17,23,24,27], 此外, 不同種屬魚(yú)類(lèi)leptin之間的氨基酸同源性同樣很低(如 河鲀 與斑馬魚(yú)、虹鱒leptin的氨基酸同源性為19%和20.9%, 鯉和虹鱒leptin的氨基酸同源性為26.8%)[12—17,23,24,27]。分析發(fā)現(xiàn), 它們用于形成二硫鍵的半胱氨酸卻高度保守, 蛋白二級(jí)結(jié)構(gòu)(4個(gè)α螺旋)也同樣高度保守, 而且三級(jí)結(jié)構(gòu)預(yù)測(cè)表明它們之間的空間結(jié)構(gòu)十分相似[12—17,23,24,27]。

1.2 Leptin受體的基因結(jié)構(gòu)

人等哺乳動(dòng)物的leptin受體(Leptin receptor, leptin-R)為單一拷貝, 但其可通過(guò)不同的剪接方式產(chǎn)生多達(dá)6種長(zhǎng)度不同的轉(zhuǎn)錄本[32]。其中, 長(zhǎng)型leptin-R在介導(dǎo)leptin的調(diào)控功能中起重要作用[32]。人的leptin-R含有20個(gè)外顯子, 非洲爪蟾的外顯子則多達(dá)26個(gè)[23]。目前, 已在海洋青鳉魚(yú)(Oryzias melastigma)[33]、 日本青 鳉[13]、 河 鲀[34]和草魚(yú)[35]等魚(yú)類(lèi)中分離了leptin-R基因, 日本青鳉leptin-R基因含有20個(gè)外顯子[13], 河 鲀leptin-R基因則含有21個(gè)外顯子[34]。目前在非洲爪蟾中僅發(fā)現(xiàn)長(zhǎng)型leptin-R一種類(lèi)型,其他在哺乳動(dòng)物中出現(xiàn)的5種類(lèi)型至今未見(jiàn)報(bào)道。

2 Leptin及l(fā)eptin受體的組織差異表達(dá)

2.1 Leptin的組織分布及分泌濃度

Leptin在多種組織中均有表達(dá), 在人等哺乳動(dòng)物中, 脂肪組織是leptin的主要合成位點(diǎn)[1,36]。此外, 其在胎盤(pán)等多種組織中也可以合成[36]。與哺乳動(dòng)物不同, 非洲爪蟾leptin在腦和心臟中大量表達(dá)[23], 寬虎紋鈍口螈 leptin主要在皮膚和卵巢中表達(dá)[24], 而魚(yú)類(lèi)的leptin雖然在包括腸道、脂肪、大腦等不同組織中都有少量表達(dá), 但主要表達(dá)部位是肝臟[11—17,19,27,34]。此外, 不同亞型leptin的組織表達(dá)情況也有差異。在日本青 鳉中, leptin-A主要表達(dá)在鰓、肝臟、腦垂腺、脾、腸、心臟等組織中, leptin-B在卵巢、腦垂腺、鰓和心臟中表達(dá)水平較高。在斑馬魚(yú)中, leptin-A 主要在肝臟中表達(dá), 而leptin-B在腦和眼中大量表達(dá)[15]。leptin亞型組織分布的不同, 提示其可能有各自獨(dú)特的功能。如leptin-B在卵巢的大量表達(dá)暗示其可能在調(diào)控生殖功能中起重要作用[13]。

在正常生理狀態(tài)下, 人的血漿leptin濃度為0.2—0.3 nmol/L[28,29], 鼠類(lèi)的血漿leptin濃度為0.09—0.3 nmol/L[37,38]。而Kling等[39]測(cè)定了多種魚(yú)類(lèi)的血漿leptin濃度, 結(jié)果表明魚(yú)類(lèi)的血漿leptin濃度為1.1—5 nmol/L, 比哺乳動(dòng)物的血漿leptin濃度高。哺乳動(dòng)物能依據(jù)血漿中的leptin濃度傳達(dá)體內(nèi)脂肪含量信息給大腦, 進(jìn)而指導(dǎo)攝食行為、代謝及生理內(nèi)分泌, 使其與機(jī)體的營(yíng)養(yǎng)狀況相一致[40]。上述leptin組織表達(dá)及分泌濃度的差異, 暗示魚(yú)類(lèi)的leptin在功能及調(diào)節(jié)通路上可能與哺乳動(dòng)物有較大差異。

2.2 Leptin受體的組織分布

不論在哺乳動(dòng)物還是魚(yú)類(lèi)中, leptin均通過(guò)其受體發(fā)揮調(diào)控?cái)z食及能量平衡等功能[41—47]。哺乳動(dòng)物長(zhǎng)型leptin-R主要在下丘腦中表達(dá)[1,32,36], 小鼠缺乏leptin-R會(huì)因食欲過(guò)強(qiáng)導(dǎo)致肥胖[48]。海洋青鳉的leptin-R主要在鰓、脾臟、腎臟和肌肉中表達(dá), 且雌性海洋青鳉leptin-R的表達(dá)量要高于雄性的[33]。薛俊蓮等[49]通過(guò)RT-PCR方法獲得鯽魚(yú)的leptin受體序列,并制備了鯽魚(yú)2個(gè)瘦素受體的多克隆抗體; 檢測(cè)了鯽魚(yú)組織和血清中的受體, 初步確定了鯽魚(yú)血清中存在可溶瘦素受體。

3 Leptin的功能

3.1 Leptin在調(diào)控?cái)z食中的作用

用哺乳動(dòng)物的 leptin在金魚(yú)體內(nèi)通過(guò)腹腔和側(cè)腦室注射后顯示其攝食減少、體重下降以及調(diào)控?cái)z食和能量代謝相關(guān)基因表達(dá)水平發(fā)生改變[50,51]。在鱸腹腔內(nèi)注射人leptin也可抑制其攝食[20]。然而, 以哺乳動(dòng)物 leptin處理銀大馬哈魚(yú)(Oncorhynchus kisutch)[52]、鯰(Ictalurus punctatus)[53]和綠海魴(Lepomis cyanellus)[54], 卻并不能改變它們的攝食行為或能量代謝。這可能與特異性的魚(yú)類(lèi) leptin的功能有關(guān)。目前在絕大多數(shù)魚(yú)類(lèi)研究中發(fā)現(xiàn) leptin具有抑制攝食的作用[16,17,25]。Murashita等[16]用重組虹鱒 leptin處理后發(fā)現(xiàn)可顯著抑制虹鱒的攝食行為、刺激抑制食欲因子阿片促黑色素原 A1/A2 (proopiomelanocorein- A1/A2, POMC-A1/A2)基因表達(dá)并降低促食欲因子神經(jīng)肽Y(neuropeptide Y, NPY)基因的表達(dá)水平。進(jìn)一步研究發(fā)現(xiàn)重組鮭 leptin也可顯著抑制大西洋鮭的生長(zhǎng), 分析原因認(rèn)為 leptin可能通過(guò)顯著提高 POMC-A1轉(zhuǎn)錄, 抑制食物攝入而導(dǎo)致生長(zhǎng)減慢[55]。Li等[17]制備了草魚(yú)leptin蛋白,通過(guò)短期(1 d)和長(zhǎng)期(13 d)腹腔注射實(shí)驗(yàn), 發(fā)現(xiàn)leptin短期處理可明顯抑制草魚(yú)的攝食、抑制 NPY等攝食相關(guān)基因的表達(dá)。在石斑魚(yú)中, 饑餓和再投喂實(shí)驗(yàn)表明, Leptin-A在調(diào)節(jié)攝食和能量代謝中發(fā)揮重要作用[30]。

3.2 Leptin在調(diào)控糖脂代謝中的作用

在哺乳動(dòng)物中l(wèi)eptin可抑制脂肪的沉積, 促進(jìn)脂肪的水解[56—58]等, 還可通過(guò)影響動(dòng)物下丘腦和后腦的葡萄糖感受性神經(jīng)元的活性, 抑制促食欲肽(NPY, AgRP, Orexin)和激活厭食欲肽(POMC, CART, CCK)的表達(dá)[59—61]進(jìn)而來(lái)調(diào)控其攝食行為, 并促進(jìn)能量消耗。因此, leptin調(diào)節(jié)攝食的作用也與對(duì)葡萄糖的代謝調(diào)控交織在一起; 除中樞神經(jīng)系統(tǒng)外, leptin還可直接調(diào)節(jié)外周組織器官, 促進(jìn)肝臟葡萄糖生成, 調(diào)控肝臟磷酸烯醇丙酮酸羧激酶(Phosphoenolpyruvate carboxykinase, PEPCK)基因表達(dá)和糖異生效率[62], 通過(guò)乳酸攝取增加直接刺激肝糖原產(chǎn)生。leptin對(duì)PEPCK及糖異生的影響限制了甘油三酯的合成, 因而哺乳類(lèi)leptin主要通過(guò)調(diào)控糖和脂代謝與攝食的偶聯(lián)來(lái)維持其體脂蓄積及機(jī)體能量代謝的穩(wěn)定。

目前, 已有一些關(guān)于魚(yú)類(lèi) leptin對(duì)脂類(lèi)代謝的研究, 如 leptin能增加太陽(yáng)魚(yú)細(xì)胞內(nèi)脂肪酸結(jié)合蛋白的量[54]; 重組草魚(yú) leptin蛋白通過(guò)腹腔注射后,可促進(jìn)脂代謝基因或能量代謝基因解偶聯(lián)蛋白2(Uncoupling protein 2, UCP2)、膽鹽活化的胰脂肪酶(Bile salt-activated lipase, BSAL)和脂肪酸延長(zhǎng)酶(Fatty acid elongase, ELO)的基因表達(dá), 這與虹鱒實(shí)驗(yàn)中所得結(jié)果相似, 也與非洲爪蟾和哺乳動(dòng)物的結(jié)果一致[17]; 筆者在草魚(yú)營(yíng)養(yǎng)性肝細(xì)胞脂變模型中的研究結(jié)果也表明, leptin劑量依賴(lài)性促進(jìn)甘油的釋放,并可影響9個(gè)脂肪代謝關(guān)鍵基因在轉(zhuǎn)錄和翻譯水平的表達(dá), 且其誘導(dǎo)脂肪分解的作用是由 JAK-STAT信號(hào)通路來(lái)介導(dǎo)的[3]。

迄今為止, 已有研究發(fā)現(xiàn)魚(yú)類(lèi)leptin和糖代謝(血糖變化)、饑餓及再投喂條件關(guān)系密切。在金魚(yú)腹腔內(nèi)注射leptin后, 可引起肝糖原、肌糖原以及循環(huán)激素水平的變化[51,52]; 在虹鱒腦室注射leptin后可提高糖合成和分解過(guò)程中相關(guān)酶的含量, GK活性以及與糖代謝反應(yīng)有關(guān)基因的mRNA水平, 研究還發(fā)現(xiàn)leptin作用后會(huì)引起血糖濃度升高[25]。Huising等[14]以鯉為模型, 研究發(fā)現(xiàn)攝食后其肝臟leptin mRNA表達(dá)量上升, 其峰值出現(xiàn)在血糖含量的升高和血漿游離脂肪酸下降之后, 這可能是因?yàn)槠鋖eptin表達(dá)量由攝食后血糖含量變化所控制。Gorissen等[15]證實(shí)斑馬魚(yú)在禁食一周后, 其肝臟leptin-B的mRNA水平顯著降低, 而leptin-A的mRNA水平則升高, 這與leptin的不同亞型有關(guān)。虹鱒在長(zhǎng)期饑餓(3周)中, leptin的表達(dá)水平顯著升高[39]。在鱸中, 饑餓3周其肝中l(wèi)eptin的mRNA水平顯著減少, 再投喂3周后leptin mRNA水平則回升[20]; 上述這些研究表明了魚(yú)類(lèi)leptin可激活糖代謝系統(tǒng), 這與高血糖條件下觀察到的變化一致, 在魚(yú)類(lèi)腦中增加或降低血糖水平[63,64]伴隨著GK的活性及其表達(dá)水平的變化、糖酵解能力以及葡萄糖和糖原水平的變化, 且這種變化與哺乳動(dòng)物的糖代謝反應(yīng)在某種程度上相類(lèi)似[65]。

哺乳動(dòng)物中的研究認(rèn)為機(jī)體的血糖水平與攝食調(diào)節(jié)及能量平衡密切相關(guān), 高血糖條件下食物的攝入被抑制[12]。而上述在絕大多數(shù)魚(yú)類(lèi)研究中的結(jié)果顯示, 特異性的魚(yú)類(lèi)leptin具有抑制魚(yú)類(lèi)攝食的作用[16,17,25], 推測(cè)魚(yú)類(lèi)leptin對(duì)攝食的調(diào)節(jié)也與對(duì)糖脂代謝的作用相偶聯(lián), 即魚(yú)類(lèi)leptin通過(guò)調(diào)節(jié)糖(血糖)及脂類(lèi)代謝進(jìn)而調(diào)節(jié)魚(yú)類(lèi)的攝食及能量代謝的平衡。眾所周知, 魚(yú)類(lèi), 特別是肉食性魚(yú)類(lèi), 對(duì)高糖具有不耐受性[66,67], 而魚(yú)類(lèi)的食性與leptin以及糖脂代謝是否存在更密切的關(guān)系, 尚需深入研究。

3.3 Leptin的其他作用

已有研究證實(shí) leptin與硬骨魚(yú)類(lèi)的繁殖活動(dòng)密切相關(guān)。leptin及其受體在大西洋鮭和斑馬魚(yú)的腦(腦垂體)及性腺中表達(dá)很豐富[15,19,42]。Peyon等[68]報(bào)道重組鼠leptin對(duì)舌齒鱸(Dicentrarchus labrax)腦垂體中促黃體生成素(luteinizing hormone, LH)的產(chǎn)生有直接作用。高濃度的重組人 leptin可刺激虹鱒離體腦垂體分泌促性腺激素(gonadotropin, GtH)[69];在北極紅點(diǎn)鮭性成熟季節(jié), leptin mRNA在肝臟中保持較高的表達(dá)水平[18]。另有研究報(bào)道[70], leptin可影響魚(yú)類(lèi)的免疫系統(tǒng), 采用重組虹鱒 leptin和虹鱒白細(xì)胞共孵育后可激活STAT3(Signal transducer and activator of transcription 3, STAT3), NF-κB(nuclear factor kappa-light-chain-enhancer of activated B cells, NF-κB), 以及三個(gè)主要的 MAPK(mitogen-activated protein kinases, MAPK)級(jí)聯(lián)的信號(hào)通路(JNK, p38和 ERK); 并能減少虹鱒血液白細(xì)胞中超氧陰離子的量; 重組尼羅羅非魚(yú)(Tilapia nilotica)leptin-A 可增強(qiáng)羅非魚(yú)垂體催乳素的合成和釋放, 而垂體催乳素反過(guò)來(lái)也可抑制肝 leptin蛋白的合成和分泌, 推測(cè)這種相互調(diào)節(jié)作用在急性高滲適應(yīng)過(guò)程中對(duì)于動(dòng)員能量?jī)?chǔ)備是必要的[71]; Baltzegar等[72]在尼羅羅非魚(yú)的研究也提示 leptin-A可能在其急性高滲應(yīng)激中和皮質(zhì)醇共同起重要的調(diào)節(jié)作用。魏 赟[73]對(duì)斜帶石斑魚(yú)(Epinephelus coioides)兩種同源的瘦素基因(leptin-A, leptin-B)進(jìn)行了多態(tài)性研究, 并與斜帶石斑魚(yú)12個(gè)生長(zhǎng)性狀進(jìn)行關(guān)聯(lián)分析, 篩選出了4個(gè)與生長(zhǎng)性狀緊密相關(guān)的分子標(biāo)記。

4 展望

綜上所述, leptin是一種具有多功能的激素, 在能量代謝、繁殖以及適應(yīng)環(huán)境等方面發(fā)揮關(guān)鍵作用。雖然在魚(yú)類(lèi)中 leptin的研究已取得了一定的進(jìn)展,但仍有很多重要的問(wèn)題尚未解決, 如(1)魚(yú)類(lèi) leptin受體是否同時(shí)作為 leptin-A和 leptin-B的受體？或是受體下游的作用機(jī)制決定 leptin類(lèi)型？在魚(yú)的全基因組中是否尚有未知的 leptin受體？(2)魚(yú)類(lèi)leptin是否具有像哺乳動(dòng)物leptin在骨骼生成、甲狀腺功能以及血管生成等方面的作用？進(jìn)一步解析leptin在魚(yú)類(lèi)中的多種生理作用, 可為最終闡明影響脊椎動(dòng)物能量穩(wěn)態(tài)的 leptin系統(tǒng)的起源及進(jìn)化奠定新的理論基礎(chǔ)。

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BIOLOGICAL CHARACTERISTICS AND FUNCTIONS OF LEPTIN IN FISH

LU Rong-Hua1, SUN Jun-Jun1, LIANG Xu-Fang2, NIE Guo-Xing1and YANG Feng1
(1. College of Fisheries, Henan Normal University, Xinxiang 453007, China; 2. College of Fisheries, Huazhong Agricultural University, Shizishan Street 1, Wuhan 430070, China)

Leptin is the product of ob gene and a kind of Type I cytokine. It is primarily synthesized and secreted by adipocytes and plays an important role in the regulation of ingestion, energy metabolism, skeletal development, thyroid function, and reproduction in mammals. To date leptin gene has been cloned in various teleostean groups, and there have been studies of the physiological functions of leptin. Previous reports have suggested that fish leptin is mainly synthesized in liver, and the amino acid sequence is different from that in mammals; however, the protein structure is highly conservative. Because of its crucial roles in ingestion, glucose and lipid metabolism, and reproduction, Leptin is potentially a new drug target for improving the glucose utilization efficiency in fish in the future. Therefore in this review we discussed about fish leptin in terms of its structure, expression, functions, tissue-specific distribution and receptors.

Leptin; Fish; Biological characteristics; Appetite regulation; Energy metabolism

Q344+.1

A

1000-3207(2015)03-0583-07

10.7541/2015.76

2014-04-23;

2014-07-15

國(guó)家自然科學(xué)基金項(xiàng)目(31172420, 31402311); 河南省基礎(chǔ)與前沿技術(shù)研究計(jì)劃項(xiàng)目(142300410158)

盧榮華(1977—), 女, 河南虞城人; 博士; 主要研究方向?yàn)轸~(yú)類(lèi)糖脂代謝調(diào)控機(jī)理研究。E-mail: laoaiyika@hotmail.com

梁旭方, 教授; E-mail: xfliang@mail.hzau.edu.cn