魚類leptin的生物學特性及功能

盧榮華孫君君梁旭方聶國興楊 峰

(1. 河南師范大學水產學院, 新鄉 453007; 2. 華中農業大學水產學院, 武漢 430070)

魚類leptin的生物學特性及功能

盧榮華1孫君君1梁旭方2聶國興1楊 峰1

(1. 河南師范大學水產學院, 新鄉 453007; 2. 華中農業大學水產學院, 武漢 430070)

瘦素(Leptin)是肥胖基因(Obese gene)的產物, 屬于I型細胞因子。在哺乳動物中, leptin主要由脂肪細胞合成與分泌, 是調控攝食、能量代謝、骨骼發育、甲狀腺功能以及繁殖等生理過程的重要激素。目前, 多種硬骨魚類的leptin基因已被克隆, 其功能也已得到初步研究。研究認為, 魚類leptin的主要合成部位在肝臟, 其在氨基酸序列上與哺乳動物存在很大差異, 但蛋白質結構高度保守; 功能方面, leptin可調節魚類的攝食、葡萄糖和脂肪代謝以及繁殖等生命活動過程。本文就魚類leptin及其受體的特征結構、組織分布、表達調控及功能研究進展進行簡要綜述。

Leptin; 魚類; 生物學特性; 食欲調節; 能量代謝

1994年, Zhang等[1]首次分離出哺乳動物的肥胖基因(Obese gene), 瘦素(Leptin)即是肥胖基因的產物, 該名字起源于希臘語leptos意為“瘦的”, 其得名是由于研究發現缺失leptin會造成哺乳動物的肥胖。哺乳動物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]以及攝食中發揮重要作用, 被認為是機體的一種飽食因子[8—10]。與對陸生動物leptin的深入研究相比, 魚類leptin雖然也已引起學者們的關注, 但相關功能研究尚開展的不多。

1 Leptin及Leptin受體的結構與同源性分析

1.1 Leptin的結構, 拷貝數及同源性分析

Johnson等[11]首次通過鼠leptin抗體在藍綠鱗鰓太陽魚(Lepomis macrochirus)、虹鱒(Oncorhynchus mykiss)、大口黑鱸(Pomonix annularis)和斑點叉尾鲴(Ictalurus punctatus)中檢測到其血液、腦、心、肝中均存在leptin。日本學者Kurokawa等[12]通過基因組同線性方法從紅鰭東方鲀(Takifugu rubripes)等變溫動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(Danio rerio)[15]、大麻哈魚(Oncorhynchus keta)[16]、虹鱒[16]、草魚(Ctenopharyngodon idella)[17]、北極鮭(Salvelinus alpinus)[18]、大西洋鮭(Salmo salar)[19]、 鱸 (Morone saxatilis)[20]、 黃 顙 魚(Pelteobagrus fulvidraco)[21]和大黃魚[22]等魚類以及非洲爪蟾(Xenopus laevis)[23]、熱帶爪蟾(Xenopus tropicalis)[12,23]、寬虎紋鈍口螈(Ambystoma tigrinum)[24]等兩棲動物的leptin基因也被先后分離, 并在鯉[14]、草魚[17]、虹鱒[16,25]和 青 鳉(Oryzias latipes)[26]等部分物種中進行了相對深入的研究。

在非洲爪蟾和目前已知的多數魚類中, 肥胖基因由3個外顯子和2個內含子組成, 與人類的肥胖基因結構相似[1], 且內含子的相對位置高度保守[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個外顯子和 1個內含子(第 2個內含子), 它們的第1個內含子在進化過程中已丟失[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物以及非洲爪蟾的基因組中, 肥胖基因僅有一個拷貝, 編碼一種蛋白產物。然而最近的研究發現, 在斑馬魚、日本青 鳉和石斑魚(Epinephelus coioides)的基因組中存在2個肥胖基因拷貝, 編碼兩種不同的產物(分別命名為leptin-A型和leptin-B型)[13,15,30]。斑馬魚的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。因此魚類可能普遍存在兩種leptin亞型[13,15]。盡管先前的研究發現鯉中也存在兩種leptin轉錄本, 然而它們之間的氨基酸同源性高達84%,系統樹分析發現它們同聚于leptin-A進化分枝, 表明它們很可能同屬于leptin-A型, 這可能是由鯉(四倍體)在～16Mya發生的基因組加倍引起。系統樹分析和氨基酸同源性分析顯示, 目前分離得到的魚類leptin絕大部分屬于leptin-A型, 包括綠河豚(Tetraodon nigroviridis)[12]、虹鱒[16]、北極紅點鮭(Salvelinus alpinus)[18]、鰱(Hypophthalmichthys molitrix)和草魚[17]等, 在鯉及其他大部分魚類中很可能還存在leptin-B型[15]。兩種leptin亞型在魚類中的出現以及它們組織表達的差異, 可能賦予leptin新的功能。最新的研究發現, 某些種類如大西洋鮭的leptin甚至出現了多達四個亞型同源物(LepA1, LepA2, LepB1/B2)[31]。

Leptin的蛋白序列在哺乳動物中高度保守, 魚類及其他變溫動物leptin與哺乳動物leptin的氨基酸同源性卻很低(如河 鲀 、斑馬魚、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, 不同種屬魚類leptin之間的氨基酸同源性同樣很低(如 河鲀 與斑馬魚、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]。分析發現, 它們用于形成二硫鍵的半胱氨酸卻高度保守, 蛋白二級結構(4個α螺旋)也同樣高度保守, 而且三級結構預測表明它們之間的空間結構十分相似[12—17,23,24,27]。

1.2 Leptin受體的基因結構

人等哺乳動物的leptin受體(Leptin receptor, leptin-R)為單一拷貝, 但其可通過不同的剪接方式產生多達6種長度不同的轉錄本[32]。其中, 長型leptin-R在介導leptin的調控功能中起重要作用[32]。人的leptin-R含有20個外顯子, 非洲爪蟾的外顯子則多達26個[23]。目前, 已在海洋青鳉魚(Oryzias melastigma)[33]、 日本青 鳉[13]、 河 鲀[34]和草魚[35]等魚類中分離了leptin-R基因, 日本青鳉leptin-R基因含有20個外顯子[13], 河 鲀leptin-R基因則含有21個外顯子[34]。目前在非洲爪蟾中僅發現長型leptin-R一種類型,其他在哺乳動物中出現的5種類型至今未見報道。

2 Leptin及leptin受體的組織差異表達

2.1 Leptin的組織分布及分泌濃度

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

在正常生理狀態下, 人的血漿leptin濃度為0.2—0.3 nmol/L[28,29], 鼠類的血漿leptin濃度為0.09—0.3 nmol/L[37,38]。而Kling等[39]測定了多種魚類的血漿leptin濃度, 結果表明魚類的血漿leptin濃度為1.1—5 nmol/L, 比哺乳動物的血漿leptin濃度高。哺乳動物能依據血漿中的leptin濃度傳達體內脂肪含量信息給大腦, 進而指導攝食行為、代謝及生理內分泌, 使其與機體的營養狀況相一致[40]。上述leptin組織表達及分泌濃度的差異, 暗示魚類的leptin在功能及調節通路上可能與哺乳動物有較大差異。

2.2 Leptin受體的組織分布

不論在哺乳動物還是魚類中, leptin均通過其受體發揮調控攝食及能量平衡等功能[41—47]。哺乳動物長型leptin-R主要在下丘腦中表達[1,32,36], 小鼠缺乏leptin-R會因食欲過強導致肥胖[48]。海洋青鳉的leptin-R主要在鰓、脾臟、腎臟和肌肉中表達, 且雌性海洋青鳉leptin-R的表達量要高于雄性的[33]。薛俊蓮等[49]通過RT-PCR方法獲得鯽魚的leptin受體序列,并制備了鯽魚2個瘦素受體的多克隆抗體; 檢測了鯽魚組織和血清中的受體, 初步確定了鯽魚血清中存在可溶瘦素受體。

3 Leptin的功能

3.1 Leptin在調控攝食中的作用

用哺乳動物的 leptin在金魚體內通過腹腔和側腦室注射后顯示其攝食減少、體重下降以及調控攝食和能量代謝相關基因表達水平發生改變[50,51]。在鱸腹腔內注射人leptin也可抑制其攝食[20]。然而, 以哺乳動物 leptin處理銀大馬哈魚(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類 leptin的功能有關。目前在絕大多數魚類研究中發現 leptin具有抑制攝食的作用[16,17,25]。Murashita等[16]用重組虹鱒 leptin處理后發現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)基因表達并降低促食欲因子神經肽Y(neuropeptide Y, NPY)基因的表達水平。進一步研究發現重組鮭 leptin也可顯著抑制大西洋鮭的生長, 分析原因認為 leptin可能通過顯著提高 POMC-A1轉錄, 抑制食物攝入而導致生長減慢[55]。Li等[17]制備了草魚leptin蛋白,通過短期(1 d)和長期(13 d)腹腔注射實驗, 發現leptin短期處理可明顯抑制草魚的攝食、抑制 NPY等攝食相關基因的表達。在石斑魚中, 饑餓和再投喂實驗表明, Leptin-A在調節攝食和能量代謝中發揮重要作用[30]。

3.2 Leptin在調控糖脂代謝中的作用

在哺乳動物中leptin可抑制脂肪的沉積, 促進脂肪的水解[56—58]等, 還可通過影響動物下丘腦和后腦的葡萄糖感受性神經元的活性, 抑制促食欲肽(NPY, AgRP, Orexin)和激活厭食欲肽(POMC, CART, CCK)的表達[59—61]進而來調控其攝食行為, 并促進能量消耗。因此, leptin調節攝食的作用也與對葡萄糖的代謝調控交織在一起; 除中樞神經系統外, leptin還可直接調節外周組織器官, 促進肝臟葡萄糖生成, 調控肝臟磷酸烯醇丙酮酸羧激酶(Phosphoenolpyruvate carboxykinase, PEPCK)基因表達和糖異生效率[62], 通過乳酸攝取增加直接刺激肝糖原產生。leptin對PEPCK及糖異生的影響限制了甘油三酯的合成, 因而哺乳類leptin主要通過調控糖和脂代謝與攝食的偶聯來維持其體脂蓄積及機體能量代謝的穩定。

目前, 已有一些關于魚類 leptin對脂類代謝的研究, 如 leptin能增加太陽魚細胞內脂肪酸結合蛋白的量[54]; 重組草魚 leptin蛋白通過腹腔注射后,可促進脂代謝基因或能量代謝基因解偶聯蛋白2(Uncoupling protein 2, UCP2)、膽鹽活化的胰脂肪酶(Bile salt-activated lipase, BSAL)和脂肪酸延長酶(Fatty acid elongase, ELO)的基因表達, 這與虹鱒實驗中所得結果相似, 也與非洲爪蟾和哺乳動物的結果一致[17]; 筆者在草魚營養性肝細胞脂變模型中的研究結果也表明, leptin劑量依賴性促進甘油的釋放,并可影響9個脂肪代謝關鍵基因在轉錄和翻譯水平的表達, 且其誘導脂肪分解的作用是由 JAK-STAT信號通路來介導的[3]。

迄今為止, 已有研究發現魚類leptin和糖代謝(血糖變化)、饑餓及再投喂條件關系密切。在金魚腹腔內注射leptin后, 可引起肝糖原、肌糖原以及循環激素水平的變化[51,52]; 在虹鱒腦室注射leptin后可提高糖合成和分解過程中相關酶的含量, GK活性以及與糖代謝反應有關基因的mRNA水平, 研究還發現leptin作用后會引起血糖濃度升高[25]。Huising等[14]以鯉為模型, 研究發現攝食后其肝臟leptin mRNA表達量上升, 其峰值出現在血糖含量的升高和血漿游離脂肪酸下降之后, 這可能是因為其leptin表達量由攝食后血糖含量變化所控制。Gorissen等[15]證實斑馬魚在禁食一周后, 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。虹鱒在長期饑餓(3周)中, leptin的表達水平顯著升高[39]。在鱸中, 饑餓3周其肝中leptin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類leptin可激活糖代謝系統, 這與高血糖條件下觀察到的變化一致, 在魚類腦中增加或降低血糖水平[63,64]伴隨著GK的活性及其表達水平的變化、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物的糖代謝反應在某種程度上相類似[65]。

哺乳動物中的研究認為機體的血糖水平與攝食調節及能量平衡密切相關, 高血糖條件下食物的攝入被抑制[12]。而上述在絕大多數魚類研究中的結果顯示, 特異性的魚類leptin具有抑制魚類攝食的作用[16,17,25], 推測魚類leptin對攝食的調節也與對糖脂代謝的作用相偶聯, 即魚類leptin通過調節糖(血糖)及脂類代謝進而調節魚類的攝食及能量代謝的平衡。眾所周知, 魚類, 特別是肉食性魚類, 對高糖具有不耐受性[66,67], 而魚類的食性與leptin以及糖脂代謝是否存在更密切的關系, 尚需深入研究。

3.3 Leptin的其他作用

已有研究證實 leptin與硬骨魚類的繁殖活動密切相關。leptin及其受體在大西洋鮭和斑馬魚的腦(腦垂體)及性腺中表達很豐富[15,19,42]。Peyon等[68]報道重組鼠leptin對舌齒鱸(Dicentrarchus labrax)腦垂體中促黃體生成素(luteinizing hormone, LH)的產生有直接作用。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];在北極紅點鮭性成熟季節, leptin mRNA在肝臟中保持較高的表達水平[18]。另有研究報道[70], leptin可影響魚類的免疫系統, 采用重組虹鱒 leptin和虹鱒白細胞共孵育后可激活STAT3(Signal transducer and activator of transcription 3, STAT3), NF-κB(nuclear factor kappa-light-chain-enhancer of activated B cells, NF-κB), 以及三個主要的 MAPK(mitogen-activated protein kinases, MAPK)級聯的信號通路(JNK, p38和 ERK); 并能減少虹鱒血液白細胞中超氧陰離子的量; 重組尼羅羅非魚(Tilapia nilotica)leptin-A 可增強羅非魚垂體催乳素的合成和釋放, 而垂體催乳素反過來也可抑制肝 leptin蛋白的合成和分泌, 推測這種相互調節作用在急性高滲適應過程中對于動員能量儲備是必要的[71]; Baltzegar等[72]在尼羅羅非魚的研究也提示 leptin-A可能在其急性高滲應激中和皮質醇共同起重要的調節作用。魏 赟[73]對斜帶石斑魚(Epinephelus coioides)兩種同源的瘦素基因(leptin-A, leptin-B)進行了多態性研究, 并與斜帶石斑魚12個生長性狀進行關聯分析, 篩選出了4個與生長性狀緊密相關的分子標記。

4 展望

綜上所述, leptin是一種具有多功能的激素, 在能量代謝、繁殖以及適應環境等方面發揮關鍵作用。雖然在魚類中 leptin的研究已取得了一定的進展,但仍有很多重要的問題尚未解決, 如(1)魚類 leptin受體是否同時作為 leptin-A和 leptin-B的受體？或是受體下游的作用機制決定 leptin類型？在魚的全基因組中是否尚有未知的 leptin受體？(2)魚類leptin是否具有像哺乳動物leptin在骨骼生成、甲狀腺功能以及血管生成等方面的作用？進一步解析leptin在魚類中的多種生理作用, 可為最終闡明影響脊椎動物能量穩態的 leptin系統的起源及進化奠定新的理論基礎。

[1] Zhang Y, Proenca R, Maffei M, et al. Positional cloning of the mouse obese gene and its human homologue [J]. Nature, 1994, 372(6505): 425—432

[2] Havel P J. Update on adipocyte hormones: regulation of energy balance and carbohydrate/lipid metabolism [J]. Diabetes, 2004, 53: S143—S151

[3] Lu R H, Liang X F, Wang M, et al. The role of leptin in lipid metabolism in fatty degenerated hepatocytes of the grass carp Ctenopharyngodon idellus [J]. Fish Physiology and Biochemistry, 2012, 38(6): 1759—1774

[4] Elias C F, Purohit D. Leptin signaling and circuits in puberty and fertility [J]. Cellular and Molecular Life Sciences, 2013, 70(5): 841—862

[5] Zieba D A, Amstalden M, Williams G L. Regulatory roles of leptin in reproduction and metabolism: a comparative review [J]. Domestic Animal Endocrinology, 2005, 29(1): 166—185

[6] Fantuzzi G, Faggioni R. Leptin in the regulation of immunity, inflammation, and hematopoiesis [J]. Journal of Leukocyte Biology, 2000, 68(4): 437—446

[7] Myers Jr M G, Simerly R B. The neuroendocrinology and neuroscience of energy balance [J]. Frontiers in Neuroendocrinology, 2010, 31(1): 1—3

[8] Ahima R S, Osei S Y. Leptin signaling [J]. Physiology & Behavior, 2004, 81(2): 223—241

[9] Schwartz M W, Niswender K D. Adiposity signaling and biological defense against weight gain: absence of protection or central hormone resistance [J]? The Journal of Clinical Endocrinology and Metabolism, 2004, 89(12): 5889—5897

[10] Marty N, Dallaporta M, Thorens B. Brain glucose sensing, counteregulation, and energy homeostasis [J]. Physiology (Bethesda), 2007, 22: 241—251

[11] Johnson R M, Johnson T M, Londraville R L. Evidence for leptin expression in fishes [J]. Journal of Experimental Zoology, 2000, 286(7): 718—724

[12] Kurokawa T, Uji S, Suzuki T. Identification of cDNA coding for a homologue to mammalian leptin from pufferfish, Takifugu rubripes [J]. Peptides, 2005, 26(5): 745—750

[13] Kurokawa T, Murashita K. Genomic characterization of multiple leptin genes and a leptin receptor gene in theJapanese medaka, Oryzias latipes [J]. General and Comparative Endocrinology, 2009, 161(2): 229—237

[14] Huising M O, Geven E J, Kruiswijk C P, et al. Increased leptin expression in common carp (Cyprinus carpio) after food intake but not after fasting or feeding to satiation [J]. Endocrinology, 2006, 147(12): 5786—5797

[15] Gorissen M, Bernier N J, Nabuurs S B, et al. Two divergent leptin paralogues in zebrafish (Danio rerio) that originate early in teleostean evolution [J]. Journal of Endocrinology, 2009, 201(3): 329—339

[16] Murashita K, Uji S, Yamamoto T, et al. Production of recombinant leptin and its effects on food intake in rainbow trout (Oncorhynchus mykiss) [J]. Comparative Biochemistry and Physiology. Part B, Biochemistry & Molecular Biology, 2008, 150(4): 377—384

[17] Li G G, Liang X F, Xie Q L, et al. Gene structure, recombinant expression and functional characterization of grass carp leptin [J]. General and Comparative Endocrinology, 2010, 166(1): 117—127

[18] Fr?iland E, Murashita K, J?rgensen E H, et al. Leptin and ghrelin in anadromous Arctic charr: cloning and change in expressions during a seasonal feeding cycle [J]. General and Comparative Endocrinology, 2010, 165(1): 136—143

[19] R?nnestad I, Nilsen T O, Murashita K, et al. Leptin and leptin receptor genes in Atlantic salmon: cloning, phylogeny, tissue distribution and expression correlated to long-term feeding status [J]. General and Comparative Endocrinology, 2010, 168(1): 55—70

[20] Won E T, Baltzegar D A, Picha M E, et al. Cloning and characterization of leptin in a Perciform fish, the striped bass (Morone saxatilis): control of feeding and regulation by nutritional state [J]. General and Comparative Endocrinology, 2012, 178(1): 98—107

[21] Gong Y, Luo Z, Zhu Q L, et al. Characterization and tissue distribution of leptin, leptin receptor and leptin receptor overlapping transcript genes in yellow catfish Pelteobagrus fulvidraco [J]. General and Comparative Endocrinology, 2013, 182: 1—6

[22] Cui W T. Cloning and distribution of three kinds of gastrointestinal peptide cDNA in large yellow croaker (Pseudosciaena crocea) [D]. Thesis for Master of Science. Zhejiang Ocean University, Zhengjiang. 2013 [崔文濤. 大黃魚三種胃腸肽基因的克隆及表達特性研究. 碩士學位論文, 浙江海洋學院, 浙江. 2013]

[23] Crespi E J, Denver R J. Leptin (ob gene) of the South African clawed frog Xenopus laevis [J]. Proceedings of the National Academy of Sciences of the United States of America, 2006, 103(26): 10092—10097

[24] Boswell T, Dunn I C, Wilson P W, et al. Identification of a non-mammalian leptin-like gene: characterization and expression in the tiger salamander (Ambystoma tigrinum) [J]. General and Comparative Endocrinology, 2006, 146(2): 157—166

[25] Aguilara A J, Marta C S, Marcos A, et al. Central leptin treatment modulates brain glucosensing function and peripheral energy metabolism of rainbow trout [J]. Peptides, 2010, 31(6): 1044—1054

[26] Chisada S, Kurokawa T, Murashita K, et al. Leptin receptor-deficient (knockout) medaka, Oryzias latipes, show chronical up-regulated levels of orexigenic neuropeptides, elevated food intake and stage specific effects on growth and fat allocation [J]. General and Comparative Endocrinology, 2014, 195: 9—20

[27] Yacobovitz M, Solomon G, Gusakovsky E E, et al. Purification and characterization of recombinant pufferfish (Takifugu rubripes) leptin [J]. General and Comparative Endocrinology, 2008, 156(1): 83—90

[28] Klein S, Fontana L, Young V L, et al. Absence of an effect of liposuction on insulin action and risk factors for coronary heart disease [J]. New England Journal of Medicine, 2004, 350: 2549—2557

[29] Shek E W, Brands M W, Hall J E. Chronic leptin infusion increases arterial pressure [J]. Hypertension, 1998, 31(1 Pt 2): 409—414

[30] Zhang H, Chen H, Zhang Y, et al. Molecular cloning, characterization and expression profiles of multiple leptin genes and a leptin receptor gene in orange-spotted grouper (Epinephelus coioides) [J]. General and Comparative Endocrinology, 2013, 181: 295—305

[31] Angotzi A R, Stefansson S O, Nilsen T O, et al. Molecular cloning and genomic characterization of novel leptin-like genes in salmonids provide new insight into the evolution of the leptin gene family [J]. General and Comparative Endocrinology, 2013, 187: 48—59

[32] Houseknecht K L, Portocarrero C P. Leptin and its receptors: regulators of whole-body energy homeostasis [J]. Domestic Animal Endocrinology, 1998, 15(6): 457—475

[33] Wong M, Yu R, Ng P, et al. Characterization of a hypoxia-responsive leptin receptor (omLepRL) cDNA from the marine medaka (Oryzias melastigma) [J]. Marine Pollution Bulletin, 2007, 54(6): 792—819

[34] Kurokawa T T, Murashita K, Suzuki T, et al. Genomic characterization and tissue distribution of leptin receptor and leptin receptor overlapping transcript genes in the pufferfish, Takifugu rubripes [J]. General and Comparative Endocrinology, 2008, 158(1): 108—114

[35] Wu X F, Li X Q, Leng X J, et al. Cloning and tissue expression analysis of the leptin receptor gene fragment sequence in grass carp (Ctenopharyngodon idella) [J]. Biotechnology Bulletin, 2011, 11: 118—124 [吳小鳳, 李小勤, 冷向軍, 等. 草魚瘦素受體基因片段序列的克隆及其組織表達分析. 生物技術通報, 2011, 11: 118—124]

[36] Magni P, Motta M, Martini L. Leptin: a possible link between food intake, energy expenditure, and reproductivefunction [J]. Regulatory Peptides, 2000, 92(1—3): 51—56

[37] Chehab F F, Mounzih K, Lu R, et al. Early onset of reproductive function in normal female mice treated with leptin [J]. Science, 1997, 275(3): 88—90

[38] Halaas J L, Boozer C, Blair-West J, et al. Physiological response to long-term peripheral and central leptin infusion in lean and obese mice [J]. Proceedings of the National Academy of Sciences of the United States of America, 1997, 94(1): 8878—8883

[39] Kling P, Ronnestad I, Stefansson S O, et al. A homologous salmonid leptin radioimmunoassay indicates elevated plasma leptin levels during fasting of rainbow trout [J]. General and Comparative Endocrinology, 2009, 62(3): 307—312

[40] Frühbeck G, Jebb S A, Prentice A M. Leptin: physiology and pathophysiology [J]. Clinical Physiology, 1998, 18(5): 399—419

[41] Ahima R S. Adipose tissue as an endocrine organ [J]. Obesity (Silver Spring), 2006, 14(5): 242S—249S

[42] Liu Q, Chen Y, Copeland D, et al. Expression of leptin receptor gene in developing and adult zebrafish [J]. General and Comparative Endocrinology, 2010, 166(2): 346—355

[43] Fuentes E N, Kling P, Einarsdottir I E, et al. Plasma leptin and growth hormone levels in the fine flounder (Paralichthys adspersus) increase gradually during fasting and decline rapidly after refeeding [J]. General and Comparative Endocrinology, 2012, 177(1): 120—127

[44] Kling P, Jonsson E, Nilsen, T O, et al. The role of growth hormone in growth, lipid homeostasis, energy utilization and partitioning in rainbow trout: interactions with leptin, ghrelin and insulin-like growth factor I [J]. General and Comparative Endocrinology, 2012, 175(1): 153—162

[45] Piccinetti C C, Migliarini B, Olivotto I, et al. Appetite regulation: the central role of melatonin in Danio rerio [J]. Hormones and Behavior, 2010, 58(5): 780—785

[46] Prokop J W, Duff R J, Ball H C, et al. Leptin and leptin receptor: analysis of a structure to function relationship in interaction and evolution from humans to fish [J]. Peptides, 2012, 38(2): 326—336

[47] Trombley S, Maugars G, Kling P, et al. Effects of long-term restricted feeding on plasma leptin, hepatic leptin expression and leptin receptor expression in juvenile Atlantic salmon (Salmo salar L.) [J]. General and Comparative Endocrinology, 2012, 175(1): 92—99

[48] Hummel K P, Dickie M M, Coleman D L. Diabetes, a new mutation in the mouse [J]. Science, 1966, 153 (3740): 1127—1128

[49] Xue J L. The identification of the soluble leptin receptor in crucian carp [D]. Thesis for Master of Science. Zhejiang Normal University. Zhengjiang. 2013 [薛俊蓮. 鯽魚血清中可溶性瘦素受體的檢測. 碩士學位論文, 浙江師范大學,浙江. 2013]

[50] Volkoff H, Eykelbosh A J, Peter R E. Role of leptin in the control of feeding of goldfish Carassius auratus: interactions with cholecystokinin, neuropeptide Y and orexin A, and modulation by fasting [J]. Brain Research, 2003, 972(1—2): 90—109

[51] De Pedro N, Martinez-Alvarez R, Delgado M J. Acute and chronic leptin reduces food intake and bodyweight in goldfish (Carassius auratus) [J]. Journal of Endocrinology, 2006, 188(3): 513—520

[52] Baker D M, Larsen D A, Swanson P, et al. Long-term peripheral treatment of immature coho salmon (Oncorhynchus kisutch) with human leptin has no clear physiologic effect [J]. General and Comparative Endocrinology, 2000, 118(1): 134—138

[53] Silverstein J T, Plisetskaya E M. The effects of NPY and insulin on food intake regulation in fish [J]. American Zoologist, 2000, 40(2): 296—308

[54] Londraville R L, Duball C S. Murine leptin injections increase intracellular fatty acid-binding protein in green sunfish (Lepomis cyanellus) [J]. General and Comparative Endocrinology, 2002, 129(1): 56—62

[55] Murashita K, Jordal A E, Nilsen T O, et al. Leptin reduces Atlantic salmon growth through the central pro-opiomelanocortin pathway [J]. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2011, 158(1): 79—86

[56] Fruhbeck G, Aguado M, Martinez J A. In vitro lipolytic effect of leptin on mouse adipocytes: evidence for a possible autocrine/paracrine role of leptin [J]. Biochemical and Biophysical Research Communications, 1997, 240(3): 590—594

[57] Siegrist-Kaiser C A, Pauli V, Juge-Aubry C E, et al. Direct effects of leptin on brown and white adipose tissue [J]. Journal of Clinical Investigation, 1997, 100(11): 2858—2864

[58] Sarmiento U, Benson B, Kaufman S, et al. Morphologic and molecular changes induced by recombinant human leptin in the white and brown adipose tissues of C57BL/6 mice [J]. Lab Investigation, 1997, 77(3): 243—256

[59] Morton G J, Cummings D E, Baskin D G, et al. Central nervous system control of food in take and body weight [J]. Nature, 2006, 443(7109): 289—295

[60] Duan J, Choi Y H, Hartzell D, et al. Effects of subcutaneous leptin injections on hypothalamic gene profiles in lean and ob/ob mice [J]. Obesity, 2007, 15(11): 2624—2633

[61] Volkoff H, Peter R E. Characterization of two forms of cocaine-and amphetamine-regulated transcript (CART) peptide precursors in goldfish: molecular cloning and distribution, modulation of expression by nutritional status, and interactions with leptin [J]. Endocrinology, 2001, 142(12): 5076—5088

[62] Ookuma M, Ookuma K, York D A. Effects of leptin on insulin secretion from isolated rat pancreatic islets [J].Diabetes, 1998, 47(2): 219—223

[63] Polakof S, Míguez J M, Soengas J L. Changes in food intake and glucosensing function of hypothalamus and hindbrain in rainbow trout subjected to hyperglycemic or hypoglycemic conditions [J]. Journal of Comparative Physiology A, 2008, 194(9): 829—839

[64] Polakof S, Míguez J M, Soengas J L. Dietary carbohydrates induce changes in glucosensing capacity and food intake in rainbow trout [J]. American Journal of Physiology, 2008, 295(2): R478—R489

[65] Marty N, Dallaporta M, Thorens B. Brain glucose sensing, counteregulation, and energy homeostasis [J]. Physiology (Bethesda), 2007, 22: 241—251

[66] Wilson R P. Utilization of dietary carbohydrate by fish [J]. Aquaculture, 1994, 124(1—4): 67—80

[67] Moon T W. Glucose intolerance in teleost fish: fact or fiction [J]? Comparative Biochemistry and Physiology Part B, 2001, 129(2—3): 243—249

[68] Peyon P, Zanuy S, Carrillo M. Action of leptin on in vitro luteinizing hormone release in the European sea bass (Dicentrarchus labrax) [J]. Biology of Reproduction, 2001, 65(5): 1573—1578

[69] Weil C, Le Bail P Y, Sabin N, et al. In vitro action of leptin on FSH and LH production in rainbow trout (Onchorynchus mykiss) at different stages of the sexual cycle [J]. General and Comparative Endocrinology, 2003, 130(1): 2—12

[70] Mariano G, Stilo R, Terrazzano G, et al. Effects of recombinant trout leptin in superoxide production and NF-κB/MAPK phosphorylation in blood leukocytes [J]. Peptides, 2013, 48: 59—69

[71] Douros J D, Baltzegar D A, Breves J P, et al. Prolactin is a major inhibitor of hepatic Leptin A synthesis and secretion: studies utilizing a homologous Leptin A ELISA in the tilapia [J]. General and Comparative Endocrinology, 2014, 207: 86—93

[72] Baltzegar D A, Reading B J, Douros J D, et al. Role for leptin in promoting glucose mobilization during acute hyperosmotic stress in teleost fishes [J]. Journal of Endocrinology, 2014, 220(1): 61—72

[73] Wei Y. Polymorphisms of leptin genes associatied with growth traits in orange-spotted grouper (Epinephelus coioides) [D]. Thesis for Master of Science. Hainan University, Hainan. 2013 [ 赟魏 . 斜帶石斑魚瘦素基因多態性與生長性狀相關性分析. 碩士學位論文, 海南大學, 海南. 2013]

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

國家自然科學基金項目(31172420, 31402311); 河南省基礎與前沿技術研究計劃項目(142300410158)

盧榮華(1977—), 女, 河南虞城人; 博士; 主要研究方向為魚類糖脂代謝調控機理研究。E-mail: laoaiyika@hotmail.com

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