皮膚橋蛋白與骨形成的研究進(jìn)展

王效杰

(沈陽醫(yī)學(xué)院基礎(chǔ)醫(yī)學(xué)院人體解剖學(xué)教研室，遼寧沈陽110034)

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皮膚橋蛋白與骨形成的研究進(jìn)展

王效杰

(沈陽醫(yī)學(xué)院基礎(chǔ)醫(yī)學(xué)院人體解剖學(xué)教研室，遼寧沈陽110034)

摘要皮膚橋蛋白(dermatopontin,DPT)是富有酪氨酸殘基的酸性蛋白,是一種重要的細(xì)胞外基質(zhì)蛋白。研究發(fā)現(xiàn)DPT可以通過多種途徑影響骨的形成，并且在骨組織的損傷修復(fù)過程中起重要作用。目前已經(jīng)有研究表明DPT可以與維生素D受體、Ⅰ型膠原蛋白、轉(zhuǎn)化生長因子等分子的相互作用調(diào)控骨組織的發(fā)生與發(fā)展。因此，研究DPT與骨組織的關(guān)系，對(duì)組織工程學(xué)的發(fā)展至關(guān)重要。本文綜述了DPT對(duì)骨組織發(fā)生、發(fā)展過程中關(guān)鍵分子蛋白的影響，進(jìn)而揭示其存在的潛在機(jī)制。

關(guān)鍵詞皮膚橋蛋白；維生素D受體；Ⅰ型膠原蛋白；骨形成

皮膚橋蛋白(dermatopontin，DPT)作為細(xì)胞外基質(zhì)(extracellular matrix，ECM)中的非膠原蛋白，分子量為22 kDa，最初是在提純牛皮膚的核心蛋白多糖實(shí)驗(yàn)中被發(fā)現(xiàn)的[1]。DPT是富含酪氨酸殘基的酸性蛋白，并被證實(shí)其中約一半的酪氨酸殘基被硫酸化。這種硫酸化的酪氨酸，在ECM蛋白間的相互作用中至關(guān)重要[2]。DPT在ECM非膠原蛋白中所占比例非常高，然而DPT的功能至今尚未完全闡明。研究發(fā)現(xiàn)DPT在上皮細(xì)胞中作為多功能黏附分子存在[3-4]；DPT在一些腫瘤中的表達(dá)量下調(diào)[2,5]；DPT在維持皮膚彈性和膠原蛋白聚集中起重要作用[6]。

骨組織擁有礦化的ECM，與組織相連接，為身體提供支撐并且影響鈣離子與磷酸鹽的代謝。成骨細(xì)胞在成骨過程中分泌ECM，隨后形成羥基磷灰石晶體參與成骨。同時(shí)大型多核破骨細(xì)胞在骨吸收中發(fā)揮積極作用。骨形成與骨吸收，即骨代謝，這一過程受局部與全身因素的調(diào)節(jié)[7]。越來越多的證據(jù)表明：在人體的生長、衰老與病變的過程中骨組織與體內(nèi)其他器官存在著一定的相互作用：成骨細(xì)胞分泌羧基化的骨鈣素可以促進(jìn)胰島β細(xì)胞分泌胰島素進(jìn)而調(diào)節(jié)能量代謝[8]。脂肪來源的激素瘦素作用于其特定的下丘腦受體，增加交感神經(jīng)在骨中的活性，并發(fā)揮抗成骨作用[9]。由嗜鉻細(xì)胞分泌的5-羥色胺結(jié)合前體成骨細(xì)胞中的5-羥色胺受體進(jìn)而抑制其增殖[10]。因此在這一領(lǐng)域?qū)Τ晒羌?xì)胞生物學(xué)功能與信號(hào)轉(zhuǎn)導(dǎo)通路的研究具有重要意義。

1DPT對(duì)維生素D受體(vitamin D receptor，VDR)的影響

在成骨細(xì)胞VDR的表達(dá)可以被甲狀旁腺激素、糖皮質(zhì)激素轉(zhuǎn)化生長因子-β和表皮生長因子所調(diào)控，同時(shí)也被其配體1,25-二羥維生素D3(1,25-dihydroxy vitamin D3，1,25D3)自身所調(diào)控[11]。VDR的表達(dá)直接決定了1,25D3對(duì)成骨細(xì)胞增殖與分化的促進(jìn)作用。在很多對(duì)人類成骨細(xì)胞與骨髓間充質(zhì)干細(xì)胞(mesenchymal stem cells，MSC)的研究中表明：1,25D3可以促進(jìn)骨形成與礦化[12-16]。1,25D3不直接參與礦物質(zhì)沉積的這一過程，它更傾向?yàn)榈V化提供一個(gè)外環(huán)境于ECM中。1,25D3調(diào)控成骨細(xì)胞分化標(biāo)記蛋白堿性磷酸酶(alkaline phosphatase，ALP)[17]和各種骨ECM蛋白：如膠原蛋白A1、Ⅰ型前膠原蛋白等[18]。有研究表明缺乏VDR基因的小鼠表現(xiàn)生長延遲，嚴(yán)重的骨缺損，免疫異常，且在15周齡時(shí)，過早死于低鈣血癥[19]。有報(bào)道提示DPT對(duì)骨形成過程存在一定的影響[20]，進(jìn)一步的研究表明DPT可以被視為VDR的一個(gè)下游靶基因，當(dāng)VDR基因過表達(dá)時(shí)可導(dǎo)致DPT蛋白的表達(dá)量上調(diào)，因此，抑制DPT表達(dá)可以抑制MSC的成骨分化[21]。

2DPT與Ⅰ型膠原蛋白的關(guān)系

Ⅰ型膠原蛋白是ECM的重要組成部分，它的聚集是纖維化過程的標(biāo)志。盡管Ⅰ型膠原蛋白在大多數(shù)組織與器官中均有表達(dá)，但其僅僅由成骨細(xì)胞、成牙本質(zhì)細(xì)胞、成纖維細(xì)胞合成分泌[22]。MacBeath等[23]于1994年報(bào)道豬DPT同系物影響膠原原纖維的形成：在膠原溶液中添加低濃度的DPT(20 μg/ml)，原纖維形成加速，這種DPT對(duì)膠原原纖維形成的影響，伴隨著短暫的時(shí)間滯后性，并且在膠原溶液冷卻后延遲纖維的解聚。由于DPT可以影響膠原原纖維的合成，我們可以合理地推斷DPT通過與膠原分子相互作用進(jìn)而調(diào)節(jié)纖維的合成過程。然而，我們并沒有發(fā)現(xiàn)它們之間的作用位點(diǎn)。經(jīng)過一系列的實(shí)驗(yàn)證明DPT與固態(tài)的膠原蛋白之間存在著一定的劑量依賴關(guān)系，并且Ⅰ型膠原蛋白的α1與α2雙鏈與DPT之間的相互作用幾乎相同[4]。這種DPT對(duì)Ⅰ型膠原蛋白的作用可能是通過特定的氨基酸序列。體外研究發(fā)現(xiàn)，Ⅰ型膠原蛋白分別通過調(diào)節(jié)ERK信號(hào)通路影響骨橋蛋白(osteopontin，OPN)的表達(dá)情況；調(diào)控FAK信號(hào)通路改變ALP的表達(dá)[24]。ALP與OPN均為骨形成的經(jīng)典標(biāo)志物，因此DPT/Collagen Ⅰ/ERK/FAK信號(hào)轉(zhuǎn)導(dǎo)通路在骨的形成與骨損傷修復(fù)過程中有重要意義。綜上所述，DPT參與膠原纖維的合成過程，但其與Ⅰ型膠原蛋白相互作用的具體機(jī)制尚為完全闡明。

3DPT與轉(zhuǎn)化生長因子β(transforming growth factor-β，TGF-β)

DPT作為ECM的重要組成部分，它具有上調(diào)TGF-β生物活性的能力[25]。TGF-β長期以來被視為骨細(xì)胞的趨化因子，在骨的損傷與修復(fù)過程中，骨細(xì)胞會(huì)沿著有損傷的骨組織與血小板釋放的，呈梯度分布的TGF-β因子向創(chuàng)面遷移[26]。TGF-β通過刺激骨祖細(xì)胞分化與促進(jìn)細(xì)胞周期抑制劑p57Kip2的降解促使成骨細(xì)胞的數(shù)量增加[27]。TGF-β調(diào)節(jié)骨基質(zhì)蛋白和蛋白酶的合成，包括ALP、Ⅰ型膠原蛋白、骨鈣素(osteocalcin，OCN)、OPN和基質(zhì)金屬蛋白酶13(matrix metalloproteinase，MMP13)[28]。在小鼠實(shí)驗(yàn)?zāi)Ｐ椭?，?dǎo)致低骨密度表型的直接原因是TGF-β通路信號(hào)增強(qiáng)(通過TGF-β配體的過表達(dá))，同樣這種現(xiàn)象也可以被逆轉(zhuǎn)(通過沉默影響TGF-β的關(guān)鍵基因Smad3)[29]。這些小鼠模型清楚地說明在骨改建過程中成骨細(xì)胞和破骨細(xì)胞活性與TGF-β之間的相互作用，以及對(duì)骨質(zhì)量的影響[30]。這樣來看DPT作為TGF-β的結(jié)合蛋白之一，在成骨過程中尤為關(guān)鍵。

4DPT與核心糖蛋白(decoirn，DCN)

DPT與DCN同為ECM的重要組成部分，DCN由一個(gè)DS鏈與一個(gè)核心蛋白構(gòu)成。DCN是抗黏附蛋白，通過結(jié)合DPT抑制其細(xì)胞黏附活性[4]。在體外培養(yǎng)人骨髓瘤細(xì)胞的實(shí)驗(yàn)中發(fā)現(xiàn)，DCN通過上調(diào)p21并且誘導(dǎo)細(xì)胞凋亡進(jìn)而抑制人骨髓瘤細(xì)胞的生長。進(jìn)一步實(shí)驗(yàn)利用慢病毒轉(zhuǎn)染在MSC細(xì)胞中過表達(dá)DCN基因，通過實(shí)驗(yàn)檢測(cè)發(fā)現(xiàn)，DCN可以為MSC細(xì)胞與成骨細(xì)胞提供適宜生長的細(xì)胞微環(huán)境，并且具有抗骨髓瘤細(xì)胞生長的作用[31]。在大鼠牙槽骨損傷修復(fù)過程中，ECM蛋白參與功能性組織的形成。45～50 kDa富含亮氨酸重復(fù)序列的核蛋白DCN是這一過程的關(guān)鍵蛋白[32]。DCN可以調(diào)節(jié)膠原原纖維的形成[33]，與生長因子如TGF-β、TNF-α相互作用[34-35]，并且調(diào)節(jié)羥基磷灰石的形成與生長發(fā)育[36]。我們推測(cè)DCN與DPT在ECM中是以復(fù)合體的形式存在，DCN與DPT對(duì)骨形成的調(diào)節(jié)，以及對(duì)成骨細(xì)胞生物活性的影響仍需要更進(jìn)一步的研究。

5小結(jié)與展望

DPT廣泛存在于ECM中，可以與VDR、膠原原纖維、DCN、TGF-β等信號(hào)因子相互作用調(diào)節(jié)骨形成與骨損傷的修復(fù)。然而，DPT直接或間接調(diào)控其他細(xì)胞轉(zhuǎn)導(dǎo)通路的基質(zhì)尚未闡明。進(jìn)一步研究DPT對(duì)成骨細(xì)胞生物活性的影響為組織工程學(xué)開創(chuàng)新的思路。

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Research Progress in Dermatopontin and Bone Formation

WANG Xiaojie

(Department of Anatomy,Shenyang Medical College,Shenyang 110034,China)

AbstractDermatopontin(DPT)is an acidic protein,rich in tyrosine residues.It is an important extracellular matrix protein.DPT can affect bone formation in many ways,and plays an important role in injury and repairing process of bone tissue.DPT can regulate the occurrence and development of bone tissue through the interaction with vitamin D receptor,collagen I,transforming growth factor etc.So it is important to study the relationship between DPT and bone tissue for the development of tissue engineering.The effect of DPT on the key proteins in the development of bone tissue are summarized and reveal the potential mechanism.

Key wordsdermatopontin;vitamin D receptor;collagen I;bone formation

通訊作者夏書月(1962—)，女(漢)，教授，主任醫(yī)師，研究方向：慢性阻塞性肺疾病與肺血栓栓塞性疾病的基礎(chǔ)與臨床研究.E-mail：syx262@126.com

收稿日期2015-10-13

doi:10.3969/j.issn.1008-2344.2015.04.002

中圖分類號(hào)R34

文獻(xiàn)標(biāo)識(shí)碼A

文章編號(hào)1008-2344(2015)04-0197-03

基金項(xiàng)目沈陽市科技局計(jì)劃項(xiàng)目(No.F-13-221-9-33)