陳 園 楊華瑞 陳江水 鮑同柱

(三峽大學(xué)第一臨床醫(yī)學(xué)院骨科，湖北 宜昌 443003)

軟骨組織工程主要通過(guò)對(duì)軟骨種子細(xì)胞、軟骨支架、細(xì)胞因子的研究，來(lái)解決修復(fù)關(guān)節(jié)軟骨損傷、退變這一難題〔1〕。多肽生長(zhǎng)因子如轉(zhuǎn)化生長(zhǎng)因子(TGF)-β、骨形態(tài)發(fā)生蛋白(BMP)、甲狀旁腺相關(guān)蛋白(PTHrP)、成纖維細(xì)胞生長(zhǎng)因子(FGF)等對(duì)關(guān)節(jié)軟骨的內(nèi)環(huán)境穩(wěn)態(tài)及修復(fù)起十分重要作用。經(jīng)典的FGF信號(hào)通路包含18個(gè)信號(hào)蛋白與4個(gè)酪氨酸激酶分子蛋白受體(FGFRs)〔2〕。在胚胎發(fā)育時(shí)期FGFs在大多數(shù)組織中差異表達(dá)，在器官形成與功能發(fā)育的早期階段具有重要調(diào)節(jié)作用。在成年個(gè)體不同組織中，F(xiàn)GFs主要承擔(dān)調(diào)節(jié)生長(zhǎng)與組織修復(fù)再生的作用。目前FGF-2、FGF-18等在調(diào)節(jié)軟骨細(xì)胞分化、維持關(guān)節(jié)軟骨內(nèi)環(huán)境穩(wěn)態(tài)及促進(jìn)骨關(guān)節(jié)炎(OA)發(fā)生發(fā)展中起重要作用。本文總結(jié)以上細(xì)胞因子在關(guān)節(jié)軟骨中的作用。

1 FGF-2

FGF-2來(lái)源于關(guān)節(jié)軟骨細(xì)胞外基質(zhì)中的一種硫酸乙酰肝素蛋白多糖,目前FGF-2 對(duì)軟骨代謝的具體作用仍存在爭(zhēng)議〔3〕。人骨髓間充質(zhì)干細(xì)胞(hMSC)屬于多能干細(xì)胞，具有增殖與分化能力。在hMSC分化時(shí)期單獨(dú)給予FGF-2，可增強(qiáng)hMSC的增殖能力，并延緩細(xì)胞的衰老，促進(jìn)hMSC向軟骨細(xì)胞分化〔4，5〕。研究發(fā)現(xiàn)FGF-2可選擇性地激活FGFR1，通過(guò)上調(diào)基質(zhì)金屬蛋白酶(MMPs)，抑制細(xì)胞外基質(zhì)(ECM)積累和蛋白多糖合成，產(chǎn)生分解代謝的作用，最終表現(xiàn)出骨關(guān)節(jié)炎樣特征〔6〕。體內(nèi)和體外的實(shí)驗(yàn)中發(fā)現(xiàn)，F(xiàn)GF-2引起軟骨外植體蛋白多糖耗竭，并抑制蛋白多糖在關(guān)節(jié)軟骨細(xì)胞的長(zhǎng)期蓄積。而且，F(xiàn)GF-2有力地拮抗骨形態(tài)發(fā)生蛋白(BMP)-7和胰島素樣生長(zhǎng)因子(IGF)-1介導(dǎo)的人關(guān)節(jié)軟骨中的蛋白多糖的生產(chǎn)。FGF-2也抑制了蛋白聚糖聚集的基因，并能促進(jìn)蛋白聚糖酶蛋白聚糖酶(ADAMTS)-5、腫瘤壞死因子(TNF)受體的表達(dá)〔7,8〕。人關(guān)節(jié)軟骨細(xì)胞表達(dá)FGFR的所有亞型(FGFR1～4)。Yan等〔8〕發(fā)現(xiàn)，F(xiàn)GF-2 對(duì)FGFR1和FGFR3激活顯著高于FGFR2和FGFR4， 并且由FGFR1介導(dǎo)進(jìn)行分解代謝活動(dòng)。FGF-2與FGFR1結(jié)合后導(dǎo)致受體磷酸化，從而激活兩個(gè)關(guān)鍵信號(hào)傳導(dǎo)介質(zhì)Ras和蛋白激酶(PK)Cδ表達(dá)增加，隨后這些分子的信號(hào)整合到Raf-絲裂原活化蛋白激酶(MAPK)/2-細(xì)胞外信號(hào)調(diào)節(jié)激酶(ERK)1/2的級(jí)聯(lián)調(diào)控靶基因表達(dá)〔9〕。與此同時(shí)，PKCδ還激活p38和C-J終端激酶(JNK)途徑〔10〕。ERK，p38和JNK是MAPK的3個(gè)亞組，三者的轉(zhuǎn)錄因子匯合于ELK-1而激活MMP-13，最終促進(jìn)軟骨退化〔11〕。在人源T/C-28a2細(xì)胞中， FGF-2通過(guò)激活PI3-K/AKT和p38通路，上調(diào)MMP-1的表達(dá)〔12〕。FGF-2信號(hào)也導(dǎo)致激活蛋白(AP)-1和Runt相關(guān)轉(zhuǎn)錄因子(RUNX)2參與ADAMTS-5誘導(dǎo)的活化人類的OA細(xì)胞與健康的細(xì)胞相比，F(xiàn)GFR1的表達(dá)增加伴隨著FGFR3的表達(dá)受到抑制〔7〕。相對(duì)于FGF-2在人軟骨組織中的誘導(dǎo)代謝作用，F(xiàn)GF-2在其他動(dòng)物關(guān)節(jié)軟骨中則表現(xiàn)出相反的作用。研究發(fā)現(xiàn)，在缺乏FGF-2的小鼠軟骨中，可加速自發(fā)或手術(shù)誘導(dǎo)的關(guān)節(jié)炎的發(fā)展，給予重組FGF-2后可得到明顯緩解〔13〕。FGF-2可促進(jìn)蛋白多糖在小鼠股骨和脛骨軟骨的沉積。與人類FGFR1高表達(dá)相反，局部注入FGF-2明顯誘發(fā)FGFR3表達(dá)。

Weng等〔14〕使用FGFR1條件基因敲除小鼠證明，缺乏FGFR1可延緩軟骨退化并發(fā)現(xiàn)FGFR1 敲除對(duì)關(guān)節(jié)軟骨的保護(hù)作用與MMP-13 表達(dá)降低相關(guān)聯(lián)。對(duì)兔軟骨的研究發(fā)現(xiàn)，軟骨缺損早期修復(fù)過(guò)程中FGF-2的mRNA表達(dá)明顯增加，當(dāng)MSC分化成軟骨細(xì)胞后，則無(wú)法檢測(cè)出FGF-2的活性，因此推測(cè)FGF-2在MSC向軟骨分化中可能扮演了重要的角色〔15〕。Argün等〔16〕利用骨膜移植術(shù)及注射重組FGF-2成功修復(fù)了兔關(guān)節(jié)軟骨全層缺損。通過(guò)FGF-2刺激成年牛關(guān)節(jié)軟骨細(xì)胞增殖，使SOX9上調(diào)，ECM生成增多〔17〕。綜上，F(xiàn)GF-2在軟骨代謝方面的作用有物種差別。

2 FGF-18

FGF-18與FGF-8、FGF-17屬于同一個(gè)亞家族，其編碼基因位于染色體5q34上。FGF-18由207個(gè)氨基酸組成，分子質(zhì)量約為23 kD。敲除小鼠胚胎FGF-18基因后，可觀察到成骨間充質(zhì)細(xì)胞增殖減少，軟骨細(xì)胞增殖分化增加。因此推測(cè)FGF-18在胚胎軟骨發(fā)育中起負(fù)向調(diào)節(jié)作用〔18〕。然而在成熟個(gè)體中， FGF-18是著名的合成代謝因子，可促進(jìn)軟骨細(xì)胞增殖并參與軟骨的形成與損傷軟骨的修復(fù)。靜脈注射FGF-18至大鼠體內(nèi)觀察2 w后，發(fā)現(xiàn)關(guān)節(jié)、氣管等多處軟骨增生〔19〕。通過(guò)手術(shù)制造小鼠半月板撕裂的OA模型，造模后21 d給予FGF-18表現(xiàn)出軟骨增殖，并隨劑量呈遞增關(guān)系〔20〕。缺乏FGF-18的小鼠表現(xiàn)出軟骨細(xì)胞增殖減少〔3〕。將重組人FGF-18注射到內(nèi)側(cè)股骨髁缺陷的羊關(guān)節(jié)腔內(nèi)，關(guān)節(jié)軟骨得到了很好的修復(fù)〔21〕。Zhang等〔22〕將OA患者的軟骨細(xì)胞與MSC共培養(yǎng)后，給予FGF-18干預(yù)，發(fā)現(xiàn)共培養(yǎng)細(xì)胞較單獨(dú)OA軟骨細(xì)胞產(chǎn)生更多Ⅱ型膠原，認(rèn)為FGF-18可重建修復(fù)已損傷的關(guān)節(jié)軟骨。細(xì)胞對(duì) FGF-18的應(yīng)答，主要通過(guò)其他信號(hào)通路的激活或抑制來(lái)調(diào)節(jié)。研究發(fā)現(xiàn)FGF-18與FGFR3高度親和，與FGFR2適度親和，通過(guò)與FGFR3 的相互作用，進(jìn)而激活I(lǐng)HH信號(hào)，負(fù)反饋調(diào)節(jié)甲狀旁腺素相關(guān)蛋白(PTHrP)參與軟骨細(xì)胞的增殖〔18〕。此外， 蛋白磷酸酶(Phlpp)1缺陷小鼠可引起叉頭蛋白(Fox)O1表達(dá)下降，導(dǎo)致FGF-18表達(dá)增加，Mek/Erk激活，軟骨細(xì)胞合成代謝活躍〔23〕。

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