美國(guó)研究人員發(fā)現(xiàn)了一種打開人體成纖維細(xì)胞（皮膚細(xì)胞）中的干細(xì)胞基因的新方法，從而避免了插入額外基因或利用病毒所帶來的健康風(fēng)險(xiǎn),。這一成果開辟了細(xì)胞重組的新途徑,，未來通過誘使患者自身細(xì)胞修復(fù)和再生受損組織，該方法將可用于治療一系列人類疾病和創(chuàng)傷,。
在7月21日的《克隆與干細(xì)胞》期刊的網(wǎng)絡(luò)版上,，美國(guó)伍斯特理工學(xué)院和CellThera公司的研究人員描述了此項(xiàng)研究成果。研究人員表示,，只需通過操縱培養(yǎng)條件,，他們就可獲得成纖維細(xì)胞的變化，這將有利于開發(fā)出病人特異性細(xì)胞療法,。
新興的再生醫(yī)學(xué)領(lǐng)域初期的研究重點(diǎn)是多能胚胎干細(xì)胞,。在多能態(tài)，已知某些基因呈活躍狀態(tài),，有助于控制干細(xì)胞,。包括OCT4、SOX2和NANOG在內(nèi)的這些基因在干細(xì)胞中很活躍,，但干細(xì)胞一旦開始分化并沿此途徑發(fā)展成為某種特定細(xì)胞類型和組織時(shí),，這些基因就變成休眠狀態(tài),，故而這些基因被認(rèn)定為多能的標(biāo)志物。
雖然胚胎干細(xì)胞研究尚在不斷產(chǎn)生更多重要的知識(shí),，但被稱為誘導(dǎo)多能干細(xì)胞（iPS）的重組細(xì)胞可用于再生組織,，同時(shí)可避免使用胚胎干細(xì)胞帶來的一些問題，如倫理問題,、胚胎干細(xì)胞有可能被患者免疫系統(tǒng)排斥的問題或是生長(zhǎng)失控導(dǎo)致癌癥的問題等,。
2007年，日本京都大學(xué)山中伸彌團(tuán)隊(duì)率先研制出iPS細(xì)胞,，在人體皮膚細(xì)胞中插入了包括OCT4和SOX2在內(nèi)的4個(gè)額外的干細(xì)胞基因,。這些基因開始表達(dá)出能將皮膚細(xì)胞變回更加多能狀態(tài)的蛋白質(zhì)。這項(xiàng)技術(shù)已在實(shí)驗(yàn)室中被重復(fù)驗(yàn)證,，而且已可實(shí)現(xiàn)用更少的添加基因來進(jìn)行重組,，這曾是一個(gè)重大的科學(xué)突破。但其在人類疾病治療方面的潛力是有限的,，因?yàn)閷⑿禄虿迦氲匠审w細(xì)胞,，或通過病毒來攜帶這些遺傳載荷都可能引發(fā)一系列的問題。
伍斯特理工學(xué)院此次的最新研究,，則是通過降低細(xì)胞暴露的大氣氧含量,，及將稱為成纖維細(xì)胞生長(zhǎng)因子（FGF2）的蛋白添加到培養(yǎng)基中，來打開現(xiàn)有的,、尚處于休眠狀態(tài)的干細(xì)胞基因OCT4,、SOX2和NANOG。FGF2是一種天然蛋白,，對(duì)維持胚胎干細(xì)胞的多能性至關(guān)重要,。
此外，該小組發(fā)現(xiàn),，一旦干細(xì)胞基因被激活并開始表達(dá)蛋白,，這些蛋白可遷移到皮膚細(xì)胞的細(xì)胞核中，準(zhǔn)確得就像是發(fā)生在誘導(dǎo)多能干細(xì)胞中,。伍斯特理工學(xué)院生物學(xué)和生物技術(shù)副教授雷蒙德·佩吉認(rèn)為,，這是一個(gè)令人興奮的發(fā)現(xiàn)，將這些蛋白定位在細(xì)胞核中是重組這些細(xì)胞的第一步,。
更令研究人員驚異的是,，干細(xì)胞基因OCT4、SOX2和NANOG并不像推定的那樣在未經(jīng)處理的皮膚細(xì)胞中是完全休眠的,。事實(shí)上,，這些基因會(huì)發(fā)送信息，只不過這些信息并沒有被轉(zhuǎn)錄成可形成細(xì)胞多能性的蛋白,。研究人員稱,，這個(gè)事實(shí)不僅迫使他們重新思考什么才是多能性的真正標(biāo)志,，而且也表明在調(diào)控干細(xì)胞基因表達(dá)的這些細(xì)胞中存在著一種天然機(jī)制，這為研究人員打開了一條研究細(xì)胞重組的全新思路,。（生物谷Bioon.com）
生物谷推薦原始出處：
Cloning and Stem Cells doi:10.1089/clo.2009.0015.
Induction of Stem Cell Gene Expression in Adult Human Fibroblasts without Transgenes
Raymond L. Page,1,2,3,4 Sakthikumar Ambady,1,2 William F. Holmes,2 Lucy Vilner,1 Denis Kole,2 Olga Kashpur,2 Victoria Huntress,2 Ina Vojtic,1 Holly Whitton,2 and Tanja Dominko1,2,4
1CellThera, Inc., Worcester, Massachusetts.
2Department of Biology and Biotechnology, Worcester Polytechnic Institute, Worcester, Massachusetts.
3Department of Biomedical Engineering, Worcester Polytechnic Institute, Worcester, Massachusetts.
4Bioengineering Institute, Worcester Polytechnic Institute, Worcester, Massachusetts.
Reprogramming of differentiated somatic cells into induced pluripotent stem (iPS) cells has potential for derivation of patient-specific cells for therapy as well as for development of models with which to study disease progression. Derivation of iPS cells from human somatic cells has been achieved by viral transduction of human fibroblasts with early developmental genes. Because forced expression of these genes by viral transduction results in transgene integration with unknown and unpredictable potential mutagenic effects, identification of cell culture conditions that can induce endogenous expression of these genes is desirable. Here we show that primary adult human fibroblasts have basal expression of mRNA for OCT4, SOX2, and NANOG. However, translation of these messages into detectable proteins and their subcellular localization depends on cell culture conditions. Manipulation of oxygen concentration and FGF2 supplementation can modulate expression of some pluripotency related genes at the transcriptional, translational, and cellular localization level. Changing cell culture condition parameters led to expression of REX1, potentiation of expression of LIN28, translation of OCT4, SOX2, and NANOG, and translocation of these transcription factors to the cell nucleus. We also show that culture conditions affect the in vitro lifespan of dermal fibroblasts, nearly doubling the number of population doublings before the cells reach replicative senescence. Our results suggest that it is possible to induce and manipulate endogenous expression of stem cell genes in somatic cells without genetic manipulation, but this short-term induction may not be sufficient for acquisition of true pluripotency. Further investigation of the factors involved in inducing this response could lead to discovery of defined culture conditions capable of altering cell fate in vitro. This would alleviate the need for forced expression by transgenesis, thus eliminating the risk of mutagenic effects due to genetic manipulation.
