全化学诱导体细胞重编程和转分化

终末分化细胞可以通过重编程和转分化转变为其他类型的细胞,对再生医学领域的研究有重要意义。化学小分子由于结构多样性,及作用剂量、时间的可控性,其在重编程和转分化领域的应用前景广阔。我国科学家在该方向的研究中也取得了许多引人瞩目的成就。对体细胞重编程和转分化的方式、小分子化合物在体细胞重编程研究领域的应用以及全化学诱导体细胞重编程和转分化研究的最新进展,尤其是我国科学家在本领域的进展进行综述。     

体细胞重编程为多能干细胞的研究进展

体细胞通过重编程转变成其他类型的细胞,在再生医学方面具有重要的应用前景。细胞重编程的方法主要有体细胞核移植、细胞融合、细胞提取物诱导、限定因子诱导等,这些方法可以不同程度地改变细胞命运。最近,限定因子诱导的多能干细胞（induced pluripotent stem cell。iPS）为重编程提供了一种崭新的方法,不仅可以避免伦理争议,还提供了一种更为便利的技术,为再生医学开辟了新的天地;同时,iPS技术为研究基因表达调控、蛋白质互作、机体生长发育等提供了一个非常重要的研究手段。本文主要论述了体细胞重编程的方法及iPS细胞的进展、面临的问题和应用前景。     

体细胞直接重编程为神经元和神经干细胞

体细胞直接重编程是由已分化细胞类型不经过诱导型多能干细胞(Induced pluripotent stem cells,i PSCs)中间阶段,直接转换为另一种细胞类型的重编程过程。体细胞直接重编程避免了i PSC技术存在的重编程效率低下、引入致癌基因等多种缺陷,并为细胞替换治疗和个性化医药研发设想贡献了新的实现途径。现代医学对于诸如神经退行性疾病、神经遗传疾病和外伤导致的神经细胞受损等一些神经系统疾病一直没有有效的治疗手段。而体细胞直接重编程为治疗这些疾病提供了另一种治疗途径,因此体细胞直接重编程为神经细胞相关领域迅速成为研究热点。回顾了体细胞重编程为诱导型神经元(Induced neurons,i Ns)和诱导型神经干细胞(Induced neural stem cells,i NSCs)的最新研究进展,并探讨i Ns和i NSCs在临床应用上的各自优势、局限性及应用前景。     

小分子重编程体细胞为神经细胞的研究进展

小分子重编程是使用化学限定的条件对体细胞重新编程,不使用基因操作,可生成临床疾病相关的细胞类型,在再生医学和临床药物发现方面有非常好的应用前景。然而,使用小分子从体细胞诱导干细胞和神经细胞需跨越体细胞特异性谱系的障碍。本文详细回顾了使用小分子化学诱导产生神经干细胞、神经元和星形胶质细胞的方法,还讨论了小分子作用的主要机制和调节化学重编程的途径。     

诱导细胞功能转化的新策略——谱系重编程

通过重编程诱导细胞功能转化是当前再生医学研究领域的热点。其中一种策略是,先将普通成体细胞转变为多能干细胞,再诱导后者向新的细胞类型分化。近来新出现的另一种策略是,直接将成熟细胞转分化为其他类型的功能细胞或祖细胞,此即谱系重编程(lineage reprogramm ing)。本文主要就谱系重编程概念的由来、相关研究进展及下一步研究方向等内容做一综述。     

microRNAs和体细胞重编程

体细胞重编程与microRNAs(miRNAs)均为近年来研究的热点问题。到目前为止,能成功诱导体细胞形成多能性干细胞的体细胞重编程方法有核移植(nuclear transfer,NT)和外源因子诱导形成多能干细胞(induced pluripotent stem cells,iPSc)两种,这两种方法让人们看到了体细胞重编程在细胞治疗方面具有诱人的应用前景。miRNAs是真核生物中存在的一类长度为22nt左右起调控作用的内源性非编码RNA,它在转录后水平调节靶基因的表达,是细胞内基因表达的基本调控机制之一。近年的研究结果表明,miRNAs在干细胞干性维持和分化过程中具有重要的调节作用,从miRNAs角度研究体细胞重编程机理将对体细胞重编程的应用具有重要意义。     

终末期肝病细胞治疗供体细胞来源的研究进展

许多因素所致的肝脏疾病都有可能发展为终末期肝病,而终末期肝病目前唯一有效的治疗方法就是原位肝移植。然而,由于受供体肝脏短缺等因素的限制,细胞治疗方法一直被临床上所期待。近年来,基于谱系重编程的诱导型肝干细胞和诱导型肝实质细胞的技术体系的出现,为解决肝脏疾病细胞治疗中细胞来源匮乏的问题提供了新的思路,也加速了肝脏疾病细胞治疗研究向临床转化的进程。该文介绍了肝脏疾病细胞治疗研究中供体细胞来源的现状,并重点介绍了谱系重编程获取肝系细胞的研究进展。     

改变细胞命运的重编程

体细胞重编程是指用特定方法使已分化的细胞重新获得多能性的过程,可通过核移植、细胞融合、多能细胞提取物共培养和诱导性多能干细胞等途径实现。其中,诱导性多能干细胞技术发展最为迅速,应用前景广阔。现主要介绍重编程领域近年的研究进展。     

体细胞重编程逆转为干细胞的研究进展

目前细胞和发育生物学上的研究成果为生物医学研究提供了广泛的前景.将完全分化的细胞重编程,不经过胚胎逆转为多能干细胞状态,这点燃了再生医学应用的新希望,这一成果从法律、道德、伦理等不同方面被人们所接受.通过体细胞克隆胚胎获得干细胞所面临的破坏胚胎的伦理限制,促使研究者去寻求将分化细胞重编程逆转为干细胞的新方法.主要论述了体细胞重编程的原理、过程及不经过胚胎逆转为多能干细胞的方法.     

细胞谱系重编程研究进展

重编程研究是近年来干细胞与再生医学领域中里程碑式的研究突破,打破了人胚胎干细胞研究带来的伦理桎梏,为再生医学临床应用带来了一片新天地.但诱导性多能干细胞(induced pluripotent stem cells,iPS)制作过程繁琐,重编程效率偏低,且仍需如同胚胎干细胞一样,经过步步诱导分化而获得目的细胞,最关键的是,目的细胞的安全性问题仍亟待解决.谱系重编程,在广义的角度上来说,至少从1987年即已展开,20世纪末引发成体干细胞研究热潮的"可塑性"研究也可归为谱系重编程研究,在iPS重编程研究的推动下,谱系重编程技术正在蓬勃发展,并被再生医学研究者给予了厚望,尤其是在可预见的将来,其在个体化治疗上具有的优势将不可比拟.     

Efficient generation of iPS cells from skeletal muscle stem cells

Reprogramming of somatic cells into inducible pluripotent stem cells generally occurs at low efficiency, although what limits reprogramming of particular cell types is poorly understood. Recent data suggest that the differentiation status of the cell targeted for reprogramming may influence its susceptibility to reprogramming as well as the differentiation potential of the induced pluripotent stem (iPS) cells that are derived from it. To assess directly the influence of lineage commitment on iPS cell derivation and differentiation, we evaluated reprogramming in adult stem cell and mature cell populations residing in skeletal muscle. Our data using clonal assays and a second-generation inducible reprogramming system indicate that stem cells found in mouse muscle, including resident satellite cells and mesenchymal progenitors, reprogram with significantly greater efficiency than their more differentiated daughters (myoblasts and fibroblasts). However, in contrast to previous reports, we find no evidence of biased differentiation potential among iPS cells derived from myogenically committed cells. These data support the notion that adult stem cells reprogram more efficiently than terminally differentiated cells, and argue against the suggestion that "epigenetic memory" significantly influences the differentiation potential of iPS cells derived from distinct somatic cell lineages in skeletal muscle.     

Advances in cell lineage reprogramming

As a milestone breakthrough of stem cell and regenerative medicine in recent years,somatic cell reprogramming has opened up new applications of regenerative medicine by breaking through the ethical shackles of embryonic stem cells.However,induced pluripotent stem(iPS) cells are prepared with a complicated protocol that results in a low reprogramming rate.To obtain differentiated target cells,iPS cells and embryonic stem cells still need to be induced using step-by-step procedures.The safety of induced target cells from iPS cells is currently a further concerning matter.More broadly conceived is lineage reprogramming that has been investigated since 1987.Adult stem cell plasticity,which triggered interest in stem cell research at the end of the last century,can also be included in the scope of lineage reprogramming.With the promotion of iPS cell research,lineage reprogramming is now considered as one of the most promising fields in regenerative medicine,will hopefully lead to customized,personalized therapeutic options for patients in the future.     

Reprogramming a somatic nucleus by trans-modification activity in germ cells.

The germ cell lineage is totipotent insofar as it provides a link between an individual and the subsequent generations. There is a series of characteristic genomic modifications in germ cells that distinguish this lineage from somatic cells. These modifications include extensive demethylation of the genome, erasure of allele-specific methylation of imprinted loci and re-activation of the silent X chromosome. To test if this is an active process capable of reprogramming a somatic nucleus, we prepared germ cell-somatic cell hybrids. A dominant trans modification activity was detected in germ cells that was capable of inducing similar modifications in the somatic nucleus. This experimental system can therefore be used to study how determined cell state can be reversed by specific genomic modifications.     

Epigenetic predisposition to reprogramming fates in somatic cells

Reprogramming to pluripotency is a low‐efficiency process at the population level. Despite notable advances to molecularly characterize key steps, several fundamental aspects remain poorly understood, including when the potential to reprogram is first established. Here, we apply live‐cell imaging combined with a novel statistical approach to infer when somatic cells become fated to generate downstream pluripotent progeny. By tracing cell lineages from several divisions before factor induction through to pluripotent colony formation, we find that pre‐induction sister cells acquire similar outcomes. Namely, if one daughter cell contributes to a lineage that generates induced pluripotent stem cells (iPSCs), its paired sibling will as well. This result suggests that the potential to reprogram is predetermined within a select subpopulation of cells and heritable, at least over the short term. We also find that expanding cells over several divisions prior to factor induction does not increase the per‐lineage likelihood of successful reprogramming, nor is reprogramming fate correlated to neighboring cell identity or cell‐specific reprogramming factor levels. By perturbing the epigenetic state of somatic populations with Ezh2 inhibitors prior to factor induction, we successfully modulate the fraction of iPSC‐forming lineages. Our results therefore suggest that reprogramming potential may in part reflect preexisting epigenetic heterogeneity that can be tuned to alter the cellular response to factor induction.