Stem Cell Clinic

Induced stem cells – Wikipedia, the free encyclopedia

Induced stem cells (iSC) are stem cells artificially derived from somatic, reproductive, pluripotent or other cell types by deliberate epigenetic reprogramming. They are classified as either totipotent (iTC), pluripotent (iPSC) or progenitor (multipotentiMSC, also called an induced multipotent progenitor celliMPC) or unipotent -- (iUSC) according to their developmental potential and degree of dedifferentiation. Progenitors are obtained by so-called direct reprogramming or directed differentiation and are also called induced somatic stem cells.

Three techniques are widely recognized:[1]

Back in 1895, Thomas Morgan remove one of the two frog blastomeres and found that amphibians are able to form whole embryo from the remaining part. This meant that the cells can change their differentiation pathway. Later, in 1924, Spemann and Mangold demonstrated the key importance of cellcell inductions during animal development.[20] The reversible transformation of cells of one differentiated cell type to another is called metaplasia.[21] This transition can be a part of the normal maturation process, or caused by an inducing stimulus. For example: transformation of iris cells to lens cells in the process of maturation and transformation of retinal pigment epithelium cells into the neural retina during regeneration in adult newt eyes. This process allows the body to replace cells not suitable to new conditions with more suitable new cells. In Drosophila imaginal discs, cells have to choose from a limited number of standard discrete differentiation states. The fact that transdetermination (change of the path of differentiation) often occurs for a group of cells rather than single cells shows that it is induced rather than part of maturation.[22]

The researchers were able to identify the minimal conditions and factors that would be sufficient for starting the cascade of molecular and cellular processes to instruct pluripotent cells to organize the embryo. They show that opposing gradients of bone morphogenetic protein (BMP) and Nodal, two transforming growth factor family members that act as morphogens, are sufficient to induce molecular and cellular mechanisms required to organize, in vivo or in vitro, uncommitted cells of the zebrafish blastula animal pole into a well-developed embryo.[23]

Some types of mature, specialized adult cells can naturally revert to stem cells. For example, "chief" cells express the stem cell marker Troy. While they normally produce digestive fluids for the stomach, they can revert into stem cells to make temporary repairs to stomach injuries, such as a cut or damage from infection. Moreover, they can make this transition even in the absence of noticeable injuries and are capable of replenishing entire gastric units, in essence serving as quiescent reserve stem cells.[24] Differentiated airway epithelial cells can revert into stable and functional stem cells in vivo.[25]

After injury, mature terminally differentiated kidney cells dedifferentiate into more primordial versions of themselves, and then differentiate into the cell types needing replacement in the damaged tissue[26] Macrophages can self-renew by local proliferation of mature differentiated cells.[27] In newts, muscle tissue is regenerated from specialized muscle cells that dedifferentiate and forget the type of cell they had been. This capacity to regenerate does not decline with age and may be linked to their ability to make new stem cells from muscle cells on demand.[28]

A variety of nontumorigenic stem cells display the ability to generate multiple cell types. For instance, multilineage-differentiating stress-enduring (Muse) cells are stress-tolerant adult human stem cells that can self-renew. They form characteristic cell clusters in suspension culture that express a set of genes associated with pluripotency and can differentiate into endodermal, ectodermal and mesodermal cells both in vitro and in vivo.[29][30][31][32][33]

Other well-documented examples of transdifferentiation and their significance in development and regeneration were described in detail.[34]

Induced totipotent cells can be obtained by reprogramming somatic cells with somatic-cell nuclear transfer (SCNT). The process involves sucking out the nucleus of a somatic (body) cell and injecting it into an oocyte that has had its nucleus removed[3][5][35][36]

Using an approach based on the protocol outlined by Tachibana et al.,[3] hESCs can be generated by SCNT using dermal fibroblasts nuclei from both a middle-aged 35-year-old male and an elderly, 75-year-old male, suggesting that age-associated changes are not necessarily an impediment to SCNT-based nuclear reprogramming of human cells.[37] Such reprogramming of somatic cells to a pluripotent state holds huge potentials for regenerative medicine. Unfortunately, the cells generated by this technology, potentially are not completely protected from the immune system of the patient (donor of nuclei), because they have the same mitochondrial DNA, as a donor of oocytes, instead of the patients mitochondrial DNA. This reduces their value as a source for autologous stem cell transplantation therapy, as for the present, it is not clear whether it can induce an immune response of the patient upon treatment.

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Induced stem cells - Wikipedia, the free encyclopedia

Pluripotency of Induced Pluripotent Stem Cells

Volume 11, Issue 5, October 2013, Pages 299303

Special Issue: Induced Pluripotent Stem Cells

Edited By Qi Zhou

Induced pluripotent stem (iPS) cells can be generated by forced expression of four pluripotency factors in somatic cells. This has received much attention in recent years since it may offer us a promising donor cell source for cell transplantation therapy. There has been great progress in iPS cell research in the past few years. However, several issues need to be further addressed in the near future before the clinical application of iPS cells, like the immunogenicity of iPS cells, the variability of differentiation potential and most importantly tumor formation of the iPS derivative cells. Here, we review recent progress in research into the pluripotency of iPS cells.

Induced pluripotent stem (iPS) cells can be derived from mouse somatic cells via the ectopic expression of four defined factors, Oct4, Sox2, Klf4 and c-Myc (also known as Yamanaka factors) [1]. The mouse iPS cells express pluripotency markers and both X chromosomes are reactivated, allowing differentiation into various cell types of three germ layers when injected into a blastocyst. iPS technology makes reprogramming much easier [2]and[3] in comparison to early reprogramming methods such as somatic cell nuclear transfer (SCNT) [4]and[5], iPS technology also circumvents the ethical problems arising from the use of human oocytes. In addition, the generation of patient-specific iPS cells could be used to screen new drugs [6]and[7]. However, there are currently several limitations in applying iPS cells clinically. Efficiency of converting somatic cells to iPS cells is still very low. In particular, only approximately 0.1% to 1% of somatic cells experience changes at the transcriptional level and finally become pluripotent stem cells when non-integration approaches are used [8]. Moreover, compared to embryonic stem (ES) cells, the developmental potential and differentiation capacity of iPS cells is significantly reduced and there is increased variability among all iPS cell lines [9]. In mice, only small proportions of these cells are fully reprogrammed based on the most stringent tetraploid complementation assay for evaluating pluripotency [10], [11], [12]and[13]. Therefore, it is necessary to establish a strict molecular standard system to distinguish fully reprogrammed iPS cells from those partially reprogrammed, as we currently lack suitable in vivo pluripotency tests for human iPS cells.

In this review, we mainly focus on recent progress on rodent, non-human primate and human iPS cells, and point out some key questions which need to be addressed in the near future, such as the pluripotency level of human iPS cells and the establishment of a new standard to assess the pluripotency level of human iPS cells.

Takahashi and Yamanaka reprogrammed mouse embryonic fibroblasts by the ectopic expression of four reprogramming factors using retroviral vectors, and finally produced iPS cells which resemble ES cells [1]. This original iPS reprogramming approach used viral vectors, including retrovirus and lentivirus which possess high reprogramming efficiency [14]and[15]. The genome may be mutated by integrating other gene sequences, thus raising concerns on the safety issue. In addition, the insertion of oncogenes, like c-Myc, increases the risk of tumor formation [16]and[17]. Subsequently, several modified methods were used to obtain much safer iPS cells, for instance, piggyBac transposon [18], adenovirus [19], sendai virus [20], plasmid [21], episomal vectors [22] and minicircle vectors [23]. However, the reprogramming efficiency is significantly decreased and it takes longer to reactivate the key pluripotency markers to achieve full reprogramming. Therefore, efficient generation of non-integrated iPS cells by new approaches may promote their clinical application.

Recent studies have described several reprogramming methods using proteins, RNAs and small-molecule compounds to derive safe iPS cells [24], [25]and[26]. Zhou et al. obtained iPS cells induced by recombination of the proteins of the four Yamanaka factors obtained by fusing the C-terminus of the proteins with poly-arginine (11R) [24]. A recent study reported that mouse and human iPS cells can be efficiently generated by miRNA mediated reprogramming [25]. Miyoshi et al. [26] successfully generated iPS cells by direct transfection of human somatic cells using mature miRNA. iPS cells can also be generated by synthetic RNAs, which bypass the innate response to viruses [27]. Recently, Houet et al. [28] showed that pluripotent stem cells can be generated from mouse somatic cells at an efficiency of 0.2% by using a combination of seven small-molecule compounds. Compared to traditional viral methods, the aforementioned approaches can be used to generate qualified iPS cells (Table 1) without the risk of insertional mutagenesis. Nonetheless, some familiar drawbacks exist, such as a longer and less efficient reprogramming process. In other words, what we need to do next is to optimize non-integration induction systems in order to resolve these drawbacks.

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Pluripotency of Induced Pluripotent Stem Cells

Induced Pluripotent Stem Cells (IPSCs) – HowStuffWorks

Save Those Teeth

Dentists usually discard wisdom teeth after they've been extracted -- but maybe they should start saving them; they just might be useful in make stem cells. Recently, a group of Japanese scientists made induced pluripotent stem cells (IPSCs) from the tooth pulp of extracted wisdom teeth. They used viruses to deliver stem cell factors to mesenchymal stromal cells isolated from the pulp of third molars. The resulting IPSCs were similar to embryonic stem cells.

In 2003, an NIH researcher, Sangtao Shi, extracted stem cells from his daughter's baby teeth. The stem cells grew in culture and could form bone when implanted into mice. Potentially, you could bank stem cells from your teeth for future use, but it would be an expensive process.

Maybe that's what the tooth fairy does with all those teeth?

Whether from embryos or adult tissues, stem cells are few. But many are needed for cell therapies. There have been ethical and political problems with using embryonic stem cells -- so if there were a way to get more stem cells from adults, it might be less controversial. Enter the IPSC.

Every cell in the body has the same genetic instructions. So what makes a heart cell different from a liver cell? The two cells express different sets of genes. Likewise, a stem cell turns on specific sets of genes to differentiate into another cell. So, is it possible to reprogram a differentiated cell so that it reverts back to a stem cell? In 2006, scientists did just that. They used a virus to deliver four stem cell factors into skin cells. The factors caused the differentiated stem cells to go into an embryonic-stem-cell-like state. The resulting cells, called induced pluripotent stem cells (IPSCs), shared many characteristics with human embryonic stem cells. The structures of IPSCs were similar, they expressed the same markers and genes, and they grew the same. And the researchers were able to grow the IPSCs into cell lines.

There are many more differentiated cells in the human body than stem cells, embryonic or adult. So, vast amounts of stem cells could be made from a patient's own differentiated cells, like skin cells. Making IPSCs does not involve embryos, so this would circumvent the ethical and political issues involved in stem cell research. However, making ISPSCs is a recent development, so scientists need to do more research before they can be used for therapies. First, we need to understand the "reprogramming" process better. And then we need to investigate whether IPSCs are just similar enough or are actually identical to embryonic stem cells. Current research is focused on these questions, but reprogramming cells to make IPSCs has great potential.

Now that you have a good idea of what stems cells are and how they work, let's see how they can be used to treat diseases.

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Induced Pluripotent Stem Cells (IPSCs) - HowStuffWorks