Reprogramming to pluripotency through a somatic stem cell intermediate

Molecular Obstacles to Clinical Translation of iPSCs

The ability to reprogram somatic cells into induced pluripotent stem cells (iPSCs) using defined factors provides new tools for biomedical research. However, some iPSC clones display tumorigenic and immunogenic potential, thus raising concerns about their utility and safety in the clinical setting. Furthermore, variability in iPSC differentiation potential has also been described. Here we discuss whether these therapeutic obstacles are specific to transcription-factor-mediated reprogramming or inherent to every cellular reprogramming method. Finally, we address whether a better understanding of the mechanism underlying the reprogramming process might improve the fidelity of reprogramming and, therefore, the iPSC quality.

Generation of an isogenic, gene-corrected control cell line of the spinocerebellar ataxia type 2 patient-derived iPSC line H266

Spinocerebellar ataxia type 2 (SCA2) is a neurodegenerative disease primarily affecting the cerebellum. Very little is known about the molecular mechanisms underlying the disease and, to date, no cure or treatment is available. We have successfully generated bona fide induced pluripotent stem cell (iPSC) lines of SCA2 patients in order to study a disease-specific phenotype. Here, we demonstrate the gene correction of the iPSC line H266 clone 10 where we have exchanged the expanded CAG repeat of the ATXN2 gene with the normal length found in healthy alleles. This gene corrected cell line will provide the ideal control to model SCA2 by iPSC technology.

Generation of spinocerebellar ataxia type 2 patient-derived iPSC line H196

Spinocerebellar ataxia type 2 (SCA2) is a neurodegenerative disease primarily affecting the cerebellum. Very little is known about the molecular mechanisms underlying the disease and, to date, no cure or treatment is available. Here, we demonstrate the generation of an induced pluripotent stem cell (iPSC) line of a SCA2 patient. The selected clone has been proven to be a bona fide iPSC line, which retains a normal karyotype. Due to its differentiation potential into neurons, this iPSC line will be a valuable tool in studying a disease-specific phenotype of SCA2.

Enhanced OCT4 transcriptional activity substitutes for exogenous SOX2 in cellular reprogramming

Adenoviral early region 1A (E1A) is a viral gene that can promote cellular proliferation and de-differentiation in mammalian cells, features required for the reprogramming of somatic cells to a pluripotent state. E1A has been shown to interact with OCT4, and as a consequence, to increase OCT4 transcriptional activity. Indeed, E1A and OCT4 are sufficient to revert neuroepithelial hybrids to pluripotency, as demonstrated in previous cell fusion experiments. However, the role that E1A might play in the generation of induced pluripotent stem cells (iPSCs) has not been investigated yet. In this report, we show that E1A can generate iPSCs in combination with OCT4 and KLF4, thus replacing exogenous SOX2. The generated iPSCs are bona fide pluripotent cells as shown by in vitro and in vivo tests. Overall, our study suggests that E1A might replace SOX2 through enhancing OCT4 transcriptional activity at the early stages of reprogramming.

Generation of an isogenic, gene-corrected control cell line of the spinocerebellar ataxia type 2 patient-derived iPSC line H271

Spinocerebellar ataxia type 2 (SCA2) is a neurodegenerative disease primarily affecting the cerebellum. Very little is known about the molecular mechanisms underlying the disease and, to date, no cure or treatment is available. We have successfully generated bona fide induced pluripotent stem cell (iPSC) lines of SCA2 patients in order to study a disease-specific phenotype. Here, we demonstrate the gene correction of the iPSC line H271 clone 1 where we have exchanged the expanded CAG repeat of the ATXN2 gene with the normal length found in healthy alleles. This gene corrected cell line will provide the ideal control to model SCA2 by iPSC technology.

Generation of spinocerebellar ataxia type 2 patient-derived iPSC line H271

Spinocerebellar ataxia type 2 (SCA2) is a neurodegenerative disease primarily affecting the cerebellum. Very little is known about the molecular mechanisms underlying the disease and, to date, no cure or treatment is available. Here, we demonstrate the generation of an induced pluripotent stem cell (iPSC) line of a SCA2 patient. The selected clone has been proven to be a bona fide iPSC line, which retains a normal karyotype. Due to its differentiation potential into neurons, this iPSC line will be a valuable tool in studying a disease-specific phenotype of SCA2.

Generation of an isogenic, gene-corrected control cell line of the spinocerebellar ataxia type 2 patient-derived iPSC line H196

Spinocerebellar ataxia type 2 (SCA2) is a neurodegenerative disease primarily affecting the cerebellum. Very little is known about the molecular mechanisms underlying the disease and, to date, no cure or treatment is available. We have successfully generated bona fide induced pluripotent stem cell (iPSC) lines of SCA2 patients in order to study a disease-specific phenotype. Here, we demonstrate the gene correction of the iPSC line H196 clone 7 where we have exchanged the expanded CAG repeat of the ATXN2 gene with the normal length found in healthy alleles. This gene corrected cell line will provide the ideal control to model SCA2 by iPSC technology.

Generation of spinocerebellar ataxia type 2 patient-derived iPSC line H266

Spinocerebellar ataxia type 2 (SCA2) is a neurodegenerative disease primarily affecting the cerebellum. Very little is known about the molecular mechanisms underlying the disease and, to date, no cure or treatment is available. Here, we demonstrate the generation of an induced pluripotent stem cell (iPSC) line of a SCA2 patient. The selected clone has been proven to be a bona fide iPSC line, which retains a normal karyotype. Due to its differentiation potential into neurons, this iPSC line will be a valuable tool in studying a disease-specific phenotype of SCA2.

Epigenetic Aberrations Are Not Specific to Transcription Factor-Mediated Reprogramming

Somatic cells can be reprogrammed to pluripotency using different methods. In comparison with pluripotent cells obtained through somatic nuclear transfer, induced pluripotent stem cells (iPSCs) exhibit a higher number of epigenetic errors. Furthermore, most of these abnormalities have been described to be intrinsic to the iPSC technology. Here, we investigate whether the aberrant epigenetic patterns detected in iPSCs are specific to transcription factor-mediated reprogramming. We used germline stem cells (GSCs), which are the only adult cell type that can be converted into pluripotent cells (gPSCs) under defined culture conditions, and compared GSC-derived iPSCs and gPSCs at the transcriptional and epigenetic level. Our results show that both reprogramming methods generate indistinguishable states of pluripotency. GSC-derived iPSCs and gPSCs retained similar levels of donor cell-type memory and exhibited comparable numbers of reprogramming errors. Therefore, our study demonstrates that the epigenetic abnormalities detected in iPSCs are not specific to transcription factor-mediated reprogramming.

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GSCs can be converted into iPSCs and into gPSCs under specific culture conditions

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iPSCs and gPSCs retain the same level of donor cell-type epigenetic memory

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Comparable numbers of reprogramming errors can be detected in iPSCs and gPSCs

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Epigenetic aberrations are not specific to transcription factor-mediated reprogramming

Expression level of pluripotent genes in incomplete reprogramming

OBJECTIVE

To compare the expression levels of pluripotent genes among incomplete reprogrammed colonies and induced pluripotent stem cells (iPSCs), to explore the relationship between the expression of pluripotent genes and incomplete reprogramming.

METHODS

Four genes (Oct4, Sox2, Klf4, C-Myc) were introduced into human foreskin fibroblasts (HFFs) by retroviruses. The HFFs were induced to reprogramming. Different forms of colonies were picked up, analyzed, and compared with iPSCs from different aspects, including the morphology of clones, alkaline phosphatase (AP) staining, immuno-fluorescence, and Q-PCR.

RESULTS

In the reprogramming process, different colonies were emerged, some of them exhibited typical human embryonic stem cell morphology (eg., compact colonies, high nucleus-to-cytoplasm ratios, and prominent nucleoli). However, these colonies couldn't maintain these characters after passage. There was an intermediate state, named partially reprogramming. Through analysis and identification, AP staining results were weakly positive, compared with iPSC colonies. The immuno-fluorescence staining demonstrated these colonies just expressed pluripotent protein Oct4. Q-PCR indicated that the expression of exogenous transcription factors was inappropriate, either at a high level or at a low level. Most of the endogenous pluripotency genes were expressed at a low level.

CONCLUSIONS

It may be one of the causes of incomplete reprogramming that the exogenous pluripotent gene is low-expressed or over-expressed, and successful reprogramming may depend on a specific stoichiometric balance of Oct4, Sox2, Klf4 and c-Myc.

Therapeutic potential of induced neural stem cells for spinal cord injury

The spinal cord does not spontaneously regenerate, and treatment that ensures functional recovery after spinal cord injury (SCI) is still not available. Recently, fibroblasts have been directly converted into induced neural stem cells (iNSCs) by the forced expression defined transcription factors. Although directly converted iNSCs have been considered to be a cell source for clinical applications, their therapeutic potential has not yet been investigated. Here we show that iNSCs directly converted from mouse fibroblasts enhance the functional recovery of SCI animals. Engrafted iNSCs could differentiate into all neuronal lineages, including different subtypes of mature neurons. Furthermore, iNSC-derived neurons could form synapses with host neurons, thus enhancing the locomotor function recovery. A time course analysis of iNSC-treated SCI animals revealed that engrafted iNSCs effectively reduced the inflammatory response and apoptosis in the injured area. iNSC transplantation also promoted the active regeneration of the endogenous recipient environment in the absence of tumor formation. Therefore, our data suggest that directly converted iNSCs hold therapeutic potential for treatment of SCI and may thus represent a promising cell source for transplantation therapy in patients with SCI.

Atypical cell populations associated with acquired resistance to cytostatics and cancer stem cell features: the role of mitochondria in nuclear encapsulation

Until recently, acquired resistance to cytostatics had mostly been attributed to biochemical mechanisms such as decreased intake and/or increased efflux of therapeutics, enhanced DNA repair, and altered activity or deregulation of target proteins. Although these mechanisms have been widely investigated, little is known about membrane barriers responsible for the chemical imperviousness of cell compartments and cellular segregation in cytostatic-treated tumors. In highly heterogeneous cross-resistant and radiorefractory cell populations selected by exposure to anticancer agents, we found a number of atypical recurrent cell types in (1) tumor cell cultures of different embryonic origins, (2) mouse xenografts, and (3) paraffin sections from patient tumors. Alongside morphologic peculiarities, these populations presented cancer stem cell markers, aberrant signaling pathways, and a set of deregulated miRNAs known to confer both stem-cell phenotypes and highly aggressive tumor behavior. The first type, named spiral cells, is marked by a spiral arrangement of nuclei. The second type, monastery cells, is characterized by prominent walls inside which daughter cells can be seen maturing amid a rich mitochondrial environment. The third type, called pregnant cells, is a giant cell with a syncytium-like morphology, a main nucleus, and many endoreplicative functional progeny cells. A rare fourth cell type identified in leukemia was christened shepherd cells, as it was always associated with clusters of smaller cells. Furthermore, a portion of resistant tumor cells displayed nuclear encapsulation via mitochondrial aggregation in the nuclear perimeter in response to cytostatic insults, probably conferring imperviousness to drugs and long periods of dormancy until nuclear eclosion takes place. This phenomenon was correlated with an increase in both intracellular and intercellular mitochondrial traffic as well as with the uptake of free extracellular mitochondria. All these cellular disorders could, in fact, be found in untreated tumor cells but were more pronounced in resistant entities, suggesting a natural mechanism of cell survival triggered by chemical injury, or a primitive strategy to ensure stemming, self-renewal, and differentiation under adverse conditions, a fact that may play a significant role in chemotherapy outcomes.

Direct conversion of mouse fibroblasts into induced neural stem cells

Terminally differentiated cells can be directly converted into different types of somatic cells by using defined factors, thus circumventing the pluripotent state. However, low reprogramming efficiency, along with the absence of proliferation of some somatic cell types, makes it difficult to generate large numbers of cells with this method. Here we describe a protocol to directly convert mouse fibroblasts into self-renewing induced neural stem cells (iNSCs) that can be expanded in vitro, thereby overcoming the limitations associated with low reprogramming efficiency. The four transcription factors required for direct conversion into iNSCs (Sox2, Klf4, Myc (also known as c-Myc) and Pou3f4 (also known as Brn4)) do not generate a pluripotent cell state, and thus the risk for tumor formation after transplantation is reduced. By following the current protocol, iNSCs are observed 4-5 weeks after transduction. Two additional months are required to establish clonal iNSC cell lines that exhibit retroviral transgene silencing and that differentiate into neurons, astrocytes and oligodendrocytes.