Enhanced OCT4 transcriptional activity substitutes for exogenous SOX2 in cellular reprogramming

The E1a Adenoviral Gene Upregulates the Yamanaka Factors to Induce Partial Cellular Reprogramming

The induction of pluripotency by enforced expression of different sets of genes in somatic cells has been achieved with reprogramming technologies first described by Yamanaka's group. Methodologies for generating induced pluripotent stem cells are as varied as the combinations of genes used. It has previously been reported that the adenoviral E1a gene can induce the expression of two of the Yamanaka factors (c-Myc and Oct-4) and epigenetic changes. Here, we demonstrate that the E1a-12S over-expression is sufficient to induce pluripotent-like characteristics closely to epiblast stem cells in mouse embryonic fibroblasts through the activation of the pluripotency gene regulatory network. These findings provide not only empirical evidence that the expression of one single factor is sufficient for partial reprogramming but also a potential mechanistic explanation for how viral infection could lead to neoplasia if they are surrounded by the appropriate environment or the right medium, as happens with the tumorogenic niche.

Extrinsic modulation of integrin α6 and progenitor cell behavior in mesenchymal stem cells

Mesenchymal stem cells (MSC) are heterogeneous cells of complex nature that show different potentials while different culture conditions can modify their functionalities through interactions with the microenviroment. Here, we found that bone marrow (BM) MSC from different donor sources and passages that expressed higher levels of α6 integrin subunit (ITGA6), showed higher clonogenicity, migration and differentiation potential. ITGA6 showed important roles improving these potentials and regulating proliferation through protein kinase B (AKT) pathway and cell cycle inhibitor proteins p53 and p21. Moreover, ITGA6 downregulation impaired migration. Cell confluence regulated ITGA6, increasing its expression in low density cultures and decreasing in high density cultures. Besides, ITGA6- cells expressed ITGA6 when seeded at low densities. We found higher ITGA6 expression on fibronectin substrates at lower confluency. Fibronectin increased proliferation, clonogenicity, activation of AKT, decreased cell cycle inhibitor proteins and augmented growth factors expression. Spheres-derived MSC showed higher ITGA6 expression and enhanced potentials for migration, clonogenicity and proliferation. In conclusion, though there is an intrinsic regulation of ITGA6 expression, associated to the progenitor potential of BM-MSC, this expression is regulated by culture conditions and is translated in changes in cell behavior and proliferation. This knowledge could be used to enhance the potential of BM-MSC for clinical application.

Reprogramming and transdifferentiation - two key processes for regenerative medicine

Regenerative medicine based on transplants obtained from donors or foetal and new-born mesenchymal stem cells, encounter important obstacles such as limited availability of organs, ethical issues and immune rejection. The growing demand for therapeutic methods for patients being treated after serious accidents, severe organ dysfunction and an increasing number of cancer surgeries, exceeds the possibilities of the therapies that are currently available. Reprogramming and transdifferentiation provide powerful bioengineering tools. Both procedures are based on the somatic differentiated cells, which are easily and unlimitedly available, like for example: fibroblasts. During the reprogramming procedure mature cells are converted into pluripotent cells - which are capable to differentiate into almost any kind of desired cells. Transdifferentiation directly converts differentiated cells of one type into another differentiated cells type. Both procedures allow to obtained patient's dedicated cells for therapeutic purpose in regenerative medicine. In combination with biomaterials, it is possible to obtain even whole anatomical structures. Those patient's dedicated structures may serve for them upon serious accidents with massive tissue damage but also upon cancer surgeries as a replacement of damaged organ. Detailed information about reprogramming and transdifferentiation procedures as well as the current state of the art are presented in our review.

Excluding Oct4 from Yamanaka Cocktail Unleashes the Developmental Potential of iPSCs

Oct4 is widely considered the most important among the four Yamanaka reprogramming factors. Here, we show that the combination of Sox2, Klf4, and cMyc (SKM) suffices for reprogramming mouse somatic cells to induced pluripotent stem cells (iPSCs). Simultaneous induction of Sox2 and cMyc in fibroblasts triggers immediate retroviral silencing, which explains the discrepancy with previous studies that attempted but failed to generate iPSCs without Oct4 using retroviral vectors. SKM induction could partially activate the pluripotency network, even in Oct4-knockout fibroblasts. Importantly, reprogramming in the absence of exogenous Oct4 results in greatly improved developmental potential of iPSCs, determined by their ability to give rise to all-iPSC mice in the tetraploid complementation assay. Our data suggest that overexpression of Oct4 during reprogramming leads to off-target gene activation during reprogramming and epigenetic aberrations in resulting iPSCs and thereby bear major implications for further development and application of iPSC technology.

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SKM can induce pluripotency in somatic cells in the absence of exogenous Oct4

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SM coexpression activates the retroviral silencing machinery in somatic cells

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Oct4 overexpression drives massive off-target gene activation during reprogramming

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OSKM, but not SKM, iPSCs show abnormal imprinting and differentiation patterns

OCT4 Silencing Triggers Its Epigenetic Repression and Impairs the Osteogenic and Adipogenic Differentiation of Mesenchymal Stromal Cells

Mechanisms mediating mesenchymal stromal/stem cells’ (MSCs) multipotency are unclear. Although the expression of the pluripotency factor OCT4 has been detected in MSCs, whether it has a functional role in adult stem cells is still controversial. We hypothesized that a physiological expression level of OCT4 is important to regulate MSCs’ multipotency and trigger differentiation in response to environmental signals. Here, we specifically suppressed OCT4 in MSCs by using siRNA technology before directed differentiation. OCT4 expression levels were reduced by 82% in siOCT4-MSCs, compared with controls. Interestingly, siOCT4-MSCs also presented a hypermethylated OCT4 promoter. OCT4 silencing significantly impaired the ability of MSCs to differentiate into osteoblasts. Histologic and macroscopic analysis showed a lower degree of mineralization in siOCT4-MSCs than in controls. Moreover, OCT4 silencing prevented the up-regulation of osteoblast lineage-associated genes during differentiation. Similarly, OCT4 silencing resulted in decreased MSC differentiation potential towards the adipogenic lineage. The accumulation of lipids was reduced 3.0-fold in siOCT4-MSCs, compared with controls. The up-regulation of genes engaged in the early stages of adipogenesis was also suppressed in siOCT4-MSCs. Our findings provide evidence of a functional role for OCT4 in MSCs and indicate that a basal expression of this transcription factor is essential for their multipotent capacity.

Schwann cells secrete extracellular vesicles to promote and maintain the proliferation and multipotency of hDPCs

OBJECTIVES

Schwann cells (SCs) are the principal glial cells in peripheral nerve system, involved in neuropathies with great regenerative potential. Dental pulp cells have been reported to maintain neurogenic potential. In contrast, the regulatory role of SCs on human dental pulp cells (hDPCs) development remains undefined.

MATERIALS AND METHODS

SC secretion and SC-derived extracellular vesicles (EVs) were collected and used to treat hDPCs; and proliferation and multiple differentiation of hDPCs were detected after EVs treatments. Finally, we analysed the proteomes of SC-EVs and SCs through mass spectrum.

RESULTS

In this study, we found SC secretion showed a predominantly regulatory role on the development of hDPCs. Further, we identified EVs from SC secretion with similar function as SC secretion in regulating hDPCs proliferation and multipotency. And expression of transcription factor Oct4 was upregulated after treatment of both SC secretion and EVs, as well as Sox2 and Nanog. We detected abundant enrichment of Oct4 in EVs, which might be responsible for the upregulation of stem cell-related genes in hDPCs. Through proteome and western blot analysis, we found enriched TGFβs in EVs, indicating that accelerated hDPCs proliferation may be mediated by activated TGFβ-Samd and TGFβ-MAPK signalling.

CONCLUSIONS

In summary, our study sheds light on critical regulatory ability of SC-derived EVs on hDPCs proliferation and multipotency, suggesting great implications for seeding cells used in tissue engineering.