Transcription factor-based modulation of neural stem cell differentiation using direct protein transduction

Oligodendrocyte progenitor cell-specific delivery of lipid nanoparticles loaded with Olig2 synthetically modified messenger RNA for ischemic stroke therapy

The transcription factor Olig2 is highly expressed throughout oligodendroglial development and is needed for the differentiation of oligodendrocyte progenitor cells (OPCs) into oligodendrocytes and remyelination. Although Olig2 overexpression in OPCs is a possible therapeutic target for enhancing myelin repair in ischemic stroke, achieving Olig2 overexpression in vivo remains a formidable technological challenge. To address this challenge, we employed lipid nanoparticle (LNP)-mediated delivery of Olig2 synthetically modified messenger RNA (mRNA) as a viable method for in vivo Olih2 protein overexpression. Specifically, we developed CD140a-targeted LNPs loaded with Olig2 mRNA (C-Olig2) to achieve targeted Olig2 protein expression within PDGFRα+ OPCs, with the goal of promoting remyelination for ischemic stroke therapy. We show that C-Olig2 promotes the differentiation of PDGFRα+ OPCs derived from mouse neural stem cells into mature oligodendrocytes in vitro, suggesting that mRNA-mediated Olig2 overexpression is a rational approach to promote oligodendrocyte differentiation and remyelination. Furthermore, when C-Olig2 was administered to a murine model of ischemic stroke, it led to improvements in blood‒brain barrier (BBB) integrity, enhanced remyelination, and rescued learning and cognitive deficits. Our comprehensive analysis, which included bulk RNA sequencing (RNA-seq) and single-nucleus RNA-seq (snRNA-seq), revealed upregulated biological processes related to learning and memory in the brains of mice treated with C-Olig2 compared to those receiving empty LNPs (Mock). Collectively, our findings highlight the therapeutic potential of multifunctional nanomedicine targeting mRNA expression for ischemic stroke and suggest that this approach holds promise for addressing various brain diseases. STATEMENT OF SIGNIFICANCE: While Olig2 overexpression in OPCs represents a promising therapeutic avenue for enhancing remyelination in ischemic stroke, in vivo strategies for achieving Olig2 expression pose considerable technological challenges. The delivery of mRNA via lipid nanoparticles is considered aa viable approach for in vivo protein expression. In this study, we engineered CD140a-targeted LNPs loaded with Olig2 mRNA (C-Olig2) with the aim of achieving specific Olig2 overexpression in mouse OPCs. Our findings demonstrate that C-Olig2 promotes the differentiation of OPCs into oligodendrocytes in vitro, providing evidence that mRNA-mediated Olig2 overexpression is a rational strategy to foster remyelination. Furthermore, the intravenous administration of C-Olig2 into a murine model of ischemic stroke not only improved blood-brain barrier integrity but also enhanced remyelination and mitigated learning and cognitive deficits. These results underscore the promising therapeutic potential of multifunctional nanomedicine targeting mRNA expression in the context of ischemic stroke.

Biocompatible chitosan/polyethylene glycol/multi-walled carbon nanotube composite scaffolds for neural tissue engineering

Carbon nanotube (CNT) composite materials are very attractive for use in neural tissue engineering and biosensor coatings. CNT scaffolds are excellent mimics of extracellular matrix due to their hydrophilicity, viscosity, and biocompatibility. CNTs can also impart conductivity to other insulating materials, improve mechanical stability, guide neuronal cell behavior, and trigger axon regeneration. The performance of chitosan (CS)/polyethylene glycol (PEG) composite scaffolds could be optimized by introducing multi-walled CNTs (MWCNTs). CS/PEG/CNT composite scaffolds with CNT content of 1%, 3%, and 5% (1%=0.01 g/mL) were prepared by freeze-drying. Their physical and chemical properties and biocompatibility were evaluated. Scanning electron microscopy (SEM) showed that the composite scaffolds had a highly connected porous structure. Transmission electron microscope (TEM) and Raman spectroscopy proved that the CNTs were well dispersed in the CS/PEG matrix and combined with the CS/PEG nanofiber bundles. MWCNTs enhanced the elastic modulus of the scaffold. The porosity of the scaffolds ranged from 83% to 96%. They reached a stable water swelling state within 24 h, and swelling decreased with increasing MWCNT concentration. The electrical conductivity and cell adhesion rate of the scaffolds increased with increasing MWCNT content. Immunofluorescence showed that rat pheochromocytoma (PC12) cells grown in the scaffolds had characteristics similar to nerve cells. We measured changes in the expression of nerve cell markers by quantitative real-time polymerase chain reaction (qRT-PCR), and found that PC12 cells cultured in the scaffolds expressed growth-associated protein 43 (GAP43), nerve growth factor receptor (NGFR), and class III β‍-tubulin (TUBB3) proteins. Preliminary research showed that the prepared CS/PEG/CNT scaffold has good biocompatibility and can be further applied to neural tissue engineering research.

Protein Production and Purification of a Codon-Optimized Human NGN3 Transcription Factor from E. coli

Neurogenin 3 (NGN3) transcription factor is vital for the development of endocrine cells of the intestine and pancreas. NGN3 is also critical for the neural precursor cell determination in the neuroectoderm. Additionally, it is one of the vital transcription factors for deriving human β-cells from specialized somatic cells. In the current study, the production and purification of the human NGN3 protein from Escherichia coli (E. coli) is reported. First, the 642 bp protein-coding nucleotide sequence of the NGN3 gene was codon-optimized to enable enhanced protein expression in E. coli strain BL21(DE3). The codon-optimized NGN3 sequence was fused in-frame to three different fusion tags to enable cell penetration, nuclear translocation, and affinity purification. The gene insert with the fusion tags was subsequently cloned into an expression vector (pET28a( +)) for heterologous expression in BL21(DE3) cells. A suitable genetic construct and the ideal expression conditions were subsequently identified that produced a soluble form of the recombinant NGN3 fusion protein. This NGN3 fusion protein was purified to homogeneity (purity > 90%) under native conditions, and its secondary structure was retained post-purification. This purified protein, when applied to human cells, did not induce cytotoxicity. Further, the cellular uptake and nuclear translocation of the NGN3 fusion protein was demonstrated followed by its biological activity in PANC-1 cells. Prospectively, this recombinant protein can be utilized for various biological applications to investigate its functionality in cell reprogramming, biological processes, and diseases.

Generation of biologically active recombinant human OCT4 protein from E. coli

Octamer-binding transcription factor 4 (OCT4) is vital for early embryonic development and is a master regulator of pluripotency in embryonic stem cells. Notably, OCT4 is a key reprogramming factor to derive induced pluripotent stem cells, which have tremendous prospects in regenerative medicine. In the current study, we report heterologous expression and purification of human OCT4 in E. coli to produce pure recombinant protein under native conditions. To achieve this, the 1083 bp coding sequence of the human OCT4 gene was codon-optimized for heterologous expression in E. coli. The codon-optimized sequence was fused with fusion tags, namely a cell-penetrating peptide sequence for intracellular delivery, a nuclear localization sequence for intranuclear delivery, and a His-tag for affinity purification. Subsequently, the codon-optimized sequence and the fusion tags were cloned in the protein expression vector, pET28a(+), and transformed into E. coli strain BL21(DE3) for expression. The recombinant OCT4 protein was purified from the soluble fraction under native conditions using immobilized metal ion affinity chromatography in a facile manner, and its identity was confirmed by Western blotting and mass spectrometry. Furthermore, the secondary structure of the recombinant protein was analyzed using far ultraviolet circular dichroism spectroscopy, which confirmed that the purified fusion protein maintained a secondary structure conformation, and it predominantly composed of α-helices. Next, the recombinant OCT4 protein was applied to human cells, and was found that it was able to enter the cells and translocate to the nucleus. Furthermore, the biological activity of the transduced OCT4 protein was also demonstrated on human cells. This recombinant tool can substitute for genetic and viral forms of OCT4 to enable the derivation of integration-free pluripotent cells. It can also be used to elucidate its biological role in various cellular processes and diseases and for structural and biochemical studies.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02758-z.

Soluble expression, purification, and secondary structure determination of human MESP1 transcription factor

Transcription factor MESP1 is a crucial factor regulating cardiac, hematopoietic, and skeletal myogenic development. Besides, it also contributes to the generation of functional cardiomyocytes. Here, we report the soluble expression and purification of the full-length human MESP1 protein from the heterologous system, which can be delivered into the target mammalian cells. To generate this biological macromolecule, we cloned its codon-optimized gene sequence fused to a nuclear localization sequence, a cell-penetrating peptide, and a His-tag into the protein expression vector and expressed in the bacterial system (E. coli strain BL21(DE3)). Subsequently, we have screened and identified the optimal expression parameters to obtain this recombinant fusion protein in soluble form from E. coli and examined its expression concerning the placement of fusion tags at either terminal. Further, we have purified this recombinant fusion protein to homogeneity under native conditions. Notably, this purified fusion protein has maintained its secondary structure after purification, primarily comprising α-helices and random coils. This molecular tool can potentially replace its genetic and viral forms in the cardiac reprogramming of fibroblasts to induce a cardiac transcriptional profile in an integration-free manner and elucidating its role in various biological processes and diseases. KEY POINTS: • Screening of the suitable gene construct was performed and identified. • Screening of optimal expression conditions was performed and identified. • Native purification of recombinant human MESP1 protein from E. coli was performed. • Recombinant MESP1 protein has retained its secondary structure after purification.

Codon Optimization, Cloning, Expression, Purification, and Secondary Structure Determination of Human ETS2 Transcription Factor

Transcription factor ETS2 regulates genes involved in development, differentiation, angiogenesis, proliferation, and apoptosis. In addition, it is one of the core reprogramming factors responsible for the generation of human cardiomyocytes from adult somatic cells. In this study, we report the heterologous expression of human ETS2 in E. coli to produce a highly pure recombinant protein. To accomplish this, the codon-optimized 1507 bp coding sequence of the human ETS2 gene in fusion with a His-tag, a cell-penetrating peptide, and a nuclear localization sequence was cloned in the protein expression vector and transformed into E. coli strain BL21(DE3) for expression. The recombinant protein was purified to homogeneity under native conditions using immobilized metal ion affinity chromatography, and its identity was confirmed by Western blotting with an ETS2 antibody. Using far-UV circular dichroism spectroscopy, we have demonstrated that the recombinant protein has retained its secondary structure, predominantly comprising of random coils and β-sheets. Prospectively, this biological recombinant ETS2 protein can substitute viral and genetic forms of ETS2 in a cell reprogramming process to facilitate the generation of clinical-grade cells. It can also be used to investigate its molecular role in various biological processes and diseases and for biochemical and structural studies.

Take the shortcut - direct conversion of somatic cells into induced neural stem cells and their biomedical applications

Second-generation reprogramming of somatic cells directly into the cell type of interest avoids induction of pluripotency and subsequent cumbersome differentiation procedures. Several recent studies have reported direct conversion of human somatic cells into stably proliferating induced neural stem cells (iNSCs). Importantly, iNSCs are easier, faster, and more cost-efficient to generate than induced pluripotent stem cells (iPSCs), and also have a higher level of clinical safety. Stably, self-renewing iNSCs can be derived from different cellular sources, such as skin fibroblasts and peripheral blood mononuclear cells, and readily differentiate into neuronal and glial lineages that are indistinguishable from their iPSC-derived counterparts or from NSCs isolated from primary tissues. This review focuses on the derivation and characterization of iNSCs and their biomedical applications. We first outline different approaches to generate iNSCs and then discuss the underlying molecular mechanisms. Finally, we summarize the preclinical validation of iNSCs to highlight that these cells are promising targets for disease modeling, autologous cell therapy, and precision medicine.

Transcription factors: Time to deliver

Transcription factors (TFs) are at the center of the broad regulatory network orchestrating gene expression programs that elicit different biological responses. For a long time, TFs have been considered as potent drug targets due to their implications in the pathogenesis of a variety of diseases. At the same time, TFs, located at convergence points of cellular regulatory pathways, are powerful tools providing opportunities both for cell type change and for managing the state of cells. This task formulation requires the TF modulation problem to come to the fore. We review several ways to manage TF activity (small molecules, transfection, nanocarriers, protein-based approaches), analyzing their limitations and the possibilities to overcome them. Delivery of TFs could revolutionize the biomedical field. Whether this forecast comes true will depend on the ability to develop convenient technologies for targeted delivery of TFs.

Optic Nerve Degeneration after Retinal Ischemia/Reperfusion in a Rodent Model

Retinal ischemia is a common pathomechanism in many ocular disorders such as age-related macular degeneration (AMD), diabetic retinopathy, glaucoma or retinal vascular occlusion. Several studies demonstrated that ischemia/reperfusion (I/R) leads to morphological and functional changes of different retinal cell types. However, little is known about the ischemic effects on the optic nerve. The goal of this study was to evaluate these effects. Ischemia was induced by raising the intraocular pressure (IOP) in one eye of rats to 140 mmHg for 1 h followed by natural reperfusion. After 21 days, histological as well as quantitative real-time PCR (qRT-PCR) analyses of optic nerves were performed. Ischemic optic nerves showed an infiltration of cells and also degeneration with signs of demyelination. Furthermore, a migration and an activation of microglia could be observed histologically as well as on mRNA level. In regard to macroglia, a trend toward gliosis could be noted after ischemia induction by vimentin staining. Additionally, an up-regulation of glial fibrillary acidic protein (GFAP) mRNA was found in ischemic optic nerves. Counting of oligodendrocyte transcription factor 2 positive (Olig2⁺) cells revealed a decrease of oligodendrocytes in the ischemic group. Also, myelin basic protein (MBP) and myelin oligodendrocyte glycoprotein (MOG) mRNA expression was down-regulated after induction of I/R. On immunohistological level, a decrease of MOG was detectable in ischemic optic nerves as well. In addition, SMI-32 stained neurofilaments of longitudinal optic nerve sections showed a strong structural damage of the ischemic optic nerves in comparison to controls. Consequently, retinal ischemia impacts optic nerve degeneration. These findings could help to better understand the course of destruction in the optic nerve after an ischemic insult. Especially for therapeutic studies, the optic nerve is important because of its susceptibility to be damaged as a result to retinal ischemic injury and also its connecting function between the eye and the brain. So, future drug screenings should target not only the retina, but also the functionality and structure of the optic nerve. In the future, these results could lead to the development of new therapeutic strategies for treatment of ischemic injury.

Enhanced effect of nuclear localization signal peptide during ultrasound‑targeted microbubble destruction‑mediated gene transfection

Ultrasound‑targeted microbubble destruction (UTMD) can promote the entry of plasmid DNA (pDNA) into the cell cytoplasm, by increasing the permeability of the cell membrane. But the transfection efficiency remains low due to inability of the pDNA to enter the nucleus. Various methods have been explored to improve the UTMD transfection efficiency, but with little success. In cells, the classic nuclear localization signal (cNLS) peptide is an amino acid sequence that signals proteins that are due for nuclear transport. The present study aimed to investigate whether binding of a cNLS peptide to the pDNA may improve the transfection efficiency of UTMD. Four experimental groups were analyzed: Control group (UTMD + pDNA), group with cNLS (UTMD + pDNA + cNLS), group with mutated NLS (mNLS; UTMD + pDNA + mNLS), and group with cNLS and the nuclear import blocker, wheat germ agglutinin (WGA; UTMD + pDNA + cNLS + WGA). The NLS was labeled by fluorescein isothiocyanate, whereas pDNA was labeled with Cy3. Different molar ratios were tested for the NLS and pDNA combination in order to achieve optimal binding of the two molecules. Human umbilical vein endothelial cells were then transfected using the optimum ultrasonic irradiation parameters and NLS/pDNA molar ratio. At 6 h post‑transfection, the rates of Cy3‑labeled pDNA inside the cells and their nuclei were detected by flow cytometry and laser confocal microscopy, and the cellular vs. nuclear uptake of pDNA was calculated. In order to further evaluate the effect of NLS on UTMD‑mediated gene transfection, the transfection efficiency and relative expression levels of mRNA and protein were detected at 48 h post‑transfection. The results demonstrated that the optimal molar ratio of NLS with pDNA was 104:1. The rates of pDNA successful entry into the cell and nucleus were significantly higher in the cNLS group compared with the control group. The transfection efficiency, and relative expression levels of mRNA and protein from the plasmid were significantly increased in the cNLS group compared with the control group. The mNLS group displayed no significant difference compared with the control group, while the WGA group exhibited significant inhibition in most indicators of transfection efficiency compared to the cNLS group. These results suggest that combining a cNLS peptide with pDNA during UTMD‑mediated transfection significantly improved transfection efficiency. Thus, a cNLS peptide may be an important mediator and a new strategy in enhancing the efficiency of UTMD‑mediated gene transfection.

Cellular Reprogramming Using Protein and Cell-Penetrating Peptides

Recently, stem cells have been suggested as invaluable tools for cell therapy because of their self-renewal and multilineage differentiation potential. Thus, scientists have developed a variety of methods to generate pluripotent stem cells, from nuclear transfer technology to direct reprogramming using defined factors, or induced pluripotent stem cells (iPSCs). Considering the ethical issues and efficiency, iPSCs are thought to be one of the most promising stem cells for cell therapy. Induced pluripotent stem cells can be generated by transduction with a virus, plasmid, RNA, or protein. Herein, we provide an overview of the current technology for iPSC generation and describe protein-based transduction technology in detail.

Cell-Penetrating Peptide as a Means of Directing the Differentiation of Induced-Pluripotent Stem Cells

Protein transduction using cell-penetrating peptides (CPPs) is useful for the delivery of large protein molecules, including some transcription factors. This method is safer than gene transfection methods with a viral vector because there is no risk of genomic integration of the exogenous DNA. Recently, this method was reported as a means for the induction of induced pluripotent stem (iPS) cells, directing the differentiation into specific cell types and supporting gene editing/correction. Furthermore, we developed a direct differentiation method to obtain a pancreatic lineage from mouse and human pluripotent stem cells via the protein transduction of three transcription factors, Pdx1, NeuroD, and MafA. Here, we discuss the possibility of using CPPs as a means of directing the differentiation of iPS cells and other stem cell technologies.

Targeted intracellular delivery of proteins with spatial and temporal control

While a host of methods exist to deliver genetic materials or small molecules to cells, very few are available for protein delivery to the cytosol. We describe a modular, light-activated nanocarrier that transports proteins into cells by receptor-mediated endocytosis and delivers the cargo to the cytosol by light triggered endosomal escape. The platform is based on hollow gold nanoshells (HGN) with polyhistidine tagged proteins attached through an avidity-enhanced, nickel chelation linking layer; here, we used green fluorescent protein (GFP) as a model deliverable cargo. Endosomal uptake of the GFP loaded nanocarrier was mediated by a C-end Rule (CendR) internalizing peptide fused to the GFP. Focused femtosecond pulsed-laser excitation triggered protein release from the nanocarrier and endosome disruption, and the released protein was capable of targeting the nucleoli, a model intracellular organelle. We further demonstrate the generality of the approach by loading and releasing Sox2 and p53. This method for targeting of individual cells, with resolution similar to microinjection, provides spatial and temporal control over protein delivery.

Olig2 overexpression accelerates the differentiation of mouse embryonic stem cells into oligodendrocyte progenitor cells in vitro

Oligodendrocyte progenitor cells (OPCs) transplantation is receiving considerable attention in the field of regenerative medicine therapy for demyelinating diseases. Although embryonic stem cells (ESCs) have been successfully induced to differentiate into OPCs with cytokines cocktails in vitro, the regulatory roles of many key transcription factors in this process are not clear. Here, we introduced oligodendrocyte lineage transcription factor 2 (Olig2), a basic helix-loop-helix transcription factor, into mouse embryonic stem cells (mESCs) to investigate its effects on the differentiation of mESCs into OPCs. The results showed that Olig2 overexpression alone did not affect pluripotency of mESCs, but in the stimulation of differentiating cocktails, Olig2 accelerated mESCs to differentiate into OPCs, shortening the induction time span from normal 21 days to 11 days. Further study demonstrated the Olig2-mESCs derived OPCs were able to differentiate into C-type natriuretic peptid (CNP) and Myelin Basic Protein (MBP) positive mature oligodendrocytes (OLs) in vitro, suggesting these induced OPCs might be favorable for myelin regeneration in vivo.

Differentiation therapy for solid tumors

Differentiation therapy for tumors refers to treating malignant tumors via the induction of cell differentiation. The best characterized clinical application of differentiation therapy is the use of all-trans retinoic acid in the treatment of acute promyelocytic leukemia (APL), which markedly improved the outcome of this disease. Unlike the situation with APL, the development of differentiation therapy for solid tumors is far from satisfactory. To date, no differentiation-inducing agents have been demonstrated to exert a curative effect on solid tumors. However, over the past decade progress in understanding the differentiation pathways and the development of differentiation-inducing agents might shed new light on the differentiation therapy for solid tumors.

Differential expression and regulatory roles of FABP5 and FABP7 in oligodendrocyte lineage cells

Fatty-acid-binding proteins (FABPs) are key intracellular molecules involved in the uptake, transportation and storage of fatty acids and in the mediation of signal transduction and gene transcription. However, little is known regarding their expression and function in the oligodendrocyte lineage. We evaluate the in vivo and in vitro expression of FABP5 and FABP7 in oligodendrocyte lineage cells in the cortex and corpus callosum of adult mice, mixed cortical culture and oligosphere culture by immunofluorescent counter-staining with major oligodendrocyte lineage markers. In all settings, FABP7 expression was detected in NG2(+)/PDGFRα(+) oligodendrocyte progenitor cells (OPCs) that did not express FABP5. FABP5 was detected in mature CC1(+)/MBP(+) oligodendrocytes that did not express FABP7. Analysis of cultured OPCs showed a significant decrease in the population of FABP7-knockout (KO) OPCs and their BrdU uptake compared with wild-type (WT) OPCs. Upon incubation of OPCs in oligodendrocyte differentiation medium, a significantly lower percentage of FABP7-KO OPCs differentiated into O4(+) oligodendrocytes. The percentage of mature MBP(+) oligodendrocytes relative to whole O4(+)/MBP(+) oligodendrocytes was significantly lower in FABP7-KO and FABP5-KO than in WT cell populations. The percentage of terminally mature oligodendrocytes with membrane sheet morphology was significantly lower in FABP5-KO compared with WT cell populations. Thus, FABP7 and FABP5 are differentially expressed in oligodendrocyte lineage cells and regulate their proliferation and/or differentiation. Our findings suggest the involvement of FABP7 and FABP5 in the pathophysiology of demyelinating disorders, neuropsychiatric disorder and glioma, conditions in which OPCs/oligodendrocytes play central roles.

ISL1 protein transduction promotes cardiomyocyte differentiation from human embryonic stem cells

BACKGROUND

Human embryonic stem cells (hESCs) have the potential to provide an unlimited source of cardiomyocytes, which are invaluable resources for drug or toxicology screening, medical research, and cell therapy. Currently a number of obstacles exist such as the insufficient efficiency of differentiation protocols, which should be overcome before hESC-derived cardiomyocytes can be used for clinical applications. Although the differentiation efficiency can be improved by the genetic manipulation of hESCs to over-express cardiac-specific transcription factors, these differentiated cells are not safe enough to be applied in cell therapy. Protein transduction has been demonstrated as an alternative approach for increasing the efficiency of hESCs differentiation toward cardiomyocytes.

METHODS

We present an efficient protocol for the differentiation of hESCs in suspension by direct introduction of a LIM homeodomain transcription factor, Islet1 (ISL1) recombinant protein into the cells.

RESULTS

We found that the highest beating clusters were derived by continuous treatment of hESCs with 40 µg/ml recombinant ISL1 protein during days 1-8 after the initiation of differentiation. The treatment resulted in up to a 3-fold increase in the number of beating areas. In addition, the number of cells that expressed cardiac specific markers (cTnT, CONNEXIN 43, ACTININ, and GATA4) doubled. This protocol was also reproducible for another hESC line.

CONCLUSIONS

This study has presented a new, efficient, and reproducible procedure for cardiomyocytes differentiation. Our results will pave the way for scaled up and controlled differentiation of hESCs to be used for biomedical applications in a bioreactor culture system.

Non-genetic modulation of Notch activity by artificial delivery of Notch intracellular domain into neural stem cells

Stem cells have become a major focus of scientific interest as a potential source of somatic cell types for biomedical applications. Understanding and controlling the elicitors and mechanisms in differentiation of pluripotent stem cell-derived somatic cell types remains a key challenge. The major types of molecular processes that control cellular differentiation involve evolutionary conserved cell signaling pathways. Notch receptors participate in a wide variety of biological processes, including cell fate decisions of stem cells. This study explores the potential of protein transduction to directly deliver recombinant Notch-1 intracellular domain (NICD) into mammalian cells in order to accomplish transgene-free Notch activation. We engineered a cell-permeant version of NICD and explored its function on mouse and human neural stem cells. We show that NICD transduction modulates known direct and indirect Notch target genes and antagonizes the DAPT-mediated inhibition of Notch signaling on the transcriptional level. Moreover, NICD enhances cell proliferation accompanied by increased cyclin D1 and decreased p27 protein levels. In the absence of growth factors NICD strongly impairs neuronal differentiation while being insufficient to keep cells in a proliferative state. Furthermore, our studies depict NICD protein transduction as a novel tool for a time and dose-dependent non-genetic modulation of Notch signaling to decipher its cellular functions.

Cellular reprogramming employing recombinant sox2 protein

Induced pluripotent stem (iPS) cells represent an attractive option for the derivation of patient-specific pluripotent cells for cell replacement therapies as well as disease modeling. To become clinically meaningful, safe iPS cells need to be generated exhibiting no permanent genetic modifications that are caused by viral integrations of the reprogramming transgenes. Recently, various experimental strategies have been applied to accomplish transgene-free derivation of iPS cells, including the use of nonintegrating viruses, episomal expression, or excision of transgenes after reprogramming by site-specific recombinases or transposases. A straightforward approach to induce reprogramming factors is the direct delivery of either synthetic mRNA or biologically active proteins. We previously reported the generation of cell-permeant versions of Oct4 (Oct4-TAT) and Sox2 (Sox2-TAT) proteins and showed that Oct4-TAT is reprogramming-competent, that is, it can substitute for Oct4-encoding virus. Here, we explore conditions for enhanced Sox2-TAT protein stabilization and functional delivery into somatic cells. We show that cell-permeant Sox2 protein can be stabilized by lipid-rich albumin supplements in serum replacement or low-serum-supplemented media. Employing optimized conditions for protein delivery, we demonstrate that Sox2-TAT protein is able to substitute for viral Sox2. Sox2-piPS cells express pluripotency-associated markers and differentiate into all three germ layers.