Characterization and neural differentiation of mouse embryonic and induced pluripotent stem cells on cadherin-based substrata

Cell adhesion molecule immobilized gold surfaces for enhanced neuron-electrode interfaces

To provide a long-term solution for increasing the biocompatibility of neuroprosthetics, approaches to reduce the side effects of invasive neuro-implantable devices are still in need of improvement. Physical, chemical, and bioactive design aspects of the biomaterials are proven to be important for providing proper cell-to-cell, cell-to-material interactions. Particularly, modification of implant surfaces with bioactive cues, especially cell adhesion molecules (CAMs) that capitalize on native neural adhesion mechanisms, are promising candidates in favor of providing efficient interfaces. Within this concept, this study utilized specific CAMs, namely N-Cadherin (Neural cadherin, N-Cad) and neural cell adhesion molecule (NCAM), to enhance neuron-electrode contact by mimicking the cell-to-ECM interactions for improving the survival of cells and promoting neurite outgrowth. For this purpose, representative gold electrode surfaces were modified with N-Cadherin, NCAM, and the mixture (1:1) of these molecules. Modifications were characterized, and the effect of surface modification on both differentiated and undifferentiated neuroblastoma SH-SY5Y cell lines were compared. The findings demonstrated the successful modification of these molecules which subsequently exhibited biocompatible properties as evidenced by the cell viability results. In cell culture experiments, the CAMs displayed promising results in promoting neurite outgrowth compared to conventional poly-l-lysine coated surfaces, especially NCAM and N-Cad/NCAM modified surfaces clearly showed significant improvement. Overall, this optimized approach is expected to provide an insight into the action mechanisms of cells against the local environment and advance processes for the fabrication of alternative neural interfaces.

Neural Differentiation of Induced Pluripotent Stem Cells for a Xenogeneic Material-Free 3D Neurological Disease Model Neurulation from Pluripotent Cells Using a Human Hydrogel

Alzheimer's Disease (AD) is characterized by synapse and neuronal loss and the accumulation of neurofibrillary tangles and Amyloid β plaques. Despite significant research efforts to understand the late stages of the disease, its etiology remains largely unknown. This is in part because of the imprecise AD models in current use. In addition, little attention has been paid to neural stem cells (NSC), which are the cells responsible for the development and maintenance of brain tissue during an individual's lifespan. Thus, an in vitro 3D human brain tissue model using induced pluripotent stem (iPS) cell-derived neural cells in human physiological conditions may be an excellent alternative to standard models to investigate AD pathology. Following the differentiation process mimicking development, iPS cells can be turned into NSCs and, ultimately, neural cells. During differentiation, the traditionally used xenogeneic products may alter the cells' physiology and prevent accurate disease pathology modeling. Hence, establishing a xenogeneic material-free cell culture and differentiation protocol is essential. This study investigated the differentiation of iPS cells to neural cells using a novel extracellular matrix derived from human platelet lysates (PL Matrix). We compared the stemness properties and differentiation efficacies of iPS cells in a PL matrix against those in a conventional 3D scaffold made of an oncogenic murine-matrix. Using well-defined conditions without xenogeneic material, we successfully expanded and differentiated iPS cells into NSCs via dual-SMAD inhibition, which regulates the BMP and TGF signaling cascades in a manner closer to human conditions. This in vitro, 3D, xenogeneic-free scaffold will enhance the quality of disease modeling for neurodegenerative disease research, and the knowledge produced could be used in developing more effective translational medicine.

VE-cadherin-based matrix promoting the self-reconstruction of pro-vascularization microenvironments and endothelial differentiation of human mesenchymal stem cells

Regulating the secretion and endothelial differentiation of human mesenchymal stem cells (hMSCs) plays an important role in the vascularization in tissue engineering and regenerative medicine. In this study, a recombinant cadherin fusion protein consisting of a human vascular endothelial-cadherin extracellular domain and immunoglobulin IgG Fc region (hVE-cad-Fc) was developed as a bioartificial matrix for modulating hMSCs. The hVE-cad-Fc matrix significantly enhanced the secretion of angiogenic factors, activated the VE-cadherin-VEGFR2/FAK-AKT/PI3K signaling pathway in hMSCs, and promoted the endothelial differentiation of hMSCs even without extra VEGF. Furthermore, the hVE-cad-Fc matrix was applied for the surface modification of a poly (lactic-co-glycolic acid) (PLGA) porous scaffold, which significantly improved the hemocompatibility and vascularization of the PLGA scaffold in vivo. These results revealed that the hVE-cad-Fc matrix should be a superior bioartificial ECM for remodeling the pro-vascularization extracellular microenvironment by regulating the secretion of hMSCs, and showed great potential for the vascularization in tissue engineering.

Direct visualization of the extracellular binding structure of E-cadherins in liquid

E-cadherin is a key Ca-dependent cell adhesion molecule, which is expressed on many cell surfaces and involved in cell morphogenesis, embryonic development, EMT, etc. The fusion protein E-cad-Fc consists of the extracellular domain of E-cadherin and the IgG Fc domain. On plates coated with this chimeric protein, ES/iPS cells are cultivated particularly well and induced to differentiate. The cells adhere to the plate via E-cad-Fc in the presence of Ca2+ and detach by a chelating agent. For the purpose of clarifying the structures of E-cad-Fc in the presence and absence of Ca2+, we analyzed the molecular structure of E-cad-Fc by AFM in liquid. Our AFM observations revealed a rod-like structure of the entire extracellular domain of E-cad-Fc in the presence of Ca2+ as well as trans-binding of E-cad-Fc with adjacent molecules, which may be the first, direct confirmation of trans-dimerization of E-cadherin. The observed structures were in good agreement with an X-ray crystallographic model. Furthermore, we succeeded in visualizing the changes in the rod-like structure of the EC domains with and without calcium. The biomatrix surface plays an important role in cell culture, so the analysis of its structure and function may help promote cell engineering based on cell recognition.

Bioactive Elastic Scaffolds Loaded with Neural Stem Cells Promote Rapid Spinal Cord Regeneration

Despite decades of research, spinal cord injury (SCI) still causes irreparable damage to the human body. Key challenges that hinder the regeneration and extension of neurons following SCI must be overcome, including the overexpressed glial scar formation and strong inflammatory responses in lesion tissue. Transplantation of neural stem cells (NSCs) represents a promising therapeutic method due to its beneficial roles like growth factor secretion and anti-inflammation. However, NSCs usually differentiate into astrocytes, which is considered as one potential limitation of current NSC therapy. Herein, we fabricate an elastic poly(sebacoyl diglyceride) (PSeD) scaffold to mimic the mechanical properties of the natural spinal cord. The PSeD scaffold is coated with poly(sebacoyl diglyceride)-isoleucine-lysine-valine-alanine-valine-serine (PSeD-IKVAVS) to create a bioactive interface. The core point of this topic is divided into two parts. First, PSeD is a bioelastomer and its mechanical properties are similar to those of the natural spinal cord. This feature reduces the direct stimulation to the spinal cord tissue by the elastomer and then reduces the immune response or resistance caused by the host spinal cord tissue. Second, the IKVAVS peptide modifies PSeD to create a bioactive interface to support NSC growth and differentiation. In the in vivo study, the number of CD68-positive macrophages decreased in the PSeD-IKVAVS/NSC group compared to that in the SCI group (20% vs 60%). The low inflammation induced by the scaffold was beneficial to NSCs, resulting in increased locomotor recovery, as indicated by the increased Basso-Beattie-Bresnahan score (5, the average score in the PSeD-IKVAVS/NSC group, vs 2, the average score in the SCI group). Based on the above two characteristics, a PSeD-IKVAVS bioelastomer is fabricated, which provides a beneficial and bioactive microenvironment for NSCs after transplantation.

Nanomaterial integration into the scaffolding materials for nerve tissue engineering: a review

The nervous system, which consists of a complex network of millions of neurons, is one of the most highly intricate systems in the body. This complex network is responsible for the physiological and cognitive functions of the human body. Following injuries or degenerative diseases, damage to the nervous system is overwhelming because of its complexity and its limited regeneration capacity. However, neural tissue engineering currently has some capacities for repairing nerve deficits and promoting neural regeneration, with more developments in the future. Nevertheless, controlling the guidance of stem cell proliferation and differentiation is a challenging step towards this goal. Nanomaterials have the potential for the guidance of the stem cells towards the neural lineage which can overcome the pitfalls of the classical methods since they provide a unique microenvironment that facilitates cell-matrix and cell-cell interaction, and they can manipulate the cell signaling mechanisms to control stem cells' fate. In this article, the suitable cell sources and microenvironment cues for neuronal tissue engineering were examined. Afterward, the nanomaterials that impact stem cell proliferation and differentiation towards neuronal lineage were reviewed.

Induced Pluripotent Stem Cells: Reprogramming Platforms and Applications in Cell Replacement Therapy

The generation of induced pluripotent stem cells (iPSCs) from differentiated mature cells is one of the most promising technologies in the field of regenerative medicine. The ability to generate patient-specific iPSCs offers an invaluable reservoir of pluripotent cells, which could be genetically engineered and differentiated into target cells to treat various genetic and degenerative diseases once transplanted, hence counteracting the risk of graft versus host disease. In this context, we review the scientific research streams that lead to the emergence of iPSCs, the roles of reprogramming factors in reprogramming to pluripotency, and the reprogramming strategies. As iPSCs serve tremendous correction potentials for various diseases, we highlight the successes and challenges of iPSCs in cell replacement therapy and the synergy of iPSCs and clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene editing tools in therapeutics research.

Neural differentiation of mouse induced pluripotent stem cells using cadherin gene-engineered PA6 feeder cells

Investigating neural differentiation of pluripotent stem cells, including induced pluripotent stem (iPS) cells, is of importance for studying early neural development and providing a potential source of cells for nerve regeneration. Stromal cell-derived inducing activity (SDIA) using PA6 stromal cells promotes neural differentiation of iPS cells. Thus, we hypothesized that cadherin gene-engineered PA6 feeder cells will enhance the performance of SDIA by facilitating cell-cell interactions. Consequently, we created cadherin gene-engineered PA6 cells. Efficiency of neural differentiation from mouse iPS cells on PA6 feeder cells overexpressing E-cadherin gene (46%) or N-cadherin gene (27%) was significantly higher compared with parental PA6 feeder cells (19%). In addition, efficiency of motor neuron differentiation from mouse iPS cells on cadherin-gene engineered feeder cells (E-cadherin, 7.4%; N-cadherin, 11%) was significantly higher compared with parental PA6 feeder cells (4.1%). Altogether, these results indicate that cadherin gene-engineered feeder cells are a potent tool for promoting neural differentiation of pluripotent stem cells.

Accelerated neural differentiation of mouse embryonic stem cells on aligned GYIGSR-functionalized nanofibers

Substrates for embryonic stem cell culture are typified by poorly defined xenogenic, whole proteins or cellular components that are difficult and expensive to generate, characterize, and recapitulate. Herein, the generation of well-defined scaffolds of Gly-Tyr-Ile-Gly-Ser-Arg (GYIGSR) peptide-functionalized poly(ε-caprolactone) (PCL) aligned nanofibers are used to accelerate the neural lineage commitment and differentiation of D3 mouse embryonic stem cells (mESCs). Gene expression trends and immunocytochemistry analysis were similar to laminin-coated glass, and indicated an earlier differentiation progression than D3 mESCs on laminin. Further, GYIGSR-functionalized nanofiber substrates yielded an increased gene expression of Sox1, a neural progenitor cell marker, and Tubb3, Cdh2, Syp, neuronal cell markers, at early time points. In addition, guidance of neurites was found to parallel the fiber direction. We demonstrate the fabrication of a well-defined, xeno-free functional nanofiber scaffold and demonstrates its use as a surrogate for xenogenic and complex matrixes currently used for the neural differentiation of stem cells ex vivo.

STATEMENT OF SIGNIFICANCE

In this paper, we report the use of GYIGSR-functionalized poly(ε-caprolactone) aligned nanofibers as a tool to accelerate the neural lineage commitment and differentiation of D3 mouse embryonic stem cells. The results indicate that functional nanofiber substrates promote faster differentiation than laminin coated substrates. The data suggest that aligned nanofibers and post-electrospinning surface modification with bioactive species can be combined to produce translationally relevant xeno-free substrates for stem cell therapy. Future development efforts are focused on additional bioactive species that are able to function as surrogates for other xenogenic factors found in differentiation media.

Decoding cell signalling and regulation of oligodendrocyte differentiation

Oligodendrocytes are fundamental for the functioning of the nervous system; they participate in several cellular processes, including axonal myelination and metabolic maintenance for astrocytes and neurons. In the mammalian nervous system, they are produced through waves of proliferation and differentiation, which occur during embryogenesis. However, oligodendrocytes and their precursors continue to be generated during adulthood from specific niches of stem cells that were not recruited during development. Deficiencies in the formation and maturation of these cells can generate pathologies mainly related to myelination. Understanding the mechanisms involved in oligodendrocyte development, from the precursor to mature cell level, will allow inferring therapies and treatments for associated pathologies and disorders. Such mechanisms include cell signalling pathways that involve many growth factors, small metabolic molecules, non-coding RNAs, and transcription factors, as well as specific elements of the extracellular matrix, which act in a coordinated temporal and spatial manner according to a given stimulus. Deciphering those aspects will allow researchers to replicate them in vitro in a controlled environment and thus mimic oligodendrocyte maturation to understand the role of oligodendrocytes in myelination in pathologies and normal conditions. In this study, we review these aspects, based on the most recent in vivo and in vitro data on oligodendrocyte generation and differentiation.

Detachment of Chain-Forming Neuroblasts by Fyn-Mediated Control of cell-cell Adhesion in the Postnatal Brain

In the rodent olfactory system, neuroblasts produced in the ventricular-subventricular zone of the postnatal brain migrate tangentially in chain-like cell aggregates toward the olfactory bulb (OB) through the rostral migratory stream (RMS). After reaching the OB, the chains are dissociated and the neuroblasts migrate individually and radially toward their final destination. The cellular and molecular mechanisms controlling cell-cell adhesion during this detachment remain unclear. Here we report that Fyn, a nonreceptor tyrosine kinase, regulates the detachment of neuroblasts from chains in the male and female mouse OB. By performing chemical screening and in vivo loss-of-function and gain-of-function experiments, we found that Fyn promotes somal disengagement from the chains and is involved in neuronal migration from the RMS into the granule cell layer of the OB. Fyn knockdown or Dab1 (disabled-1) deficiency caused p120-catenin to accumulate and adherens junction-like structures to be sustained at the contact sites between neuroblasts. Moreover, a Fyn and N-cadherin double-knockdown experiment indicated that Fyn regulates the N-cadherin-mediated cell adhesion between neuroblasts. These results suggest that the Fyn-mediated control of cell-cell adhesion is critical for the detachment of chain-forming neuroblasts in the postnatal OB.SIGNIFICANCE STATEMENT In the postnatal brain, newly born neurons (neuroblasts) migrate in chain-like cell aggregates toward their destination, where they are dissociated into individual cells and mature. The cellular and molecular mechanisms controlling the detachment of neuroblasts from chains are not understood. Here we show that Fyn, a nonreceptor tyrosine kinase, promotes the somal detachment of neuroblasts from chains, and that this regulation is critical for the efficient migration of neuroblasts to their destination. We further show that Fyn and Dab1 (disabled-1) decrease the cell-cell adhesion between chain-forming neuroblasts, which involves adherens junction-like structures. Our results suggest that Fyn-mediated regulation of the cell-cell adhesion of neuroblasts is critical for their detachment from chains in the postnatal brain.

Exploiting Advanced Hydrogel Technologies to Address Key Challenges in Regenerative Medicine

Regenerative medicine aims to tackle a panoply of challenges from repairing focal damage to articular cartilage to preventing pathological tissue remodeling after myocardial infarction. Hydrogels are water-swollen networks formed from synthetic or naturally derived polymers and are emerging as important tools to address these challenges. Recent advances in hydrogel chemistries are enabling researchers to create hydrogels that can act as 3D ex vivo tissue models, allowing them to explore fundamental questions in cell biology by replicating tissues' dynamic and nonlinear physical properties. Enabled by cutting edge techniques such as 3D bioprinting, cell-laden hydrogels are also being developed with highly controlled tissue-specific architectures, vasculature, and biological functions that together can direct tissue repair. Moreover, advanced in situ forming and acellular hydrogels are increasingly finding use as delivery vehicles for bioactive compounds and in mediating host cell response. Here, advances in the design and fabrication of hydrogels for regenerative medicine are reviewed. It is also addressed how controlled chemistries are allowing for precise engineering of spatial and time-dependent properties in hydrogels with a look to how these materials will eventually translate to clinical applications.

Dual repression of endocytic players by ESCC microRNAs and the Polycomb complex regulates mouse embryonic stem cell pluripotency

Cell fate determination in the early mammalian embryo is regulated by multiple mechanisms. Recently, genes involved in vesicular trafficking have been shown to play an important role in cell fate choice, although the regulation of their expression remains poorly understood. Here we demonstrate for the first time that multiple endocytosis associated genes (EAGs) are repressed through a novel, dual mechanism in mouse embryonic stem cells (mESCs). This involves the action of the Polycomb Repressive Complex, PRC2, as well as post-transcriptional regulation by the ESC-specific cell cycle-regulating (ESCC) family of microRNAs. This repression is relieved upon differentiation. Forced expression of EAGs in mESCs results in a decrease in pluripotency, highlighting the importance of dual repression in cell fate regulation. We propose that endocytosis is critical for cell fate choice, and dual repression may function to tightly regulate levels of endocytic genes.

Concentration dependent survival and neural differentiation of murine embryonic stem cells cultured on polyethylene glycol dimethacrylate hydrogels possessing a continuous concentration gradient of n-cadherin derived peptide His-Ala-Val-Asp-Lle

N-cadherin cell-cell signaling plays a key role in the structure and function of the nervous system. However, few studies have incorporated bioactive signaling from n-cadherin into tissue engineering matrices. The present study uses a continuous gradient approach in polyethylene glycol dimethacrylate hydrogels to identify concentration dependent effects of n-cadherin peptide, His-Ala-Val-Asp-Lle (HAVDI), on murine embryonic stem cell survival and neural differentiation. The n-cadherin peptide was found to affect the expression of pluripotency marker, alkaline phosphatase, in murine embryonic stem cells cultured on n-cadherin peptide containing hydrogels in a concentration dependent manner. Increasing n-cadherin peptide concentrations in the hydrogels elicited a biphasic response in neurite extension length and mRNA expression of neural differentiation marker, neuron-specific class III β-tubulin, in murine embryonic stem cells cultured on the hydrogels. High concentrations of n-cadherin peptide in the hydrogels were found to increase the expression of apoptotic marker, caspase 3/7, in murine embryonic stem cells compared to that of murine embryonic stem cell cultures on hydrogels containing lower concentrations of n-cadherin peptide. Increasing the n-cadherin peptide concentration in the hydrogels facilitated greater survival of murine embryonic stem cells exposed to increasing oxidative stress caused by hydrogen peroxide exposure. The combinatorial approach presented in this work demonstrates concentration dependent effects of n-cadherin signaling on mouse embryonic stem cell behavior, underscoring the need for the greater use of systematic approaches in tissue engineering matrix design in order to understand and optimize bioactive signaling in the matrix for tissue formation.

STATEMENT OF SIGNIFICANCE

Single cell encapsulation is common in tissue engineering matrices. This eliminates cellular access to cell-cell signaling. N-cadherin, a cell-cell signaling molecule, plays a vital role in the development of neural tissues, but has not been well studied as a bioactive signaling element in neural tissue engineering matrices. The present study uses a systematic continuous gradient approach to identify concentration dependent effects of n-cadherin derived peptide, HAVDI, on the survival and neural differentiation of murine embryonic stem cells. This work underscores the need for greater use to combinatorial strategies to understand the effect complex bioactive signaling, such as n-cadherin, and the need to optimize the concentration of such bioactive signaling within tissue engineering matrices for maximal cellular response.

Membrane translocation of t-SNARE protein syntaxin-4 abrogates ground-state pluripotency in mouse embryonic stem cells

Embryonic stem (ES) and induced pluripotent stem (iPS) cells are attractive tools for regenerative medicine therapies. However, aberrant cell populations that display flattened morphology and lose ground-state pluripotency often appear spontaneously, unless glycogen synthase kinase 3β (GSK3β) and mitogen-activated protein kinase kinase (MEK1/2) are inactivated. Here, we show that membrane translocation of the t-SNARE protein syntaxin-4 possibly is involved in this phenomenon. We found that mouse ES cells cultured without GSK3β/MEK1/2 inhibitors (2i) spontaneously extrude syntaxin-4 at the cell surface and that artificial expression of cell surface syntaxin-4 induces appreciable morphological changes and mesodermal differentiation through dephosphorylation of Akt. Transcriptome analyses revealed several candidate elements responsible for this, specifically, an E-to P-cadherin switch and a marked downregulation of Zscan4 proteins, which are DNA-binding proteins essential for ES cell pluripotency. Embryonic carcinoma cell lines F9 and P19CL6, which maintain undifferentiated states independently of Zscan4 proteins, exhibited similar cellular behaviors upon stimulation with cell surface syntaxin-4. The functional ablation of E-cadherin and overexpression of P-cadherin reproduced syntaxin-4-induced cell morphology, demonstrating that the E- to P-cadherin switch executes morphological signals from cell surface syntaxin-4. Thus, spontaneous membrane translocation of syntaxin-4 emerged as a critical element for maintenance of the stem-cell niche.

Molecular Analysis of Stromal Cells-Induced Neural Differentiation of Mouse Embryonic Stem Cells

Deriving specific neural cells from embryonic stem cells (ESCs) is a promising approach for cell replacement therapies of neurodegenerative diseases. When co-cultured with certain stromal cells, mouse ESCs (mESCs) differentiate efficiently to neural cells. In this study, a comprehensive gene and protein expression analysis of differentiating mESCs is performed over a two-week culture period to track temporal progression of cells from a pluripotent state to specific terminally-differentiated neural cells such as neurons, astrocytes, and oligodendrocytes. Expression levels of 26 genes consisting of marker genes for pluripotency, neural progenitors, and specific neuronal, astroglial, and oligodendrocytic cells are tracked using real time q-PCR. The time-course gene expression analysis of differentiating mESCs is combined with the hierarchal clustering and functional principal component analysis (FPCA) to elucidate the evolution of specific neural cells from mESCs at a molecular level. These statistical analyses identify three major gene clusters representing distinct phases of transition of stem cells from a pluripotent state to a terminally-differentiated neuronal or glial state. Temporal protein expression studies using immunohistochemistry demonstrate the generation of neural stem/progenitor cells and specific neural lineages and show a close agreement with the gene expression profiles of selected markers. Importantly, parallel gene and protein expression analysis elucidates long-term stability of certain proteins compared to those with a quick turnover. Describing the molecular regulation of neural cells commitment of mESCs due to stromal signaling will help identify major promoters of differentiation into specific cell types for use in cell replacement therapy applications.

Construction of a Defined Biomimetic Matrix for Long-Term Maintenance of Mouse Induced Pluripotent Stem Cells

The existing in vitro culture systems often use undefined and animal-derived components for the culture of pluripotent stem cells. Artificial bioengineered peptides have the potential to become alternatives to these components of extracellular matrix (ECM). Integrins and cadherins are two cell adhesion proteins important for stem cell self-renewal, differentiation, and phenotype stability. In the present study, we sought to mimic the physico-biochemical properties of natural ECMs that allow self-renewal of mouse induced pluripotent stem cells (iPSCs). We develop a genetically engineered ECM protein (ERE-CBP) that contains (i) an integrin binding peptide sequence (RGD/R), (ii) an E-/N-cadherin binding peptide sequence (SWELYYPLRANL/CBP), and (iii) 12 repeats of APGVGV elastin-like polypeptides (ELPs/E).While ELPs allow efficient coating by binding to nontreated hydrophobic tissue culture plates, RGD/R and CBP support integrin- and cadherin-dependent cell attachment, respectively. Mouse iPSCs on this composite matrix exhibit a more compact phenotype compared to cells on control gelatin substrate. We also demonstrated that the ERE-CBP supports proliferation and long-term self-renewal of mouse iPSCs for up to 17 passages without GSK3β (CHIR99021) and Erk (PD0325901) inhibitors. Overall, our engineered ECM protein, which is cost-effective to produce in prokaryotic origin and flexible to modify with other cell adhesion peptides or growth factors, provides a novel approach for expansion of mouse iPSCs in vitro.

Dynamic polyrotaxane-coated surface for effective differentiation of mouse induced pluripotent stem cells into cardiomyocytes

Increasing molecular mobility of hydrated polyrotaxane (PRX)-coated surfaces was effective to promote the differentiation of mouse induced pluripotent stem cells (iPS cells) into cardiomyocytes.

An Engineered N-Cadherin Substrate for Differentiation, Survival, and Selection of Pluripotent Stem Cell-Derived Neural Progenitors

For stem cell-based treatment of neurodegenerative diseases a better understanding of key developmental signaling pathways and robust techniques for producing neurons with highest homogeneity are required. In this study, we demonstrate a method using N-cadherin-based biomimetic substrate to promote the differentiation of mouse embryonic stem cell (ESC)- and induced pluripotent stem cell (iPSC)-derived neural progenitor cells (NPCs) without exogenous neuro-inductive signals. We showed that substrate-dependent activation of N-cadherin reduces Rho/ROCK activation and β-catenin expression, leading to the stimulation of neurite outgrowth and conversion into cells expressing neural/glial markers. Besides, plating dissociated cells on N-cadherin substrate can significantly increase the differentiation yield via suppression of dissociation-induced Rho/ROCK-mediated apoptosis. Because undifferentiated ESCs and iPSCs have low affinity to N-cadherin, plating dissociated cells on N-cadherin-coated substrate increase the homogeneity of differentiation by purging ESCs and iPSCs (~30%) from a mixture of undifferentiated cells with NPCs. Using this label-free cell selection approach we enriched differentiated NPCs plated as monolayer without ROCK inhibitor. Therefore, N-cadherin biomimetic substrate provide a powerful tool for basic study of cell—material interaction in a spatially defined and substrate-dependent manner. Collectively, our approach is efficient, robust and cost effective to produce large quantities of differentiated cells with highest homogeneity and applicable to use with other types of cells.

N-cadherin-based adherens junction regulates the maintenance, proliferation, and differentiation of neural progenitor cells during development

This review addresses our current understanding of the regulatory mechanism by which N-cadherin, a classical cadherin, affects neural progenitor cells (NPCs) during development. N-cadherin is responsible for the integrity of adherens junctions (AJs), which develop in the sub-apical region of NPCs in the neural tube and brain cortex. The apical domain, which contains the sub-apical region, is involved in the switching from symmetric proliferative division to asymmetric neurogenic division of NPCs. In addition, N-cadherin-based AJ is deeply involved in the apico-basal polarity of NPCs and the regulation of Wnt-β-catenin, hedgehog (Hh), and Notch signaling. In this review, we discuss the roles of N-cadherin in the maintenance, proliferation, and differentiation of NPCs through components of AJ, β-catenin and αE-catenin.

Modulation of integrin and E-cadherin-mediated adhesions to spatially control heterogeneity in human pluripotent stem cell differentiation

Heterogeneity in human pluripotent stem cell (PSC) fates is partially caused by mechanical asymmetry arising from spatial polarization of cell-cell and cell-matrix adhesions. Independent studies have shown that integrin and E-cadherin adhesions promote opposing differentiation and pluripotent fates respectively although their crosstalk mechanism in modulating cell fate heterogeneity remains unknown. Here, we demonstrated that spatial polarization of integrin and E-cadherin adhesions in a human PSC colony compete to recruit Rho-ROCK activated myosin II to different localities to pattern pluripotent-differentiation decisions, resulting in spatially heterogeneous colonies. Cell micropatterning was used to modulate the spatial polarization of cell adhesions, which enabled us to prospectively determine localization patterns of activated myosin II and mesoendoderm differentiation. Direct inhibition of Rho-ROCK-myosin II activation phenocopied E-cadherin rather than integrin inhibition to form uniformly differentiated colonies. This indicated that E-cadherin was the primary gatekeeper to differentiation progression. This insight allows for biomaterials to be tailored for human PSC maintenance or differentiation with minimal heterogeneity.

Engineered N-cadherin and L1 biomimetic substrates concertedly promote neuronal differentiation, neurite extension and neuroprotection of human neural stem cells

We investigated the design of neurotrophic biomaterial constructs for human neural stem cells, guided by neural developmental cues of N-cadherin and L1 adhesion molecules. Polymer substrates fabricated either as two-dimensional (2-D) films or three-dimensional (3-D) microfibrous scaffolds were functionalized with fusion chimeras of N-cadherin-Fc alone and in combination with L1-Fc, and the effects on differentiation, neurite extension and survival of H9 human-embryonic-stem-cell-derived neural stem cells (H9-NSCs) were quantified. Combinations of N-cadherin and L1-Fc co-operatively enhanced neuronal differentiation profiles, indicating the critical nature of the two complementary developmental cues. Notably, substrates presenting low levels of N-cadherin-Fc concentrations, combined with proportionately higher L1-Fc concentration, most enhanced neurite outgrowth and the degree of MAP2+ and neurofilament-M+ H9-NSCs. Low N-cadherin-Fc alone promoted improved cell survival following oxidative stress, compared to higher concentrations of N-cadherin-Fc alone or combinations with L1-Fc. Pharmacological and antibody blockage studies revealed that substrates presenting low levels of N-cadherin are functionally competent so long as they elicit a threshold signal mediated by homophilic N-cadherin and fibroblast growth factor signaling. Overall, these studies highlight the ability of optimal combinations of N-cadherin and L1 to recapitulate a "neurotrophic" microenvironment that enhances human neural stem cell differentiation and neurite outgrowth. Additionally, 3-D fibrous scaffolds presenting low N-cadherin-Fc further enhanced the survival of H9-NSCs compared to equivalent 2-D films. This indicates that similar biofunctionalization approaches based on N-cadherin and L1 can be translated to 3-D "transplantable" scaffolds with enhanced neurotrophic behaviors. Thus, the insights from this study have fundamental and translational impacts for neural-stem-cell-based regenerative medicine.

Induced pluripotent stem cells for regenerative medicine

With the discovery of induced pluripotent stem (iPS) cells, it is now possible to convert differentiated somatic cells into multipotent stem cells that have the capacity to generate all cell types of adult tissues. Thus, there is a wide variety of applications for this technology, including regenerative medicine, in vitro disease modeling, and drug screening/discovery. Although biological and biochemical techniques have been well established for cell reprogramming, bioengineering technologies offer novel tools for the reprogramming, expansion, isolation, and differentiation of iPS cells. In this article, we review these bioengineering approaches for the derivation and manipulation of iPS cells and focus on their relevance to regenerative medicine.

Neural differentiation from pluripotent stem cells: The role of natural and synthetic extracellular matrix

Neural cells differentiated from pluripotent stem cells (PSCs), including both embryonic stem cells and induced pluripotent stem cells, provide a powerful tool for drug screening, disease modeling and regenerative medicine. High-purity oligodendrocyte progenitor cells (OPCs) and neural progenitor cells (NPCs) have been derived from PSCs recently due to the advancements in understanding the developmental signaling pathways. Extracellular matrices (ECM) have been shown to play important roles in regulating the survival, proliferation, and differentiation of neural cells. To improve the function and maturation of the derived neural cells from PSCs, understanding the effects of ECM over the course of neural differentiation of PSCs is critical. During neural differentiation of PSCs, the cells are sensitive to the properties of natural or synthetic ECMs, including biochemical composition, biomechanical properties, and structural/topographical features. This review summarizes recent advances in neural differentiation of human PSCs into OPCs and NPCs, focusing on the role of ECM in modulating the composition and function of the differentiated cells. Especially, the importance of using three-dimensional ECM scaffolds to simulate the in vivo microenvironment for neural differentiation of PSCs is highlighted. Future perspectives including the immediate applications of PSC-derived neural cells in drug screening and disease modeling are also discussed.

The effects of artificial E-cadherin matrix-induced embryonic stem cell scattering on paxillin and RhoA activation via α-catenin

Mechanical forces have been shown to affect stem cell behavior in a large array of ways. However, our understanding of how these mechanical cues may regulate the behavior of embryonic stem cells (ESCs) remains in its infancy. Here, we aim to clarify the effect of cell scattering on the regulation of Rho family GTPases Rac1 and RhoA as well as paxillin. Allowing ESCs to spread and scatter on a synthetically designed E-cadherin substratum causes phosphorylation of paxillin on consensus phosphorylation sites leading to activation of Rac1 and inactivation of RhoA. By culturing cells in presence of RhoA activator or growing cells to a highly confluent state reverses the effect of cell scattering phenotype. Knockdown of E-cadherin-adapter protein α-catenin revealed that it negatively affects paxillin phosphorylation and up-regulates RhoA activity in compact cellular aggregates. Collectively these results indicate that cell scattering might cause a conformational change of α-catenin limiting its capacity to inhibit paxillin phosphorylation that causes an increase in Rac1 activation and RhoA deactivation. Understanding how synthetically designed extracellular matrix affect ESC signaling through mechanical cues brings a new aspect for stem cell engineers to develop technologies for controlling cell function.

Chitosan stabilizes platelet growth factors and modulates stem cell differentiation toward tissue regeneration

The idea of using chitosan as a functional delivery aid to support simultaneously PRP, stem cells and growth factors (GF) is associated with the intention to use morphogenic biomaterials to modulate the natural healing sequence in bone and other tissues. For example, chitosan-chondroitin sulfate loaded with platelet lysate was included in a poly(D,L-lactate) foam that was then seeded with human adipose-derived stem cells and cultured in vitro under osteogenic stimulus: the platelet lysate provided to the bone tissue the most suitable assortment of GF which induces the osteogenic differentiation of the mesenchymal stem cells. PDGF, FGF, IGF and TGF-β were protagonists in the repair of callus fractures. The release of GF from the composites of chitosan-PRP and either nano-hydroxyapatite or tricalcium phosphate was highly beneficial for enhancing MSC proliferation and differentiation, thus qualifying chitosan as an excellent vehicle. A number of biochemical characteristics of chitosan exert synergism with stem cells in the regeneration of soft tissues.

Comparison of odontogenic differentiation of human dental follicle cells and human dental papilla cells

Classical tooth development theory suggests that dental papilla cells (DPCs) are the precursor cells of odontoblasts, which are responsible for dentin development. However, our previous studies have indicated that dental follicle cells (DFCs) can differentiate into odontoblasts. To further our understanding of tooth development, and the differences in dentinogenesis between DFCs and DPCs, the odontogenic differentiation of DFCs and DPCs was characterized in vitro and in vivo. DFCs and DPCs were individually combined with treated dentin matrix (TDM) before they were subcutaneously implanted into the dorsum of mice for 8 weeks. Results showed that 12 proteins were significantly differential, and phosphoserine aminotransferase 1 (PSAT1), Isoform 2 of hypoxia-inducible factor 1-alpha (HIF1A) and Isoform 1 of annexin A2 (ANXA2), were the most significantly differential proteins. These proteins are related to regulation of bone balance, angiogenesis and cell survival in an anoxic environment. Both DFCs and DPCs express odontogenic, neurogenic and peridontogenic markers. Histological examination of the harvested grafts showed that both DFCs and DPCs form pulp-dentin/cementum-periodentium-like tissues in vivo. Hence, DFCs and DPCs have similar odontogenic differentiation potential in the presence of TDM. However, differences in glucose and amino acid metabolism signal transduction and protein synthesis were observed for the two cell types. This study expands our understanding on tooth development, and provides direct evidence for the use of alternative cell sources in tooth regeneration.

Spatial pattern dynamics of 3D stem cell loss of pluripotency via rules-based computational modeling

Pluripotent embryonic stem cells (ESCs) have the unique ability to differentiate into cells from all germ lineages, making them a potentially robust cell source for regenerative medicine therapies, but difficulties in predicting and controlling ESC differentiation currently limit the development of therapies and applications from such cells. A common approach to induce the differentiation of ESCs in vitro is via the formation of multicellular aggregates known as embryoid bodies (EBs), yet cell fate specification within EBs is generally considered an ill-defined and poorly controlled process. Thus, the objective of this study was to use rules-based cellular modeling to provide insight into which processes influence initial cell fate transitions in 3-dimensional microenvironments. Mouse embryonic stem cells (D3 cell line) were differentiated to examine the temporal and spatial patterns associated with loss of pluripotency as measured through Oct4 expression. Global properties of the multicellular aggregates were accurately recapitulated by a physics-based aggregation simulation when compared to experimentally measured physical parameters of EBs. Oct4 expression patterns were analyzed by confocal microscopy over time and compared to simulated trajectories of EB patterns. The simulations demonstrated that loss of Oct4 can be modeled as a binary process, and that associated patterns can be explained by a set of simple rules that combine baseline stochasticity with intercellular communication. Competing influences between Oct4+ and Oct4- neighbors result in the observed patterns of pluripotency loss within EBs, establishing the utility of rules-based modeling for hypothesis generation of underlying ESC differentiation processes. Importantly, the results indicate that the rules dominate the emergence of patterns independent of EB structure, size, or cell division. In combination with strategies to engineer cellular microenvironments, this type of modeling approach is a powerful tool to predict stem cell behavior under a number of culture conditions that emulate characteristics of 3D stem cell niches.

Efficient neuronal differentiation and maturation of human pluripotent stem cells encapsulated in 3D microfibrous scaffolds

Developing an efficient culture system for controlled human pluripotent stem cell (hPSC) differentiation into selected lineages is a major challenge in realizing stem cell-based clinical applications. Here, we report the use of chitin-alginate 3D microfibrous scaffolds, previously developed for hPSC propagation, to support efficient neuronal differentiation and maturation under chemically defined culture conditions. When treated with neural induction medium containing Noggin/retinoic acid, the encapsulated cells expressed much higher levels of neural progenitor markers SOX1 and PAX6 than those in other treatment conditions. Immunocytochemisty analysis confirmed that the majority of the differentiated cells were nestin-positive cells. Subsequently transferring the scaffolds to neuronal differentiation medium efficiently directed these encapsulated neural progenitors into mature neurons, as detected by RT-PCR and positive immunostaining for neuron markers βIII tubulin and MAP2. Furthermore, flow cytometry confirmed that >90% βIII tubulin-positive neurons was achieved for three independent iPSC and hESC lines, a differentiation efficiency much higher than previously reported. Implantation of these terminally differentiated neurons into SCID mice yielded successful neural grafts comprising MAP2 positive neurons, without tumorigenesis, suggesting a potential safe cell source for regenerative medicine. These results bring us one step closer toward realizing large-scale production of stem cell derivatives for clinical and translational applications.