Developmental cues and persistent neurogenic potential within an in vitro neural niche

Current progress and challenges in the development of brain tissue models: How to grow up the changeable brain in vitro?

In vitro modeling of brain tissue is a promising but not yet resolved problem in modern neurobiology and neuropharmacology. Complexity of the brain structure and diversity of cell-to-cell communication in (patho)physiological conditions make this task almost unachievable. However, establishment of novel in vitro brain models would ultimately lead to better understanding of development-associated or experience-driven brain plasticity, designing efficient approaches to restore aberrant brain functioning. The main goal of this review is to summarize the available data on methodological approaches that are currently in use, and to identify the most prospective trends in development of neurovascular unit, blood-brain barrier, blood-cerebrospinal fluid barrier, and neurogenic niche in vitro models. The manuscript focuses on the regulation of adult neurogenesis, cerebral microcirculation and fluids dynamics that should be reproduced in the in vitro 4D models to mimic brain development and its alterations in brain pathology. We discuss approaches that are critical for studying brain plasticity, deciphering the individual person-specific trajectory of brain development and aging, and testing new drug candidates in the in vitro models.

Composite Coatings Based on Recombinant Spidroins and Peptides with Motifs of the Extracellular Matrix Proteins Enhance Neuronal Differentiation of Neural Precursor Cells Derived from Human Induced Pluripotent Stem Cells

The production and transplantation of functionally active human neurons is a promising approach to cell therapy. Biocompatible and biodegradable matrices that effectively promote the growth and directed differentiation of neural precursor cells (NPCs) into the desired neuronal types are very important. The aim of this study was to evaluate the suitability of novel composite coatings (CCs) containing recombinant spidroins (RSs) rS1/9 and rS2/12 in combination with recombinant fused proteins (FP) carrying bioactive motifs (BAP) of the extracellular matrix (ECM) proteins for the growth of NPCs derived from human induced pluripotent stem cells (iPSC) and their differentiation into neurons. NPCs were produced by the directed differentiation of human iPSCs. The growth and differentiation of NPCs cultured on different CC variants were compared with a Matrigel (MG) coating using qPCR analysis, immunocytochemical staining, and ELISA. An investigation revealed that the use of CCs consisting of a mixture of two RSs and FPs with different peptide motifs of ECMs increased the efficiency of obtaining neurons differentiated from iPSCs compared to Matrigel. CC consisting of two RSs and FPs with Arg-Gly-Asp-Ser (RGDS) and heparin binding peptide (HBP) is the most effective for the support of NPCs and their neuronal differentiation.

Biodegradable and Electrically Conductive Melanin-Poly (3-Hydroxybutyrate) 3D Fibrous Scaffolds for Neural Tissue Engineering Applications

Due to the severity of peripheral nerve injuries (PNI) and spinal cord injuries (SCI), treatment options for patients are limited. In this context, biomaterials designed to promote regeneration and reinstate the lost function are being explored. Such biomaterials should be able to mimic the biological, chemical, and physical cues of the extracellular matrix for maximum effectiveness as therapeutic agents. Development of biomaterials with desirable physical, chemical, and electrical properties, however, has proven challenging. Here a novel biomaterial formulation achieved by blending the pigment melanin and the natural polymer Poly-3-hydroxybutyrate (PHB) is proposed. Physio-chemical measurements of electrospun fibers reveal a feature rich surface nano-topography, a semiconducting-nature, and brain-tissue-like poroviscoelastic properties. Resulting fibers improve cell adhesion and growth of mouse sensory and motor neurons, without any observable toxicity. Further, the presence of polar functional groups positively affect the kinetics of fibers degradation at a pH (≈7.4) comparable to that of body fluids. Thus, melanin-PHB blended scaffolds are found to be physio-chemically, electrically, and biologically compatible with neural tissues and could be used as a regenerative modality for neural tissue injuries. A biomaterial for scaffolds intended to promote regeneration of nerve tissue after injury is developed. This biomaterial, obtained by mixing the pigment melanin and the natural polymer PHB, is biodegradable, electrically conductive, and beneficial to the growth of motor and sensory neurons. Thus, it is believed that this biomaterial can be used in the context of healthcare applications.

NXN Gene Epigenetic Changes in an Adult Neurogenesis Model of Alzheimer's Disease

In view of the proven link between adult hippocampal neurogenesis (AHN) and learning and memory impairment, we generated a straightforward adult neurogenesis in vitro model to recapitulate DNA methylation marks in the context of Alzheimer’s disease (AD). Neural progenitor cells (NPCs) were differentiated for 29 days and Aβ peptide 1–42 was added. mRNA expression of Neuronal Differentiation 1 (NEUROD1), Neural Cell Adhesion Molecule 1 (NCAM1), Tubulin Beta 3 Class III (TUBB3), RNA Binding Fox-1 Homolog 3 (RBFOX3), Calbindin 1 (CALB1), and Glial Fibrillary Acidic Protein (GFAP) was determined by RT-qPCR to characterize the culture and framed within the multistep process of AHN. Hippocampal DNA methylation marks previously identified in Contactin-Associated Protein 1 (CNTNAP1), SEPT5-GP1BB Readthrough (SEPT5-GP1BB), T-Box Transcription Factor 5 (TBX5), and Nucleoredoxin (NXN) genes were profiled by bisulfite pyrosequencing or bisulfite cloning sequencing; mRNA expression was also measured. NXN outlined a peak of DNA methylation overlapping type 3 neuroblasts. Aβ-treated NPCs showed transient decreases of mRNA expression for SEPT5-GP1BB and NXN on day 9 or 19 and an increase in DNA methylation on day 29 for NXN. NXN and SEPT5-GP1BB may reflect alterations detected in the brain of AD human patients, broadening our understanding of this disease.

Study of NSCLC cell migration promoted by NSCLC-derived extracellular vesicle using atomic force microscopy

Extracellular vesicles (EVs) secreted by cancer cells play a key role in the cancer microenvironment and progression. Previous studies have mainly focused on molecular functions, cellular components and biological processes using chemical and biological methods. However, whether the mechanical properties of cancer cells change due to EVs remains poorly understood. This work studies the effects of mechanical changes in non-small cell lung cancer (NSCLC) cells after treatment with EVs on migration by atomic force microscopy (AFM). Different concentrations of EVs were added into the experimental groups based on co-culture experiments, while the control group was cultured without EVs for 48 h. Cellular migration was evaluated by wound healing experiments. The cellular morphology, cell stiffness and surface adhesion were investigated by AFM. Cytoskeleton changes were detected by fluorescence staining assay. By comparison to the control group, the cell migration was enhanced. After treatment with EVs, the cell length and height show an upward trend, and the adhesion force and Young's modulus show a downward trend, and filopodia were also detected in the cells. Overall, the EVs promoted the migration of NSCLC cells by regulating cells' physical properties and skeletal rearrangement.

Building Organs Using Tissue-Specific Microenvironments: Perspectives from a Bioprosthetic Ovary

Recent research in tissue engineering and regenerative medicine has elucidated the importance of the matrisome. The matrisome, effectively the skeleton of an organ, provides physical and biochemical cues that drive important processes such as differentiation, proliferation, migration, and cellular morphology. Leveraging the matrisome to control these and other tissue-specific processes will be key to developing transplantable bioprosthetics. In the ovary, the physical and biological properties of the matrisome have been implicated in controlling the important processes of follicle quiescence and folliculogenesis. This expanding body of knowledge is being applied in conjunction with new manufacturing processes to enable increasingly complex matrisome engineering, moving closer to emulating tissue structure, composition, and subsequent functions which can be applied to a variety of tissue engineering applications.

Migration of BEAS-2B cells enhanced by H1299 cell derived-exosomes

Previous studies reported that exosomes (Exos) secreted by tumor cells could affect the tumor cells themselves and normal cells. However, the effects of exosomes derived from tumor cells on normal cells' migration and mechanical characteristics are rarely reported. This work explores the effects of H1299 cell-derived exosomes (H1299-Exos) on the migration of BEAS-2B cells, and analyzes possible mechanical mechanisms. In the experiments, exosomes were isolated from the culture supernatants of H1299 cells by ultracentrifugation. The H1299-Exos were confirmed by scanning electron microscope (SEM) and western blotting (WB). The BEAS-2B cell migration was assessed using scratch assays. Cytoskeletal structure changes were detected by immunofluorescence. Surface morphology and mechanical properties were measured by atomic force microscopy (AFM). After incubation with H1299-Exos for 48 h, BEAS-2B cells enhanced migration ability, with increased filopodia and cytoskeletal rearrangements. The changes in the morphology and mechanical properties of the cells caused by H1299-Exos were detected using AFM, including the increase in cell length and the decrease in cell height, Young's modulus and adhesion. In short, H1299-Exos promoted the BEAS-2B cell migrations. It indicates that the morphological and mechanical properties can be used as a means to assess normal cell alterations induced by tumor cell derived-exosomes. This provides a method for studying the effects of exosomes secreted by tumor cells on normal cells and the changes in their physical properties.

Bioactive Nanofibers Induce Neural Transdifferentiation of Human Bone Marrow Mesenchymal Stem Cells

The combination of biomaterials with stem cells is a promising therapeutic strategy to repair traumatic injuries in the central nervous system, and human bone marrow mesenchymal stem cells (BMSCs) offer a clinically translatable option among other possible sources of stem cells. We report here on the use of a supramolecular bioactive material based on a peptide amphiphile (PA), displaying a laminin-mimetic IKVAV sequence to drive neural transdifferentiation of human BMSCs. The IKVAV-PA self-assembles into supramolecular nanofibers that induce neuroectodermal lineage commitment after 1 week, as evidenced by the upregulation of the neural progenitor gene nestin ( NES) and glial fibrillary acidic protein ( GFAP). After 2 weeks, the bioactive IKVAV-PA nanofibers induce significantly higher expression of neuronal markers β-III tubulin (TUJ-1), microtubule-associated protein-2 (MAP-2), and neuronal nuclei (NEUN), as well as the extracellular matrix laminin (LMN). Furthermore, the human BMSCs exposed to the biomaterial reveal a polarized cytoskeletal architecture and a decrease in cellular size, resembling neuron-like cells. We conclude that the investigated supramolecular biomaterial opens the opportunity to transdifferentiate adult human BMSCs into neuronal lineage.

A patient-specific induced pluripotent stem cell model for West syndrome caused by ST3GAL3 deficiency

ST3GAL3 encodes the Golgi enzyme beta-galactoside-alpha-2,3-sialyltransferase-III that in humans forms, among others, the sialyl Lewis a (sLe^a) epitope on proteins. Functionally deleterious variants in this gene were previously identified in patients with either non-syndromic or syndromic intellectual disability such as West syndrome, an age-dependent epileptic encephalopathic syndrome associated with developmental arrest or regression. The aim of this study was to further elucidate the molecular and cellular mechanisms causing West syndrome by lack of ST3GAL3 function. For this purpose we generated induced pluripotent stem cell (iPSC) lines from fibroblasts obtained from a patient with West syndrome, carrying a variant in exon 12 (c.958G>C, p.(Ala320Pro)) of ST3GAL3, and a healthy sibling, using lentiviral reprogramming. iPSCs and cortical neurons derived thereof were analysed by lectin blots, mRNA sequencing, adherence assays, and FACS. While no significant difference was observed at stem cell or fibroblast level between patient and control cells, patient-derived cortical neurons displayed an altered lectin blot staining pattern, enhanced adherence to a poly-L-ornithine/laminin-coated surface and decreased levels of neurons expressing T-box transcription factor brain 1. Our results suggest that changes in the sialylation pattern on the surface of specific neuronal cell types affect adhesive interactions during development, which in turn may cause subtle changes in tissue composition that could result in the occurrence of epilepsy and might impair neural development to an extent that is detrimental to the development and maintenance of normal cognitive functions.

Blood-brain barrier-supported neurogenesis in healthy and diseased brain

Adult neurogenesis is one of the most important mechanisms contributing to brain development, learning, and memory. Alterations in neurogenesis underlie a wide spectrum of brain diseases. Neurogenesis takes place in highly specialized neurogenic niches. The concept of neurogenic niches is becoming widely accepted due to growing evidence of the important role of the microenvironment established in the close vicinity to stem cells in order to provide adequate control of cell proliferation, differentiation, and apoptosis. Neurogenic niches represent the platform for tight integration of neurogenesis and angiogenesis supported by specific properties of cerebral microvessel endothelial cells contributing to establishment of partially compromised blood-brain barrier (BBB) for the adjustment of local conditions to the current metabolic needs of stem and progenitor cells. Here, we review up-to-date data on microvascular dynamics in activity-dependent neurogenesis, specific properties of BBB in neurogenic niches, endothelial-driven mechanisms of clonogenic activity, and future perspectives for reconstructing the neurogenic niches in vitro.

Physical exercise induces hippocampal neurogenesis and prevents cognitive decline

Accumulating evidence from animal and human research indicate that adult hippocampal neurogenesis plays a key role in cognition. Meanwhile, cognitive decline is well known to associate with ageing-related neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). Therefore, prevention of hippocampal neurogenesis reduction should be critical for these diseases. Physical exercise, a potent enhancer of adult hippocampal neurogenesis, has emerged as a potential therapy or an adjunctive therapeutic strategy for cognitive decline. In this review, we discuss the recent findings on hippocampal neurogenesis and the incorporation of new born neurons into the neuronal network in humans and in rodents. By focusing on hippocampal neurogenesis, we illustrate the role and possible mechanisms of physical exercise in cognition preservation.

An efficient and reproducible method to culture Bergmann and cortical radial glia using textured PMMA

BACKGROUND

Radial glia cells comprise the principal population of neural stem cells (NSC) during development. Attempts to develop reproducible radial glia and NSC culture methods have met with variable results, yielding non-adherent cultures or requiring the addition of growth factors. Recent studies demonstrated that a 2-μm patterned poly-methyl methacrylate (ln2 PMMA) grooved scaffold, by mimicking the biophysical and microtopographic properties of the embryonic NSC niche, induces the de-differentiation of glial cells into functional radial glia cells.

NEW METHOD

Here we describe a method for obtaining cultures of adherent Bergmann radial glia (BRG) and cortical radial glia (CRG). The growth substrate is ln2 PMMA and the addition of growth factors is not required.

RESULTS

Postnatal glia obtained from mouse cerebellum or cerebral cortex and grown on ln2 PMMA adopted a BRG/CRG phenotype characterized by a bipolar shape, the up-regulation of progenitor markers such as nestin and Sox2, and the down-regulation of vimentin and GFAP. Neurons cultured over the BRG/CRG aligned their processes with those of the glial shafts, thus mimicking the behavior of migrating neuronal cells.

COMPARISON WITH EXISTING METHODS

The ln2 PMMA culture method offers an ideal system for analyzing both the biochemical factors controlling the neurogenic potential of BRG/CRG and neuronal migration.

CONCLUSIONS

The ln2 PMMA method is a reproducible system to obtain immature BRG/CRG preparations in vitro. It can be used to study the properties of CNS progenitor cells as well as the interactions between radial glia and neurons, and supports cultured progenitors for use in different applications.

Adhesive proteins linked with focal adhesion kinase regulate neurite outgrowth of PC12 cells

Adhesive proteins existing in the extracellular matrix (ECM) play important roles in the regulation of neuronal cell behavior, including cell adhesion, motility and neurite outgrowth. Herein we show the effects of a series of adhesive proteins on the neurite outgrowth of PC12 cells and elucidate that this is closely related to the activation of focal adhesion kinase (FAK). For this we prepared culture substrates by coating tissue culture plastic with either collagen (Col), fibronectin (FN) or laminin (LN) and investigated the neurite outgrowth behavior. The results demonstrated that neurite outgrowth was highly dependent on the particular type of adhesive protein. While neurite number was comparable on all the coated surfaces, the length of neurites was greater on the FN- and LN-coated ones (greatest on the LN-coated one). In particular, FAK expression was highly up-regulated in the FN- and LN-coated surfaces, as revealed by Western blot analysis. A knock-down experiment further supported the idea that neurite outgrowth was largely suppressed in cells transfected with a FAK knock-down gene. Taken together, the neurite outgrowth of PC12 cells was greatly affected by adhesive proteins of the ECM, particularly FN and LN, and this is considered to be closely related to FAK intracellular signaling. This study may be useful in the consideration and design of nerve guidance and three-dimensional scaffolds which are appropriate to promote neuronal growth and nerve tissue regeneration.

Collagen gel three-dimensional matrices combined with adhesive proteins stimulate neuronal differentiation of mesenchymal stem cells

Three-dimensional gel matrices provide specialized microenvironments that mimic native tissues and enable stem cells to grow and differentiate into specific cell types. Here, we show that collagen three-dimensional gel matrices prepared in combination with adhesive proteins, such as fibronectin (FN) and laminin (LN), provide significant cues to the differentiation into neuronal lineage of mesenchymal stem cells (MSCs) derived from rat bone marrow. When cultured within either a three-dimensional collagen gel alone or one containing either FN or LN, and free of nerve growth factor (NGF), the MSCs showed the development of numerous neurite outgrowths. These were, however, not readily observed in two-dimensional culture without the use of NGF. Immunofluorescence staining, western blot and fluorescence-activated cell sorting analyses demonstrated that a large population of cells was positive for NeuN and glial fibrillary acidic protein, which are specific to neuronal cells, when cultured in the three-dimensional collagen gel. The dependence of the neuronal differentiation of MSCs on the adhesive proteins containing three-dimensional gel matrices is considered to be closely related to focal adhesion kinase (FAK) activation through integrin receptor binding, as revealed by an experiment showing no neuronal outgrowth in the FAK-knockdown cells and stimulation of integrin β1 gene. The results provided herein suggest the potential role of three-dimensional collagen-based gel matrices combined with adhesive proteins in the neuronal differentiation of MSCs, even without the use of chemical differentiation factors. Furthermore, these findings suggest that three-dimensional gel matrices might be useful as nerve-regenerative scaffolds.

Extracellular matrix: functions in the nervous system

An astonishing number of extracellular matrix glycoproteins are expressed in dynamic patterns in the developing and adult nervous system. Neural stem cells, neurons, and glia express receptors that mediate interactions with specific extracellular matrix molecules. Functional studies in vitro and genetic studies in mice have provided evidence that the extracellular matrix affects virtually all aspects of nervous system development and function. Here we will summarize recent findings that have shed light on the specific functions of defined extracellular matrix molecules on such diverse processes as neural stem cell differentiation, neuronal migration, the formation of axonal tracts, and the maturation and function of synapses in the peripheral and central nervous system.