In vitro culture and labeling of neural cell aggregates followed by transplantation

Nanostructured gold electrodes promote neural maturation and network connectivity

Progress in the clinical application of recording and stimulation devices for neural diseases is still limited, mainly because of suboptimal material engineering and unfavorable interactions with biological entities. Nanotechnology is providing upgraded designs of materials to better mimic the native extracellular environment and attain more intimate contacts with individual neurons, besides allowing for the miniaturization of the electrodes. However, little progress has been done to date on the understanding of the biological impact that such neural interfaces have on neural network maturation and functionality. In this work, we elucidate the effect of a gold (Au) highly ordered nanostructure on the morphological and functional interactions with neural cells and tissues. Alumina-templated Au nanostructured electrodes composed of parallel nanowires of 160 nm in diameter and 1.2 μm in length (Au-NWs), with 320 nm of pitch, are designed and characterized. Equivalent non-structured Au electrodes (Au-Flat) are used for comparison. By using diverse techniques in in vitro cell cultures including live calcium imaging, we found that Au-NWs interfaced with primary neural cortical cells for up to 14 days allow neural networks growth and increase spontaneous activity and ability of neuronal synchronization, thus indicating that nanostructured features favor neuronal network. The enhancement in the number of glial cells found is hypothesized to be behind these beneficial functional effects. The in vivo effect of the implantation of these nanostructured electrodes and its potential relevance for future clinical applicability has been explored in an experimental model of rat spinal cord injury. Subacute responses to implanted Au-NWs show no overt reactive or toxic biological reactions besides those triggered by the injury itself. These results highlight the translational potential of Au-NWs electrodes for in vivo applications as neural interfaces in contact with central nervous tissues including the injured spinal cord.

Brain Organoids: Filling the Need for a Human Model of Neurological Disorder

Neurological disorders are among the leading causes of death worldwide, accounting for almost all onsets of dementia in the elderly, and are known to negatively affect motor ability, mental and cognitive performance, as well as overall wellbeing and happiness. Currently, most neurological disorders go untreated due to a lack of viable treatment options. The reason for this lack of options is s poor understanding of the disorders, primarily due to research models that do not translate well into the human in vivo system. Current models for researching neurological disorders, neurodevelopment, and drug interactions in the central nervous system include in vitro monolayer cell cultures, and in vivo animal models. These models have shortcomings when it comes to translating research about disorder pathology, development, and treatment to humans. Brain organoids are three-dimensional (3D) cultures of stem cell-derived neural cells that mimic the development of the in vivo human brain with high degrees of accuracy. Researchers have started developing these miniature brains to model neurodevelopment, and neuropathology. Brain organoids have been used to model a wide range of neurological disorders, including the complex and poorly understood neurodevelopmental and neurodegenerative disorders. In this review, we discuss the brain organoid technology, placing special focus on the different brain organoid models that have been developed, discussing their strengths, weaknesses, and uses in neurological disease modeling.

Induction of mice adult bone marrow mesenchymal stem cells into functional motor neuron-like cells

The differentiation of mesenchymal stem cells (MSC) into acetylcholine secreted motor neuron-like cells, followed by elongation of the cell axon, is a promising treatment for spinal cord injury and motor neuron cell dysfunction in mammals. Differentiation is induced through a pre-induction step using Beta- mercaptoethanol (BME) followed by four days of induction with retinoic acid and sonic hedgehog. This process results in a very efficient differentiation of BM-MSCs into motor neuron-like cells. Immunocytochemistry showed that these treated cells had specific motor neural markers: microtubule associated protein-2 and acetylcholine transferase. The ability of these cells to function as motor neuron cells was assessed by measuring acetylcholine levels in a culture media during differentiation. High-performance liquid chromatography (HPLC) showed that the differentiated cells were functional. Motor neuron axon elongation was then induced by adding different concentrations of a nerve growth factor (NGF) to the differentiation media. Using a collagen matrix to mimic the natural condition of neural cells in a three-dimensional model showed that the MSCs were successfully differentiated into motor neuron-like cells. This process can efficiently differentiate MSCs into functional motor neurons that can be used for autologous nervous system therapy and especially for treating spinal cord injuries.

Labeling of olfactory ensheathing glial cells with fluorescent tracers for neurotransplantation

Development of cell-based treatment strategies for repair of the injured nervous system requires cell tracing techniques to follow the fate of transplanted cells and their interaction with the host tissue. The present study investigates the efficacy of fluorescent cell tracers Fast Blue, PKH26, DiO and CMFDA for long-term labeling of olfactory ensheathing glial cells (OEC) in culture and following transplantation into the rat spinal cord. All tested dyes produced very efficient initial labeling of p75-positive OEC in culture. The number of Fast Blue-positive cells remained largely unchanged during the first 4 weeks but only about 21% of the cells retained tracer 6 weeks after labeling. In contrast, the number of cells labeled with PKH26 and DiO was reduced to 51-55% after 2 weeks in culture and reached 8-12% after 4-6 weeks. CMFDA had completely disappeared from the cells 2 weeks after labeling. AlamarBlue assay showed that among four tested tracers only CMFDA reduced proliferation rate of the OEC. After transplantation into spinal cord, Fast Blue-labeled OEC survived for at least 8 weeks but demonstrated very limited migration from the injection sites. Additional immunostaining with glial and neuronal markers revealed signs of dye leakage from the transplanted cells resulted in weak labeling of microglia and spinal neurons. The results show that Fast Blue is an efficient cell marker for cultured OEC. However, transfer of the dye from the transplanted cells to the host tissue should be considered and correctly interpreted.

Biotinylated dextran amine as a marker for fetal hypothalamic homografts and their efferents

We have explored the use of biotinylated dextran amine (BDA) as a marker for labeling fetal brain grafts and their connections with the host. As a model system we used transplantation of the hamster suprachiasmatic nucleus, the site of an endogenous biological clock governing circadian rhythms. Similar transplants into arrhythmic hosts have been shown to restore behavioral function with a period specific to the donor. For locomotor rhythms, efferent connections are not necessary. For other responses, including endocrine rhythms, efferent connections may be necessary. In order to visualize homografts and their efferents, injections of BDA, an anterograde tracer, were made into the anterior hypothalamic (AH) region containing the SCN or into the dorsal cortex (CTX) of fetal hamster brains. The fetal AH or CTX was microdissected out and stereotaxically implanted into the third ventricle of intact, adult hamsters. After 2, 4, 8, or 12 weeks, hosts were sacrificed and their brains were processed for detection of BDA by either histochemistry or immunofluorescence. BDA intensely labeled graft neurons, their dendrites, and axons with minimal or no spread to the adjacent host brain. Labeled graft axons could be followed for long distances (>1 mm) into the host brain and graft-derived varicosities formed close contacts with host neurons. BDA-labeled graft neurons, located at the perimeter of the graft, also extended dendrite-like processes into the host parenchyma. We conclude that BDA is a useful marker for fetal homografts and their efferents for survival times of less than 2 months.

Redistribution of bisbenzimide Hoechst 33342 from transplanted cells to host cells

Identification of transplanted cells within host tissue is an important component of many transplantation experiments. In this study, Schwann cells labelled with the fluorochrome bisbenzimide (Hoechst 33342, H33342) and transduced with the lac-Z gene were introduced into normal white matter and their distribution was examined 2 h, 24 h and 4 weeks after transplantation. At 2 and 24 h following transplantation, H33342-labelled cells were more widely distributed than lac-Z-labelled cells in both longitudinal and transverse directions. By 4 weeks following transplantation, no lac-Z-labelled cells could be found. However, H33342-labelled cells were observed in and around the glial scar. Therefore, labelling of host cells by transfer of H33342 dye from transplanted cells has to be considered whenever this dye is used as a transplant marker.

Ex vivo astroglial-induced radial glia express in vivo markers

Ex vivo induction of radial-like glia has been previously reported to occur following exposure of cerebral cortex subcultures from fetal origin to cerebral cortex astroglial-conditioned medium. The present report further confirms similarities between in vivo and ex vivo radial glia, using additional criteria: adhesion of primary cell dissociates to glial processes, with presumptive cell migration along them, punctuate labelling for laminin, and immunolabelling with Rat-401 antisera.

Regional differences in in vitro growth of neural cell processes during development

Primary cell cultures from cerebral cortex, striatum and ventral mesencephalon obtained from rat fetal (embryonic day 17, E17) or postnatal (day 2, PN2) donors were grown either in media conditioned by subcultured astroglia from the same regions, an artificial trophic medium, normal human amniotic fluid, or in normal human cerebrospinal fluid. To estimate the presence of neuronal-like and non-neuronal cells, cell morphology and immunocytochemistry against microtubule-associated proteins and beta-tubulin were taken into consideration. The percentage of emitting neural cells and length of cell processes were determined after 24 hr in culture. Growth of cell processes in neuronal and non-neuronal cells from prenatal striatum was minimal compared with that in cerebral cortex and ventral mesencephalon, regardless of the culture condition. Nerve growth factor, basic fibroblast growth factor or epidermal growth factor did not significantly modify cell growth in E17 cultures, except for epidermal growth factor, which reduced the number of emitting cells in striatal cultures and increased it in cerebral cortex ones. Cultures derived from postnatal striatum showed a significant increase in neurite length when grown in an astroglial conditioned medium as compared to cultures derived from prenatal (E17) striatum. Results suggest significant regional differences in the brain regarding growth of cell processes at age E17, and reversal of striatal ability to grow cell processes by postnatal day 2. Reduced growth of cell processes showed by E17 striatum cultures was rather independent of the culture media. This fact could suggest that such early regional differences would depend on characteristics of sublineages present at this developmental stage, which would modulate the organization of regional neuropils. The restricted growth of cell processes in cultures from E17 striatum, no longer present in postnatal striatum, suggests that inputs to the striatum may modify expression of cell lineages at later stages of development.

Cortical astroglial conditioned medium induces in vitro radial-like forms

Cerebral cortex and striatal cell dissociates obtained from rat fetuses (E 17) were subcultured and enriched in astroglial cells before being grown in regional (cerebral cortex, striatum) astroglial conditioned media (CM) or defined basal medium. Incidence of radial-like astroglia (vimentin+ or glial fibrillary acid protein, GFAP+) and length of processes in cortical cell subcultures showed a greater increase when exposed to cerebral cortex CM than to striatal CM or basal medium. Stellate (GFAP+) forms prevailed in subcultures grown in basal medium while striatal cells exposed to CM of either origin remained undifferentiated. Additionally, cultures were treated with various concentrations of cAMP (0.25 and 0.5 mM) and calcitonin gene related peptide (CGRP) (0.1, 0.5, and 1.0 microM). Under these conditions CM-exposed cultures (with predominant "radial-like" forms) did not increase stellate glial numbers, while fetal calf serum (FCS)-exposed cultures (morphologically undifferentiated) underwent significant degrees of stellate transformation. When CM-exposed cultures were shifted to FCS supplemented basal medium for 24-48 hr and then to basal medium alone prior to treatment, cAMP and CGRP were effective in transforming flat astroglia into stellate morphology. Results are indicative of the existence of astroglial diffusible factors affecting the in vitro expression of astroglial morphotypes from the cerebral cortex. Previous exposure to CM interferes with cytoskeletal astrocytic changes induced by cAMP and CGRP. It is speculated that astroglial factors could act in vivo to maintain the expression of radial-like cells during early developmental stages of the cerebral cortex, but it would not be effective in E 17 striatum.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro labeling strategies for identifying primary neural tissue and a neuronal cell line after transplantation in the CNS

Potential labels for identifying embryonic raphe neurons and a clonal, neuronally differentiating, raphe-derived cell line, RN33B, in CNS transplantation studies were tested by first characterizing the labels in vitro. The labels that were tested included 4',6-diamidino-2-phenylindole hydrochloride, 1,1'-dioctadecyl-3,3,3'-tetramethylindocarbocyanine perchlorate, the Escherichia coli lacZ gene, Fast Blue, Fluoro-Gold, fluorescein-conjugated latex microspheres, fluorescein isothiocyanate-conjugated or nonconjugated Phaseolus vulgaris leucoagglutinin, methyl o-(6-amino-3'-imino-3H-xanthen-9-yl) benzoate monohydrochloride, or tetanus toxin C fragment. Subsequently, the optimal in vitro labels for embryonic raphe neurons and for RN33B cells were characterized in vivo after CNS transplantation. In vitro, 1,1'-dioctadecyl-3,3,3'-tetramethylindocarbocyanine perchlorate (DiI) optimally labeled embryonic neurons. The Escherichia coli lacZ gene optimally labeled RN33B cells. Most labels were rapidly diluted in cultures of embryonic astrocytes and proliferating RN33B cells. Some labels were toxic and were often retained in cellular debris. In vivo, DiI was visualized in transplanted, DiI-labeled raphe neurons, but not in astrocytes up to 1 mo posttransplant. DiI-labeled host cells were seen after transplantation of lysed, DiI-labeled cells. beta-Galactosidase was visualized in transplanted, Escherichia coli lacZ gene-labeled RN33B cells after 15 days in vivo. No beta-galactosidase was seen in host cells after transplantation of lysed, lacZ-labeled RN33B cells. The results demonstrate that labels for use in CNS transplantation studies should be optimized for the specific population of donor cells under study, with the initial step being characterization in vitro followed by in vivo analysis. Appropriate controls for false-positive labeling of host cells should always be assessed.

Fluorescent labeling of dissociated fetal cells for tissue culture

The ability to pre-label cells used in transplantation experiments would have the potential benefits of identification of cell type and associated processes and the analysis of graft migration in the host. We have used an in vitro tissue culture system as a model to test several fluorescent dyes for this application. Fetal rat hippocampal tissue (E17-E18) was dissociated and incubated in the presence of carboxyfluorescein ester (CFSE), rhodamine-B dextran amine (RBD), DiI, or rhodamine-labeled latex microspheres. Cells were cultured in defined medium for up to 1 month. Cells labeled with CFSE were initially bright but faded over several days. RBD labeled the soma of cells, but fluorescence intensity was lost over a period of a few weeks. Cells labeled with DiI possessed brilliant staining of neuronal processes for weeks. Latex microspheres brightly labeled the soma but not the processes of neurons; fluorescent debris and sterility were problems with this label. We conclude that CFSE and DiI have significant potential usefulness in vitro as markers of cell viability and process formation with mammalian fetal CNS cells, whereas RBD is much less permanent. Latex microspheres may be suitable for pre-labeling of cells for transplantation if purification and sterility can be enhanced over present preparations.

Anatomical and physiological localization of prelabeled grafts in rat hippocampus

Dissociated rat fetal hippocampal cells were grafted into normal adult rats. The fetal cells were incubated with one of a number of fluorescent compounds at the time of the dissociation to facilitate identification of the individual grafted cells. The fluorescent labels which were analyzed for this purpose included rhodamine latex microspheres, Cascade blue latex beads, rhodamine-dextran-amine, DiI, and carboxyfluorescein ester. The labeled cells were stereotaxically placed as a suspension into normal rat host hippocampi. The rats were sacrificed 2 to 6 weeks after the grafting for in vitro physiological recordings, and the prelabeled grafts were located using fluorescence optics. During intracellular recordings neurons within the prelabeled grafts were injected with Lucifer yellow to visualize the morphology and integration of neuronal processes within the host. Following the recordings the host slices with the grafts were fixed in 4% paraformaldehyde for anatomical analysis. The ability to prelabel cellular grafts allows subsequent anatomical and physiological analysis of the integration of grafted neurons at the resolution of a single neuron. Such an analysis will improve our understanding of the survival, differentiation, migration, and integration of the grafted neurons and their potential to replace lost function in the lesioned hippocampus.

Latex nanosphere delivery system (LNDS): novel nanometer-sized carriers of fluorescent dyes and active agents selectively target neuronal subpopulations via uptake and retrograde transport

A wide range of latex particles are described which are capable of carrying high concentrations of fluorescent dyes, drugs, and photoactive agents selectively to subpopulations of neurons in vitro and in vivo. Particle size, charge, and concentration were all found to influence uptake into cultured neurons or retrograde transport in vivo. Chromophore loadings of greater than 14% (w/w) were obtained. Incorporation of a photoactivated dye (chlorin e6) into the polymer did not compromise the ability of the dye to produce singlet oxygen following light exposure. We refer to this unique family of latex particles as the latex nanosphere delivery system (LNDS). The LNDS will be usefull for studies of neuroanatomy and nervous system development, as well as more general areas of biomedical research where it is desirable to selectively label subpopulations of cells. The LNDS also offers a means of providing targeted delivery of drugs or photoactive agents to selected subpopulations of cells; this will allow experimentation not currently possible using any existent methodology.