Gastruloids generated without exogenous Wnt activation develop anterior neural tissues.

When stimulated with a pulse from an exogenous WNT pathway activator, small aggregates of mouse embryonic stem cells (ESCs) can undergo embryo-like axial morphogenesis and patterning along the three major body axes. However, these structures, called gastruloids, currently lack the anterior embryonic regions, such as those belonging to the brain. Here, we describe an approach to generate gastruloids that have a more complete antero-posterior development. We used hydrogel microwell arrays to promote the robust derivation of mouse ESCs into post-implantation epiblast-like (EPI) aggregates in a reproducible and scalable manner. These EPI aggregates break symmetry and axially elongate without external chemical stimulation. Inhibition of WNT signaling in early stages of development leads to the formation of gastruloids with anterior neural tissues. Thus, we provide a new tool to study the development of the mouse after implantation in vitro, especially the formation of anterior neural regions.

A bioinspired 3D shape olibanum-collagen-gelatin scaffolds with tunable porous microstructure for efficient neural tissue regeneration.

There are a number of procedures for regeneration of injured nerves; however, tissue engineering scaffolds seems to be a promising approach for recovery of the functionality of the injured nerves. Consequently, in this study, olibanum-collagen-gelatin scaffolds were fabricated by freeze-cast technology. For this purpose, the olibanum and collagen were extracted from natural sources. The effect of solidification gradient on microstructure and properties of scaffolds was investigated. Scanning electron microscopy micrographs showed the formation of lamellar-type microstructure in which the average pore size reduced with an increase in freezing rate. According to the results, the prepared scaffolds at lower freezing rate showed a slight reduction in mechanical strength while the swelling and biodegradation ratio were increased due to the presence of larger pores and unidirectional channels. The composition of scaffolds and oriented microstructure improved cellular interaction. In addition, scaffolds with lower freezing rate exhibited promising results in terms of adhesion, spreading, and proliferation. In brief, the synthesized scaffolds at lower solidification rate have the potential for more in vitro and in vivo analyses to regeneration of neural defects.

Synthetic 3D PEG-Anisogel Tailored with Fibronectin Fragments Induce Aligned Nerve Extension.

An enzymatically cross-linked polyethylene glycol (PEG)-based hydrogel was engineered to promote and align nerve cells in a three-dimensional manner. To render the injectable, otherwise bioinert, PEG-based material supportive for cell growth, its mechanical and biochemical properties were optimized. A recombinant fibronectin fragment (FNIII9*-10/12-14) was coupled to the PEG backbone during gelation to provide cell adhesive and growth factor binding domains in close vicinity. Compared to full-length fibronectin, FNIII9*-10/12-14 supports nerve growth at similar concentrations. In a 3D environment, only the ultrasoft 1 w/v% PEG hydrogels with a storage modulus of ∼10 Pa promoted neuronal growth. This gel was used to establish the first fully synthetic, injectable Anisogel by the addition of magnetically aligned microelements, such as rod-shaped microgels or short fibers. The Anisogel led to linear neurite extension and represents a large step in the direction of clinical translation with the opportunity to treat acute spinal cord injuries.

Effect of Motor versus Sensory Nerve Autografts on Regeneration and Functional Outcomes of Rat Facial Nerve Reconstruction.

Cranial nerve injury is disabling for patients, and facial nerve injury is particularly debilitating due to combined functional impairment and disfigurement. The most widely accepted approaches for reconstructing nerve gap injuries involve using sensory nerve grafts to bridge the nerve defect. Prior work on preferential motor reinnervation suggests, however, that motor pathways may preferentially support motoneuron regeneration after nerve injury. The effect of motor versus sensory nerve grafting after facial nerve injury has not been previously investigated. Insights into outcomes of motor versus sensory grafting may improve understanding and clinical treatment of facial nerve paralysis, mitigating facial asymmetry, aberrant reinnervation, and synkinesis. This study examined motor versus sensory grafting of the facial nerve to investigate effect of pathway on regeneration across a 5-mm rodent facial nerve defect. We enrolled 18 rats in 3 cohorts (motor, sensory, and defect) and recorded outcome measures including fiber count/nerve density, muscle endplate reinnervation, compound muscle action potential, and functional whisker twitch analysis. Outcomes were similar for motor versus sensory groups, suggesting similar ability of sensory and motor grafts to support regeneration in a clinically relevant model of facial nerve injury.

Promoting Neurite Growth and Schwann Cell Migration by the Harnessing Decellularized Nerve Matrix onto Nanofibrous Guidance.

Synergistic intercellular interactions have been widely acknowledged in tuning functional cell behaviors in vivo, and these interactions have inspired the development of a variety of scaffolds for regenerative medicine. In this paper, the promotion of Schwann cell (SC)-neurite interactions through the use of a nerve extracellular matrix-coated nanofiber composite in vitro was demonstrated using a cell culturing platform consisting of either random or aligned electrospun poly(l-lactic acid) nanofibers and decellularized peripheral nerve matrix gel (pDNM gel) from porcine peripheral nervous tissue. The pDNM-coated nanofiber platform served as a superior substrate for dorsal root ganglion culturing. Furthermore, SC migration was facilitated by pDNM gel coating on the nanofibers, accompanied with much faster axonal extension, in comparison with the effect of topographical guidance from the aligned electrospun fibers only. Finally, the decellularized nerve matrix promoted the ability of SCs to wrap around bundled neurites, triggering axonal remyelination toward nerve fiber functionalization.

Directed glial differentiation and transdifferentiation for neural tissue regeneration.

Glial cells which are indispensable for the central nervous system development and functioning, are proven to be vulnerable to a harmful influence of pathological cues and tissue misbalance. However, they are also highly sensitive to both in vitro and in vivo modulation of their commitment, differentiation, activity and even the fate-switch by different types of bioactive molecules. Since glial cells (comprising macroglia and microglia) are an abundant and heterogeneous population of neural cells, which are almost uniformly distributed in the brain and the spinal cord parenchyma, they all create a natural endogenous reservoir of cells for potential neurogenerative processes required to be initiated in response to pathophysiological cues present in the local tissue microenvironment. The past decade of intensive investigation on a spontaneous and enforced conversion of glial fate into either alternative glial (for instance from oligodendrocytes to astrocytes) or neuronal phenotypes, has considerably extended our appreciation of glial involvement in restoring the nervous tissue cytoarchitecture and its proper functions. The most effective modulators of reprogramming processes have been identified and tested in a series of pre-clinical experiments. A list of bioactive compounds which are potent in guiding in vivo cell fate conversion and driving cell differentiation includes a selection of transcription factors, microRNAs, small molecules, exosomes, morphogens and trophic factors, which are helpful in boosting the enforced neuro-or gliogenesis and promoting the subsequent cell maturation into desired phenotypes. Herein, an issue of their utility for a directed glial differentiation and transdifferentiation is discussed in the context of elaborating future therapeutic options aimed at restoring the diseased nervous tissue.

An In Vivo Murine Sciatic Nerve Model of Perineural Invasion.

Cancer cells invade nerves through a process termed perineural invasion (PNI), in which cancer cells proliferate and migrate in the nerve microenvironment. This type of invasion is exhibited by a variety of cancer types, and very frequently is found in pancreatic cancer. The microscopic size of nerve fibers within mouse pancreas renders the study of PNI difficult in orthotopic murine models. Here, we describe a heterotopic in vivo model of PNI, where we inject syngeneic pancreatic cancer cell line Panc02-H7 into the murine sciatic nerve. In this model, sciatic nerves of anesthetized mice are exposed and injected with cancer cells. The cancer cells invade in the nerves proximally toward the spinal cord from the point of injection. The invaded sciatic nerves are then extracted and processed with OCT for frozen sectioning. H&E and immunofluorescence staining of these sections allow quantification of both the degree of invasion and changes in protein expression. This model can be applied to a variety of studies on PNI given its versatility. Using mice with different genetic modifications and/or different types of cancer cells allows for investigation of the cellular and molecular mechanisms of PNI and for different cancer types. Furthermore, the effects of therapeutic agents on nerve invasion can be studied by applying treatment to these mice.

Nerve Growth and Interaction in Gelfoam® Histoculture: A Nervous System Organoid.

Nestin-expressing hair follicle-associated pluripotent (HAP) stem cells reside mainly in the bulge area (BA) of the hair follicle but also in the dermal papilla (DP). The BA appears to be origin of HAP stem cells. Long-term Gelfoam® histoculture was established of whiskers isolated from transgenic mice, in which there is nestin-driven green fluorescent protein (ND-GFP). HAP stem cells trafficked from the BA toward the DP area and extensively grew out onto Gelfoam® forming nerve-like structures. These fibers express the neuron marker ß-III tubulin-positive fibers and consisted of ND-GFP-expressing cells and extended up to 500 mm from the whisker nerve stump in Gelfoam® histoculture. The growing fibers had growth cones on their tips expressing F-actin indicating that the fibers were growing axons. HAP stem cell proliferation resulted in elongation of the follicle nerve and interaction with other nerves in 3D Gelfoam® histoculture, including the sciatic nerve, trigeminal nerve, and trigeminal nerve ganglion.

The neurotrophic effects of different human dental mesenchymal stem cells.

The current gold standard treatment for peripheral nerve injury is nerve grafting but this has disadvantages such as donor site morbidity. New techniques focus on replacing these grafts with nerve conduits enhanced with growth factors and/or various cell types such as mesenchymal stem cells (MSCs). Dental-MSCs (D-MSCs) including stem cells obtained from apical papilla (SCAP), dental pulp stem cells (DPSC), and periodontal ligament stem cells (PDLSC) are potential sources of MSCs for nerve repair. Here we present the characterization of various D-MSCs from the same human donors for peripheral nerve regeneration. SCAP, DPSC and PDLSC expressed BDNF, GDNF, NGF, NTF3, ANGPT1 and VEGFA growth factor transcripts. Conditioned media from D-MSCs enhanced neurite outgrowth in an in vitro assay. Application of neutralizing antibodies showed that brain derived neurotrophic factor plays an important mechanistic role by which the D-MSCs stimulate neurite outgrowth. SCAP, DPSC and PDLSC were used to treat a 10 mm nerve gap defect in a rat sciatic nerve injury model. All the stem cell types significantly enhanced axon regeneration after two weeks and showed neuroprotective effects on the dorsal root ganglia neurons. Overall the results suggested SCAP to be the optimal dental stem cell type for peripheral nerve repair.

[Establishment of pelvic nerve denervation modal in mice].

OBJECTIVE: To establishment and verify pelvic nerve denervation (PND) model in mice. METHODS: (1) Establishment of models. Seventy-two healthy male SPE class C57 mice with age of 7 weeks and body weight of (25±1) g were chosen. These 72 mice were randomly divided into PND group containing 36 mice and sham operation group containing 36 mice. Referring to the establishment method of PND rats, after anesthesia, a laparotomy was performed on the mouse with an abdominal median incision. Under the dissection microscope, the pelvic nerves behind and after each sides of the prostate gland were bluntly separated with cotton swabs and cut with a dissecting scissor. After the operation, the urination of mice was assisted twice every day. For the mice of sham operation group, the pelvic nerves were only exposed without cutting. (2) Detection of models. Colonic transit test was performed in 18 mice chosen randomly from each group to detect the colonic transit ratio (colored colon by methylene blue/ whole colon) and visceral sensitivity tests was performed in the rest mice to observe and record the changes of electromyogram. RESULTS: Three mice died of colonic transit test in each group. Uroschesis occurred in all the mice of PND group and needed bladder massage to assist the urination. Colonic transit test showed that the colonic transit ratios of sham operation group at postoperative day (POD) 1, 3 and 7 were (0.4950±0.3858)%, (0.6386±0.1293)% and (0.6470±0.1088)% without significant difference (F=0.3647, P=0.058), while in PND group, the colonic transit ratio at POD 7 [(0.6044±0.1768) %] was obviously higher than that both at POD 3[(0.3876±0.1364)%, P=0.022] and POD 1[(0.2542±0.0371)%, P=0.001], indicating a recovery trend of colonic transit function (F=9.143, P=0.004). Compared with the sham operation group, the colonic transit function in PND group decreased significantly at POD 1 and POD 3(both P<0.05), and at POD 7, there was no significant difference between two groups. Visceral sensitivity test showed that the visceral sensitivity of sham operation group at POD 1, 3 and 7 was 24.2808±9.5566, 33.6725±7.9548 and 43.9086±12.1875 with significant difference (F=5.722, P=0.014). The visceral sensitivity of PND group at POD 1, 3 and 7 was 11.7609±2.1049, 21.8415±8.1527 and 26.2310±4.2235 with significant difference as well (F=11.154, P=0.001). The visceral sensitivity at POD 3 and POD 7 was obviously higher than that at POD 1 (P=0.006, P<0.001), and there was no significant difference between POD 3 and POD 7 (P=0.183). Compared with sham operation group, the visceral sensitivity of PND group decreased significantly at POD 1, 3 and 7(all P<0.05). CONCLUSIONS: Denervation of pelvic nerves can obviously decrease the colonic transit function and the visceral sensitivity of mice, but these changes can recover over time, which suggests that the establishment of PND model in mice is successful.

YY1 in Cell Differentiation and Tissue Development.

Yin Yang1 (YY1) is a ubiquitous expressed transcription factor that modulates a variety of biologic processes with prominent roles in cellular differentiation and tissue development. Recent advances in molecular biology, mouse genetics, and particularly high-throughput sequencing have greatly enhanced our understanding of YY1 functions and underlying mechanisms in regulating transcription and epigenetics. In this review, we summarize findings on the roles of YY1 in cell differentiation and tissue development, in particular in muscle, nerve, and immune cells/tissues.

RNA activation of haploinsufficient Foxg1 gene in murine neocortex.

More than one hundred distinct gene hemizygosities are specifically linked to epilepsy, mental retardation, autism, schizophrenia and neuro-degeneration. Radical repair of these gene deficits via genome engineering is hardly feasible. The same applies to therapeutic stimulation of the spared allele by artificial transactivators. Small activating RNAs (saRNAs) offer an alternative, appealing approach. As a proof-of-principle, here we tested this approach on the Rett syndrome-linked, haploinsufficient, Foxg1 brain patterning gene. We selected a set of artificial small activating RNAs (saRNAs) upregulating it in neocortical precursors and their derivatives. Expression of these effectors achieved a robust biological outcome. saRNA-driven activation (RNAa) was limited to neural cells which normally express Foxg1 and did not hide endogenous gene tuning. saRNAs recognized target chromatin through a ncRNA stemming from it. Gene upregulation required Ago1 and was associated to RNApolII enrichment throughout the Foxg1 locus. Finally, saRNA delivery to murine neonatal brain replicated Foxg1-RNAa in vivo.

Pore structure and dielectric behaviour of the 3D collagen-DAC scaffolds designed for nerve tissue repair.

The design and selection of a suitable scaffold with well-defined pores size distribution and dielectric properties are critical features for neural tissue engineering. In this study we use mercury porosimetry and the dielectric spectroscopy in the alpha-dispersion region of the electric field to determine the microarchitecture and activation energy of collagen (Col) modified by 2,3 dialdehyde cellulose (DAC). The scaffold was synthesized in three steps: (i) preparation of DAC by oxidation of cellulose, (ii) construction of a 3D Col sponge-shape or film, (iii) cross-linkage of the Col samples using DAC. The activation energy needed to break the bonds formed by water in the Col-DAC composite is approximately 2 times lower than that in the unmodified Col. In addition, the magnitude of conductivity for modified Col at 70°C is approximately 40% lower than that recorded for the unmodified Col. The largest fraction, of which at least 70% of the total pore volume comprises the sponge, is occupied by pores ranging from 20 to 100µm in size. The knowledge on the dielectric behaviour and microstructure of the Col-DAC scaffold may prove relevant to neural tissue engineering focused on the regeneration of the nervous system.

Self-organization of "fibro-axonal" composite tissue around unmodified metallic micro-electrodes can form a functioning interface with a peripheral nerve: A new direction for creating long-term neural interfaces.

INTRODUCTION: A long-term peripheral neural interface is an area of intense research. The use of electrode interfaces is limited by the biological response to the electrode material. METHODS: We created an electrode construct to harbor the rat sciatic nerve with interposition of autogenous adipose tissue between the nerve and the electrode. The construct was implanted for 10 weeks. RESULTS: Immunohistochemistry showed a unique laminar pattern of axonal growth layered between fibro-collagenous tissue, forming a physical interface with the tungsten micro-electrode. Action potentials transmitted across the intrerface showed mean conduction velocities varying between 6.99 ± 2.46 and 20.14 ± 4 m/s. CONCLUSIONS: We have demonstrated the feasibility of a novel peripheral nerve interface through modulation of normal biologic phenomena. It has potential applications as a chronic implantable neural interface.

Handcrafted multilayer PDMS microchannel scaffolds for peripheral nerve regeneration.

Injuries that result in the loss of limb functionality may be caused by the severing of the peripheral nerves within the affected limb. Several bioengineered peripheral nerve scaffolds have been developed in order to provide the physical support and topographical guidance necessary for the naturally disorganized axon outgrowth to reattach to distal nerve stumps as an alternative to other procedures, like nerve grafting. PDMS has been chosen for the base material of the scaffolds due to its biocompatibility, flexibility, transparency, and well-developed fabrication techniques. The process of observing the axon outgrowth across the nerve gaps with PDMS scaffolds has been challenging due to the limited number and fineness of longitudinal sections that can be extracted from harvested nerve tissue samples after implantation. To address this, multilayer microchannel scaffolds were developed with the object of providing more refined longitudinal observation of axon outgrowth by longitudinally 'sectioning' the device during fabrication, removing the need for much of the sample preparation process. This device was then implanted into the sciatic nerves of Lewis rats, and then harvested after two and four weeks to analyze the difference in nerve regeneration between two different time periods. The present layer by layer structure, which is separable after nerve regeneration and is treated as an individual layer during the histology process, provides the details of biological events during axonal regeneration. Confocal microscopic imaging showed the details of peripheral nerve regeneration including nerve branches and growth cones observable from within the microchannels of the multilayer PDMS microchannel scaffolds.

Laser microbeam targeting of single nerve axons in cell culture.

By focusing a laser with short pulses to a diffraction-limited spot, single nerve axons can be precisely targeted and injured. Subsequent repair can be analyzed using various imaging and biochemical techniques to understand the repair process. In this chapter, we will describe a robotic laser microscope system used to injure nerve axons while simultaneously observing repair using phase and fluorescence microscopy. We provide procedures for controlled laser targeting and an experimental approach for studying axonal repair in embryonic rat hippocampus neurons.

Controlled formation of cross-linked collagen fibers for neural tissue engineering applications.

Fibrous scaffolds engineered to direct the growth of tissues can be important in forming architecturally functional tissue such as aligning regenerating nerves with their target. Collagen is a commonly used substrate used for neuronal growth applications in the form of surface coatings and hydrogels. The wet spinning technique can create collagen fibers without the use of organic solvents and is typically accomplished by extruding a collagen dispersion into a coagulation bath. To create well-controlled and uniform collagen fibers, we developed an automatic wet spinning device with precise control over the spinning and fiber collection parameters. A fiber collection belt allowed the continuous formation of very soft and delicate fibers up to half a meter in length. Wet-spun collagen fibers were characterized by tensile and thermal behavior, diameter uniformity, the swelling response in phosphate buffered saline and their biocompatibility with dorsal root ganglion (DRG) neurons and Schwann cells. Fibers formed from 0.75% weight by volume (w/v) collagen dispersions formed the best fibers in terms of tensile behavior and fiber uniformity. Fibers post-treated with the cross-linkers glutaraldehyde and genipin exhibited increased mechanical stability and reduced swelling. Importantly, genipin-treated fibers were conducive to DRG neurons and Schwann cell survival and growth, which validated the use of this cross-linker for neural tissue engineering applications.

Nestin-expressing hair follicle-accessible pluripotent stem cells for nerve and spinal cord repair.

Nestin-expressing stem cells of the hair follicle, discovered by our laboratory, have been shown to be able to form neurons and other nonfollicle cell types. We have shown that the nestin-expressing stem cells from the hair follicle can effect the repair of peripheral nerve and spinal cord injury. The hair follicle stem cells differentiate into neuronal and glial cells after transplantation to the injured peripheral nerve and spinal cord, and enhance injury repair and locomotor recovery. We have termed these cells hair follicle-accessible pluripotent (HAP) stem cells. When the excised hair follicle with its nerve stump was placed in Gelfoam 3D histoculture, HAP stem cells grew and extended the hair follicle nerve which consisted of ßIII-tubulin-positive fibers with F-actin expression at the tip. These findings indicate that ßIII-tubulin-positive fibers elongating from the whisker follicle sensory nerve stump were growing axons. The growing whisker sensory nerve was highly enriched in HAP stem cells, which appeared to play a major role in its elongation and interaction with other nerves in 3D Gelfoam histoculture, including the sciatic nerve, the trigeminal nerve, and the trigeminal nerve ganglion. Our results suggest that a major function of the HAP stem cells in the hair follicle is for growth of the follicle sensory nerve. HAP stem cells have critical advantages over embryonic stem cells and induced pluripotent stem cells in that they are highly accessible, require no genetic manipulation, are nontumorigenic, and do not present ethical issues for regenerative medicine.

Real-time confocal imaging of trafficking of nestin-expressing multipotent stem cells in mouse whiskers in long-term 3-D histoculture.

We have previously demonstrated that nestin-expressing multipotent hair follicle stem cells are located above the hair follicle bulge and can differentiate into neurons and other cell types in vitro. The nestin-expressing hair follicle stem cells promoted the recovery of pre-existing axons when they were transplanted to the severed sciatic nerve or injured spinal cord. We have also previously demonstrated that the whisker hair follicle contains nestin-expressing stem cells in the dermal papilla (DP) as well as in the bulge area (BA), but that their origin is in the BA. In the present study, we established the technique of long-term Gelfoam® histoculture of whiskers isolated from transgenic mice in which nestin drives green fluorescent protein (ND-GFP). Confocal imaging was used to monitor ND-GFP-expressing stem cells trafficking in real time between the BA and DP to determine the fate of the stem cells. It was observed over a 2-week period that the stem cells trafficked from the BA toward the DP area and extensively grew out onto Gelfoam® forming nerve-like structures. This new method of long-term histoculture of whiskers from ND-GFP mice will enable the extensive study of the behavior of nestin-expressing multipotent stem cells of the hair follicle.