Synaptic Differentiation Research Articles

Epigenomic landscapes during prefrontal cortex development and aging in rhesus.

The prefrontal cortex (PFC) is essential for higher-level cognitive functions. How epigenetic dynamics participates in PFC development and aging is largely unknown. Here, we profiled epigenomic landscapes of rhesus monkey PFCs from prenatal to aging stages. The dynamics of chromatin states, including higher-order chromatin structure, chromatin interaction and histone modifications are coordinated to regulate stage-specific gene transcription, participating in distinct processes of neurodevelopment. Dramatic changes of epigenetic signals occur around the birth stage. Notably, genes involved in neuronal cell differentiation and layer specification are pre-configured by bivalent promoters. We identified a cis-regulatory module and the transcription factors (TFs) associated with basal radial glia development, which was associated with large brain size in primates. These TFs include GLI3, CREB5 and SOX9. Interestingly, the genes associated with the basal radial glia (bRG)-associated cis-element module, such as SRY and SOX9, are enriched in sex differentiation. Schizophrenia-associated single nucleotide polymorphisms are more enriched in super enhancers (SEs) than typical enhancers, suggesting that SEs play an important role in neural network wiring. A cis-regulatory element of DBN1 is identified, which is critical for neuronal cell proliferation and synaptic neuron differentiation. Notably, the loss of distal chromatin interaction and H3K27me3 signal are hallmarks of PFC aging, which are associated with abnormal expression of aging-related genes and transposon activation, respectively. Collectively, our findings shed light on epigenetic mechanisms underlying primate brain development and aging.

Engineering 3D microenvironments with femtosecond laser-fabricated microtubes to direct neuronal network formation

The regulation of cell growth characteristics through physical structures on material surfaces plays a crucial role in advancing our understanding of cell behavior. Three-dimensional (3D) microstructures, offering multidimensional growth space and a richer nutrient environment compared to their two-dimensional counterparts, have attracted significant attention from researchers. However, the fabrication of high-precision 3D microstructures, especially those with a high aspect ratio (H-AR), remains challenging. In this study, we employ femtosecond laser to achieve exceptional precision and patterning capabilities in fabricating 3D microstructures. To enhance the manufacturing efficiency of axial 3D structures, we introduce a novel single pulse multi-photon polymerization (SP-MPP) method for efficient fabrication of H-AR micropillar and microtube structures. Our innovative approach involves a dual-aperture optical modulation method that effectively modulates the annular energy distribution, enabling the creation of H-AR microstructures. We can achieve a maximum processing height of up to 130 μm with an aspect ratio of 16 within single pulse exposure of 217 fs. Compared to the layer-by-layer scanning method, our proposed approach enhances the axial manufacturing efficiency of 3D structures by 1–2 orders of magnitude. Through experimentation, we validate the applicability of microtube structures for guiding neuronal orientation by utilizing microtube arrays in hippocampal neuronal cell culture. Our results demonstrate that neurons not only grow along the patterned microtubes but also exhibit preliminary synaptic differentiation. Furthermore, we effectively regulate the 3D patterning of neuronal growth by implementing diverse patterned microtube arrays. This proposed method enables the rapid construction of a large-scale 3D cell growth environment, offering significant advantages in inducing neuronal orientation. Consequently, this technique holds immense potential for diverse applications in biomedicine and tissue engineering, including the establishment of isolated neural networks.

Expression of Transposable Elements in the Brain of the Drosophila melanogaster Model for Fragile X Syndrome.

Fragile X syndrome is a neuro-developmental disease affecting intellectual abilities and social interactions. Drosophila melanogaster represents a consolidated model to study neuronal pathways underlying this syndrome, especially because the model recapitulates complex behavioural phenotypes. Drosophila Fragile X protein, or FMRP, is required for a normal neuronal structure and for correct synaptic differentiation in both the peripheral and central nervous systems, as well as for synaptic connectivity during development of the neuronal circuits. At the molecular level, FMRP has a crucial role in RNA homeostasis, including a role in transposon RNA regulation in the gonads of D. m. Transposons are repetitive sequences regulated at both the transcriptional and post-transcriptional levels to avoid genomic instability. De-regulation of transposons in the brain in response to chromatin relaxation has previously been related to neurodegenerative events in Drosophila models. Here, we demonstrate for the first time that FMRP is required for transposon silencing in larval and adult brains of Drosophila "loss of function" dFmr1 mutants. This study highlights that flies kept in isolation, defined as asocial conditions, experience activation of transposable elements. In all, these results suggest a role for transposons in the pathogenesis of certain neurological alterations in Fragile X as well as in abnormal social behaviors.

Organizing the synaptic junctions

Synaptic adhesion molecules (SAMs) are essential for driving the formation, maturation, and plasticity of synaptic connections for neural networks. MAM domain-containing glycosylphosphatidylinositol anchors (MDGAs) are a type of SAM that regulates the formation of trans-synaptic bridges, which are critical for neurotransmission and synaptic differentiation. In a recent issue of the JBC, Lee etal. uncovered that MDGA1 can control protein-protein interactions and synaptic cleft activity by adopting different global 3D conformations. This novel molecular mechanism may be applicable to other SAMs that regulate protein-protein interactions and nanoscale organization in the synaptic cleft.

Can Brain-derived Neurotrophic Factor (BDNF) Mimetics be a Way Out for Neurodegenerative Diseases?

Neurodegenerative diseases are chronic and progressive disease groups characterized by the decline of neural transmission because of the loss of structure and function of neurons. Although there is currently no effective treatment for neurodegenerative diseases, new treatment strategies need to be developed urgently. Among neurotrophins, BDNF has been extensively investigated, and it has emerged as an important regulator of synaptic plasticity, neuronal survival, and differentiation. Changes in BDNF levels and signaling pathways have been identified in several neurodegenerative diseases. Moreover, promising results have been obtained for BDNF in many experimental studies on animal models. In addition, BDNF serves as a crucial molecular target for developing drugs to treat neurological diseases. However, several pharmacokinetic difficulties have limited its use in clinical practice, such as its inability to cross the blood-brain barrier, short half-life, and potential adverse effects. To avoid these difficulties, several approaches have been explored, but they have led to disappointing results. One way to overcome the limitations of BDNF may be with mimetic molecules that can effectively stimulate the receptors it has an affinity with and thus activates BDNF pathways. In this perspective article, an evaluation of the efficacy of different BDNF mimetics against neurodegenerative diseases was made.

Neurexin-β Mediates the Synaptogenic Activity of Amyloid Precursor Protein.

In addition to its role in Alzheimer's disease, amyloid precursor protein (APP) has physiological roles in synapse development and function. APP induces presynaptic differentiation when presented to axons, but the mechanism is unknown. Here we show that APP binds neurexin to mediate this synaptogenic activity. APP specifically binds β not α neurexins modulated by splice site 4. Binding to neurexin heparan sulfate glycan and LNS protein domains is required for high-affinity interaction and for full-length APP to recruit axonal neurexin. The synaptogenic activity of APP is abolished by triple knockdown of neurexins in hippocampal neurons pooled from male and female rats. Based on these and previous results, our model is that a dendritic-axonal trans dimer of full-length APP binds to axonal neurexin-β to promote synaptic differentiation and function. Furthermore, soluble sAPPs also bind neurexin-β and inhibit its interaction with neuroligin-1, raising the possibility that disruption of neurexin function by altered levels of full-length APP and its cleavage products may contribute to early synaptic deficits in Alzheimer's disease.SIGNIFICANCE STATEMENT The prevailing model for the basis of Alzheimer's disease is the amyloid cascade triggered by altered cleavage of amyloid precursor protein (APP). APP also has physiological roles at the synapse, but the molecular basis for its synaptic functions is not well understood. Here, we show that APP binds the presynaptic organizing protein neurexin-β and that neurexin is essential for the synaptogenic activity of APP. Furthermore, soluble APP forms generated by APP cleavage also bind neurexin-β and can block interaction with transmembrane synaptogenic ligands of neurexin. These findings reveal a role for neurexin-APP interaction in synapse development and raise the possibility that disruptions of neurexin function may contribute to synaptic and cognitive deficits in the critical early stage of Alzheimer's disease.

Mapping genomic loci implicates genes and synaptic biology in schizophrenia.

Schizophrenia has a heritability of 60-80%1, much of which is attributable to common risk alleles. Here, in a two-stage genome-wide association study of up to 76,755 individuals with schizophrenia and 243,649 control individuals, we report common variant associations at 287 distinct genomic loci. Associations were concentrated in genes that are expressed in excitatory and inhibitory neurons of the central nervous system, but not in other tissues or cell types. Using fine-mapping and functional genomic data, we identify 120 genes (106 protein-coding) that are likely to underpin associations at some of these loci, including 16 genes with credible causal non-synonymous or untranslated region variation. We also implicate fundamental processes related to neuronal function, including synaptic organization, differentiation and transmission. Fine-mapped candidates were enriched for genes associated with rare disruptive coding variants in people with schizophrenia, including the glutamate receptor subunit GRIN2A and transcription factor SP4, and were also enriched for genes implicated by such variants in neurodevelopmental disorders. We identify biological processes relevant to schizophrenia pathophysiology; show convergence of common and rare variant associations in schizophrenia and neurodevelopmental disorders; and provide a resource of prioritized genes and variants to advance mechanistic studies.

On the Nature of Functional Differentiation: The Role of Self-Organization with Constraints.

The focus of this article is the self-organization of neural systems under constraints. In 2016, we proposed a theory for self-organization with constraints to clarify the neural mechanism of functional differentiation. As a typical application of the theory, we developed evolutionary reservoir computers that exhibit functional differentiation of neurons. Regarding the self-organized structure of neural systems, Warren McCulloch described the neural networks of the brain as being “heterarchical”, rather than hierarchical, in structure. Unlike the fixed boundary conditions in conventional self-organization theory, where stationary phenomena are the target for study, the neural networks of the brain change their functional structure via synaptic learning and neural differentiation to exhibit specific functions, thereby adapting to nonstationary environmental changes. Thus, the neural network structure is altered dynamically among possible network structures. We refer to such changes as a dynamic heterarchy. Through the dynamic changes of the network structure under constraints, such as physical, chemical, and informational factors, which act on the whole system, neural systems realize functional differentiation or functional parcellation. Based on the computation results of our model for functional differentiation, we propose hypotheses on the neuronal mechanism of functional differentiation. Finally, using the Kolmogorov–Arnold–Sprecher superposition theorem, which can be realized by a layered deep neural network, we propose a possible scenario of functional (including cell) differentiation.

Multiple Molecular Pathways Are Influenced by Progranulin in a Neuronal Cell Model–A Parallel Omics Approach

Progranulin (PGRN) is critical in supporting a healthy CNS. Its haploinsufficiency results in frontotemporal dementia, while in experimental models of age-related neurodegenerative diseases, the targeted expression of PGRN greatly slows the onset of disease phenotypes. Nevertheless, much remains unclear about how PGRN affects its target cells. In previous studies we found that PGRN showed a remarkable ability to support the survival of NSC-34 motor neuron cells under conditions that would otherwise lead to their apoptosis. Here we used the same model to investigate other phenotypes of PGRN expression in NSC-34 cells. PGRN significantly influenced morphological differentiation, resulting in cells with enlarged cell bodies and extended projections. At a molecular level this correlated with pathways associated with the cytoskeleton and synaptic differentiation. Depletion of PGRN led to increased expression of several neurotrophic receptors, which may represent a homeostatic mechanism to compensate for loss of neurotrophic support from PGRN. The exception was RET, a neurotrophic tyrosine receptor kinase, which, when PGRN levels are high, shows increased expression and enhanced tyrosine phosphorylation. Other receptor tyrosine kinases also showed higher tyrosine phosphorylation when PGRN was elevated, suggesting a generalized enhancement of receptor activity. PGRN was found to bind to multiple plasma membrane proteins, including RET, as well as proteins in the ER/Golgi apparatus/lysosome pathway. Understanding how these various pathways contribute to PGRN action may provide routes toward improving neuroprotective therapies.

Distinct Effects of BDNF and NT-3 on the Dendrites and Presynaptic Boutons of Developing Olfactory Bulb GABAergic Interneurons In Vitro.

Brain-derived neurotrophic factor (BDNF) and neurotrophin 3 (NT-3) are known to regulate neuronal morphology and the formation of neural circuits, yet the neuronal targets of each neurotrophin are still to be defined. To address how these neurotrophins regulate the morphological and synaptic differentiation of developing olfactory bulb (OB) GABAergic interneurons, we analyzed the effect of BDNF and NT-3 on GABA+-neurons and on different subtypes of these neurons: tyrosine hydroxylase (TH+); calretinin (Calr+); calbindin (Calb+); and parvalbumin (PVA+). These cells were generated from cultured embryonic mouse olfactory bulb neural stem cells (eOBNSCs) and after 14days in vitro (DIV), when the neurons expressed TrkB and/or TrkC receptors, BDNF and NT-3 did not significantly change the number of neurons. However, long-term BDNF treatment did produce a longer total dendrite length and/or more dendritic branches in all the interneuron populations studied, except for PVA+-neurons. Similarly, BDNF caused an increase in the cell body perimeter in all the interneuron populations analyzed, except for PVA+-neurons. GABA+- and TH+-neurons were also studied at 21 DIV, when BDNF produced significantly longer neurites with no clear change in their number. Notably, these neurons developed synaptophysin+ boutons at 21 DIV, the size of which augmented significantly following exposure to either BDNF or NT-3. Our results show that in conditions that maintain neuronal survival, BDNF but not NT-3 promotes the morphological differentiation of developing OB interneurons in a cell-type-specific manner. In addition, our findings suggest that BDNF and NT-3 may promote synapse maturation by enhancing the size of synaptic boutons.

Activation of the Notch signaling pathway in the anterior cingulate cortex is involved in the pathological process of neuropathic pain.

Plastic changes in the anterior cingulate cortex (ACC) are critical in pain hypersensitivity caused by peripheral nerves injury. The Notch signaling pathway has been shown to regulate synaptic differentiation and transmission. Therefore, this study was to investigate the function of the Notch signaling pathway in the ACC during nociceptive transmission induced by neuropathic pain. We adopted Western blotting, N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester (DAPT) microinjections, RNA interference targeting Notch1, Hairy and enhancer of split (Hes) 1 or Hes5, electrophysiological recordings, and behavioral tests to verify the link between Notch signaling in ACC and neuropathic pain with adult male Sprague-Dawley rats. Levels of the Notch intracellular domain were increased in ACC on day 7 after chronic constriction injury surgery or spared nerve injury. Meanwhile, the mRNA level of the downstream effector of Notch signaling Hes1 was increased, whereas the level of Hes5 mRNA did not change. Microinjection of DAPT, a γ-secretase (a key enzyme involved in Notch pathway) inhibitor, into ACC significantly reversed neuropathic pain behaviors. Intra-ACC injection of short hairpin RNA-Notch reduced Notch intracellular domain expression and decreased the potentiation of synaptic transmission in the ACC. Moreover, pain perceptions were also alleviated in rats subjected to chronic constriction injury or spared nerve injury. This process was mainly mediated by the downstream effector Hes1, but not Hes5. Based on these results, the activation of the Notch/Hes1 signaling pathway in the ACC participates in the development of neuropathic pain, indicating that the Notch pathway may be a new therapeutic target for treating chronic pain.

Perinatal Lead Exposure Alters Calsyntenin-2 and Calsyntenin-3 Expression in the Hippocampus and Causes Learning Deficits in Mice Post-weaning.

Calsyntenin-2 (Clstn2) and calsyntenin-3 (Clstn3) are the members of the cadherin superfamily and function to regulate the postsynaptic activity. Both proteins are known to play an important role in memory and learning. This study was designed to test the hypothesis that exposure of mothers to Pb in drinking water may alter the expression of Clstn2 and Clstn3 in offspring, which contributes to the Pb-induced learning deficiency. Pregnant mice were exposed to Pb in drinking water as Pb acetate from gestation to weaning. At the postnatal day 21, the learning and memory ability of pups was tested by Morris water maze, and the blood and brain tissues from pups were collected for metal and protein analyses. Data showed that perinatal Pb exposure resulted in a dose-dependent increase of Pb concentrations in blood (6-20-fold), hippocampus (2-7-fold), and cerebral cortex (2-8-fold) in offspring, as compared to controls (p < 0.05).The ability of learning and memory was decreased in lead exposure group, as compared to controls (p < 0.05). Both immunofluorescence and Western blot analyses revealed a striking difference in the expression of Clstn2 vs. Clstn3 following perinatal Pb exposure. In pregnant mice exposed to 0.1%, 0.2%, and 0.5% Pb, the expression of Clstn2 in offspring showed a Pb dose-related decrease by 39.2%, 76.5%, and 96.1% in hippocampus and by12.5%, 59.4%, and 78.1% in cerebral cortex, respectively (p < 0.05). In contrast, Clstn3 expression in these offspring brain regions was significantly increased (p < 0.05), after perinatal Pb exposure. The nature of Pb differential effect on Clstn2 and Clstn3 remains unknown. These observations suggest that Clstn2 and Clstn3 may have different roles in synaptic development and differentiation. Pb-induced learning defects may partly relate to the altered expression of calsyntenin proteins.

Optogenetic control of excitatory post-synaptic differentiation through neuroligin-1 tyrosine phosphorylation.

Neuroligins (Nlgns) are adhesion proteins mediating trans-synaptic contacts in neurons. However, conflicting results around their role in synaptic differentiation arise from the various techniques used to manipulate Nlgn expression level. Orthogonally to these approaches, we triggered here the phosphorylation of endogenous Nlgn1 in CA1 mouse hippocampal neurons using a photoactivatable tyrosine kinase receptor (optoFGFR1). Light stimulation for 24 hr selectively increased dendritic spine density and AMPA-receptor-mediated EPSCs in wild-type neurons, but not in Nlgn1 knock-out neurons or when endogenous Nlgn1 was replaced by a non-phosphorylatable mutant (Y782F). Moreover, light stimulation of optoFGFR1 partially occluded LTP in a Nlgn1-dependent manner. Combined with computer simulations, our data support a model by which Nlgn1 tyrosine phosphorylation promotes the assembly of an excitatory post-synaptic scaffold that captures surface AMPA receptors. This optogenetic strategy highlights the impact of Nlgn1 intracellular signaling in synaptic differentiation and potentiation, while enabling an acute control of these mechanisms.

Characterization of pathogenic monoclonal autoantibodies derived from muscle-specific kinase myasthenia gravis patients.

Myasthenia gravis (MG) is a chronic autoimmune disorder characterized by muscle weakness and caused by pathogenic autoantibodies that bind to membrane proteins at the neuromuscular junction. Most patients have autoantibodies against the acetylcholine receptor (AChR), but a subset of patients have autoantibodies against muscle-specific tyrosine kinase (MuSK) instead. MuSK is an essential component of the pathway responsible for synaptic differentiation, which is activated by nerve-released agrin. Through binding MuSK, serum-derived autoantibodies inhibit agrin-induced MuSK autophosphorylation, impair clustering of AChRs, and block neuromuscular transmission. We sought to establish individual MuSK autoantibody clones so that the autoimmune mechanisms could be better understood. We isolated MuSK autoantibody-expressing B cells from 6 MuSK MG patients using a fluorescently tagged MuSK antigen multimer, then generated a panel of human monoclonal autoantibodies (mAbs) from these cells. Here we focused on 3 highly specific mAbs that bound quantitatively to MuSK in solution, to MuSK-expressing HEK cells, and at mouse neuromuscular junctions, where they colocalized with AChRs. These 3 IgG isotype mAbs (2 IgG4 and 1 IgG3 subclass) recognized the Ig-like domain 2 of MuSK. The mAbs inhibited AChR clustering, but intriguingly, they enhanced rather than inhibited MuSK phosphorylation, which suggests an alternative mechanism for inhibiting AChR clustering.

Lysophosphatidic Acid and Glutamatergic Transmission.

Signaling through bioactive lipids regulates nervous system development and functions. Lysophosphatidic acid (LPA), a membrane-derived lipid mediator particularly enriched in brain, is able to induce many responses in neurons and glial cells by affecting key processes like synaptic plasticity, neurogenesis, differentiation and proliferation. Early studies noted sustained elevations of neuronal intracellular calcium, a primary response to LPA exposure, suggesting functional modifications of NMDA and AMPA glutamate receptors. However, the crosstalk between LPA signaling and glutamatergic transmission has only recently been shown. For example, stimulation of presynaptic LPA receptors in hippocampal neurons regulates glutamate release from the presynaptic terminal, and excess of LPA induce seizures. Further evidence indicating a role of LPA in the modulation of neuronal transmission has been inferred from animal models with deficits on LPA receptors, mainly LPA1 which is the most prevalent receptor in human and mouse brain tissue. LPA1 null-mice exhibit cognitive and attention deficits characteristic of schizophrenia which are related with altered glutamatergic transmission and reduced neuropathic pain. Furthermore, silencing of LPA1 receptor in mice induced a severe down-regulation of the main glutaminase isoform (GLS) in cerebral cortex and hippocampus, along with a parallel sharp decrease on active matrix-metalloproteinase 9. The downregulation of both enzymes correlated with an altered morphology of glutamatergic pyramidal cells dendritic spines towards a less mature phenotype, indicating important implications of LPA in synaptic excitatory plasticity which may contribute to the cognitive and memory deficits shown by LPA1-deficient mice. In this review, we present an updated account of current evidence pointing to important implications of LPA in the modulation of synaptic excitatory transmission.

MACF1 links Rapsyn to microtubule- and actin-binding proteins to maintain neuromuscular synapses.

Complex mechanisms are required to form neuromuscular synapses, direct their subsequent maturation, and maintain the synapse throughout life. Transcriptional and post-translational pathways play important roles in synaptic differentiation and direct the accumulation of the neurotransmitter receptors, acetylcholine receptors (AChRs), to the postsynaptic membrane, ensuring for reliable synaptic transmission. Rapsyn, an intracellular peripheral membrane protein that binds AChRs, is essential for synaptic differentiation, but how Rapsyn acts is poorly understood. We screened for proteins that coisolate with AChRs in a Rapsyn-dependent manner and show that microtubule actin cross linking factor 1 (MACF1), a scaffolding protein with binding sites for microtubules (MT) and actin, is concentrated at neuromuscular synapses, where it binds Rapsyn and serves as a synaptic organizer for MT-associated proteins, EB1 and MAP1b, and the actin-associated protein, Vinculin. MACF1 plays an important role in maintaining synaptic differentiation and efficient synaptic transmission in mice, and variants in MACF1 are associated with congenital myasthenia in humans.

Robust Induced Presynapse on Artificial Substrates as a Neural Interfacing Method.

Over the recent years, the development of neural interface systems has stuck to using electrical cues to stimulate neurons and read out neural signals, although neurons relay signals via chemical release and recognition at synapses. In addition, conventional neural interfaces are vulnerable to cell migration and glial encapsulation due to the absence of connection anchoring the neuron into the device unlike synapses, which are firmly sustained by protein bonding. To close this discrepancy, we conducted an intensive investigation into the induced synapse interface by employing engineered synaptic proteins from a neural interface perspective. The strong potential of induced synaptic differentiation as an emerging neural interfacing technique is demonstrated by exploring its structural features, chemical release kinetics, robustness, and scalability to the brain tissue. We show that the exocytosis kinetics of induced synapses is similar to that of endogenous synapses. Moreover, induced synapses show remarkable stability, despite cell migration and growth. The synapse-inducing technique has broad applications to cultured hippocampal and cortex tissues and suggests a promising method to integrate neural circuits with digital elements.

Perspectives of RAS and RHEB GTPase Signaling Pathways in Regenerating Brain Neurons.

Cellular activation of RAS GTPases into the GTP-binding “ON” state is a key switch for regulating brain functions. Molecular protein structural elements of rat sarcoma (RAS) and RAS homolog protein enriched in brain (RHEB) GTPases involved in this switch are discussed including their subcellular membrane localization for triggering specific signaling pathways resulting in regulation of synaptic connectivity, axonal growth, differentiation, migration, cytoskeletal dynamics, neural protection, and apoptosis. A beneficial role of neuronal H-RAS activity is suggested from cellular and animal models of neurodegenerative diseases. Recent experiments on optogenetic regulation offer insights into the spatiotemporal aspects controlling RAS/mitogen activated protein kinase (MAPK) or phosphoinositide-3 kinase (PI3K) pathways. As optogenetic manipulation of cellular signaling in deep brain regions critically requires penetration of light through large distances of absorbing tissue, we discuss magnetic guidance of re-growing axons as a complementary approach. In Parkinson’s disease, dopaminergic neuronal cell bodies degenerate in the substantia nigra. Current human trials of stem cell-derived dopaminergic neurons must take into account the inability of neuronal axons navigating over a large distance from the grafted site into striatal target regions. Grafting dopaminergic precursor neurons directly into the degenerating substantia nigra is discussed as a novel concept aiming to guide axonal growth by activating GTPase signaling through protein-functionalized intracellular magnetic nanoparticles responding to external magnets.

Collagen/β‐TCP nerve guidance conduits promote facial nerve regeneration in mini‐swine and the underlying biological mechanism: A pilot in vivo study

This study aimed to evaluate the efficiency of new nerve guidance conduits (NGCs) in bridging facial nerve gaps, and investigate the underlying biological mechanisms implicated in the regeneration process. A collagen/β-TCP conduit was prepared and applied to a facial nerve gap in a mini-swine model. Functional recovery and axonal regeneration were further evaluated by electrophysiological and histological examinations at 3 months after surgery. Furthermore, the global transcriptomic profiles of regenerated and normal tissues were analyzed by gene microarray to identify the differentially expressed genes at day three and seven, postoperatively. Subsequently, associated biological processes were analyzed by gene ontology (GO) enrichment analysis. The electrophysiological examination and morphological analysis revealed that significant nerve regeneration effects were achieved in the Col/β-TCP group (p < 0.05). Transcriptional analysis revealed that at day three post-surgery, the majority of overexpressed genes were associated with inflammatory, immune and stimuli response, accompanied by angiogenesis, while at day seven, the majority of overexpressed genes were associated with cell, tissue and organ regeneration and development, synaptic transmission, neurogenesis, and neuronal differentiation, as well as the WNT, MAPK/ERK, and JAK/STAT signaling pathways. In conclusion, the present results suggest that collagen/β-TCP NGCs provide a promising tubular micro-environment for nerve regeneration. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1122-1131, 2019.

Histone acetylation as a new mechanism for bilirubin-induced encephalopathy in the Gunn rat

Bilirubin neurotoxicity has been studied for decades and has been shown to affect various mechanisms via significant modulation of gene expression. This suggests that vital regulatory mechanisms of gene expression, such as epigenetic mechanisms, could play a role in bilirubin neurotoxicity. Histone acetylation has recently received attention in the CNS due to its role in gene modulation for numerous biological processes, such as synaptic plasticity, learning, memory, development and differentiation. Aberrant epigenetic regulation of gene expression in psychiatric and neurodegenerative disorders has also been described. In this work, we followed the levels of histone 3 lysine 14 acetylation (H3K14Ac) in the cerebellum (Cll) of the developing (2, 9, 17 days after the birth) and adult Gunn rat, the natural model for neonatal hyperbilirubinemia and kernicterus. We observed an age-specific alteration of the H3K14Ac in the hyperbilirubinemic animals. The GeneOntology analysis of the H3K14Ac linked chromatin revealed that almost 45% of H3K14Ac ChiP-Seq TSS-promoter genes were involved in CNS development including maturation and differentiation, morphogenesis, dendritogenesis, and migration. These data suggest that the hallmark Cll hypoplasia in the Gunn rat occurs also via epigenetically controlled mechanisms during the maturation of this brain structure, unraveling a novel aspect of the bilirubin-induced neurotoxicity.