[Show abstract][Hide abstract] ABSTRACT: Direct cell-reprogramming technology is based on the dominant action of cell-lineage transcription factors (TFs) in converting adult somatic cells into different cell types (Graf and Enver, 2009). This technique represents a promising avenue in the field of regenerative medicine, with the potential to generate cellular sources suitable for cell-replacement therapies (Chambers and Studer, 2011). In fact, since the groundbreaking discovery of the induced pluripotent stem cells (iPSCs) (Takahashi and Yamanaka, 2006), increasing approaches of direct cell reprogramming have been established, culminating with the development of induced cellular types for neurons, cardiomyocytes, and hepatocytes (Vierbuchen et al., 2010, Ieda et al., 2010 and Huang et al., 2011). In addition, we and others employed the forced expression of defined sets of TFs to generate specific induced neuronal sublineages for dopaminergic, cholinergic, and motor neurons (Caiazzo et al., 2011, Pfisterer et al., 2011, Kim et al., 2002, Son et al., 2011, Liu et al., 2013 and Theka et al., 2013). More recently, two groups succeeded in the generation of induced oligodendrocyte precursors by direct conversion of fibroblasts (Najm et al., 2013 and Yang et al., 2013). Surprisingly, to date, there is no report for the generation of astrocyte by means of direct cell reprogramming. Astrocytes are the most-abundant cell type in the CNS and a critical neural cell type responsible for the maintenance of brain homeostasis. Indeed, they play irreplaceable roles in neurotransmitter trafficking and recycling, nutrient and ion metabolism, regulation of blood supply, release of transmitters and growth factors, and protection against oxidative stress (Molofsky et al., 2012). Consistent with such a variety of fundamental functions exerted by astrocytes in supporting neuronal survival and function, astrocyte dysfunctions have been found to contribute to several neurological diseases, such as epilepsy, amyotrophic lateral sclerosis (ALS), Alzheimer’s disease, lysosomal storage diseases (Di Malta et al., 2012), and Rett syndrome (Molofsky et al., 2012). Conversely, recent data showed that transplanted astrocyte progenitors display robust survival and differentiation in the host brain and are able to decelerate the disease course in ALS and Alzheimer’s disease models (Lepore et al., 2008 and Pihlaja et al., 2008). However, current protocols rely on the isolation of astrocyte progenitors from neonatal brains with serious limitations for any therapeutic approach as the paucity of cell supply and unmatched immunoprofile with the host, leading to immune reaction and possible rejection after transplantation. Cell-reprogramming approaches, by generating astrocytes starting from adult skin fibroblasts from an immunomatched or autologous source, can represent a promising alternative system for overcoming those bottlenecks. Notably, procedures of direct iPSC differentiation into astrocytes have been established only very recently (Krencik et al., 2011, Emdad et al., 2012, Juopperi et al., 2012, Roybon et al., 2013, Serio et al., 2013 and Shaltouki et al., 2013). However, these approaches rely on the previous generation of stable and mutation-free iPSC lines, and the cell differentiation protocols are considerably time-consuming, complex, and required extensive time up to 180 days. We therefore considered that a direct reprogramming approach could have interesting advantages, providing a more practical procedure to generate astrocyte-like cells. Indeed, after the identification of the reprogramming cocktail composed by the astroglial TFs NFIA, NFIB, and SOX9, we defined a straightforward and fast (∼2 weeks) protocol to generate induced astrocytes (iAstrocytes) derived from mouse embryonic and postnatal fibroblasts. Our experiments indicate that iAstrocyte molecular phenotype and biological functions closely recapitulate that of native astrocytes, thus validating the direct reprogramming technology as an alternative for the generation of astrocytes.
[Show abstract][Hide abstract] ABSTRACT: During cortical development, NMDA receptors (NMDARs) facilitate presynaptic terminal formation, enhance neurotransmitter release, and are required in presynaptic neurons for spike timing-dependent LTD. However, the extent to which NMDARs are found within cortical presynaptic terminals has remained controversial, and the sub-synaptic localization and dynamics of axonal NMDARs are unknown. Here, using live confocal imaging and biochemical purification of presynaptic membranes, we provide strong evidence that NMDARs localize to presynaptic terminals in vitro and in vivo, in a developmentally regulated manner. NR1 and NR2B subunits are found within the active zone membrane, where they could respond to synaptic glutamate release. Surprisingly, NR1 also appears in glutamatergic and GABAergic synaptic vesicles. During synaptogenesis, NR1 is mobile throughout axons - including growth cones and filopodia, structures that are involved in synaptogenesis. Upon synaptogenic contact, NMDA receptors are quickly recruited to terminals by neuroligin-1/neurexin signaling. Unlike dendrites, the trafficking and distribution of axonal NR1 are insensitive to activity changes, including NMDA exposure, local glutamate uncaging or action potential blockade. These results support the idea that presynaptic NMDARs play an early role in presynaptic development.
Journal of Cell Science 12/2014; · 5.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An overview of the optical methods available to modulate the cellular activity in cell cultures and biological tissues is presented, with a focus on the use of exogenous functional materials that absorb electromagnetic radiation and transduce it into a secondary stimulus for cell excitation, with high temporal and spatial resolution. Both organic and inorganic materials are critically evaluated, for in vitro and in vivo applications. Finally, as a direct practical application of optical-stimulation techniques, the most recent results in the realization of artificial visual implants are discussed.
[Show abstract][Hide abstract] ABSTRACT: Synapsins (Syns) are synaptic vesicle (SV)-associated proteins involved in the regulation of synaptic transmission and plasticity, which display a highly conserved ATP binding site in the central C-domain, whose functional role is unknown. Using molecular dynamics simulations, we demonstrated that ATP binding to SynI is mediated by a conformational transition of a flexible loop that opens to make the binding site accessible; such transition, prevented in the K269Q mutant, is not significantly affected in the absence of Ca(2+) or by the E373K mutation that abolishes Ca(2+)-binding. Indeed, the ATP binding to SynI also occurred under Ca(2+)-free conditions and increased its association with purified rat SVs regardless of the presence of Ca(2+) and promoted SynI oligomerization. However, although under Ca(2+)-free conditions, SynI dimerization and SV clustering were enhanced, Ca(2+) favored the formation of tetramers at the expense of dimers and did not affect SV clustering, indicating a role of Ca(2+)-dependent dimer/tetramer transitions in the regulation of ATP-dependent SV clustering. To elucidate the role of ATP/SynI binding in synaptic physiology, mouse SynI knock-out hippocampal neurons were transduced with either wild-type or K269Q mutant SynI and inhibitory transmission was studied by patch-clamp and electron microscopy. K269Q-SynI expressing inhibitory synapses showed increased synaptic strength due to an increase in the release probability, an increased vulnerability to synaptic depression and a dysregulation of SV trafficking, when compared with wild-type SynI-expressing terminals. The results suggest that the ATP-SynI binding plays predocking and postdocking roles in the modulation of SV clustering and plasticity of inhibitory synapses.
Journal of Neuroscience 10/2014; 34(44):14752-68. · 6.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Devising and constructing biocompatible devices for nervous system regeneration is an extremely challenging task. Besides tackling the issue of biocompatibility, biomaterials for neuroscience applications should mimic the complex environment of the extracellular matrix, which in vivo provides neurons with a series of cues and signals to guide cells towards their appropriate targets. In this work, a novel nanopatterned biocompatible poly-ε-caprolactone (PCL) film is realized to assist the attachment and growth of primary hippocampal neurons. Costly and time-consuming processes can be avoided using plasma-surface nanotexturing obtained by a mixed gas SF6/Ar at -5°C. The intrinsic composition and line topography of nanopatterned PCL ensure healthy development of the neuronal network, as shown by confocal microscopy, by analysing the expression of a range of neuronal markers typical of mature cultures, as well as by scanning electron microscopy. In addition, we show that surface nanopatterning improves differentiation of neurons compared to flat PCL films, while no neural growth was observed on either flat or nanopatterned substrates in the absence of poly-D-lysine coating. Thus, we successfully optimized a nanofabrication protocol to obtain nanostructured PCL layers endowed with several mechanical and structural characteristics that make them a promising, versatile tool for future tissue engineering studies aimed at neural tissue regeneration.
[Show abstract][Hide abstract] ABSTRACT: Autism spectrum disorders (ASDs) are heterogeneous neurodevelopmental disorders characterized by deficits in social interaction and social communication, restricted interests, and repetitive behaviors. Many synaptic protein genes are linked to the pathogenesis of ASDs, making them prototypical synaptopathies. An array of mutations in the synapsin (Syn) genes in humans has been recently associated with ASD and epilepsy, diseases that display a frequent comorbidity. Syns are pre-synaptic proteins regulating synaptic vesicle traffic, neurotransmitter release, and short-term synaptic plasticity. In doing so, Syn isoforms control the tone of activity of neural circuits and the balance between excitation and inhibition. As ASD pathogenesis is believed to result from dysfunctions in the balance between excitatory and inhibitory transmissions in neocortical areas, Syns are novel ASD candidate genes. Accordingly, deletion of single Syn genes in mice, in addition to epilepsy, causes core symptoms of ASD by affecting social behavior, social communication, and repetitive behaviors. Thus, Syn knockout mice represent a good experimental model to define synaptic alterations involved in the pathogenesis of ASD and epilepsy.
[Show abstract][Hide abstract] ABSTRACT: Acetylcholinesterase (ACHE) is a glycoprotein with a key role in terminating synaptic transmission in cholinergic neurons of both vertebrates and invertebrates. ACHE is also involved in the regulation of cell growth and morphogenesis during embryogenesis and regeneration acting through its non-cholinergic sites. The mollusk Octopus vulgaris provides a powerful model for investigating the mechanisms underlying tissue morphogenesis due to its high regenerative power. Here, we performed a comparative investigation of arm morphogenesis during adult arm regeneration and embryonic arm development which may provide insights on the conserved ACHE pathways. In this study, we cloned and characterized O. vulgaris ACHE, finding a single highly conserved ACHE hydrophobic variant, characterized by prototypical catalytic sites and a putative consensus region for a glycosylphosphatidylinositol (GPI)-anchor attachment at the COOH-terminus. We then show that its expression level is correlated to the stage of morphogenesis in both adult and embryonic arm. In particular, ACHE is localized in typical neuronal sites when adult-like arm morphology is established and in differentiating cell locations during the early stages of arm morphogenesis. This possibility is also supported by the presence in the ACHE sequence and model structure of both cholinergic and non-cholinergic sites. This study provides insights into ACHE conserved roles during processes of arm morphogenesis. In addition, our modeling study offers a solid basis for predicting the interaction of the ACHE domains with pharmacological blockers for in vivo investigations. We therefore suggest ACHE as a target for the regulation of tissue morphogenesis.
[Show abstract][Hide abstract] ABSTRACT: Idiopathic epilepsies have frequently been linked to mutations in voltage-gated channels (channelopathies); recently, mutations in several genes encoding presynaptic proteins have been shown to cause epilepsy in humans and mice, indicating that epilepsy can also be considered a synaptopathy. However, the functional mechanisms by which presynaptic dysfunctions lead to hyperexcitability and seizures are not well understood. We show that deletion of synapsin II (Syn II), a presynaptic protein contributing to epilepsy predisposition in humans, leads to a loss of tonic inhibition in mouse hippocampal slices due to a dramatic decrease in presynaptic asynchronous GABA release. We also show that the asynchronous GABA release reduces postsynaptic cell firing, and the parallel impairment of asynchronous GABA release and tonic inhibition results in an increased excitability at both single-neuron and network levels. Restoring tonic inhibition with THIP (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol; gaboxadol), a selective agonist of δ subunit-containing GABAA receptors, fully rescues the SynII(-/-) epileptic phenotype both ex vivo and in vivo. The results demonstrate a causal relationship between the dynamics of GABA release and the generation of tonic inhibition, and identify a novel mechanism of epileptogenesis generated by dysfunctions in the dynamics of release that can be effectively targeted by novel antiepileptic strategies.
[Show abstract][Hide abstract] ABSTRACT: Direct lineage reprogramming through genetic-based strategies enables the conversion of differentiated somatic cells into functional neurons and distinct neuronal subtypes. Induced dopaminergic (iDA) neurons can be generated by direct conversion of skin fibroblasts; however, their in vivo phenotypic and functional properties remain incompletely understood, leaving their impact on Parkinson's disease (PD) cell therapy and modeling uncertain. Here, we determined that iDA neurons retain a transgene-independent stable phenotype in culture and in animal models. Furthermore, transplanted iDA neurons functionally integrated into host neuronal tissue, exhibiting electrically excitable membranes, synaptic currents, dopamine release, and substantial reduction of motor symptoms in a PD animal model. Neuronal cell replacement approaches will benefit from a system that allows the activity of transplanted neurons to be controlled remotely and enables modulation depending on the physiological needs of the recipient; therefore, we adapted a DREADD (designer receptor exclusively activated by designer drug) technology for remote and real-time control of grafted iDA neuronal activity in living animals. Remote DREADD-dependent iDA neuron activation markedly enhanced the beneficial effects in transplanted PD animals. These data suggest that iDA neurons have therapeutic potential as a cell replacement approach for PD and highlight the applicability of pharmacogenetics for enhancing cellular signaling in reprogrammed cell-based approaches.
The Journal of clinical investigation 06/2014; · 15.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Graphing graphene: Because the naming of graphene-based materials (GBMs) has led to confusion and inconsistency, a classification approach is necessary. Three physical-chemical properties of GBMs have been defined by the GRAPHENE Flagship Project of the European Union for the unequivocal classification of these materials (see grid).
Angewandte Chemie International Edition in English 06/2014; · 13.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Postsynaptic long-term potentiation of inhibition (iLTP) can rely on increased GABAA receptors (GABAARs) at synapses by promoted exocytosis. However, the molecular mechanisms that enhance the clustering of postsynaptic GABAARs during iLTP remain obscure. Here we demonstrate that during chemically induced iLTP (chem-iLTP), GABAARs are immobilized and confined at synapses, as revealed by single-particle tracking of individual GABAARs in cultured hippocampal neurons. Chem-iLTP expression requires synaptic recruitment of the scaffold protein gephyrin from extrasynaptic areas, which in turn is promoted by CaMKII-dependent phosphorylation of GABAAR-β3-Ser(383). Impairment of gephyrin assembly prevents chem-iLTP and, in parallel, blocks the accumulation and immobilization of GABAARs at synapses. Importantly, an increase of gephyrin and GABAAR similar to those observed during chem-iLTP in cultures were found in the rat visual cortex following an experience-dependent plasticity protocol that potentiates inhibitory transmission in vivo. Thus, phospho-GABAAR-β3-dependent accumulation of gephyrin at synapses and receptor immobilization are crucial for iLTP expression and are likely to modulate network excitability.
[Show abstract][Hide abstract] ABSTRACT: Cyclin-dependent kinase-5 (Cdk5) was reported to downscale neurotransmission by sequestering synaptic vesicles (SVs) in the release-reluctant resting pool, but the molecular targets mediating this activity remain unknown. Synapsin I (SynI), a major SV phosphoprotein involved in the regulation of SV trafficking and neurotransmitter release, is one of the presynaptic substrates of Cdk5, which phosphorylates it in its C-terminal region at Ser(549) (site 6) and Ser(551) (site 7). Here we demonstrate that Cdk5 phosphorylation of SynI fine tunes the recruitment of SVs to the active recycling pool and contributes to the Cdk5-mediated homeostatic responses. Phosphorylation of SynI by Cdk5 is physiologically regulated and enhances its binding to F-actin. The effects of Cdk5 inhibition on the size and depletion kinetics of the recycling pool, as well as on SV distribution within the nerve terminal, are virtually abolished in mouse SynI knock-out (KO) neurons or in KO neurons expressing the dephosphomimetic SynI mutants at sites 6,7 or site 7 only. The observation that the single site-7 mutant phenocopies the effects of the deletion of SynI identifies this site as the central switch in mediating the synaptic effects of Cdk5 and demonstrates that SynI is necessary and sufficient for achieving the effects of the kinase on SV trafficking. The phosphorylation state of SynI by Cdk5 at site 7 is regulated during chronic modification of neuronal activity and is an essential downstream effector for the Cdk5-mediated homeostatic scaling.
Journal of Neuroscience 05/2014; 34(21):7266-80. · 6.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The use of implants that allow chronic electrical stimulation and recording in the brain of human patients is currently limited by a series of events that cause the deterioration over time of both the electrode surface and the surrounding tissue. The main reason of failure is the tissue inflammatory reaction that eventually causes neuronal loss and glial encapsulation, resulting in a progressive increase of the electrode-electrolyte impedance. Here, we describe a new method to create bio-inspired electrodes to mimic the mechanical properties and biological composition of the host tissue. This combination has a great potential to increase the implant lifetime by reducing tissue reaction and improving electrical coupling. Our method implies coating the electrode with reprogrammed neural or glial cells encapsulated within a hydrogel layer. We chose fibrin as a hydrogel and primary hippocampal neurons or astrocytes from rat brain as cellular layer. We demonstrate that fibrin coating is highly biocompatible, forms uniform coatings of controllable thickness, does not alter the electrochemical properties of the microelectrode and allows good quality recordings. Moreover, it reduces the amount of host reactive astrocytes - over time - compared to a bare wire and is fully reabsorbed by the surrounding tissue within 7 days after implantation, avoiding the common problem of hydrogels swelling. Both astrocytes and neurons could be successfully grown onto the electrode surface within the fibrin hydrogel without altering the electrochemical properties of the microelectrode. This bio-hybrid device has therefore a good potential to improve the electrical integration at the neuron-electrode interface and support the long-term success of neural prostheses.
[Show abstract][Hide abstract] ABSTRACT: Alterations in the formation of brain networks are associated with several neurodevelopmental disorders. Mutations in TBC1 domain family member 24 (TBC1D24) are responsible for syndromes that combine cortical malformations, intellectual disability, and epilepsy, but the function of TBC1D24 in the brain remains unknown. We report here that in utero TBC1D24 knockdown in the rat developing neocortex affects the multipolar-bipolar transition of neurons leading to delayed radial migration. Furthermore, we find that TBC1D24-knockdown neurons display an abnormal maturation and retain immature morphofunctional properties. TBC1D24 interacts with ADP ribosylation factor (ARF)6, a small GTPase crucial for membrane trafficking. We show that in vivo, overexpression of the dominant-negative form of ARF6 rescues the neuronal migration and dendritic outgrowth defects induced by TBC1D24 knockdown, suggesting that TBC1D24 prevents ARF6 activation. Overall, our findings demonstrate an essential role of TBC1D24 in neuronal migration and maturation and highlight the physiological relevance of the ARF6-dependent membrane-trafficking pathway in brain development.
Proceedings of the National Academy of Sciences 01/2014; · 9.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Intrinsic homeostasis enables neuronal circuits to maintain activity levels within an appropriate range by modulating neuronal voltage-gated conductances, but the signalling pathways involved in this process are largely unknown. We characterized the process of intrinsic homeostasis induced by sustained electrical activity in cultured hippocampal neurons based on the activation of the Repressor Element-1 Silencing Transcription Factor/Neuron-Restrictive Silencer Factor (REST/NRSF). We showed that 4-aminopyridine-induced hyperactivity enhances the expression of REST/NRSF, which in turn, reduces the expression of voltage-gated Na(+) channels, thereby decreasing the neuronal Na(+) current density. This mechanism plays an important role in the downregulation of the firing activity at the single-cell level, re-establishing a physiological spiking activity in the entire neuronal network. Conversely, interfering with REST/NRSF expression impaired this homeostatic response. Our results identify REST/NRSF as a critical factor linking neuronal activity to the activation of intrinsic homeostasis and restoring a physiological level of activity in the entire neuronal network.
[Show abstract][Hide abstract] ABSTRACT: The ability of regenerate whole-body structures has been long studied in both vertebrate and invertebrate animal models. Regeneration of arms in Cephalopods and in particular in Octopods has been the subject of several studies. Octopods often lose arms or part of them throughout life and they are endowed with a high regenerative power. Due to this extraordinary regeneration capability here we propose the use of the Cephalopod Octopus vulgaris as a model of regeneration. This study represents the first attempt to exploit regeneration markers to identify the pattern and distribution of proliferating cell type during the octopus arm morphogenesis. In order to follow cell replacement in various arm regions, we first assessed the expression of specific markers involved in cellular proliferation (AgNOR and PCNA). Several studies have pointed toward the role of acetylcholine esterase (AChE) in the regeneration process in both vertebrate and invertebrate. Due to the typical cholinergic innervation of the octopus arm we investigated the possible role of the AChE in arm regeneration. We tested the hypothesis that AChE activity plays a major role in the regenerative process. Our data show that the activity and localization of this enzyme vary during regeneration and are related to the proliferation stage of the regenerative process. This suggests AChE may have an important influence in the regeneration process and it could then be considered as a potential target to promote or regulate the regenerative process.
Journal of Experimental Marine Biology and Ecology 09/2013; · 2.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An increasing number of genes predisposing to autism spectrum disorders (ASD) has been identified, many of which are implicated in synaptic function. This "synaptic autism pathway" notably includes disruption of SYN1 that is associated with epilepsy, autism and abnormal behavior in both human and mice models. Synapsins constitute a multigene family of neuron-specific phosphoproteins (SYN1-3) present in the majority of synapses where they are implicated in the regulation of neurotransmitter release and synaptogenesis. Synapsins I and II, the major Syn isoforms in the adult brain, display partially overlapping functions and defects in both isoforms are associated with epilepsy and autistic-like behavior in mice. In this study, we show that nonsense (A94fs199X) and missense (Y236S and G464R) mutations in SYN2 are associated with ASD in humans. The phenotype is apparent in males. Female carriers of SYN2 mutations are unaffected, suggesting that SYN2 is another example of autosomal sex-limited expression in ASD. When expressed in SYN2 knockout neurons, wild type human Syn II fully rescues the SYN2 knockout phenotype, whereas the nonsense mutant is not expressed and the missense mutants are virtually unable to modify the SYN2 knockout phenotype. These results identify for the first time SYN2 as a novel predisposing gene for ASD and strengthen the hypothesis that a disturbance of synaptic homeostasis underlies ASD.
Human Molecular Genetics 08/2013; · 6.68 Impact Factor