Doublecortin-like expressing astrocytes of the suprachiasmatic nucleus are implicated in the biosynthesis of vasopressin and influences circadian rhythms.

We have recently identified a novel plasticity protein, doublecortin-like (DCL), that is specifically expressed in the shell of the mouse suprachiasmatic nucleus (SCN). DCL is implicated in neuroplastic events, such as neurogenesis, that require structural rearrangements of the microtubule cytoskeleton, enabling dynamic movements of cell bodies and dendrites. We have inspected DCL expression in the SCN by confocal microscopy and found that DCL is expressed in GABA transporter-3 (GAT3)-positive astrocytes that envelope arginine vasopressin (AVP)-expressing cells. To investigate the role of these DCL-positive astrocytes in circadian rhythmicity, we have used transgenic mice expressing doxycycline-induced short-hairpin (sh) RNA's targeting DCL mRNA (DCL knockdown mice). Compared with littermate wild type (WT) controls, DCL-knockdown mice exhibit significant shorter circadian rest-activity periods in constant darkness and adjusted significantly faster to a jet-lag protocol. As DCL-positive astrocytes are closely associated with AVP-positive cells, we analyzed AVP expression in DCL-knockdown mice and in their WT littermates by 3D reconstructions and transmission electron microscopy (TEM). We found significantly higher numbers of AVP-positive cells with increased volume and more intensity in DCL-knockdown mice. We found alterations in the numbers of dense core vesicle-containing neurons at ZT8 and ZT20 suggesting that the peak and trough of neuropeptide biosynthesis is dampened in DCL-knockdown mice compared to WT littermates. Together, our data suggest an important role for the astrocytic plasticity in the regulation of circadian rhythms and point to the existence of a specific DCL+ astrocyte-AVP+ neuronal network located in the dorsal SCN implicated in AVP biosynthesis.

A predominantly glial origin of axonal ribosomes after nerve injury.

Axonal mRNA transport and local protein synthesis are crucial for peripheral axon regeneration. To date, it remains unclear how ribosomes localize to axons. They may be co-transported with mRNAs or, as suggested by recent studies, transferred from Schwann cells (SC). Here, we generated transgenic "RiboTracker" mice expressing tdTomato-tagged ribosomal protein L4 in specific cell types when crossed with Cre lines. Two neuronal RiboTracker-Cre lines displayed extremely low levels of axonal L4-tdTomato-positive ribosomes. In contrast, two glial RiboTracker-Cre lines revealed tagged ribosomes in sciatic nerve (SN) axons with increasing amounts after injury. Furthermore, non-RiboTracker dorsal root ganglia co-cultured with L4-tdTomato-expressing SCs displayed tagged ribosomes in axons. These data provide unequivocal evidence that SN axons receive ribosomes from SCs upon injury and indicate that glial cells are the main source of axonal ribosomes.

Demyelination induces transport of ribosome-containing vesicles from glia to axons: evidence from animal models and MS patient brains.

Glial cells were previously proven capable of trafficking polyribosomes to injured axons. However, the occurrence of such transfer in the general pathological context, such as demyelination-related diseases, needs further evidence. Since this may be a yet unidentified universal contributor to axonal survival, we study putative glia-axonal ribosome transport in response to demyelination in animal models and patients in both peripheral and central nervous system. In the PNS we investigate whether demyelination in a rodent model has the potential to induce ribosome transfer. We also probe the glia-axonal ribosome supply by implantation of transgenic Schwann cells engineered to produce fluorescent ribosomes in the same demyelination model. We furthermore examine the presence of axonal ribosomes in mouse experimental autoimmune encephalomyelitis (EAE), a well-established model for multiple sclerosis (MS), and in human MS autopsy brain material. We provide evidence for increased axonal ribosome content in a pharmacologically demyelinated sciatic nerve, and demonstrate that at least part of these ribosomes originate in the transgenic Schwann cells. In the CNS one of the hallmarks of MS is demyelination, which is associated with severe disruption of oligodendrocyte-axon interaction. Here, we provide evidence that axons from spinal cords of EAE mice, and in the MS human brain contain an elevated amount of axonal ribosomes compared to controls. Our data provide evidence that increased axonal ribosome content in pathological axons is at least partly due to glia-to-axon transfer of ribosomes, and that demyelination in the PNS and in the CNS is one of the triggers capable to initiate this process.

The molecular physiology of the axo-myelinic synapse.

Myelinated axons efficiently transmit information over long distances. The apposed myelin sheath confers favorable electrical properties, but restricts access of the axon to its extracellular milieu. Therefore, axonal metabolic support may require specific axo-myelinic communication. Here we explored activity-dependent glutamate-mediated signaling from axon to myelin. 2-Photon microscopy was used to image Ca(2+) changes in myelin in response to electrical stimulation of optic nerve axons ex vivo. We show that optic nerve myelin responds to axonal action potentials by a rise in Ca(2+) levels mediated by GluN2D and GluN3A-containing NMDA receptors. Glutamate is released from axons in a vesicular manner that is tetanus toxin-sensitive. The Ca(2+) source for vesicular fusion is provided by ryanodine receptors on axonal Ca(2+) stores, controlled by L-type Ca(2+) channels that sense depolarization of the internodal axolemma. Genetic ablation of GluN2D and GluN3A subunits results in greater lability of the compact myelin. Our results support the existence of a novel synapse between the axon and its myelin, suggesting a means by which traversing action potentials can signal the overlying myelin sheath. This may be an important physiological mechanism by which an axon can signal companion glia for metabolic support or adjust properties of its myelin in a dynamic manner. The axo-myelinic synapse may contribute to learning, while its disturbances may play a role in the pathophysiology of central nervous system disorders such as schizophrenia, where subtle abnormalities of myelinated white matter tracts have been shown in the human, or to frank demyelinating disorders such as multiple sclerosis.

Fluorescent Phosphorus Dendrimer as a Spectral Nanosensor for Macrophage Polarization and Fate Tracking in Spinal Cord Injury.

Dendrimers and dendriplexes, highly branched synthetic macromolecules, have gained popularity as new tools for a variety of nanomedicine strategies due to their unique structure and properties. We show that fluorescent phosphorus dendrimers are well retained by bone marrow-derived macrophages and exhibit robust spectral shift in its emission in response to polarization conditions. Fluorescence properties of this marker can also assist in identifying macrophage presence and phenotype status at different time points after spinal cord injury. Potential use of a single dendrimer compound as a drug/siRNA carrier and phenotype-specific cell tracer offers new avenues for enhanced cell therapies combined with monitoring of cell fate and function in spinal cord injury.

Stimulation of monocytes, macrophages, and microglia by amphotericin B and macrophage colony-stimulating factor promotes remyelination.

Approaches to stimulate remyelination may lead to recovery from demyelinating injuries and protect axons. One such strategy is the activation of immune cells with clinically used medications, since a properly directed inflammatory response can have healing properties through mechanisms such as the provision of growth factors and the removal of cellular debris. We previously reported that the antifungal medication amphotericin B is an activator of circulating monocytes, and their tissue-infiltrated counterparts and macrophages, and of microglia within the CNS. Here, we describe that amphotericin B activates these cells through engaging MyD88/TRIF signaling. When mice were subjected to lysolecithin-induced demyelination of the spinal cord, systemic injections of nontoxic doses of amphotericin B and another activator, macrophage colony-stimulating factor (MCSF), further elevated the representation of microglia/macrophages at the site of injury. Treatment with amphotericin B, particularly in combination with MCSF, increased the number of oligodendrocyte precursor cells and promoted remyelination within lesions; these pro-regenerative effects were mitigated in mice treated with clodronate liposomes to reduce circulating monocytes and tissue-infiltrated macrophages. Our results have identified candidates among currently used medications as potential therapies for the repair of myelin.

Increased axonal ribosome numbers is an early event in the pathogenesis of amyotrophic lateral sclerosis.

Myelinating glia cells support axon survival and functions through mechanisms independent of myelination, and their dysfunction leads to axonal degeneration in several diseases. In amyotrophic lateral sclerosis (ALS), spinal motor neurons undergo retrograde degeneration, and slowing of axonal transport is an early event that in ALS mutant mice occurs well before motor neuron degeneration. Interestingly, in familial forms of ALS, Schwann cells have been proposed to slow disease progression. We demonstrated previously that Schwann cells transfer polyribosomes to diseased and regenerating axons, a possible rescue mechanism for disease-induced reductions in axonal proteins. Here, we investigated whether elevated levels of axonal ribosomes are also found in ALS, by analysis of a superoxide dismutase 1 (SOD1)(G93A) mouse model for human familial ALS and a patient suffering from sporadic ALS. In both cases, we found that the disorder was associated with an increase in the population of axonal ribosomes in myelinated axons. Importantly, in SOD1(G93A) mice, the appearance of axonal ribosomes preceded the manifestation of behavioral symptoms, indicating that upregulation of axonal ribosomes occurs early in the pathogenesis of ALS. In line with our previous studies, electron microscopy analysis showed that Schwann cells might serve as a source of axonal ribosomes in the disease-compromised axons. The early appearance of axonal ribosomes indicates an involvement of Schwann cells early in ALS neuropathology, and may serve as an early marker for disease-affected axons, not only in ALS, but also for other central and peripheral neurodegenerative disorders.

Skin-derived precursor Schwann cell myelination capacity in focal tibial demyelination.

INTRODUCTION: Skin-derived precursor cells (SKPs) are neural crest progenitor cells that can attain a Schwann cell-like phenotype through in vitro techniques (SKP-SCs). We hypothesized that SKP-SCs could produce mature myelin and, in doing so, facilitate the recovery of a focal demyelination injury. METHODS: We unilaterally injected DiI-labeled, green fluorescent protein (GFP)-producing SKP-SCs into the tibial nerves of 10 adult Lewis rats (with contralateral media control), 9 days after bilateral doxorubicin injury (0.38 µg). Tibial compound motor action potentials (CMAPs) were followed for 57 days. A separate morphometric cohort also included a Schwann cell injection group. RESULTS: SKP-injected nerves recovered fastest in terms of electrophysiology and morphometry. SKP-SCs formed morphologically mature myelin, accounting for 15.3 ± 5.3% of the total myelin in SKP-SC-injected nerves. CONCLUSIONS: SKP-SCs are robustly capable of myelination. They improve the recovery of a focal tibial nerve demyelination model by myelinating a measured percentage of axons.

Measuring fast-temporal sediment fluxes with an analogue acoustic sensor: a wind tunnel study.

In aeolian research, field measurements are important for studying complex wind-driven processes for land management evaluation and model validation. Consequently, there have been many devices developed, tested, and applied to investigate a range of aeolian-based phenomena. However, determining the most effective application and data analysis techniques is widely debated in the literature. Here we investigate the effectiveness of two different sediment traps (the BEST trap and the MWAC catcher) in measuring vertical sediment flux. The study was performed in a wind tunnel with sediment fluxes characterized using saltiphones. Contrary to most studies, we used the analogue output of five saltiphones mounted on top of each other to determine the total kinetic energy, which was then used to calculate aeolian sediment budgets. Absolute sediment losses during the experiments were determined using a balance located beneath the test tray. Test runs were conducted with different sand sizes and at different wind speeds. The efficiency of the two traps did not vary with the wind speed or sediment size but was affected by both the experimental setup (position of the lowest trap above the surface and number of traps in the saltation layer) and the technique used to calculate the sediment flux. Despite this, good agreement was found between sediment losses calculated from the saltiphone and those measured using the balance. The results of this study provide a framework for measuring sediment fluxes at small time resolution (seconds to milliseconds) in the field.

NALCN ion channels have alternative selectivity filters resembling calcium channels or sodium channels.

NALCN is a member of the family of ion channels with four homologous, repeat domains that include voltage-gated calcium and sodium channels. NALCN is a highly conserved gene from simple, extant multicellular organisms without nervous systems such as sponges and placozoans and mostly remains a single gene compared to the calcium and sodium channels which diversified into twenty genes in humans. The single NALCN gene has alternatively-spliced exons at exons 15 or exon 31 that splices in novel selectivity filter residues that resemble calcium channels (EEEE) or sodium channels (EKEE or EEKE). NALCN channels with alternative calcium, (EEEE) and sodium, (EKEE or EEKE) -selective pores are conserved in simple bilaterally symmetrical animals like flatworms to non-chordate deuterostomes. The single NALCN gene is limited as a sodium channel with a lysine (K)-containing pore in vertebrates, but originally NALCN was a calcium-like channel, and evolved to operate as both a calcium channel and sodium channel for different roles in many invertebrates. Expression patterns of NALCN-EKEE in pond snail, Lymnaea stagnalis suggest roles for NALCN in secretion, with an abundant expression in brain, and an up-regulation in secretory organs of sexually-mature adults such as albumen gland and prostate. NALCN-EEEE is equally abundant as NALCN-EKEE in snails, but is greater expressed in heart and other muscle tissue, and 50% less expressed in the brain than NALCN-EKEE. Transfected snail NALCN-EEEE and NALCN-EKEE channel isoforms express in HEK-293T cells. We were not able to distinguish potential NALCN currents from background, non-selective leak conductances in HEK293T cells. Native leak currents without expressing NALCN genes in HEK-293T cells are NMDG(+) impermeant and blockable with 10 µM Gd(3+) ions and are indistinguishable from the hallmark currents ascribed to mammalian NALCN currents expressed in vitro by Lu et al. in Cell. 2007 Apr 20;129(2):371-83.

Early regenerative effects of NGF-transduced Schwann cells in peripheral nerve repair.

Peripheral nerve injury leads to a rapid and robust increase in the synthesis of neurotrophins which guide and support regenerating axons. To further optimize neurotrophin supply at the earliest stages of regeneration, we over-expressed NGF in Schwann cells (SCs) by transducing these cells with a lentiviral vector encoding NGF (NGF-SCs). Transplantation of NGF-SCs in a rat sciatic nerve transection/repair model led to significant increase of NGF levels 2weeks after injury and correspondingly to substantial improvement in axonal regeneration. Numbers of NF200, ChAT and CGRP-positive axon profiles, as well as the gastrocnemius muscle weights, were significantly higher in the NGF-Schwann cell group compared to the animals that received control SCs transduced with a lentiviral vector encoding GFP (GFP-SCs). Comparison with other models of NGF application signifies the important role of this neurotrophin during the early stages of regeneration, and supports the importance of developing combined gene and cell therapy for peripheral nerve repair.

Will the real multiple sclerosis please stand up?

Multiple sclerosis (MS) is considered to be an autoimmune, inflammatory disease of the CNS. In most patients, the disease follows a relapsing-remitting course and is characterized by dynamic inflammatory demyelinating lesions in the CNS. Although on the surface MS may appear consistent with a primary autoimmune disease, questions have been raised as to whether inflammation and/or autoimmunity are really at the root of the disease, and it has been proposed that MS might in fact be a degenerative disorder. We argue that MS may be an 'immunological convolution' between an underlying primary degenerative disorder and the host's aberrant immune response. To better understand this disease, we might need to consider non-inflammatory primary progressive MS as the 'real' MS, with inflammatory forms reflecting secondary, albeit very important, reactions.

Evidence for a systemic regulation of neurotrophin synthesis in response to peripheral nerve injury.

Up-regulation of neurotrophin synthesis is an important mechanism of peripheral nerve regeneration after injury. Neurotrophin expression is regulated by a complex series of events including cell interactions and multiple molecular stimuli. We have studied neurotrophin synthesis at 2 weeks time-point in a transvertebral model of unilateral or bilateral transection of sciatic nerve in rats. We have found that unilateral sciatic nerve transection results in the elevation of nerve growth factor (NGF) and NT-3, but not glial cell-line derived neurotrophic factor or brain-derived neural factor, in the uninjured nerve on the contralateral side, commonly considered as a control. Bilateral transection further increased NGF but not other neurotrophins in the nerve segment distal to the transection site, as compared to the unilateral injury. To further investigate the distinct role of NGF in regeneration and its potential for peripheral nerve repair, we transduced isogeneic Schwann cells with NGF-encoding lentivirus and transplanted the over-expressing cells into the distal segment of a transected nerve. Axonal regeneration was studied at 2 weeks time-point using pan-neuronal marker NF-200 and found to directly correlate with NGF levels in the regenerating nerve.

Limited availability of ZBP1 restricts axonal mRNA localization and nerve regeneration capacity.

Subcellular localization of mRNAs is regulated by RNA-protein interactions. Here, we show that introduction of a reporter mRNA with the 3'UTR of ß-actin mRNA competes with endogenous mRNAs for binding to ZBP1 in adult sensory neurons. ZBP1 is needed for axonal localization of ß-actin mRNA, and introducing GFP with the 3'UTR of ß-actin mRNA depletes axons of endogenous ß-actin and GAP-43 mRNAs and attenuates both in vitro and in vivo regrowth of severed axons. Consistent with limited levels of ZBP1 protein in adult neurons, mice heterozygous for the ZBP1 gene are haploinsufficient for axonal transport of ß-actin and GAP-43 mRNAs and for regeneration of peripheral nerve. Exogenous ZBP1 can rescue the RNA transport deficits, but the axonal growth deficit is only rescued if the transported mRNAs are locally translated. These data support a direct role for ZBP1 in transport and translation of mRNA cargos in axonal regeneration in vitro and in vivo.

Morphological evidence for a transport of ribosomes from Schwann cells to regenerating axons.

Recently, we showed that Schwann cells transfer ribosomes to injured axons. Here, we demonstrate that Schwann cells transfer ribosomes to regenerating axons in vivo. For this, we used lentiviral vector-mediated expression of ribosomal protein L4 and eGFP to label ribosomes in Schwann cells. Two approaches were followed. First, we transduced Schwann cells in vivo in the distal trunk of the sciatic nerve after a nerve crush. Seven days after the crush, 12% of regenerating axons contained fluorescent ribosomes. Second, we transduced Schwann cells in vitro that were subsequently injected into an acellular nerve graft that was inserted into the sciatic nerve. Fluorescent ribosomes were detected in regenerating axons up to 8 weeks after graft insertion. Together, these data indicate that regenerating axons receive ribosomes from Schwann cells and, furthermore, that Schwann cells may support local axonal protein synthesis by transferring protein synthetic machinery and mRNAs to these axons.

Antidepressant fluoxetine suppresses neuronal growth from both vertebrate and invertebrate neurons and perturbs synapse formation between Lymnaea neurons.

Current treatment regimes for a variety of mental disorders involve various selective serotonin reuptake inhibitors such as Fluoxetine (Prozac). Although these drugs may 'manage' the patient better, there has not been a significant change in the treatment paradigm over the years and neither have the outcomes improved. There is also considerable debate as to the effectiveness of various selective serotonin reuptake inhibitors and their potential side-effects on neuronal architecture and function. In this study, using mammalian cortical neurons, a dorsal root ganglia cell line (F11 cells) and identified Lymnaea stagnalis neurons, we provide the first direct and unequivocal evidence that clinically relevant concentrations of Fluoxetine induce growth cone collapse and neurite retraction of both serotonergic and non-serotonergic neurons alike in a dose-dependent manner. Using intracellular recordings and calcium imaging techniques, we further demonstrate that the mechanism underlying Fluoxetine-induced effects on neurite retraction from Lymnaea neurons may involve lowering of intracellular calcium and a subsequent retardation of growth cone cytoskeleton. Using soma-soma synapses between identified presynaptic and postsynaptic Lymnaea neurons, we provide further direct evidence that clinically used concentrations of Fluoxetine also block synaptic transmission and synapse formation between cholinergic neurons. Our study raises alarms over potentially devastating side-effects of this antidepressant drug on neurite outgrowth and synapse formation in a developing/regenerating brain. Our data also demonstrate that drugs such as Fluoxetine may not just affect communication between serotonergic neurons but that the detrimental effects are widespread and involve neurons of various phenotypes from both vertebrate and invertebrate species.

Modification of superoxide dismutase 1 (SOD1) properties by a GFP tag--implications for research into amyotrophic lateral sclerosis (ALS).

BACKGROUND: Since the discovery that mutations in the enzyme SOD1 are causative in human amyotrophic lateral sclerosis (ALS), many strategies have been employed to elucidate the toxic properties of this ubiquitously expressed mutant protein, including the generation of GFP-SOD1 chimaeric proteins for studies in protein localization by direct visualization using fluorescence microscopy. However, little is known about the biochemical and physical properties of these chimaeric proteins, and whether they behave similarly to their untagged SOD1 counterparts. METHODOLOGY/PRINCIPAL FINDINGS: Here we compare the physicochemical properties of SOD1 and the effects of GFP-tagging on its intracellular behaviour. Immunostaining demonstrated that SOD1 alone and GFP-SOD1 have an indistinguishable intracellular distribution in PC12 cells. Cultured primary motor neurons expressing GFP or GFP-SOD1 showed identical patterns of cytoplasmic expression and of movement within the axon. However, GFP tagging of SOD1 was found to alter some of the intrinsic properties of SOD1, including stability and specific activity. Evaluation of wildtype and mutant SOD1, tagged at either the N- or C-terminus with GFP, in PC12 cells demonstrated that some chimaeric proteins were degraded to the individual proteins, SOD1 and GFP. CONCLUSIONS/SIGNIFICANCE: Our findings indicate that most, but not all, properties of SOD1 remain the same with a GFP tag.

An ENU-induced mutation in mouse glycyl-tRNA synthetase (GARS) causes peripheral sensory and motor phenotypes creating a model of Charcot-Marie-Tooth type 2D peripheral neuropathy.

Mutations in the enzyme glycyl-tRNA synthetase (GARS) cause motor and sensory axon loss in the peripheral nervous system in humans, described clinically as Charcot-Marie-Tooth type 2D or distal spinal muscular atrophy type V. Here, we characterise a new mouse mutant, Gars(C201R), with a point mutation that leads to a non-conservative substitution within GARS. Heterozygous mice with a C3H genetic background have loss of grip strength, decreased motor flexibility and disruption of fine motor control; this relatively mild phenotype is more severe on a C57BL/6 background. Homozygous mutants have a highly deleterious set of features, including movement difficulties and death before weaning. Heterozygous animals have a reduction in axon diameter in peripheral nerves, slowing of nerve conduction and an alteration in the recovery cycle of myelinated axons, as well as innervation defects. An assessment of GARS levels showed increased protein in 15-day-old mice compared with controls; however, this increase was not observed in 3-month-old animals, indicating that GARS function may be more crucial in younger animals. We found that enzyme activity was not reduced detectably in heterozygotes at any age, but was diminished greatly in homozygous mice compared with controls; thus, homozygous animals may suffer from a partial loss of function. The Gars(C201R) mutation described here is a contribution to our understanding of the mechanism by which mutations in tRNA synthetases, which are fundamentally important, ubiquitously expressed enzymes, cause axonopathy in specific sets of neurons.

Long-term proteasome dysfunction in the mouse brain by expression of aberrant ubiquitin.

Many neurodegenerative diseases are characterized by deposits of ubiquitinated and aberrant proteins, suggesting a failure of the ubiquitin-proteasome system (UPS). The aberrant ubiquitin UBB(+1) is one of the ubiquitinated proteins accumulating in tauopathies such as Alzheimer's disease (AD) and polyglutamine diseases such as Huntington's disease. We have generated UBB(+1) transgenic mouse lines with post-natal neuronal expression of UBB(+1), resulting in increased levels of ubiquitinated proteins in the cortex. Moreover, by proteomic analysis, we identified expression changes in proteins involved in energy metabolism or organization of the cytoskeleton. These changes show a striking resemblance to the proteomic profiles of both AD brain and several AD mouse models. Moreover, UBB(+1) transgenic mice show a deficit in contextual memory in both water maze and fear conditioning paradigms. Although UBB(+1) partially inhibits the UPS in the cortex, these mice do not have an overt neurological phenotype. These mouse models do not replicate the full spectrum of AD-related changes, yet provide a tool to understand how the UPS is involved in AD pathological changes and in memory formation.