Neurotrophic Activity and Its Modulation by Zinc Ion of a Dimeric Peptide Mimicking the Brain-Derived Neurotrophic Factor N-Terminal Region.

Brain-derived neurotrophic factor (BDNF) is a neurotrophin (NT) essential for neuronal development and synaptic plasticity. Dysregulation of BDNF signaling is implicated in different neurological disorders. The direct NT administration as therapeutics has revealed to be challenging. This has prompted the design of peptides mimicking different regions of the BDNF structure. Although loops 2 and 4 have been thoroughly investigated, less is known regarding the BDNF N-terminal region, which is involved in the selective recognition of the TrkB receptor. Herein, a dimeric form of the linear peptide encompassing the 1-12 residues of the BDNF N-terminal (d-bdnf) was synthesized. It demonstrated to act as an agonist promoting specific phosphorylation of TrkB and downstream ERK and AKT effectors. The ability to promote TrkB dimerization was investigated by advanced fluorescence microscopy and molecular dynamics (MD) simulations, finding activation modes shared with BDNF. Furthermore, d-bdnf was able to sustain neurite outgrowth and increase the expression of differentiation (NEFM, LAMC1) and polarization markers (MAP2, MAPT) demonstrating its neurotrophic activity. As TrkB activity is affected by zinc ions in the synaptic cleft, we first verified the ability of d-bdnf to coordinate zinc and then the effect of such complexation on its activity. The d-bdnf neurotrophic activity was reduced by zinc complexation, demonstrating the role of the latter in tuning the activity of the new peptido-mimetic. Taken together our data uncover the neurotrophic properties of a novel BDNF mimetic peptide and pave the way for future studies to understand the pharmacological basis of d-bdnf action and develop novel BDNF-based therapeutic strategies.

Effect of Chemical Vapor Deposition WS2 on Viability and Differentiation of SH-SY5Y Cells.

In recent years, transition metal dichalcogenides have been attracting an increasing interest in the biomedical field, thus implying the need of a deeper understanding of their impact on cell behavior. In this study we investigate tungsten disulfide (WS2) grown via chemical vapor deposition (CVD) on a transparent substrate (sapphire) as a platform for neural-like cell culture. We culture SH-SY5Y human neuroblastoma cells on WS2, using graphene, sapphire and standard culture well as controls. The quality, thickness and homogeneity of the materials is analyzed using atomic force microscopy and Raman spectroscopy. The cytocompatibility of CVD WS2 is investigated for the first time by cell viability and differentiation assessment on SH-SY5Y cells. We find that cells differentiated on WS2, displaying a viability and neurite length comparable with the controls. These findings shine light on the possibility of using WS2 as a cytocompatible material for interfacing neural cells.

The chemokine CXCL12 mediates the anti-amyloidogenic action of painless human nerve growth factor.

Nerve growth factor is a therapeutic candidate for Alzheimer's disease. Due to its pain-inducing activity, in current clinical trials nerve growth factor is delivered locally into the brain by neurosurgery, but data on the efficacy of local nerve growth factor delivery in decreasing amyloid-ß deposition are not available. To reduce the nerve growth factor pain-inducing side effects, thus avoiding the need for local brain injection, we developed human painless nerve growth factor (hNGFp), inspired by the human genetic disease hereditary sensory and autonomic neuropathy type V. hNGFp has identical neurotrophic potency as wild-type human nerve growth factor, but a 10-fold lower pain sensitizing activity. In this study we first mimicked, in the 5xFAD mouse model, the intraparenchymal delivery of hNGFp used in clinical trials and found it to be ineffective in decreasing amyloid-ß plaque load. On the contrary, the same dose of hNGFp delivered intranasally, which was widely biodistributed in the brain and did not induce pain, showed a potent anti-amyloidogenic action and rescued synaptic plasticity and memory deficits. We found that hNGFp acts on glial cells, modulating inflammatory proteins such as the soluble TNFα receptor II and the chemokine CXCL12. We further established that the rescuing effect by hNGFp is mediated by CXCL12, as pharmacological inhibition of CXCL12 receptor CXCR4 occludes most of hNGFp effects. These findings have significant therapeutic implications: (i) we established that a widespread exposure of the brain is required for nerve growth factor to fully exert its neuroprotective actions; and (ii) we have identified a new anti-neurodegenerative pathway as a broad target for new therapeutic opportunities for neurodegenerative diseases.

Precursor and mature NGF live tracking: one versus many at a time in the axons.

The classical view of nerve growth factor (NGF) action in the nervous system is linked to its retrograde axonal transport. However, almost nothing is known on the trafficking properties of its unprocessed precursor proNGF, characterized by different and generally opposite biological functions with respect to its mature counterpart. Here we developed a strategy to fluorolabel both purified precursor and mature neurotrophins (NTs) with a controlled stoichiometry and insertion site. Using a single particle tracking approach, we characterized the axonal transport of proNGF versus mature NGF in living dorsal root ganglion neurons grown in compartmentalized microfluidic devices. We demonstrate that proNGF is retrogradely transported as NGF, but with a lower flux and a different distribution of numbers of neurotrophins per vesicle. Moreover, exploiting a dual-color labelling technique, we analysed the transport of both NT forms when simultaneously administered to the axon tips.

Site-specific labeling of neurotrophins and their receptors via short and versatile peptide tags.

We present a toolbox for the study of molecular interactions occurring between NGF and its receptors. By means of a suitable insertional mutagenesis method we show the insertion of an 8 amino acid tag (A4) into the sequence of NGF and of 12 amino acid tags (A1 and S6) into the sequence of TrkA and P75NTR NGF-receptors. These tags are shortened versions of the acyl and peptidyl carrier proteins; they are here covalently conjugated to the biotin-substituted arm of a coenzyme A (coA) substrate by phosphopantetheinyl transferase enzymes (PPTases). We demonstrate site-specific biotinylation of the purified recombinant tagged neurotrophin, in both the immature proNGF and mature NGF forms. The resulting tagged NGF is fully functional: it can signal and promote PC12 cells differentiation similarly to recombinant wild-type NGF. Furthermore, we show that the insertion of A1 and S6 tags into human TrkA and P75NTR sequences leads to the site-specific biotinylation of these receptors at the cell surface of living cells. Crucially, the two tags are labeled selectively by two different PPTases: this is exploited to reach orthogonal fluorolabeling of the two receptors co-expressed at low density in living cells. We describe the protocols to obtain the enzymatic, site-specific biotinylation of neurotrophins and their receptors as an alternative to their chemical, nonspecific biotinylation. The present strategy has three main advantages: i) it yields precise control of stoichiometry and site of biotin conjugation; ii) the tags used can be functionalized with virtually any small probe that can be carried by coA substrates, besides (and in addition to) biotin; iii) above all it makes possible to image and track interacting molecules at the single-molecule level in living systems.

Ligand signature in the membrane dynamics of single TrkA receptor molecules.

The neurotrophin receptor TrkA (also known as NTRK1) is known to be crucially involved in several physio-pathological processes. However, a clear description of the early steps of ligand-induced TrkA responses at the cell plasma membrane is missing. We have exploited single particle tracking and TIRF microscopy to study TrkA membrane lateral mobility and changes of oligomerization state upon binding of diverse TrkA agonists (NGF, NGF R100E HSANV mutant, proNGF and NT-3). We show that, in the absence of ligands, most of the TrkA receptors are fast moving monomers characterized by an average diffusion coefficient of 0.47 µm(2)/second; about 20% of TrkA molecules move at least an order of magnitude slower and around 4% are almost immobile within regions of about 0.6 µm diameter. Ligand binding results in increased slow and/or immobile populations over the fast one, slowing down of non-immobile trajectories and reduction of confinement areas, observations that are consistent with the formation of receptor dimeric and oligomeric states. We demonstrate that the extent of TrkA lateral mobility modification is strictly ligand dependent and that each ligand promotes distinct trajectory patterns of TrkA receptors at the cell membrane (ligand 'fingerprinting' effect). This ligand signature of receptor dynamics results from a differential combination of receptor-binding affinity, intracellular effectors recruited in the signalling platforms and formation of signalling and/or recycling endosome precursors. Thus, our data uncover a close correlation between the initial receptor membrane dynamics triggered upon binding and the specific biological outcomes induced by different ligands for the same receptor.

The positional identity of mouse ES cell-generated neurons is affected by BMP signaling.

We investigated the effects of bone morphogenetic proteins (BMPs) in determining the positional identity of neurons generated in vitro from mouse embryonic stem cells (ESCs), an aspect that has been neglected thus far. Classical embryological studies in lower vertebrates indicate that BMPs inhibit the default fate of pluripotent embryonic cells, which is both neural and anterior. Moreover, mammalian ESCs generate neurons more efficiently when cultured in a minimal medium containing BMP inhibitors. In this paper, we show that mouse ESCs produce, secrete, and respond to BMPs during in vitro neural differentiation. After neuralization in a minimal medium, differentiated ESCs show a gene expression profile consistent with a midbrain identity, as evaluated by the analysis of a number of markers of anterior-posterior and dorsoventral identity. We found that BMPs endogenously produced during neural differentiation mainly act by inhibiting the expression of a telencephalic gene profile, which was revealed by the treatment with Noggin or with other BMP inhibitors. To better characterize the effect of BMPs on positional fate, we compared the global gene expression profiles of differentiated ESCs with those of embryonic forebrain, midbrain, and hindbrain. Both Noggin and retinoic acid (RA) support neuronal differentiation of ESCs, but they show different effects on their positional identity: whereas RA supports the typical gene expression profile of hindbrain neurons, Noggin induces a profile characteristic of dorsal telencephalic neurons. Our findings show that endogenously produced BMPs affect the positional identity of the neurons that ESCs spontaneously generate when differentiating in vitro in a minimal medium. The data also support the existence of an intrinsic program of neuronal differentiation with dorsal telencephalic identity. Our method of ESC neuralization allows for fast differentiation of neural cells via the same signals found during in vivo embryonic development and for the acquisition of cortical identity by the inhibition of BMP alone.

Intranasal "painless" human Nerve Growth Factor [corrected] slows amyloid neurodegeneration and prevents memory deficits in App X PS1 mice.

Nerve Growth Factor (NGF) is being considered as a therapeutic candidate for Alzheimer's disease (AD) treatment but the clinical application is hindered by its potent pro-nociceptive activity. Thus, to reduce systemic exposure that would induce pain, in recent clinical studies NGF was administered through an invasive intracerebral gene-therapy approach. Our group demonstrated the feasibility of a non-invasive intranasal delivery of NGF in a mouse model of neurodegeneration. NGF therapeutic window could be further increased if its nociceptive effects could be avoided altogether. In this study we exploit forms of NGF, mutated at residue R100, inspired by the human genetic disease HSAN V (Hereditary Sensory Autonomic Neuropathy Type V), which would allow increasing the dose of NGF without triggering pain. We show that "painless" hNGF displays full neurotrophic and anti-amyloidogenic activities in neuronal cultures, and a reduced nociceptive activity in vivo. When administered intranasally to APPxPS1 mice ( n = 8), hNGFP61S/R100E prevents the progress of neurodegeneration and of behavioral deficits. These results demonstrate the in vivo neuroprotective and anti-amyloidogenic properties of hNGFR100 mutants and provide a rational basis for the development of "painless" hNGF variants as a new generation of therapeutics for neurodegenerative diseases.

IGF-1 restores visual cortex plasticity in adult life by reducing local GABA levels.

The central nervous system architecture is markedly modified by sensory experience during early life, but a decline of plasticity occurs with age. Recent studies have challenged this dogma providing evidence that both pharmacological treatments and paradigms based on the manipulation of environmental stimulation levels can be successfully employed as strategies for enhancing plasticity in the adult nervous system. Insulin-like growth factor 1 (IGF-1) is a peptide implicated in prenatal and postnatal phases of brain development such as neurogenesis, neuronal differentiation, synaptogenesis, and experience-dependent plasticity. Here, using the visual system as a paradigmatic model, we report that IGF-1 reactivates neural plasticity in the adult brain. Exogenous administration of IGF-1 in the adult visual cortex, indeed, restores the susceptibility of cortical neurons to monocular deprivation and promotes the recovery of normal visual functions in adult amblyopic animals. These effects were accompanied by a marked reduction of intracortical GABA levels. Moreover, we show that a transitory increase of IGF-1 expression is associated to the plasticity reinstatement induced by environmental enrichment (EE) and that blocking IGF-1 action by means of the IGF-1 receptor antagonist JB1 prevents EE effects on plasticity processes.

Food restriction enhances visual cortex plasticity in adulthood.

Neural circuits display a heightened sensitivity to external stimuli during well-established windows in early postnatal life. After the end of these critical periods, brain plasticity dramatically wanes. The visual system is one of the paradigmatic models for studying experience-dependent plasticity. Here we show that food restriction can be used as a strategy to restore plasticity in the adult visual cortex of rats. A short period of food restriction in adulthood is able both to reinstate ocular dominance plasticity and promote recovery from amblyopia. These effects are accompanied by a reduction of intracortical inhibition without modulation of brain-derived neurotrophic factor expression or extracellular matrix structure. Our results suggest that food restriction could be investigated as a potential way of modulating plasticity.

Experience-dependent reactivation of ocular dominance plasticity in the adult visual cortex.

A crucial issue in neurobiology is to understand the main mechanisms restricting neural plasticity to brief windows of early postnatal life. The visual system is one of the paradigmatic models for studying experience-dependent plasticity. The closure of one eye (monocular deprivation, MD) causes a marked ocular dominance (OD) shift of neurons in the primary visual cortex only during the critical period. Here, we report that environmental enrichment (EE), a condition of increased sensory-motor stimulation, reactivates OD plasticity in the adult visual cortex, as assessed with both visual evoked potentials and single-unit recordings. This effect is accompanied by a marked increase in cerebral serotonin (5-HT) levels. Blocking 5-HT enhancement in the visual cortex of EE rats completely prevents the OD shift induced by MD. We also found that EE leads to a reduced intracortical GABAergic inhibition and an increased BDNF expression and that the modulation of these molecular factors is neutralized by cortical infusion of the 5-HT synthesis inhibitor pCPA. Our results show that EE rejuvenates the adult visual cortex and that 5-HT is a crucial factor in this process, triggering a cascade of molecular events that allow the reinstatement of neural plasticity. The non-invasive nature of EE makes this paradigm particularly eligible for clinical application.

Reducing intracortical inhibition in the adult visual cortex promotes ocular dominance plasticity.

Experience-dependent plasticity in the cortex is often higher during short critical periods in postnatal development. The mechanisms limiting adult cortical plasticity are still unclear. Maturation of intracortical GABAergic inhibition is suggested to be crucial for the closure of the critical period for ocular dominance (OD) plasticity in the visual cortex. We find that reduction of GABAergic transmission in the adult rat visual cortex partially reactivates OD plasticity in response to monocular deprivation (MD). This is accompanied by an enhancement of activity-dependent potentiation of synaptic efficacy but not of activity-dependent depression. We also found a decrease in the expression of chondroitin sulfate proteoglycans in the visual cortex of MD animals with reduced inhibition, after the reactivation of OD plasticity. Thus, intracortical inhibition is a crucial limiting factor for the induction of experience-dependent plasticity in the adult visual cortex.

The obesity and inflammatory marker haptoglobin attracts monocytes via interaction with chemokine (C-C motif) receptor 2 (CCR2).

BACKGROUND: Obesity is a chronic low inflammatory state. In the obesity condition the white adipose tissue (WAT) is massively infiltrated with monocytes/macrophages, and the nature of the signals recruiting these inflammatory cells has yet to be fully elucidated. Haptoglobin (Hp) is an inflammatory marker and its expression is induced in the WAT of obese subjects. In an effort to elucidate the biological significance of Hp presence in the WAT and of its upregulation in obesity we formulated the hypothesis that Hp may serve as a macrophage chemoattractant. RESULTS: We demonstrated by chemotaxis assay that Hp is able to attract chemokine (C-C motif) receptor 2 (CCR2)-transfected pre-B lymphocytes and monocytes in a dose-dependent manner. Moreover, Hp-mediated migration of monocytes is impaired by CCR2-specific inhibition or previous cell exposure to monocyte chemoattractant protein 1 (MCP1) (also known as CCR2 ligand or chemokine (C-C motif) ligand 2 (CCL2)). Downstream effects of Hp/CCR2 interaction were also investigated: flow cytometry proved that monocytes treated with Hp show reduced CCR2 expression on their surface; Hp interaction induces calcium release that is reduced upon pretreatment with CCR2 antagonist; extracellular signal-regulated kinase (ERK)1/2, a signal transducer activated by CCR2, is phosphorylated following Hp treatment and this phosphorylation is reduced when cells are pretreated with a specific CCR2 inhibitor. Consistently, blocking the ERK1/2 pathway with U0126, the selective inhibitor of the ERK upstream mitogen-activated protein (MAP)-ERK kinase (MEK), results in a dramatic reduction (by almost 100%) of the capability of Hp to induce monocyte migration. CONCLUSIONS: Our data show that Hp is a novel monocyte chemoattractant and that its chemotactic potential is mediated, at least in part. by its interaction with CCR2.

Massage accelerates brain development and the maturation of visual function.

Environmental enrichment (EE) was shown recently to accelerate brain development in rodents. Increased levels of maternal care, and particularly tactile stimulation through licking and grooming, may represent a key component in the early phases of EE. We hypothesized that enriching the environment in terms of body massage may thus accelerate brain development in infants. We explored the effects of body massage in preterm infants and found that massage accelerates the maturation of electroencephalographic activity and of visual function, in particular visual acuity. In massaged infants, we found higher levels of blood IGF-1. Massage accelerated the maturation of visual function also in rat pups and increased the level of IGF-1 in the cortex. Antagonizing IGF-1 action by means of systemic injections of the IGF-1 antagonist JB1 blocked the effects of massage in rat pups. These results demonstrate that massage has an influence on brain development and in particular on visual development and suggest that its effects are mediated by specific endogenous factors such as IGF-1.

Serotonin hyperinnervation abolishes seizure susceptibility in Otx2 conditional mutant mice.

The homeobox-containing transcription factor Otx2 is crucially involved in fate determination of midbrain neurons. Mutant mice, in which Otx2 was conditionally inactivated by a Cre recombinase expressed under the transcriptional control of the Engrailed1 (En1) gene (En1(cre/+); Otx2(flox/flox)), show a reduced number of dopaminergic neurons and an increased number of serotonergic neurons in the ventral midbrain. Despite these developmental anatomical alterations, En1(cre/+); Otx2(flox/flox) adult mice display normal motor function. Here, we further investigated the neurological consequences of Otx2 inactivation in adult En1(cre/+); Otx2(flox/flox) mice. Adult En1(cre/+); Otx2(flox/flox) mice showed increased serotonin (5-HT) levels in the pons, ventral midbrain, hippocampus (CA3 subfield), and cerebral cortex, as indicated by HPLC and immunohistochemistry. Conversely, SERT (5-HT transporter) levels were decreased in conditional mutant brains. As a consequence of this increased 5-HT hyperinnervation, En1(cre/+); Otx2(flox/flox) mice were resistant to generalized seizures induced by the glutamate agonist kainic acid (KA). Indeed, prolonged pretreatment of En1(cre/+); Otx2(flox/flox) mice with the 5-HT synthesis inhibitor para-chlorophenylalanine (pCPA) restored brain 5-HT content to control levels, fully reestablishing KA seizure susceptibility. Accordingly, c-fos mRNA induction after KA was restricted to the hippocampus in En1(cre/+); Otx2(flox/flox) mice, whereas a widespread c-fos mRNA labeling was observed throughout the brain of En1(cre/+); Otx2(flox/flox) mice pretreated with pCPA. These results clearly show that increased brain 5-HT levels are responsible for seizure resistance in En1(cre/+); Otx2(flox/flox) mice and confirm the important role of 5-HT in the control of seizure spread.

The antidepressant fluoxetine restores plasticity in the adult visual cortex.

We investigated whether fluoxetine, a widely prescribed medication for treatment of depression, restores neuronal plasticity in the adult visual system of the rat. We found that chronic administration of fluoxetine reinstates ocular dominance plasticity in adulthood and promotes the recovery of visual functions in adult amblyopic animals, as tested electrophysiologically and behaviorally. These effects were accompanied by reduced intracortical inhibition and increased expression of brain-derived neurotrophic factor in the visual cortex. Cortical administration of diazepam prevented the effects induced by fluoxetine, indicating that the reduction of intracortical inhibition promotes visual cortical plasticity in the adult. Our results suggest a potential clinical application for fluoxetine in amblyopia as well as new mechanisms for the therapeutic effects of antidepressants and for the pathophysiology of mood disorders.

Antiepileptic effects of botulinum neurotoxin E.

Experimental studies suggest that the delivery of antiepileptic agents into the seizure focus might be of potential utility for the treatment of focal-onset epilepsies. Botulinum neurotoxin E (BoNT/E) causes a prolonged inhibition of neurotransmitter release after its specific cleavage of the synaptic protein synaptosomal-associated protein of 25 kDa (SNAP-25). Here, we show that BoNT/E injected into the rat hippocampus inhibits glutamate release and blocks spike activity of pyramidal neurons. BoNT/E effects persist for at least 3 weeks, as determined by immunodetection of cleaved SNAP-25 and loss of intact SNAP-25. The delivery of BoNT/E to the rat hippocampus dramatically reduces both focal and generalized kainic acid-induced seizures as documented by behavioral and electrographic analysis. BoNT/E treatment also prevents neuronal loss and long-term cognitive deficits associated with kainic acid seizures. Moreover, BoNT/E-injected rats require 50% more electrical stimulations to reach stage 5 of kindling, thus indicating a delayed epileptogenesis. We conclude that BoNT/E delivery to the hippocampus is both antiictal and antiepileptogenic in experimental models of epilepsy.

Nicotinic acetylcholine receptor subtypes expression during rat retina development and their regulation by visual experience.

By acting through retinal nicotinic acetylcholine receptors (nAChRs), acetylcholine plays an important role in the development of both the retina and central visual pathways. Ligand binding and immunoprecipitation studies with subunit-specific antibodies showed that the expression of alphaBungarotoxin (alphaBgtx) and high-affinity epibatidine (Epi) receptors is regulated developmentally and increases until postnatal day 21 (P21). The increase in Epi receptors is caused by a selective increase in the subtypes containing the alpha2, alpha4, alpha6, beta2, and beta3 subunits. Immunopurification studies revealed three major populations of Epi receptors on P21: alpha6(*) receptors (26%), which contain the alpha6beta3beta2, alpha6alpha4beta3beta2, and alpha6alpha3/alpha2beta3beta2 subtypes; alpha4(non-alpha6)(*) receptors (60%), which contain the alpha2alpha4beta2 and alpha4beta2 subtypes; and (non-alpha4/non-alpha6)(*) receptors (14%), which contain the alpha2beta2/beta4 and alpha3beta2/beta4 subtypes. These three populations can be pharmacologically discriminated using alphaconotoxin MII, which binds the alpha6(*) population with high affinity. In situ hybridization showed that the transcripts for all of the subunits are heterogeneously distributed throughout retinal neurons at P21, with alpha3, alpha6, and beta3 transcripts preferentially concentrated in the ganglion cell layer, alpha5 in the inner nuclear layer, and alpha4 and beta2 distributed rather homogeneously. To investigate whether nAChR expression is affected by visual experience, we also studied dark-reared P21 rats. Visual deprivation had no effect on the expression of alphaBgtx receptors or the developmentally regulated Epi receptors containing the alpha2, alpha6, and/or beta3 subunits but significantly increased the expression of the Epi receptors containing the alpha4 and beta2 subunits. Overall, this study demonstrates that the retina is the rat neural region that expresses the widest array of nAChR subtypes. These receptors have a specific distribution, and their expression is finely regulated during development and by visual experience.

Acceleration of visual system development by environmental enrichment.

Thus far, the developmental plasticity of the visual system has been studied by altering or reducing visual experience. Here, we investigated whether a complex sensory-motor stimulation, provided by rearing animals in an enriched environment, affects visual system development. We found that raising mice in this condition causes an earlier eye opening, a precocious development of visual acuity, and an accelerated decline of white matter-induced long-term potentiation. These effects are accompanied by a precocious cAMP response element-mediated gene expression and a significant increase of BDNF protein and GAD65/67 expression in enriched pups. In addition, we showed that enriched pups experienced higher levels of licking behavior provided by adult females. Thus, rearing mice from birth in an enriched environment leads to a conspicuous acceleration of visual system development as ascertained at behavioral, electrophysiological, and molecular level.