Prolonged myelin deficits contribute to neuron loss and functional impairments after ischaemic stroke

Ischaemic stroke causes neuron loss and long-term functional deficits. Unfortunately, effective approaches to preserving neurons and promoting functional recovery remain unavailable. Oligodendrocytes, the myelinating cells in the CNS, are susceptible to oxygen and nutrition deprivation and undergo degeneration after ischaemic stroke. Technically, new oligodendrocytes and myelin can be generated by the differentiation of oligodendrocyte precursor cells (OPCs). However, myelin dynamics and their functional significance after ischaemic stroke remain poorly understood. Here, we report numerous denuded axons accompanied by decreased neuron density in sections from ischaemic stroke lesions in human brain, suggesting that neuron loss correlates with myelin deficits in these lesions. To investigate the longitudinal changes in myelin dynamics after stroke, we labelled and traced pre-existing and newly-formed myelin, respectively, using cell-specific genetic approaches. Our results indicated massive oligodendrocyte death and myelin loss 2 weeks after stroke in the transient middle cerebral artery occlusion (tMCAO) mouse model. In contrast, myelin regeneration remained insufficient 4 and 8 weeks post-stroke. Notably, neuronal loss and functional impairments worsened in aged brains, and new myelin generation was diminished. To analyse the causal relationship between remyelination and neuron survival, we manipulated myelinogenesis by conditional deletion of Olig2 (a positive regulator) or muscarinic receptor 1 (M1R, a negative regulator) in OPCs. Deleting Olig2 inhibited remyelination, reducing neuron survival and functional recovery after tMCAO. Conversely, enhancing remyelination by M1R conditional knockout or treatment with the pro-myelination drug clemastine after tMCAO preserved white matter integrity and neuronal survival, accelerating functional recovery. Together, our findings demonstrate that enhancing myelinogenesis is a promising strategy to preserve neurons and promote functional recovery after ischaemic stroke.

Transplantation of dorsal root ganglia overexpressing the NaChBac sodium channel improves locomotion after complete SCI

Spinal cord injury (SCI) is a debilitating condition currently lacking treatment. Severe SCI causes the loss of most supraspinal inputs and neuronal activity caudal to the injury, which, coupled with the limited endogenous capacity for spontaneous regeneration, can lead to complete functional loss even in anatomically incomplete lesions. We hypothesized that transplantation of mature dorsal root ganglia (DRGs) genetically modified to express the NaChBac sodium channel could serve as a therapeutic option for functionally complete SCI. We found that NaChBac expression increased the intrinsic excitability of DRG neurons and promoted cell survival and neurotrophic factor secretion in vitro. Transplantation of NaChBac-expressing dissociated DRGs improved voluntary locomotion 7 weeks after injury compared to control groups. Animals transplanted with NaChBac-expressing DRGs also possessed higher tubulin-positive neuronal fiber and myelin preservation, although serotonergic descending fibers remained unaffected. We observed early preservation of the corticospinal tract 14 days after injury and transplantation, which was lost 7 weeks after injury. Nevertheless, transplantation of NaChBac-expressing DRGs increased the neuronal excitatory input by an increased number of VGLUT2 contacts immediately caudal to the injury. Our work suggests that the transplantation of NaChBac-expressing dissociated DRGs can rescue significant motor function, retaining an excitatory neuronal relay activity immediately caudal to injury.

Inhibition of Apoptosis in a Model of Ischemic Stroke Leads to Enhanced Cell Survival, Endogenous Neural Precursor Cell Activation and Improved Functional Outcomes

Stroke results in neuronal cell death, which causes long-term disabilities in adults. Treatment options are limited and rely on a narrow window of opportunity. Apoptosis inhibitors demonstrate efficacy in improving neuronal cell survival in animal models of stroke. However, many inhibitors non-specifically target apoptosis pathways and high doses are needed for treatment. We explored the use of a novel caspase-3/7 inhibitor, New World Laboratories (NWL) 283, with a lower IC50 than current caspase-3/7 inhibitors. We performed in vitro and in vivo assays to determine the efficacy of NWL283 in modulating cell death in a preclinical model of stroke. In vitro and in vivo assays show that NWL283 enhances cell survival of neural precursor cells. Delivery of NWL283 following stroke enhances endogenous NPC migration and leads to increased neurogenesis in the stroke-injured cortex. Furthermore, acute NWL283 administration is neuroprotective at the stroke injury site, decreasing neuronal cell death and reducing microglia activation. Coincident with NWL283 delivery for 8 days, stroke-injured mice exhibited improved functional outcomes that persisted following cessation of the drug. Therefore, we propose that NWL283 is a promising therapeutic warranting further investigation to enhance stroke recovery.

Development of Pleiotropic TrkB and 5-HT4 Receptor Ligands as Neuroprotective Agents

One common event that is the most detrimental in neurodegenerative disorders, even though they have a complex pathogenesis, is the increased rate of neuronal death. Endogenous neurotrophins consist of the major neuroprotective factors, while brain-derived neurotrophic factor (BDNF) and its high-affinity tyrosine kinase receptor TrkB are described in a number of studies for their important neuronal effects. Normal function of this receptor is crucial for neuronal survival, differentiation, and synaptic function. However, studies have shown that besides direct activation, the TrkB receptor can be transactivated via GPCRs. It has been proven that activation of the 5-HT4 receptor and transactivation of the TrkB receptor have a positive influence on neuronal differentiation (total dendritic length, number of primary dendrites, and branching index). Because of that and based on the main structural characteristics of LM22A-4, a known activator of the TrkB receptor, and RS67333, a partial 5-HT4 receptor agonist, we have designed and synthesized a small data set of novel compounds with potential dual activities in order to not only prevent neuronal death, but also to induce neuronal differentiation in neurodegenerative disorders.

Lost in Translation: Neurotrophins Biology and Function in the Neurovascular Unit

The neurovascular unit (NVU) refers to the functional building unit of the brain and the retina, where neurons, glia, and microvasculature orchestrate to meet the demand of the retina's and brain's function. Neurotrophins (NTs) are structural families of secreted proteins and are known for exerting neurotrophic effects on neuronal differentiation, survival, neurite outgrowth, synaptic formation, and plasticity. NTs include several molecules, such as nerve growth factor, brain-derived neurotrophic factor, NT-3, NT-4, and their precursors. Furthermore, NTs are involved in signaling pathways such as inflammation, apoptosis, and angiogenesis in a nonneuronal cell type. Interestingly, NTs and the precursors can bind and activate the p75 neurotrophin receptor (p75NTR) at low and high affinity. Mature NTs bind their cognate tropomyosin/tyrosine-regulated kinase receptors, crucial for maintenance and neuronal development in the brain and retina axis. Activation of p75NTR results in neuronal apoptosis and cell death, while tropomysin receptor kinase upregulation contributes to differentiation and cell growth. Recent findings indicate that modulation of NTs and their receptors contribute to neurovascular dysfunction in the NVU. Several chronic metabolic and acute ischemic diseases affect the NVU, including diabetic and ischemic retinopathy for the retina, as well as stroke, acute encephalitis, and traumatic brain injury for the brain. This work aims to review the current evidence through published literature studying the impact of NTs and their receptors, including the p75NTR receptor, on the injured and healthy brain-retina axis.

The GluN2B-Containing NMDA Receptor Alleviates Neuronal Apoptosis in Neonatal Hypoxic-Ischemic Encephalopathy by Activating PI3K-Akt-CREB Signaling Pathwa

Neonatal hypoxic-ischemic encephalopathy (HIE) is a disease caused by insufficient blood supply in the brain in newborns during the perinatal period. Severe HIE leads to patient death, and patients with mild HIE are at increased risk of cognitive deficits and behavioral abnormalities. The NMDA receptor is an important excitatory receptor in the central nervous system, and in adult hypoxic-ischemic injury both subtypes of the NMDA receptor play important but distinct roles. The GluN2A-containing NMDA receptor (GluN2A-NMDAR) could activate neuronal protective signaling pathway, while the GluN2B-NMDAR subtype is coupled to the apoptosis-inducing signaling pathway and leads to neuronal death. However, the expression level of GluN2B is higher in newborns than in adults, while the expression of GluN2A is lower. Therefore, it is not clear whether the roles of different NMDA receptor subtypes in HIE are consistent with those in adults. We investigated this issue in this study and found that in HIE, GluN2B plays a protective role by mediating the protective pathway through binding with PSD95, which is quite different to that in adults. The results of this study provided new theoretical support for the clinical treatment of neonatal hypoxic ischemia.

Voluntary Running Improves Behavioral and Structural Abnormalities in a Mouse Model of CDKL5 Deficiency Disorder

Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) is a rare neurodevelopmental disease caused by mutations in the X-linked CDKL5 gene. CDD is characterized by a broad spectrum of clinical manifestations, including early-onset refractory epileptic seizures, intellectual disability, hypotonia, visual disturbances, and autism-like features. The Cdkl5 knockout (KO) mouse recapitulates several features of CDD, including autistic-like behavior, impaired learning and memory, and motor stereotypies. These behavioral alterations are accompanied by diminished neuronal maturation and survival, reduced dendritic branching and spine maturation, and marked microglia activation. There is currently no cure or effective treatment to ameliorate the symptoms of the disease. Aerobic exercise is known to exert multiple beneficial effects in the brain, not only by increasing neurogenesis, but also by improving motor and cognitive tasks. To date, no studies have analyzed the effect of physical exercise on the phenotype of a CDD mouse model. In view of the positive effects of voluntary running on the brain of mouse models of various human neurodevelopmental disorders, we sought to determine whether voluntary daily running, sustained over a month, could improve brain development and behavioral defects in Cdkl5 KO mice. Our study showed that long-term voluntary running improved the hyperlocomotion and impulsivity behaviors and memory performance of Cdkl5 KO mice. This is correlated with increased hippocampal neurogenesis, neuronal survival, spine maturation, and inhibition of microglia activation. These behavioral and structural improvements were associated with increased BDNF levels. Given the positive effects of BDNF on brain development and function, the present findings support the positive benefits of exercise as an adjuvant therapy for CDD.

The role of microRNA in neuronal inflammation and survival in the post ischemic brain: a review

Each year, more than 790 000 people in the United States suffer from a stroke. Although progress has been made in diagnosis and treatment of ischemic stroke (IS), new therapeutic interventions to protect the brain during an ischemic insult is highly needed. MicroRNAs (miRNAs) are small, non-coding RNAs that regulate gene expression post-transcriptionally. Growing evidence suggests that miRNAs have a profound impact on ischemic stroke progression and are potential targets of novel treatments. Notably, inflammatory pathways play an important role in the pathogenesis of ischemic stroke and its pathophysiologic progression. Experimental and clinical studies have illustrated that inflammatory molecular events collaboratively contribute to neuronal and glial cell survival, edema formation and regression, and vascular integrity. In the present review, we examine recent discoveries regarding miRNAs and their roles in post-ischemic stroke neuropathogenesis.

Interaction of L1CAM with LC3 Is Required for L1-Dependent Neurite Outgrowth and Neuronal Survival

The neural cell adhesion molecule L1 (also called L1CAM or CD171) functions not only in cell migration, but also in cell survival, differentiation, myelination, neurite outgrowth, and signaling during nervous system development and in adults. The proteolytic cleavage of L1 in its extracellular domain generates soluble fragments which are shed into the extracellular space and transmembrane fragments that are internalized into the cell and transported to various organelles to regulate cellular functions. To identify novel intracellular interaction partners of L1, we searched for protein-protein interaction motifs and found two potential microtubule-associated protein 1 light-chain 3 (LC3)-interacting region (LIR) motifs within L1, one in its extracellular domain and one in its intracellular domain. By ELISA, immunoprecipitation, and proximity ligation assay using L1 mutant mice lacking the 70 kDa L1 fragment (L1-70), we showed that L1-70 interacts with LC3 via the extracellular LIR motif in the fourth fibronectin type III domain, but not by the motif in the intracellular domain. The disruption of the L1-LC3 interaction reduces L1-mediated neurite outgrowth and neuronal survival.

Impacts of methotrexate on survival, dendrite development, and synapse formation of cortical neurons

Methotrexate (MTX) is an anti-metabolite that has been used for the treatment of patients of acute lymphocytic leukemia or non-Hodgikin lymphoma for decades. In some cases, MTX-treated patients suffer from neurological side effects, including seizures and cognitive dysfunctions. While most patients are at developmental stages, information of the mechanisms of the side effects of MTX treatment on the developing neurons has been limited. Neurons develop in five steps in the human brain: neurogenesis, polarity formation, dendrite and axon development, synapse formation, and neuronal death. Except for neurogenesis, these processes can be recapitulated in the primary culture system of cortical neurons. Using primary cultured cortical neurons, we studied the impact of MTX treatment on dendrite development, synapse formation, and neuronal death in the present report. MTX treatment impaired neuronal survival, dendrite development, and synapse formation. Interestingly, half maximal effective concentrations (EC₅₀ s) of MTX for all three processes are at the similar range and lower than the MTX concentration in the cerebrospinal fluid in treated patients. Our results provide possible mechanisms of neurological side effects in treated patients.

MANF regulates neuronal survival and UPR through its ER-located receptor IRE1α

Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an endoplasmic reticulum (ER)-located protein with cytoprotective effects in neurons and pancreatic β cells in vitro and in models of neurodegeneration and diabetes in vivo. However, the exact mode of MANF action has remained elusive. Here, we show that MANF directly interacts with the ER transmembrane unfolded protein response (UPR) sensor IRE1α, and we identify the binding interface between MANF and IRE1α. The expression of wild-type MANF, but not its IRE1α binding-deficient mutant, attenuates UPR signaling by decreasing IRE1α oligomerization; phosphorylation; splicing of Xbp1, Atf6, and Txnip levels; and protecting neurons from ER stress-induced death. MANF-IRE1α interaction and not MANF-BiP interaction is crucial for MANF pro-survival activity in neurons in vitro and is required to protect dopamine neurons in an animal model of Parkinson's disease. Our data show IRE1α as an intracellular receptor for MANF and regulator of neuronal survival.

The Role of MEF2 Transcription Factor Family in Neuronal Survival and Degeneration

The family of myocyte enhancer factor 2 (MEF2) transcription factors comprises four highly conserved members that play an important role in the nervous system. They appear in precisely defined time frames in the developing brain to turn on and turn off genes affecting growth, pruning and survival of neurons. MEF2s are known to dictate neuronal development, synaptic plasticity and restrict the number of synapses in the hippocampus, thus affecting learning and memory formation. In primary neurons, negative regulation of MEF2 activity by external stimuli or stress conditions is known to induce apoptosis, albeit the pro or antiapoptotic action of MEF2 depends on the neuronal maturation stage. By contrast, enhancement of MEF2 transcriptional activity protects neurons from apoptotic death both in vitro and in preclinical models of neurodegenerative diseases. A growing body of evidence places this transcription factor in the center of many neuropathologies associated with age-dependent neuronal dysfunctions or gradual but irreversible neuron loss. In this work, we discuss how the altered function of MEF2s during development and in adulthood affecting neuronal survival may be linked to neuropsychiatric disorders.

The Interactions of the 70 kDa Fragment of Cell Adhesion Molecule L1 with Topoisomerase 1, Peroxisome Proliferator-Activated Receptor γ and NADH Dehydrogenase (Ubiquinone) Flavoprotein 2 Are Involved in Gene Expression and Neuronal L1-Dependent Functions

The cell adhesion molecule L1 is essential not only for neural development, but also for synaptic functions and regeneration after trauma in adulthood. Abnormalities in L1 functions cause developmental and degenerative disorders. L1's functions critically depend on proteolysis which underlies dynamic cell interactions and signal transduction. We showed that a 70 kDa fragment (L1-70) supports mitochondrial functions and gene transcription. To gain further insights into L1-70's functions, we investigated several binding partners. Here we show that L1-70 interacts with topoisomerase 1 (TOP1), peroxisome proliferator-activated receptor γ (PPARγ) and NADH dehydrogenase (ubiquinone) flavoprotein 2 (NDUFV2). TOP1, PPARγ and NDUFV2 siRNAs reduced L1-dependent neurite outgrowth, and the topoisomerase inhibitors topotecan and irinotecan inhibited L1-dependent neurite outgrowth, neuronal survival and migration. In cultured neurons, L1 siRNA reduces the expression levels of the long autism genes neurexin-1 (Nrxn1) and neuroligin-1 (Nlgn1) and of the mitochondrially encoded gene NADH:ubiquinone oxidoreductase core subunit 2 (ND2). In mutant mice lacking L1-70, Nrxn1 and Nlgn1, but not ND2, mRNA levels are reduced. Since L1-70's interactions with TOP1, PPARγ and NDUFV2 contribute to the expression of two essential long autism genes and regulate important neuronal functions, we propose that L1 may not only ameliorate neurological problems, but also psychiatric dysfunctions.

Functional and Pathological Effects of α-Synuclein on Synaptic SNARE Complexes

α-Synuclein is an abundant protein at the neuronal synapse that has been implicated in Parkinson's disease for over 25 years and characterizes the hallmark pathology of a group of neurodegenerative diseases now known as the synucleinopathies. Physiologically, α-synuclein exists in an equilibrium between a synaptic vesicle membrane-bound α-helical multimer and a cytosolic largely unstructured monomer. Through its membrane-bound state, α-synuclein functions in neurotransmitter release by modulating several steps in the synaptic vesicle cycle, including synaptic vesicle clustering and docking, SNARE complex assembly, and homeostasis of synaptic vesicle pools. These functions have been ascribed to α-synuclein's interactions with the synaptic vesicle SNARE protein VAMP2/synaptobrevin-2, the synaptic vesicle-attached synapsins, and the synaptic vesicle membrane itself. How α-synuclein affects these processes, and whether disease is due to loss-of-function or gain-of-toxic-function of α-synuclein remains unclear. In this review, we provide an in-depth summary of the existing literature, discuss possible reasons for the discrepancies in the field, and propose a working model that reconciles the findings in the literature.

The KDET Motif in the Intracellular Domain of the Cell Adhesion Molecule L1 Interacts with Several Nuclear, Cytoplasmic, and Mitochondrial Proteins Essential for Neuronal Functions

Abnormal functions of the cell adhesion molecule L1 are linked to several neural diseases. Proteolytic L1 fragments were reported to interact with nuclear and mitochondrial proteins to regulate events in the developing and the adult nervous system. Recently, we identified a 55 kDa L1 fragment (L1-55) that interacts with methyl CpG binding protein 2 (MeCP2) and heterochromatin protein 1 (HP1) via the KDET motif. We now show that L1-55 also interacts with histone H1.4 (HistH1e) via this motif. Moreover, we show that this motif binds to NADH dehydrogenase ubiquinone flavoprotein 2 (NDUFV2), splicing factor proline/glutamine-rich (SFPQ), the non-POU domain containing octamer-binding protein (NonO), paraspeckle component 1 (PSPC1), WD-repeat protein 5 (WDR5), heat shock cognate protein 71 kDa (Hsc70), and synaptotagmin 1 (SYT1). Furthermore, applications of HistH1e, NDUFV2, SFPQ, NonO, PSPC1, WDR5, Hsc70, or SYT1 siRNAs or a cell-penetrating KDET-carrying peptide decrease L1-dependent neurite outgrowth and the survival of cultured neurons. These findings indicate that L1's KDET motif binds to an unexpectedly large number of molecules that are essential for nervous system-related functions, such as neurite outgrowth and neuronal survival. In summary, L1 interacts with cytoplasmic, nuclear and mitochondrial proteins to regulate development and, in adults, the formation, maintenance, and flexibility of neural functions.

Neuroprotective Effects of σ2R/TMEM97 Receptor Modulators in the Neuronal Model of Huntington's Disease

Huntington's disease (HD) is a genetic neurodegenerative disease caused by an expanded CAG repeat in the Huntingtin (HTT) gene that encodes for an expanded polyglutamine (polyQ) repeat in exon-1 of the human mutant huntingtin (mHTT) protein. The presence of this polyQ repeat results in neuronal degeneration, for which there is no cure or treatment that modifies disease progression. In previous studies, we have shown that small molecules that bind selectively to σ₂R/TMEM97 can have significant neuroprotective effects in models of Alzheimer's disease, traumatic brain injury, and several other neurodegenerative diseases. In the present work, we extend these investigations and show that certain σ₂R/TMEM97-selective ligands decrease mHTT-induced neuronal toxicity. We first synthesized a set of compounds designed to bind to σ₂R/TMEM97 and determined their binding profiles (K_i values) for σ₂R/TMEM97 and other proteins in the central nervous system. Modulators with high affinity and selectivity for σ₂R/TMEM97 were then tested in our HD cell model. Primary cortical neurons were cultured in vitro for 7 days and then co-transfected with either a normal HTT construct (Htt N-586-22Q/GFP) or the mHTT construct Htt-N586-82Q/GFP. Transfected neurons were treated with either σ₂R/TMEM97 or σ₁R modulators for 48 h. After treatment, neurons were fixed and stained with Hoechst, and condensed nuclei were quantified to assess cell death in the transfected neurons. Significantly, σ₂R/TMEM97 modulators reduce the neuronal toxicity induced by mHTT, and their neuroprotective effects are not blocked by NE-100, a selective σ₁R antagonist known to block neuroprotection by σ₁R ligands. These results indicate for the first time that σ₂R/TMEM97 modulators can protect neurons from mHTT-induced neuronal toxicity, suggesting that targeting σ₂R/TMEM97 may lead to a novel therapeutic approach to treat patients with HD.

The alternative 3' splice site of GPNMB may promote neuronal survival after neonatal hypoxic-ischemic encephalopathy injury

This study aimed to decipher the effect of glycoprotein nonmetastatic melanoma protein B (GPNMB) on neonatal hypoxic-ischemic encephalopathy (NHIE) and its potential molecular mechanism. The hypoxic-ischemic (HI) model was established in 7-day-old rats, and then, Zea-Longa scores and Nissl staining were performed to measure brain damage post-HI. In addition, gene sequencing was used to detect the differential expression genes (DEGs), and then, Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases were used to determine the function of DEGs. Furthermore, an oxygen-glucose deprivation (OGD) model was developed in SY5Y cells and human fetal neurons, and then, the level of GPNMB was verified by quantitative real-time polymerase chain reaction. In addition, methyl thiazolyl tetrazolium and cell counting kit-8 assays were applied after GPNMB interference. Finally, the alternative splicing of GPNMB expression was analyzed using Splice Grapher software. The results indicated that HI induced marked neurological impairment and neuron injury in rats. Also, GPNMB was the most obviously upregulated gene in DEGs. Additionally, GPNMB was upregulated significantly in SY5Y and fetal neurons after OGD, and GPNMB-si promoted an increase in cell viability and number. Moreover, we found that the GPNMB alternative splicing type was the Alternative 3' splice site, with the alternative splicing site in 143382985:143404102. Herein, GPNMB promotes a crucial regulatory mechanism with alternative splicing for neuronal survival after NHIE.

ALS-associated KIF5A mutations abolish autoinhibition resulting in a toxic gain of function

Understanding the pathogenic mechanisms of disease mutations is critical to advancing treatments. ALS-associated mutations in the gene encoding the microtubule motor KIF5A result in skipping of exon 27 (KIF5AΔExon27) and the encoding of a protein with a novel 39 amino acid residue C-terminal sequence. Here, we report that expression of ALS-linked mutant KIF5A results in dysregulated motor activity, cellular mislocalization, altered axonal transport, and decreased neuronal survival. Single-molecule analysis revealed that the altered C terminus of mutant KIF5A results in a constitutively active state. Furthermore, mutant KIF5A possesses altered protein and RNA interactions and its expression results in altered gene expression/splicing. Taken together, our data support the hypothesis that causative ALS mutations result in a toxic gain of function in the intracellular motor KIF5A that disrupts intracellular trafficking and neuronal homeostasis.

Using IPA tools to characterize molecular pathways underlying the involvement of IRF7 in antiviral response to HIV

Objectives

Interferon Regulatory Factors (IRFs) regulate transcription of type-I interferons (IFNs) and IFN-stimulated genes. We previously reported that IFN-regulatory factor 7 (IRF7) is significantly upregulated in the brain of HIV-1 transgenic (HIV-1Tg) rats compared to F344 control rats in a region dependent manner [Li MD, Cao J, Wang S, Wang J, Sarkar S, Vigorito M, et al. Transcriptome sequencing of gene expression in the brain of the HIV-1 transgenic rat. PLoS One 2013]. The RNA deep-sequencing data were deposited in the NCBI SRA database with Gene Expression Omnibus (GEO) number GSE47474. Our current study utilized QIAGEN CLC Genomics Workbench and Ingenuity Pathway Analysis (IPA) to identify molecular pathways underlying the involvement of IRF7 in the HIV antiviral response.

Methods

The differential RNA expression data between HIV-1Tg and F344 rats as well as HAND+ and HIV+ cognitively normal patients was collected from GSE47474 and GSE152416, respectively. The "Core Expression Data Analysis" function identified the significant canonical pathways in the datasets with or without IRF7 and its 455 associated molecules.

Results

It was found that IRF7 and its 455 associated molecules altered the expression of pathways involving neurotransmission, neuronal survival, and immune function.

Conclusions

This in-silico study reveals that IRF7 is involved in the promotion of macrophage activity, neuronal differentiation, the modulation of the Th-1/Th-2 ratio, and the suppression of HIV-1 translation. Furthermore, we demonstrate that bioinformatics tools such as IPA can be employed to simulate the complete knockout of a target molecule such as IRF7 to study its involvement in biological pathways.

Inhibition of LncRNA Vof-16 expression promotes nerve regeneration and functional recovery after spinal cord injury

Our previous RNA sequencing study showed that the long non-coding RNA ischemia-related factor Vof-16 (lncRNA Vof-16) was upregulated after spinal cord injury, but its precise role in spinal cord injury remains unclear. Bioinformatics predictions have indicated that lncRNA Vof-16 may participate in the pathophysiological processes of inflammation and apoptosis. PC12 cells were transfected with a pHBLV-U6-MCS-CMV-ZsGreen-PGK-PURO vector to express an lncRNA Vof-16 knockdown lentivirus and a pHLV-CMVIE-ZsGree-Puro vector to express an lncRNA Vof-16 overexpression lentivirus. The overexpression of lncRNA Vof-16 inhibited PC12 cell survival, proliferation, migration, and neurite extension, whereas lncRNA Vof-16 knockdown lentiviral vector resulted in the opposite effects in PC12 cells. Western blot assay results showed that the overexpression of lncRNA Vof-16 increased the protein expression levels of interleukin 6, tumor necrosis factor-α, and Caspase-3 and decreased Bcl-2 expression levels in PC12 cells. Furthermore, we established rat models of spinal cord injury using the complete transection at T10. Spinal cord injury model rats were injected with the lncRNA Vof-16 knockdown or overexpression lentiviral vectors immediately after injury. At 7 days after spinal cord injury, rats treated with lncRNA Vof-16 knockdown displayed increased neuronal survival and enhanced axonal extension. At 8 weeks after spinal cord injury, rats treated with the lncRNA Vof-16 knockdown lentiviral vector displayed improved neurological function in the hind limb. Notably, lncRNA Vof-16 knockdown injection increased Bcl-2 expression and decreased tumor necrosis factor-α and Caspase-3 expression in treated animals. Rats treated with the lncRNA Vof-16 overexpression lentiviral vector displayed opposite trends. These findings suggested that lncRNA Vof-16 is associated with the regulation of inflammation and apoptosis. The inhibition of lncRNA Vof-16 may be useful for promoting nerve regeneration and functional recovery after spinal cord injury. The experiments were approved by the Institutional Animal Care and Use Committee of Guangdong Medical University, China.

The Neuroprotective Effect of L-Carnitine against Glyceraldehyde-Induced Metabolic Impairment: Possible Implications in Alzheimer's Disease

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by progressive cognitive regression and memory loss. Dysfunctions of both glucose metabolism and mitochondrial dynamics have been recognized as the main upstream events of the degenerative processes leading to AD. It has been recently found that correcting cell metabolism by providing alternative substrates can prevent neuronal injury by retaining mitochondrial function and reducing AD marker levels. Here, we induced an AD-like phenotype by using the glycolysis inhibitor glyceraldehyde (GA) and explored whether L-carnitine (4-N-trimethylamino-3-hydroxybutyric acid, LC) could mitigate neuronal damage, both in SH-SY5Y neuroblastoma cells and in rat primary cortical neurons. We have already reported that GA significantly modified AD marker levels; here we demonstrated that GA dramatically compromised cellular bioenergetic status, as revealed by glycolysis and oxygen consumption rate (OCR) evaluation. We found that LC ameliorated cell survival, improved OCR and ATP synthesis, prevented the loss of the mitochondrial membrane potential (Δψ_m) and reduced the formation of reactive oxygen species (ROS). Of note, the beneficial effect of LC did not rely on the glycolytic pathway rescue. Finally, we noticed that LC significantly reduced the increase in pTau levels induced by GA. Overall, these findings suggest that the use of LC can promote cell survival in the setting of the metabolic impairments commonly observed in AD. Our data suggest that LC may act by maintaining mitochondrial function and by reducing the pTau level.

Role of NMDA Receptors in Adult Neurogenesis and Normal Development of the Dentate Gyrus

The NMDA receptors are a type of glutamate receptors, which is involved in neuronal function, plasticity and development in the mammalian brain. However, how the NMDA receptors contribute to adult neurogenesis and development of the dentate gyrus is unclear. In this study, we investigate this question by examining a region-specific knock-out mouse line that lacks the NR1 gene, which encodes the essential subunit of the NMDA receptors, in granule cells of the dentate gyrus (DG-NR1KO mice). We found that the survival of newly-generated granule cells, cell proliferation and the size of the granule cell layer are significantly reduced in the dorsal dentate gyrus of adult DG-NR1KO mice. Our results also show a significant reduction in the number of immature neurons and in the volume of the granule cell layer, starting from three weeks of postnatal age. DG-NR1KO mice also showed impairment in the expression of an immediate early gene, Arc, and behavior during the novelty-suppressed feeding and open field test. These results suggest that the NMDA receptors in granule cells have a role in adult neurogenesis in the adult brain and contributes to the normal development of the dentate gyrus.

Argon treatment after experimental subarachnoid hemorrhage: evaluation of microglial activation and neuronal survival as a subanalysis of a randomized controlled animal trial

Hereinafter, we evaluate argon's neuroprotective and immunomodulatory properties after experimental subarachnoid hemorrhage (SAH) examining various localizations (hippocampal and cortical regions) with respect to neuronal damage and microglial activation 6, 24 and 72 hours after SAH. One hour after SAH (endovascular perforation rat model) or sham surgery, a mixture of gas containing 50% argon (argon group) or 50% nitrogen (control group) was applied for 1 hour. At 6 hours after SAH, argon reduced neuronal damage in the hippocampal regions in the argon group compared to the control group (P < 0.034). Hippocampal microglial activation did not differ between the treatment groups over time. The basal cortical regions did not show a different lesion pattern, but microglial activation was significantly reduced in the argon group 72 hours after SAH (P = 0.034 vs. control group). Whereas callosal microglial activation was significantly reduced at 24 hours in the argon-treated group (P = 0.018). Argon treatment ameliorated only early hippocampal neuronal damage after SAH. Inhibition of microglial activation was seen in some areas later on. Thus, argon may influence the microglial inflammatory response and neuronal survival after SAH; however, due to low sample sizes the interpretation of our results is limited. The study protocol was approved by the Government Agency for Animal Use and Protection (Protocol number: TVA 10416G1; initially approved by the "Landesamt für Natur, Umwelt und Verbraucherschutz NRW," Recklinghausen, Germany, on April 28, 2009).

Lysosomal calcium is modulated by STIM1/TRPML1 interaction which participates to neuronal survival during ischemic preconditioning

A robust activity of the lysosomal Ca²⁺ channel TRPML1 is sufficient to correct cellular defects in neurodegeneration. Importantly, lysosomes are refilled by the endoplasmic reticulum (ER). However, it is unclear how TRPML1 function could be modulated by the ER. Here, we deal with this issue in rat primary cortical neurons exposed to different oxygen conditions affecting neuronal survival. Under normoxic conditions, TRPML1: (1) showed a wide distribution within soma and along neuronal processes; (2) was stimulated by the synthetic agonist ML-SA1 and the analog of its endogenous modulator, PI(3,5)P₂ diC8; (3) its knockdown by siRNA strategy produced an ER Ca²⁺ accumulation; (4) co-localized and co-immunoprecipitated with the ER-located Ca²⁺ sensor stromal interacting molecule 1 (STIM1). In cortical neurons lacking STIM1, ML-SA1 and PI(3,5)P₂ diC8 failed to induce Ca²⁺ release and, more deeply, they induced a negligible Ca²⁺ passage through the channel in neurons transfected with the genetically encoded Ca²⁺ indicator GCaMP3-ML1. Moreover, TRPML1/STIM1 interplay changed at low-oxygen conditions: both proteins were downregulated during the ischemic preconditioning (IPC) while during IPC followed by 1 hour of normoxia, at which STIM1 is upregulated, TRPML1 protein was reduced. However, during oxygen and glucose deprivation (OGD) followed by reoxygenation, TRPML1 and STIM1 proteins peaked at 8 hours of reoxygenation, when the proteins were co-immunoprecipitated and reactive oxygen species (ROS) hyperproduction was measured in cortical neurons. This may lead to a persistent TRPML1 Ca²⁺ release and lysosomal Ca²⁺ loss. Collectively, we showed a new modulation exerted by STIM1 on TRPML1 activity that may differently intervene during hypoxia to regulate organellar Ca²⁺ homeostasis.

Amelioration of the abnormal phenotype of a new L1 syndrome mouse mutation with L1 mimetics

L1 syndrome is a rare developmental disorder characterized by hydrocephalus of varying severity, intellectual deficits, spasticity of the legs, and adducted thumbs. Therapy is limited to symptomatic relief. Numerous gene mutations in the L1 cell adhesion molecule (L1CAM, hereafter abbreviated L1) were identified in L1 syndrome patients, and those affecting the extracellular domain of this transmembrane type 1 glycoprotein show the most severe phenotypes. Previously analyzed rodent models of the L1 syndrome focused on L1-deficient animals or mouse mutants with abrogated cell surface expression of L1, making it difficult to test L1 function-triggering mimetic compounds with potential therapeutic value. To overcome this impasse, we generated a novel L1 syndrome mouse with a mutation of aspartic acid at position 201 in the extracellular part of L1 (p.D201N, hereafter termed L1-201) that displays a cell surface-exposed L1 accessible to the L1 mimetics. Behavioral assessment revealed an increased neurological deficit score and increased locomotor activity in male L1-201 mice carrying the mutation on the X-chromosome. Histological analyses of L1-201 mice showed features of the L1 syndrome, including enlarged ventricles and reduced size of the corpus callosum. Expression levels of L1-201 protein as well as extent of cell surface biotinylation and immunofluorescence labelling of cultured cerebellar neurons were normal. Importantly, treatment of these cultures with the L1 mimetic compounds duloxetine, crotamiton, and trimebutine rescued impaired cell migration and survival as well as neuritogenesis. Altogether, the novel L1 syndrome mouse model provides a first experimental proof-of-principle for the potential therapeutic value of L1 mimetic compounds.

Treatment with a GSK-3β/HDAC Dual Inhibitor Restores Neuronal Survival and Maturation in an In Vitro and In Vivo Model of CDKL5 Deficiency Disorder

Mutations in the X-linked cyclin-dependent kinase-like 5 (CDKL5) gene cause a rare neurodevelopmental disorder characterized by early-onset seizures and severe cognitive, motor, and visual impairments. To date there are no therapies for CDKL5 deficiency disorder (CDD). In view of the severity of the neurological phenotype of CDD patients it is widely assumed that CDKL5 may influence the activity of a variety of cellular pathways, suggesting that an approach aimed at targeting multiple cellular pathways simultaneously might be more effective for CDD. Previous findings showed that a single-target therapy aimed at normalizing impaired GSK-3β or histone deacetylase (HDAC) activity improved neurodevelopmental and cognitive alterations in a mouse model of CDD. Here we tested the ability of a first-in-class GSK-3β/HDAC dual inhibitor, Compound 11 (C11), to rescue CDD-related phenotypes. We found that C11, through inhibition of GSK-3β and HDAC6 activity, not only restored maturation, but also significantly improved survival of both human CDKL5-deficient cells and hippocampal neurons from Cdkl5 KO mice. Importantly, in vivo treatment with C11 restored synapse development, neuronal survival, and microglia over-activation, and improved motor and cognitive abilities of Cdkl5 KO mice, suggesting that dual GSK-3β/HDAC6 inhibitor therapy may have a wider therapeutic benefit in CDD patients.

Microglial Adenosine Receptors: From Preconditioning to Modulating the M1/M2 Balance in Activated Cells

Neuronal survival depends on the glia, that is, on the astroglial and microglial support. Neurons die and microglia are activated not only in neurodegenerative diseases but also in physiological aging. Activated microglia, once considered harmful, express two main phenotypes: the pro-inflammatory or M1, and the neuroprotective or M2. When neuroinflammation, i.e., microglial activation occurs, it is important to achieve a good M1/M2 balance, i.e., at some point M1 microglia must be skewed into M2 cells to impede chronic inflammation and to afford neuronal survival. G protein-coupled receptors in general and adenosine receptors in particular are potential targets for increasing the number of M2 cells. This article describes the mechanisms underlying microglial activation and analyzes whether these cells exposed to a first damaging event may be ready to be preconditioned to better react to exposure to more damaging events. Adenosine receptors are relevant due to their participation in preconditioning. They can also be overexpressed in activated microglial cells. The potential of adenosine receptors and complexes formed by adenosine receptors and cannabinoids as therapeutic targets to provide microglia-mediated neuroprotection is here discussed.

Striatal Projection Neurons Require Huntingtin for Synaptic Connectivity and Survival

Huntington's disease (HD) is caused by an autosomal dominant polyglutamine expansion mutation of Huntingtin (HTT). HD patients suffer from progressive motor, cognitive, and psychiatric impairments, along with significant degeneration of the striatal projection neurons (SPNs) of the striatum. HD is widely accepted to be caused by a toxic gain-of-function of mutant HTT. However, whether loss of HTT function, because of dominant-negative effects of the mutant protein, plays a role in HD and whether HTT is required for SPN health and function are not known. Here, we delete Htt from specific subpopulations of SPNs using the Cre-Lox system and find that SPNs require HTT for motor regulation, synaptic development, cell health, and survival during aging. Our results suggest that loss of HTT function in SPNs could play a critical role in HD pathogenesis.

O-GlcNAcylation regulates dopamine neuron function, survival and degeneration in Parkinson disease

The dopamine system in the midbrain is essential for volitional movement, action selection, and reward-related learning. Despite its versatile roles, it contains only a small set of neurons in the brainstem. These dopamine neurons are especially susceptible to Parkinson’s disease and prematurely degenerate in the course of disease progression, while the discovery of new therapeutic interventions has been disappointingly unsuccessful. Here, we show that O-GlcNAcylation, an essential post-translational modification in various types of cells, is critical for the physiological function and survival of dopamine neurons. Bidirectional modulation of O-GlcNAcylation importantly regulates dopamine neurons at the molecular, synaptic, cellular, and behavioural levels. Remarkably, genetic and pharmacological upregulation of O-GlcNAcylation mitigates neurodegeneration, synaptic impairments, and motor deficits in an animal model of Parkinson’s disease. These findings provide insights into the functional importance of O-GlcNAcylation in the dopamine system, which may be utilized to protect dopamine neurons against Parkinson’s disease pathology.

Endogenous Mechanisms of Neuroprotection: To Boost or Not to Boost

Postmitotic cells, like neurons, must live through a lifetime. For this reason, organisms/cells have evolved with self-repair mechanisms that allow them to have a long life. The discovery workflow of neuroprotectors during the last years has focused on blocking the pathophysiological mechanisms that lead to neuronal loss in neurodegeneration. Unfortunately, only a few strategies from these studies were able to slow down or prevent neurodegeneration. There is compelling evidence demonstrating that endorsing the self-healing mechanisms that organisms/cells endogenously have, commonly referred to as cellular resilience, can arm neurons and promote their self-healing. Although enhancing these mechanisms has not yet received sufficient attention, these pathways open up new therapeutic avenues to prevent neuronal death and ameliorate neurodegeneration. Here, we highlight the main endogenous mechanisms of protection and describe their role in promoting neuron survival during neurodegeneration.

miR-143-3p inhibition promotes neuronal survival in an Alzheimer's disease cell model by targeting neuregulin-1

INTRODUCTION

Alzheimer's disease (AD) is still the fifth leading cause of death and most common dementia worldwide. To date, there is no efficient strategy that can slow down the progression of AD owing to delayed diagnosis and limited therapies. MiR-143-3p is up-regulated in serum of AD patients, yet the exact role it plays in AD pathology is still poorly understood. The aim of this study was to investigate the effect of miR-143-3p on neuronal survival.

MATERIAL AND METHODS

We induced neuronal differentiation in SH-SY5Y cells using all-trans-retinoic acid (RA), and Aβ1-42 was used to establish the in vitro AD cell model. The expression of tubulin β III and neuregulin-1 (NRG1) was evaluated by immunofluorescence. TUNEL assay was performed to assess cell apoptosis. Cell viability was evaluated using the Cell Counting Kit-8 assay. The binding interaction between miR-143-3p and NRG1 was verified using the luciferase reporter assay.

RESULTS

Typical neuronal-like axons were observed in RA-induced SH-SY5Y cells, followed by increased tubulin β III. A dramatically increased apoptotic rate and reduced cell viability were observed in the AD cell model. Then we silenced the miR-143-3p expression, and Aβ1-42 induced cell apoptosis was alleviated after miR-143-3p inhibition, accompanied by decreased cleaved caspase-3 and cleaved caspase-9 levels. Additionally, NRG1 was confirmed to be a downstream target of miR-143-3p, increased cell viability and suppressed cell apoptosis after miR-143-3p inhibition was abolished by NRG1 knockdown.

CONCLUSIONS

Our findings reveal that miR-143-3p inhibition promotes neuronal survival in an in vitro cell model via targeting NRG1, and the miR-143-3p/NRG1 axis is a potential therapeutic target and promising biomarker for AD treatment.

Role of Sirtuins in Modulating Neurodegeneration of the Enteric Nervous System and Central Nervous System

Neurodegeneration of the central and enteric nervous systems is a common feature of aging and aging-related diseases, and is accelerated in individuals with metabolic dysfunction including obesity and diabetes. The molecular mechanisms of neurodegeneration in both the CNS and ENS are overlapping. Sirtuins are an important family of histone deacetylases that are important for genome stability, cellular response to stress, and nutrient and hormone sensing. They are activated by calorie restriction (CR) and by the coenzyme, nicotinamide adenine dinucleotide (NAD⁺). Sirtuins, specifically the nuclear SIRT1 and mitochondrial SIRT3, have been shown to have predominantly neuroprotective roles in the CNS while the cytoplasmic sirtuin, SIRT2 is largely associated with neurodegeneration. A systematic study of sirtuins in the ENS and their effect on enteric neuronal growth and survival has not been conducted. Recent studies, however, also link sirtuins with important hormones such as leptin, ghrelin, melatonin, and serotonin which influence many important processes including satiety, mood, circadian rhythm, and gut homeostasis. In this review, we address emerging roles of sirtuins in modulating the metabolic challenges from aging, obesity, and diabetes that lead to neurodegeneration in the ENS and CNS. We also highlight a novel role for sirtuins along the microbiota-gut-brain axis in modulating neurodegeneration.

Tissue engineered axon-based "living scaffolds" promote survival of spinal cord motor neurons following peripheral nerve repair

Peripheral nerve injury (PNI) impacts millions annually, often leaving debilitated patients with minimal repair options to improve functional recovery. Our group has previously developed tissue engineered nerve grafts (TENGs) featuring long, aligned axonal tracts from dorsal root ganglia (DRG) neurons that are fabricated in custom bioreactors using the process of axon "stretch-growth." We have shown that TENGs effectively serve as "living scaffolds" to promote regeneration across segmental nerve defects by exploiting the newfound mechanism of axon-facilitated axon regeneration, or "AFAR," by simultaneously providing haptic and neurotrophic support. To extend this work, the current study investigated the efficacy of living versus nonliving regenerative scaffolds in preserving host sensory and motor neuronal health following nerve repair. Rats were assigned across five groups: naïve, or repair using autograft, nerve guidance tube (NGT) with collagen, NGT + non-aligned DRG populations in collagen, or TENGs. We found that TENG repairs yielded equivalent regenerative capacity as autograft repairs based on preserved health of host spinal cord motor neurons and acute axonal regeneration, whereas NGT repairs or DRG neurons within an NGT exhibited reduced motor neuron preservation and diminished regenerative capacity. These acute regenerative benefits ultimately resulted in enhanced levels of functional recovery in animals receiving TENGs, at levels matching those attained by autografts. Our findings indicate that TENGs may preserve host spinal cord motor neuron health and regenerative capacity without sacrificing an otherwise uninjured nerve (as in the case of the autograft) and therefore represent a promising alternative strategy for neurosurgical repair following PNI.

The therapeutic potential of mitochondrial transplantation for the treatment of neurodegenerative disorders

Mitochondrial activity is essential to support neural functions, and changes in the integrity and activity of the mitochondria can contribute to synaptic damage and neuronal death, especially in degenerative diseases associated with age, such as Alzheimer's and Parkinson's disease. Currently, different approaches are used to treat these conditions, and one strategy under research is mitochondrial transplantation. For years, mitochondria have been shown to be transferred between cells of different tissues. This process has allowed several attempts to develop transplantation schemes by isolating functional mitochondria and introducing them into damaged tissue in particular to counteract the harmful effects of myocardial ischemia. Recently, mitochondrial transfer between brain cells has also been reported, and thus, mitochondrial transplantation for disorders of the nervous system has begun to be investigated. In this review, we focus on the relevance of mitochondria in the nervous system, as well as some mitochondrial alterations that occur in neurodegenerative diseases associated with age. In addition, we describe studies that have performed mitochondrial transplantation in various tissues, and we emphasize the advances in mitochondrial transplantation aimed at treating diseases of the nervous system.

Functions of Small Organic Compounds that Mimic the HNK-1 Glycan

Because of the importance of the HNK-1 carbohydrate for preferential motor reinnervation after injury of the femoral nerve in mammals, we screened NIH Clinical Collection 1 and 2 Libraries and a Natural Product library comprising small organic compounds for identification of pharmacologically useful reagents. The reason for this attempt was to obviate the difficult chemical synthesis of the HNK-1 carbohydrate and its isolation from natural sources, with the hope to render such compounds clinically useful. We identified six compounds that enhanced neurite outgrowth from cultured spinal motor neurons at nM concentrations and increased their neurite diameter, but not their neurite branch points. Axons of dorsal root ganglion neurons did not respond to these compounds, a feature that is in agreement with their biological role after injury. We refer to the positive functions of some of these compounds in animal models of injury and delineate the intracellular signaling responses elicited by application of compounds to cultured murine central nervous system neurons. Altogether, these results point to the potential of the HNK-1 carbohydrate mimetics in clinically-oriented settings.

Two boron-containing compounds affect the cellular viability of SH-SY5Y cells in an in vitro amyloid-beta toxicity model

Boron is a naturally occurring trace element found in organic and inorganic complexes. Boron-containing compounds are required for living organisms for diverse metabolic functions, including nitrogen fixation in microorganisms, cell wall stability in plants, and bone and carbohydrate metabolism in animals. The number of studies about the effect of boron in biological model systems is very limited; so far, there has been no study on the correlation between boron and amyloid-beta toxicity. Here, we investigated the possible effects of 2 boron-containing compounds—sodium borate decahydrate and boric acid—against amyloid-beta toxicity. In our in vitro amyloid-beta toxicity model, we showed that these 2 compounds increase the survival of the SH-SY5Y cells. Furthermore, boron in these 2 forms increases the expression of Sirt1, which has protective functions against cellular stress. The compounds also change the expressions of GSK-3α/β; by doing so, boron may contribute to the stimulation of intracellular prosurvival pathways. This is the first experimental study indicating the prosurvival effect of boron in an amyloid-beta toxicity model.

Gateways for Glutamate Neuroprotection in Parkinson's Disease (PD): Essential Role of EAAT3 and NCX1 Revealed in an In Vitro Model of PD

Increasing evidence suggests that metabolic alterations may be etiologically linked to neurodegenerative disorders such as Parkinson's disease (PD) and in particular empathizes the possibility of targeting mitochondrial dysfunctions to improve PD progression. Under different pathological conditions (i.e., cardiac and neuronal ischemia/reperfusion injury), we showed that supplementation of energetic substrates like glutamate exerts a protective role by preserving mitochondrial functions and enhancing ATP synthesis through a mechanism involving the Na⁺-dependent excitatory amino acid transporters (EAATs) and the Na⁺/Ca²⁺ exchanger (NCX). In this study, we investigated whether a similar approach aimed at promoting glutamate metabolism would be also beneficial against cell damage in an in vitro PD-like model. In retinoic acid (RA)-differentiated SH-SY5Y cells challenged with α-synuclein (α-syn) plus rotenone (Rot), glutamate significantly improved cell viability by increasing ATP levels, reducing oxidative damage and cytosolic and mitochondrial Ca²⁺ overload. Glutamate benefits were strikingly lost when either EAAT3 or NCX1 expression was knocked down by RNA silencing. Overall, our results open the possibility of targeting EAAT3/NCX1 functions to limit PD pathology by simultaneously favoring glutamate uptake and metabolic use in dopaminergic neurons.

Presenilin1 familial Alzheimer disease mutants inactivate EFNB1- and BDNF-dependent neuroprotection against excitotoxicity by affecting neuroprotective complexes of N-methyl-d-aspartate receptor

Excitotoxicity is thought to play key roles in brain neurodegeneration and stroke. Here we show that neuroprotection against excitotoxicity by trophic factors EFNB1 and brain-derived neurotrophic factor (called here factors) requires de novo formation of 'survival complexes' which are factor-stimulated complexes of N-methyl-d-aspartate receptor with factor receptor and presenilin 1. Absence of presenilin 1 reduces the formation of survival complexes and abolishes neuroprotection. EPH receptor B2- and N-methyl-d-aspartate receptor-derived peptides designed to disrupt formation of survival complexes also decrease the factor-stimulated neuroprotection. Strikingly, factor-dependent neuroprotection and levels of the de novo factor-stimulated survival complexes decrease dramatically in neurons expressing presenilin 1 familial Alzheimer disease mutants. Mouse neurons and brains expressing presenilin 1 familial Alzheimer disease mutants contain increased amounts of constitutive presenilin 1-N-methyl-d-aspartate receptor complexes unresponsive to factors. Interestingly, the stability of the familial Alzheimer disease presenilin 1-N-methyl-d-aspartate receptor complexes differs from that of wild type complexes and neurons of mutant-expressing brains are more vulnerable to cerebral ischaemia than neurons of wild type brains. Furthermore, N-methyl-d-aspartate receptor-mediated excitatory post-synaptic currents at CA1 synapses are altered by presenilin 1 familial Alzheimer disease mutants. Importantly, high levels of presenilin 1-N-methyl-d-aspartate receptor complexes are also found in post-mortem brains of Alzheimer disease patients expressing presenilin 1 familial Alzheimer disease mutants. Together, our data identify a novel presenilin 1-dependent neuroprotective mechanism against excitotoxicity and indicate a pathway by which presenilin 1 familial Alzheimer disease mutants decrease factor-depended neuroprotection against excitotoxicity and ischaemia in the absence of Alzheimer disease neuropathological hallmarks which may form downstream of neuronal damage. These findings have implications for the pathogenic effects of familial Alzheimer disease mutants and therapeutic strategies.

Insulin and Exendin-4 Reduced Mutated Huntingtin Accumulation in Neuronal Cells

Patients with diabetes mellitus (DM) are more prone to develop cognitive decline and neurodegenerative diseases. A pathological association between an autosomal dominant neurological disorder caused by brain accumulation in mutated huntingtin (mHTT), known as Huntington disease (HD), and DM, has been reported. By using a diabetic mouse model, we previously suggested a central role of the metabolic pathways of HTT, further suggesting the relevance of this protein in the pathology of DM. Furthermore, it has also been reported that intranasal insulin (Ins) administration improved cognitive function in patients with neurodegenerative disorders such as Alzheimer disease, and that exendin-4 (Ex-4) enhanced lifespan and ameliorated glucose homeostasis in a mouse model of HD. Although antioxidant properties have been proposed, the underlying molecular mechanisms are still missing. Therefore, the aim of the present study was to investigate the intracellular pathways leading to neuroprotective effect of Ins and Ex-4 hypoglycemic drugs by using an in vitro model of HD, developed by differentiated dopaminergic neurons treated with the pro-oxidant neurotoxic compound 6-hydroxydopamine (6-ohda). Our results showed that 6-ohda increased mHTT expression and reduced HTT phosphorylation at Ser421, a post-translational modification, which protects against mHTT accumulation. Pre-treatment with Ins or Ex-4 reverted the harmful effect induced by 6-ohda by activating AKT1 and SGK1 kinases, and by reducing the phosphatase PP2B. AKT1 and SGK1 are crucial nodes on the Ins activation pathway and powerful antioxidants, while PP2B dephosphorylates HTT contributing to mHTT neurotoxic effect. In conclusion, present results highlight that Ins and Ex-4 may counteract the neurotoxic effect induced by mHTT, opening novel pharmacological therapeutic strategies against neurodegenerative disorders, with the main focus on HD, still considered an orphan illness.

Neurotrophic Effects of Vascular Endothelial Growth Factor B and Novel Mimetic Peptides on Neurons from the Central Nervous System

Vascular endothelial growth factor B (VEGFB) is a pleiotropic trophic factor, which in contrast to the closely related VEGFA is known to have a limited effect on angiogenesis. VEGFB improves survival in various tissues including the nervous system, where the effect was observed mainly for peripheral neurons. The neurotrophic effect of VEGFB on central nervous system neurons has been less investigated. Here we demonstrated that VEGFB promotes neurite outgrowth from primary cerebellar granule, hippocampal, and retinal neurons in vitro. VEGFB protected hippocampal and retinal neurons from both oxidative stress and glutamate-induced neuronal death. The VEGF receptor 1 (VEGFR1) is required for VEGFB-induced neurotrophic and neuroprotective effects. Using a structure-based approach, we designed short peptides, termed Vefin1-7, mimicking the binding interface of VEGFB to VEGFR1. Vefins were analyzed for their secondary structure and binding to VEGF receptors and compared with previously described peptides derived from VEGFA, another ligand of VEGFR1. We show that Vefins have neurotrophic and neuroprotective effects on primary hippocampal, cerebellar granule, and retinal neurons in vitro with potencies comparable to VEGFB. Similar to VEGFB, Vefins were not mitogenic for MCF-7 cancer cells. Furthermore, one of the peptides, Vefin7, even dose-dependently inhibited the proliferation of MCF-7 cells in vitro. Unraveling the neurotrophic and neuroprotective potentials of VEGFB, the only nonangiogenic factor of the VEGF family, is promising for the development of neuroprotective peptide-based therapies.

Transcranial direct current stimulation treated by multilead brain reflex instrument accelerates neural functional recovery in a rat model of stroke

PURPOSE

Clinical research suggests that transcranial direct current stimulation (tDCS) at bilateral supraorbital foramen and inferior orbital rim and nose intersections may facilitate rehabilitation after stroke. However, the underlying neurobiological mechanisms of tDCS remain poorly understood, impeding its clinical application. Here, we investigated the effect of tDCS applied after stroke on neural cells.

MATERIALS AND METHODS

Middle cerebral arterial occlusion (MCAO) reperfusion was induced in rats. Animals with comparable infarcts were randomly divided into MCAO group and MCAO + tDCS group. Recovery of neurological function was assessed behaviorally by modified neurological severity score (mNSS). Ischemic tissue damage verified histologically by TTC and HE staining. Immunohistochemical staining, real-time qPCR, and western blot were applied to determine the changes of neural cells in ischemic brains.

RESULTS

The results reveal that tDCS treated by multilead brain reflex instrument can promote the recovery of neurological function, remarkably reduce cerebral infarct volume, promote brain tissue rehabilitation, and can effectively inhibit astrocytosis and enhance neuronal survival and synaptic function in ischemic brains.

CONCULSIONS

Our study suggests that tDCS treated by multilead brain reflex instrument could be prospectively developed into a clinical treatment modality.

Novel Targets for Stroke Therapy: Special Focus on TRPC Channels and TRPC6

Stroke remains a leading cause of death, disability, and medical care burden worldwide. However, transformation from laboratory findings toward effective pharmacological interventions for clinical stroke has been unsatisfactory. Novel evidence has been gained on the underlying mechanisms and therapeutic potential related to the transient receptor potential (TRP) channels in several disorders. The TRP superfamily consists of a diverse group of Ca²⁺ permeable non-selective cation channels. In particular, the members of TRP subfamilies, TRP canonical (TRPC) channels and TRPC6, have been found in different cell types in the whole body and have high levels of expression in the central nervous system (CNS). Notably, the TRPCs and TRPC6 channel have been implicated in neurite outgrowth and neuronal survival during normal development and in a range of CNS pathological conditions. Recent studies have shown that suppression of TRPC6 channel degradation prevents ischemic neuronal cell death in experimental stroke. Accumulating evidence supports the important functions of TRPC6 in brain ischemia. We have highlighted some crucial advancement that points toward an important involvement of TRPCs and TRPC6 in ischemic stroke. This review will make an overview of the TRP and TRPC channels due to their roles as targets for clinical trials and CNS disorders. Besides, the primary goal is to discuss and update the critical role of TRPC6 channels in stroke and provide a promising target for stroke prevention and therapy.

Neuroprotective actions of cerebellar and pineal allopregnanolone on Purkinje cells

The brain produces steroids de novo from cholesterol, so‐called “neurosteroids.” The Purkinje cell, a cerebellar neuron, was discovered as a major site of the biosynthesis of neurosteroids including sex steroids, such as progesterone, from cholesterol in the brain. Allopregnanolone, a progesterone metabolite, is also synthesized in the cerebellum and acts on the Purkinje cell to prevent cell death of this neuron. Recently, the pineal gland was discovered as an important site of the biosynthesis of neurosteroids. Allopregnanolone, a major pineal neurosteroid, acts on the Purkinje cell for the survival of this neuron by suppressing the expression of caspase‐3, a crucial mediator of apoptosis. This review summarizes the discovery of cerebellar and pineal allopregnanolone and its neuroprotective action on Purkinje cells.

Models and treatments for traumatic optic neuropathy and demyelinating optic neuritis

Pathologies of the optic nerve could result as primary insults in the visual tract or as secondary deficits due to inflammation, demyelination, or compressing effects of the surrounding tissue. The extent of damage may vary from mild to severe, differently affecting patient vision, with the most severe forms leading to complete uni- or bilateral visual loss. The aim of researchers and clinicians in the field is to alleviate the symptoms of these, yet uncurable pathologies, taking advantage of known and novel potential therapeutic approaches, alone or in combinations, and applying them in a limited time window after the insult. In this review, we discuss the epidemiological and clinical profile as well as the pathophysiological mechanisms of two main categories of optic nerve pathologies, namely traumatic optic neuropathy and optic neuritis, focusing on the demyelinating form of the latter. Moreover, we report on the main rodent models mimicking these pathologies or some of their clinical aspects. The current treatment options will also be reviewed and novel approaches will be discussed.

Rifampicin and Its Derivative Rifampicin Quinone Reduce Microglial Inflammatory Responses and Neurodegeneration Induced In Vitro by α-Synuclein Fibrillary Aggregates

: Aggregated forms of the synaptic protein α-synuclein (αS) have been proposed to operate as a molecular trigger for microglial inflammatory processes and neurodegeneration in Parkinson´s disease. Here, we used brain microglial cell cultures activated by fibrillary forms of recombinant human αS to assess the anti-inflammatory and neuroprotective activities of the antibiotic rifampicin (Rif) and its autoxidation product rifampicin quinone (RifQ). Pretreatments with Rif and RifQ reduced the secretion of prototypical inflammatory cytokines (TNF-, IL-6) and the burst of oxidative stress in microglial cells activated with αS fibrillary aggregates. Note, however, that RifQ was constantly more efficacious than its parent compound in reducing microglial activation. We also established that the suppressive effects of Rif and RifQ on cytokine release was probably due to inhibition of both PI3K- and non-PI3K-dependent signaling events. The control of oxidative stress appeared, however, essentially dependent on PI3K inhibition. Of interest, we also showed that RifQ was more efficient than Rif in protecting neuronal cells from toxic factors secreted by microglia activated by αS fibrils. Overall, data with RifQ are promising enough to justify further studies to confirm the potential of this compound as an anti-parkinsionian drug.

Serotonin regulates mitochondrial biogenesis and function in rodent cortical neurons via the 5-HT2A receptor and SIRT1-PGC-1α axis

Neuronal mitochondria are crucial organelles that regulate bioenergetics and also modulate survival and function under environmental challenges. Here, we show that the neurotransmitter serotonin (5-HT) plays an important role in the making of new mitochondria (mitochondrial biogenesis) in cortical neurons, through the 5-HT_2A receptor and via master regulators of mitochondrial biogenesis, SIRT1 and PGC-1α. Mitochondrial function is also enhanced by 5-HT, increasing cellular respiration and ATP, the energy currency of the cell. We found 5-HT reduces cellular reactive oxygen species and exerts potent neuroprotective action in neurons challenged with stress, an effect that requires SIRT1. These findings highlight a role for the mitochondrial effects of 5-HT in the facilitation of stress adaptation and identify drug targets to ameliorate mitochondrial dysfunction in neurons.

Mitochondria in neurons, in addition to their primary role in bioenergetics, also contribute to specialized functions, including regulation of synaptic transmission, Ca²⁺ homeostasis, neuronal excitability, and stress adaptation. However, the factors that influence mitochondrial biogenesis and function in neurons remain poorly elucidated. Here, we identify an important role for serotonin (5-HT) as a regulator of mitochondrial biogenesis and function in rodent cortical neurons, via a 5-HT_2A receptor-mediated recruitment of the SIRT1–PGC-1α axis, which is relevant to the neuroprotective action of 5-HT. We found that 5-HT increased mitochondrial biogenesis, reflected through enhanced mtDNA levels, mitotracker staining, and expression of mitochondrial components. This resulted in higher mitochondrial respiratory capacity, oxidative phosphorylation (OXPHOS) efficiency, and a consequential increase in cellular ATP levels. Mechanistically, the effects of 5-HT were mediated via the 5-HT_2A receptor and master modulators of mitochondrial biogenesis, SIRT1 and PGC-1α. SIRT1 was required to mediate the effects of 5-HT on mitochondrial biogenesis and function in cortical neurons. In vivo studies revealed that 5-HT_2A receptor stimulation increased cortical mtDNA and ATP levels in a SIRT1-dependent manner. Direct infusion of 5-HT into the neocortex and chemogenetic activation of 5-HT neurons also resulted in enhanced mitochondrial biogenesis and function in vivo. In cortical neurons, 5-HT enhanced expression of antioxidant enzymes, decreased cellular reactive oxygen species, and exhibited neuroprotection against excitotoxic and oxidative stress, an effect that required SIRT1. These findings identify 5-HT as an upstream regulator of mitochondrial biogenesis and function in cortical neurons and implicate the mitochondrial effects of 5-HT in its neuroprotective action.

Activity-Independent Effects of CREB on Neuronal Survival and Differentiation during Mouse Cerebral Cortex Development

Neuronal survival and morphological maturation depends on the action of the transcription factor calcium responsive element binding protein (CREB), which regulates expression of several target genes in an activity-dependent manner. However, it remains largely unknown whether CREB-mediated transcription could play a role at early stages of neuronal differentiation, prior to the establishment of functional synaptic contacts. Here, we show that CREB is phosphorylated at very early stages of neuronal differentiation in vivo and in vitro, even in the absence of depolarizing agents. Using genetic tools, we also show that inhibition of CREB-signaling affects neuronal growth and survival in vitro without affecting cell proliferation and neurogenesis. Expression of A-CREB or M-CREB, 2 dominant-negative inhibitors of CREB, decreases cell survival and the complexity of neuronal arborization. Similar changes are observed in neurons treated with protein kinase A (PKA) and Ca2+/calmodulin-dependent protein kinase II (CaMKII) inhibitors, which also show decreased levels of pCREBSer133. Notably, expression of CREB-FY, a Tyr134Phe CREB mutant with a lower Km for phosphorylation, partly rescues the effects of PKA and CaMKII inhibition. Our data indicate that CREB-mediated signaling play important roles at early stages of cortical neuron differentiation, prior to the establishment of fully functional synaptic contacts.

Promotion of Peripheral Nerve Regeneration by Stimulation of the Extracellular Signal-Regulated Kinase (ERK) Pathway

Peripherally projecting neurons undergo significant morphological changes during development and regeneration. This neuroplasticity is controlled by growth factors, which bind specific membrane bound kinase receptors that in turn activate two major intracellular signal transduction cascades. Besides the PI3 kinase/AKT pathway, activated extracellular signal‐regulated kinase (ERK) plays a key role in regulating the mode and speed of peripheral axon outgrowth in the adult stage. Cell culture studies and animal models revealed that ERK signaling is mainly involved in elongative axon growth in vitro and long‐distance nerve regeneration in vivo. Here, we review ERK dependent morphological plasticity in adult peripheral neurons and evaluate the therapeutic potential of interfering with regulators of ERK signaling to promote nerve regeneration. Anat Rec, 302:1261–1267, 2019. © 2019 Wiley Periodicals, Inc.

CDKL5 deficiency predisposes neurons to cell death through the deregulation of SMAD3 signaling

CDKL5 deficiency disorder (CDD) is a rare encephalopathy characterized by early onset epilepsy and severe intellectual disability. CDD is caused by mutations in the X-linked cyclin-dependent kinase-like 5 (CDKL5) gene, a member of a highly conserved family of serine-threonine kinases. Only a few physiological substrates of CDKL5 are currently known, which hampers the discovery of therapeutic strategies for CDD. Here, we show that SMAD3, a primary mediator of TGF-β action, is a direct phosphorylation target of CDKL5 and that CDKL5-dependent phosphorylation promotes SMAD3 protein stability. Importantly, we found that restoration of the SMAD3 signaling through TGF-β1 treatment normalized defective neuronal survival and maturation in Cdkl5 knockout (KO) neurons. Moreover, we demonstrate that Cdkl5 KO neurons are more vulnerable to neurotoxic/excitotoxic stimuli. In vivo treatment with TGF-β1 prevents increased NMDA-induced cell death in hippocampal neurons from Cdkl5 KO mice, suggesting an involvement of the SMAD3 signaling deregulation in the neuronal susceptibility to excitotoxic injury of Cdkl5 KO mice. Our finding reveals a new function for CDKL5 in maintaining neuronal survival that could have important implications for susceptibility to neurodegeneration in patients with CDD.