VGF (TLQP-62)-induced neurogenesis targets early phase neural progenitor cells in the adult hippocampus and requires glutamate and BDNF signaling

VGF is required for recovery after focal stroke

The high incidence of ischemic stroke worldwide and poor efficacy of neuroprotective drugs has increased the need for novel therapies in stroke recovery. Transcription of the neurosecretory protein VGF (non-acronym) is enhanced following ischemic stroke and proposed to be important for stroke recovery. To determine the requirement for VGF in recovery, we created Vgf^fl/fl:Nestin-Cre conditional knockout (Vgf cKO) mice and induced a photothrombotic focal ischemic stroke. Naïve Vgf cKO mice had significant less body weight in the absence of gross defects in brain size, cortical lamination, or deficits in locomotor activity compared to wildtype controls. Following a focal stroke, the Vgf cKO mice had greater deficits including impaired recovery of forepaw motor deficits at 2- and 4-weeks post stroke. The increase in deficits occurred in the absence of any difference in lesion size and was accompanied by a striking loss of stroke-induced migration of SVZ-derived immature neurons to the peri-infarct region. Importantly, exogenous adenoviral delivery of VGF (AdVGF) significantly improved recovery in the Vgf cKO mice and was able to rescue the immature neuron migration defect observed. Taken together, our results define a requirement for VGF in post stroke recovery and identify VGF peptides as a potential future therapeutic.

CSF peptides from VGF and other markers enhance prediction of MCI to AD progression using the ATN framework

The amyloid beta, tau, neurodegenerative markers framework has been proposed to serve as a system to classify and combine biomarkers for Alzheimer's Disease (AD). Although cerebrospinal (CSF) fluid AT (amyloid beta and tau)-based biomarkers have a well-established track record to distinguish AD from control subjects and to predict conversion from mild cognitive impairment (MCI) to AD, there is not an established non-tau based neurodegenerative ("N") marker from CSF. Here, we examine the ability of several candidate peptides in the CSF to serve as "N" markers to both classify disease state and predict MCI to AD conversion. We observed that although many putative N markers involved in synaptic processing and neuroinflammation were able to, when examined in isolation, distinguish MCI converters from non-converters, a derivative from VGF, when combined with AT markers, most strongly enhanced prediction of MCI to AD conversion. Low CSF VGF levels were also predictive of MCI to dementia conversion in the setting of normal AT markers, suggesting that it may serve as a very early predictor of dementia conversion. Other markers derived from neuronal pentraxin 2, GAP-43 and a 14-3-3 protein were also able to enhance MCI to AD prediction when used as a marker of neurodegeneration, but VGF had the highest predictive capacity. Thus, we propose that low levels of VGF in CSF may serve as "N" in the amyloid beta, tau, neurodegenerative markers framework to enhance the prediction of MCI to AD conversion.

ERK1/2-dependent BDNF synthesis and signaling is required for the antidepressant effect of microglia stimulation

Depressed mice have lower numbers of microglia in the dentate gyrus (DG). Reversal of this decline by a single low dose of lipopolysaccharide (LPS) may have antidepressant effects, but there is little information on the molecular mechanisms underlying this effect. It is known that impairment of brain-derived neurotrophic factor (BDNF) signaling is involved in the development of depression. Here, we used a combination of neutralizing antibodies, mutant mice, and pharmacological approaches to test the role of BDNF-tyrosine kinase receptor B (TrkB) signaling in the DG in the effect of microglial stimulation. Our results suggest that inhibition of BDNF signaling by infusion of an anti-BDNF antibody, the BDNF receptor antagonist K252a, or knock-in of the mutant BDNF Val68Met allele abolished the antidepressant effect of LPS in chronically stressed mice. Increased BDNF synthesis in DG, mediated by extracellular signal-regulated kinase1/2 (ERK1/2) signaling but not protein kinase B (Akt)-mammalian target of rapamycin (mTOR) signaling, was essential for the antidepressant effect of microglial stimulation. These results suggest that increased BDNF synthesis through activation of ERK1/2 caused by a single LPS injection and subsequent TrkB signaling are required for the antidepressant effect of hippocampal microglial stimulation.

Neurotrophin Crosstalk in the Etiology and Treatment of Neuropsychiatric and Neurodegenerative Disease

This article reviews the current progress in our understanding of the mechanisms by which growth factors, including brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF), and select neurotrophin-regulated gene products, such as VGF (non-acronymic) and VGF-derived neuropeptides, function in the central nervous system (CNS) to modulate neuropsychiatric and neurodegenerative disorders, with a discussion of the possible therapeutic applications of these growth factors to major depressive disorder (MDD) and Alzheimer’s disease (AD). BDNF and VEGF levels are generally decreased regionally in the brains of MDD subjects and in preclinical animal models of depression, changes that are associated with neuronal atrophy and reduced neurogenesis, and are reversed by conventional monoaminergic and novel ketamine-like antidepressants. Downstream of neurotrophins and their receptors, VGF was identified as a nerve growth factor (NGF)- and BDNF-inducible secreted protein and neuropeptide precursor that is produced and trafficked throughout the CNS, where its expression is greatly influenced by neuronal activity and exercise, and where several VGF-derived peptides modulate neuronal activity, function, proliferation, differentiation, and survival. Moreover, levels of VGF are reduced in the CSF of AD subjects, where it has been repetitively identified as a disease biomarker, and in the hippocampi of subjects with MDD, suggesting possible shared mechanisms by which reduced levels of VGF and other proteins that are similarly regulated by neurotrophin signaling pathways contribute to and potentially drive the pathogenesis and progression of co-morbid neuropsychiatric and neurodegenerative disorders, particularly MDD and AD, opening possible therapeutic windows.

VGF: A prospective biomarker and therapeutic target for neuroendocrine and nervous system disorders

Neuroendocrine regulatory polypeptide VGF (nerve growth factor inducible) was firstly found in the rapid induction of nerve growth factor on PC12 cells. It was selectively distributed in neurons and many neuroendocrine tissues. This paper reviewed the latest literatures on the gene structure, transcriptional regulation, protein processing, distribution and potential receptors of VGF. The neuroendocrine roles of VGF and its derived polypeptides in regulating energy, water electrolyte balance, circadian rhythm and reproductive activities were also summarized. Furthermore, based on the experimental evidence in vivo and in vitro, dysregulation of VGF in different neuroendocrine diseases and the possible mechanism mediated by VGF polypeptides were discussed. We next discussed the potential as the clinical diagnosis and therapy for VGF related diseases in the future.

Thalamocortical axons regulate neurogenesis and laminar fates in the early sensory cortex

This study addresses how the cerebral cortex is partitioned into specialized areas during development. Although both early embryonic patterning and postnatal synaptic input from sensory thalamic nuclei are known to be critical, early roles of thalamic axons in area-specific regulation of cortical neurogenesis are poorly understood. We examined this by developing a genetic mouse model in which thalamocortical projections fail to properly form during embryogenesis, and found these axons are required not only for an enhanced production of superficial layer neurons but also for promoting the layer 4 cell fate, a hallmark of the primary sensory cortex. These findings provide a mechanism by which thalamocortical axons complement the intrinsic programs of neurogenesis and early fate specification.

Area-specific axonal projections from the mammalian thalamus shape unique cellular organization in target areas in the adult neocortex. How these axons control neurogenesis and early neuronal fate specification is poorly understood. By using mutant mice lacking the majority of thalamocortical axons, we show that these axons are required for the production and specification of the proper number of layer 4 neurons in primary sensory areas by the neonatal stage. Part of these area-specific roles is played by the thalamus-derived molecule, VGF. Our work reveals that extrinsic cues from sensory thalamic projections have an early role in the formation of cortical cytoarchitecture by enhancing the production and specification of layer 4 neurons.

Effects of Septin-14 Gene Deletion on Adult Cognitive/Emotional Behavior

While various septin GTPases have been reported for their physiological functions, their roles in orchestrating complex cognitive/emotional functions in adult mammals remained scarcely explored. A comprehensive behavioral test battery was administered to two sexes of 12-week-old Septin-14 (SEPT14) knockout (KO) and wild-type (WT) mice. The sexually dimorphic effects of brain SEPT14 KO on inhibitory avoidance (IA) and hippocampal mGluR5 expression were noticed with greater IA latency and elevated mGluR5 level exclusively in male KO mice. Moreover, SEPT14 KO appeared to be associated with stress-provoked anxiety increase in a stress-related navigation task regardless of animals’ sexes. While male and female WT mice demonstrated comparable cell proliferation in the dorsal and ventral hippocampal dentate gyrus (DG), both sexes of SEPT14 KO mice had increased cell proliferation in the ventral DG. Finally, male and female SEPT14 KO mice displayed dampened observational fear conditioning magnitude and learning-provoked corticosterone secretion as compared to their same-sex WT mice. These results, taken together, prompt us to conclude that male, but not female, mice lacking the Septin-14 gene may exhibit increased aversive emotion-related learning and dorsal/ventral hippocampal mGluR5 expressions. Moreover, deletion of SEPT14 may be associated with elevated ventral hippocampal DG cell proliferation and stress-provoked anxiety-like behavior, while dampening vicarious fear conditioning magnitudes.

Potentials of Neuropeptides as Therapeutic Agents for Neurological Diseases

Despite recent leaps in modern medicine, progress in the treatment of neurological diseases remains slow. The near impermeable blood-brain barrier (BBB) that prevents the entry of therapeutics into the brain, and the complexity of neurological processes, limits the specificity of potential therapeutics. Moreover, a lack of etiological understanding and the irreversible nature of neurological conditions have resulted in low tolerability and high failure rates towards existing small molecule-based treatments. Neuropeptides, which are small proteinaceous molecules produced by the body, either in the nervous system or the peripheral organs, modulate neurological function. Although peptide-based therapeutics originated from the treatment of metabolic diseases in the 1920s, the adoption and development of peptide drugs for neurological conditions are relatively recent. In this review, we examine the natural roles of neuropeptides in the modulation of neurological function and the development of neurological disorders. Furthermore, we highlight the potential of these proteinaceous molecules in filling gaps in current therapeutics.

Could VGF and/or its derived peptide act as biomarkers for the diagnosis of neurodegenerative diseases: A systematic review

BACKGROUND

The increasing ageing population has led to an increase in the prevalence of neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). However, as yet, there are no simple biomarkers to predict the onset of such diseases. Recently, VGF and its peptides have been highlighted in neurodegenerative diseases. VGF (non-acronymic) is a polypeptide induced in PC12 cells by neurotrophic factors.

OBJECTIVE

This systematic review aimed to determine whether VGF and/or its derived peptides can be used as biomarkers for the diagnosis of ALS, PD, and AD with specific attention to (1) the levels of VGF and/or its derived peptides, (2) amyloid-beta, (3) dopamine, and (4) cognitive score.

METHODOLOGY

A search was undertaken in the Ovid EMBASE, Cochrane Library, PubMed, Scopus, and Web of Science for observational studies. Publications that assessed the level of VGF and/or its derived peptides among people with neurodegenerative diseases and compared them with healthy people were included. The quality of the included studies was assessed using the National Heart, Lung, and Blood Institute Quality Assessment Tool.

RESULT

A search of the databases yielded 834 studies, of which, eight observational studies met the inclusion criteria with a total of 673 participants (51.7% males) aged >18 years. Seven studies showed significant decreases in VGF and its derived peptides in adults with AD, PD, and ALS compared to healthy controls (p<0.05). However, one study showed that there was no significant difference in VGF in AD compared to healthy control(p>0.05). Furthermore, only one study reported that VGF levels were positively correlated with those of tissue dopamine but not with Aβ1-42, and low levels of VGF were associated to cognitive deficits.

CONCLUSION

The use of VGF and its derivatives for the diagnosis of PD, ALS, AD remains unclear, so further investigation of the role of VGF in neurodegenerative diseases and pathophysiology is needed to provide new insights.

Fluoride Stimulates Anxiety- and Depression-like Behaviors Associated with SIK2-CRTC1 Signaling Dysfunction

Using Sprague-Dawley rats and rat PC12 cells treated with sodium fluoride (NaF), we investigated the effects of SIK2-CRTC1 signaling on the neurobehavioral toxicity induced by fluoride. The in vivo results demonstrated that NaF treatment induced anxiety- and depression-like behaviors in juvenile rats, resulting in histological and ultrastructural abnormalities in the rat hippocampus and medial prefrontal cortex. Moreover, NaF exposure induced neuronal loss and excessive apoptosis. We also found that NaF elevated the expression of SIK2 and reduced the expression of CRTC1, brain-derived neurotrophic factor (BDNF), and VGF. The in vitro results showed that NaF suppressed cell viability, induced SIK2-CRTC1 signaling dysfunction, and caused excessive apoptosis in PC12 cells. Notably, targeted knockout of SIK2 with SIK2-siRNA or blocking of SIK2-CRTC1 signaling with 7,8-dihydroxyflavone (7,8-DHF) (as well as venlafaxine) can reduce apoptosis and increase cell viability in vitro. These findings suggest that neuronal death resulting from abnormal SIK2-CRTC1 signaling contributes to neurobehavioral toxicity induced by fluoride.

Trophic factors as potential therapies for treatment of major mental disorders

Notwithstanding major advances in psychotherapeutics, their efficacy and specificity remain limited. The slow onset of beneficial outcomes and numerous adverse effects of widely used medications remain of chief concern, warranting in-depth studies. The majority of frontline therapies are thought to enhance the endogenous monoaminergic drive, to initiate a cascade of molecular events leading to lasting functional and structural plasticity. They also involve alterations in trophic factor signalling, including brain-derived neurotrophic factor (BDNF), VGF (non-acronymic), vascular endothelial growth factor (VEGF), fibroblast growth factor 2 (FGF2), glial cell-derived neurotrophic factor (GDNF), and others. In several major mental disorders, emerging data suggest protective and restorative effects of trophic factors in preclinical models, when applied on their own. Antidepressant outcomes of VGF and FGF2, for instance, were shown in experimental animals, while BDNF and GDNF prove useful in the treatment of addiction, schizophrenia, and autism spectrum disorders. The main challenge with the effective translation of these and other findings in the clinic is the knowledge gap in action mechanisms with potential risks, as well as the lack of effective platforms for validation under clinical settings. Herein, we review the state-of-the-art and advances in the therapeutic use of trophic factors in several major neuropsychiatric disorders.

VGF as a biomarker and therapeutic target in neurodegenerative and psychiatric diseases

Neurosecretory protein VGF (non-acronymic) belongs to the granin family of neuropeptides. VGF and VGF-derived peptides have been repeatedly identified in well-powered and well-designed multi-omic studies as dysregulated in neurodegenerative and psychiatric diseases. New therapeutics is urgently needed for these devastating and costly diseases, as are new biomarkers to improve disease diagnosis and mechanistic understanding. From a list of 537 genes involved in Alzheimer's disease pathogenesis, VGF was highlighted by the Accelerating Medicines Partnership in Alzheimer's disease as the potential therapeutic target of greatest interest. VGF levels are consistently decreased in brain tissue and CSF samples from patients with Alzheimer's disease compared to controls, and its levels correlate with disease severity and Alzheimer's disease pathology. In the brain, VGF exists as multiple functional VGF-derived peptides. Full-length human VGF1-615 undergoes proteolytic processing by prohormone convertases and other proteases in the regulated secretory pathway to produce at least 12 active VGF-derived peptides. In cell and animal models, these VGF-derived peptides have been linked to energy balance regulation, neurogenesis, synaptogenesis, learning and memory, and depression-related behaviours throughout development and adulthood. The C-terminal VGF-derived peptides, TLQP-62 (VGF554-615) and TLQP-21 (VGF554-574) have differential effects on Alzheimer's disease pathogenesis, neuronal and microglial activity, and learning and memory. TLQP-62 activates neuronal cell-surface receptors and regulates long-term hippocampal memory formation. TLQP-62 also prevents immune-mediated memory impairment, depression-like and anxiety-like behaviours in mice. TLQP-21 binds to microglial cell-surface receptors, triggering microglial chemotaxis and phagocytosis. These actions were reported to reduce amyloid-β plaques and decrease neuritic dystrophy in a transgenic mouse model of familial Alzheimer's disease. Expression differences of VGF-derived peptides have also been associated with frontotemporal lobar dementias, amyotrophic lateral sclerosis, Lewy body diseases, Huntington's disease, pain, schizophrenia, bipolar disorder, depression and antidepressant response. This review summarizes current knowledge and highlights questions for future investigation regarding the roles of VGF and its dysregulation in neurodegenerative and psychiatric disease. Finally, the potential of VGF and VGF-derived peptides as biomarkers and novel therapeutic targets for neurodegenerative and psychiatric diseases is highlighted.

A Review of Brain-Targeted Nonviral Gene-Based Therapies for the Treatment of Alzheimer's Disease

Diseases of the central nervous system (CNS) are difficult to treat owing to the complexity of the brain and the presence of a natural blood-brain-barrier (BBB). Alzheimer's disease (AD) is one of the major progressive and currently incurable neurodegenerative disorders of the CNS, which accounts for 60-80% of cases of dementia. The pathophysiology of AD involves the accumulation of amyloid beta (Aβ) plaques and neurofibrillary tangles (NFTs) in the brain. Additionally, synaptic loss and imbalance of neuronal signaling molecules are characterized as important markers of AD. Existing treatments of AD help in the management of its symptoms and aim toward the maintenance of cognitive functions, behavior, and attenuation of gradual memory loss. Over the past decade, nonviral gene therapy has attracted increasing interest due to its various advantages over its viral counterparts. Moreover, advancements in nonviral gene technology have led to their increasing contributions in clinical trials. However, brain-targeted nonviral gene delivery vectors come across various extracellular and intracellular barriers, limiting their ability to transfer the therapeutic gene into the target cells. Chief barriers to nonviral gene therapy have been discussed briefly in this review. We have also highlighted the rapid advancement of several nonviral gene therapies for AD, which are broadly categorized into physical and chemical methods. These methods aim to modulate Aβ, beta-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1), apolipoprotein E, or neurotrophic factors' expression in the CNS. Overall, this review discusses challenges and recent advancements of nonviral gene therapy for AD.

In vitro and in vivo optimization of liposomal nanoparticles based brain targeted vgf gene therapy

Vgf (non-acronymic), a neurotrophin stimulated protein which plays a crucial role in learning, synaptic activity, and neurogenesis, is markedly downregulated in the brain of Alzheimer's disease (AD) patients. However, since vgf is a large polar protein, a safe and efficient gene delivery vector is critical for its delivery across the blood brain barrier (BBB). This research work demonstrates brain-targeted liposomal nanoparticles optimized for delivering plasmid encoding vgf across BBB and transfecting brain cells. Brain targeting was achieved by surface functionalization using glucose transporter-1 targeting ligand (mannose) and brain targeted cell-penetrating peptides (chimeric rabies virus glycoprotein fragment, rabies virus derived peptide, penetratin peptide, or CGNHPHLAKYNGT peptide). The ligands were conjugated to lipid via nucleophilic substitution reaction resulting in >75% binding efficiency. The liposomes were formed by film hydration technique demonstrating size <200 nm, positive zeta potential (15-20 mV), and polydispersity index <0.3. The bifunctionalized liposomes demonstrated ∼3 pg/µg protein vgf transfection across in vitro BBB, and ∼80 pg/mg protein in mice brain which was 1.5-2 fold (p < 0.05) higher compared to untreated control. The nanoparticles were also biocompatible in vitro and in vivo, suggesting a safe and efficient gene delivery system to treat AD.

Neuro-Signals from Gut Microbiota: Perspectives for Brain Glioma

Glioblastoma (GBM) is the most aggressive form of glioma tumor in adult brain. Among the numerous factors responsible for GBM cell proliferation and invasion, neurotransmitters such as dopamine, serotonin and glutamate can play key roles. Studies performed in mice housed in germ-free (GF) conditions demonstrated the relevance of the gut-brain axis in a number of physiological and pathological conditions. The gut-brain communication is made possible by vagal/nervous and blood/lymphatic routes and pave the way for reciprocal modulation of functions. The gut microbiota produces and consumes a wide range of molecules, including neurotransmitters (dopamine, norepinephrine, serotonin, gamma-aminobutyric acid [GABA], and glutamate) that reach their cellular targets through the bloodstream. Growing evidence in animals suggests that modulation of these neurotransmitters by the microbiota impacts host neurophysiology and behavior, and affects neural cell progenitors and glial cells, along with having effects on tumor cell growth. In this review we propose a new perspective connecting neurotransmitter modulation by gut microbiota to glioma progression.

Multiscale causal networks identify VGF as a key regulator of Alzheimer's disease

Though discovered over 100 years ago, the molecular foundation of sporadic Alzheimer's disease (AD) remains elusive. To better characterize the complex nature of AD, we constructed multiscale causal networks on a large human AD multi-omics dataset, integrating clinical features of AD, DNA variation, and gene- and protein-expression. These probabilistic causal models enabled detection, prioritization and replication of high-confidence master regulators of AD-associated networks, including the top predicted regulator, VGF. Overexpression of neuropeptide precursor VGF in 5xFAD mice partially rescued beta-amyloid-mediated memory impairment and neuropathology. Molecular validation of network predictions downstream of VGF was also achieved in this AD model, with significant enrichment for homologous genes identified as differentially expressed in 5xFAD brains overexpressing VGF. Our findings support a causal role for VGF in protecting against AD pathogenesis and progression.

Human VGF-Derived Antidepressant Neuropeptide TLQP62 Promotes SH-SY5Y Neurite Outgrowth

TLQP62 is a neuropeptide derived from the neurotrophin-inducible VGF (non-acronymic) protein with antidepressant-like properties capable of inducing increased memory on the mouse hippocampus by promoting neurogenesis and synaptic plasticity through brain-derived neurotropic factor (BDNF) and its receptor tyrosine receptor kinase B (TrkB). Human SH-SY5Y neuroblastoma-derived cell line is widely used in neuroscience research and is known to undergo neurodifferentiation in the presence of all-trans retinoic acid by upregulating the expression of TrkB, making cells responsive to BDNF. As TLQP62 promotes BDNF expression, which in turn activates a BDNF/TrkB/CREB (cAMP response element-binding protein) pathway that upregulates VGF expression, there is a VGF-BDNF regulatory loop that seems to regulate neurogenesis. Therefore, here, we evaluate by morphological observation the ability of human TLQP62 to induce neuritogenesis of human SH-SY5Y neuroblastoma-derived cell line in a retinoic acid and BDFN-like way, making this cell line a suitable cell model for further studies concerning TLQP62 molecular mechanisms and signalling pathways. SIGNIFICANCE STATEMENT: VGF has been widely explored for its role in emotional behaviour and neuropsychiatric illness (Bartolomucci et al. 2011). Although VGF levels were found reduced in leukocytes of depressed patients, after antidepressant treatment or voluntary exercise, those levels were found to be restored in the hippocampus (Hunsberger et al. 2007; Thakker-Varia et al. 2007). Administration to hippocampal cells of TLQP62 produced an increase in synaptic charge that could explain this antidepressants effects (Alder et al. 2003). This interesting role of TLQP62 in the brain, especially in the hippocampus, makes this neuropeptide an attractive target for further investigation of its role in neurogenesis, learning, memory, and neurological disorders, and possible treatment development. Thus, the identification of a receptor(s) for this peptide and associated signalling pathway(s) is of high importance, as well as a proper cell model to perform those studies.

CIC is a critical regulator of neuronal differentiation

Capicua (CIC), a member of the high mobility group-box (HMG-box) superfamily of transcriptional repressors, is frequently mutated in human oligodendrogliomas. However, its functions in brain development and tumorigenesis remain poorly understood. Here, we report that brain-specific deletion of Cic compromises developmental transition of neuroblasts to immature neurons in mouse hippocampus and compromises normal neuronal differentiation. Combined gene expression and ChIP-seq analyses identified VGF as an important CIC-repressed transcriptional surrogate involved in neuronal lineage regulation. Aberrant VGF expression promotes neural progenitor cell proliferation by suppressing their differentiation. Mechanistically, we demonstrated that CIC represses VGF expression by tethering SIN3-HDAC to form a transcriptional corepressor complex. Mass spectrometry analysis of CIC-interacting proteins further identified the BRG1-containing mSWI/SNF complex whose function is necessary for transcriptional repression by CIC. Together, this study uncovers a potentially novel regulatory pathway of CIC-dependent neuronal differentiation and may implicate these molecular mechanisms in CIC-dependent brain tumorigenesis.

Transgenic models for investigating the nervous system: Currently available neurofluorescent reporters and potential neuronal markers

Recombinant DNA technologies have enabled the development of transgenic animal models for use in studying a myriad of diseases and biological states. By placing fluorescent reporters under the direct regulation of the promoter region of specific marker proteins, these models can localize and characterize very specific cell types. One important application of transgenic species is the study of the cytoarchitecture of the nervous system. Neurofluorescent reporters can be used to study the structural patterns of nerves in the central or peripheral nervous system in vivo, as well as phenomena involving embryologic or adult neurogenesis, injury, degeneration, and recovery. Furthermore, crucial molecular factors can also be screened via the transgenic approach, which may eventually play a major role in the development of therapeutic strategies against diseases like Alzheimer's or Parkinson's. This review describes currently available reporters and their uses in the literature as well as potential neural markers that can be leveraged to create additional, robust transgenic models for future studies.

Grape-derived polyphenols produce antidepressant effects via VGF- and BDNF-dependent mechanisms

Recent studies suggest that bioactive dietary polyphenol preparation (BDPP) and individual polyphenolic compounds ameliorate stress-induced depression-like behaviors, but the underlying molecular mechanisms are incompletely understood. VGF (non-acronymic) in the dorsal hippocampus (dHc) has been shown to play a role in depression-like behaviors and antidepressant efficacy, and the VGF-derived peptide TLQP-62 (named by the N-terminal 4 amino acids and length) infused into dHc has been shown to have antidepressant efficacy that is BDNF-TrkB dependent. Here, we investigated whether BDPP influences VGF expression in the dHc, and whether dHc VGF is required for BDPP antidepressant efficacy. We found that BDPP produced antidepressant-like effects in naive mice and reversed the depression-like behaviors induced by chronic variable stress. In addition, we found that BDPP had no detectable antidepressant efficacy in floxed mice with prior knockdown in the dHc of either VGF or BDNF, achieved by adeno-associated virus-Cre infusion. Our data indicate that dHc VGF and BDNF expression are required for the antidepressant actions of BDPP, and therefore suggest that a VGF(TLQP-62)-BDNF-TrkB autoregulatory feedback loop could play a role in the regulation of BDPP antidepressant efficacy, much as it has been suggested to function in the antidepressant efficacies of ketamine and TLQP-62.

VGF in Cerebrospinal Fluid Combined With Conventional Biomarkers Enhances Prediction of Conversion From MCI to AD

BACKGROUND

Previous work has suggested that the brain and cerebrospinal fluid (CSF) levels of a neural protein involved in synaptic transmission, VGF (a noninitialism), may be altered in mild cognitive impairment (MCI) and Alzheimer Disease (AD). The objective of the current work is to examine the potential of CSF levels of a peptide derived from VGF to predict conversion from MCI to AD.

MATERIALS AND METHODS

Using multivariate analytical approaches, the performance of the conventional biomarkers (CSF Aβ1-42 and phosphorylated tau +/- hippocampal volume) was compared with the same biomarkers combined with CSF VGF peptide levels in a large publicly available data set from human subjects.

RESULTS

It was observed that VGF peptides are lowered in CSF of patients with AD compared with controls and that combinations of CSF Aβ1-42 and phosphorylated tau, hippocampal volume, and VGF peptide levels outperformed conventional biomarkers alone (hazard ratio=2.2 vs. 3.9), for predicting MCI to AD conversion.

CONCLUSIONS

CSF VGF enhances the ability of conventional biomarkers to predict MCI to AD conversion. Future work will be needed to determine the specificity of VGF for AD versus other neurodegenerative diseases.

VGF: a biomarker and potential target for the treatment of neuropathic pain?

Supplemental Digital Content is Available in the Text.

Neuropathic pain (NP) remains an area of considerable unmet medical need. A persistent challenge in the management of NP is to target the specific mechanisms leading to a change from normal to abnormal sensory perception while ensuring that the defensive pain perception remains intact. Targeting VGF-derived neuropeptides may offer this opportunity. VGF was first identified in 1985 and is highly expressed after nerve injury and inflammation in neurons of both the peripheral and central nervous system. Subsequent studies implicate the vgf gene and its products in pain pathways. This narrative review was supported by a systematic search to identify, select, and critically appraise all relevant research investigating the role of VGF-derived neuropeptides in pain pathways. It predominantly focuses on in vivo investigations of the role of VGF in the initiation and maintenance of NP. VGF expression levels are very low under normal physiological conditions and nerve injury results in rapid and robust upregulation, increasing mechanical and thermal hypersensitivity. The identification of the 2 complement receptors with which VGF neuropeptides interact suggests a novel interplay of neuronal and immune signalling mediators. The understanding of the molecular mechanisms and signalling events by which VGF-derived active neuropeptides exert their physiological actions is in its infancy. Future work should aim to improve understanding of the downstream consequences of VGF neuropeptides thereby providing novel insights into pain mechanisms potentially leading to the identification of novel therapeutic targets.

VGF and its C-terminal peptide TLQP-62 in ventromedial prefrontal cortex regulate depression-related behaviors and the response to ketamine

Patients with major depressive disorder (MDD) often have structural and functional deficits in the ventromedial prefrontal cortex (vmPFC), but the underlying molecular pathways are incompletely understood. The neuropeptide precursor VGF (non-acronymic) plays a critical role in depression and antidepressant efficacy in hippocampus and nucleus accumbens, however its function in vmPFC has not been investigated. Here, we show that VGF levels were reduced in Brodmann area 25 (a portion of human vmPFC) of MDD patients and in mouse vmPFC following chronic restraint stress (CRS), and were increased by ketamine in mouse vmPFC. VGF overexpression in vmPFC prevented behavioral deficits induced by CRS, and VGF knockdown in vmPFC increased susceptibility to subchronic variable stress (SCVS) and reduced ketamine's antidepressant efficacy. Acute intra-vmPFC TLQP-62 infusion induced behavioral phenotypes that mimic those produced by antidepressant drug treatment. These antidepressant-like effects were sustained for 7 days and were abolished by local Bdnf gene ablation, or pretreatment with xestospongin C, an inhibitor of IP₃-mediated Ca²⁺ release, or SKF96365, an inhibitor of store-operated and TRPC channel-mediated Ca²⁺ entry. In conclusion, VGF in the vmPFC regulates susceptibility to stress and the antidepressant response to ketamine. TLQP-62 infusion produces sustained antidepressant responses that require BDNF expression and calcium mobilization in vmPFC.

Involvement of the VGF-derived peptide TLQP-62 in nerve injury-induced hypersensitivity and spinal neuroplasticity

Neuroplasticity in the dorsal horn after peripheral nerve damage contributes critically to the establishment of chronic pain. The neurosecretory protein VGF (nonacronymic) is rapidly and robustly upregulated after nerve injury, and therefore, peptides generated from it are positioned to serve as signals for peripheral damage. The goal of this project was to understand the spinal modulatory effects of the C-terminal VGF-derived peptide TLQP-62 at the cellular level and gain insight into the function of the peptide in the development of neuropathic pain. In a rodent model of neuropathic pain, we demonstrate that endogenous levels of TLQP-62 increased in the spinal cord, and its immunoneutralization led to prolonged attenuation of the development of nerve injury-induced hypersensitivity. Using multiphoton imaging of submaximal glutamate-induced Ca responses in spinal cord slices, we demonstrate the ability of TLQP-62 to potentiate glutamatergic responses in the dorsal horn. We further demonstrate that the peptide selectively potentiates responses of high-threshold spinal neurons to mechanical stimuli in singe-unit in vivo recordings. These findings are consistent with a function of TLQP-62 in spinal plasticity that may contribute to central sensitization after nerve damage.

Higher serum VGF protein levels discriminate bipolar depression from major depressive disorder

Misdiagnosis between major depressive disorder (MDD) and bipolar depression (BD) is quite common. Our previous study found significantly lower serum VGF (non-acronymic) in MDD patients. However, it is unclear whether same changes occur in BD patients. Therefore, we aimed to investigate the relationship between serum VGF levels in BD and MDD patients. General information, scores of 17-item Hamilton Depression Rating Scale (HDRS), and fasting blood samples of all participants including 30 MDD patients, 20 BD patients, and 30 healthy controls (HC) were collected. Serum VGF levels were measured by Enzyme-linked immunosorbent assay kits. Pearson correlation analysis was used to analyze correlations between serum VGF levels and clinical information. Receiver operating characteristic (ROC) curve and likelihood ratios (LRs) were used to analyze the differential potential of serum VGF. Serum VGF levels were significantly lower in MDD patients but higher in BD patients compared with HC (both P_Tukey < 0.01). No correlation was found between serum VGF levels and any data of subjects. The optimal cutoff for serum VGF in discriminating BD patients from MDD patients was ≥1093.85 pg/ml (AUC = 0.990, sensitivity of 95%, specificity of 100% and accuracy of 95%). LRs further confirmed the differential efficiency of serum VGF in distinguishing BD and MDD patients with +LR of infinity and -LR of 0. The results suggest that serum VGF level changed significantly in MDD and BD patients and serum VGF may be an indicator for differentiating BD patients from MDD patients.

Impaired Cerebellar Development in Mice Overexpressing VGF

VGF nerve growth factor inducible (VGF) is a neuropeptide precursor induced by brain-derived neurotrophic factor and nerve growth factor. VGF is increased in the prefrontal cortex and cerebrospinal fluid in schizophrenia patients. In our previous study, VGF-overexpressing mice exhibited schizophrenia-like behaviors and smaller brain weights. Brain developmental abnormality is one cause of mental illness. Research on brain development is important for discovery of pathogenesis of mental disorders. In the present study, we investigated the role of VGF on cerebellar development. We performed a histological analysis with cerebellar sections of adult and postnatal day 3 mice by Nissl staining. To investigate cerebellar development, we performed immunostaining with antibodies of immature and mature granule cell markers. To understand the mechanism underlying these histological changes, we examined MAPK, Wnt, and sonic hedgehog signaling by Western blot. Finally, we performed rotarod and footprint tests using adult mice to investigate motor function. VGF-overexpressing adult mice exhibited smaller cerebellar sagittal section area. In postnatal day 3 mice, a cerebellar sagittal section area reduction of the whole cerebellum and external granule layer and a decrease in the number of mature granule cells were found in VGF-overexpressing mice. Additionally, the number of proliferative granule cell precursors was lower in VGF-overexpressing mice. Phosphorylation of Trk and Erk1 were increased in the cerebellum of postnatal day 3 VGF-overexpressing mice. Adult VGF-overexpressing mice exhibited motor disability. All together, these findings implicate VGF in the development of cerebellar granule cells via promoting MAPK signaling and motor function in the adult stage.

VGF nerve growth factor inducible is involved in retinal ganglion cells death induced by optic nerve crush

VGF nerve growth factor inducible (VGF) is a polypeptide that is induced by neurotrophic factors and is involved in neurite growth and neuroprotection. The mRNA of the Vgf gene has been detected in the adult rat retina, however the roles played by VGF in the retina are still undetermined. Thus, the purpose of this study was to determine the effects of VGF on the retinal ganglion cells (RGCs) of mice in the optic nerve crush (ONC) model, rat-derived primary cultured RGCs and human induced pluripotent stem cells (iPSCs)-derived RGCs. The mRNA and protein of Vgf were upregulated after the ONC. Immunostaining showed that the VGF was located in glial cells including Müller glia and astrocytes but not in the retinal neurons and their axons. AQEE-30, a VGF peptide, suppressed the loss of RGCs induced by the ONC, and it increased survival rat-derived RGCs and promoted the outgrowth of neurites of rat and human iPSCs derived RGCs in vitro. These findings indicate that VGF plays important roles in neuronal degeneration and has protective effects against the ONC on RGCs. Thus, VGF should be considered as a treatment of RGCs degeneration.

The Molecular and Neuropathological Consequences of Genetic Risk for Alzheimer's Dementia

Alzheimer's dementia commonly impacts the health of older adults and lacks any preventative therapy. While Alzheimer's dementia risk has a substantial genetic component, the specific molecular mechanisms and neuropathologies triggered by most of the known genetic variants are unclear. Resultantly, they have shown limited influence on drug development portfolios to date. To facilitate our understanding of the consequences of Alzheimer's dementia susceptibility variants, we examined their relationship to a wide range of clinical, molecular and neuropathological features. Because the effect size of individual variants is typically small, we utilized a polygenic (overall) risk approach to identify the global impact of Alzheimer's dementia susceptibility variants. Under this approach, each individual has a polygenic risk score (PRS) that we related to clinical, molecular and neuropathological phenotypes. Applying this approach to 1,272 individuals who came to autopsy from one of two longitudinal aging cohorts, we observed that an individual's PRS was associated with cognitive decline and brain pathologies including beta-amyloid, tau-tangles, hippocampal sclerosis, and TDP-43, MIR132, four proteins including VGF, IGFBP5, and STX1A, and many chromosomal regions decorated with acetylation on histone H3 lysine 9 (H3K9Ac). While excluding the APOE/TOMM40 region (containing the single largest genetic risk factor for late-onset Alzheimer's dementia) in the calculation of the PRS resulted in a slightly weaker association with the molecular signatures, results remained significant. These PRS-associated brain pathologies and molecular signatures appear to mediate genetic risk, as they attenuated the association of the PRS with cognitive decline. Notably, the PRS induced changes in H3K9Ac throughout the genome, implicating it in large-scale chromatin changes. Thus, the PRS for Alzheimer's dementia (AD-PRS) showed effects on diverse clinical, molecular, and pathological systems, ranging from the epigenome to specific proteins. These convergent targets of a large number of genetic risk factors for Alzheimer's dementia will help define the experimental systems and models needed to test therapeutic targets, which are expected to be broadly effective in the aging population that carries diverse genetic risks for Alzheimer's dementia.

A Peptidomic Approach to Characterize Peptides Involved in Cerebellar Cortex Development Leads to the Identification of the Neurotrophic Effects of Nociceptin

The cerebellum is a brain structure involved in motor and cognitive functions. The development of the cerebellar cortex (the external part of the cerebellum) is under the control of numerous factors. Among these factors, neuropeptides including PACAP or somatostatin modulate the survival, migration and/or differentiation of cerebellar granule cells. Interestingly, such peptides contributing to cerebellar ontogenesis usually exhibit a specific transient expression profile with a low abundance at birth, a high expression level during the developmental processes, which take place within the first two postnatal weeks in rodents, and a gradual decline toward adulthood. Thus, to identify new peptides transiently expressed in the cerebellum during development, rat cerebella were sampled from birth to adulthood, and analyzed by a semi-quantitative peptidomic approach. A total of 33 peptides were found to be expressed in the cerebellum. Among these 33 peptides, 8 had a clear differential expression pattern during development, 4 of them i.e. cerebellin 2, nociceptin, somatostatin and VGF [353-372], exhibiting a high expression level during the first two postnatal weeks followed by a significative decrease at adulthood. A focus by a genomic approach on nociceptin, confirmed that its precursor mRNA is transiently expressed during the first week of life in granule neurons within the internal granule cell layer of the cerebellum, and showed that the nociceptin receptor is also actively expressed between P8 and P16 by the same neurons. Finally, functional studies revealed a new role for nociceptin, acting as a neurotrophic peptide able to promote the survival and differentiation of developing cerebellar granule neurons.

Role of a VGF/BDNF/TrkB Autoregulatory Feedback Loop in Rapid-Acting Antidepressant Efficacy

Members of the neurotrophin family and in particular brain-derived neurotrophic factor (BDNF) regulate the response to rapid- and slow-acting chemical antidepressants and voluntary exercise. Recent work suggests that rapid-acting antidepressants that modulate N-methyl-D-aspartate receptor (NMDA-R) signaling (e.g., ketamine and GLYX-13) require expression of VGF (non-acronymic), the BDNF-inducible secreted neuronal protein and peptide precursor, for efficacy. In addition, the VGF-derived C-terminal peptide TLQP-62 (named by its 4 N-terminal amino acids and length) has antidepressant efficacy following icv or intra-hippocampal administration, in the forced swim test (FST). Similar to ketamine, the rapid antidepressant actions of TLQP-62 require BDNF expression, mTOR activation (rapamycin-sensitive), and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor activation (NBQX-sensitive) and are associated with GluR1 insertion. We review recent findings that identify a rapidly induced autoregulatory feedback loop, which likely plays a critical role in sustained efficacy of rapid-acting antidepressants, depression-like behavior, and cognition, and requires VGF, its C-terminal peptide TLQP-62, BDNF/TrkB signaling, the mTOR pathway, and AMPA receptor activation and insertion.

VGF function in depression and antidepressant efficacy

Brain-derived neurotrophic factor (BDNF) is a critical effector of depression-like behaviors and antidepressant responses. Here, we show that VGF (non-acronymic), which is robustly regulated by BDNF/TrkB signaling, is downregulated in hippocampus (male/female) and upregulated in nucleus accumbens (NAc) (male) in depressed human subjects and in mice subjected to chronic social defeat stress (CSDS). Adeno-associated virus (AAV)-Cre-mediated Vgf ablation in floxed VGF mice, in dorsal hippocampus (dHc) or NAc, led to pro-depressant or antidepressant behaviors, respectively, while dHc- or NAc-AAV-VGF overexpression induced opposite outcomes. Mice with reduced VGF levels in the germ line (Vgf+/-) or in dHc (AAV-Cre-injected floxed mice) showed increased susceptibility to CSDS and impaired responses to ketamine treatment in the forced swim test. Floxed mice with conditional pan-neuronal (Synapsin-Cre) but not those with forebrain (αCaMKII-Cre) Vgf ablation displayed increased susceptibility to subthreshold social defeat stress, suggesting that neuronal VGF, expressed in part in inhibitory interneurons, regulates depression-like behavior. Acute antibody-mediated sequestration of VGF-derived C-terminal peptides AQEE-30 and TLQP-62 in dHc induced pro-depressant effects. Conversely, dHc TLQP-62 infusion had rapid antidepressant efficacy, which was reduced in BDNF floxed mice injected in dHc with AAV-Cre, and in NBQX- and rapamycin-pretreated wild-type mice, these compounds blocking α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor and mammalian target of rapamycin (mTOR) signaling, respectively. VGF is therefore a critical modulator of depression-like behaviors in dHc and NAc. In hippocampus, the antidepressant response to ketamine is associated with rapid VGF translation, is impaired by reduced VGF expression, and as previously reported, requires coincident, rapid BDNF translation and release.

TLQP Peptides in Amyotrophic Lateral Sclerosis: Possible Blood Biomarkers with a Neuroprotective Role

While the VGF-derived TLQP peptides have been shown to prevent neuronal apoptosis, and to act on synaptic strengthening, their involvement in Amyotrophic Lateral Sclerosis (ALS) remains unclarified. We studied human ALS patients' plasma (taken at early to late disease stages) and primary fibroblast cultures (patients vs controls), in parallel with SOD1-G93A transgenic mice (taken at pre-, early- and late symptomatic stages) and the mouse motor neuron cell line (NSC-34) treated with Sodium Arsenite (SA) to induce oxidative stress. TLQP peptides were measured by enzyme-linked immunosorbent assay, in parallel with gel chromatography characterization, while their localization was studied by immunohistochemistry. In controls, TLQP peptides, including forms compatible with TLQP-21 and 62, were revealed in plasma and spinal cord motor neurons, as well as in fibroblasts and NSC-34 cells. TLQP peptides were reduced in ALS patients' plasma starting in the early disease stage (14% of controls) and remaining so at the late stage (16% of controls). In mice, a comparable pattern of reduction was shown (vs wild type), in both plasma and spinal cord already in the pre-symptomatic phase (about 26% and 70%, respectively). Similarly, the levels of TLQP peptides were reduced in ALS fibroblasts (31% of controls) and in the NSC-34 treated with Sodium Arsenite (53% of decrease), however, the exogeneous TLQP-21 improved cell viability (SA-treated cells with TLQP-21, vs SA-treated cells only: about 83% vs. 75%). Hence, TLQP peptides, reduced upon oxidative stress, are suggested as blood biomarkers, while TLQP-21 exerts a neuroprotective activity.

The dose makes the poison: from glutamate-mediated neurogenesis to neuronal atrophy and depression

Experimental evidence has demonstrated that glutamate is an essential factor for neurogenesis, whereas another line of research postulates that excessive glutamatergic neurotransmission is associated with the pathogenesis of depression. The present review shows that such paradox can be explained within the framework of hormesis, defined as biphasic dose responses. Low glutamate levels activate adaptive stress responses that include proteins that protect neurons against more severe stress. Conversely, abnormally high levels of glutamate, resulting from increased release and/or decreased removal, cause neuronal atrophy and depression. The dysregulation of the glutamatergic transmission in depression could be underlined by several factors including a decreased inhibition (γ-aminobutyric acid or serotonin) or an increased excitation (primarily within the glutamatergic system). Experimental evidence shows that the activation of N-methyl-D-aspartate receptor (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors (AMPAR) can exert two opposite effects on neurogenesis and neuron survival depending on the synaptic or extrasynaptic concentration. Chronic stress, which usually underlies experimental and clinical depression, enhances glutamate release. This overactivates NMDA receptors (NMDAR) and consequently impairs AMPAR activity. Various studies show that treatment with antidepressants decreases plasma glutamate levels in depressed individuals and regulates glutamate receptors by reducing NMDAR function by decreasing the expression of its subunits and by potentiating AMPAR-mediated transmission. Additionally, it has been shown that chronic treatment with antidepressants having divergent mechanisms of action (including tricyclics, selective serotonin reuptake inhibitors, and ketamine) markedly reduced depolarization-evoked glutamate release in the hippocampus. These data, taken together, suggest that the glutamatergic system could be a final common pathway for antidepressant treatments.

Sensorimotor gating deficits and effects of antipsychotics on the hyperactivity in VGF-overexpressing mice

BACKGROUND

VGF nerve growth factor inducible (VGF) is a neuropeptide which is expressed in neuronal cells and endocrine cells. VGF is induced by several neurotrophic factors. The expression level of VGF in patients with schizophrenia is increased in cerebrospinal fluid (CSF) and prefrontal cortex. In our previous study, we generated mice in which the expression level of VGF in the brain was increased. VGF-overexpressing mice exhibited abnormal behaviors including hyperactivity. However, it remains unknown whether VGF-overexpressing mice exhibit the endophenotype of schizophrenia and whether abnormal behaviors in these mice can be improved by antipsychotics.

METHODS

In the present study, we investigated schizophrenia-like behaviors and the responsiveness to antipsychotics in transgenic mice.

RESULTS

VGF-overexpressing mice (1) exhibited prepulse inhibition (PPI) impairment, (2) showed normalized hyperactivity following antipsychotic drug treatment, and (3) showed abnormal responsiveness to haloperidol.

CONCLUSION

Upregulation of VGF may be implicated in the pathophysiology of schizophrenia and abnormalities of dopaminergic signaling.

Neuropeptide VGF C-Terminal Peptide TLQP-62 Alleviates Lipopolysaccharide-Induced Memory Deficits and Anxiety-like and Depression-like Behaviors in Mice: The Role of BDNF/TrkB Signaling

Peripheral inflammatory responses affect central nervous system (CNS) function, manifesting in symptoms of memory deficits, depression, and anxiety. Previous studies have revealed that neuropeptide VGF (nonacronymic) C-terminal peptide TLQP-62 rapidly reinforces brain-derived neurotrophic factor (BDNF)/tropomyosin receptor kinase B (TrkB) signaling, regulating memory consolidation and antidepressant-like action. However, whether it is beneficial for lipopolysaccharide (LPS)-induced neuropsychiatric dysfunction in mice is unknown. Herein, we explored the involvement of BDNF/TrkB signaling and biochemical alterations in inflammatory or oxidative stress markers in the alleviating effects of TLQP-62 on LPS-induced neuropsychiatric dysfunction. The mice were treated with TLQP-62 (2 μg/side) via intracerebroventricular (i.c.v.) injection 1 h before LPS (0.5 mg/kg, i.p.) administration. Our results showed that a single treatment with LPS (0.5 mg/kg, i.p) is sufficient to produce recognition memory deficits (in the novel object recognition test), depression-like behavior (in the forced swim test and sucrose preference test), and anxiety-like behavior (in the elevated zero maze). However, pretreatment with TLQP-62 prevented LPS-induced behavioral dysfunction, neuroinflammatory, and oxidative responses. In addition, our results further demonstrated that a reduction in BDNF expression mediated by BDNF-shRNA lentivirus significantly blocked the effects of TLQP-62, suggesting the critical role of BDNF/TrkB signaling in the neuroprotective effects of TLQP-62 in the mice. In conclusion, TLQP-62 could be a therapeutic approach for neuropsychiatric disorders, which are closely associated with neuroinflammation and oxidative stress.

Behavioral abnormalities with disruption of brain structure in mice overexpressing VGF

VGF nerve growth factor inducible (VGF) is a neuropeptide induced by nerve growth factor and brain-derived neurotrophic factor. This peptide is involved in synaptic plasticity, neurogenesis, and neurite growth in the brain. Patients with depression and bipolar disorder have lower-than-normal levels of VGF, whereas patients with schizophrenia and other cohorts of patients with depression have higher-than-normal levels. VGF knockout mice display behavioral abnormalities such as higher depressive behavior and memory dysfunction. However, it is unclear whether upregulation of VGF affects brain function. In the present study, we generated mice that overexpress VGF and investigated several behavioral phenotypes and the brain structure. These adult VGF-overexpressing mice showed (a) hyperactivity, working memory impairment, a higher depressive state, and lower sociality compared with wild-type mice; (b) lower brain weight without a change in body weight; (c) increased lateral ventricle volume compared with wild-type mice; and (d) striatal morphological defects. These results suggest that VGF may modulate a variety of behaviors and brain development. This transgenic mouse line may provide a useful model for research on mental illnesses.

Tweety-Homolog 1 Drives Brain Colonization of Gliomas

Early and progressive colonization of the healthy brain is one hallmark of diffuse gliomas, including glioblastomas. We recently discovered ultralong (>10 to hundreds of microns) membrane protrusions [tumor microtubes (TMs)] extended by glioma cells. TMs have been associated with the capacity of glioma cells to effectively invade the brain and proliferate. Moreover, TMs are also used by some tumor cells to interconnect to one large, resistant multicellular network. Here, we performed a correlative gene-expression microarray and in vivo imaging analysis, and identified novel molecular candidates for TM formation and function. Interestingly, these genes were previously linked to normal CNS development. One of the genes scoring highest in tests related to the outgrowth of TMs was tweety-homolog 1 (TTYH1), which was highly expressed in a fraction of TMs in mice and patients. Ttyh1 was confirmed to be a potent regulator of normal TM morphology and of TM-mediated tumor-cell invasion and proliferation. Glioma cells with one or two TMs were mainly responsible for effective brain colonization, and Ttyh1 downregulation particularly affected this cellular subtype, resulting in reduced tumor progression and prolonged survival of mice. The remaining Ttyh1-deficient tumor cells, however, had more interconnecting TMs, which were associated with increased radioresistance in those small tumors. These findings imply a cellular and molecular heterogeneity in gliomas regarding formation and function of distinct TM subtypes, with multiple parallels to neuronal development, and suggest that Ttyh1 might be a promising target to specifically reduce TM-associated brain colonization by glioma cells in patients.SIGNIFICANCE STATEMENT In this report, we identify tweety-homolog 1 (Ttyh1), a membrane protein linked to neuronal development, as a potent driver of tumor microtube (TM)-mediated brain colonization by glioma cells. Targeting of Ttyh1 effectively inhibited the formation of invasive TMs and glioma growth, but increased network formation by intercellular TMs, suggesting a functional and molecular heterogeneity of the recently discovered TMs with potential implications for future TM-targeting strategies.

Neuropeptide VGF Promotes Maturation of Hippocampal Dendrites That Is Reduced by Single Nucleotide Polymorphisms

The neuropeptide VGF (non-acronymic) is induced by brain-derived neurotrophic factor and promotes hippocampal neurogenesis, as well as synaptic activity. However, morphological changes induced by VGF have not been elucidated. Developing hippocampal neurons were exposed to VGF through bath application or virus-mediated expression in vitro. VGF-derived peptide, TLQP-62, enhanced dendritic branching, and outgrowth. Furthermore, VGF increased dendritic spine density and the proportion of immature spines. Spine formation was associated with increased synaptic protein expression and co-localization of pre- and postsynaptic markers. Three non-synonymous single nucleotide polymorphisms (SNPs) were selected in human VGF gene. Transfection of N2a cells with plasmids containing these SNPs revealed no relative change in protein expression levels and normal protein size, except for a truncated protein from the premature stop codon, E525X. All three SNPs resulted in a lower proportion of N2a cells bearing neurites relative to wild-type VGF. Furthermore, all three mutations reduced the total length of dendrites in developing hippocampal neurons. Taken together, our results suggest VGF enhances dendritic maturation and that these effects can be altered by common mutations in the VGF gene. The findings may have implications for people suffering from psychiatric disease or other conditions who may have altered VGF levels.

NPAS3 Regulates Transcription and Expression of VGF: Implications for Neurogenesis and Psychiatric Disorders

Neuronal PAS domain protein 3 (NPAS3) and VGF (VGF Nerve Growth Factor (NGF) Inducible) are important for neurogenesis and psychiatric disorders. Previously, we have demonstrated that NPAS3 regulates VGF at the transcriptional level. In this study, VGF (non-acronymic) was found regulated by NPAS3 in neuronal stem cells. However, the underlying mechanism of this regulation remains unclear. The aim of this study was to explore the correlation of NPAS3 and VGF, and their roles in neural cell proliferation, in the context of psychiatric illnesses. First, we focused on the structure of NPAS3, to identify the functional domain of NPAS3. Truncated NPAS3 lacking transactivation domain was also found to activate VGF, which suggested that not only transactivation domain but other structural motifs were also involved in the regulation. Second, Mutated enhancer box (E-box) of VGF promoter showed a significant response to this basic helix-loop-helix (bHLH) transcription factor, which suggested an indirect regulatory mechanism for controlling VGF expression by NPAS3. κB site within VGF promoter was identified for VGF activation induced by NPAS3, apart from direct binding to E-box. Furthermore, ectopically expressed NPAS3 in PC12 cells produced parallel responses for nuclear factor kappa-light-chain-enhancer of activated B cells [NF-κB (P65)] expression, which specifies that NPAS3 regulates VGF through the NF-κB signaling pathway. Over-expression of NPAS3 also enhances the cell proliferation, which can be blocked by knockdown of VGF. Finally, NPAS3 was found to influence proliferation of neural cells through VGF. Therefore, downstream signaling pathways that are responsible for NPAS3-VGF induced proliferation via glutamate receptors were explored. Combining this work and published literature, a potential network composed by NPAS3, NF-κB, Brain-Derived Neurotrophic Factor (BDNF), NGF and VGF, was proposed. This network collectively detailed how NPAS3 connects with VGF and intersected neural cell proliferation, synaptic activity and psychiatric disorders.

Thyroid hormone and vitamin D regulate VGF expression and promoter activity

The Siberian hamster (Phodopus sungorus) survives winter by decreasing food intake and catabolizing abdominal fat reserves, resulting in a sustained, profound loss of body weight. Hypothalamic tanycytes are pivotal for this process. In these cells, short-winter photoperiods upregulate deiodinase 3, an enzyme that regulates thyroid hormone availability, and downregulate genes encoding components of retinoic acid (RA) uptake and signaling. The aim of the current studies was to identify mechanisms by which seasonal changes in thyroid hormone and RA signaling from tanycytes might ultimately regulate appetite and energy expenditure. proVGF is one of the most abundant peptides in the mammalian brain, and studies have suggested a role for VGF-derived peptides in the photoperiodic regulation of body weight in the Siberian hamster. In silico studies identified possible thyroid and vitamin D response elements in the VGF promoter. Using the human neuroblastoma SH-SY5Y cell line, we demonstrate that RA increases endogenous VGF expression (P<0.05) and VGF promoter activity (P<0.0001). Similarly, treatment with 1,25-dihydroxyvitamin D3 increased endogenous VGF mRNA expression (P<0.05) and VGF promoter activity (P<0.0001), whereas triiodothyronine (T3) decreased both (P<0.01 and P<0.0001). Finally, intra-hypothalamic administration of T3 blocked the short day-induced increase in VGF expression in the dorsomedial posterior arcuate nucleus of Siberian hamsters. Thus, we conclude that VGF expression is a likely target of photoperiod-induced changes in tanycyte-derived signals and is potentially a regulator of seasonal changes in appetite and energy expenditure.

Brain recovery mediated by toll-like receptor 4 in rats after intracerebral hemorrhage

Activation of the immune system via toll-like receptor 4 (TLR4) is implicated in both negative and positive processes in the central nervous system, including inflammation and angiogenesis. Whether TLR4 also participates in brain recovery following intracerebral hemorrhage (ICH) has not been investigated. We used the rat model of collagenase-induced ICH to determine whether TLR4 acts as a key regulator of brain recovery in the late phase of injury. After ICH, TLR4 levels in the ipsilateral striatum were significantly higher in the ICH group than in the Sham group on days 1, 3, 7 and 14 after ICH induction. By 14 d, the ICH group showed significantly higher levels of vascular endothelial growth factor, brain-derived neurotrophic factor, and MMP-9 than the Sham group, as well as greater numbers of vessels and BrdU- and DCX-positive cells. All these ICH-induced increases were significantly smaller in the TAK-242 group. The TLR4 antagonist also inhibited the recovery of neurological function after ICH. A TLR4 antagonist reduced ICH-induced neurogenesis and angiogenesis in a rat. These findings suggest that TLR4 may promote brain repair in the late phase of ICH.

The brain-derived neurotrophic factor (BDNF) val66met polymorphism differentially affects performance on subscales of the Wechsler Memory Scale - Third Edition (WMS-III)

Single nucleotide polymorphisms in the brain-derived neurotrophic factor (BDNF) gene and the catechol-O-methyltransferase (COMT) gene influence brain structure and function, as well as cognitive abilities. They are most influential in the hippocampus and prefrontal cortex (PFC), respectively. Recall and recognition are forms of memory proposed to have different neural substrates, with recall having a greater dependence on the PFC and hippocampus. This study aimed to determine whether the BDNF val⁶⁶met or COMT val¹⁵⁸met polymorphisms differentially affect recall and recognition, and whether these polymorphisms interact. A sample of 100 healthy adults was assessed on recall and familiarity-based recognition using the Faces and Family Pictures subscales of the Wechsler Memory Scale – Third Edition (WMS-III). COMT genotype did not affect performance on either task. The BDNF polymorphism (i.e., met carriers relative to val homozygotes) was associated with poorer recall ability, while not influencing recognition. Combining subscale scores in memory tests such as the WMS might obscure gene effects. Our results demonstrate the importance of distinguishing between recall and familiarity-based recognition in neurogenetics research.

The VGF-derived peptide TLQP-62 modulates insulin secretion and glucose homeostasis

Insulin secretion control is critical for glucose homeostasis. Paracrine and autocrine molecules secreted by cells of the islet of Langerhans, as well as by intramural and autonomic neurons, control the release of different hormones that modulate insulin secretion. In pancreatic islets, the abundant presence of the granin protein VGF (nonacronymic; unrelated to VEGF) suggests that some of its proteolytically derived peptides could modulate hormone release. Thus, in the present study, we screened several VGF-derived peptides for their ability to induce insulin secretion, and we identified the VGF C-terminal peptide TLQP-62 as the most effective fragment. TLQP-62 induced a potent increase in basal insulin secretion as well as in glucose-stimulated insulin secretion in several insulinoma cell lines. We found that this peptide stimulated insulin release via increased intracellular calcium mobilization and fast expression of the insulin 1 gene. Moreover, the peripheral injection of TLQP-62 in mice improved glucose tolerance. Together, the present findings suggest that TLQP-62, acting as an endocrine, paracrine, or autocrine factor, can be considered a new, strong insulinotropic peptide that can be targeted for innovative antidiabetic drug discovery programs.

PI3K/AKT/mTOR signaling-mediated neuropeptide VGF in the hippocampus of mice is involved in the rapid onset antidepressant-like effects of GLYX-13

BACKGROUND

VGF (nonacryonimic) and phosphatidylinositol 3-kinase (PI3K)/AKT (also known as protein kinase B, PKB)/mammalian target of rapamycin (mTOR) signaling play pivotal roles in depression. However, whether phosphatidylinositol 3-kinase/AKT/mTOR signaling-mediated VGF participates in rapid-acting antidepressant-like actions of GLYX-13 is unclear.

METHODS

Herein, we evaluated the effects of acute treatment of GLYX-13 (0.5, 5, and 10mg/kg, i.p.) in the forced swim test. In addition, we assessed whether the acute treatment with GLYX-13 reverses the depressive-like behaviors induced by chronic unpredictable mild stress. Furthermore, we determined whether the Vgf knockdown in hippocampus of mice blocks the effects of GLYX-13. Moreover, we also demonstrated the effects of intra-hippocampus infusion of LY294002 (10 nmol/side), a specific phosphatidylinositol 3-kinase inhibitor prior to the treatment of GLYX-13 in the forced swim test. Lastly, whether alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor and mTOR activation involves in the antidepressant-like effects of GLYX-13 was examined.

RESULTS

Our results shown that GLYX-13 dose-dependently reversed the depressive-like behaviors in forced swim test. Additionally, GLYX-13 significantly reversed the downregulation of phosphorylation of AKT, mTOR, and eukaryotic elongation factor 2 as well as VGF induced by chronic unpredictable mild stress in hippocampus. Further, Vgf knockdown in hippocampus of mice significantly blocked the rapid-acting antidepressant-like effects and upregulation on phosphatidylinositol 3-kinase/AKT/mTOR/VGF signaling of GLYX-13. Moreover, intra-hippocampus infusion of LY294002 significantly abolished the antidepressant-like effects and upregulation on phosphatidylinositol 3-kinase/AKT/mTOR/VGF signaling of GLYX-13. Finally, antidepressant-like effects of GLYX-13 required AMPA receptor and mTOR activation, as evidenced by the ability of NBQX and rapamycin to block the effects of GLYX-13, respectively.

CONCLUSIONS

Our results suggest that phosphatidylinositol 3-kinase/AKT/mTOR signaling-mediated VGF in hippocampus may be involved in the antidepressant-like effects of GLYX-13.

Neuroendocrine Role for VGF

The vgf gene (non-acronymic) is highly conserved and was identified on the basis of its rapid induction in vitro by nerve growth factor, although can also be induced by brain-derived neurotrophic factor, and glial-derived growth factor. The VGF gene gives rise to a 68 kDa precursor polypeptide, which is induced robustly, relatively selectively and is synthesized exclusively in neuronal and neuroendocrine cells. Post-translational processing by neuroendocrine specific prohormone convertases in these cells results in the production of a number of smaller peptides. The VGF gene and peptides are widely expressed throughout the brain, particularly in the hypothalamus and hippocampus, in peripheral tissues including the pituitary gland, the adrenal glands, and the pancreas, and in the gastrointestinal tract in both the myenteric plexus and in endocrine cells. VGF peptides have been associated with a number of neuroendocrine roles, and in this review, we aim to describe these roles to highlight the importance of VGF as therapeutic target for a number of disorders, particularly those associated with energy metabolism, pain, reproduction, and cognition.