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

Paeonol alleviates postmenopause-induced neuropsychiatric symptoms through the modulation of GPR30 in ovariectomized mice

ETHNOPHARMACOLOGICAL RELEVANCE

The Moutan cortex (MC), the root bark of Paeonia suffruticosa Anderws (Paeoniaceae), has been historically employed in traditional herbal medicine for addressing women's ailments by replenishing kidney Yin.

AIM OF THE STUDY

We aimed to explore if paeonol, an active constituent of MC, could ameliorate neuropsychiatric symptoms, such as anxiety, depression, and cognitive impairments, associated with post-menopausal syndrome (PMS) in an ovariectomized (OVX) mouse model.

MATERIALS AND METHODS

The experimental design comprised 6 groups, including a sham group, OVX group, paeonol administration groups (3, 10 or 30 mg/kg, p.o.), and an estradiol (E2)-treated positive control group. Behavioral tests including the open field, novel object recognition, Y-maze, elevated plus-maze, splash, and forced swimming tests were conducted. In addition, we investigated the effets of paeonol on the phosphorylated levels of phosphatidylinositol 3-kinase (PI3K), Akt, and mammalian target of rapamycin (mTOR), as well as on the expression levels of G protein-coupled receptor (GPR30) and brain-derived neurotrophic factor (BDNF) in the prefrontal cortex and hippocampus.

RESULTS

Paeonol treatment (10 and 30 mg/kg, p.o.) effectively reversed the cognitive decline in OVX mice, measured by the novel object recognition and Y-maze tests, similar to that in the positive control group. Additionally, it alleviated anxiety- and depressive-like behaviors, as evaluated by the elevated plus-maze test, splash test, and forced swimming test. Paeonol restored GPR30 expression levels in the prefrontal cortex and hippocampus, mirroring the effects of E2 administration. Furthermore, it reversed the reduced expression levels of the PI3K-Akt-mTOR signaling pathway in the prefrontal cortex and hippocampus and increased BDNF expression in the hippocampus of OVX mice.

CONCLUSION

This research suggests that paeonol would be beneficial for alleviating PMS-associated cognitive impairment, anxiety and depression.

Probe-dependent Proximity Profiling (ProPPr) Uncovers Similarities and Differences in Phospho-Tau-Associated Proteomes Between Tauopathies

Tauopathies represent a diverse group of neurodegenerative disorders characterized by the abnormal aggregation of the microtubule-associated protein tau. Despite extensive research, the precise mechanisms underlying the complexity of different types of tau pathology remain incompletely understood. Here we describe an approach for proteomic profiling of aggregate-associated proteomes on slides with formalin-fixed, paraffin-embedded (FFPE) tissue that utilizes proximity labelling upon high preservation of aggregate morphology, which permits the profiling of pathological aggregates regardless of their size. To comprehensively investigate the common and unique protein interactors associated with the variety of tau lesions present across different human tauopathies, Alzheimer's disease (AD), corticobasal degeneration (CBD), Pick's disease (PiD), and progressive supranuclear palsy (PSP), were selected to represent the major tauopathy diseases. Implementation of our widely applicable Probe-dependent Proximity Profiling (ProPPr) strategy, using the AT8 antibody, permitted identification and quantification of proteins associated with phospho-tau lesions in well-characterized human post-mortem tissue. The analysis revealed both common and disease-specific proteins associated with phospho-tau aggregates, highlighting potential targets for therapeutic intervention and biomarker development. Candidate validation through high-resolution co-immunofluorescence of distinct aggregates across disease and control cases, confirmed the association of retromer complex protein VPS35 with phospho-tau lesions across the studied tauopathies. Furthermore, we discovered disease-specific associations of proteins including ferritin light chain (FTL) and the neuropeptide precursor VGF within distinct pathological lesions. Notably, examination of FTL-positive microglia in CBD astrocytic plaques indicate a potential role for microglial involvement in the pathogenesis of these tau lesions. Our findings provide valuable insights into the proteomic landscape of tauopathies, shedding light on the molecular mechanisms underlying tau pathology. This first comprehensive characterization of tau-associated proteomes across different tauopathies enhances our understanding of disease heterogeneity and provides a resource for future functional investigation, as well as development of targeted therapies and diagnostic biomarkers.

The endogenous opioid system in the medial prefrontal cortex mediates ketamine's antidepressant-like actions

Recent studies have implicated the endogenous opioid system in the antidepressant actions of ketamine, but the underlying mechanisms remain unclear. We used a combination of pharmacological, behavioral, and molecular approaches in rats to test the contribution of the prefrontal endogenous opioid system to the antidepressant-like effects of a single dose of ketamine. Both the behavioral actions of ketamine and their molecular correlates in the medial prefrontal cortex (mPFC) are blocked by acute systemic administration of naltrexone, a competitive opioid receptor antagonist. Naltrexone delivered directly into the mPFC similarly disrupts the behavioral effects of ketamine. Ketamine treatment rapidly increases levels of β-endorphin and the expression of the μ-opioid receptor gene (Oprm1) in the mPFC, and the expression of gene that encodes proopiomelanocortin, the precursor of β-endorphin, in the hypothalamus, in vivo. Finally, neutralization of β-endorphin in the mPFC using a specific antibody prior to ketamine treatment abolishes both behavioral and molecular effects. Together, these findings indicate that presence of β-endorphin and activation of opioid receptors in the mPFC are required for the antidepressant-like actions of ketamine.

Deep brain stimulation of ventromedial prefrontal cortex reverses depressive-like behaviors via BDNF/TrkB signaling pathway in rats

AIM

Deep brain stimulation (DBS) is currently under investigation as a potential therapeutic approach for managing major depressive disorder (MDD) and ventromedial prefrontal cortex (vmPFC) is recognized as a promising target region. Therefore, the present study aimed to investigate a preclinical paradigm of bilateral vmPFC DBS and examine the molecular mechanisms underlying its antidepressant-like effects using chronic unpredictable stress (CUS) model in rats.

MAIN METHODS

Male rats were subjected to stereotaxic surgery and deep brain stimulation paradigm in non-stressed and CUS rats respectively, and the therapeutic effect of DBS were assessed by a series of behavioral tests including sucrose preference test, open field test, elevated plus maze test, and forced swim test. The potential involvement of the BDNF/TrkB signaling pathway and its downstream effects in this process were also investigated using western blot.

KEY FINDINGS

We identified that a stimulation protocol consisting of 130 Hz, 200 μA, 90 μs pulses administered for 5 h per day over a period of 7 days effectively mitigated CUS-induced depressive-like and anxiety-like behaviors in rats. These therapeutic effects were associated with the enhancement of the BDNF/TrkB signaling pathway and its downstream ERK1/2 activity.

SIGNIFICANCE

These findings provide valuable insights into the potential clinical utility of vmPFC DBS as an approach of improving the symptoms experienced by individuals with MDD. This evidence contributes to our understanding of the neurobiological basis of depression and offers promise for the development of more effective treatments.

Probiotics in Postoperative Pain Management

Postoperative pain is the unpleasant sensory and emotional experience after surgery, its origin being both the inflammatory reaction induced by the surgical trauma on the abdominal wall and the splanchnic pain induced by the activation of nociceptors of the viscera, which are highly sensitive to distension, ischemia, and inflammation. Nowadays, it is well recognized that there is a close relationship between the gut microbiome and pain perception, and that microbiome is highly affected by both anesthesia and surgical manipulation. Thus, efforts to restore the disturbed microbiome via supplementation with beneficial bacteria, namely probiotics, seem to be effective. In this article, the knowledge gained mainly from experimental research on this topic is analyzed, the concluding message being that each probiotic strain works in its own way towards pain relief.

The endogenous opioid system in the medial prefrontal cortex mediates ketamine's antidepressant-like actions

Recent studies have implicated the endogenous opioid system in the antidepressant actions of ketamine, but the underlying mechanisms remain unclear. We used a combination of pharmacological, behavioral, and molecular approaches in rats to test the contribution of the prefrontal endogenous opioid system to the antidepressant-like effects of a single dose of ketamine. Both the behavioral actions of ketamine and their molecular correlates in the medial prefrontal cortex (mPFC) were blocked by acute systemic administration of naltrexone, a competitive opioid receptor antagonist. Naltrexone delivered directly into the mPFC similarly disrupted the behavioral effects of ketamine. Ketamine treatment rapidly increased levels of β-endorphin and the expression of the μ-opioid receptor gene (Oprm1) in the mPFC, and the expression of the gene that encodes proopiomelanocortin, the precursor of β-endorphin, in the hypothalamus, in vivo. Finally, neutralization of β-endorphin in the mPFC using a specific antibody prior to ketamine treatment abolished both behavioral and molecular effects. Together, these findings indicate that presence of β-endorphin and activation of opioid receptors in the mPFC are required for the antidepressant-like actions of ketamine.

Activation of TrkB signaling mitigates cerebellar anomalies caused by Rbm4-Bdnf deficiency

A molecular and functional link between neurotrophin signaling and cerebellar foliation is lacking. Here we show that constitutive knockout of two homologous genes encoding the RNA binding protein RBM4 results in foliation defects at cerebellar lobules VI-VII and delayed motor learning in mice. Moreover, the features of Rbm4 double knockout (dKO), including impaired differentiation of cerebellar granule cells and dendritic arborization of Purkinje cells, are reminiscent of neurotrophin deficiency. Loss of RBM4 indeed reduced brain-derived neurotrophic factor (BDNF). RBM4 promoted the expression of BDNF and full-length TrkB, implicating RBM4 in efficient BDNF-TrkB signaling. Finally, prenatal supplementation with 7,8-dihydroxyflavone, a TrkB agonist, restored granule cell differentiation, Purkinje cell dendritic complexity and foliation-the intercrural fissure in particular-in the neonatal cerebellum of Rbm4dKO mice, which also showed improved motor learning in adulthood. This study provides evidence that prenatal activation of TrkB signaling ameliorates cerebellar malformation caused by BDNF deficiency.

Effects of neuronavigation-guided rTMS on serum BDNF, TrkB and VGF levels in depressive patients with suicidal ideation

BACKGROUND

Neuronavigation-guided high-dose repetitive transcranial magnetic stimulation (rTMS) could rapidly treat depressive patients with suicidal ideation. But the mechanism of rTMS still needs to be elucidated. This study aims to investigate if rTMS improves suicidal ideation and depressive symptoms by influencing brain-derived neurotrophic factor (BDNF), tropomysin receptor kinase B (TrkB) and VGF levels.

METHODS

In the present 1-week study, 59 treatment-naive depressive patients with suicidal ideation were randomly assigned to the active (n = 31) or sham (n = 28) rTMS group. The severity of suicidal ideation and depression were measured by the Beck Scale for Suicide Ideation, the Hamilton Depression Rating Scale and Montgomery-Asberg Depression Rating Scale. Fasting venous blood samples were collected at baseline and after treatment. Serum protein concentrations of BDNF, TrkB and VGF were measured by enzyme linked immunosorbent assay.

RESULTS

We found after treatment the levels of BDNF in the active rTMS group were higher than the sham group (p = 0.011), TrkB levels were decreased in the active group (p < 0.001), VGF levels were increased in the active group (p = 0.005). Post-treatment VGF levels in the active group were higher than the sham group (p = 0.008). However, there were no significant correlation between changes in BDNF, TrkB and VGF levels and the changes in clinical variables.

LIMITATIONS

Participants taking medication may affect the results.

CONCLUSIONS

Our results suggest that the BDNF-TrkB pathway and VGF may be implicated in the mechanisms underlying neuronavigation-guided rTMS for treating depressive patients with suicidal ideation.

Ketamine, benzoate, and sarcosine for treating depression

Studies have demonstrated the beneficial therapeutic effects of sarcosine, benzoate, and ketamine (including esketamine and arketamine) on depression. These drugs mainly act by modulating N-methyl-d-aspartate glutamate receptors (NMDARs) and reducing inflammation in the brain. Although ketamine, benzoate, and sarcosine act differently as the antagonists or coagonists of NMDARs, they all have demonstrated efficacy in animal models or human trials. In vitro and in vivo studies have indicated that sarcosine, benzoate, and ketamine exert their anti-inflammatory effects by inhibiting microglial activity. This review summarizes and compares the efficacy of the possible therapeutic mechanisms of sarcosine, benzoate, ketamine, esketamine, and arketamine. These compounds act as both NMDAR modulators and anti-inflammatory drugs and thus can be effective in the treatment of depression.

ERK/mTOR signaling may underlying the antidepressant actions of rapastinel in mice

Rapastinel as the allosteric modulator of N-methyl-D-aspartate receptor (NMDAR) produces rapid antidepressant-like effects dependent on brain-derived neurotrophic factor (BDNF) and VGF (nonacryonimic) release. Herein, we further explore the molecular mechanisms of the antidepressant effects of repeated administration with rapastinel in mice. Our results showed that continuous 3-day rapastinel (5 and 10 mg/kg, i.v.) produced antidepressant-like actions dependent on the increase in extracellular regulated protein kinase (ERK)/mammalian target of rapamycin (mTOR) signaling and downstream substrates p70S6 kinase (p70S6k) and the eukaryotic initiation factor 4E-binding protein 1 (4E-BP1), which may induce the expression of VGF and BDNF in the hippocampus and prefrontal cortex of mice. Furthermore, compared with a single treatment, our data indicated that 3-day repeated rapastinel treatment produced antidepressant-like actions accompanied by potentiation of ERK/mTOR/VGF/BDNF/tropomyosin-related kinase receptor B (TrkB) signaling. Based on previous and our supplementary data that showed the pivotal role of on α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) in the rapid release of VGF and BDNF and activation of TrkB by a single dose of rapastinel, we postulate that the antidepressant-like effects of single or repeated administration of rapastinel may result in the rapid release of VGF and BDNF or ERK/mTOR signaling pathway-mediated VGF/BDNF/TrkB autoregulatory feedback loop respectively. Our current work adds new knowledge to the molecular mechanisms that underlie the antidepressant-like actions of rapastinel in mice.

Dual-Specificity Protein Phosphatase 4 (DUSP4) Overexpression Improves Learning Behavior Selectively in Female 5xFAD Mice, and Reduces β-Amyloid Load in Males and Females

Recent multiscale network analyses of banked brains from subjects who died of late-onset sporadic Alzheimer's disease converged on VGF (non-acronymic) as a key hub or driver. Within this computational VGF network, we identified the dual-specificity protein phosphatase 4 (DUSP4) [also known as mitogen-activated protein kinase (MAPK) phosphatase 2] as an important node. Importantly, DUSP4 gene expression, like that of VGF, is downregulated in postmortem Alzheimer's disease (AD) brains. We investigated the roles that this VGF/DUSP4 network plays in the development of learning behavior impairment and neuropathology in the 5xFAD amyloidopathy mouse model. We found reductions in DUSP4 expression in the hippocampi of male AD subjects, correlating with increased CDR scores, and in 4-month-old female and 12-18-month-old male 5xFAD hippocampi. Adeno-associated virus (AAV5)-mediated overexpression of DUSP4 in 5xFAD mouse dorsal hippocampi (dHc) rescued impaired Barnes maze performance in females but not in males, while amyloid loads were reduced in both females and males. Bulk RNA sequencing of the dHc from 5-month-old mice overexpressing DUSP4, and Ingenuity Pathway and Enrichr analyses of differentially expressed genes (DEGs), revealed that DUSP4 reduced gene expression in female 5xFAD mice in neuroinflammatory, interferon-gamma (IFNγ), programmed cell death protein-ligand 1/programmed cell death protein 1 (PD-L1/PD-1), and extracellular signal-regulated kinase (ERK)/MAPK pathways, via which DUSP4 may modulate AD phenotype with gender-specificity.

The Role of the Human Microbiome in the Pathogenesis of Pain

Understanding of the gut microbiome's role in human physiology developed rapidly in recent years. Moreover, any alteration of this microenvironment could lead to a pathophysiological reaction of numerous organs. It results from the bidirectional communication of the gastrointestinal tract with the central nervous system, called the gut-brain axis. The signals in the gut-brain axis are mediated by immunological, hormonal, and neural pathways. However, it is also influenced by microorganisms in the gut. The disturbances in the gut-brain axis are associated with gastrointestinal syndromes, but recently their role in the development of different types of pain was reported. The gut microbiome could be the factor in the central sensitization of chronic pain by regulating microglia, astrocytes, and immune cells. Dysbiosis could lead to incorrect immune responses, resulting in the development of inflammatory pain such as endometriosis. Furthermore, chronic visceral pain, associated with functional gastrointestinal disorders, could result from a disruption in the gut microenvironment. Any alteration in the gut-brain axis could also trigger migraine attacks by affecting cytokine expression. Understanding the gut microbiome's role in pain pathophysiology leads to the development of analgetic therapies targeting microorganisms. Probiotics, FODMAP diet, and fecal microbiota transplantation are reported to be beneficial in treating visceral pain.

The molecular pathophysiology of depression and the new therapeutics

Major depressive disorder (MDD) is a highly prevalent and disabling disorder. Despite the many hypotheses proposed to understand the molecular pathophysiology of depression, it is still unclear. Current treatments for depression are inadequate for many individuals, because of limited effectiveness, delayed efficacy (usually two weeks), and side effects. Consequently, novel drugs with increased speed of action and effectiveness are required. Ketamine has shown to have rapid, reliable, and long-lasting antidepressant effects in treatment-resistant MDD patients and represent a breakthrough therapy for patients with MDD; however, concerns regarding its efficacy, potential misuse, and side effects remain. In this review, we aimed to summarize molecular mechanisms and pharmacological treatments for depression. We focused on the fast antidepressant treatment and clarified the safety, tolerability, and efficacy of ketamine and its metabolites for the MDD treatment, along with a review of the potential pharmacological mechanisms, research challenges, and future clinical prospects.

Antidepressant-like effects of trophic factor receptor signaling

A significant body of research has demonstrated that antidepressants regulate neurotrophic factors and that neurotrophins themselves are capable of independently producing antidepressant-like effects. While brain derived neurotrophic factor (BDNF) remains the best studied molecule in this context, there are several structurally diverse trophic factors that have shown comparable behavioral effects, including basic fibroblast growth factor (FGF-2), insulin-like growth factor 1 (IGF-1) and vascular endothelial growth factor (VEGF). In this review we discuss the structural and biochemical signaling aspects of these neurotrophic factors with antidepressant activity. We also include a discussion on a cytokine molecule erythropoietin (EPO), widely known and prescribed as a hormone to treat anemia but has recently been shown to function as a neurotrophic factor in the central nervous system (CNS).

Low VGF is associated with executive dysfunction in patients with major depressive disorder

OBJECTIVES

Executive dysfunction is considered to be one of the cognitive impairment dimensions that are easily observed in depression, but its underlying molecular mechanism is still unclear. Study have shown that the neuropeptide VGF (non-acronymic) plays an important role in the regulation of hippocampal neurogenesis and neuroplasticity. Previous studies have shown that VGF may be related to the psychopathology of depression and cognitive impairment. However, the correlation between VGF and executive dysfunction in MDD has not been investigated.

METHODS

A total of 35 MDD patients and 31 healthy control patients were enrolled in this study. The 17-item Hamilton Depression Rating Scale (HDRS) was used to measure the severity of depression, and the Wisconsin Card Sorting Test (WCST) was used to assess executive dysfunction. Double antibody sandwich enzyme-linked immunosorbent assay (ELISA) was used to determine serum VGF in peripheral blood.

RESULTS

The level of serum VGF in MDD patients was significantly lower compared to that in the healthy control group (p < 0.001). Moreover, Response Administered (RA) scores, Response preservative errors (RPE), and Non-response preservative errors (NRPE) were all higher in the MDD group (all p < 0.05). In contrast, Categories Completed (CC) and Response Correct (RC) scores were lower (all p < 0.05). Further results showed a significant correlation between serum VGF with RA (r = -0.372, p = 0.028) and RPE scores (r = 0.507, p = 0.002) in patients with depression, while serum VGF showed no correlation with the severity of depression in either group.

CONCLUSIONS

VGF may play an important role in executive function dysfunction in MDD patients, and VGF levels may become a new marker for predicting executive function dysfunction in depression.

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.

Hippocampal Volume and Plasma Brain-Derived Neurotrophic Factor Levels in Patients With Depression and Healthy Controls

The aim of the present study was to investigate associations between hippocampal subfield volumes and plasma levels of brain-derived neurotrophic factor (BDNF) in patients experiencing a first episode of major depression (MD) (n = 30) as compared to healthy controls (HC) (n = 49). Covariate-adjusted linear regression was performed to compare the MD and healthy groups, adjusting for age, sex, and total estimated intracranial volume. We demonstrated that there were no differences in total hippocampal volume between the MD and HC groups. However, the volumes of the hippocampus-amygdala-transition-area (HATA) on the left side of the brain as well as the parasubiculum, presubiculum, and fimbria on the right side were statistically significantly smaller in the MD group than in the HC group. Furthermore, the volume of the hippocampal fissure on the right side was statistically significantly smaller in the HC group than in the MD group. In the MD group, we found a positive linear correlation between hippocampal volume and plasma BDNF concentrations in the CA4 area on the left side (p = 0.043). In contrast, in the HC group, we found a negative linear correlation between parasubiculum volume on the right side and plasma BDNF concentrations (p = 0.04). These results suggest that some hippocampal subfields may already be atrophic at the start of MD. In addition, our findings suggest that the sensitivity of the right parasubiculum region to BDNF may differ between MD and HC groups. These findings guide future research directions and, if confirmed, may ultimately inform medical guidelines.

Microbiota and Pain: Save Your Gut Feeling

Recently, a growing body of evidence has emerged regarding the interplay between microbiota and the nervous system. This relationship has been associated with several pathological conditions and also with the onset and regulation of pain. Dysregulation of the axis leads to a huge variety of diseases such as visceral hypersensitivity, stress-induced hyperalgesia, allodynia, inflammatory pain and functional disorders. In pain management, probiotics have shown promising results. This narrative review describes the peripheral and central mechanisms underlying pain processing and regulation, highlighting the role of the gut-brain axis in the modulation of pain. We summarized the main findings in regard to the stress impact on microbiota’s composition and its influence on pain perception. We also focused on the relationship between gut microbiota and both visceral and inflammatory pain and we provided a summary of the main evidence regarding the mechanistic effects and probiotics use.

New Insights Into the Pivotal Role of CREB-Regulated Transcription Coactivator 1 in Depression and Comorbid Obesity

Depression and obesity are major public health concerns, and there is mounting evidence that they share etiopathophysiological mechanisms. The neurobiological pathways involved in both mood and energy balance regulation are complex, multifactorial and still incompletely understood. As a coactivator of the pleiotropic transcription factor cAMP response element-binding protein (CREB), CREB-regulated transcription coactivator 1 (CRTC1) has recently emerged as a novel regulator of neuronal plasticity and brain functions, while CRTC1 dysfunction has been associated with neurodegenerative and psychiatric diseases. This review focuses on recent evidence emphasizing the critical role of CRTC1 in the neurobiology of depression and comorbid obesity. We discuss the role of CRTC1 downregulation in mediating chronic stress-induced depressive-like behaviors, and antidepressant response in the light of the previously characterized Crtc1 knockout mouse model of depression. The putative role of CRTC1 in the alteration of brain energy homeostasis observed in depression is also discussed. Finally, we highlight rodent and human studies supporting the critical involvement of CRTC1 in depression-associated obesity.

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.

Brain-derived neurotrophic factor upregulates synaptic GluA1 in the amygdala to promote depression in response to psychological stress

Psychological stress impairs neuronal structure and function and leads to emotional disorders, but the underlying mechanisms have not yet been fully elucidated. The amygdala is closely correlated with emotional regulation. In the present study, we analyzed whether the amygdala plasticity is regulated by psychological stress and explored their regulatory mechanism. We established a mouse psychological stress model using an improved communication box, wherein mice were exposed to chronic fear and avoided physical stress interference. After the 14-day psychological stress paradigm, mice exhibited significantly increased depressive behaviors (decreased sucrose consumption in the sucrose preference test and longer immobility time in the forced swimming test). HPLC, ELISA, and molecular and morphological evidences showed that psychological stress increased the content of glutamate and the expression of glutamatergic neurons, upregulated the content of the stress hormone corticosterone, and activated the CREB/BDNF pathway in the amygdala. Furthermore, psychological stress induced an increased density of dendritic spines and LTD impairment in the amygdala. Importantly, virus-mediated silencing of BDNF in the basolateral amygdala (BLA) nuclei reversed the depression-like behaviors and the increase of synaptic GluA1 and its phosphorylation at Ser831 and Ser845 sites in psychologically stressed mice. This process was likely achieved through mTOR signaling activation. Finally, we treated primary amygdala neurons with corticosterone to mimic psychological stress; corticosterone-induced upregulation of GluA1 was prevented by BDNF and mTOR antagonists. Thus, activation of the CREB/BDNF pathway in the amygdala following psychological stress upregulates synaptic GluA1 via mTOR signaling, which dysregulates synaptic plasticity of the amygdala, eventually promoting depression.

An increase in VGF expression through a rapid, transcription-independent, autofeedback mechanism improves cognitive function

The release of neuropeptides from dense core vesicles (DCVs) modulates neuronal activity and plays a critical role in cognitive function and emotion. The granin family is considered a master regulator of DCV biogenesis and the release of DCV cargo molecules. The expression of the VGF protein (nonacronymic), a secreted neuropeptide precursor that also belongs to the extended granin family, has been previously shown to be induced in the brain by hippocampus-dependent learning, and its downregulation is mechanistically linked to neurodegenerative diseases such as Alzheimer's disease and other mood disorders. Currently, whether changes in translational efficiency of Vgf and other granin mRNAs may be associated and regulated with learning associated neural activity remains largely unknown. Here, we show that either contextual fear memory training or the administration of TLQP-62, a peptide derived from the C-terminal region of the VGF precursor, acutely increases the translation of VGF and other granin proteins, such as CgB and Scg2, via an mTOR-dependent signaling pathway in the absence of measurable increases in mRNA expression. Luciferase-based reporter assays confirmed that the 3'-untranslated region (3'UTR) of the Vgf mRNA represses VGF translation. Consistently, the truncation of the endogenous Vgf mRNA 3'UTR results in substantial increases in VGF protein expression both in cultured primary neurons and in brain tissues from knock in mice expressing a 3'UTR-truncation mutant encoded by the modified Vgf gene. Importantly, Vgf 3'UTR-truncated mice exhibit enhanced memory performance and reduced anxiety- and depression-like behaviors. Our results therefore reveal a rapid, transcription-independent induction of VGF and other granin proteins after learning that are triggered by the VGF-derived peptide TLQP-62. Our findings suggest that the rapid, positive feedforward increase in the synthesis of granin family proteins might be a general mechanism to replenish DCV cargo molecules that have been released in response to neuronal activation and is crucial for memory function and mood stability.

Transient Stimulation with Psychoplastogens Is Sufficient to Initiate Neuronal Growth

Cortical neuron atrophy is a hallmark of depression and includes neurite retraction, dendritic spine loss, and decreased synaptic density. Psychoplastogens, small molecules capable of rapidly promoting cortical neuron growth, have been hypothesized to produce long-lasting positive effects on behavior by rectifying these deleterious structural and functional changes. Here we demonstrate that ketamine and LSD, psychoplastogens from two structurally distinct chemical classes, promote sustained growth of cortical neurons after only short periods of stimulation. Furthermore, we show that psychoplastogen-induced cortical neuron growth can be divided into two distinct epochs: an initial stimulation phase requiring TrkB activation and a growth period involving sustained mTOR and AMPA receptor activation. Our results provide important temporal details concerning the molecular mechanisms by which next-generation antidepressants produce persistent changes in cortical neuron structure, and they suggest that rapidly excreted psychoplastogens might still be effective neurotherapeutics with unique advantages over compounds like ketamine and LSD.

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.

Involvement of muscarinic receptor mechanisms in antidepressant drug action

Conventional antidepressants typically require weeks of daily dosing to achieve full antidepressant response in antidepressant responders. A newly evolving group of compounds can engender more rapid response times in depressed patients. These drugs include the newly approved antidepressant (S)-ketamine (esketamine, Spravato). A seminal study by Furey and Drevets in 2006 showed antidepressant response in patients after only a few doses with the antimuscarinic drug scopolamine. Several clinical reports have generally confirmed scopolamine as a rapid-acting antidepressant. The data with scopolamine are consistent with the adrenergic/cholinergic hypothesis of mania/depression derived from clinical reports originating in the 1970s from Janowsky and colleagues. Additional support for a role for muscarinic receptors in mood disorders comes from the greater efficacy of conventional antidepressants that have relatively high levels of muscarinic receptor blocking actions (e.g., the tricyclic antidepressant amitriptyline vs the selective serotonin reuptake inhibitor fluoxetine). There appears to be appreciable overlap in the mechanisms of action of scopolamine and other rapid-acting antidepressants (ketamine) or putative rapid-acting agents (mGlu2/3 receptor antagonists) although gaps exist in the experimental literature. Current hypotheses regarding the mechanisms underlying the rapid antidepressant response to scopolamine posit an M₁ receptor subtype-initiated cascade of biological events that involve the amplification of AMPA receptors. Consequent impact on brain-derived neurotrophic factor and mTor signaling pathways result in the induction of dendritic spines that enable augmented functional connectivity in brain areas regulating mood. Two major goals for research in this area focus on finding ways in which scopolamine might best be utilized for depressed patients and the discovery of alternative compounds that improve upon the efficacy and safety of scopolamine.

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 has Roles in the Pathogenesis of Major Depressive Disorder and Schizophrenia: Evidence from Transgenic Mouse Models

Mental disorders, such as major depressive disorder and schizophrenia, are complex multigenetic conditions, but focused studies of single genes might reveal genes involved in the pathogenesis of mental disorders, including major depressive disorder and schizophrenia. Several candidate genes have been identified using transgenic mice. VGF nerve growth factor inducible (VGF) is a neuropeptide expression of which is induced by nerve growth factor (NGF). VGF is robustly and exclusively synthesized in neuronal and neuroendocrine cells. In central nervous system (CNS), VGF is extensively expressed especially in the cerebral cortex, hippocampus, and hypothalamus. VGF has many roles in the CNS, such as promotion of synaptic plasticity, neurogenesis, and neurite outgrowth. In clinical studies, altered expression and genetic mutations of VGF have been reported in patients with major depressive disorder and schizophrenia. On this basis, studies using transgenic mice to overexpress or knockout VGF have been performed to investigate the roles of upregulation or downregulation of VGF. In this review, we will discuss studies of the roles of VGF using transgenic mice and its relevance to pathologies in major depressive disorder and schizophrenia.

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.

Glutamatergic Signaling Along The Microbiota-Gut-Brain Axis

A complex bidirectional communication system exists between the gastrointestinal tract and the brain. Initially termed the “gut-brain axis” it is now renamed the “microbiota-gut-brain axis” considering the pivotal role of gut microbiota in maintaining local and systemic homeostasis. Different cellular and molecular pathways act along this axis and strong attention is paid to neuroactive molecules (neurotransmitters, i.e., noradrenaline, dopamine, serotonin, gamma aminobutyric acid and glutamate and metabolites, i.e., tryptophan metabolites), sustaining a possible interkingdom communication system between eukaryota and prokaryota. This review provides a description of the most up-to-date evidence on glutamate as a neurotransmitter/neuromodulator in this bidirectional communication axis. Modulation of glutamatergic receptor activity along the microbiota-gut-brain axis may influence gut (i.e., taste, visceral sensitivity and motility) and brain functions (stress response, mood and behavior) and alterations of glutamatergic transmission may participate to the pathogenesis of local and brain disorders. In this latter context, we will focus on two major gut disorders, such as irritable bowel syndrome and inflammatory bowel disease, both characterized by psychiatric co-morbidity. Research in this area opens the possibility to target glutamatergic neurotransmission, either pharmacologically or by the use of probiotics producing neuroactive molecules, as a therapeutic approach for the treatment of gastrointestinal and related psychiatric disorders.

Understanding depression: the hippocampus might hold the answer in a CREB-regulated transcription coactivator: An Editorial for 'AAV-mediated over-expression of CRTC1 in the hippocampal dentate gyrus ameliorates lipopolysaccharide-induced depression-like behavior in mice' on page 111

The pathophysiology of major depressive disorders is not completely understood. In this issue of Journal of Neurochemistry, Ni and colleagues investigate the role of cyclic adenosine monophosphate response element-binding protein (CREB)-dependent signaling in the hippocampus on depressive-like behaviors. This editorial highlights the key findings reported by Ni et al., (2018) and how they demonstrated the importance of CREB-regulated transcription cofactor 1 in LPS-induced neuroinflammation and depressive-like behaviors.