Injection of Anti-proBDNF in Anterior Cingulate Cortex (ACC) Reverses Chronic Stress-Induced Adverse Mood Behaviors in Mice

The expression of ProBDNF and its high affinity receptor P75NTR in the neurons of emotion-related brain regions of post-stroke depression rats

OBJECTIVE

To investigate the expression of the precursor of brain-derived neurotrophic factor (proBDNF) and its high-affinity receptor p75NTR in neurons of emotion-related brain areas (prefrontal cortex, hippocampus, and amygdala) in rats with post-stroke depression (PSD), and to explore the expression levels of proBDNF and p75NTR in neurons of emotion-related brain areas by injecting tissue plasminogen activator (t-PA) into the lateral ventricle of PSD rats, this significantly improved the stress-induced depression-like behavior,thus further validating the above results.

METHODS

Rats were randomly divided into four groups: a normal control group (n = 8), a depression group (n = 8), a stroke group (n = 8), and a PSD group (n = 8). The rat model of stroke was established by thread embolism, and the PSD animal model was induced by chronic unpredictable mild stress (CUMS) and solitary feeding. Behavioral tests were conducted, including weight measurement, open field tests, and sucrose preference tests. Immunofluorescence double labeling was used to detect the expression of proBDNF and p75NTR in neurons of emotion-related brain regions in the PSD rat model. Four weeks after CUMS treatment, the PSD group was selected. Rats were infused with t-PA (3 μg dissolved in 6 μL saline, Boehringer Ingelheim), proBDNF (3 μg dissolved in 6 μL saline, Abcam), or equal-volume NS once per day for 7 consecutive days using the syringe pump connecting to injection needles. After 7 days of continuous administration, animal behavior was assessed through scoring, and the expression of proBDNF and p75NTR in the emotion-related brain regions of the PSD rat model was detected using immunofluorescence double labeling.

RESULTS

Compared with the normal control group and the stroke group, the body weight, sucrose water consumption, and vertical movement distance in the PSD group were significantly lower (P < 0.05). In contrast, when compared with the proBDNF injection group and saline injection group, the weight, sucrose water consumption, field horizontal movement, and vertical movement distance of the t-PA injection group significantly increased after PSD lateral ventricle intubation.Double immunofluorescence revealed a higher neuronal expression of proBDNF as well as p75NTR in the prefrontal cortex and hippocampus of PSD rats compared to control animals (P < 0.05). In the amygdala, the expression levels of proBDNF and P75NTR were significantly reduced in the PSD group compared to the control group (P < 0.05). The results of the expression levels of proBDNF and P75NTR in the emotion-related brain regions of PSD rats injected with t-PA showed that proBDNF and P75NTR was significantly reduced in the prefrontal cortex, hippocampus, and amygdala of PSD rats compared to those of the NS and proBDNF groups (P < 0.05).

CONCLUSIONS

The increased expression of the brain-derived neurotrophic factor precursor proBDNF and its receptor p75NTR in neurons of emotion-related brain regions may play an important role in the pathogenesis of PSD.t-PA reduced the expression of proBDNF and its receptor p75NTR in neurons emotion-related brain regions and significantly improved the stress-induced depression-like behavior. Therefore, it is reasonable to assume that exogenous injection of t-PA may alleviate the depressive symptoms of PSD patients.Reducing the expression of proBDNF by injecting t-PA may provide a novel therapeutic approach for the treatment of stress-related mood disorders.

Upregulation of proBDNF/p75NTR signaling in immune cells and its correlation with inflammatory markers in patients with major depression

ProBDNF is the precursor protein of brain-derived neurotrophic factor (BDNF) expressed in the central nervous system and peripheral tissues. Previous studies showed that the blood levels of both proBDNF and p75 neurotrophic receptors (p75NTR) in major depressive disorder (MDD) were increased, but which blood cell types express proBDNF and its receptors is not known. Furthermore, the relationship between proBDNF/p75NTR and inflammatory cytokines in peripheral blood of MDD is unclear. Peripheral blood mononuclear cells (PBMCs) and serum were obtained from depressive patients (n = 32) and normal donors (n = 20). We examined the expression of proBDNF and inflammatory markers and their correlative relationship in patients with major depression. Using flow cytometry analysis, we examined which blood cells express proBDNF and its receptors. Finally, the role of proBDNF/p75NTR signal in inflammatory immune activity of PBMCs was verified in vitro experiments. Inflammatory cytokines in PBMC from MDD patients were increased and correlated with the major depression scores. The levels of IL-1β and IL-10 were also positively correlated with the major depression scores, while the levels of TNF-α and IL-6 were negatively correlated with the major depression scores. Intriguingly, the levels of sortilin were positively correlated with IL-1β. Q-PCR and Western blots showed proBDNF, p75NTR, and sortilin levels were significantly increased in PBMCs from MDD patients compared with that from the normal donors. Flow cytometry studies showed that proBDNF and p75NTR were present mainly in CD4+ and CD8+ T cells. The number of proBDNF and p75NTR positive CD4+ and CD8+ T cells from MDD patients was increased and subsequently reversed after therapeutic management. Exogenous proBDNF protein or p75ECD-Fc treatment of cultured PBMC affected the release of inflammatory cytokines in vitro. ProBDNF promoted the expression of inflammatory cytokines, while p75ECD-Fc inhibited the expression of inflammatory cytokines. Given there was an inflammatory response of lymphocytes to proBDNF, it is suggested that proBDNF/p75NTR signaling may upstream inflammatory cytokines in MDD. Our data suggest that proBDNF/p75NTR signaling may not only serve as biomarkers but also may be a potential therapeutic target for MDD.

Clostridium butyricum RH2 Alleviates Chronic Foot Shock Stress-Induced Behavioral Deficits in Rats via PAI-1

Recent investigations have demonstrated that the chronic stress-induced behavioral disorders can be ameliorated by probiotics including Clostridium butyricum (C. butyricum) via the gut-brain-axis. However, the molecular mechanisms underlying the beneficial effects of C. butyricum on brain remain largely unknown. Here, we investigated whether chronic foot shock stress (CFSS) paradigm used for a hypertensive animal model could induce mood disorders such as anxiety, depression and cognitive impairments. Then, we assessed the impact of C. butyricum RH2 on the behavior disorders and neurobiological alterations in the hippocampus. Male Sprague-Dawley (SD) rats received intermittent electric shocks for consecutive 14 days and were treated with C. butyricum RH2 for 17 days. Anxiety- or depression-like behaviors were evaluated by open field test (OFT), and elevated plus maze (EPM). The Morris water maze test (MWM) was used to evaluate the cognitive functions. CFSS intervention led to mild anxiety- or depression-like behavior or cognitive impairment and C. butyricum RH2 treatment reversed the CFSS-induced symptoms. The serum ACTH or CORT was increased following CFSS but was completely reversed by C. butyricum RH2 treatment. In the hippocampus of CFSS rats, the expressions of BDNF and TrkB were downregulated but proBDNF and P75^NTR were upregulated. These expression changes were partially reversed by C. butyricum RH2, suggesting a mode of action on BDNF and proBDNF balance. CFSS exposure resulted in downregulation of tissue-type plasminogen activator (tPA) but upregulation of plasminogen activator inhibitor 1(PAI-1), which could contribute to the decrease in BDNF by reduced conversion from proBDNF to BDNF in the hippocampus. C. butyricum RH2 treatment reversed the upregulated PAI-1 but not the downregulated tPA, which was in parallel with the amelioration of behavioral abnormalities, suggesting a novel tPA independent mechanism for PAI-1 action. Our results demonstrate for the first time that C. butyricum RH2 attenuates stress-induced behavior disorders via inhibiting the expression of brain PAI-1.

Neuroimmune crosstalk through brain-derived neurotrophic factor and its precursor pro-BDNF: New insights into mood disorders

Mood disorders are the most common mental disorders, affecting approximately 350 million people globally. Recent studies have shown that neuroimmune interaction regulates mood disorders. Brain-derived neurotrophic factor (BDNF) and its precursor pro-BDNF, are involved in the neuroimmune crosstalk during the development of mood disorders. BDNF is implicated in the pathophysiology of psychiatric and neurological disorders especially in antidepressant pharmacotherapy. In this review, we describe the functions of BDNF/pro-BDNF signaling in the central nervous system in the context of mood disorders. In addition, we summarize the developments for BDNF and pro-BDNF functions in mood disorders. This review aims to provide new insights into the impact of neuroimmune interaction on mood disorders and reveal a new basis for further development of diagnostic targets and mood disorders.

Alleviative effects of foraging exercise on depressive-like behaviors in chronic mild stress-induced ischemic rat model

BACKGROUND

Poststroke depression (PSD) is a common complication that seriously affects the functional recovery and prognosis of an individual. As some patients with PSD fail to respond to drug therapy, it is urgent to find a viable alternative treatment.

METHODS

An active exercise program known as foraging exercise (FE), using food as bait, was designed. First, focal ischemia and chronic unpredictable mild stress (CUMS) were used to establish a PSD model in rats. FE was then performed for 4 weeks. Body weight and behavioral assessments were conducted at the end of the 4^th and 8^th weeks.

RESULTS

After 8 weeks, the results revealed that, compared with the PSD group, the behavioral scores of the rats in the PSD/FE group were significantly improved, the expression of Iba-1 in the affected frontal lobe and striatum was decreased, and serum levels of IL-6 and the IL-6/IL-10 ratio were downregulated. However, the ratio of residual brain volume in rats that had experienced CUMS was significantly less than that in the stroke group.

CONCLUSION

FE can alleviate the behavioral scores of PSD rats, and its mechanism may be related to a modulation of the immune-inflammation response of microglia. Furthermore, chronic, persistent stress may increase the volume of cerebral infarction after stroke.

The role of pro- and mature neurotrophins in the depression

Neurotrophic factors, which can provide nutritional support to neurons and neuronal cells, also played an important role in their proliferation and survival. As signaling molecules, it also mediated the learning, memory and other activities in the brain. The latest study shows that neurotrophic factors have diametrically opposing effects of the pro- and mature form through distinct receptors. In this review, we summarize the different forms of neurotrophic factors, related receptors, and the corresponding biological effects. More importantly, we expounded the physiology and pathology mechanisms of brain-derived neurotrophic factor(BDNF)in depression. It is hopefully to provide new idea on the relationship of neurotrophic factors and depression.

Brain-derived neurotrophic factor precursor in the immune system is a novel target for treating multiple sclerosis

Rationale: Brain-derived neurotrophic factor precursor (proBDNF) is expressed in the central nervous system (CNS) and the immune system. However, the role of proBDNF in the pathogenesis of multiple sclerosis (MS) is unknown.

Methods: Peripheral blood and post-mortem brain and spinal cord specimens were obtained from multiple sclerosis patients to analyze proBDNF expression in peripheral lymphocytes and infiltrating immune cells in the lesion site. The proBDNF expression profile was also examined in the experimental autoimmune encephalomyelitis (EAE) mouse model, and polyclonal and monoclonal anti-proBDNF antibodies were used to explore their therapeutic effect in EAE. Finally, the role of proBDNF in the inflammatory immune activity of peripheral blood mononuclear cells (PBMCs) was verified in vitro experiments.

Results: High proBDNF expression was detected in the circulating lymphocytes and infiltrated inflammatory cells at the lesion sites of the brain and spinal cord in MS patients. In the EAE mouse model, proBDNF was upregulated in CNS and in circulating and splenic lymphocytes. Systemic but not intracranial administration of anti-proBDNF blocking antibodies attenuated clinical scores, limited demyelination, and inhibited proinflammatory cytokines in EAE mice. Immuno-stimulants treatment increased the proBDNF release and upregulated the expression of p75 neurotrophic receptors (p75^NTR) in lymphocytes. The monoclonal antibody against proBDNF inhibited the inflammatory response of PBMCs upon stimulations.

Conclusion: The findings suggest that proBDNF from immune cells promotes the immunopathogenesis of MS. Monoclonal Ab-proB may be a promising therapeutic agent for treating MS.

Blockage of p75NTR ameliorates depressive-like behaviours of mice under chronic unpredictable mild stress

The precursor of brain derived neurotrophic factor (proBDNF) and its receptor p75NTR are upregulated in depressive patients and chronic stress-induced depressive animals, suggesting that activation of p75NTR signalling may underlie pathogenesis of depression. In the present study we hypothesize that the blockade of p75NTR may have therapeutic effect on depressive mice under chronic stress. The treatment of mice with the recombinant fusion protein of p75NTR extracellular domain and fragment C of immunoglobulin (p75ECD-Fc) significantly reduced the immobility time in the forced swim test and tail suspension test, and increased the time spent in the central zone in the open field test in mice exposed to chronic unpredictable mild stress (CUMS). p75ECD-Fc treatment also significantly increased the length and density of neuronal dendritic spines in the dentate gyrus and amygdala. Our data indicate that blocking p75NTR signalling can alleviate depressive and anxiety-like behaviours of chronically stressed mice and improve the dendritic spinogenesis of neurons under stress.

Early-Life Multiple Sevoflurane Exposures Alleviate Long-term Anxiety-Like Behaviors in Mice via the proBDNF/ERK Pathway

Early-life multiple anesthetics exposure causes neurotoxicity and hence cognitive dysfunction on developing brain. However, the effects of early-life multiple sevoflurane exposures on emotional changes, especially upon stress, are far beyond understood. In young male C57BL6/J mice, the present study showed that 3% sevoflurane inhalation for 2 h in three consecutive days did not influence anxiety-like behaviors as measured by open field test, light dark transition, and elevated plus maze test. In addition, foot shocks stress induced both the short- and long-term anxiety-like behaviors. However, triple sevoflurane exposures ameliorated the long-term anxiety-like behaviors induced by the foot shocks. In parallel, foot shocks stress upregulated the expression of phosphorylated extracellular signal-regulated kinase (p-ERK) and brain-derived neurotrophic factor precursor (proBDNF) in the anterior cingulate cortex (ACC), which were significantly inhibited by triple sevoflurane exposures. Immunofluorescence further indicated that the increased p-ERK was mainly expressed in the proBDNF-positive staining cells. Intra-ACC injection of recombinant proBDNF protein upregulated the p-ERK expression and blocked the anxiolytic effect of sevoflurane exposure on long-term anxiety-like behaviors. Therefore, our study demonstrated that multiple sevoflurane exposures alleviate long-term anxiety-like behaviors upon acute stress in young mice by inhibiting proBDNF-ERK signaling in the ACC.

Hippocampal LASP1 ameliorates chronic stress-mediated behavioral responses in a mouse model of unpredictable chronic mild stress

Substantial evidence has revealed that abnormalities in synaptic plasticity play important roles during the process of depression. LASP1 (LIM and SH3 domain protein 1), a member of actin-binding proteins, has been shown to be associated with the regulation of synaptic plasticity. However, the role of LASP1 in the regulation of mood is still unclear. Here, using an unpredictable chronic mild stress (UCMS) paradigm, we found that the mRNA and protein levels of LASP1 were decreased in the hippocampus of stressed mice and that UCMS-induced down-regulation of LASP1 was abolished by chronic administration of fluoxetine. Adenosine-associated virus-mediated hippocampal LASP1 overexpression alleviated the UCMS-induced behavioral results of forced swimming test and sucrose preference test in stressed mice. It also restored the dendritic spine density, elevated the levels of AKT (a serine/threonine protein kinase), phosphorylated-AKT, insulin-like growth factor 2, and postsynaptic density protein 95. These findings suggest that LASP1 alleviates UCMS-provoked behavioral defects, which may be mediated by an enhanced dendritic spine density and more activated AKT-dependent LASP1 signaling, pointing to the antidepressant role of LASP1.

Reduced Amygdala Microglial Expression of Brain-Derived Neurotrophic Factor and Tyrosine Kinase Receptor B (TrkB) in a Rat Model of Poststroke Depression

Background

Previous studies have implicated reduced brain-derived neurotrophic factor (BDNF) expression and BDNF-TrkB receptor signaling as well as microglial activation and neuroinflammation in poststroke depression (PSD). However, the contributions of microglial BDNF-TrkB signaling to PSD pathogenesis are unclear.

Material/Methods

We compared depression-like behaviors as well as neuronal and microglial BDNF and TrkB expression levels in the amygdala, a critical mood-relating limbic structure, in rat models of stroke, depression, and PSD. Depression-like behaviors were assessed using the sucrose preference test, open-field test, and weight measurements, while immunofluorescence double staining was employed to estimate BDNF and TrkB expression by CD11b-positive amygdala microglia and NeuN-positive amygdala neuron. Another group of PSD model rats were examined following daily intracerebroventricular injection of proBDNF, tissue plasminogen activator (t-PA), or normal saline (NS) for 7 days starting 4 weeks after chronic unpredictable mild stress (CUMS).

Results

The numbers of BDNF/CD11b- and TrkB/CD11b-immunofluorescence-positive cells were lowest in the PSD group at 4 and 8 weeks after CUMS (P<0.05). PSD rats also showed reduced weight, sucrose preference, locomotion, and rearing compared with controls (P<0.05). The coexpression of BDNF/NeuN- and TrkB/NeuN-positive cells were not significantly different between groups at 4 and 8 weeks after CUMS (P>0.05). Injection of t-PA increased BDNF/CD11b- and TrkB/CD11b-positive cells in the amygdala of PSD rats and normalized behavior compared with NS or proBDNF injection (P<0.05). In contrast, proBDNF injection reduced BDNF and TrkB expression compared with NS (P<0.05).

Conclusions

These results suggest that decreased BDNF and TrkB expression by amygdala microglia may contribute to PSD pathogenesis and depression-like behaviors.

Downregulation of Adhesion Molecule CHL1 in B Cells but Not T Cells of Patients with Major Depression and in the Brain of Mice with Chronic Stress

Depression is a common serious mental disorder with unclear pathogenesis. Currently, specific diagnostic biomarkers are yet to be characterized. The close homolog of L1 (CHL1) is a L1 family cell adhesion molecule involved in the regulation of neuronal survival and growth. Although genome-wide expression profiling of human lymphoblastoid cell lines (LCLs) reported neural cell adhesion molecule (NCAM) L1 as a tentative biomarker for selective serotonin reuptake inhibitor (SSRI) antidepressant response, the involvement of CHL1 in depression is unclear. In this study, using a well-established chronic unpredictable mild stress (CUMS) depression mouse model, we examined the mRNA and protein expression of CHL1 in normal control, CUMS, vehicle (VEH), fluoxetine (FLU), and clozapine (CLO) groups. We found that in the CUMS group, both mRNA and protein expression of CHL1 were downregulated in both the hippocampus and the cortex. Treatment of CUMS mice with FLU and CLO reversed CHL1 mRNA and protein expression. In the human study, we showed that CHL1 expression was significantly downregulated in monocytes of unipolar and bipolar depressive patients compared with healthy donors (HD) at both mRNA and protein levels. Consistently, ELISA showed that CHL1 levels in the serum of patients with depression were reduced and negatively correlated with their HRSD-21 scores. Further flow cytometry studies showed that the reduced number of CHL1 positive CD19⁺ and CD20⁺ B cells of patients with depression was subsequently reversed with antidepressant treatment. Our findings suggested that downregulation of CHL1 from both immune cells and the brain may be linked to the immunopathogenesis of depression. In conclusion, CHL1 may be an important predictive marker for both diagnosis and treatment outcome of depression.

Antidepressant Drugs Correct the Imbalance Between proBDNF/p75NTR/Sortilin and Mature BDNF/TrkB in the Brain of Mice with Chronic Stress

Depression is a worldwide problem with a great social and economic burden in many countries. In our previous research, we found that the expression of proBDNF/p75NTR/sortilin is upregulated in patients with major depressive disorder. In addition, the treatment of proBDNF antibodies reversed both the depressive behaviors and the reduced BDNF mRNA detected in our rodent chronic stress models. Antidepressant drugs are usually only effective in a subpopulation of patients with major depression with a delayed time window of 2-4 weeks to exert their efficacy. The mechanism underlying such delayed response is not known. In this study, we hypothesize that antidepressant drugs exert their therapeutic effect by modulating proBDNF/p75NTR and mature BDNF/TrkB signaling pathways. To test the hypothesis, C57 mice were randomly divided into normal control, chronic unpredictable mild stress (CUMS), vehicle (VEH), fluoxetine (FLU), and clozapine (CLO) groups. Behavioral tests (sucrose preference, open field, and tail suspension tests) were performed before and after 4 weeks of CUMS. The gene and protein expression of proBDNF, the neurotrophin receptor (p75NTR), sortilin, and TrkB in the cortex and hippocampus were examined. At the protein level, CUMS induced a significant increase in proBDNF, p75NTR, and sortilin production while the TrkB protein level was found to be lower in the cortex and hippocampus compared with the control group. Consistently, at the mRNA level, p75NTR expression increased with reduced BDNF/TrkB mRNA in both cortex and hippocampus, while sortilin increased only in the hippocampus after CUMS. FLU and CLO treatments of CUMS mice reversed all protein and mRNA expression of the biomarkers in both cortex and hippocampus, except for sortilin mRNA in the cortex and proBDNF in the hippocampus, respectively. This study further confirms that the imbalance between proBDNF/p75NTR/sortilin and mBDNF/TrkB production is important in the pathogenesis of depression. It is likely that antidepressant FLU and antipsychotic CLO exert their antidepressant-like effect correcting the imbalance between proBDNF/p75NTR/sortilin and mBDNF/TrkB.

Fecal microbiota transplantation from chronic unpredictable mild stress mice donors affects anxiety-like and depression-like behavior in recipient mice via the gut microbiota-inflammation-brain axis

Recent studies have demonstrated that there are significant changes in the gut microbiota (GM) of humans with depression and animal models of depression and chronic stress. In our present study, we determined whether an alteration in GM is a decisive factor in anxiety-like and depression-like behavior and its impact on brain neurochemistry. An antibiotic cocktail was used to deplete the GM of mice before they were colonized, via fecal microbiota transplantation (FMT), by the GM of control mice or mice that had been exposed to chronic unpredictable mild stress (CUMS donors). The CUMS-donor group of mice and the mice that were colonized by their microbiota (the CUMS-recipient group) both showed higher levels of anxiety- and depression-like behavior compared to the controls. The GM community of the CUMS-donor and CUMS-recipient was distinctively different from the controls, with the CUMS group characterized by a lower relative abundance of Lactobacillus and a higher relative abundance of Akkermansia. Interestingly, FMT affected both behavior and neuroinflammation. Mice given the CUMS microbiota had significant elevations of interferon-γ (IFN-γ) and the tumor necrosis factor-alpha (TNF-α) in the hippocampus, which were accompanied by upregulated indoleamine 2,3-dioxygenase 1 (IDO1) in the hippocampus. These results suggest that GM modulates pro-inflammatory cytokines in the hippocampus through dysfunctional microbiota-gut-brain axis, exacerbating anxiety- and depression-like phenotypes. Key Points Chronic unpredictable mild stress increased anxiety- and depression-like behavior in mice. Mice colonized with gut microbiota (GM) from stressed mice showed similar behaviors. The GM composition of the donor and recipient mice was also comparable. Their relative pattern of two bacteria has been tied to neuroinflammatory activity. The results suggest a link between GM, brain function, and anxiety and depression.

Developmental nicotine exposure elicits multigenerational disequilibria in proBDNF proteolysis and glucocorticoid signaling in the frontal cortices, striata, and hippocampi of adolescent mice

Maternal smoking of conventional or vapor cigarettes during pregnancy, a form of developmental nicotine exposure (DNE), enhances the risk of neurodevelopmental disorders such as ADHD, autism, and schizophrenia in children. Modeling the multigenerational effects of smoking during pregnancy and nursing in the first- (F1) and second- (F2) generation adolescent offspring of oral nicotine-treated female C57BL/6J mice, we have previously reported that DNE precipitates intergenerational transmission of nicotine preference, hyperactivity and impulsivity-like behaviors, altered rhythmicity of home cage activity, corticostriatal nicotinic acetylcholine receptor and dopamine transporter dysfunction, and corticostriatal global DNA methylome deficits. In aggregate, these DNE-evoked behavioral, neuropharmacological, and epigenomic anomalies mirror fundamental etiological aspects of neurodevelopmental disorders including ADHD, autism, and schizophrenia. Expanding this line of research, the current study profiled the multigenerational neurotrophic and neuroendocrine consequences of DNE. Results reveal impaired proBDNF proteolysis as indicated by proBDNF-BDNF imbalance, downregulation of the proBDNF processing enzyme furin, atypical glucocorticoid receptor (GR) activity as implied by decreased relative nuclear GR localization, and deficient basal plasma corticosterone (CORT) levels in adolescent DNE offspring and grandoffspring. Collectively, these data recapitulate the BDNF deficits and HPA axis dysregulation characteristic of neurodevelopmental disorders such as ADHD, autism, and schizophrenia as well as the children of maternal smokers. Notably, as BDNF is a quintessential mediator of neurodevelopment, our prior findings of multigenerational DNE-induced behavioral and neuropharmacological abnormalities may stem from neurodevelopmental insults conferred by the proBDNF-BDNF imbalance detected in DNE mice. Similarly, our findings of multigenerational GR hypoactivity may contribute to the increased risk-taking behaviors and aberrant circadian rhythmicity of home cage activity that we previously documented in first- and second-generation DNE mice.

Prefrontal cortical trkB, glucocorticoids, and their interactions in stress and developmental contexts

The tropomyosin/tyrosine receptor kinase B (trkB) and glucocorticoid receptor (GR) regulate neuron structure and function and the hormonal stress response. Meanwhile, disruption of trkB and GR activity (e.g., by chronic stress) can perturb neuronal morphology in cortico-limbic regions implicated in stressor-related illnesses like depression. Further, several of the short- and long-term neurobehavioral consequences of stress depend on the developmental timing and context of stressor exposure. We review how the levels and activities of trkB and GR in the prefrontal cortex (PFC) change during development, interact, are modulated by stress, and are implicated in depression. We review evidence that trkB- and GR-mediated signaling events impact the density and morphology of dendritic spines, the primary sites of excitatory synapses in the brain, highlighting effects in adolescents when possible. Finally, we review the role of neurotrophin and glucocorticoid systems in stress-related metaplasticity. We argue that better understanding the long-term effects of developmental stressors on PFC trkB, GR, and related factors may yield insights into risk for chronic, remitting depression and related neuropsychiatric illnesses.

Oral Probiotics Ameliorate the Behavioral Deficits Induced by Chronic Mild Stress in Mice via the Gut Microbiota-Inflammation Axis

In recent years, a burgeoning body of research has revealed links between depression and the gut microbiota, leading to the therapeutic use of probiotics for stress-related disorders. In this study, we explored the potential antidepressant efficacy of a multi-strain probiotics treatment (Lactobacillus helveticus R0052, Lactobacillus plantarum R1012, and Bifidobacterium longum R0175) in a chronic mild stress (CMS) mouse model of depression and determined its probable mechanism of action. Our findings revealed that mice subjected to CMS exhibited anxiety- and depressive-like behaviors in the sucrose preference test, elevated plus maze, and forced swim test, along with increased interferon-γ, tumor necrosis factor-α, and indoleamine 2,3-dioxygenase-1 levels in the hippocampus. Moreover, the microbiota distinctly changed from the non-stress group and was characterized by highly diverse bacterial communities associated with significant reductions in Lactobacillus species. Probiotics attenuated CMS-induced anxiety- and depressive-like behaviors, significantly increased Lactobacillus abundance, and reversed the CMS-induced immune changes in the hippocampus. Thus, the possible mechanism involved in the antidepressant-like activity of probiotics is correlated with Lactobacillus species via the gut microbiota-inflammation-brain axis.

Pro-BDNF Contributes to Hypoxia/Reoxygenation Injury in Myocardial Microvascular Endothelial Cells: Roles of Receptors p75NTR and Sortilin and Activation of JNK and Caspase 3

The aim of this study was to identify the role of the precursor of the brain-derived neurotrophic factor (pro-BDNF) in myocardial hypoxia/reoxygenation injury (H/R) and to address the underlying mechanisms. For this purpose, myocardial microvascular endothelial cells (MMECs) exposed to a high concentration of glucose (30 mM) for 48 h were subjected to 4 h of hypoxia followed by 2 h of reoxygenation. Terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling (TUNEL) staining and flow-cytometric analysis were performed to detect apoptosis. Cell scratch and capillary-like-structure formation assays were employed to evaluate cell function. The levels of apoptosis-related proteins were evaluated by Western blotting and immunofluorescence assays. Our results showed that H/R resulted in MMEC injury, as indicated by significant increases in TUNEL-positive cell numbers and a reduction in MMEC migration and in capillary-like-structure formation coupled with increased pro-BDNF protein expression. In addition, overexpression of pro-BDNF in MMECs via a viral vector led to increased pro-BDNF expression, and this upregulation induced apoptosis. Mechanistic experiments revealed that H/R did not influence BDNF, JNK, and caspase 3 expression, but upregulated pro-BDNF, p75^NTR, sortilin, phospho-JNK, and cleaved caspase 3 protein levels. In contrast, neutralization of endogenous pro-BDNF with an antibody significantly attenuated H/R-induced upregulation of pro-BDNF, p75^NTR, sortilin, p-JNK, and cleaved caspase 3 protein levels, indicating that p75^NTR-sortilin signaling and activation of JNK and caspase 3 may be involved in these effects. In conclusion, H/R-induced injury may be mediated by pro-BDNF, at least in part through the regulation of p75^NTR-sortilin signaling and activation of JNK and caspase 3.

Beyond good and evil: A putative continuum-sorting hypothesis for the functional role of proBDNF/BDNF-propeptide/mBDNF in antidepressant treatment

Depression and posttraumatic stress disorder are assumed to be maladaptive responses to stress and antidepressants are thought to counteract such responses by increasing BDNF (brain-derived neurotrophic factor) levels. BDNF acts through TrkB (tropomyosin-related receptor kinase B) and plays a central role in neuroplasticity. In contrast, both precursor proBDNF and BDNF propeptide (another metabolic product from proBDNF cleavage) have a high affinity to p75 receptor (p75R) and usually convey apoptosis and neuronal shrinkage. Although BDNF and proBDNF/propeptide apparently act in opposite ways, neuronal turnover and remodeling might be a final common way that both act to promote more effective neuronal networking, avoiding neuronal redundancy and the misleading effects of environmental contingencies. This review aims to provide a brief overview about the BDNF functional role in antidepressant action and about p75R and TrkB signaling to introduce the "continuum-sorting hypothesis." The resulting hypothesis suggests that both BDNF/proBDNF and BDNF/propeptide act as protagonists to fine-tune antidepressant-dependent neuroplasticity in crucial brain structures to modulate behavioral responses to stress.

Role of tissue-type plasminogen activator and plasminogen activator inhibitor-1 in psychological stress and depression

Major depressive disorder is a common illness worldwide, but the pathogenesis of the disorder remains incompletely understood. The tissue-type plasminogen activator-plasminogen proteolytic cascade is highly expressed in the brain regions involved in mood regulation and neuroplasticity. Accumulating evidence from animal and human studies suggests that tissue-type plasminogen activator and its chief inhibitor, plasminogen activator inhibitor-1, are related to stress reaction and depression. Furthermore, the neurotrophic hypothesis of depression postulates that compromised neurotrophin brain-derived neurotrophic factor (BDNF) function is directly involved in the pathophysiology of depression. In the brain, the proteolytic cleavage of proBDNF, a BDNF precursor, to mature BDNF through plasmin represents one mechanism that can change the direction of BDNF action. We also discuss the implications of tissue-type plasminogen activator and plasminogen activator inhibitor-1 alterations as biomarkers for major depressive disorder. Using drugs that increase tissue-type plasminogen activator or decrease plasminogen activator inhibitor-1 levels may open new avenues to develop conceptually novel therapeutic strategies for depression treatment.

Hippocampal BDNF overexpression or microR124a silencing reduces anxiety- and autism-like behaviors in rats

MicroRNA124a (miR124a) has emerged recently as a key player for multiple neuropsychiatric disorders including depression, anxiety, alcoholism, and cocaine addiction. Although we have previously reported that miR124a and its target the brain-derived neutrophic factor (BDNF) play an important role in autism-like behaviors, the molecular and behavioral dysfunctions remain unknown. The aim of this study was to understand the effects of sustained decreases in miR124a and increases of BDNF in the dentate gyrus (DG) on neonatal isolation-induced anxiety-and autism like behaviors in rats. Here we report that lentiviral-mediated silencing of miR124a in the adult DG attenuated neonatal isolation-induced anxiety-like behavior in the elevated plus maze (EPM) and open-field (OF) tests. Also, miR124a silencing decreased autism-like phenotype in the marble burying test (MBT), self-grooming (SG), and social interaction tests. Pearson's correlations demonstrated that high levels of BDNF, a direct target of miR124a, were negatively correlated with miR124a expression. Interestingly, viral-mediated BDNF overexpression in the DG also reversed the neonatal isolation-induced anxiety-and autism like phenotypes. Collectively, these findings suggest that miR124a, through its target BDNF, may influence neonatal isolation-induced anxiety-and autism like behaviors. In conclusion, these results do support the hypothesis that miR124a in discrete hippocampal areas contributes to anxiety- and autism-like behaviors and may be involved in the neuroadaptations underlying the development of autism spectrum disorders as a persistent and lasting condition, and therefore provide a clearer mechanistic framework for understanding the physiopathology of such psychiatric illnesses.