Engeletin alleviates depression-like phenotype by increasing synaptic plasticity via the BDNF-TrkB-mTORC1 signalling pathway.

Major depressive disorder (MDD) is a severe mental disorder associated with high rates of morbidity and mortality. Current first-line pharmacotherapies for MDD are based on enhancement of monoaminergic neurotransmission, but these antidepressants are still insufficient and produce significant side-effects. Consequently, the development of novel antidepressants and therapeutic targets is desired. Engeletin, a natural Smilax glabra rhizomilax derivative, is a compound with proven efficacy in treating ischemic stroke, yet its therapeutic effects and mechanisms for depression remain unexplored. The effects of engeletin were assessed in the forced swimming test (FST) and tail suspension test (TST) in mice. Engeletin was also investigated in the chronic restraint stress (CRS) mouse model of depression with fluoxetine (FLX) as the positive control. Changes in prefrontal cortex (PFC) spine density, synaptic plasticity-linked protein expressions and the brain-derived neurotrophic factor (BDNF)-tyrosine kinase B (TrkB)- mammalian target of rapamycin complex 1 (mTORC1) signalling pathway after chronic stress and engeletin treatment were then investigated. The TrkB and mTORC1 selective inhibitors, ANA-12 and rapamycin, respectively, were utilized to assess the engeletin's antidepressive mechanisms. Our data shows that engeletin exhibited antidepressant-like activity in the FST and TST in mice without affecting locomotor activity. Furthermore, it exhibited efficiency against the depression of CRS model. Moreover, it enhanced the BDNF-TrkB-mTORC1 pathway in the PFC during CRS and altered the reduction in dendritic spine density and levels of synaptic plasticity-linked protein induced by CRS. In conclusion, engeletin has antidepressant activity via activation of the BDNF-TrkB-mTORC1 signalling pathway and upregulation of PFC synaptic plasticity.

The Toll-like receptor 4 antagonist TAK-242 induces antidepressant-like effects in a rat learned helplessness model of depression through BDNF-TrkB signaling and AMPA receptor activation.

Finding from animal models of depression indicated that Toll-like receptor 4 (TLR4) is associated with the pathophysiology of depression. Herein, the TLR4 antagonists TAK-242 and baicalin induced antidepressant-like effects in a rat learned helplessness model of depression. The antidepressant-like effects of both TLR4 antagonists were blocked by the TrkB inhibitor ANA-12. Also, the antidepressant-like effects of TAK-242 were blocked by the treatment with AMPA receptor antagonist NBQX. The antidepressant-like effects of the TLR4 antagonist TAK-242 involves BDNF-TrkB signaling and AMPA receptor activation.

7,8-Dihydroxyflavone protects retinal ganglion cells against chronic intermittent hypoxia-induced oxidative stress damage via activation of the BDNF/TrkB signaling pathway.

PURPOSE: Chronic intermittent hypoxia (CIH) plays a key role in the complications of obstructive sleep apnea (OSA), which is strongly associated with retinal and optic nerve diseases. Additionally, the brain-derived neurotrophic factor (BDNF)/tropomyosin receptor kinase B (TrkB) signaling pathway plays an important protective role in neuronal injury. In the present study, we investigated the role of 7,8-dihydroxyflavone (7,8-DHF) in regulating CIH-induced injury in mice retinas and rat primary retinal ganglion cells (RGCs). METHODS: C57BL/6 mice and in vitro primary RGCs were exposed to CIH or normoxia and treated with or without 7,8-DHF. The mice eyeballs or cultured cells were then taken for histochemistry, immunofluorescence or biochemistry, and the protein expression of the BDNF/TrkB signaling pathway analysis. RESULTS: Our results showed that CIH induced oxidative stress (OS) in in vivo and in vitro models and inhibited the conversion of BDNF precursor (pro-BDNF) to a mature form of BDNF, which increased neuronal cell apoptosis. 7,8-DHF reduced the production of reactive oxygen species (ROS) caused by CIH and effectively activated TrkB signals and downstream protein kinase B (Akt) and extracellular signal-regulated kinase (Erk) survival signaling pathways, which upregulated the expression of mature BDNF. ANA-12 (a TrkB specific inhibitor) blocked the protective effect of 7,8-DHF. CONCLUSION: In short, the activation of the BDNF/TrkB signaling pathway alleviated CIH-induced oxidative stress damage of the optic nerve and retinal ganglion cells. 7,8-DHF may serve as a promising agent for OSA related neuropathy.

Targeting both BDNF/TrkB pathway and delta-secretase for treating Alzheimer's disease.

Alzheimer's disease (AD) is the most common dementia, and no disease-modifying therapeutic agents are currently available. BDNF/TrkB signaling is impaired in AD and is associated with prominent delta-secretase (δ-secretase, also known as asparaginyl endopeptidase or legumain) activation, which simultaneously cleaves both APP and Tau and promotes Aß production and neurofibrillary tangles (NFT) pathologies. Here we show that the optimized δ-secretase inhibitor (#11a) or TrkB receptor agonist (CF3CN) robustly blocks δ-secretase activity separately, and their combination synergistically blunts δ-secretase, exhibiting promising therapeutic efficacy in 3xTg AD mouse model. The optimal δ-secretase inhibitor reveals demonstrable brain exposure and oral bioavailability, suppressing APP N585 and Tau N368 cleavage by δ-secretase. Strikingly, CF3CN treatment evidently escalates BDNF levels. Both #11a and CF3CN display strong in vivo PK/PD properties and ability to suppress δ-secretase activity in the brain. Orally administrated CF3CN strongly activates TrkB that triggers active Akt to phosphorylate δ-secretase T322, preventing its proteolytic activation and mitigating AD pathologies. #11a or CF3CN significantly diminishes AD pathogenesis and improves cognitive functions with the combination exhibiting the maximal effect. Thus, our data support that these derivatives are strong pharmaceutical candidates for the treatment of AD.

Decreased spasticity of Baishaoluoshi Decoction through the BDNF/TrKB-KCC2 pathway on poststroke spasticity rats.

OBJECTIVE: K+-Cl- cotransporter-2 (KCC2), which primarily extrudes chloride in mature neurons, triggers hemiplegia limb spasticity after ischemic stroke by affecting neuronal excitability. Our previous study revealed that the Chinese herb Baishaoluoshi Decoction decreases hemiplegia limb spasticity in poststroke spasticity (PSS) patients. This study aimed at elucidating on the effects of Baishaoluoshi Decoction on the BDNF/TrKB-KCC2 pathway in PSS rat models. METHODS: Middle cerebral artery occlusion (MCAO) was adopted for the establishment of PSS rat models. Muscle tension was evaluated by Modified Ashworth Scale. Nissl staining and transmission electron microscopy were used to measure the protective effects of Baishaoluoshi Decoction on ischemic injury-induced neuronal damage due to MCAO. Expression levels of BDNF, TrKB, and KCC2 in brain tissues around the infarct and brainstem were detected by immunohistochemical staining. RESULTS: It was found that Baishaoluoshi Decoction suppressed hemiplegia limb spasticity and alleviated the damage in neurons and synapses in PSS rat models. Importantly, the expression of BDNF, TrKB, and KCC2 in brain tissues around the infarct and brainstem were significantly upregulated after treatment with low-dose and high-dose Baishaoluoshi Decoction. CONCLUSION: Suppression of spasticity by Baishaoluoshi Decoction in PSS rat models may be correlated with upregulated BDNF/TrKB-KCC2 pathway, which may be a complementary therapeutic strategy for PSS.

Apelin-13 activates the hippocampal BDNF/TrkB signaling pathway and suppresses neuroinflammation in male rats with cisplatin-induced cognitive dysfunction.

It has been established that cisplatin causes neuronal damage and cognitive impairment. However, the mechanism is not sufficiently clear. Apelin-13 is an endogenous peptide with strong neuroprotective effects through the synthesis of neurotrophic factors and suppression of inflammation. The aim of this study was to investigate the role of brain-derived neurotrophic factor/tropomyosin receptor kinase B (BDNF/TrkB) signaling pathway and the potential inhibitory effects of apelin-13 in the mechanism of cisplatin-induced hippocampal damage and cognitive impairment. Apelin-13 was administered to adult sprague dawley male rats at a dose of 20 nmol/kg every day for 4 weeks, cisplatin was administered at a dose of 5 mg/kg once a week for 4 weeks. The spatial and recognition memory tests of the rats were performed on the 5th week. BDNF and the inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-1ß (IL-1ß) levels were measured by ELISA in hippocampal homogenates. Pyramidal neuron and glial cell damage in the hippocampal CA1, CA3 and dentate gyrus (DG) were analyzed histologically. TrkB activity in the hippocampus was determined by immunohistochemical methods. Cisplatin impaired spatial and recognition memory in rats, while apelin-13 improved spatial memory but did not affect recognition memory. Cisplatin suppressed BDNF in the hippocampus while increased IL-1ß and TNF-α. In contrast, apelin-13 administration increased BDNF but significantly suppressed TNF-α and IL-1B. Cisplatin caused pyramidal neuron and glial cell damage in CA1, CA3 and DG. In the cisplatin + apelin-13 group, however, pyramidal neuron and glial cell damage was less than those without apelin-13. Cisplatin increased TrkB activity in the hippocampus, which was counteracted by apelin-13. In conclusion, apelin-13 reduced the cisplatin-induced cognitive deficiency, by suppressing inflammation and stimulating the synthesis and activation of neurotrophic factors in hippocampal tissue.

Protective effect of ginsenoside Rb1 against chronic restraint stress (CRS)-induced memory impairments in rats.

Ginsenoside Rb1 (Rb1) is one of the most active components found in ginseng and provides important benefits to the central nervous system, especially for the improvement of learning and memory. Previous studies demonstrated that Rb1 protected against scopolamine-induced amnesia and exhibited memory-enhancing effects in the SAMP8 mouse model. However, the effects of Rb1 against chronic restraint stress (CRS)-induced cognitive impairments, especially the role of Rg1 on the performance of reward directed instrumental conditioning have not been investigated. In this study, rats were subjected to CRS (6 h/day) for 28 days. Thereafter, behavioural tests including reward-directed instrumental conditioning task (RICT) and the Morris water maze (MWM) task were conducted. Administered of Rb1 (6.75 and 13.5 mg/kg, i.p.) remarkably ameliorated the memory impairments caused by CRS as evident from the results of RICT and MWM task, and this effect was accompanied by noticeable alterations in the levels of oxidative markers (superoxide dismutase, catalase, and lipid peroxidation) in the hippocampus. Additionally, Rb1 reduced the ratio of Bax:Bcl-2 and the expression of cleaved caspase-3 and cleaved caspase-9, increased the levels of synaptophysin (SYP) and postsynaptic density 95 (PSD95) and activated the BDNF/TrkB pathway in the hippocampus. In summary, the present study demonstrated that Rb1 rescues cognitive deficits induced by CRS is partially mediated by antagonizing oxidative stress and apoptosis, improving synaptic plasticity and restoring the BDNF/TrkB signalling pathway. This newly discovered effect of Rb1 sheds light on its applications in the development of therapeutic interventions to alleviate the deleterious effects of chronic stress.

Prophylactic effects of sporoderm-removed Ganoderma lucidum spores in a rat model of streptozotocin-induced sporadic Alzheimer's disease.

ETHNOPHARMACOLOGICAL RELEVANCE: Ganoderma lucidum (G. lucidum, Lingzhi), also known as "immortality mushroom" has been broadly used to improve health and longevity for thousands of years in Asia. G. lucidum and its spores have been used to promote health, based on its broad pharmacological and therapeutic activity. This species is recorded in Chinese traditional formula as a nootropic and has been suggested to improve cognitive dysfunction in Alzheimer's disease. However, little is known about the nootropic effects and molecular mechanism of action of G. lucidum spores. AIM OF THE STUDY: The present study investigated the protective effects of sporoderm-deficient Ganoderma lucidum spores (RGLS) against learning and memory impairments and its mechanism of action. MATERIALS AND METHODS: In the Morris water maze, the effects of RGLS on learning and memory impairments were evaluated in a rat model of sporadic Alzheimer's disease that was induced by an intracerebroventricular injection of streptozotocin (STZ). Changes in amyloid ß (Aß) expression, Tau expression and phosphorylation, brain-derived neurotrophic factor (BDNF), and the BDNF receptor tropomyosin-related kinase B (TrkB) in the hippocampus were evaluated by Western blot. RESULTS: Treatment with RGLS (360 and 720 mg/kg) significantly enhanced memory in the rat model of STZ-induced sporadic Alzheimer's disease and reversed the STZ-induced increases in Aß expression and Tau protein expression and phosphorylation at Ser199, Ser202, and Ser396. The STZ-induced decreases in neurotrophic factors, including BDNF, TrkB and TrkB phosphorylation at Tyr816, were reversed by treatment with RGLS. CONCLUSION: These findings indicate that RGLS prevented learning and memory impairments in the present rat model of STZ-induced sporadic Alzheimer's disease, and these effects depended on a decrease in Aß expression and Tau hyperphosphorylation and the modulation of BDNF-TrkB signaling in the hippocampus.

Allopregnanolone induces antidepressant-like effects through BDNF-TrkB signaling independent from AMPA receptor activation in a rat learned helplessness model of depression.

Allopregnanolone (ALLO, 3α5α-tetrahydroprogesterone) was found to be effective for depressed patients. Animal models of depression indicate that ALLO is associated with the pathophysiology of depression. Traditional antidepressant drugs produce antidepressant effects via the monoamine system, with consequent up-regulation of brain-derived neurotrophic factor (BDNF). This study was designed to examine whether the antidepressant effects of ALLO involve BDNF-TrkB signaling or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor activation on the learned helplessness paradigm. The antidepressant-like effect of ALLO infusion into the cerebral ventricle was blocked by coinfusion of TrkB inhibitor ANA-12, but not by co-administration of AMPA receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfoamoylbenzo(f)quinoxaline (NBQX). Thus, the antidepressant-like effect of ALLO involves BDNF signaling independent from AMPA receptor activation.

Binge and Subchronic Exposure to Ketamine Promote Memory Impairments and Damages in the Hippocampus and Peripheral Tissues in Rats: Gallic Acid Protective Effects.

Ketamine (KET) is a dissociative anesthetic for restrict medical use with high potential for abuse and neurotoxicity which does not prevent its recreational use. Gallic acid (GA) is a natural free radical "scavenger." We evaluated the GA protective role regarding binge or subchronic (SbChro) KET-induced toxicity in adolescent rats. In the binge protocol, animals were treated with GA (one dose of 13.5 mg/kg, p.o. every 2 h, totaling 3 doses) 12 h after KET exposure (one dose of 10 mg/kg, i.p., every 3 h, totaling 5 doses). In the SbChro, animals were treated with GA (one dose of 13.5 mg/kg/day, p.o., for 3 days) 48 h following KET exposure (one dose of 10 mg/kg/day, i.p) for 10 days. Our findings show that binge-KET impaired memory, increased pro-BDNF and TrkB levels in the hippocampus, and increased lipid peroxidation (LP) in the kidney and hippocampus, while SbChro-KET impaired memory, increased pro-BDNF, and decreased both BDNF and TrkB levels in the hippocampus, and increased LP in the kidney, liver, and hippocampus. GA treatment reversed the subchronically KET-induced harmful influences better. Interestingly, only memory impairment observed in the SbChro-KET protocol was reversed by GA. Memory impairments showed a positive correlation with hippocampal BDNF levels and negative with LP levels in the same brain area. This last hippocampal damage (LP) showed a negative correlation with BDNF levels in the hippocampus, indicating an interesting and close causal connection. Our outcomes show that the deleterious effects of SbChro-KET exposure can be attenuated or abolished with GA administration, a natural antioxidant that could be considered in KET abuse treatment.

Acute vitamin B12 supplementation evokes antidepressant response and alters Ntrk-2.

Depression is the leading cause of disability worldwide. Although most research into risk factors focuses on stress, dietary factors also have a strong link with depression. For instance, chronic vitamin B12-supplementation may reduce depression risk and helps to reverse the prodepressive effects of early life stress in animal models. However, it is still unclear whether a single acute dose of vitamin B12 is sufficient to induce antidepressant effects on molecular or behavioral levels. Based on pharmacological work and CRISPR-dCas9 epigenome editing in Neuro2A-cells we provide in vitro evidence for a link between vitamin B12, gene expression and DNA methylation of the antidepressant-associated gene Ntrk-2, which codes for the BDNF-receptor TRKB. Using stress-induction protocols in C57Bl/6 J mice combined with behavioral testing and subsequent molecular tissue analysis, we establish in vivo evidence for antidepressant effects of vitamin B12. Acute supplementation with vitamin B12, but not folic acid, selectively altered DNA methylation and gene expression of Ntrk-2 in vitro, albeit DNA methylation and Ntrk-2 gene expression do not correlate in vivo. Importantly, one acute vitamin B12 injection improved multiple behavioral measures in tests for antidepressant action and at the same time reversed the effects of chronic and acute stress on Ntrk-2 levels in vivo, however causality has not been proven at this stage. Taken together, acute vitamin B12 supplementation can reverse stress effects on Ntrk-2 gene expression and improve behaviors that are associated with depression-like behavior in mice. Our findings encourage further investigation of vitamin B12-supplementation as a novel model for antidepressant action.

Behavioral alterations induced by post-weaning isolation rearing of rats are accompanied by reduced VGF/BDNF/TrkB signaling in the hippocampus.

Post-weaning social isolation has been shown to be a relevant animal model for studying the mechanisms underlying psychopathological states induced by early-life stressful experiences. Besides extensively studied brain-derived neurotrophic factor (BDNF) and tyrosine receptor kinase B (TrkB) receptor, increasing attention is being given to a neuropeptide precursor VGF (non-acronymic). Several lines of evidence indicate an interplay between the neurotrophins and nitric oxide signaling. This study investigated the long-term consequences of post-weaning social isolation on behavior, VGF/BDNF/TrkB pathway and two isoforms of nitric oxide synthase (NOS) in the hippocampus and examined whether these effects were sex-specific. Male and female Sprague-Dawley rats were reared either in social isolation or social groups from postnatal day 21 for 9 weeks (n = 12-15/group and sex). Post-weaning social isolation induced impairments in sensorimotor gating and increased anxiety-like behavior in rats of both sexes. These behavioral alterations were accompanied by attenuated gene expression of VGF and TrkB receptor in the hippocampus. Isolation-induced reduction in VGF gene expression was more evident in male isolates. Similar changes were found in neuronal NOS (nNOS) gene expression with reduced mRNA levels in male isolates. Gene expression of BDNF and inducible NOS was not influenced by isolation rearing or sex. In addition, sex-specific patterns of VGF and nNOS gene expression in the hippocampus with higher mRNA levels in males than in females were revealed. The present study demonstrates a relationship between nNOS, VGF, BDNF, and TrkB confirming a link between nitric oxide and neurotrophins signaling pathways. Our findings indicate that long-term post-weaning social isolation alters signaling via VGF/BDNF/TrkB and nNOS that could interfere with neurodevelopmental processes which may contribute to pathological behavioral symptoms in adulthood. Future studies are needed to support this suggestion since the direct mechanistic link has not been approached in this study.

Activation of the TRKB receptor mediates the panicolytic-like effect of the NOS inhibitor aminoguanidine.

Nitric oxide (NO) triggers escape reactions in the dorsal periaqueductal gray matter (dPAG), a core structure mediating panic-associated response, and decreases the release of BDNF in vitro. BDNF mediates the panicolytic effect induced by antidepressant drugs and produces these effects per se when injected into the dPAG. Based on these findings, we hypothesize that nitric oxide synthase (NOS) inhibitors would have panicolytic properties associated with increased BDNF signaling in the dPAG. We observed that the repeated (7 days), but not acute (1 day), systemic administration of the NOS inhibitor aminoguanidine (AMG; 15 mg/kg/day) increased the latency to escape from the open arm of the elevated T-maze (ETM) and inhibited the number of jumps in hypoxia-induced escape reaction in rats, suggesting a panicolytic-like effect. Repeated, but not acute, AMG administration (15 mg/kg) also decreased nitrite levels and increased TRKB phosphorylation at residues Y706/7 in the dPAG. Notwithstanding the lack of AMG effect on total BDNF levels in this structure, the microinjection of the TRK antagonist K252a into the dPAG blocked the anti-escape effect of this drug in the ETM. Taken together our data suggest that the inhibition of NO production by AMG increases the levels of pTRKB, which is required for the panicolytic-like effect observed.

Reduced Hippocampal Dendrite Branching, Spine Density and Neurocognitive Function in Premature Rabbits, and Reversal with Estrogen or TrkB Agonist Treatment.

Preterm-born children suffer from neurological and behavioral disorders. Herein, we hypothesized that premature birth and non-maternal care of preterm newborns might disrupt neurobehavioral function, hippocampal dendritic arborization, and dendritic spine density. Additionally, we assessed whether 17ß-estradiol (E2) replacement or the TrkB receptor agonist, 7,8-dihydroxyflavone (DHF), would reverse compromised dendritic development and cognitive function in preterm newborns. These hypotheses were tested by comparing preterm (E28.5) rabbit kits cared and gavage-fed by laboratory personnel and term-kits reared and breast-fed by their mother doe at an equivalent postconceptional age. Neurobehavioral tests showed that both premature-birth and formula-feeding with non-maternal care led to increased anxiety behavior, poor social interaction, and lack of novelty preference compared with term-kits. Dendritic branching and number of total or mushroom dendritic spines were reduced in the CA1 field of preterm-kits compared with term controls. While CDC42 and Rac1/2/3 expression levels were lower, RhoA-activity was higher in preterm-kits compared with term controls. Both E2 and DHF treatment reversed prematurity-induced reduction in spine density, reduced total RhoA-GTPase levels, and enhanced cognitive function. Hence, prematurity and non-maternal care result in cognitive deficits, and reduced dendritic arbors and spines in CA1. E2 replacement or DHF treatment might reverse changes in dendritic spines and improve neurodevelopment in premature infants.

Astrocyte-Conditioned Medium Protects Prefrontal Cortical Neurons from Glutamate-Induced Cell Death by Inhibiting TNF-α Expression.

OBJECTIVE: Both excitotoxicity and neurotrophin deficiency may contribute to the etiology of depression and neurodegeneration. Astrocytes not only regulate glutamate metabolism and clearance, they also produce neurotrophins in the brain. However, the direct interaction between neurons and astrocytes remains unknown. METHODS: This study evaluated the cellular mechanisms by which astrocyte-conditioned medium (ACM) protects prefrontal cortical neurons from glutamate-induced death by measuring cell viability and morphology as well as mRNA and protein expression of brain-derived neurotrophic factor (BDNF), BDNF receptors, glial cell line-derived neurotrophic factor (GDNF), and the proinflammatory cytokine, tumor necrosis factor (TNF)-α. Neurons and astrocytes were purified from the brains of neonatal 1-day-old Sprague-Dawley rats. ACM was harvested after exposing astrocytes to culture medium containing 100 µM glutamate for 48 h. RESULTS: Glutamate insult (100 µM for 6 h) significantly reduced neuronal cell viability and increased the mRNA expression of BDNF. Glutamate (24 h) decreased neuronal viability and the expression of BDNF, but increased mRNA expression of GFAP, p75 neurotrophin receptor (p75NTR), and TNF-α. ACM pretreatment (2 h) reversed glutamate-decreased cell viability and increased BDNF, but reduced the expression of GDNF, P75NTR, and TNF-α at the mRNA level. Western blotting generally confirmed the mRNA expression following 24 glutamate insults. Furthermore, the glutamate-induced decrease in the protein expression of BDNF and full-length TrkB receptor and increase in pro-BDNF, truncated TrkB isoform 1 receptor, p75NTR, GDNF, and TNF-α were significantly attenuated by ACM pretreatment. CONCLUSIONS: The study demonstrates that ACM exerts neuroprotective effects on cell viability, and this effect is most likely mediated through the modulation of neurotrophin and TNF-α expression.

ERK1/2-mediated disruption of BDNF-TrkB signaling causes synaptic impairment contributing to fluoride-induced developmental neurotoxicity.

Excessive exposure to fluoride has adverse effects on neurodevelopment, but the mechanisms remain unclear. This study aimed to investigate the effects of fluoride exposure on synaptogenesis, and focused on the role of brain-derived neurotrophic factor (BDNF)-tyrosine kinase B (TrkB) signaling in these effects. Using Sprague-Dawley rats developmentally exposed to sodium fluoride (NaF) from pregnancy until 6 months of delivery as in vivo model, we showed that fluoride impaired the cognitive abilities of offspring rats, decreased the density of dendritic spines and the expression of synapse proteins synaptophysin (SYN) and postsynaptic density protein-95 (PSD-95) in hippocampus, suggesting fluoride-induced cognitive deficit associates with synaptic impairment. Consistently, NaF treatment reduced dendritic outgrowth and expression of SYN and PSD-95 in human neuroblastoma SH-SY5Y cells. Further studies demonstrated that the BDNF-TrkB axis was disrupted in vivo and in vitro, as manifested by BDNF accumulation and TrkB reduction. Importantly, fluoride treatment increased phospho-extracellular signal-regulated kinases 1 and 2 (p-ERK1/2) expression, while inhibition of p-ERK1/2 significantly attenuated the effects of NaF, indicating a regulating role of p-ERK1/2 in BDNF-TrkB signaling disruption. Collectively, these data suggest that the developmental neurotoxicity of fluoride is associated with the impairment of synaptogenesis, which is caused by ERK1/2-mediated BDNF-TrkB signaling disruption.

Arsenic trioxide induces cell cycle arrest and affects Trk receptor expression in human neuroblastoma SK-N-SH cells.

BACKGROUND: Arsenic trioxide (As2O3), a drug that has been used in China for approximately two thousand years, induces cell death in a variety of cancer cell types, including neuroblastoma (NB). The tyrosine kinase receptor (Trk) family comprises three members, namely TrkA, TrkB and TrkC. Various studies have confirmed that TrkA and TrkC expression is associated with a good prognosis in NB, while TrkB overexpression can lead to tumor cell growth and invasive metastasis. Previous studies have shown that As2O3 can inhibit the growth and proliferation of a human NB cell line and can also affect the N-Myc mRNA expression. It remains unclear whether As2O3 regulates Trks for the purposes of treating NB. METHODS: The aim of the present study was to investigate the effect of As2O3 on Trk expression in NB cell lines and its potential therapeutic efficacy. SK-N-SH cells were grown with increasing doses of As2O3 at different time points. We cultured SK-N-SH cells, which were treated with increasing doses of As2O3 at different time points. Trk expression in the NB samples was quantified by immunohistochemistry, and the cell cycle was analyzed by flow cytometry. TrkA, TrkB and TrkC mRNA expression was evaluated by real-time PCR analysis. RESULTS: Immunohistochemical and real-time PCR analyses indicated that TrkA and TrkC were over-expressed in NB, and specifically during stages 1, 2 and 4S of the disease progression. TrkB expression was increased in stage 3 and 4 NB. As2O3 significantly arrested SK-N-SH cells in the G2/M phase. In addition, TrkA, TrkB and TrkC expression levels were significantly upregulated by higher concentrations of As2O3 treatment, notably in the 48-h treatment period. Our findings suggested that to achieve the maximum effect and appropriate regulation of Trk expression in NB stages 1, 2 and 4S, As2O3 treatment should be at relatively higher concentrations for longer delivery times;however, for NB stages 3 and 4, an appropriate concentration and infusion time for As2O3 must be carefully determined. CONCLUSION: The present findings suggested that As2O3 induced Trk expression in SK-N-SH cells to varying degrees and may be a promising adjuvant to current treatments for NB due to its apoptotic effects.

Phycoerythrin Peptide from Pyropia yezoensis Alleviates Endoplasmic Reticulum Stress Caused by Perfluorooctane Sulfonate-Induced Calcium Dysregulation.

Perfluorooctane sulfonate (PFOS), a stable fluorosurfactant, causes endoplasmic reticulum (ER) stress in the brain. This study was designed to investigate whether a phycoerythrin-derived peptide of Pyropia yezoensis (PYP) reduces PFOS-induced ER stress associated with calcium dysregulation. The protective effects of PYP were determined by cell viability, immunoblotting for ER stress response protein glucose-regulated protein 78 (GRP78) and calcium-dependent protein kinases in rat frontal cortical neurons. PFOS-induced decrease in cell viability was attenuated by PYP pretreatment (1 µg/mL) for 24 h, which was downregulated by inhibiting tropomyosin-receptor kinase B (TrkB). PYP pretreatment downregulated the increase in intracellular calcium levels and phosphorylation of calcium/calmodulin-dependent protein kinase II and c-Jun N-terminal kinase which are associated with a PFOS-induced increase in GRP78. The PFOS-induced increase in GRP78 was downregulated via activation of TrkB receptor-linked extracellular signal-regulated kinases 1/2 (ERK1/2) by PYP pretreatment. Moreover, PYP microinjections (1 µg/kg, 0.54 nmol) attenuated the GRP78 expression in rat prefrontal cortex caused by PFOS (10 mg/kg) exposure for 2 weeks. These findings demonstrate that PYP enhances frontal cortical neuron viability via activation of TrkB receptor-ERK1/2 signaling and attenuation of ER stress in rat prefrontal cortex against PFOS exposure, suggesting that PYP might prevent neuronal dysfunctions caused by PFOS-induced ER stress.

BDNF release and signaling are required for the antidepressant actions of GLYX-13.

Conventional antidepressant medications, which act on monoaminergic systems, display significant limitations, including a time lag of weeks to months and low rates of therapeutic efficacy. GLYX-13 is a novel glutamatergic compound that acts as an N-methyl-D-aspartate (NMDA) modulator with glycine-like partial agonist properties; like the NMDA receptor antagonist ketamine GLYX-13 produces rapid antidepressant actions in depressed patients and in preclinical rodent models. However, the mechanisms underlying the antidepressant actions of GLYX-13 have not been characterized. Here we use a combination of neutralizing antibody (nAb), mutant mouse and pharmacological approaches to test the role of brain-derived neurotrophic factor-tropomyosin-related kinase B (BDNF-TrkB) signaling in the actions of GLYX-13. The results demonstrate that the antidepressant effects of GLYX-13 are blocked by intra-medial prefrontal cortex (intra-mPFC) infusion of an anti-BDNF nAb or in mice with a knock-in of the BDNF Val66Met allele, which blocks the processing and activity-dependent release of BDNF. We also demonstrate that pharmacological inhibitors of BDNF-TrkB signaling or of L-type voltage-dependent Ca2+ channels (VDCCs) block the antidepressant behavioral actions of GLYX-13. Finally, we examined the role of the Rho GTPase proteins by injecting a selective inhibitor into the mPFC and found that activation of Rac1 but not RhoA is involved in the antidepressant effects of GLYX-13. Together, these findings indicate that enhanced release of BDNF through exocytosis caused by activation of VDCCs and subsequent TrkB-Rac1 signaling is required for the rapid and sustained antidepressant effects of GLYX-13.