High-affinity Receptor For Brain-derived Neurotrophic Factor Research Articles

Alpha-2-macroglobulin prevents platelet aggregation induced by brain-derived neurotrophic factor

The brain-derived neurotrophic factor (BDNF) has been recently shown to have activating effects in isolated platelets. However, BDNF circulates in plasma and a mechanism to preclude constant activation of platelets appears necessary. Hence, we investigated the mechanism regulating BDNF bioavailability in blood.Protein-protein interactions were predicted by molecular docking and validated through immunoprecipitation. Platelet aggregation was assessed using light transmission aggregometry with washed platelets in response to classical agonists or BDNF, in the absence or presence of alpha-2-macroglobulin (α2M), and in platelet-rich plasma. BDNF signaling was assessed with phospho-blots.As little as 25% autologous plasma was sufficient to completely abolish platelet aggregation in response to BDNF. Docking predicted two forms of BDNF binding to native or activated α2M, in parallel and perpendicular arrangements, and the model suggested that the BDNF-α2M complex cannot bind to the high-affinity BDNF receptor, tropomyosin receptor kinase B (TrkB). Experimentally, native and activated α2M formed stable complexes with BDNF preventing BDNF-induced TrkB activation and signal transduction. Both native and activated α2M inhibited BDNF induced-platelet aggregation in a concentration-dependent manner with comparable half-maximal inhibitory concentrations (IC50≈ 125–150 nM).Our study implicates α2M as a physiological regulator of BDNF bioavailability, and as an inhibitor of BDNF-induced platelet activation in blood.

Inhibiting BDNF/TrkB.T1 receptor improves resiniferatoxin-induced postherpetic neuralgia through decreasing ASIC3 signaling in dorsal root ganglia

BackgroundPostherpetic neuralgia (PHN) is a devastating complication after varicella-zoster virus infection. Brain-derived neurotrophic factor (BDNF) has been shown to participate in the pathogenesis of PHN. A truncated isoform of the tropomyosin receptor kinase B (TrkB) receptor TrkB.T1, as a high-affinity receptor of BDNF, is upregulated in multiple nervous system injuries, and such upregulation is associated with pain. Acid-sensitive ion channel 3 (ASIC3) is involved in chronic neuropathic pain, but its relation with BDNF/TrkB.T1 in the peripheral nervous system (PNS) during PHN is unclear. This study aimed to investigate whether BDNF/TrkB.T1 contributes to PHN through regulating ASIC3 signaling in dorsal root ganglia (DRGs).MethodsResiniferatoxin (RTX) was used to induce rat PHN models. Mechanical allodynia was assessed by measuring the paw withdrawal thresholds (PWTs). Thermal hyperalgesia was determined by detecting the paw withdrawal latencies (PWLs). We evaluated the effects of TrkB.T1-ASIC3 signaling inhibition on the behavior, neuronal excitability, and inflammatory response during RTX-induced PHN. ASIC3 short hairpin RNA (shRNA) transfection was used to investigate the effect of exogenous BDNF on inflammatory response in cultured PC-12 cells.ResultsRTX injection induced mechanical allodynia and upregulated the protein expression of BDNF, TrkB.T1, ASIC3, TRAF6, nNOS, and c-Fos, as well as increased neuronal excitability in DRGs. Inhibition of ASIC3 reversed the abovementioned effects of RTX, except for BDNF and TrkB.T1 protein expression. In addition, inhibition of TrkB.T1 blocked RTX-induced mechanical allodynia, activation of ASIC3 signaling, and hyperexcitability of neurons. RTX-induced BDNF upregulation was found in both neurons and satellite glia cells in DRGs. Furthermore, exogenous BDNF activated ASIC3 signaling, increased NO level, and enhanced IL-6, IL-1β, and TNF-α levels in PC-12 cells, which was blocked by shRNA-ASIC3 transfection.ConclusionThese findings demonstrate that inhibiting BDNF/TrkB.T1 reduced inflammation, decreased neuronal hyperexcitability, and improved mechanical allodynia through regulating the ASIC3 signaling pathway in DRGs, which may provide a novel therapeutic target for patients with PHN.

Inhibition of BDNF signaling in the paraventricular nucleus of the hypothalamus lowers acute stress-induced pressor responses.

Brain-derived neurotrophic factor (BDNF) expression increases in the paraventricular nucleus of the hypothalamus (PVN) during stress, and our recent studies indicate that BDNF induces sympathoexcitatory and hypertensive responses when injected acutely or overexpressed chronically in the PVN. However, it remained to be investigated whether BDNF is involved in the mediation of stress-induced cardiovascular responses. Here we tested the hypothesis that inhibition of the high-affinity BDNF receptor TrkB in the PVN diminishes acute stress-induced cardiovascular responses. Male Sprague-Dawley rats were equipped with radiotelemetric transmitters for blood pressure measurement. BDNF-TrkB signaling was selectively inhibited by viral vector-mediated bilateral PVN overexpression of a dominant-negative truncated TrkB receptor (TrkB.T1, n = 7), while control animals ( n = 7) received green fluorescent protein (GFP)-expressing vector injections. Rats were subjected to acute water and restraint stress 3-4 wk after vector injections. We found that body weight, food intake, baseline mean arterial pressure (MAP), and heart rate were unaffected by TrkB.T1 overexpression. However, peak MAP increases were significantly reduced in the TrkB.T1 group compared with GFP both during water stress (GFP: 39 ± 2 mmHg, TrkB.T1: 27 ± 4 mmHg; P < 0.05) and restraint stress (GFP: 41 ± 3 mmHg, TrkB.T1: 34 ± 2 mmHg; P < 0.05). Average MAP elevations during the poststress period were also significantly reduced after both water and restraint stress in the TrkB.T1 group compared with GFP. In contrast, heart rate elevations to both stressors remained unaffected by TrkB.T1 overexpression. Our results demonstrate that activation of BDNF high-affinity TrkB receptors within the PVN is a major contributor to acute stress-induced blood pressure elevations. NEW & NOTEWORTHY We have shown that inhibition of the high-affinity brain-derived neurotrophic factor receptor TrkB in the paraventricular nucleus of the hypothalamus significantly reduces blood pressure elevations to acute stress without having a significant impact on resting blood pressure, body weight, and food intake.

Protection Of Neurocognitive Function During Cranial Irradiation Of Brain Tumors

Although radiation therapy can be effective against cancer, potential damage to normal tissues limits the amount that can be safely administered. In the central nervous system (CNS), radiation damage to normal tissues is associated with cognitive impairments. Chronic oxidative stress, neuroinflammation, suppressed hippocampal neurogenesis, and down regulation of the brain-derived neurotrophic factor (BDNF) have been identified as the causes for cognitive impairments following radiation therapy of the CNS. Based on these mechanisms, we tested two experimental drugs, each targeting a different pathway, for their ability to preserve normal tissue functions in experimental animals following cranial irradiation. The Mn porphyrin (MnP)-based redox active drug, MnTnBuOE-2-PyP5+ (MnBuOE), is able to cross the blood brain barrier and has been shown to protect normal tissues from radiation damage. Administration of MnBuOE for one week before cranial irradiation and continued for one week afterwards supported production and long-term survival of newborn neurons in the hippocampal dentate gyrus. However, prolonged administration of MnBuOE following cranial irradiation did not increase the efficacy further, suggesting the best therapeutic window for redox active drugs is centered around the time of irradiation. The small flavonoid compound 7,8-dihydroxyflavone (7,8-DHF) has been shown to activate the high affinity BDNF receptor, TrkB, and enhance dendrite outgrowth and neuronal survival. Chronic treatment with 7,8-DHF following cranial irradiation significantly restored spatial, contextual, and working memory, and this was achieved most likely by preservation of hippocampal neurogenesis and synaptic plasticity during the recovery phase following cranial irradiation. Given the different biological effects of the two experimental drugs, strategic use during their optimal therapeutic windows before and after cranial radiation therapy may achieve the best efficacy in preserving normal tissue functions.

Brain-derived neurotrophic factor and airway fibrosis in asthma

Airway remodeling in asthma driven by inflammation involves proliferation of epithelial cells and airway smooth muscle (ASM), as well as enhanced extracellular matrix (ECM) generation and deposition, i.e., fibrosis. Accordingly, understanding profibrotic mechanisms is important for developing novel therapeutic strategies in asthma. Recent studies, including our own, have suggested a role for locally produced growth factors such as brain-derived neurotrophic factor (BDNF) in mediating and modulating inflammation effects. In this study, we explored the profibrotic influence of BDNF in the context of asthma by examining expression, activity, and deposition of ECM proteins in primary ASM cells isolated from asthmatic vs. nonasthmatic patients. Basal BDNF expression and secretion, and levels of the high-affinity BDNF receptor TrkB, were higher in asthmatic ASM. Exogenous BDNF significantly increased ECM production and deposition, especially of collagen-1 and collagen-3 (less so fibronectin) and the activity of matrix metalloproteinases (MMP-2, MMP-9). Exposure to the proinflammatory cytokine TNFα significantly increased BDNF secretion, particularly in asthmatic ASM, whereas no significant changes were observed with IL-13. Chelation of BDNF using TrkB-Fc reversed TNFα-induced increase in ECM deposition. Conditioned media from asthmatic ASM enhanced ECM generation in nonasthmatic ASM, which was blunted by BDNF chelation. Inflammation-induced changes in MMP-2, MMP-9, and tissue inhibitor metalloproteinases (TIMP-1, TIMP-2) were reversed in the presence of TrkB-Fc. These novel data suggest ASM as an inflammation-sensitive source of BDNF within human airways, with autocrine effects on fibrosis relevant to asthma.

Early-postnatal iron deficiency impacts plasticity in the dorsal and ventral hippocampus in piglets

In this study, we investigated whether alterations in plasticity markers such as brain-derived neurotrophic factor (BDNF), p75 neurotrophin receptor (p75NTR) and tyrosine receptor kinase B (TrkB) are underlying iron deficiency (ID)-induced cognitive impairments in iron depleted piglets. Newborn piglets were either fed an iron-depleted diet (21mg Fe/kg) or an iron-sufficient diet (88mg Fe/kg) for four weeks. Subsequently, eight weeks after iron repletion (190–240mg Fe/kg) we found a significant decrease in mature BDNF (14kDa) and proBDNF (18kDa and 24kDa) protein levels in the ventral hippocampus, whereas we found increases in the dorsal hippocampus. The phosphorylation of cAMP response element binding protein (CREB) follows the mature BDNF protein level pattern. No effects were found on BDNF and CREB protein levels in the prefrontal cortex. The protein levels of the high affinity BDNF receptor, TrkB, was significantly decreased in both dorsal and ventral hippocampus of ID piglets, whereas it was increased in the prefrontal cortex. Together, our data suggest a disrupted hippocampal plasticity upon postnatal ID.

Integral Characterization of Defective BDNF/TrkB Signalling in Neurological and Psychiatric Disorders Leads the Way to New Therapies.

Enhancement of brain-derived neurotrophic factor (BDNF) signalling has great potential in therapy for neurological and psychiatric disorders. This neurotrophin not only attenuates cell death but also promotes neuronal plasticity and function. However, an important challenge to this approach is the persistence of aberrant neurotrophic signalling due to a defective function of the BDNF high-affinity receptor, tropomyosin-related kinase B (TrkB), or downstream effectors. Such changes have been already described in several disorders, but their importance as pathological mechanisms has been frequently underestimated. This review highlights the relevance of an integrative characterization of aberrant BDNF/TrkB pathways for the rational design of therapies that by combining BDNF and TrkB targets could efficiently promote neurotrophic signalling.

MP60-06 PATHOGENIC ROLE OF TRUNCATED TRKB RECEPTOR ISOFORM (TRKB.T1) IN BDNF INDUCED DETRUSOR OVERACTIVITY (DO)

INTRODUCTION AND OBJECTIVES: Overexpression of brain derived neurotrophic factor (BDNF) is well known in overactive bladder (OAB). Amelioration of cyclophosphamide induced DO by antibody mediated sequestration of BDNF highlighted the pathogenic role of BDNF receptors and their downstream signaling. Tropomyosin receptor kinase B (TrkB) is the high affinity receptor for BDNF, which is either expressed as a full length receptor (TrkB FL) or as a splice variant called truncated, TrkB (TrkB.T1). Here, we tested whether gene silencing targeted for TrkB.T1 can overcome the BDNF induced DO. METHODS: Under isoflurane anesthesia, the bladder wall of female Sprague-dawley rats was injected with BDNF plasmid complexed with liposomes (n1⁄45) alone (10mg) or together with either antisense (n1⁄45) or scrambled oligonucleotide against TrkB.T1 (n1⁄45). 7 days later, cystometry was performed followed by bladder harvest to analyze the expression of small Rho GTPase and phosphorylation of Myosin light chain (MLC). RESULTS: As reported earlier, bladder wall injection of BDNF plasmid complexed with liposomes causes BDNF overexpression and DO is observed 7 days later. BDNF induced DO is evident from reduced intercontractile intervals (ICI) and voided volume in rat group injected with BDNF plasmid + scrambled oligonucleotide. In contrast, gene silencing of TrkB.T1 by antisense significantly reversed the DO and increased the ICI and voided urine volume. DO in the scrambled group was associated with the higher expression of Rho kinases viz., RhoA, Cdc42, Rac1 along with the increase phosphorylation of pMLC at Th18 and Ser 19 position. Gene silencing of TrkB.T1 reduced the expression of Rho kinases and completely blocked the phosphorylation of MLC at both positions. CONCLUSIONS: Here, we report that BDNF induced DO is primarily driven by the dominant negative characteristic of TrkB.T1. The tyrosine kinase domain of full length TrkB FL is missing in TrkB.T1, but there exists a domain which interacts with RhoGDi proteins and regulates cell contractility via Rho kinase-mediated increase in phosphorylation of MLC. The C-terminal sequence of TrkB is completely conserved in mammals and therefore verification of TrkB.T1 expression in bladder biopsy of OAB patients is the appropriate next step to establish it as a drug target for treating voiding dysfunctions.

BDNF acting in the hypothalamus induces acute pressor responses under permissive control of angiotensin II

Brain-derived neurotrophic factor (BDNF) expression increases in the paraventricular nucleus of the hypothalamus (PVN) during hypertensive stimuli including stress and hyperosmolarity, but its role in PVN cardiovascular regulatory mechanisms is unclear. Chronic BDNF overexpression in the PVN has been shown to elevate sympathetic tone and blood pressure in part by modulating central angiotensin (Ang) II mechanisms. However, the cardiovascular effects of short-term increases in PVN levels of BDNF and the mechanisms governing them are unknown. Therefore, we investigated whether acute BDNF microinjections into the PVN of conscious and anesthetized Sprague-Dawley rats induce blood pressure elevations and whether Ang II signaling is involved in these hypertensive responses. In conscious rats, unilateral BDNF (12.5ng) microinjections into the PVN increased mean arterial pressure (MAP) by 27±1mmHg (P<0.001 vs vehicle), which was significantly attenuated by intracerebroventricular infusion of the Ang II-type-1 receptor (AT1R) antagonist losartan and by ganglionic blockade with intravenous hexamethonium infusion. In anesthetized rats, unilateral PVN microinjection of BDNF increased MAP by 31±4mmHg (P<0.001 vs vehicle), which was prevented by PVN microinjection pretreatments with the high-affinity BDNF receptor TrkB antagonist ANA-12, losartan, the angiotensin converting enzyme inhibitor lisinopril, or by intravenous hexamethonium. Additional experiments in hypothalamic samples including the PVN revealed that BDNF-induced TrkB receptor phosphorylation was prevented by ANA-12 and losartan pretreatments. Collectively, these data indicate that BDNF acting within the PVN acutely raises blood pressure under permissive control of Ang II-AT1R mechanisms and therefore may play an important role in mediating acute pressor responses to hypertensive stimuli.

Cognitive impairments following cranial irradiation can be mitigated by treatment with a tropomyosin receptor kinase B agonist

Brain radiotherapy is frequently used successfully to treat brain tumors. However, radiotherapy is often associated with declines in short-term and long-term memory, learning ability, and verbal fluency. We previously identified a downregulation of the brain-derived neurotrophic factor (BDNF) following cranial irradiation in experimental animals. In the present study, we investigated whether targeting the BDNF high affinity receptor, tropomysin receptor kinase B (TrkB), could mitigate radiation-induced cognitive deficits. After irradiation, chronic treatment with a small molecule TrkB agonist, 7,8-dihydroxyflavone (DHF) in mice led to enhanced activation of TrkB and its downstream targets ERK and AKT, both important factors in neuronal development. DHF treatment significantly restored spatial, contextual, and working memory, and the positive effects persisted for at least 3months after completion of the treatment. Consistent with preservation of cognitive functions, chronic DHF treatment mitigated radiation-induced suppression of hippocampal neurogenesis. Spine density and major components of the excitatory synapses, including glutamate receptors and postsynaptic density protein 95 (PSD-95), were also maintained at normal levels by DHF treatment after irradiation. Taken together, our results show that chronic treatment with DHF after irradiation significantly mitigates radiation-induced cognitive defects. This is achieved most likely by preservation of hippocampal neurogenesis and synaptic plasticity.

Inflammation and activity augment brain-derived neurotrophic factor peripheral release

Brain-derived neurotrophic factor (BDNF) release to nerve terminals in the central nervous system is crucial in synaptic transmission and neuronal plasticity. However, BDNF release peripherally from primary afferent neurons has not been investigated. In the present study, we show that BDNF is synthesized by primary afferent neurons located in the dorsal root ganglia (DRG) in rat, and releases to spinal nerve terminals in response to depolarization or visceral inflammation. In two-compartmented culture that separates DRG neuronal cell bodies and spinal nerve terminals, application of 50mM K+ to either the nerve terminal or the cell body evokes BDNF release to the terminal compartment. Inflammatory stimulation of the visceral organ (e.g. the urinary bladder) also facilitates an increase in spontaneous BDNF release from the primary afferent neurons to the axonal terminals. In the inflamed viscera, we show that BDNF immunoreactivity is increased in nerve fibers that are immuno-positive to the neuronal marker PGP9.5. Both BDNF and pro-BDNF levels are increased, however, pro-BDNF immunoreactivity is not expressed in PGP9.5-positive nerve-fiber-like structures. Determination of receptor profiles in the inflamed bladder demonstrates that BDNF high affinity receptor TrkB and general receptor p75 expression levels are elevated, with an increased level of TrkB tyrosine phosphorylation/activity. These results suggest a possibility of pro-proliferative effect in the inflamed bladder. Consistently we show that the proliferation marker Ki67 expression levels are enhanced in the inflamed organ. Our results imply that in vivo BDNF release to the peripheral organ is an important event in neurogenic inflammatory state.

Role of TrkB during the postnatal development of the rat carotid body

Brain-derived neurotrophic factor (BDNF) supports innervation of the carotid body by neurons projecting from the petrosal ganglion. Although carotid body glomus cells also express TrkB, BDNF's high affinity receptor, the role of BDNF in carotid body growth and O2 sensitivity has not been studied. Neonatal rats were treated with the TrkB antagonist K252a (100μgkg−1, i.p., b.i.d.) or vehicle on postnatal days P0–P6 and studied on P7. Carotid body volume was decreased by 35% after chronic K252a (P<0.001); a reduction in carotid body size was also elicited using the more selective TrkB antagonist ANA-12 (500μgkg−1, i.p., b.i.d.). In contrast, single-unit chemoafferent responses to 5% O2, measured in vitro, were unaffected by chronic K252a administration. Normoxic and hypoxic ventilation, measured by head–body plethysmography, were also normal after chronic K252a administration, but acute K252a administration produced a slower, deeper breathing pattern during the transition into hypoxia. These data suggest that BDNF regulates postnatal carotid body growth but does not influence the development of glomus cell O2 sensitivity.

MP89-20 BDNF OVEREXPRESSION ALTERS THE PHENOTYPE OF CHOLINERGIC NEURONS IN RAT BLADDER

You have accessJournal of UrologyUrodynamics/Incontinence/Female Urology: Non-Neurogenic Voiding Dysfunction1 Apr 2015MP89-20 BDNF OVEREXPRESSION ALTERS THE PHENOTYPE OF CHOLINERGIC NEURONS IN RAT BLADDER Mahendra Kashyap, Subrata Pore, Willam C. Degroat, Christopher J. Chermansky, Naoki Yoshimura, and Pradeep Tyagi Mahendra KashyapMahendra Kashyap More articles by this author , Subrata PoreSubrata Pore More articles by this author , Willam C. DegroatWillam C. Degroat More articles by this author , Christopher J. ChermanskyChristopher J. Chermansky More articles by this author , Naoki YoshimuraNaoki Yoshimura More articles by this author , and Pradeep TyagiPradeep Tyagi More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2015.02.1819AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Evidence for Brain-derived neurotrophic factor (BDNF) overexpression in OAB is indicated by urine analysis of OAB patients and from animal studies involving detrusor overactivity induced by chemicals or by spinal cord injury. Studies in cardiac field indicate that BDNF signaling enhances parasympathetic tone, but the effect of BDNF overexpression on the phenotype of cholinergic neurons in bladder remain to be investigated. Since spinal cord injury and chemicals induces several other chemicals besides BDNF, we investigated its effect on cholinergic neurons in rat bladder transfected with exogenous BDNF plasmid. METHODS Under isoflurane anesthesia, the bladder wall of adult female Sprague-Dawley rats were non-virally transfected with either 10μg of plasmid DNA encoding the rat BDNF transgene or luciferase plasmid. A week later, bladder tissue was harvested to analyze the expression by immunoreactivity, qPCR and Western blot for BDNF and the proteins involved in neuroexocytosis of acetylcholine. RESULTS 10 fold higher expression of cholinergic neuron specific proteins such as choline acetyltransferase (ChAT) red stain merged with green immunoreactivity for BDNF expression in rat injected with BDNF transgene, compared to rat group injected with luciferase (LUCI). Lumen is indicated by arrow and blue DAPI stains the nucleus in image. Significant upregulation (P<0.05) in high-affinity and low affinity receptor for BDNF namely, TrkB and P75NTR by 4.2 fold and 3.6 fold, respectively was observed. There was 14 fold increase in expression of □1 receptors along with modest rise in Vesicular ACh transporter (VAChT) for facilitating ACh release. Expression of molecules involved in downstream signaling pathways namely, phospholipase C-γ (PLCγ2) and PLCγ1 was increased 51 and 5.5 fold, respectively. CONCLUSIONS Our findings reveal a previously unknown role for BDNF in enhancing the Ach release in bladder through altered phenotype of cholinergic neurons innervating bladder. BDNF induced alterations in the expressions of proteins involved in neuroexocytosis of ACh, especially ChAT, VAChT and α1 adrenergic receptors in bladder establish a mechanistic link between detrusor overactivity and BDNF overexpression induced by chemical or by genetic means. © 2015 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 193Issue 4SApril 2015Page: e1108 Advertisement Copyright & Permissions© 2015 by American Urological Association Education and Research, Inc.MetricsAuthor Information Mahendra Kashyap More articles by this author Subrata Pore More articles by this author Willam C. Degroat More articles by this author Christopher J. Chermansky More articles by this author Naoki Yoshimura More articles by this author Pradeep Tyagi More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Subtoxic levels of hydrogen peroxide induce brain-derived neurotrophic factor expression to protect PC12 cells.

BackgroundOxidative stress is one of the mechanisms underlying pathogenesis in neurodegenerative diseases such as Alzheimer’s disease. Generally, oxidative stress represents cell toxicity; however, we recently found that oxidative stress promotes the expression of growth factor progranulin (PGRN) in HT22 murine hippocampus cells, thereby protecting the HT22 cells. In this study, we attempted to clarify whether a similar system exists in the other neuronal cell model, rat pheochromocytoma (PC12) cells.ResultsAfter confirming that high concentrations of hydrogen peroxide (H2O2; 100–250 μM) initiate PC12 cell death, we analyzed growth factor expressional changes after H2O2 treatment. We found, intriguingly, that gene expression of brain-derived neurotrophic factor (BDNF), but not PGRN was significantly induced by H2O2. Although little expression of the high affinity BDNF receptor tropomyosin-related kinase TrkB was observed in PC12 cells, expression of low affinity neurotrophin receptor, p75NTR, was clearly observed. This BDNF signaling appeared to contribute to PC12 cell protection, since PC12 cell death was significantly attenuated by BDNF treatment.ConclusionsBased on our results, we conclude that the induction of BDNF by subtoxic levels of H2O2 and its signaling may have roles in PC12 cell protection.

Exercise ameliorates depression-like behavior and increases hippocampal BDNF level in ovariectomized rats

The aims of the present study were to investigate whether exercise can improve the depression-like behavior caused by estrogen deficiency. Given that decreased level of brain-derived neurotrophic factor (BDNF) in many brain areas including hippocampus and prefrontal cortex is associated with estrogen deficiency-induced depression-like behavior, we also determined whether exercise affects the levels of BDNF and its receptor in hippocampus and prefrontal cortex (PFC). It was found that ovariectomy (OVX) caused an increase in depression-like behavior in rats and a decrease in BDNF level in hippocampus but not in PFC. The expression of TrkB, a high affinity BDNF receptor in hippocampus and PFC was not affected by OVX. 17β-estradiol (E2) treatment ameliorated depression-like behavior and increased BDNF level in hippocampus in OVX rats. Serum E2 level inversely correlated to depression-like behavior and positively correlated to BDNF level in hippocampus. Exercise ameliorated depression-like behavior, increased serum E2 level and BDNF level in hippocampus in OVX rats. The increased E2 level did not correlate to BDNF level but correlated with some of the behaviors in the rats subjected to exercise. Our results suggested that E2 maintains BDNF in hippocampus, thereby ameliorating depression-like behavior. Exercise amelioration of depression-like behavior in OVX rats is partly due to increased serum E2 level.

Green tea catechins potentiate the neuritogenic action of brain-derived neurotrophic factor: Role of 67-kDa laminin receptor and hydrogen peroxide

Delivery of optimal amounts of brain-derived neurotrophic factor (BDNF) to regions of the brain affected by neurodegenerative diseases is a daunting task. Using natural products with neuroprotective properties, such as green tea polyphenols, would be a highly useful complementary approach for inexpensive long-term treatment of these diseases. In this study, we used PC12(TrkB) cells which ectopically express TrkB, a high affinity receptor for BDNF. They differentiate and induce neurite outgrowth in response to BDNF. Using this model, we show for the first time that treatment with extremely low concentrations (<0.1μg/ml) of unfractionated green tea polyphenols (GTPP) and low concentrations (<0.5μM) of their active ingredient, epigallocatechin-3-gallate (EGCG), potentiated the neuritogenic ability of a low concentration (2ng/ml) of BDNF. A synergistic interaction was observed between GTPP constituents, where epigallocatechin and epicatechin, both individually lacking this activity, promoted the action of EGCG. GTPP-induced potentiation of BDNF action required the cell-surface associated 67kDa laminin receptor (67LR) to which EGCG binds with high affinity. A cell-permeable catalase abolished GTPP/EGCG-induced potentiation of BDNF action, suggesting the possible involvement of H2O2 in the potentiation. Consistently, exogenous sublethal concentrations of H2O2, added as a bolus dose (5μM) or more effectively through a steady-state generation (1μM), potentiated BDNF action. Collectively, these results suggest that EGCG, dependent on 67LR and H2O2, potentiates the neuritogenic action of BDNF. Intriguingly, this effect requires only submicromolar concentrations of EGCG. This is significant as extremely low concentrations of polyphenols are believed to reach the brain after drinking green tea.

Expression of full-length and truncated trkB in human striatum and substantia nigra neurons: implications for Parkinson’s disease

Brain derived neurotrophic factor (BDNF) is a potent mediator of cell survival and differentiation and can reverse neuronal injury associated with Parkinson's disease (PD). Tropomyosin receptor kinase B (trkB) is the high affinity receptor for BDNF. There are two major trkB isoforms, the full-length receptor (trkB.tk(+)) and the truncated receptor (trkB.t1), that mediate the diverse, region specific functions of BDNF. Both trkB isoforms are widely distributed throughout the brain, but the isoform specific distribution of trkB.t1 and trkB.tk(+) to human neurons is not well characterized. Therefore, we report the regional and neuronal distribution of trkB.tk(+) and trkB.t1 in the striatum and substantia nigra pars compacta (SNpc) of human autopsy tissues from control and PD cases. In both PD and control tissues, we found abundant, punctate distribution of trkB.tk(+) and trkB.t1 proteins in striatum and SNpc neurons. In PD, trkB.tk(+) is decreased in striatal neurites, increased in striatal somata, decreased in SNpc somata and dendrites, and increased in SNpc axons. TrkB.t1 is increased in striatal somata, decreased in striatal axons, and increased in SNpc distal dendrites. We believe changes in trkB isoform distribution and expression levels may be markers of pathology and affect the neuronal response to BDNF.

Sensitivity of hippocampal 5-HT1A receptors to mild stress in BDNF-deficient mice

Serotonin 1A (5-HT(1A)) receptors in brain play an important role in cognitive and integrative functions, as well as emotional states. Decreased brain-derived neurotrophic factor (BDNF) expression and/or function, particularly in hippocampus, are implicated in the pathophysiology of stress-related disorders such as major depression. BDNF(+/-) mice are more vulnerable to stress than wild-type mice, exhibiting behavioural despair after mild handling stress. We examined the effect of mild handling stress on 5-HT(1A) receptor function, as measured by 8-OH-DPAT stimulated [(35)S]GTPγS binding, in BDNF(+/-) mice and mice with a forebrain-specific reduction in BDNF (embryonic BDNF inducible knockout mice). Our data show a remarkable sensitivity of hippocampal 5-HT1A receptors to mild stress and a deficiency in BDNF. Other 5-HT(1A) receptor populations, specifically in frontal cortex and dorsal raphe, were resistant to the combined detrimental effects of mild stress and reductions in BDNF expression. Decreases in hippocampal 5-HT(1A) receptor function induced by mild stress in BDNF-deficient mice were prevented by administration of the selective serotonin reuptake inhibitor fluoxetine, which increased activation of TrkB, the high affinity receptor for BDNF, in wild-type and BDNF(+/-) mice. In hippocampal cultures, BDNF increased the capacity of 5-HT(1A) receptors to activate G proteins, an effect eliminated by the knockout of TrkB, confirming TrkB activation increases 5-HT(1A) receptor function. The mechanisms underlying the sensitivity of hippocampal 5-HT(1A) receptors to mild stress and decreased BDNF expression remain to be elucidated and may have important implications for the emotional and cognitive impairments associated with stress-related mental illness.

Brain-Derived Neurotrophic Factor Promotes Vasculature-Associated Migration of Neuronal Precursors toward the Ischemic Striatum

Stroke induces the recruitment of neuronal precursors from the subventricular zone (SVZ) into the ischemic striatum. In injured areas, de-routed neuroblasts use blood vessels as a physical scaffold to their migration, in a process that resembles the constitutive migration seen in the rostral migratory stream (RMS). The molecular mechanism underlying injury-induced vasculature-mediated migration of neuroblasts in the post-stroke striatum remains, however, elusive. Using adult mice we now demonstrate that endothelial cells in the ischemic striatum produce brain-derived neurotrophic factor (BDNF), a neurotrophin that promotes the vasculature-mediated migration of neuronal precursors in the RMS, and that recruited neuroblasts maintain expression of p75NTR, a low-affinity receptor for BDNF. Reactive astrocytes, which are widespread throughout the damaged area, ensheath blood vessels and express TrkB, a high-affinity receptor for BDNF. Despite the absence of BDNF mRNA, we observed strong BDNF immunolabeling in astrocytes, suggesting that these glial cells trap extracellular BDNF. Importantly, this pattern of expression is reminiscent of the adult RMS, where TrkB-expressing astrocytes bind and sequester vasculature-derived BDNF, leading to the entry of migrating cells into the stationary phase. Real-time imaging of cell migration in acute brain slices revealed a direct role for BDNF in promoting the migration of neuroblasts to ischemic areas. We also demonstrated that cells migrating in the ischemic striatum display higher exploratory behavior and longer stationary periods than cells migrating in the RMS. Our findings suggest that the mechanisms involved in the injury-induced vasculature-mediated migration of neuroblasts recapitulate, at least partially, those observed during constitutive migration in the RMS.

Conditional ablation of brain-derived neurotrophic factor-TrkB signaling impairs striatal neuron development

Neurotrophic factors, such as brain-derived neurotrophic factor (BDNF), are associated with the physiology of the striatum and the loss of its normal functioning under pathological conditions. The role of BDNF and its downstream signaling in regulating the development of the striatum has not been fully investigated, however. Here we report that ablation of Bdnf in both the cortex and substantia nigra depletes BDNF in the striatum, and leads to impaired striatal development, severe motor deficits, and postnatal lethality. Furthermore, striatal-specific ablation of TrkB, the gene encoding the high-affinity receptor for BDNF, is sufficient to elicit an array of striatal developmental abnormalities, including decreased anatomical volume, smaller neuronal nucleus size, loss of dendritic spines, reduced enkephalin expression, diminished nigral dopaminergic projections, and severe deficits in striatal dopamine signaling through DARPP32. In addition, TrkB ablation in striatal neurons elicits a non-cell-autonomous reduction of tyrosine hydroxylase protein level in the axonal projections of substantia nigral dopaminergic neurons. Thus, our results establish an essential function for TrkB in regulating the development of striatal neurons.