Platelet activation during tumor development, the potential role of BDNF-TrkB autocrine loop

Mechanisms underlying unidirectional laminar shear stress-mediated Nrf2 activation in endothelial cells: Amplification of low shear stress signaling by primary cilia

Endothelial cells are sensitive to mechanical stress and respond differently to oscillatory flow versus unidirectional flow. This review highlights the mechanisms by which a wide range of unidirectional laminar shear stress induces activation of the redox sensitive antioxidant transcription factor nuclear factor-E2-related factor 2 (Nrf2) in cultured endothelial cells. We propose that fibroblast growth factor-2 (FGF-2), brain-derived neurotrophic factor (BDNF) and 15-Deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) are potential Nrf2 activators induced by laminar shear stress. Shear stress-dependent secretion of FGF-2 and its receptor-mediated signaling is tightly controlled, requiring neutrophil elastase released by shear stress, αvβ3 integrin and the cell surface glycocalyx. We speculate that primary cilia respond to low laminar shear stress (<10 dyn/cm2), resulting in secretion of insulin-like growth factor 1 (IGF-1), which facilitates αvβ3 integrin-dependent FGF-2 secretion. Shear stress induces generation of heparan-binding epidermal growth factor-like growth factor (HB-EGF), which contributes to FGF-2 secretion and gene expression. Furthermore, HB-EGF signaling modulates FGF-2-mediated NADPH oxidase 1 activation that favors casein kinase 2 (CK2)-mediated phosphorylation/activation of Nrf2 associated with caveolin 1 in caveolae. Higher shear stress (>15 dyn/cm2) induces vesicular exocytosis of BDNF from endothelial cells, and we propose that BDNF via the p75NTR receptor could induce CK2-mediated Nrf2 activation. Unidirectional laminar shear stress upregulates gene expression of FGF-2 and BDNF and generation of 15d-PGJ2, which cooperate in sustaining Nrf2 activation to protect endothelial cells against oxidative damage.

The brain-derived neurotrophic factor prompts platelet aggregation and secretion

Brain-derived neurotrophic factor (BDNF) has both autocrine and paracrine roles in neurons, and its release and signaling mechanisms have been extensively studied in the central nervous system. Large quantities of BDNF have been reported in circulation, essentially stored in platelets with concentrations reaching 100- to 1000-fold those of neurons. Despite this abundance, the function of BDNF in platelet biology has not been explored. At low concentrations, BDNF primed platelets, acting synergistically with classical agonists. At high concentrations, BDNF induced complete biphasic platelet aggregation that in part relied on amplification from secondary mediators. Neurotrophin-4, but not nerve growth factor, and an activating antibody against the canonical BDNF receptor tropomyosin-related kinase B (TrkB) induced similar platelet responses to BDNF, suggesting TrkB could be the mediator. Platelets expressed, both at their surface and in their intracellular compartment, a truncated form of TrkB lacking its tyrosine kinase domain. BDNF-induced platelet aggregation was prevented by inhibitors of Ras-related C3 botulinum toxin substrate 1 (Rac1), protein kinase C, and phosphoinositide 3-kinase. BDNF-stimulated platelets secreted a panel of angiogenic and inflammatory cytokines, which may play a role in maintaining vascular homeostasis. Two families with autism spectrum disorder were found to carry rare missense variants in the BDNF gene. Platelet studies revealed defects in platelet aggregation to low concentrations of collagen, as well as reduced adenosine triphosphate secretion in response to adenosine diphosphate. In summary, circulating BDNF levels appear to regulate platelet activation, aggregation, and secretion through activation of a truncated TrkB receptor and downstream kinase-dependent signaling.

BDNF levels and liver stiffness in subjects with alcohol use disorder: Evaluation after alcohol withdrawal

Background: Brain-derived neurotrophic factor (BDNF) plays a key role in the processes of withdrawal and addiction in alcohol use disorder (AUD), and is also involved in liver homeostasis. The role of BDNF in liver damage and its link with liver stiffness are not known. We hypothesize that serum BDNF levels are linked to changes in hepatic elasticity, both of which depend on variations in alcohol consumption.Objectives: We aimed to study the evolution of BDNF levels and changes in the liver stiffness (LS) of AUD subjects, within two months following withdrawal.Methods: We measured LS by FibroScan® (as an indicator of the degree of liver fibrosis), gamma glutamyl transferase (GGT) levels (as a nonspecific but sensitive marker of liver status) and serum BDNF levels of 62 alcohol-dependent subjects without previously identified liver complications. Measures were obtained at the time of withdrawal (M0) and two months later (M2). Results: BDNF levels increased after alcohol withdrawal and small variations of LS were observed. BDNF values increased significantly according to fibrosis stages measured by LS (p = .028 at M0), and were predicted by GGT levels in a regression model (p = .007 at M0 and p = .003 at M2).Conclusion: In AUD, BDNF levels were associated with measured LS when divided into fibrosis risk categories. Changes in LS and BDNF levels after alcohol withdrawal may be related to changes in homeostatic mechanisms, in addition to those of liver status.

Relevance of number and physiological status of conspecifics in preventing stress-induced decreases in newly proliferated cells and neuroblasts

RATIONALE AND OBJECTIVE

The presence of three conspecifics prevents stress-induced decreases in newly proliferated cells and neuroblasts in mouse dentate gyrus (DG). In this study, we sought to determine how many conspecifics are required to exert these protective effects against stress. In addition, we manipulated the physiological status of those conspecifics in the context of their stress-buffering effects and used airborne oxytocin exposure as a substitute for the presence of conspecifics.

MATERIALS AND METHODS

Bromodeoxyuridine staining was used to indicate the newly proliferated cells and co-staining with doublecortin to reveal the proliferative neuroblasts.

RESULTS

Presentation of three intact and lipopolysaccharide-treated conspecifics prevented the stress-induced decreases in the number of newly proliferated cells and neuroblasts in DG. Presentation of one saline- or oxytocin (OT)-treated conspecific did not exert observable stress-buffering effects. In contrast, airborne oxytocin prevented the stress-induced decreases in DG cell proliferation and early neurogenesis, while pretreatment with L-371,257, a selective OT receptor antagonist, abolished the buffering effects of OT.

CONCLUSIONS

Physical interaction with the conspecifics and conspecifics' sickness, at best, play a minor role in mediating the buffering effects against stress-induced decreases in DG cell proliferation or early neurogenesis. Moreover, stress-buffering effects are negligible with the presence of only one conspecific. Finally, airborne OT produced stress-buffering effects possibly via its stimulation of OT receptors. Oxytocin merits further study as a substitute for the stress-buffering effects of companions.

Proliferative role of BDNF/TrkB signaling is associated with anoikis resistance in cervical cancer

Brain-derived neurotrophic factor (BDNF) is known as one of the members of the neurotropin family. BDNF-induced activation of its receptor tyrosine kinase B (TrkB) is associated with anoikis tolerance, tumor progression and poor prognosis in many types of malignancy. However, to the best of our knowledge, there are no reports describing the contribution of the BDNF/TrkB axis to cervical cancer. BDNF and TrKB expression in cervical cancer (CC) tissues and adjacent normal tissues from 87 patients were analyzed by immunohistochemistry, western blot analysis and quantitative PCR assays and the results showed that they were significantly higher in cancer tissues than that in normal adjacent tissues, respectively. Higher expression rates of BDNF and TrKB were observed in stage IIB or higher and BDNF expression was positively associated with lymph node metastasis. Notably, a high expression of TrKB may be contributed to poor survival time, which confirmed by Kaplan-Meier analysis. Compared to the corresponding CC cell lines, HeLa, SiHa, CASKI, C4-1 and C-33a, BDNF and TrKB expression was enhanced in anoikis-like apoptotic tolerance (AAT), a cell model established from cervical cancer cell lines. AAT cells showed a higher proliferation activity compared with CC cell lines, which was confirmed by a shorter G0/G1 phase, elevated cyclin A, cyclin D1 and c-myc, decreased caspase-3 and Bax, and increased Bcl-2. By contrast, the knockdown of TrKB expression reversed these changes in AAT cells, induced G0/G1 arrest and suppressed proliferation activity. The results of the present study show that PI3K/Akt signaling is involved in the BDNF/TrKB-induced proliferation of AAT cells in cervical cancer. These findings indicate that BDNF/TrKB pathway is a potential target for the treatment of cervical cancer.

Nervous system and primary liver cancer

Recent advances have found irregular activities of the nervous system-associated factors in the development and progression of primary liver cancer. These factors contributed in the regulation of migration, proliferation, and apoptosis of cancer cells, and took a role in modulating invasion, metastasis, and recurrence after curative treatment. In clinical researches, neural-related factors were found to be significant prognostic factors, suggesting that the interactions between nervous system and primary liver cancer are indispensable in understanding underlying biological mechanisms. Herein, we reviewed up-to-date achievements in this area and the future perspectives of the interactions between the nervous system and primary liver cancer.

Upregulation of the BDNF/TrKB pathway promotes epithelial-mesenchymal transition, as well as the migration and invasion of cervical cancer

Brain-derived neurotrophic factor (BDNF) has previously been demonstrated to be associated with several types of cancer. In addition, its receptor, tropomyosin related kinase B (TrkB) is involved in tumor invasion and metastasis. Epithelial-mesenchymal transition (EMT) is associated with metastasis in cancers. Thus, The aim of the present study was to examine whether BDNF/TrKB expression is linked to a poor survival and the acquisition of the EMT phenotype in cervical cancer. We found that a high positive expression of BDNF/TrKB was associated with poor survival in cervical cancer. Our results revealed that high expression levels of BDNF/TrKB were observed in cervical cancer compared to normal cells. Importantly, we demonstrated that the silencing of TrKB suppressed the activation of EMT via the downregulation of N-cadherin, vimentin, matrix metalloproteinase (MMP)2 and MMP9, and the upregulation of E-cadherin and tissue inhibitor of metalloproteinases (TIMP)2, which resulted in suppressed cell proliferation, migration and invasion. Furthermore, high phosphorylation levels of ERK and Akt were observed in the cervical cancer cells, while these levels were decreased in the cells in which TrKB was knocked down. On the whole, these findings suggest that the BDNF/TrKB pathway is a promising target for the prevention of tumor proliferation, invasion, metastasis and EMT in cervical cancer cells.

Patterns and functional implications of platelets upon tumor "education"

While platelets are traditionally recognized to play a predominant role in hemostasis and thrombosis, increasing evidence verifies its involvement in malignancies. As a component of the tumor microenvironment, platelets influence carcinogenesis, tumor metastasis and chemotherapy efficiency. Platelets status is thus predictable as a hematological biomarker of cancer prognosis and a hot target for therapeutic intervention. On the other hand, the role of circulating tumor cells (CTCs) as an inducer of platelet activation and aggregation has been well acknowledged. The cross-talk between platelets and CTCs is reciprocal on that the CTCs activate platelets while platelets contribute to CTCs' survival and dissemination. This review covers some of the current issues related to the loop between platelets and tumor aggression, including the manners of tumor cells in "educating" platelets and biofunctional alterations of platelets upon tumor "education". We also highlight the potential clinical applications on the interplay between tumors and platelets. Further studies with well-designed prospective multicenter trials may contribute to clinical "liquid biopsy" diagnosis by evaluating the global changes of platelets.

Brain-derived Neurotrophic Factor Is Associated With Disease Severity and Clinical Outcome in Ugandan Children Admitted to Hospital With Severe Malaria

BACKGROUND

Malaria remains a leading cause of childhood death and neurologic disability in sub-Saharan Africa. Here, we test the hypothesis that malaria-induced alterations to circulating brain-derived neurotrophic factor (BDNF) are associated with poor clinical outcomes in children with severe malaria.

METHODS

We quantified BDNF (by enzyme-linked immunosorbent assay) in plasma samples collected [at presentation (day 1), day 3 and day 14], during a prospective study of Ugandan children admitted to hospital with severe malaria (n = 179).

RESULTS

BDNF concentration at presentation (day 1) was lower in children with cerebral malaria (P < 0.01), coma (P < 0.01), Lambaréné Organ Dysfunction Score >1 (P < 0.05) and respiratory distress (P < 0.01). Higher BDNF concentration at presentation was associated with shorter time to coma recovery [hazard ratio = 1.655 (1.194-2.293); P = 0.002] and a reduced odds ratio of disability [0.50 (0.27-0.94); P = 0.047] and death [0.45 (0.22-0.92); P = 0.035]. BDNF concentration was lower on day 1 and increased in children surviving severe malaria (day 14; P < 0.0001).

CONCLUSIONS

Our findings provide the new evidence linking circulating BDNF with disease severity, coma recovery and clinical outcome in children with severe malaria.

Platelets contribute to growth and metastasis in hepatocellular carcinoma

To determine the association of platelets with hepatocellular carcinoma (HCC) growth and its metastasis. We examined platelets, laboratory, and radiological data of consecutive 420 HCC and 1008 cirrhosis cases. Follow-up information of platelet count in cirrhosis to HCC, pre- to post-therapy, and post-therapy to HCC outcome was analyzed. Cytokine profiling was performed in HCC and cirrhosis (n = 10 each). On the basis of imaging, HCC was divided into six subgroups. Cytosmears of HCC were assessed for platelet clustering around tumor cells. An in vitro Matrigel invasion assay was performed on human HCC cell lines using graded concentration of platelets. Baseline platelet numbers and platelet/lymphocyte ratios (PLRs) were significantly higher (p < 0.001) in HCC than cirrhosis. IL-1, IL-6, FGF, G-CSF, thrombopoietin, and VEGF were higher in HCC than cirrhosis. Platelet counts were increased after HCC conversion of cirrhosis (p < 0.001) and decreased (p < 0.001) after therapy. Platelets and PLR in recurrence cases were higher than in responders at baseline. AFP, PIVKAII, platelets, and PLR increase (p < 0.001 each) with advancement in HCC growth. Multivariate analysis showed platelets (p = 0.002), PLR (p = 0.004), and AFP (p < 0.001) associated with distant metastasis. Platelet clustering seen in 75.7% of HCC group 3, 45% in group 2, and 12.5% in group 1 cases (p < 0.001). Invaded cells in Matrigel assay positively correlated with platelet concentration. Platelets can contribute to the development, growth, invasion, and metastasis of HCC. Rising platelet count after HCC therapy is indicative of incomplete response or recurrence.

Are the changes in the peripheral brain-derived neurotrophic factor levels due to platelet activation?

Brain-derived neurotrophic factor (BDNF) plays an important role in central nervous system development, neurogenesis and neuronal plasticity. BDNF is also expressed in several non-neuronal tissues, and it could play an important role in other processes, such as cancer, angiogenesis, etc. Platelets are the major source of peripheral BDNF. However, platelets also contain high amounts of serotonin; they express specific surface receptors during activation, and a multitude of pro-inflammatory and immunomodulatory bioactive compounds are secreted from the granules. Until recently, there was insufficient knowledge regarding the relationship between BDNF and platelets. Recent studies showed that BDNF is present in two distinct pools in platelets, in α-granules and in the cytoplasm, and only the BDNF in the granules is secreted following stimulation, representing 30% of the total BDNF in platelets. BDNF has an important role in the pathophysiology of depression. Low levels of serum BDNF have been described in patients with major depressive disorder, and BDNF levels increased with chronic antidepressant treatment. Interestingly, there is an association between depression and platelet function. This review analyzed studies that evaluated the relationship between BDNF and platelet activation and the effect of treatments on both parameters. Only a few studies consider this possible confounding factor, and it could be very important in diseases such as depression, which show changes in both parameters.

[Effect of shRNA-mediated silencing of BDNF gene on VEGF expression of RPMI8226 cells]

OBJECTIVE

To investigate the expression of vascular endothelial growth factor (VEGF) of human multiple myeloma (MM) cell line RPMI8226 regulated by brain-derived neurotrophic factor (BDNF), and preliminarily approach the close relationship between BDNF and angiogenesis of MM.

METHODS

The recombinant eukaryotic BDNF siRNA expression vector was designed and constructed. The empty vector pGenesil-1, and the recombinant plasmid, pGenesil-shRNA-BDNF were transfected into RPMI8226 cells using Lipofectamine™ 2000 (groups P0 and P1, respectively). BDNF mRNA and protein level in RPMI8226 cells were detected by RT-PCR and Western blotting, respectively; the cellular proliferation activity was determined by MTT assay, while the cell apoptosis was measured by flow cytometry; the variation of VEGF mRNA level in RPMI8226 cells via transfection was determined by RT-PCR, the secretion of VEGF was detected by ELISA.

RESULTS

(1)The recombinant eukaryotic BDNF siRNA expression vectors were successfully constructed. BDNF mRNA expression and protein level in P1 group were significantly inhibited compared to those in non-transfected group (Pn) and P0 groups (P<0.05); (2)MTT tests demonstrated that the cellular proliferation activities were obviously decreased in Pn (0.42 ± 0.06) vs P0 (0.56 ± 0.06) and P1 (0.50 ± 0.04) groups (P<0.05); (3)The early cell apoptosis rates were statistically increased in P1 [(53.84 ± 9.95)%] vs Pn [(5.23 ± 2.46)%] and P0 [(9.10 ± 3.46)%] groups (P<0.01); (4)The silence of endogenous BDNF significantly decreased the expression of VEGF in RPMI8226 cells:the relative expression level of VEGF121, VEGF145 and VEGF165 in P1 group were (0.62 ± 0.07), (0.47 ± 0.09) and (0.57 ± 0.02) folds compared to Pn group (P<0.05); (5)ELISA demonstrated that secretion of VEGF in P1 group were (0.36 ± 0.05) and (0.44 ± 0.06) folds compared to Pn and P0 group, respectively (P<0.05).

CONCLUSION

BDNF gene silence can obviously increase apoptosis of RPMI8226 cells, inhibit their proliferation and decrease the expression of VEGF. BDNF might mediate the expression of VEGF in MM cells, which may be involved in MM angiogenesis.

May BDNF Be Implicated in the Exercise-Mediated Regulation of Inflammation? Critical Review and Synthesis of Evidence

Introduction:

Exercise attenuates inflammation and enhances levels of brain-derived neurotrophic factor (BDNF). Exercise also enhances parasympathetic tone, although its role in activating the cholinergic anti-inflammatory pathway is unclear. The physiological pathways of exercise’s effect on inflammation are obscure.

Aims:

To critically review the evidence on the role of BDNF in the anti-inflammatory effects of exercise and its potential involvement in the cholinergic anti-inflammatory pathway.

Methods:

Critical literature review of studies published in MEDLINE, PubMed, CINAHL, Embase, and Cochrane databases.

Results:

BDNF is critically involved in the bidirectional signaling between immune and neurosensory cells and in the regulation of parasympathetic system responses. BDNF is also intricately involved in the inflammatory response: inflammation induces BDNF production, and, in turn, BDNF exerts pro- and/or anti-inflammatory effects. Although exercise modulates BDNF and its receptors in lymphocytes, data on BDNF’s immunoregulatory/anti-inflammatory effects in relation to exercise are scarce. Moreover, BDNF increases cholinergic activity and is modulated by parasympathetic system activation. However, its involvement in the cholinergic anti-inflammatory pathway has not been investigated.

Conclusion:

Converging lines of evidence implicate BDNF in exercise-mediated regulation of inflammation; however, data are insufficient to draw concrete conclusions. We suggest that there is a need to investigate BDNF as a potential modulator/mediator of the anti-inflammatory effects of exercise and of the cholinergic anti-inflammatory pathway during exercise. Such research would have implications for a wide range of inflammatory diseases and for planning targeted exercise protocols.

Identification of two clinical hepatocellular carcinoma patient phenotypes from results of standard screening parameters

Previous work has shown that two general processes contribute to hepatocellular cancer (HCC) prognosis: liver damage, monitored by indices such as blood bilirubin, prothrombin time (PT), and aspartate aminostransferase (AST); and tumor biology, monitored by indices such as tumor size, tumor number, presence of portal vein thrombosis (PVT) and blood alpha-fetoprotein (AFP) levels. These processes may affect one another, with prognostically significant interactions between multiple tumor and host parameters. These interactions form a context that provide personalization of the prognostic meaning of these factors for every patient. Thus, a given level of bilirubin or tumor diameter might have a different significance in different personal contexts. We previously applied network phenotyping strategy (NPS) to characterize interactions between liver function indices of Asian HCC patients and recognized two clinical phenotypes, S and L, differing in tumor size and tumor nodule numbers. Our aim was to validate the applicability of the NPS-based HCC S/L classification on an independent European HCC cohort, for which survival information was additionally available. Four sets of peripheral blood parameters, including AFP-platelets, derived from routine blood parameter levels and tumor indices from the ITA.LI.CA database, were analyzed using NPS, a graph-theory-based approach that compares personal patterns of complete relationships between clinical data values to reference patterns with significant association to disease outcomes. Without reference to the actual tumor sizes, patients were classified by NPS into two subgroups with S and L phenotypes. These two phenotypes were recognized using solely the HCC screening test results, consisting of eight common blood parameters, paired by their significant correlations, including an AFP-platelets relationship. These trends were combined with patient age, gender, and self-reported alcoholism into NPS personal patient profiles. We subsequently validated (using actual scan data) that patients in L phenotype group had 1.5× larger mean tumor masses relative to S, P = 6 × 10(-16). Importantly, with the new data, liver test pattern-identified S-phenotype patients had typically 1.7× longer survival compared to L-phenotype patients. NPS integrated the liver, tumor, and basic demographic factors. Cirrhosis-associated thrombocytopenia was typical for smaller S tumors. In L tumor phenotype, typical platelet levels increased with the tumor mass. Hepatic inflammation and tumor factors contributed to more aggressive L tumors, with parenchymal destruction and shorter survival. NPS provides integrative interpretation for HCC behavior, identifying two tumor and survival phenotypes by clinical parameter patterns. The NPS classifier is provided as an Excel tool. The NPS system shows the importance of considering each tumor marker and parameter in the total context of all the other parameters of an individual patient.

Platelet extracts induce growth, migration and invasion in human hepatocellular carcinoma in vitro

Background

Thrombocytopenia has been reported to be associated with small size HCCs, and thrombocytosis to be associated with large size HCCs. The aim was to examine the effects of platelets in relation to HCC cell growth.

Methods

The effects of time-expired pooled normal human platelets were examined on human HCC cell line growth and invasion.

Results

Blood platelet numbers increased with increasing HCC tumor size and portal vein invasion. Platelet extracts enhanced cell growth in 4 human HCC cell lines, as well as cell migration, medium AFP levels and decreased apoptosis. Cell invasion was significantly enhanced, using a Matrigel-coated trans-well membrane and3D (Real-Time Imaging) invasion assay. Western blots showed that platelets caused enhanced phospho-ERK and phospho–JNK signaling and anti-apoptotic effect with increase of Bcl-xL (anti-apoptotic marker) and decrease of Bid (pro-apoptotic marker) levels. Their growth effects were blocked by a JNK inhibitor.

Conclusions

Platelets stimulated growth and invasion of several HCC cell lines in vitro, suggesting that platelets or platelet growth factors could be a potential pharmacological target.

Thrombocytosis and hepatocellular carcinoma

BACKGROUND

Thrombocytopenia has been reported to be both a risk factor for hepatocellular carcinoma (HCC) development as well as a prognostic factor. Many HCCs also occur in presence of normal platelets.

AIM

To examine a cohort of HCC patients with associated thrombocytosis.

METHODS

Records were examined of a cohort of 634 biopsy-proven and randomly presenting HCC patients without thrombocytopenia.

RESULTS

In the total cohort, 52 patients were identified with thrombocytosis (platelet levels >400 × 10(9)/L) and compared with 582 patients with normal platelet values. The average tumor sizes were 13.1 versus 8.8 cm (p < 0.0001), and their total average bilirubin levels were 0.9 versus 1.5 (p = 0.02), comparing thrombocytosis patients versus normal platelet count HCC patients. These differences were even more pronounced in patients with HCC sizes >5 cm. Thrombocytosis patients were younger and had less cirrhosis, but similar percent with hepatitis B or C or alcohol consumption.

CONCLUSION

Thrombocytosis in association with HCC occurs in patients with larger tumor sizes and better liver function.

Human platelet concentrates: a source of solvent/detergent-treated highly enriched brain-derived neurotrophic factor

BACKGROUND

Human blood platelets (PLTs) contain brain-derived neurotrophic factor (BDNF), a neurotrophin that binds to neurotrophic tropomyosin-related kinase B (TrkB) receptor on central nervous system cells. This binding promotes neural synaptic plasticity and memory and prevents neuronal degeneration. Alterations in BDNF homeostasis are associated with aging and are found in several neurodegenerative conditions such as Alzheimer's, Huntington's, and Parkinson's diseases and multiple sclerosis. We have developed PLT viral inactivation and chromatographic fractionation processes and decided here to identify fractions enriched in BDNF.

STUDY DESIGN AND METHODS

PLT concentrates (PCs) were treated by solvent/detergent (S/D), extracted by oil, and subjected to fractionation (C18, sulfopropyl [SP]-Sepharose, diethylaminoethyl [DEAE]-Sepharose, or activated charcoal). BDNF and pro-BDNF were evaluated by enzyme-linked immunosorbent assay, and Western blot. TrkB was studied by Western blot. Tri-n-butyl phosphate (TnBP) was quantified by high-performance liquid chromatography, and Triton X-45 by gas chromatography.

RESULTS

The mean BDNF content of 2.9 ± 0.7 ng/mL in PC was noted to increase to 56.2 ± 2.4 ng/mL after S/D treatment and remained stable during oil extraction. Approximately 70% of the BDNF content was recovered after C18 chromatography. BDNF did not bind to DEAE-Sepharose and was almost completely adsorbed by charcoal. Chromatography on SP-Sepharose yielded a highly enriched 13-kDa mature BDNF fraction that was more than 170-fold purified, with a mean of 137 ± 29.4 ng/mL and 82% chromatographic recovery, devoid of detectable TnBP and Triton X-45. Pro-BDNF and TrkB proteins were not detected in the PLT extracts.

CONCLUSION

We obtained a S/D-treated, highly enriched mature PLT-derived BDNF fraction that could help unveil the pharmacokinetics, pharmacodynamic, and potential therapeutic applications of the BDNF neurotrophin.

Release reaction of brain-derived neurotrophic factor (BDNF) through PAR1 activation and its two distinct pools in human platelets

Brain-derived neurotrophic factor (BDNF) is a cytokine that plays important roles in the survival, development, and plasticity of neurons. BDNF is also expressed in peripheral tissues and cells. In this article, we report the BDNF release reaction through thrombin stimulation and its localization in human platelets. Platelets from healthy volunteers were subjected to PAR1-AP or PAR4-AP stimulation. Release of BDNF was measured by ELISA. Localization of BDNF in resting and thrombin-activated platelets was examined by immunoelectron microscopy and sucrose gradient ultracentrifugation following western blotting. BDNF was released dose-dependently with PAR1-AP concentrations with drastic release at low PAR1-AP concentrations and gently release at high PAR1-AP concentrations. Maximum BDNF release was approximately 37% at 132 μM PAR1-AP. In contrast, 3.8% BDNF was released with 1.13 mM PAR4-AP stimulation. In immunoelectron microscopy and sucrose gradient ultracentrifugation analyses, BDNF was detected not only in α-granules but also cytoplasm in of the resting platelets, and it was distributed in the swollen open canalicular system fused to α-granules at 1 min and disappeared at 5 min after stimulation by thrombin. However, BDNF in cytoplasm remained throughout platelet activation. In conclusions, we demonstrate that BDNF is released from platelets through predominately PAR1 regulation. Furthermore, we identified two pools of BDNF in the α-granules and cytoplasm of human platelets, and only BDNF in α-granules is released through platelet activation.

Vascular BDNF expression and oxidative stress during aging and the development of chronic hypertension

Brain-derived neurotrophic factor (BDNF) and TrK receptors play an important role in vascular development and response to injury. In this study, we investigated the participation of the BDNF/TrK pathway and oxidative stress during the development of hypertension in spontaneously hypertensive rats (SHR). In SHR and normotensive rats (WKY) at 6 and 13 weeks of age, we studied (i) plasma antioxidant capacity, (ii) production of superoxide and NAD(P)H oxidase activity in aorta (iii) plasma BDNF and vascular expression of BDNF, TrKB, NAD(P)H oxidase subunits, AT1 receptor, and MCP-1. In 6- and 13-week-old SHR aorta, superoxide level was twice than in WKY aorta. At 13 weeks, when blood pressure in SHR was 60 mmHg higher in SHR than in WKY, an enhancement of NAD(P)H oxidase activity in SHR was associated with an increase in p47phox, AT1, and BDNF expression in vessels. MCP-1 expression increased with blood pressure. Our study demonstrated that in SHR rats, an increase in levels of vascular oxidative stress and in aortic BDNF and TrKB expression occurs prior to the rise in blood pressure, while a reinforcement of vascular and circulating oxidative stress markers is brought about later by hypertension.

Effect of antidepressants on brain-derived neurotrophic factor (BDNF) release from platelets in the rats

Brain-derived neurotrophic factor (BDNF) belongs to the neurotrophin family, and enhances the growth and maintenance of several neuronal systems. In addition, BDNF may promote neurogenesis and protect against hippocampal volume loss in depressive disorders. Although first detected in brain, BDNF also exists in peripheral tissues and is mainly stored in platelets and circulates in blood. Recent reports indicate that serum BDNF levels in depressive patients are lower than in control subjects, and antidepressant treatment increases serum BDNF levels in responders. A single report suggests that decreased serum BDNF in major depression is related to mechanisms of platelet BDNF release; however, the mechanisms of changes in BDNF blood levels are still poorly understood. In the present study, we investigated the direct influence of antidepressants on BDNF release from platelets and their effects on serum levels. We used samples of washed platelets prepared from rat blood, and investigated the platelet BDNF release and serum BDNF concentration changes in response to adding antidepressants. We found that BDNF was dose-dependently released from platelets by direct treatment with various kinds of antidepressants in vitro, and serum BDNF concentration was also increased by intravenous antidepressant treatment. These results confirm that BDNF release from platelets is affected by antidepressants, which may relate to the circulating BDNF level change in peripheral blood. The response of BDNF release differs depending on the type and amount of antidepressants, making BDNF a serious candidate as a predictor of antidepressant treatment response.

Strain-specific BDNF expression of rat primary astrocytes

By producing brain-derived neurotrophic factor (BDNF), astrocytes play a role in disease resistance. This study was undertaken to investigate whether primary astrocytes derived from LEW/N and F344/N rats differentially express BDNF. LEW/N astrocytes expressed more BDNF mRNA and protein than F344/N astrocytes in basal and valproic acid (VPA)-stimulated conditions. VPA suppresses HDAC enzyme activity without affecting HDAC gene and protein expression in astrocytes of both strains. Blockade of TrkB receptors resulted in similar fold decreases in basal BDNF mRNA levels between two strains. The results suggest that inhibition of HDAC activity and BDNF-TrkB autocrine loop are involved in regulation of astrocytic BDNF transcription, whereas the mechanisms for elevated constitutive gene BDNF expression of LEW/N astrocytes remain to be investigated.

Cardio-respiratory fitness, habitual physical activity and serum brain derived neurotrophic factor (BDNF) in men and women

Short episodes of high intensity exercise transiently increase serum levels of BDNF in humans, but serum levels of BDNF at rest appear to be lower in more physically active humans with greater levels of energy expenditure. The relationship between serum BDNF concentration, cardio-respiratory fitness (Astrand-Rhyming test estimated VO2 max) and volume of long-term, regular exercise and sporting activity (Baecke Habitual Physical Activity Index) was investigated in 44 men and women between the age range of 18-57 years. In this group an inverse relationship between resting serum BDNF concentration and measures of both estimated VO2 max (r=-0.352; P<0.05) and long-term sporting activity (r=-0.428, P<0.01) was found. These results indicate that increased levels of cardio-respiratory fitness and habitual exercise are associated with lower resting levels of serum BDNF in healthy humans. This is the first study to demonstrate an inverse relationship between a physiological estimate of cardio-respiratory fitness and serum BDNF.

Up-regulation of Tropomyosin related kinase B contributes to resistance to detachment-induced apoptosis in hepatoma multicellular aggregations

To elucidate the molecular mechanisms of resistance to detachment-induced apoptosis, we cultured BEL7402 hepatoma cells on plates coated with poly (2-hydroxyethyl methacrylate), which blocked access to the extracellular matrix. When BEL7402 hepatoma cells were suspended, they could self-assemble into aggregations and resist to detachment-induced apoptosis. Expression of TrkB on detached cells was much higher than that of attached ones. Protein structure analysis revealed that TrkB contained adhesion domain, which might contribute to the aggregation formation of hepatoma cells. These aggregations had higher proliferation indices with BDNF treatment. These data demonstrate that TrkB may contribute to metastasis by facilitating formation of multicellular aggregations and induce their resistance to detachment-induced apoptosis.

Polarized signaling endosomes coordinate BDNF-induced chemotaxis of cerebellar precursors

During development, neural precursors migrate in response to positional cues such as growth factor gradients. However, the mechanisms that enable precursors to sense and respond to such gradients are poorly understood. Here we show that cerebellar granule cell precursors (GCPs) migrate along a gradient of brain-derived neurotrophic factor (BDNF), and we demonstrate that vesicle trafficking is critical for this chemotactic process. Activation of TrkB, the BDNF receptor, stimulates GCPs to secrete BDNF, thereby amplifying the ambient gradient. The BDNF gradient stimulates endocytosis of TrkB and associated signaling molecules, causing asymmetric accumulation of signaling endosomes at the subcellular location where BDNF concentration is maximal. Thus, regulated BDNF exocytosis and TrkB endocytosis enable precursors to polarize and migrate in a directed fashion along a shallow BDNF gradient.

Measurements of brain-derived neurotrophic factor: methodological aspects and demographical data

Although numerous studies have dealt with changes in blood brain-derived neurotrophic factor (BDNF), methodological issues about BDNF measurements have only been incompletely resolved. We validated BDNF ELISA with respect to accuracy, reproducibility and the effect of storage and repeated freezing cycles on BDNF concentrations. Additionally, the effect of demographic characteristics in healthy subjects on BDNF was verified. Whole blood and serum was collected from 206 healthy subjects and a subgroup was genotyped for BDNF Val66Met polymorphism. The effect of age, gender, BDNF genotype and thrombocyte count on whole blood BDNF was assessed. The BDNF ELISA measurement was accurate, 91.6+/-3.0%, and showed high reproducibility, whereas inter-assay and intra-subject variations were modest, 8.4+/-5.2% and 17.5+/-14.1%, respectively. Storage of whole blood samples at 4 degrees C significantly decreased BDNF concentration, while repeated freezing cycles and storage at -20 degrees C was without any effect. Storage at -20 degrees C of serum, but not whole blood, was associated with a significant decrease in BDNF concentration. Women had significantly higher whole blood BDNF concentrations than men (18.6+/-1.3 ng/ml versus 16.5+/-1.4 ng/ml), and showed a right-skewed BDNF concentration distribution. No association between whole blood BDNF concentrations and thrombocyte count, age, or BDNF genotype was found. In conclusion, the BDNF ELISA assay determines whole blood BDNF accurately and with high reproducibility. Female gender is associated with higher whole blood BDNF concentrations whereas age, thrombocyte count and BDNF Val66Met polymorphism were un-associated.