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BDNF, Reduced leads to Synaptogenesis, Decreased
Key Event Relationship Overview
AOPs Referencing Relationship
|AOP Name||Adjacency||Weight of Evidence||Quantitative Understanding||Point of Contact||Author Status||OECD Status|
|Inhibition of Na+/I- symporter (NIS) leads to learning and memory impairment||non-adjacent||Moderate||Low||Arthur Author (send email)||Open for citation & comment||WPHA/WNT Endorsed|
Life Stage Applicability
|During brain development||High|
Key Event Relationship Description
Disruption of BDNF signaling (and other factors, such as NGF or Reelin, etc.) during brain development was shown to interfere with synaptogenesis in the hippocampus (Sanchez-Martin et al., 2013; Neal et al., 2010; Stansfiled et al., 2012). In the adult brain, BDNF is involved in synaptic plasticity (Lu et al., 2013; Leal et al., 2014), which is a fundamental process linked with learning and memory. Synaptic dysfunction is a key pathophysiological hallmark in neurodegenerative disorders, including Alzheimer's disease, and synaptic repair therapies based on the use of trophic factors, such as BDNF, are currently under consideration (Lu et al., 2013).
BDNF is released by the BDNF-producing neurons of the CNS and binds to Trk-B of the PV-interneurons, an interaction necessary for the subsequent developmental effects of this neurotrophin (Polleux et al., 2002; Jin et al., 2003; Rico et al., 2002; Aguado et al., 2003). BDNF promotes the morphological and neurochemical maturation of hippocampal and neocortical interneurons and promotes GABAergic synaptogenesis (Danglot et al., 2006; Hu and Russek, 2008).
BDNF plays an important role in axonal and dendritic differentiation during embryonic stages of neuronal development, as well as in the formation and maturation of dendritic spines during postnatal development (Chapleau et al., 2009). Recent studies have also implicated vesicular trafficking of BDNF via secretory vesicles, and both secretory and endosomal trafficking of vesicles containing synaptic proteins, such as neurotransmitter and neurotrophin receptors, in the regulation of axonal and dendritic differentiation, and in dendritic spine morphogenesis. Abnormalities in dendritic and synaptic structure are consistently observed in human neurodevelopmental disorders associated with mental retardation, as well as in mouse models of these disorders (Chapleau et al., 2009).
Evidence Supporting this KER
BDNF, in addition to its pro-survival effects, has powerful synaptic effects, promoting synaptic transmission, synaptic plasticity and synaptogenesis (Lu et al., 2013; Sanchez-Martin et al., 2013; Neal et al., 2010; Stansfiled et al., 2012; Danglot et al., 2006; Hu and Russek, 2008). NMDAR activity has been linked to the signaling of the trans-synaptic neurotorophin BDNF (Neal et al., 2010).
Use of selective agonist or antagonist of BDNF receptor TrkB demonstrates the contribution of BDNF in synaptogenesis in adult-generated neurons in the rat dentate gyrus (Ambrogini et al., 2013). In this regard, exogenous application of BDNF significantly increased the number of functional synapses in culture (Vicario-Abejon et al., 1998; Marty et al., 2000), while blocking of BDNF with antibodies greatly reduced the formation of inhibitory synapses (Seil and Drake-Baumann, 2000). Similar results were described also in an in vivo study on mutant mice characterized by deletion of the trkB gene in cerebellar precursors (obtained by Wnt1-driven Cre--mediated recombination). TrkB mutant mice showed reduced amounts of GABAergic markers and develop reduced numbers of GABAergic boutons and synaptic specializations, whilst granule and Purkinje cell dendrites appeared normal and the former presented typical numbers of excitatory synapses. This study demonstrated that TrkB is essential to the development of GABAergic neurons and the regulation of synapse formation (Rico et al., 2002). BDNF is also a potent regulator of spontaneous neuronal activity in GABAergic neurons and interneurons, as shown in in embryonic (E18) hippocampal slices (Aguado et al., 2003), and plays a critical role in controlling the emergence, complexity and networking properties of spontaneous networks.
TH deficiency during the foetal and/or the neonatal period, apart from reducing synaptogenesis, can produce several other deleterious effects for neural growth and development (e.g., such as reduced synaptic connectivity, delayed myelination, disturbed neuronal migration, deranged axonal projections, and alterations in neurotransmitters' levels), possibly through decreased BDNF levels (Koromilas et al., 2010; Shafiee et al., 2016).
Uncertainties and Inconsistencies
Alterations of BDNF signaling is probably not the only mechanism leading to impaired synaptogenesis and synaptic plasticity. Indeed NMDAR activity can also modulate nitric oxide (NO) signaling. Exogenous NO addition during Pb exposure results in complete recovery of whole-cell synaptophysin levels and partial recovery of synaptophysin and synaptobrevin in synapses in Pb-exposed neurons (Neal et al., 2012). In addition, in Wistar rats, the anti-oxidant and radical scavenger quercetin was able to relieve the impairment of synaptic plasticity induced by chronic Pb exposure (from parturition through adulthood (PND 60); 0.2% Pb in drinking water of mothers and post-weaning pups) (Hu et al., 2008), suggesting that oxidative stress can also interfere with synapse formation.
Additionally, while PTU (a TPO inhibitor) has been shown to decrease brain BDNF levels and expression in offspring born from PTU-treated rat dams (Shafiee et al. 2016; Chakraborty et al., 2012; Gilbert et al. 2016), in the study from Cortés and colleagues (Cortés et al., 2012), treatment of adult male Sprague-Dawley rats with PTU induced an increase in the amount of BDNF mRNA in the hippocampus, while the content of TrkB protein, the BDNF receptor, resulted reduced at the PSD of the CA3 region compared with controls. Treated rats presented also thinner PSD than control rats, and a reduced content of NMDAr subunits (NR1 and NR2A/B subunits) at the PSD. These indicate differential effects elicited by PTU (i.e., TPO inhibition) on BDNF expression/regulation comparing the adult vs foetal brain. However, even though BDNF levels were increased, the decrease of BDNF receptor (TrkB) compromises the signalling pathway under BDNF control.
Results variability from study to study is due to different experimental study designs, accounting for differences in brain development stages (PND vs adult), times of exposures to chemicals, and regional brain differences.
Known modulating factors
Known Feedforward/Feedback loops influencing this KER
Domain of Applicability
Empirical evidence comes from work with laboratory rodent-derived cells and brain slices, and rodent in vivo studies.
Aguado F, Carmona MA, Pozas E, Aguiló A, Martínez-Guijarro FJ, Alcantara S, Borrell V, Yuste R, Ibañez CF, SorianoE. (2003). BDNF regulates spontaneous correlated activity at early developmental stages by increasing synaptogenesis and expression of the K+/Cl–co-transporter KCC2. Development 130:1267-1280.
Ambrogini P, Lattanzi D, Ciuffoli S, Betti M, Fanelli M, Cuppini R. (2013). Physical exercise and environment exploration affect synaptogenesis in adult-generated neurons in the rat dentate gyrus: possible role of BDNF. Brain Res 1534: 1-12.
Buckmaster PS, Ingram EA, Wen X. (2009). Inhibition of the mammalian target of rapamycin signaling pathway suppresses dentate granule cell axon sprouting in a rodent model of temporal lobe epilepsy. J Neurosci. Jun 24; 29(25):8259-69.
Chakraborty G, Magagna-Poveda A, Parratt C, Umans JG, MacLusky NJ, Scharfman HE. (2012). Reduced hippocampal brain-derived neurotrophic factor (BDNF) in neonatal rats after prenatal exposure to propylthiouracil (PTU). Endocrinology 153:1311–1316.
Chapleau CA, Larimore JL, Theibert A, Pozzo-Miller L. (2009). Modulation of dendritic spine development and plasticity by BDNF and vesicular trafficking: fundamental roles in neurodevelopmental disorders associated with mental retardation and autism. J Neurodev Disord;1:185–196.
Chen WH, Wang M, Yu SS, Su L, Zhu DM, She JQ, et al. (2007). Clioquinol and vitamin B12 (cobalamin) synergistically rescue the lead-induced impairments of synaptic plasticity in hippocampal dentate gyrus area of the anesthetized rats in vivo. Neuroscience 147(3): 853-864.
Cortés C, Eugenin E, Aliaga E, Carreño LJ, Bueno SM, Gonzalez PA, Gayol S, Naranjo D, Noches V, Marassi MP, Rosenthal D, Jadue C, Ibarra P, Keitel C, Wohllk N, Court F, Kalergis AM, Riedel CA. (2012). Hypothyroidism in the adult rat causes incremental changes in brain-derived neurotrophic factor, neuronal and astrocyte apoptosis, gliosis, and deterioration of postsynaptic density. Thyroid. Sep;22(9):951-63.
Danglot L, Triller A, Marty S. (2006). The development of hippocampal interneurons in rodents. Hippocampus. 16:1032-1060.
Gilbert ME, Sanchez-Huerta K, Wood C. (2016). Mild Thyroid Hormone Insufficiency During Development Compromises Activity-Dependent Neuroplasticity in the Hippocampus of Adult Male Rats. Endocrinology, Feb;157(2):774-87
Hu Y, Russek SJ. (2008). BDNF and the diseased nervous system: a delicate balance between adaptive and pathological processes of gene regulation. J Neurochem. 105:1-17.
Hu P, Wang M, Chen WH, Liu J, Chen L, Yin ST, et al. (2008). Quercetin relieves chronic lead exposure-induced impairment of synaptic plasticity in rat dentate gyrus in vivo. Naunyn Schmiedebergs Arch Pharmacol. Jul;378(1):43-51.
Jin X, Hu H, Mathers PH, Agmon A. (2003). Brain-derived neurotrophic factor mediates activity-dependent dendritic growth in nonpyramidal neocortical interneurons in developing organotypic cultures. J Neurosci 23:5662–5673.
Koibuchi N, Yamaoka S, Chin WW. (2001). Effect of altered thyroid status on neurotrophin gene expression during postnatal development of the mouse cerebellum. Thyroid 11:205–210.
Koromilas C, Liapi C, Schulpis KH, Kalafatakis K, Zarros A, Tsakiris S. Structural and functional alterations in the hippocampus due to hypothyroidism. Metab Brain Dis. 2010 Sep;25(3):339-54.
Leal G, Comprido D, Duarte CB. (2014). BDNF-induced local protein synthesis and synaptic plasticity. Neuropharmacology 76 Pt C: 639-656.
Lu B, Nagappan G, Guan X, Nathan PJ, Wren P. (2013). BDNF-based synaptic repair as a disease-modifying strategy for neurodegenerative diseases. Nat Rev Neurosci 14(6): 401-416.
Marty S, Wehrle R, Sotelo C. (2000). Neuronal activity and brain-derived neurotrophic factor regulate the density of inhibitory synapses in organotypic slice cultures of postnatal hippocampus. J Neurosci 20: 8087–8095.
Neal AP, Stansfield KH, Worley PF, Thompson RE, Guilarte TR. (2010). Lead exposure during synaptogenesis alters vesicular proteins and impairs vesicular release: potential role of NMDA receptor-dependent BDNF signaling. Toxicol Sci 116(1): 249-263.
Neal AP, Stansfield KH, Guilarte TR. (2012). Enhanced nitric oxide production during lead (Pb(2)(+)) exposure recovers protein expression but not presynaptic localization of synaptic proteins in developing hippocampal neurons. Brain Res 1439: 88-95.
Polleux F, Whitford KL, Dijkhuizen PA, Vitalis T, Ghosh A. (2002). Control of cortical interneuron migration by neurotrophins and PI3-kinase signaling. Development 129:3147–60.
Rico B, Xu B, Reichardt LF. (2002). TrkB receptor signaling is required for establishment of GABAergic synapses in the cerebellum. Nat Neurosci 5:225–233.
Sanchez-Martin FJ, Fan Y, Lindquist DM, Xia Y, Puga A. (2013). Lead induces similar gene expression changes in brains of gestationally exposed adult mice and in neurons differentiated from mouse embryonic stem cells. PLoS One 8(11): e80558.
Sato K, Akaishi T, Matsuki N, Ohno Y, Nakazawa K. (2007). beta-Estradiol induces synaptogenesis in the hippocampus by enhancing brain-derived neurotrophic factor release from dentate gyrus granule cells. Brain Res. May 30;1150:108-20.
Schildt S, Endres T, Lessmann V, Edelmann E. (2013). Acute and chronic interference with BDNF/TrkB-signaling impair LTP selectively at mossy fiber synapses in the CA3 region of mouse hippocampus. Neuropharmacology. Aug;71:247-54.
Schjetnan AG, Escobar ML. (2012). In vivo BDNF modulation of hippocampal mossy fiber plasticity induced by high frequency stimulation. Hippocampus. Jan;22(1):1-8.
Seil FJ, Drake-Baumann R. (2000). TrkB receptor ligands promote activity-dependent inhibitory synaptogenesis. J Neurosci 20: 5367–73.
Shafiee SM, Vafaei AA, Rashidy-Pour A. (2016). Effects of maternal hypothyroidism during pregnancy on learning, memory and hippocampal BDNF in rat pups: Beneficial effects of exercise. Neuroscience. Aug 4;329:151-61.
Stansfield KH, Pilsner JR, Lu Q, Wright RO, Guilarte TR. (2012). Dysregulation of BDNF-TrkB signaling in developing hippocampal neurons by Pb(2+): implications for an environmental basis of neurodevelopmental disorders. Toxicol Sci 127(1): 277-295.
Vicario-Abejon C, Collin C, McKay RD, Segal M. (1998). Neurotrophins induce formation of functional excitatory and inhibitory synapses between cultured hippocampal neurons. J Neurosci 18:7256–71
Westerholz S, de Lima AD, Voigt T. (2013). Thyroid hormone-dependent development of early cortical networks: temporal specificity and the contribution of trkB and mTOR pathways. Front Cell Neurosci 7:121.
Xiao Y, Fu H, Han X, Hu X, Gu H, Chen Y, et al. (2014). Role of synaptic structural plasticity in impairments of spatial learning and memory induced by developmental lead exposure in Wistar rats. PLoS One 9(12): e115556.