Neurotrophins induce structural and functional changes in neurons to modulate synaptic efficacy;our long term goal is to identify molecular mechanisms that regulate BDNF targeting and release at synapses to modulate neuronal structure and neurotransmission. BDNF is initially synthesized as a precursor form (proBDNF) that is sorted to a regulated secretory pathway, and released in an activity-dependent manner. When proBDNF is released at the synapse, it can bind to p75 receptors to induce LTD, and potentially reduce spine density and dendritic complexity. However, if proBDNF is converted to mature BDNF in the secretory vesicle or synaptic cleft, TrkB is selectively activated to enhance synaptic transmission and promote axonal branching and dendritic growth. TrkB receptors are present both pre- and post-synaptically in the Schaffer collateral pathway, and mature BDNF can activate both pre- and post-synaptic TrkB receptors to facilitate neurotransmission. Thus, the molecular mechanisms that regulate conversion of proBDNF to mature BDNF, and that regulate intracellular trafficking to dendrites or axons are critical to modulate structural and functional neuronal plasticity. We have developed new genetic tools to facilitate detection of endogenous BDNF, and identified new sorting receptors that direct BDNF intracellular trafficking. Specifically, we have generated knock-in mice that express HA tagged BDNF to markedly enhance detection of endogenous BDNF. We have also identified intracellular chaperones, including sortilin, and other sortilin family members that bind to proBDNF. With these tools, three aims are proposed to dissect BDNF trafficking, cleavage, and depolarization dependent release: (1) Using neurons from the BDNF-HA tagged mouse, identify if conversion of proBDNF to mature BDNF occurs during synthesis and sorting to secretory vesicles, or whether conversion occurs following vesicle release. We predict that the location of BDNF conversion may differ among neuronal subtypes and across early postnatal time points when synaptic connections are being refined and synaptogenesis is robust. (2) We will investigate how sortilin family members alter intracellular cleavage of proBDNF and modulate pro- vs. mature BDNF release in neuronal cultures. (3) We will identify the sortilin family members that chaperone proBDNF to the constitutive or regulated secretory pathway, and to dendrites or axons. We posit that different sortilin family members direct intracellular trafficking to different subcellular compartments and regulate cleavage to mature BDNF and its release. These studies will rely on the BDNF- HA tagged mouse, and overexpression or shRNA knockdown of different chaperones. These studies will identify molecular mechanisms that regulate BDNF processing and trafficking, to induce structural and functional changes in the developing postnatal central nervous system.

Public Health Relevance

The neurotrophin BDNF plays critical roles in regulating neuronal survival, morphology, and activity-dependent forms of synaptic plasticity. Interestingly, BDNF is initially synthesized as a precursor, proBDNF, which exhibits biological actions that are distinct, and even opposing those of its mature form. Here we will identify molecular mechanisms that (1) regulate the trafficking of BDNF to synapses, (2) regulate the conversion of proBDNF to mature BDNF and (3) determine how these processes are regulated in early postnatal development, a critical period of robust synaptogenesis. It is well established that even modest changes in the level of BDNF secreted by neurons has significant effects on learning, memory, anxiety states and depression, and these studies will test the hypothesis that BDNF trafficking and release is regulated by differential use of intracellular chaperones.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS064114-04
Application #
8206532
Study Section
Neurogenesis and Cell Fate Study Section (NCF)
Program Officer
Mamounas, Laura
Project Start
2009-01-01
Project End
2013-12-31
Budget Start
2012-01-01
Budget End
2012-12-31
Support Year
4
Fiscal Year
2012
Total Cost
$360,150
Indirect Cost
$145,775
Name
Weill Medical College of Cornell University
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
060217502
City
New York
State
NY
Country
United States
Zip Code
10065
Yang, Jianmin; Harte-Hargrove, Lauren C; Siao, Chia-Jen et al. (2014) proBDNF negatively regulates neuronal remodeling, synaptic transmission, and synaptic plasticity in hippocampus. Cell Rep 7:796-806
Hempstead, B L (2014) Deciphering proneurotrophin actions. Handb Exp Pharmacol 220:17-32
Lorentz, Christina U; Parrish, Diana C; Alston, Eric N et al. (2013) Sympathetic denervation of peri-infarct myocardium requires the p75 neurotrophin receptor. Exp Neurol 249:111-9
Anastasia, Agustin; Deinhardt, Katrin; Chao, Moses V et al. (2013) Val66Met polymorphism of BDNF alters prodomain structure to induce neuronal growth cone retraction. Nat Commun 4:2490
Deinhardt, Katrin; Kim, Taeho; Spellman, Daniel S et al. (2011) Neuronal growth cone retraction relies on proneurotrophin receptor signaling through Rac. Sci Signal 4:ra82
Evans, Sarah Felice; Irmady, Krithi; Ostrow, Katya et al. (2011) Neuronal brain-derived neurotrophic factor is synthesized in excess, with levels regulated by sortilin-mediated trafficking and lysosomal degradation. J Biol Chem 286:29556-67
Skucas, Vanessa A; Mathews, Ian B; Yang, Jianmin et al. (2011) Impairment of select forms of spatial memory and neurotrophin-dependent synaptic plasticity by deletion of glial aquaporin-4. J Neurosci 31:6392-7
Teng, Kenneth K; Felice, Sarah; Kim, Taeho et al. (2010) Understanding proneurotrophin actions: Recent advances and challenges. Dev Neurobiol 70:350-9
Greenberg, Michael E; Xu, Baoji; Lu, Bai et al. (2009) New insights in the biology of BDNF synthesis and release: implications in CNS function. J Neurosci 29:12764-7