Carboxypeptidase E Regulates Activity-Dependent TrkB Neuronal Surface Insertion and Hippocampal Memory

J Neurosci. 2021 Aug 18;41(33):6987-7002. doi: 10.1523/JNEUROSCI.0236-21.2021. Epub 2021 Jul 15.

Abstract

Activity-dependent insertion of the tropomyosin-related kinase B (TrkB) receptor into the plasma membrane can explain, in part, the preferential effect of brain-derived neurotrophic factor (BDNF) on active neurons and synapses; however, the underlying molecular mechanisms remain obscure. Here, we report a novel function for carboxypeptidase E (CPE) in controlling chemical long-term potentiation stimuli-induced TrkB surface delivery in hippocampal neurons. Total internal reflection fluorescence assays and line plot assays showed that CPE facilitates TrkB transport from dendritic shafts to the plasma membrane. The Box2 domain in the juxtamembrane region of TrkB and the C terminus of CPE are critical for the activity-dependent plasma membrane insertion of TrkB. Moreover, the transactivator of transcription TAT-CPE452-466, which could block the association between CPE and TrkB, significantly inhibited neuronal activity-enhanced BDNF signaling and dendritic spine morphologic plasticity in cultured hippocampal neurons. Microinfusion of TAT-CPE452-466 into the dorsal hippocampus of male C57BL/6 mice inhibited the endogenous interaction between TrkB and CPE and diminished fear-conditioning-induced TrkB phosphorylation, which might lead to an impairment in hippocampal memory acquisition and consolidation but not retrieval. These results suggest that CPE modulates activity-induced TrkB surface insertion and hippocampal-dependent memory and sheds light on our understanding of the role of CPE in TrkB-dependent synaptic plasticity and memory modulation.SIGNIFICANCE STATEMENT It is well known that BDNF acts preferentially on active neurons; however, the underlying molecular mechanism is not fully understood. In this study, we found that the cytoplasmic tail of CPE could interact with TrkB and facilitate the neuronal activity-dependent movement of TrkB vesicles to the plasma membrane. Blocking the association between CPE and TrkB decreased fear-conditioning-induced TrkB phosphorylation and led to hippocampal memory deficits. These findings provide novel insights into the role of CPE in TrkB intracellular trafficking as well as in mediating BDNF/TrkB function in synaptic plasticity and hippocampal memory.

Keywords: TrkB; activity; carboxypeptidase E; chemical long-term potentiation; hippocampal memory; surface insertion.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Avoidance Learning / physiology*
  • Biotinylation
  • Carboxypeptidase H / physiology*
  • Fear / physiology
  • HEK293 Cells
  • Hippocampus / physiology*
  • Humans
  • Intravital Microscopy
  • Male
  • Maze Learning / physiology*
  • Membrane Glycoproteins / metabolism*
  • Membrane Proteins / metabolism*
  • Mice
  • Mice, Inbred C57BL
  • Nerve Tissue Proteins / physiology*
  • Neurons / enzymology*
  • Neurons / ultrastructure
  • Open Field Test
  • Protein Transport
  • Protein-Tyrosine Kinases / metabolism*
  • RNA Interference
  • RNA, Small Interfering / genetics
  • Rats
  • Rats, Sprague-Dawley
  • Recognition, Psychology / physiology*
  • Signal Transduction

Substances

  • Membrane Glycoproteins
  • Membrane Proteins
  • Nerve Tissue Proteins
  • RNA, Small Interfering
  • Ntrk2 protein, mouse
  • Protein-Tyrosine Kinases
  • Carboxypeptidase H