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Mechanisms of PTP?-Mediated Presynaptic Differentiation.

ABSTRACT: Formation of synapses between neurons depends in part on binding between axonal and dendritic cell surface synaptic organizing proteins, which recruit components of the developing presynaptic and postsynaptic specializations. One of these presynaptic organizing molecules is protein tyrosine phosphatase ? (PTP?). Although the protein domains involved in adhesion between PTP? and its postsynaptic binding partners are known, the mechanisms by which it signals into the presynaptic neuron to recruit synaptic vesicles and other necessary components for regulated transmitter release are not well understood. One attractive candidate to mediate this function is liprin-?, a scaffolding protein with well-established roles at the synapse. We systematically mutated residues of the PTP? intracellular region (ICR) and used the yeast dihydrofolate reductase (DHFR) protein complementation assay to screen for disrupted interactions between these mutant forms of PTP? and its various binding partners. Using a molecular replacement strategy, we show that disrupting the interaction between PTP? and liprin-?, but not between PTP? and itself or another binding partner, caskin, abolishes presynaptic differentiation. Furthermore, phosphatase activity of PTP? and binding to extracellular heparan sulfate (HS) proteoglycans are dispensable for presynaptic induction. Previous reports have suggested that binding between PTP? and liprin-? is mediated by the PTP? membrane-distal phosphatase-like domain. However, we provide evidence here that both of the PTP? phosphatase-like domains mediate binding to liprin-? and are required for PTP?-mediated presynaptic differentiation. These findings further our understanding of the mechanistic basis by which PTP? acts as a presynaptic organizer.

SUBMITTER: Bomkamp C

PROVIDER: S-EPMC6540616 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature

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Mechanisms of PTPσ-Mediated Presynaptic Differentiation.

Bomkamp Claire C Padmanabhan Nirmala N Karimi Benyamin B Ge Yuan Y Chao Jesse T JT Loewen Christopher J R CJR Siddiqui Tabrez J TJ Craig Ann Marie AM

Frontiers in synaptic neuroscience 20190522

Formation of synapses between neurons depends in part on binding between axonal and dendritic cell surface synaptic organizing proteins, which recruit components of the developing presynaptic and postsynaptic specializations. One of these presynaptic organizing molecules is protein tyrosine phosphatase σ (PTPσ). Although the protein domains involved in adhesion between PTPσ and its postsynaptic binding partners are known, the mechanisms by which it signals into the presynaptic neuron to recruit ...[more]

PMID: 31191292

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Project description:Perineuronal nets (PNNs) have an important physiological role in the retention of learning by restricting cognitive flexibility. Their deposition peaks after developmental periods of intensive learning, usually in late childhood, and they help in long-term preservation of newly acquired skills and information. Modulation of PNN function by various techniques enhances plasticity and regulates the retention of memories, which may be beneficial when memory persistence entails negative symptoms such as post-traumatic stress disorder (PTSD). In this study, we investigated the role of PTPσ [receptor-type tyrosine-protein phosphatase S, a phosphatase that is activated by binding of chondroitin sulfate proteoglycans (CSPGs) from PNNs] in retention of memories using Novel Object Recognition and Fear Conditioning models. We observed that mice haploinsufficient for PTPRS gene (PTPσ+/-), although having improved short-term object recognition memory, display impaired long-term memory in both Novel Object Recognition and Fear Conditioning paradigm, as compared to WT littermates. However, PTPσ+/- mice did not show any differences in behavioral tests that do not heavily rely on cognitive flexibility, such as Elevated Plus Maze, Open Field, Marble Burying, and Forced Swimming Test. Since PTPσ has been shown to interact with and dephosphorylate TRKB, we investigated activation of this receptor and its downstream pathways in limbic areas known to be associated with memory. We found that phosphorylation of TRKB and PLCγ are increased in the hippocampus, prefrontal cortex, and amygdaloid complex of PTPσ+/- mice, but other TRKB-mediated signaling pathways are not affected. Our data suggest that PTPσ downregulation promotes TRKB phosphorylation in different brain areas, improves short-term memory performance but disrupts long-term memory retention in the tested animal models. Inhibition of PTPσ or disruption of PNN-PTPσ-TRKB complex might be a potential target for disorders where negative modulation of the acquired memories can be beneficial.

Project description:Leukocyte common antigen-receptor protein tyrosine phosphatases (LAR-RPTPs) are hub proteins that organize excitatory and inhibitory synapse development through binding to various extracellular ligands. Here, we report that knockdown (KD) of the LAR-RPTP family member PTP? reduced excitatory synapse number and transmission in cultured rat hippocampal neurons, whereas KD of PTP? produced comparable decreases at inhibitory synapses, in both cases without altering expression levels of interacting proteins. An extensive series of rescue experiments revealed that extracellular interactions of PTP? with Slitrks are important for excitatory synapse development. These experiments further showed that the intracellular D2 domain of PTP? is required for induction of heterologous synapse formation by Slitrk1 or TrkC, suggesting that interaction of LAR-RPTPs with distinct intracellular presynaptic proteins, drives presynaptic machinery assembly. Consistent with this, double-KD of liprin-?2 and -?3 or KD of PTP? substrates (N-cadherin and p250RhoGAP) in neurons inhibited Slitrk6-induced, PTP?-mediated heterologous synapse formation activity. We propose a synaptogenesis model in presynaptic neurons involving LAR-RPTP-organized retrograde signaling cascades, in which both extracellular and intracellular mechanisms are critical in orchestrating distinct synapse types.SIGNIFICANCE STATEMENT In this study, we sought to test the unproven hypothesis that PTP? and PTP? are required for excitatory and inhibitory synapse formation/transmission, respectively, in cultured hippocampal neurons, using knockdown-based loss-of-function analyses. We further performed extensive structure-function analyses, focusing on PTP?-mediated actions, to address the mechanisms of presynaptic assembly at excitatory synaptic sites. Using interdisciplinary approaches, we systematically applied a varied set of PTP? deletion variants, point mutants, and splice variants to demonstrate that both extracellular and intracellular mechanisms are involved in organizing presynaptic assembly. Strikingly, extracellular interactions of PTP? with heparan sulfates and Slitrks, intracellular interactions of PTP? with liprin-? and its associated proteins through the D2 domain, as well as distinct substrates are all critical.

Dataset Information

Mechanisms of PTP?-Mediated Presynaptic Differentiation.

Publications

Mechanisms of PTPσ-Mediated Presynaptic Differentiation.

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