NPTXR

NPTXR is a pentraxin-domain synaptic organizing protein that, in cooperation with NPTX2, clusters GluA4-containing AMPA receptors at excitatory synapses onto parvalbumin fast-spiking interneurons to drive circuit maturation and excitatory/inhibitory balance; loss of NPTXR (with NPTX2) reduces synaptic GluA4 and AMPAR currents, prolongs the developmental critical period, weakens feedforward inhibition, and produces epileptiform activity (PMID:25754824). Its synapse-organizing activity is mediated through trans-synaptic adhesion: NPTXR participates in a C1QL3-bridged complex with the postsynaptic adhesion GPCR ADGRB3/BAI3, co-expressed with C1QL3 in the same excitatory neurons consistent with presynaptic secretion and postsynaptic engagement (PMID:33337553), and these ligand interactions are anchored by the conserved C-terminal pentraxin domain whose structure has been characterized by NMR (PMID:41495486). Beyond the CNS, NPTXR functions as a cognate receptor for NPTX2 in pruriceptive CGRP+/IB4+ peripheral sensory neurons, where it potentiates p-ERK-dependent itch signaling and supports scratching behavior (PMID:41564473). NPTXR also drives malignant phenotypes in gastric and esophageal carcinoma cells, where its silencing suppresses proliferation, invasion, adhesion, and stemness and promotes apoptosis via PI3K-AKT-mTOR, FAK-JNK, and YAP signaling, and anti-NPTXR antibody limits tumor growth and metastasis (PMID:32847597, PMID:38717547).

1. 2015 High

   Established the core synaptic function of NPTXR: whether it organizes AMPA receptors at specific synapses was unknown, and the double knockout showed it is required, with NPTX2, for GluA4 clustering and proper circuit maturation.

   Evidence NPTX2-/-/NPTXR-/- double knockout mice with electrophysiology, immunofluorescence, and GluA4 quantification

   PMID:25754824

   Open questions at the time

   • Redundancy with NPTX2 prevents attribution of an NPTXR-specific contribution
   • Molecular interface that recruits GluA4 not defined
   • No structural basis for the synaptic interaction established here
2. 2021 Medium

   Addressed how NPTXR is positioned at the synapse by identifying a trans-synaptic adhesion complex in which C1QL3 bridges NPTXR to the postsynaptic adhesion GPCR ADGRB3.

   Evidence In vivo interactome co-immunoprecipitation/pulldown plus single-cell RNA-seq co-expression analysis

   PMID:33337553

   Open questions at the time

   • Functional consequence of the complex inferred, not tested by mutagenesis or reconstitution
   • Single lab without reciprocal validation
   • Stoichiometry and direct binding interfaces undefined
3. 2026 Medium

   Began structural dissection of the ligand-binding module by producing the conserved C-terminal pentraxin domain and obtaining backbone NMR assignments, providing a foundation for mapping NPTXR-ligand interactions.

   Evidence NMR backbone resonance assignment of uniformly 15N,13C-labeled NPTXR pentraxin domain

   PMID:41495486

   Open questions at the time

   • Assignments only; no full structure or ligand-bound complex
   • No functional mutagenesis validation of the domain
   • Does not yet map interaction surfaces with NPTX2, C1QL3, or ADGRB3
4. 2020 Medium

   Extended NPTXR function beyond neurons by showing it promotes malignant behavior in gastric cancer through oncogenic signaling and is a therapeutic target.

   Evidence siRNA knockdown, in vitro functional assays, mouse xenograft, and anti-NPTXR monoclonal antibody treatment with signaling pathway analysis

   PMID:32847597

   Open questions at the time

   • Mechanistic link between NPTXR and PI3K-AKT-mTOR/FAK-JNK/YAP activation not resolved at the receptor level
   • Single lab and single cancer context
   • Ligand driving oncogenic signaling not identified
5. 2024 Medium

   Tested generality of the oncogenic role by replicating NPTXR-dependent proliferation, survival, and adhesion phenotypes and antibody sensitivity in a second tumor type, esophageal squamous cell carcinoma.

   Evidence siRNA knockdown with proliferation, apoptosis, adhesion assays and anti-NPTXR monoclonal antibody treatment in vitro

   PMID:38717547

   Open questions at the time

   • No in vivo validation in ESCC
   • Downstream signaling not profiled as in gastric cancer
   • Mechanism of antibody action undefined
6. 2026 Medium

   Identified a peripheral function: NPTXR acts as a cognate receptor for NPTX2 in pruriceptive sensory neurons to drive p-ERK-dependent itch signaling and scratching behavior.

   Evidence Intra-trigeminal-ganglion Nptxr siRNA, immunohistochemistry, scratch behavioral assay, and p-ERK western blot in an atopic dermatitis model

   PMID:41564473

   Open questions at the time

   • Direct NPTX2-NPTXR binding not demonstrated biochemically here
   • Coupling between NPTXR and ERK activation not defined
   • Single lab and single disease model
7. 2024 Low

   Associated NPTXR levels with glutamatergic synapse integrity by showing prefrontal cortex downregulation in a stress-induced anhedonia model.

   Evidence High-throughput proteomics of prefrontal cortex in a chronic variable stress rat model with sucrose preference testing

   PMID:39488299

   Open questions at the time

   • Associative proteomics only with no direct manipulation of NPTXR
   • Causality versus correlate of anhedonic state unresolved
   • Not a direct (R)-ketamine target
8. 2006 Low

   Earliest expression observation linking NPTXR to non-neural tissue, showing delayed Nptxr mRNA upregulation in post-infarct myocardium.

   Evidence cDNA filter array with ranked ratio analysis in a rat myocardial infarction model

   PMID:16497176

   Open questions at the time

   • Single array-based measurement with no protein-level or functional follow-up
   • No mechanistic role in cardiac tissue established
   • Significance of the delayed kinetics unexplained

• How the pentraxin domain physically engages NPTX2, C1QL3/ADGRB3, and oncogenic signaling partners to transduce both synaptic organization and tumor-promoting signals remains unresolved.
• No ligand-bound structure linking the pentraxin domain to its partners
• No defined receptor-to-effector mechanism for ERK or PI3K-AKT-mTOR activation
• NPTXR-specific contribution distinct from NPTX2 not isolated