Pleiotrophin regulates presynaptic assembly and function through heparan sulfate-dependent binding to neurexin1

Synapses are the fundamental units of neural circuits, and their dysfunction contributes to numerous neuropsychiatric disorders. Although synaptic adhesion proteins have been well studied, how extracellular cues and matrix glycans specify synaptic properties remains much less well understood. Here, we identify pleiotrophin (Ptn) as a regulator of presynaptic development. Affinity purification-based proteomics shows that Ptn associates with heparan sulfate (HS)-modified neurexin1 (HS-Nrxn1) in the brain through an HS-glycan-dependent mechanism. Glycan microarray analyses further reveal that Ptn selectively recognizes defined HS sulfation motifs. Functionally, Ptn requires both HS glycans and Nrxns to induce presynaptic assembly in cultured neurons. In vivo, Ptn deletion disrupts presynaptic protein clustering, reduces neurotransmitter release probability at CA3-CA1 synapses, and impairs contextual fear discrimination. Together, these findings establish Ptn as an extracellular organizer of presynaptic development and support a model in which Nrxn1's HS glycan provides a platform for extracellular ligand recruitment.