HAPLN4

HAPLN4, or hyaluronan and proteoglycan link protein 4, is a protein encoded by the HAPLN4 gene in humans. It is a member of the hyaluronan and proteoglycan link protein (HAPLN) family, which stabilizes extracellular matrix by mediating interactions between hyaluronan and lectican proteoglycans in the brain.

In the nervous system, HAPLN family proteins contribute to the organization of perineuronal nets, specialized extracellular matrix structures that envelope certain neurons and regulate synaptic stabilization and plasticity. HAPLN4 is believed to participate in the assembly and maintenance of these nets by binding hyaluronan and proteoglycans, promoting the formation of ternary complexes that anchor lecticans to the hyaluronan-rich matrix.

Expression of HAPLN4 is enriched in brain tissue, with localization to the extracellular matrix surrounding neurons. Structurally, HAPLN4 contains a conserved link module that mediates binding to hyaluronan, enabling its role in ECM organization.

Clinical relevance for HAPLN4 is not yet fully defined. While specific disease associations are not well established, alterations in extracellular matrix components and perineuronal nets have been linked to neurodevelopmental and neurodegenerative processes, making HAPLN4 a subject of ongoing research.

See also: HAPLN family, perineuronal nets, extracellular matrix.