HAPLN2

HAPLN2, also known as brain hyaluronan and proteoglycan binding protein 2 or brain link protein 2, is a member of the hyaluronan and proteoglycan link protein (HAPLN) family. The gene HAPLN2 encodes a secreted extracellular matrix protein that stabilizes aggregates by linking hyaluronan to proteoglycans, thereby contributing to the structure of the extracellular matrix (ECM).

In humans, HAPLN2 expression is enriched in the central nervous system, particularly in the brain and spinal cord. It is associated with glial cells and is a component of perineuronal nets, the lattice-like ECM structures that surround certain neurons and play a role in synaptic stabilization and regulation of plasticity.

The protein contains the characteristic link module common to HAPLN family members and binds hyaluronan as well as proteoglycans, notably lecticans such as aggrecan, brevican, and neurocan. Through these interactions, HAPLN2 helps assemble and maintain ECM aggregates that modulate neuronal connectivity and ECM integrity in the CNS.

Research suggests roles for HAPLN2 in brain development and synaptic plasticity, particularly through perineuronal nets that influence critical periods of plasticity. While there is ongoing study into its involvement in neurological conditions, no specific disease has been universally established as caused by HAPLN2 mutations or dysregulation. Ongoing work aims to clarify its functions in CNS development, ECM dynamics, and potential clinical relevance.