neuritin

Neuritin, also known as NRN1, is a small neural plasticity–related protein encoded by the NRN1 gene. It was first identified as an activity-regulated gene in developing neurons and was formerly referred to as candidate plasticity gene 15 (cpg15).

Molecular characteristics and expression: Neuritin is a glycosylphosphatidylinositol (GPI)–anchored cell surface protein. It can be shed to form a soluble factor by cleavage of the GPI anchor; this soluble form promotes neurite outgrowth in cultured neurons. In the brain, NRN1 is expressed broadly with higher levels in regions such as the cortex and hippocampus. Its transcription is increased by neuronal activity and by neurotrophic signals such as BDNF.

Functions: Neuritin promotes neurite outgrowth and dendritic branching, increases synapse formation and density, and supports neuronal survival in some contexts. By enhancing dendritic complexity and synaptic connectivity, it contributes to activity-dependent plasticity and may influence learning and memory.

Mechanisms: The signaling pathways downstream of neuritin include activation of PI3K–Akt and mitogen-activated protein kinase (MAPK) cascades, leading to cytoskeletal remodeling. The exact cell-surface receptor mediating neuritin effects remains unclear.

Clinical and research relevance: Animal studies show that increasing neuritin levels can enhance axonal regeneration and functional recovery after CNS injury. Altered NRN1 expression has been studied in relation to neurodevelopmental and psychiatric disorders, though the clinical significance is not fully established. Neuritin is used as a molecular marker of neuronal activity and plasticity in research.