Reticulon-4

Reticulon-4 (RTN4) is a multifunctional protein that regulates endoplasmic reticulum (ER) membrane morphogenesis by promoting tubular ER formation and stabilization (UniProt: Q9NQC3). In the nervous system, it acts as a negative regulator of axon-axon adhesion and neurite growth while facilitating branching and regulating cortical neuronal migration. RTN4 also modulates vascular function and immune responses through effects on endothelial cells, sphingolipid biosynthesis, and leukocyte migration.

RTN4 is primarily expressed in endothelial cells and the nervous system, with roles spanning ER biogenesis, neurodevelopment, and vascular regulation (UniProt: Q9NQC3). Notably, certain isoforms inhibit BACE1 activity and amyloid precursor protein processing, linking RTN4 to amyloidogenic pathways central to neurodegeneration.

In Alzheimer's disease, RTN4 is significantly downregulated in human post-mortem AD brain tissue compared to age-matched controls (mean log2FC: −0.2619, Chaparral AD proteomics). This downregulation may impair ER tubulation, neuronal regulation, and BACE1 inhibition, potentially contributing to pathological features of AD including amyloid accumulation and neuronal dysfunction.