Norepinephrine-mediated regulation of endogenous Aβ42 peptide levels: effects of noradrenergic depletion and restoration.

The locus coeruleus (LC), a cluster of noradrenergic neurons in the dorsal pons, is the brain's main source of norepinephrine (NE), crucial for memory, cognition, and stress response. NE dysregulation has been linked to mood disorders, chronic stress, and neurodegenerative diseases such as Alzheimer's disease (AD). Amyloid-β42 (Aβ42) is a key protein in AD pathology, and forms plaques that trigger neurodegeneration. Studies show elevated Aβ42 levels are associated with anxiety symptoms, even in cognitively normal individuals. Previous research suggests a positive correlation between NE and Aβ42, with Aβ42 present in NE-producing LC neurons. NE may affect Aβ42 levels through adrenergic receptors on neurons or microglia. However, the exact role of NE in modulating Aβ42 remains unclear. Using the NE depletion models, N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP-4) lesions and dopamine β-hydroxylase (DBH) knockout (KO) mice, researchers found reduced Aβ42 levels without changes in amyloid precursor protein processing. A newer model, DBH internal ribosome entry site-Cre × floxed tyrosine hydroxylase (DBH-IRES-Cre × floxed-TH) preserved dopamine (DA) but eliminated NE in adrenergic neurons, further supporting the specific influence of NE on Aβ42. Findings indicate that decreased Aβ42 in NE-depleted mice stems not from altered DA but from NE loss. This highlights the NE-mediated regulation of endogenous Aβ42 and the role of NE in AD-related pathology.