Early Locus Coeruleus noradrenergic axon loss drives olfactory dysfunction in Alzheimer’s disease
Carolin Meyer, Theresa Niedermeier, Paul Feyen, Felix L. Struebing, Boris‐Stephan Rauchmann, Katerina Karali, Johanna Gentz, Yannik Tillmann, Nicolas Landgraf, S Rumpf, Katharina Ochs, Karin Wind, Gloria Biechele, Jessica Wagner, Selim Guersel, Carolin Kurz, Meike Schweiger, Danilo Prtvar, Yuan Shi, Richard B. Banati, Guo Jun Liu, Ryan J. Middleton, Gerda Mitteregger-Kretzschmar, Robert Perneczky, Thomas Koeglsperger, Jonas J. Neher, Sabina Tahirović, Matthias Brendel, Jochen Herms, Lars Paeger
Abstract
Abstract Alzheimer’s disease (AD) often begins with non-cognitive symptoms such as olfactory deficits, which can predict later cognitive decline, though the mechanisms remain unclear. Pathologically, the brainstem locus coeruleus (LC), the main source of the neurotransmitter noradrenalin (NA) modulating olfactory information processing is affected early. Here we show early and distinct loss of noradrenergic input to the olfactory bulb (OB) coinciding with impaired olfaction in an AD mouse model, before appearance of amyloid plaques. Mechanistically, OB microglia recognize and phagocytose LC axons. Reducing phagocytosis genetically preserves LC axons and olfaction. Prodromal AD patients display elevated TSPO-PET signals in the OB, similarly to App NL-G-F mice. We further confirm early LC axon degeneration in post-mortem OBs in patients with early AD. Our findings reveal a mechanism linking early LC damage to hyposmia in AD, suggesting olfactory testing and neurocircuit imaging for early diagnosis and enable timely therapeutic intervention for Alzheimer’s disease.