Choroid plexus APP regulates adult brain proliferation and animal behavior.

Elevated amyloid precursor protein (APP) expression in the choroid plexus suggests an important role for extracellular APP metabolites such as sAPPα in cerebrospinal fluid. Despite widespread App brain expression, we hypothesized that specifically targeting choroid plexus expression could alter animal physiology. Through various genetic and viral approaches in the adult mouse, we show that choroid plexus APP levels significantly impact proliferation in both subventricular zone and hippocampus dentate gyrus neurogenic niches. Given the role of Aß peptides in Alzheimer disease pathogenesis, we also tested whether favoring the production of Aß in choroid plexus could negatively affect niche functions. After AAV5-mediated long-term expression of human mutated APP specifically in the choroid plexus of adult wild-type mice, we observe reduced niche proliferation, reduced hippocampus APP expression, behavioral defects in reversal learning, and deficits in hippocampal long-term potentiation. Our findings highlight the unique role played by the choroid plexus in regulating brain function and suggest that targeting APP in choroid plexus may provide a means to improve hippocampus function and alleviate disease-related burdens.

OTX2 Signals from the Choroid Plexus to Regulate Adult Neurogenesis.

Proliferation and migration during adult neurogenesis are regulated by a microenvironment of signaling molecules originating from local vasculature, from CSF produced by the choroid plexus, and from local supporting cells including astrocytes. Here, we focus on the function of OTX2 homeoprotein transcription factor in the mouse adult ventricular-subventricular zone (V-SVZ), which generates olfactory bulb neurons. We find that OTX2 secreted by choroid plexus is transferred to the supporting cells of the V-SVZ and rostral migratory stream. Deletion of Otx2 in choroid plexus affects neuroblast migration and reduces the number of olfactory bulb newborn neurons. Adult neurogenesis was also decreased by expressing secreted single-chain antibodies to sequester OTX2 in the CSF, demonstrating the importance of non-cell-autonomous OTX2. We show that OTX2 activity modifies extracellular matrix components and signaling molecules produced by supporting astrocytes. Thus, we reveal a multilevel and non-cell-autonomous role of a homeoprotein and reinforce the choroid plexus and astrocytes as key niche compartments affecting adult neurogenesis.