γ-Secretase component presenilin is important for microglia β-amyloid clearance

Objective: The cleavage of amyloid precursor protein by γ-secretase is an important aspect of the pathogenesis of Alzheimer's disease. γ-Secretase also cleaves other membrane proteins (eg, Notch), which control cell development and homeostasis. Presenilin 1 and 2 are considered important determinants of the γ-secretase catalytic site. Our aim was to investigate whether γ-secretase can be important for microglial phagocytosis of Alzheimer's disease β-amyloid. Methods We investigated the role of γ-secretase in microglia activity toward β-amyloid phagocytosis in cell culture using γ-secretase inhibitors and small hairpin RNA and presenilin-deficient mice. Results We found that γ-secretase inhibitors impair microglial activity as measured in gene expression, protein levels, and migration ability, which resulted in a reduction of soluble β-amyloid phagocytosis. Moreover, microglia deficient in presenilin 1 and 2 showed impairment in phagocytosis of soluble β-amyloid. Dysfunction in the γ-secretase catalytic site led to an impairment in clearing insoluble β-amyloid from brain sections taken from an Alzheimer's disease mouse model when compared to microglia from wild-type mice. Interpretation We suggest for the first time, a dual role for γ-secretase in Alzheimer's disease. One role is the cleavage of the amyloid precursor protein for pathologic β-amyloid production and the other is to regulate microglia activity that is important for clearing neurotoxic β-amyloid deposits. Further studies of γ-secretase-mediated cellular pathways in microglia may provide useful insights into the development of Alzheimer's disease and other neurodegenerative diseases, providing future avenues for therapeutic intervention.