SPP1 and Alzheimer disease: Secreted Phosphoprotein 1 (Spp1), also known as osteopontin, is a multifunctional phosphoglycoprotein that is widely expressed across various tissues and cell types, playing significant roles in numerous biological processes, including immune regulation, cell adhesion, migration, and signal transduction.23, 24, 25, 26 Studies have shown that during the progression of AD, Spp1 promotes microglial phagocytosis of functional neuronal synapses, leading to a reduction in synaptic density and impairing neural transmission.27