In this study, we analyzed the relationship of BACE1 with astrocytes and blood vessels in human brains with sporadic and familial dementia [Autosomal dominant cerebral arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), sporadic Alzheimer’s disease (SAD), and familial Alzheimer’s disease (FAD)] and how BACE1 inhibition affects astrocytes and endothelial cells under conditions of glutamate toxicity. The gene discussed is BACE1; the disease is CADASIL.