Protective effects of BACE1 inhibitory ligand molecules against amyloid beta-induced synaptic and mitochondrial toxicities in Alzheimer's disease

Amyloid-beta (A beta) peptides are the major drivers of Alzheimer's disease (AD) pathogenesis, and are formed by successive cleavage of the amyloid precursor protein (APP) by the beta and gamma secretases. Mounting evidence suggests that A beta and mitochondrial structural and functional abnormalities are critically involved in the loss of synapses and cognitive decline, in patients with AD. In AD brain, state the sequential proteolytic cleavage of APP by beta secretase 1 enzyme (BACE1) and gamma-secretase leads to the production and release of A beta 40 and 42. BACE1 expression and activity increased in the brains of AD patients. Structurally, beta-secretase has a very large binding site (1000 angstrom) with fewer hydrophobic domains that makes a challenge to identify the specific targets/binding sites of BACE1. In the present study, we constructed a BACE1 pharmacophore with pepstatin and screened through molecular docking studies. We found one potential candidate (referred as ligand 1) that binds to the key catalytic residues of BACE1 and predicts to inhibit abnormal APP processing and reduce A beta levels in AD neurons. Using biochemical, molecular, transmission electron microscopy, immunoblotting and immunofluorescence analyses, we studied the protective effects of ligand 1 against A beta-induced synaptic and mitochondrial toxicities in mouse neuroblastoma (N2a) cells that express mutant APP. We found interaction between ligand 1 and BACE1 and this interaction decreased BACE1 activity, A beta 40 and 42 levels. We also found increased mitochondrial biogenesis, mitochondrial fusion and synaptic activity and reduced mitochondrial fission in ligand 1-treated mutant APP cells. Based on these results, we cautiously conclude that ligand 1 reduces A beta-induced mitochondrial and synaptic toxicities, and maintains mitochondrial dynamics and neuronal function in AD.