A Proteomics Profiling Reveals the Neuroprotective Effects of Melatonin on Exogenous β-amyloid-42 Induced Mitochondrial Impairment, Intracellular β-amyloid Accumulation and Tau Hyperphosphorylation in Human SH-SY5Y Cells

Alzheimer's disease (AD) is prevalent in the elderly population and characterized by the intracellular accumulation of neurofibrillary tangles (NFTs), composed of tau proteins, and extracellular deposition of beta-amyloid protein (Aβ). The present study aimed to investigate the neuroprotective effects of melatonin on Aβ42-induced AD-like pathology in SH-SY5Y cell lines. To assess the effects of melatonin on Aβ42-exposed cells, we performed a proteomics analysis of altered protein expression in Aβ42-treated cells, with or without melatonin Pretreatment, using label-free nano-LC-MS/MS. Experimental validations of pathways related to the neuroprotective effects of melatonin were carried out using Milliplex amyloid beta and tau magnetic bead assays, Western blot analysis, and measurements of mitochondrial membrane potential and ROS levels. Our results show that Aβ42 exposure led to an increase in an accumulation of intracellular Aβ42/40 and phosphorylated tau (Thr181)/Tau ratios. Pretreatment with melatonin effectively reduced the levels of these pathogenic proteins. Proteomics analysis has revealed protein markers associated with the Alzheimer's disease pathway, neuronal synapses, cellular apoptosis, and mitochondrial functions. Changes in proteins regulating the mitochondrial permeability transition pore, the electron transport chain, and mitochondrial oxidative stress were observed in Aβ42-treated cells. Pretreatment with melatonin protected the cells against Aβ42-induced cellular damages by regulating the expression of several proteins underpinning these biological processes, including the suppression of mitochondrial ROS generation and mitigation of mitochondrial membrane depolarization.