Effect of alternating nicotinamide phosphoribosyltransferase expression levels on mitophagy in Alzheimer's disease mouse models

AD is the abbreviation for Alzheimer's Disease, which is a neurodegenerative disorder that features progressive dysfunction in cognition. Previous research has reported that mitophagy impairment and mitochondrial dysfunction have been crucial factors in the AD's pathogenesis. More recently, literature has emerged which offers findings suggesting that the nicotinamide adenine dinucleotide (short for NAD⁺) augmentation eliminates the defective mitochondria and restores mitophagy. Meanwhile, as an enzyme which is rate-limiting, the Nicotinamide phosphoribosyltransferase, or NAMPT, is part of the salvage pathway of NAD⁺ synthesis. Therefore, the aim of the research project has been to produce proof for how the NAMPT-NAD ⁺-silent information-regulated transcription factors1/3 (short for SIRT1/3) axis function in mediating mitophagy in APP/PS1 mice aged six months. The results revealed that the NAMPT-NAD⁺-SIRT1/3 axis in the APP/PS1 mice's hippocampus was considerably declined. Surprisingly, P7C3 (an NAMPT activator) noticeably promoted the NAD⁺-SIRT1/3 axis, improved mitochondrial structure and function, enhanced mitophagy activity along with the ability of learning and memory. While FK866 (an NAMPT inhibitor) reversed the decreased NAD⁺-SIRT1/3 axis, and even exacerbated Aβ plaque deposition level in the APP/PS1 mice's hippocampus. The findings observed in this study indicate two main points: avoiding downregulation of the NAMPT activity can prevent AD-related mitophagy impairment; on the other hand, NAMPT characterizes a potential therapeutic intervention regarding AD pathogenesis.