Abstract
Alzheimer's disease (AD) is a progressive neurodegenerative disorder typified by several neuropathological features including amyloid-beta (Aβ) plaque and neurofibrillary tangles (NFTs). Cholesterol retention and oxidative stress (OS) are the major contributors of elevated β- and γ-secretase activities, leading to excessive Aβ deposition, signifying the importance of altered cholesterol homeostasis and OS in the progression of Aβ-mediated neurodegeneration and cognitive deficit. However, the effect of Aβ on cholesterol metabolism is lesser-known. In this study, we evaluated the effect of quinovic acid (QA; 50 mg/kg body weight, i.p.) against the intracerebroventricular (i.c.v.) injection of Aβ (1-42)-induced cholesterol dyshomeostasis, oxidative stress, and neurodegeneration in the cortex and hippocampal brain regions of wild-type male C57BL/6J mice. Our results indicated that Aβ (1-42)-treated mice have increased Aβ oligomer formation along with increased β-secretase expression. The enhanced amyloidogenic pathway in Aβ (1-42)-treated mice intensified brain cholesterol accumulation due to increased expressions of p53 and 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) enzyme. Importantly, we further confirmed the p53-mediated HMGCR axis activation by using pifithrin-α (PFT) in SH-SY5Y cells. Furthermore, the augmented brain cholesterol levels were also associated with increased OS. However, the QA administration to Aβ (1-42)-injected mice significantly ameliorated the Aβ burden, p53 expression, and cholesterol accumulation by deterring the oxidative stress through upregulating the Nrf2/HO-1 pathway. Moreover, the QA downregulated gliosis, neuroinflammatory mediators (p-NF-κB and IL-1β), and the expression of mitochondrial apoptotic markers (Bax, cleaved caspase-3, and cytochrome c). QA treatment also reversed the deregulated synaptic markers (PSD-95 and synaptophysin) and improved spatial learning and memory behaviors in the Aβ-treated mouse brains. These results suggest that Aβ (1-42) induces its acute detrimental effects on cognitive functions probably by increasing brain cholesterol levels through a possible activation of the p53/HMGCR axis. However, QA treatment reduces the cholesterol-induced oxidative stress, neuroinflammation, and neurodegeneration, leading to the restoration of cognitive deficit after Aβ (1-42) i.c.v. injection in mice.