Autophagy is a conserved catabolic process that helps the body to replenish nutrients under starving conditions, is crucial in maintaining neuronal health. It aids in the removal of toxic proteins and damaged organelles which are the primary cause of age-related neurodegenerative disorders like Alzheimer's, Parkinson's, Huntington's, etc. (Guo et al., 2018). In the case of Alzheimer's disease (AD), the accumulation of Amyloid beta (Aβ) plaques leads to severe neuronal degeneration and synapse loss. As the person ages, the process of autophagy starts declining, and the toxic clumps of misfolded Aβ plaques keep accumulating between neurons, exacerbating the disruption of neural networks and neuronal loss (Barmaki et al., 2023) which is irreversible in AD. Autophagy, with its role in regulating neuronal survival (Son et al., 2012), is not just a process but a key to understanding and potentially enhancing body's repair process against neurodegenerative disorders. Autophagy and oxidative stress are deeply interconnected cellular processes that play critical roles in maintaining neuronal homeostasis. Oxidative stress, caused by the accumulation of reactive oxygen species (ROS), can damage proteins, lipids, and DNA, ultimately leading to neuronal dysfunction and death (Jiang and Mizushima, 2014; Bhardwaj et al., 2023). In response, autophagy is activated to eliminate damaged organelles (especially mitochondria, via mitophagy) and misfolded proteins, thus limiting further ROS production and cellular injury. Under stress conditions, ROS damages mitochondria and proteins, prompting autophagy, particularly mitophagy, to selectively remove these damaged components, thereby reducing ROS production at the source (Lyu et al., 2024).

During autophagy initiation, the Unc51-like kinase 1 (ULK1) forms a complex with essential autophagy proteins – ATG101, ATG13, and FIP200/RB1CC1. This complex is necessary for autophagosome formation, regulated by autophagy regulatory proteins AMPK & mTOR (Lin and Hurley, 2016). The production of autophagic vesicles relies on ATG5, a crucial autophagy protein. Knocking down ATG5 completely inhibits or down regulates autophagy, highlighting its essential role (Ye et al., 2018). Meanwhile, p62, a scaffold protein, facilitates autophagic degradation by binding to LC3 and acting as a receptor to clear unwanted protein aggregates (Pankiv et al., 2007).

When core autophagy-related genes such as ATG101, ATG13, ULK1, SQSTM1 (p62), and ATG5 are dysregulated, it can result in faulty autophagosome formation, impaired lysosomal degradation, and disrupted mitophagy (Aman et al., 2021). This, in turn, hinders cellular clearance mechanisms, accumulating toxic protein aggregates and organelle dysfunction, ultimately culminating in neuronal death. The severity increases as more neurons die, and the collapse of the synaptic network leads to cognitive and motor decline. In the early AD stage, the neurons most affected are primarily located in the entorhinal cortex and the hippocampus. In the later stages of AD, the neurodegeneration spreads extensively throughout the brain, including the areas responsible for vital body functions. The brain experiences atrophy, a significant loss of brain mass. Neurons in the entorhinal cortex and hippocampus are highly connected and rely on extensive synaptic communication. These regions are metabolically active and particularly vulnerable to the disruptions caused by Aβ plaques (Rao et al., 2022). The excitatory neurons, which are glutamatergic, cholinergic, and pyramidal neurons, are significantly impacted by Aβ plaques. Aβ interferes with glutamate uptake and disrupts acetylcholine release, leading to excitotoxicity (overactivation of receptors such as N-methyl-d-aspartate NMDA) and impairment in cognitive functions like memory and attention, resulting in neuronal death (Danysz and Parsons, 2012). Loss of cholinergic signaling is a significant factor behind the cognitive decline seen in AD (Chen et al., 2022).

AD is a progressive neurodegenerative disorder characterized by hallmark features such as accumulation of extracellular amyloid-beta (Aβ) plaque, hyper phosphorylation of intracellular tau proteins complex, synaptic loss and subsequent neuronal death, leading to cognitive decline (Butterfield and Halliwell, 2019). It is the most common cause of dementia, accounting for 60–70 % of cases worldwide, with over 55 million people are currently affected globally, a number projected to rise to 139 million by 2050 according to the World Health Organization. In vitro models, particularly Aβ-treated neuronal and neuroblastoma cell lines such as SHSY5Y, are extensively used to recapitulate cellular events relevant to AD pathology, including oxidative stress, mitochondrial dysfunction, impaired autophagy, and apoptosis (Xicoy et al., 2017; Singh et al., 2017). These models offer mechanistic insights and facilitate high-throughput screening of neuroprotective compounds. In vivo, transgenic mouse models harbouring human familial AD mutations such as 5xFAD, APP/PS1 (Oakley et al., 2006; Jankowsky and Zheng, 2017) develop age-dependent Aβ deposition, neuroinflammation, synaptic degeneration, and behavioral deficits, closely mimicking the disease progression observed in humans. Together, these models provide complementary platforms for understanding AD pathogenesis and evaluating therapeutic candidates in both cellular and systemic contexts.

During the pathogenesis of AD excessive mitochondrial fission results in neuronal death and compromised mitochondrial function (Kim et al., 2016). As a result, crucial biogenesis which helps the cells to increase their mitochondrial mass via the fusion/fission process is impaired (Misrani et al., 2021). While various available treatments aim to slow progression, yet they cannot stop or reverse the neurodegenerative damage. Therefore, finding new treatments and prevention strategies is required to significantly improve the quality of life for individuals with neurodegenerative diseases.

This study explored the neuroprotective potential of Fisetin and chlorogenic acid (CGA) against Aβ-induced neurotoxicity in differentiated SHSY5Y cells via autophagy induction and maintaining redox homeostasis. Autophagy dysfunction is a critical factor in Alzheimer's disease, contributing to the accumulation of Aβ plaques and tau tangles, which drive neurodegeneration (Barmaki et al., 2023). Both fisetin and CGA have shown a potential to enhance autophagy (Meng et al., 2023; Jia et al., 2019b; Jin et al., 2023) and immune responses, improving metabolic functions and antioxidant activities (Roy et al., 2023; Zhu et al., 2024; Jia et al., 2019a). Although autophagy has been implicated in Aβ production and deposition, its precise role in AD pathogenesis—whether protective or harmful—remains unclear, a particularly intriguing finding that warrants further investigation.