Human Tau has been implicated in the pathogenesis of neurodegenerative tauopathies including Alzheimer's disease (AD), frontotemporal dementia (FTD), Pick's disease, and others (Williams, 2006). Abnormally hyperphosphorylated Tau proteins form pathologic oligomers and fibrillar aggregates leading to neuronal dysfunction and cell death (Gong and Iqbal, 2008). Tau is a microtubule-associated protein that stabilizes neuronal microtubules and thus promotes axonal outgrowth. Encoded by MAPT (microtubule associated protein Tau) gene on chromosome 17q21, Tau is exclusively expressed in human brain (Neve et al., 1986). Through alternative splicing of exons 2, 3, and 10, six Tau isoforms are produced and exons 9–12 together encode four highly conserved copies of Tau repeat domain (TauRD) which binds to microtubule through a flexible array of distributed sites (Andreadis, 2005). Distinct FTD mutations in TauRD reduce Tau's ability to regulate microtubule assembly and promote Tau filamentous aggregation (Nacharaju et al., 1999; Vogelsberg-Ragaglia et al., 2000). Tau mutations including G272V, N279K, V337 M, P301L, P301S, S305 N, and R406W can cause FTD, and the resulting tau filamentous aggregates are similar to those in AD (Goedert et al., 2000). The deletion mutation ΔK280 in Tau has also been found in patients with FTD (Hutton, 2001). The ΔK280 also results in phenotype of AD (Momeni et al., 2009). In addition, H1 haplotype of MAPT also contributes to the risk of progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD), both of which are parkinsonism caused by tauopathy (van Slegtenhorst et al., 2000; Rademakers et al., 2005). Among Tau mutations, ΔK280 and P301L mutations have a much stronger tendency for aggregation of paired helical filaments (PHF) (von Bergen et al., 2001). Transgenic mice expressing TauRD-ΔK280 have demonstrated increased neurofibrillary tangles that are toxic to neurons (Hochgräfe et al., 2015). Compared to deletion of K280, acetylation of K280 is observed in most sporadic 4R-tauopathies. Evidence has shown that K280 acetylation impairs tau-mediated MT assembly function and also significantly enhances tau aggregation (Trzeciakiewicz et al., 2017). Mitochondrial dysfunction is one of the most early and prominent features in vulnerable neurons in the brain of AD patients (Zhu et al., 2013). Aside from helping microtubule assembly, Tau also interacts with other cytoskeleton components to support axonal transport (Lee and Leugers, 2012). Studies using preclinical models of tauopathy have shown that overexpression of hyperphosphorylated and aggregated Tau impairs mitochondrial dynamics, mitophagy, and bioenergetics and further causes mitochondrial dysfunction, oxidative stress, and neuronal damage (Cheng and Bai, 2018; Gilley et al., 2012; Rodríguez-Martín et al., 2016; Schulz et al., 2012; Szabo et al., 2020; Liu et al., 2023). Magnetic resonance spectroscopy studies also showed metabolic alterations involving mitochondrial dysfunction, oxidative stress and neuroinflammation in AD patients (Song et al., 2021). Taken together, mitochondrial dysfunction and oxidative stress significantly contributes to the pathogenesis of AD and may be a potential target for treatment (Reiss et al., 2022; Pszczołowska et al., 2024).

Neuroinflammation triggered by protein aggregates plays an important role in disease progression and severity of AD (Heneka et al., 2015; Botella Lucena and Heneka, 2024). Microglial activation is correlated with neurofibrillary tangle (NFT) formation in postmortem hippocampus of AD (DiPatre and Gelman, 1997). Furthermore, elevated glial reactivity and T cell infiltration have been shown in postmortem brains of patients with frontotemporal lobar degeneration with tau pathology (Hartnell et al., 2024). In addition, microglial activation promotes Tau phosphorylation and aggregation (Bhaskar et al., 2010) and drives tau-induced pathology (Maphis et al., 2015), and oligomeric Tau induces further inflammation to lead to neuronal damage (Nilson et al., 2017). Tau interacts with polyglutamine binding protein 1 (PQBP1) to drive innate immune response of microglia in mouse brain (Jin et al., 2021). Transgenic models of tauopathy demonstrated activation of microglia and astrocytes associated with increased pro-inflammatory cytokines, which causes oxidative damage on neuron (Bellucci et al., 2004; Sasaki et al., 2008; Rubio-Perez and Morillas-Ruiz, 2012; Laurent et al., 2017). Besides, blocking IL-1 signaling ameliorated tau pathology and improved cognition in an AD mouse model (Kitazawa et al., 2011). Being a critical component in pathogenesis, neuroinflammation provides an attractive therapeutic target in the treatment and prevention of AD and other tauopathies (Ardura-Fabregat et al., 2017; Kiraly et al., 2023; Chen and Yu, 2023).

Mulberry leaves are dried and collected from mulberry trees (Morus alba L., also known as white mulberry). As a commonly used Chinese herb for both medicine and food, it has a large range of health benefits arising from their bioactive properties, such as antioxidative, antidiabetic, antibacterial, antiviral, anticancer, and neuroprotective activities (Chen et al., 2021). Given that mulberry leaves have demonstrated its anti-inflammatory, antioxidative, and mitochondria-enhancing activities, which are all playing important roles in the pathogenesis of tauopathy, we assume mulberry leaves may have potential in inhibiting Tau-mediated pathogenesis and provide neuroprotective effects (Tang et al., 2023; Bai et al., 2024; Chen et al., 2025). In this study, we examined the underlying pathogenesis of AD and other tauopathies using a Tau aggregation cell model (Chang et al., 2016) and tested if M. alba leaf extract may provide therapeutic effects via targeting neuroinflammation and mitochondrial dysfunction.