Modulation of Tau Phosphorylation by Oxidative Stress: Insights into the Interplay among LKB1, AMPK, and Akt Pathways in Differentiated SH-SY5Y Cells

Abstract

Background: Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the accumulation of hyperphosphorylated tau (p-tau) in neurofibrillary tangles and beta-amyloid plaques. The role of oxidative stress (OS) in AD progression remains unclear. Methods: Using SH-SY5Y human neuroblastoma cells as an in vitro model, we investigated the impact of OS on tau phosphorylation. Mature neurons were exposed to varying concentrations of hydrogen peroxide for different durations (1-5 days) to simulate OS. Western blot analysis was employed to quantify key signalling pathways (LKB1, AMPK, and Akt) and antioxidant enzymes (SOD2, p1, p4, and catalase). Results: Prolonged OS exposure resulted in tau hyperphosphorylation at Ser262, a tau residue sensitive to AMPK, despite initial dephosphorylation. Treatment with compound C (CC), an AMPK inhibitor, prevented this effect. OS activated LKB1 and AMPK, enhanced by CC and rapamycin, while CC and rapamycin suppressed OS-induced Akt activity. SOD2, the primary defence against OS, increased, whereas p1 and catalase, the secondary defence, decreased. P4 activity remained unchanged. Notably, CC consistently reduced antioxidant enzyme activity across experimental groups. Conclusion: OS activates the LKB1, AMPK, and Akt signalling pathways. The interplay between LKB1's stimulatory effect and Akt's inhibitory effect on AMPK leads to AMPK activation and subsequent tau hyperphosphorylation. AMPK facilitates the protective response mediated by SOD2 against OS, but prolonged OS exposure induces tau hyperphosphorylation. Therefore, OS likely serves as a trigger for AD pathology.