DNA double-strand breaks (DSBs) are the most severe form of DNA damage, accumulating with age. In dividing cells, cytoskeletal proteins play a crucial role in DSB repair. Given tau's role as a microtubule-associated protein (MAP), this research explores the involvement of DSBs in tau-related pathologies in Alzheimer's disease (AD). AD is characterized by the accumulation of amyloid-beta plaques and neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau protein. The precise mechanisms underlying AD pathogenesis are not fully understood, but accumulating evidence suggests that DNA damage contributes to neurodegeneration. Previous studies have reported increased DNA damage, including DSBs, in the brains of AD patients. This study hypothesizes that impaired DSB repair contributes to the development of tauopathy in AD, and that tau plays a previously unrecognized role in this process. Understanding this potential link between DSB repair and tau pathology could lead to the development of novel therapeutic strategies for AD.

The existing literature supports a link between DNA damage and neurodegeneration. Studies have shown an increased accumulation of DSBs in the brains of AD patients, suggesting a potential role in disease pathogenesis. Research also highlights the importance of DSB repair mechanisms in neuronal survival. Furthermore, studies have examined the role of tau protein in various cellular processes, including microtubule stability and intracellular transport. However, the precise interaction between tau and DSB repair mechanisms has not been thoroughly investigated. This study builds upon this foundation, aiming to bridge the gap in our understanding of the connection between DSBs, tau, and AD pathology. The authors cite several studies that demonstrate the accumulation of DNA damage in the aging brain and in neurodegenerative diseases, including AD. They also review the literature on the role of cytoskeletal proteins, including tau, in DNA repair and maintenance of genomic integrity.

The study employed both in vivo and in vitro approaches. Immunohistochemistry was performed on postmortem brain tissue from AD patients and controls to assess the co-localization of DSB markers (γH2AX) and phosphorylated tau (AT8). In vitro experiments utilized primary mouse cortical neurons. DSBs were induced using etoposide, a topoisomerase II inhibitor. Subcellular localization of tau (both phosphorylated and non-phosphorylated) was examined using Western blotting and immunocytochemistry after DSB induction. The effect of tau knockdown on DSB levels was investigated using lentivirus-mediated shRNA. Additionally, the synergistic effect of DSB induction and microtubule disassembly (using 5HPP-33) on tau aggregation and apoptosis was evaluated. Several techniques were used, including immunohistochemistry, immunofluorescence, Western blotting, in situ PLA (Proximity Ligation Assay), and electron microscopy, providing multi-faceted data to validate findings. Statistical analyses including one-way and two-way ANOVA, Tukey-Kramer HSD test, and Student's t-test were performed.

The study found a significant co-localization of γH2AX (DSB marker) and phosphorylated tau (AT8) in the cortex of AD patients, indicating a link between DNA damage and tau pathology. In vitro studies revealed that DSB induction caused a perinuclear accumulation of non-phosphorylated tau along with tubulin, followed by a subsequent increase in phosphorylated tau. Knockdown of endogenous tau resulted in a significant increase in γH2AX levels after DSB induction, suggesting a protective role of tau in DNA repair. The combination of DSB induction and microtubule depolymerization (by 5HPP-33) synergistically increased aberrant phosphorylated tau aggregation and apoptosis, mimicking neurofibrillary tangle formation. The in situ PLA assays confirmed the interaction between non-phosphorylated tau and tubulin post-DSB induction. These data indicate that DSBs induce perinuclear accumulation of non-phosphorylated tau, potentially involving microtubule assembly, and subsequent phosphorylation, which if not repaired, leads to neurotoxicity.

The findings of this study strongly suggest a previously underappreciated role for tau in DSB repair and the pathogenesis of AD. The observed co-localization of DSB markers and phosphorylated tau in AD brains, coupled with the in vitro data showing that tau knockdown exacerbates DSBs, points towards a protective role for tau in the early stages of DNA damage response. However, when DSB repair fails, the excessive DNA damage, along with microtubule disassembly, drives the aberrant aggregation of phosphorylated tau and subsequent neurotoxicity. This explains the observed accumulation of phosphorylated tau specifically around the nucleus. The synergistic effect of DSB induction and microtubule depolymerization underscores the importance of maintaining microtubule stability in the context of DNA repair. The study's findings highlight a potential therapeutic target: maintaining efficient DSB repair and microtubule stability could mitigate tau pathology in AD.

This study provides compelling evidence linking DNA double-strand break repair failure with tauopathy in Alzheimer's disease. The results demonstrate a previously unknown protective role of tau in early-stage DNA repair, but also show that the failure of this repair, especially in the context of microtubule instability, leads to neurodegeneration. These findings could inform the development of novel therapeutic strategies targeting both DSB repair and microtubule stability to manage AD pathogenesis. Further research is needed to elucidate the precise molecular mechanisms governing tau's involvement in DSB repair and explore the therapeutic potential of interventions targeting these pathways.

The study utilizes an in vitro model, which may not fully recapitulate the complexity of AD pathogenesis in vivo. The specific molecular mechanisms underlying tau's involvement in DSB repair remain to be fully elucidated. Further research using in vivo models is required to validate the findings and translate them into clinical applications. The study focused on a specific DSB inducer (etoposide), and additional inducers should be examined to ensure the generalizability of the findings.