Curated Optogenetic Publication Database

Abstract: Tauopathy is a group of diseases where fibrillary tau aggregates are formed in neurons and glial cells in the brain. In Alzheimer's disease (AD), the most common form of tauopathy, tau aggregation begins in the brainstem and entorhinal cortex and then spreads throughout the brain. Understanding the mechanism by which locally formed tau pathology propagates throughout the brain is crucial for comprehending the pathogenesis of AD. Therefore, a novel model of tau pathology that artificially induces tau aggregation in targeted cells at specific times is essential. In this study, we report a novel optogenetic module, OptoTau, human tau with the P301L mutation fused with a photosensitive protein Cry2Olig, which could induce various forms of tau depending on the pattern of blue light illumination. Continuous blue light illumination for 12 h to Neuro2a cells stably expressing OptoTau (OptoTauKI cells) resulted in cluster formation along microtubules, many of which eventually accumulated in aggresomes. On the other hand, when alternating light exposure and darkness in 30-minute cycles for 8 sets per day were repeated over 8 days, methanol-insoluble tau aggregation was formed. Methanol-insoluble tau was induced more rapidly by repeating cycles of 5-minute illumination followed by 25 minutes of darkness over 24 hours. These findings suggest that OptoTau can induce various stages of tau aggregation depending on the pattern of blue light exposure. Thus, this technique holds promise as a novel approach to creating specific tau aggregation in targeted cells at desired time points.

Abstract: Intracellular tau aggregation requires a local protein concentration increase, referred to as "droplets". However, the cellular mechanism for droplet formation is poorly understood. Here, we expressed OptoTau, a P301L mutant tau fused with CRY2olig, a light-sensitive protein that can form homo-oligomers. Under blue light exposure, OptoTau increased tau phosphorylation and was sequestered in aggresomes. Suppressing aggresome formation by nocodazole formed tau granular clusters in the cytoplasm. The granular clusters disappeared by discontinuing blue light exposure or 1,6-hexanediol treatment suggesting that intracellular tau droplet formation requires microtubule collapse. Expressing OptoTau-ΔN, a species of N-terminal cleaved tau observed in the Alzheimer’s disease brain, formed 1,6-hexanediol and detergent-resistant tau clusters in the cytoplasm with blue light stimulation. This intracellular stable tau clusters acted as a seed for tau fibrils in vitro. These results suggest that tau droplet formation and N-terminal cleavage are necessary for neurofibrillary tangles formation in neurodegenerative diseases.