A conserved serotonin receptor pathway is a druggable modifier of Tau pathology, neural circuit formation and neurodegeneration

Tauopathies are devastating neurodegenerative disorders characterized by Tau hyperphosphorylation, neurofibrillary tangle (NFT) formation, neuronal dysfunction, and cognitive decline. Here, we establish a new Drosophila tauopathy model expressing eGFP-tagged human TauWT or the disease-associated TauP301L variant in the nervous system. TauP301L expression recapitulates key pathological and behavioral hallmarks of tauopathy, including elevated Tau hyperphosphorylation, accumulation of NFT-like, pTau-positive assemblies in vivo, reduced lifespan, hyperactivity, sleep loss, progressive locomotor decline, and age-dependent brain degeneration. Strikingly, TauP301L also disrupts the architecture of the mushroom body, a learning- and memory-related circuit in Drosophila, revealing an early disruption of neural circuit formation that is distinct from adult neurodegenerative phenotypes. We further show that suppression of serotonin 5-HT7R-CDK5 signaling pathway, either by genetic knockdown or pharmacological inhibition with inverse agonist, rescues Tau-induced behavioral and anatomical phenotypes. These findings identify 5-HT7R signaling as a conserved and druggable modifier of Tau toxicity and establish this model as a powerful in vivo platform for mechanistic studies and therapeutic discovery in tauopathies.