Constitutive 5-HT7 receptor activity as a target for treatment of tauopathy

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Multiple neurodegenerative diseases are induced by the formation and deposition of protein aggregates. In particular, aggregation of the microtubule-associated protein, Tau, leads to the development of so-called tauopathies, which are characterized by the aggregation of hyperphosphorylated Tau protein within neurons. We recently showed that the constitutive serotonin 5-HT7 receptor (5-HT7R) activity is required for Tau hyperphosphorylation and formation of highly bundled Tau structures through G12-protein-independent, CDK5-dependent mechanism. Moreover, selective 5-HT7R knockdown in mouse cortex fully abrogated impairments in long-term potentiation and memory induced by the overexpression of pathological human mutant Tau[R406W] associated with frontotemporal dementia (FTD). Within this proposal, we aim to characterize structural requirements for 5-HT7R-CDK5 complex formation. Based on this knowledge, we will specifically interfere with 5-HT7R-CDK5 signaling by expressing the mutated form of 5-HT7R (not binding to CDK5). This would enable us to study the role 5-HT7R-CDK5 signaling in small GTPase activities, actin filament dynamics, spinogenesis and synaptic plasticity under physiological conditions and in two forms of tauopathy induced by neuronal overexpression of either human Tau[R406W] or Tau[P301L] mutants. Since we identified several clinically approved drugs to be potential 5-HT7R inverse agonists, we shall compare their efficacies to prevent Tau hyperphosphorylation and aggregation using a high throughput bimolecular fluorescence complementation (BiFC) technique. The most potent drugs will be then investigated for their ability to abrogate pathological Tau effects both in vitro and in vivo using synergistic combination of cutting edge techniques present in participating labs, including biochemical and molecular biological assays, viral manipulations, quantitative intravital microscopy, FRET measurements, electrophysiological recordings, and behavioral analyses. Moreover, a preregistered double-blind randomized preclinical trial of the most efficient 5-TH7R inverse agonist inhibiting Tau hyperphosphorylation and aggregation will be performed to evaluate its effects on multiple cognitive, social, emotional and locomotor functions in male and female Tg4510 mice, also controlling for potential extrapyramidal side effects. Finally, we will evaluate the role of 5-HT7R/CDK5 signaling using human induced pluripotent stem cells (hiPSCs)-derived neurons, which will help to bridge the genetic and phenotypic gap between animal models and humans. Thus, the outcome of this project is expected to improve our understanding of the physiological and pathophysiological significance of 5-HT7R-CDK5 signaling in neurodegenerative diseases and to identify and characterize the therapeutic effects of 5-HT7R-targeting drug for treatment of tauopathy-related disorders.