TDP-43 cytoplasmic accumulation in clock neurons disrupts circadian rhythms without affecting sleep in a novel Drosophila melanogaster model of proteinopathy

Sleep and circadian alterations are frequently observed in neurodegenerative disorders such as amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Although aggregation and cytoplasmic mislocalization of TDP-43 constitute central pathological hallmarks of ALS/FTD, their contribution to circadian dysfunction remains poorly understood. To investigate its role in rhythmicity and sleep, we generated novel Drosophila melanogaster models expressing different TDP-43 variants. In young adult males, overexpression of wild-type human TDP-43 (WT) in circadian neurons did not significantly alter circadian period (Tau) compared to controls, although a trend toward reduced Tau power was observed. However, these flies exhibited reduced both total and daytime sleep duration. In contrast, expression of a nuclear localization-deficient TDP-43 variant (ΔNLS), produced a profound disruption of circadian rhythmicity, with almost no flies showing identifiable period. Remarkably, this phenotype was not accompanied by detectable sleep abnormalities. To assess the role of endogenous TBPH (TDP-43 homologue), we downregulated its levels specifically in the neurons of the circadian circuit. We found two types of phenotypes: either period lengthening or arrhythmicity. Together, these results suggest that cytoplasmic mislocalization of hTDP-43 disrupts circadian behavioral output and may contribute to circadian dysfunction associated with the ALS/FTD spectrum.