# Drosophila Pyruvate Kinase Links Metabolic State with Circadian Output via TARANIS and PDF

## TL;DR

This study shows how a key metabolic enzyme in fruit flies connects energy levels to daily biological rhythms, offering new insight into how metabolism affects circadian clocks.

## Contribution

The paper identifies a novel regulatory pathway involving Pyruvate kinase, TARANIS, and PDF that links glycolytic activity to circadian output.

## Key findings

- Pyruvate kinase knock-down in adult Drosophila shortens circadian period and reduces PDF levels.
- TARANIS mediates the effect of Pyruvate kinase on circadian rhythm and PDF expression.
- Overexpression of TARANIS rescues the circadian and PDF defects caused by Pyruvate kinase knock-down.

## Abstract

The circadian clock generates approximately 24-hour rhythms in behavior and physiology enabling organisms to anticipate daily environmental fluctuations. Circadian clock and glucose metabolism are tightly interconnected, and their disruption commonly co-occurs in aging and disease. However, how glucose hypometabolism specifically impacts circadian rhythm remains unclear. Here, we investigated this relationship by genetically downregulating key glycolytic enzymes - Hexokinase-C (Hex-C), Phosphofructokinase (Pfk), and Pyruvate kinase (Pyk) - in Drosophila clock cells. Only Hex-C and Pyk knock-down (KD) altered circadian period in accordance with their mRNA reduction, inducing period lengthening and shortening, respectively. Notably, Pyk KD induced period shortening persisted in adult-specific KD (AKD), minimizing developmental confounds. Mechanistic analyses revealed that Pyk AKD reduced both PERIOD protein and Pigment-dispersing factor (PDF) levels. We identified TARANIS (TARA), a transcriptional coregulator recently shown to positively regulate PDF, as a crucial mediator of PYK’s effect. Pyk AKD lowered tara mRNA and protein levels, whereas tara overexpression in Pyk AKD rescued both the short-period phenotype and reduced PDF levels. Together, our findings establish a novel PYK-TARA-PDF regulatory axis linking glycolytic enzyme activity to circadian neuropeptide output, providing mechanistic insight into how metabolic dysfunction contributes to circadian disruption associated with aging and neurodegenerative diseases.