(183ac) Dual Role of Skn-1: The Regulation of Neuronal Activity and Oxidative Stress Resistance in C. Elegans

Reactive oxygen species (ROS), byproducts of mitochondrial respiration, can oxidize biomolecules and disrupt cellular function. To maintain redox homeostasis, cells employ antioxidant enzymes that scavenge excessive ROS. An imbalance between ROS production and scavenging causes oxidative stress; it is said to be involved in the progression of various neurodegenerative diseases and is also theorized to be a cause of aging. Due to their high energy demands, neurons inherently generate substantial amounts of ROS. In Caenorhabditis elegans (C. elegans), oxidative stress is primarily mitigated by the skn-1 pathway. Activation of skn-1 enhances oxidative stress resistance while simultaneously reducing neuronal activity. However, the precise mechanism by which skn-1 modulates neuronal activity—and whether this regulation is independent of its role in antioxidant transcription—remains unclear.

To address this, we investigated the relationship between skn-1 activation and neuronal activity suppression. C. elegans were exposed to varying concentrations of juglone, an oxidative stress inducer, and skn-1 activity was quantified using gst-4 expression. Neuronal activity was assessed through an aldicarb-induced paralysis assay. Our findings indicate that neuronal activity reduction is proportional to skn-1 activation. Interestingly, skn-1 activity peaked at an intermediate juglone concentration but declined at higher concentrations, corresponding to an increase in neuronal activity.

To identify the downstream effectors of skn-1 at the neuromuscular junction, we analyzed publicly available RNA-sequencing data. We then performed an RNA interference (RNAi) screen that identified four genes involved in regulating neuronal activity downstream of skn-1. Previous studies suggest that C. elegans mutants with elevated neuronal activity (such as those carrying mutations in spr-3, spr-4, and slo-1) typically exhibit reduced oxidative stress resistance. Consistent with this, we found that silencing the identified skn-1 downstream genes decreased oxidative stress resistance.

We then examined the tissue-specific roles of skn-1, by selectively knocking down its expression in neuronal and non-neuronal tissues using RNAi. Our results revealed that skn-1 regulates neuronal activity primarily through its action in neurons, whereas its role in oxidative stress resistance is mediated via non-neuronal tissues.

In conclusion, our findings demonstrate that skn-1 independently governs neuronal activity and oxidative stress resistance via distinct gene networks and tissue-specific pathways in C. elegans.