Seven in Absentia Homolog 1 Is Critical for Hypoxia-Induced Lifespan Extension in Caenorhabditis elegans by Regulating the Expression of Skinhead-1

INTRODUCTION: Hypoxia has been shown to extend lifespan in Caenorhabditis elegans through mechanisms involving HIF-1 and DAF-16, but the interplay with SKN-1/Nrf, a key regulator of oxidative stress responses, remains complex. Studies have shown that SKN-1 reduced lifespan when overexpressed in hypoxic environments. However, the mechanism behind SKN-1 regulation under hypoxia is largely unknown. This study aimed to elucidate the hypoxic regulation of SKN-1, particularly by the E3 ubiquitin ligase Siah-1. METHODS: Lifespan analyses were performed in wild-type and mutant C. elegans under normoxic (O₂ = 21%) and hypoxic (O₂ = 1%) conditions. Protein levels were evaluated by immunoblotting, while transcriptional activity of SKN-1 was assessed by measuring the expression downstream target genes (gcs-1, gss-1, and sod-3) using RT-qPCR. Quantification of reactive oxygen species (ROS) were performed using DCFDA/H2DCFDA cellular ROS assay kit. RESULTS: Under normoxia, SKN-1 promoted lifespan extension, with its stability regulated by WDR-23. In contrast, under hypoxia, SKN-1 exerted a detrimental effect on lifespan. Both genetic disruption and pharmacological inhibition of Siah-1 indicated that SKN-1 stability under hypoxia is regulated by Siah-1. Hypoxia increased Siah-1 protein levels and were associated with reduced SKN-1 transcriptional activity, as evidenced by decreased expression of gcs-1, gss-1, and sod-3, alongside elevated ROS. Mechanistically, PMK-1 was required for hypoxia-induced Siah-1 upregulation and SKN-1 suppression. CONCLUSION: The present study identifies Siah-1 as a novel mediator linking hypoxic signaling to SKN-1-dependent transcriptional programs, providing insights into conserved mechanisms of stress adaptation and aging. This work underscores the importance of ubiquitin-mediated regulatory nodes in coordinating longevity pathways under environmental stressors.