Towards Understanding Cellular Stress Responses and Signalling Pathways Impacted by klo-1/ KL and klo-2/ KL Deletion in Caenorhabditis elegans

Background: Klotho (KL) and its paralog β-klotho (KLB) are transmembrane proteins that function as co-factors to aid binding of endocrine fibroblast growth factors (eFGFs) to their respective fibroblast growth factor receptors (FGFR). Klotho has been found to have protective effects at cellular and organismal levels, although the signalling pathways governing these are yet to be determined.

Methods: C. elegans strains with genetic deletions in klo-1/ KL and klo-2/ KL were subject to health and stress resistance analyses. To determine signalling pathways governed by klotho, C. elegans strains with null klo-1/ KL and klo-2/ KL alleles were crossed into mutants for intracellular signalling components then subject to health and stress analyses.

Due to reported impacts of Klotho function in oxidative stress responses, staining for reactive oxygen species was performed in wild-type and klo-2 (ok1862); klo-1 (ok2925) double mutant C. elegans to determine ROS levels in these strains prior to and following stress exposure. Fluorescent reporters for klo-1 and klo-2 gene expression were analysed in wild-type and klo-2; klo-1 double mutant genetic backgrounds before and after pharmacological intervention using reported AMPK activators and TOR pathway inhibitors to elucidate whether AMPK or TOR signalling pathways are impacted by klo-1 and klo-2 deletion.

Results: C. elegans with deletion of klo-1/ KL, klo-2/ KL, or both, have increased survival upon exposure to acute oxidative stress, and show reduced levels of reactive oxygen species (ROS) compared to wild-type counterparts in untreated (control) conditions. Interestingly, in heat stress responses while there is some survival advantage displayed by klo-1/ KL or klo-2/ KL single mutants compared to wild-type counterparts at the 8 hour time point, deletion of both genes does not increase survival in C. elegans. The survival advantages demonstrated by klotho mutant nematodes is dependent on functional AAK-2/ AMPK.

Conclusions: In contrast to literature, which suggests removal of klotho would diminish stress responses, C. elegans strains with klo-1/ KL or klo-2/ KL deletion backgrounds have a survival advantage upon acute stress exposure. This survival advantage is characterised by lowered ROS levels in these animals. The current working theory is that klo-2; klo-1 double mutant mutants could have increased AAK-2/AMPK activity compared to wild-type animals however further research is needed to support this hypothesis.