Royalactin extends lifespan of Caenorhabditis elegans through epidermal growth factor signaling

Abstract

Royalactin is a glycoprotein essential for the development of long-lived queen honeybees. Only larvae fed with royal jelly, containing royalactin, develop into queens. Royalactin plays a central role in this process by switching on the epidermal growth factor (EGF) receptor signaling pathway which ultimately leads to epigenetic changes and a long-lived queen phenotype. Recently it was shown that royalactin by itself also extends lifespan in Drosophila melanogaster. Yet, the mechanism by which royalactin promotes longevity remains largely unknown. We set out to characterize the effects of royalactin on Caenorhabditis elegans lifespan, and clarify the possible involvement of EGF signaling in this process. We demonstrate that royalactin extends lifespan of this nematode and that both EGF (LIN-3) and its receptor (LET-23) are essential to this process. To our knowledge, this is the first report of royalactin-mediated lifespan extension in a non-insect species. Additionally, we show that royalactin enhances locomotion in adult nematodes, implying that royalactin also influences healthspan. Our results suggest that royalactin is an important lifespan-extending factor in royal jelly and acts by promoting EGF signaling in C. elegans. Further work will now be needed to clarify which (secondary) signaling pathways are activated by royalactin, and how this ultimately translates into an extended health- and lifespan.

SKN-1-independent transcriptional activation of glutathione S-transferase 4 (GST-4) by EGF signaling

“…This EOR-1 dependence is consistent with our previous findings showing that royalactin-mediated longevity is reliant on EGF signaling. 34 Functional SKN-1 is seemingly not needed to increase gst-4 p -controlled GFP levels following royalactin treatment, whereas the increase in fluorescence levels is abolished in a mutant lacking functional EOR-1. This implies that EOR-1, but not SKN-1, is necessary for the royalactin-dependent transcription of gst-4.…”

“…34 The EGF pathway regulates longevity via maintaining protein homeostasis, largely independent of insulin/IGF-like signaling (IIS). 36 Here we pinpoint the EOR-1 protein, a BTB/zinc-finger transcription factor similar to mammalian promyelocytic leukemia zinc-finger protein (PLZF), as a mediator of royalactin's beneficial effects regarding resistance to exogenously applied oxidative stress in C. elegans.…”

“…Additionally, a microarray study of Liu et al found gst-4 to be highly upregulated in an EGFR gain-of-function mutant, 38 in line with our results showing enhanced gst-4 transcription after stimulating EGF signaling. Considering previous evidence 34,[38][39][40] it is reasonable to assume that the activation of EOR-1 is itself dependent on the EGF pathway. We hypothesize that enhanced EOR-1 activity alone is sufficient to induce gst-4 transcription, and acts in parallel to the classical SKN-1 cascade which is generally activated upon exposure to oxidative stress (Fig.…”

“…Age-synchronization was performed through a timed egg-lay using gravid adults or through hypochlorite treatment as described previously. 34 …”

“…34 Since SKN-1 has been shown to be activated through EGF signaling under certain conditions, 35,36 enhanced SKN-1 activation and a corresponding increase in gst-4 transcription can be anticipated in royalactin-treated worms. Here we show, however, that while EGF signaling indeed activates gst-4, this is controlled by EOR-1 and occurs independently of SKN-1.…”