Function Of Intestinal SMK-1-DAF-16 Signaling Cascade In Suppressing Graphene Oxide Toxicity Is Activated By Mir-231 Inhibition In Nematode Caenorhabditis Elegans

Grapheneoxide(GO),a member of the carbon family of nanomaterials with fascinating physical and chemical properties.Along with its gradually world-wild production and possible application,the issue of potential GO toxicity has been rasied.Studies of in vitro and in vivo GO toxicity have suggested that generation of reactive oxygen species(ROS),cell apoptosis,inflammatory were potential cellular mechanism.Caenorhabditis elegans,one of the most classic model animals,has been used as an important non-mamrmalian alternative toxicity assay system,and can be used for toxicity assessment and toxicological studies.Previous studies have demonstrated that exposure to GO can cause the toxic effects on nematodes,such as the enhanced permeability of intestinal,reduce lifespan,decreased locomotion behavior.some specific signaling pathways such as insulin,innate immune and cell apoptosis signaling pathway have been shown to be involved in the control of GO toxicity in nematodes.More recently,some dysregulated microRNAs(miRNAs)have been identified in GO exposed nematodes.Among the dysregulated miRNA,mutation of mir-244,or mir-235 was susceptible to GO toxicity,whereas mutation of mir-247,mir-74,or mir-231 was resistant to GO toxicity.However,the biological functions and the underlying mechanisms for these miRNAs are still largely unknown.In this study,we investigated the molecular mechanism for mir-231 in regulating GO toxicity.GO exposure inhibited the expression of mir-231::GFP in tissues,especially in intestine.Tissue-specific activitying of mir-231 in mir-231 mutant imply that mir-231 acted in intestine to regulate the GO toxicity,and overexpression of mir-231 in intestine caused a susceptible property of nematodes to GO toxicity.Therefore,mir-231 may act in intestine to regulate GO toxicity in nematodes.smk-1 encoding a homologue to mammalian SMEK functioned as the targeted gene of mir-231,and also acted in intestine to regulate the GO toxicity.Mutation of smk-1 induced a susceptible property to GO toxicity,whereas overexpression of smk-1 in intestine resulted in a resistant property to GO toxicity.Moreover,mutation of smk-1 suppressed the resistant property of mir-231 mutant to GO toxicity.In nematodes,SMK-1 further acted upstream of DAF-16/FOXO transcriptional factor in insulin signaling pathway to regulate the GO toxicity.Therefore,mir-231 encodes a protection mechanism for nematodes against the GO toxicity,and mir-231 regulates the GO toxicity by suppressing the function of SMK-1-DAF-16 signaling cascade.