Molecular Basis For Epidermal Barrier Against Toxicity Of PEG Modified Graphene Oxide In Caenorhabditis Elegans

Graphene oxide(GO)is a very important engineering nanomaterial.GO has been widely applied in the field of biomedicine due to its unique physical and chemical properties in recent years.Once GO is modified by polyethylene glycol,it can significantly increase the stability in aqueous solution,and improve the biocompatibility.Caenorhabditis elegans,a classical model animal,has been widely used in the research of nanotoxicology.Consider the fact that the developmental basis for epidermal barrier against the translocation of nanomaterials is still largely unclear,we aimed to investigate the effect of deficits in epidermal barrier on translocation and toxicity of PEG modified graphene oxide(GO-PEG)in nematodes and the underlying molecular mechanism.In nematodes,GO-PEG exposure did not cause toxicity and affect expressions of epidermal-development related genes.However,GO-PEG exposure resulted in toxicity in mlt-7 mutant nematodes with deficit in function of epidermal barrier.GO-PEG at concentrations ? 0.1 mg/L resulted in the toxic effects on mlt-7(tm1794)mutant nematodes.mlt-7 mutation allowed GO-PEG accumulation and translocation into targeted organs through epidermal barrier.Epidermal-development related proteins of BLI-1 and IFB-1 were identified as targets for MLT-7 in the regulation of GO-PEG toxicity and accounted for MLT-7 function in maintaining the epidermal barrier.AAK-2,a catalytic ? subunits of AMP-activated protein kinase,was identified as another target for MLT-7 in the regulation of GO-PEG toxicity.AAK-2 functioned synergistically with BLI-1 or IFB-1 in the regulation of GO-PEG toxicity.During the control of GO-PEG toxicity,let-7 might act as the potential target for BLI-1 in nematodes.Epidermal-specific RNAi knockdown of bli-1 could enhance the expressions of let-7.Mutation of let-7 did not influence the biological permeability,and mutation of let-7 could even suppress the deficits in epidermal function in bli-1 mutant.Epidermal specific RNAi knock down of bli-1,hbl-1,or lin-41 could induce the severe accumulation of GO-PEG in the body of nematode.Therefore,BLI-1 may regulate the function of epidermal barrier against the GO-PEG toxicity by acting an upstream regulator of let-7 to influence the functions of HBL-1 and LIN-41.In summary,our data highlights the importance of epidermal barriers against external environmental stresses.We proved the important function of epidermal development proteins of MLT-7,BLI-1,and IFB-1 in the regulation of epidermal barrier against the GO-PEG toxicity.We identified a signaling cascade of BLI-1-let-7-HBL-1-LIN-41 in the regulation of GO-PEG,which is helpful for explaining the function of BLI-1 in the regulation of epidermal function against GO-PEG.