Functional Disruption In Epidermal Barrier Enhances Toxicity And Accumulation Of Graphene Oxide In Caenorhabditis Elegans

Graphene oxide(GO)is a derivative of the graphene family.Because of its superior physical and chemical properties,it has been widely used in the biological field,such as cell imaging,drug loading,biosensors,and photothermal therapy etc.Although GO has brought great benefits to us,the potential GO toxicity has received the more and more attention with its has increased application.Caenorhabditis elegans is a soil worm,and has been used as a model animal for various basic and applied biological studies.It has been shown that GO exposure could cause the damage on locomotive behavior,lifespans,reproduction,and defecation.Meanwhile,some important signaling pathways would be activated in GO exposured nematode.In this study,we aimed to invertigate the effect of epidermal disruption on GO toxicity formation and the underlying mechanism.MLT-7 is a peroxidase expressed in the epidermis.Mutation of mlt-7 induced the enhanced epidermal permeability.GO exposure at the concentration of 100 mg/L or lg/L did not significantly affect the transcriptional expression of mlt-7.Epidermal-specific RNAi knockdown of mlt-7 may result in a susceptibility to GO toxicity,and the more severe accumulation of GO/Rho B in the pharynx,the intestine,and the reproductive organs of spermatheca.GO toxicity in decreasing locomotion behavior and in inducing intestinal ROS production in GO exposed transgenic strain Is(Pmlt-7-mlt-7)was similar to that in GO exposed wild-type nematodes.Epidermal-development related proteins of BLI-1 and IFB-1 were identified as downstream targets for MLT-7 in the regulation of GO toxicity,and mediated the function of MLT-7 in maintaining the epidermal barrier.Antimicrobial proteins of NLP-30 and CNC-2 were identified as the other downstream targets for MLT-7 in the regulation of GO toxicity.Epidermal-specific RNAi knockdown of nlp-30 or cnc-2 enhanced the toxicity and accumulation of GO in nematodes with epidermal-specific RNAi knockdown of bli-1 or ifb-1.UNC-52,a perlecan protein,is a component of ECM.In nematodes,some proteins,such as perlecan protein,have been shown to be required for the developmental control of epidermis at different aspects.GO exposure at the concentration of 1,10,or 100 mg/L did not significantly affect the transcriptional expression of unc-52.Epidermal-specific RNAi knockdown of unc-52 may result in a susceptibility to GO toxicity,and cause the more severe accumulation of GO/Rho B in the pharynx,the intestine,and the reproductive organs of spermatheca.Epidermal proteins of SAX-7 and FBL-1 were identified as downstream targets for UNC-52 in the regulation of GO toxicity.Antimicrobial proteins of PRX-11 and CNC-2 were identified as the other downstream targets for UNC-52 in the regulation of GO toxicity.Epidermal-specific RNAi knockdown of prx-11 or cnc-2 enhanced the toxicity and accumulation of GO in nematodes with epidermal-specific RNAi knockdown of sax-7 or fbl-1.In conclusion,epidermal barrier is an important biological barrier for organisms against environmental toxicants or stress.Epidermal-specific RNAi knok down of mlt-7 or unc-52 can exacerbate GO distribution and toxicity in C.elegans.Our result highlight the importance of the epidermal barrier in the protection of animals against environmental toxicants.