Toxicity of Graphene Oxide in Nematodes with a Deficit in the Epidermal Barrier Caused by RNA Interference Knockdown of unc-52

The epidermal barrier is important for the defense of environmental organisms against the damage from engineered nanomaterials (ENMs). We employed Caenorhabditis elegans to examine the possible influence of a deficit in the epidermal barrier caused by RNA interference (RNAi) knockdown of unc-52 encoding a perlecan protein on the toxicity of graphene oxide (GO). Epidermal RNAi knockdown of unc-52 caused a functional deficit in the epidermal barrier and susceptibility to GO toxicity. Epidermal knockdown of unc-52 decreased the level of expression of fbl-1 encoding a membrane protein fibulin and sax-7 encoding a cell adhesion receptor, and epidermal knockdown of fbl-1 or sax-7 also resulted in a functional deficit in the epidermal barrier and susceptibility to GO toxicity. Additionally, epidermal knockdown of unc-52 inhibited expression of cnc-2 and prx-11 encoding two antimicrobial proteins, and epidermal knockdown of cnc-2 or prx-11 could strengthen the GO toxicity in fbl-1(RNAi) or sax-7(RNAi) nematodes. Our data further highlight the important function of the epidermal barrier against toxicity of environmental ENMs.