Polylactic acid microplastics cause transgenerational reproductive toxicity associated with activation of insulin and hedgehog ligands in C. elegans

As a member of biodegradable plastics, exposure risk of polylactic acid microplastic (PLA-MP) has received attention recently. Toxicity of PLA-MP at parental generation (P0-G) has been observed in some organisms; however, its possible transgenerational toxicity and underlying mechanisms remain unclear. In Caenorhabditis elegans, 10 and 100 μg/L PLA-MP resulted in transgenerational inhibition in reproductive capacity and transgenerational damage on gonad development. Meanwhile, transgenerational increase in germline apoptosis was detected after PLA-MP exposure at P0-G, which was associated with transgenerational dysregulation in expressions of genes governing apoptosis (ced-3, ced-4, egl-1, and ced-9) and DNA damage related genes (cep-1, mrt-2, hus-1, and clk-2). Among secreted ligand genes, PLA-MP exposure induced transgenerational increase in expression of ins-39 and wrt-3, and RNAi of ins-39 and wrt-3 inhibited germline apoptosis in PLA-MP exposed nematodes. Additionally, PLA-MP caused transgenerational increase in expression of met-2 and set-6 encoding histone methylation transferases, and germline apoptosis induced by PLA-MP could be suppressed by RNAi of met-2 and set-6. Dysregulated expressions of some apoptosis and DNA damage related genes caused by PLA-MP were reversed by RNAi of ins-39, wrt-3, met-2, and set-6. Moreover, in PLA-MP exposed animals, expression of ins-39 and wrt-3 could be further inhibited by RNAi of met-2 and set-6. Therefore, PLA-MP potentially induced reproductive toxicity across multiple generations, which was under the control of MET-2 and SET-6 activated ligands of INS-39 and WRT-3.