Single-Cell RNA Sequencing Profiling Cellular Heterogeneity and Specific Responses of Fish Gills to Microplastics and Nanoplastics

Fish gills are highly sensitive organs for microplastic (MP) and nanoplastic (NP) invasions, but the cellular heterogeneity of fish gills to MPs and NPs remains largely unknown. We employed single-cell RNA sequencing to investigate the responses of individual cell populations in tilapia <i>Oreochromis niloticus</i> gills to MP and NP exposure at an environmentally relevant concentration. Based on the detected differentially expressed gene (DEG) numbers, the most affected immune cells by MP exposure were macrophages, while the stimulus of NPs primarily targeted T cells. In response to MPs and NPs, H⁺-ATPase-rich cells exhibited distinct changes as compared with Na⁺/K⁺-ATPase-rich cells and pavement cells. Fibroblasts were identified as a potential sensitive cell-type biomarker for MP interaction with <i>O. niloticus</i> gills, as evidenced by the largely reduced cell counts and the mostly detected DEGs among the 12 identified cell populations. The most MP-sensitive fibroblast subpopulation in <i>O. niloticus</i> gills was lipofibroblasts. Cell-cell communications between fibroblasts and H⁺-ATPase-rich cells, neurons, macrophages, neuroepithelial cells, and Na⁺/K⁺-ATPase-rich cells in <i>O. niloticus</i> gills were significantly inhibited by MP exposure. Collectively, our study demonstrated the cellular heterogeneity of <i>O. niloticus</i> gills to MPs and NPs and provided sensitive markers for their toxicological mechanisms at single-cell resolution.