Possible Role of Gut Microbiota in Polypropylene Microplastics-Induced Immunity and Reproductive Dysfunction in Mice

Polypropylene microplastics (PP-MPs) are ubiquitous in our daily lives, but their toxicological effects on mammals remain poorly understood. This study investigated the toxicity effects of PP-MPs on C57BL/6 mice using 16S rRNA gene amplicon sequencing and transcriptome sequencing. Female and male mice were randomly classified into the control and PP-MPs-treated groups, respectively, and the experiment lasted for 5 weeks. We found that PP-MPs exposure did not affect the levels of immunoglobulin G (IgG), interleukin-4 (IL-4), and interferon gamma (IFN-γ), indicating that humoral immunity and inflammatory levels were not influenced by PP-MPs treatment. However, PP-MPs exposure reduced the PHA response in female mice, but not in male mice. It also did not alter the wet mass of testicles and ovaries, nor the levels of testosterone and estradiol. Exposure to PP-MPs altered the expression of the testicular genes. G protein-coupled receptor signaling pathways, olfactory receptor activity, and protein digestion and absorption were downregulated in the PP group. Collagen genes (Col9a3, Col11a2, Col27a1, Col26a1, Col7a1) play a significant role in downregulating protein digestion and absorption. In addition, PP-MPs exposure caused a change in beta diversity of gut microbiota, indicating the alteration of their community structure. PP-MPs exposure reduced the relative abundance of the probiotic Lactobacillus. Changes in the gut microbiota may be related to the expression levels of testicular genes. Overall, PP-MPs exposure altered both the community structure of the gut microbiota and the expression levels of testicular genes in mice, and collagen genes may serve as a critical factor influencing testicular function.