Effects of scratching and engineered nanomaterials on gene profiles and microbiota in SKH-1 mice

Scratching damages upper layers of the skin, breaks this first line of immune defence, and leads to inflammation response, which often also modifies the microbiota of the skin. Although the healing of incision wounds is well-described, there are fewer studies on superficial wounds. We used a simulated model of skin scratching to study changes in the host transcriptome, skin microbiota, and their relationship. Additionally, we examined the effect of nanosized ZnO, TiO2, and Ag on both intact and damaged skin. At 24 h after exposure, the number of neutrophils was increased, 396 genes were differentially expressed, and microbiota compositions changed between scratched and intact control skin. At 7 d, the skin was still colonised by gut-associated microbes, including Lachnospiraceae, present in the cage environment, while the transcriptomic responses decreased. To sum up, the nanomaterial exposures reduced the relative abundance of cutaneous microbes on healthy skin, but the effect of scratching was more significant for the transcriptome than the nanomaterial exposure both at 24 h and 7 d. We conclude that superficial skin scratching induces inflammatory cell accumulation and changes in gene expression especially at 24 h, while the changes in the microbiota last at least 7 days. The hairless SKH-1 mice were assigned into groups of 8 mice/group according to the timepoint (24 h or 7 d) and treatment (naive, PBS, scratching and PBS, scratching only, nanomaterial treatment, scratching and nanomaterial). Total RNA was extracted from upper back skin biopsies, and 6/8 mice per group were chosen for sequencing with the Drop-seq-like protocol, which includes sample pooling. Differential gene expression analysis was performed with the obtained gene expression matrix.