Skin transcriptome affected by digital dermatitis in lactating dairy cows

Bovine digital dermatitis (DD) is a polymicrobial disease that can lead to an inflammatory response of the hoof, keratinization loss, and lameness. Therefore, we performed skin tissue biopsies from the center of lesion or healthy skin of lactating dairy cows to assess the impact of DD on the skin transcriptome. Multiparous Holstein dairy cows were selected based on their condition as clinically healthy (HDD, n = 7), or cows diagnosed with DD (n = 7). Lameness was assessed based on locomotion score (scale 1 to 5), and it was 1 ± 0 and 2.3 ± 0.8 (mean ± SD) for HDD and DD, respectively. The skin biopsies were performed using a sterile biopsy punch. All samples were immediately flash-frozen in liquid nitrogen. The RNA integrity number for all samples was 7.9 ± 1.1. The RNA samples were sequenced (NGS; Illumina, NovaSeq S4) at the University of Minnesota Genomics Center. Processed reads were aligned to the bovine genome using HISAT2. Differential transcript analysis was performed using a quasi-likelihood test in R-package (EdgeR) and False Discovery Rate \u3c0.05 correction was applied. Genes mediators of a proinflammatory response including IL1A, IL1B, IL1RAP, IL18RAP, and the transcription factor NFKB1 were upregulated (P \u3c 0.002) in DD cows in comparison to HDD. Greater (P \u3c 0.03) expression of CXCL6, CXCL8, and CXCL13, related to innate immunity and chemo-attractants, was observed in DD in comparison to HDD. The type II cytokeratins KRT3 and KRT4 were upregulated (P ≤ 0.002) in the skin of DD cows compared with HDD; however, KRT18 was downregulated (P = 0.003) in the DD group. Tight junctions related-genes including the claudins CLDN2, CLDN5, and CLDN10, were downregulated (P ≤ 0.004) in the skin of DD cows in comparison to HDD. Our preliminary data suggest DD can alter skin paracellular epithelial permeability and keratinization. Enrichment pathway analyses will be performed to better understand these findings and to further identify molecular targets for nutritional or management interventions