Lysine-Specific Demethylase 4D Is Critical for the Regulation of the Cell Cycle and Antioxidant Capacity in Goat Fibroblast Cells

SIMPLE SUMMARY: This paper focuses on the roles of lysine-specific demethylase 4D (Kdm4d) regarding its antioxidant capacity in goat fibroblast cells (GFCs). We identified 1013 down-regulated genes following the knockdown of Kdm4d in GFCs, and these genes were enriched in the cell cycle, DNA replication, mitotic processes, and the oxidative phosphorylation pathway. Consistently, we found the cell proliferation rate was significantly decreased after the knockdown of Kdm4d in the GFCs. Of note, the mRNA and protein expression levels of superoxide dismutase 2 (SOD2), one of the major antioxidant enzymes, was decreased, while the reactive oxygen species (ROS) level was significantly increased in the Kdm4d knockdown GFCs. The expression of γH2A histone family member X (γH2AX) was increased significantly, indicating the presence of DNA double-strand breaks after the knockdown of the Kdm4d enzyme. Taken together, Kdm4d is essential for DNA replication, the cell cycle, and antioxidant capacity. The knockdown of Kdm4d repressed the expression of SOD2 and increased the generation of ROS, which led to DNA damage in GFCs. Our data will be helpful for understanding the mechanism underlying antioxidant capacity regulation in fibroblast cells. ABSTRACT: Oxidative damage to skin fibroblast cells is a causative factor in many skin diseases. Previous studies have reported that lysine-specific demethylase 4D (Kdm4d) is involved in DNA replication, but its role on antioxidant capacity remains unclear. In the present study, we used goat fibroblast cells (GFCs) as the research model and identified 504 up-regulated and 1013 down-regulated genes following the knockdown of Kdm4d, respectively. The down-regulated genes of this enzyme were found to be enriched in the cell cycle, DNA replication, mitotic processes, and the oxidative phosphorylation pathway, as previously revealed from gene ontology (GO), Kyoto encyclopedia of genes and genomes (KEGG), and gene set enrichment analysis (GSEA), suggesting vital roles of the Kdm4d enzyme in the cell cycle and in antioxidant regulation. To this end, we found the cell proliferation rate was significantly decreased after the knockdown of Kdm4d. Moreover, both the mRNA and protein expression levels of superoxide dismutase 2 (SOD2), one of the major antioxidant enzymes, was decreased, while the reactive oxygen species (ROS) level was significantly increased in Kdm4d knocked-down cells. In addition, the expression of γH2A histone family member X (γH2AX) increased significantly, indicating the presence of DNA double-strand breaks after the knockdown of the Kdm4d enzyme. In conclusion, the knockdown of Kdm4d inhibited DNA replication and the cell cycle, repressed the expression of SOD2, and increased the generation of ROS, which led to the production of DNA damage in GFCs. Our data will be helpful for understanding the mechanism underlying antioxidant capacity regulation in fibroblast cells.