CTSG and periodontitis: The GSEA results showed CTSG-associated DEGs were mainly implicated in inflammation- and immune-related pathways, such as neutrophil degranulation, signaling by interleukins, natural killer cell-mediated cytotoxicity, B-cell receptor signaling pathway, inflammatory response pathway, etc. Previous studies have revealed that CTSG could activate matrix metalloproteinases and regulate inflammation, and play an important role in a variety of inflammatory diseases such as acute respiratory distress syndrome, rheumatoid arthritis, chronic obstructive pulmonary disease, and periodontitis [19,24,25].