KLF4 and sarcopenia: To refine sarcopenia-relevant biomarkers regulated by Klf4, we cross-referenced the Klf4 target genes based on the ChEA (ChIP-X Enrichment Analysis) Transcription Factor Targets dataset provided by Harmonizome 3.0 [15], with muscle-related candidate genes identified from aging-associated differentially expressed genes (DEGs) in the first step of our analysis.