COL3A1 and sarcopenia: In addition, old SAMP8 mice showed remarkable difference from young controls in terms of the expression level of marker genes, including muscle atrophy genes (fbxo32 and trim63), inflammation and fibrosis- related genes (il1b, tnfa, col1a, and col3a1), and senescence genes (p16 and p21), whose patterns were similar to that in sarcopenia mice 28.