FNDC5 and Hepatic fibrosis: Quantitative PCR analysis of transforming growth factor-β (TGF-β) and tissue inhibitor of metalloproteinase-1 (TIMP-1), two well-established molecular maker of liver fibrosis 31, also showed that NR treatment decreased HFD-induced hepatic TGF-β and TIMP-1 mRNA expression in WT mice but not in Fndc5-/- mice (Figure 5C).