FGF21 is a hepatokine mainly produced by the liver. We examined liver Fgf21 mRNA expression (figure 5A) and plasma FGF21 levels (figure 5B) in fed and fasted animals. We identified a constitutive expression peak during the day (ZT8) in both groups, and a fasting-triggered night-time peak (ZT16). In Pparαhep−/− mice, we examined whether fasting-induced FGF21 expression/production was strictly dependent on PPARα hepatic activity. Pparα−/− and Pparαhep−/− mice showed very low plasma FGF21 protein at ZT8 or at ZT16 with fasting (figure 5C).
