Peroxisome Proliferator-Activated Receptor Alpha Contributes to Hepcidin up-Regulation in Mice during Fasting

Nutritional fasting is associated with hypoferremia; however serum iron parameters otherwise differ from those observed with dietary iron deficiency. Activation of the hepcidin gene via the transcription factor CREB-H has been implicated in inducing this hypoferremia. We examined the contribution of the PPARα another hepatocellular transcription factor induced by fasting in this regulation. Six week old male AKR mice (N = 6) were fed diet with 60 ppm Fe ad libitum and fasted for overnight (18 hours). Tissue and blood samples were collected to evaluate iron parameters and gene expression in comparison to fed controls. All mice were provided water ad libitum. In the fasted mice, serum iron (321 and 199 µg/dL, respectively for fed and fasted mice, P = 0.001) as well as transferrin saturation (80% and 64% respectively for fed and fasted mice, P = 0.04) decreased significantly. Fasted mice also had elevated hematocrit (43% and 47%, respectively, for the fed and fasted mice, P = 0.001) in association with weight loss (22g and 18g, respectively, for the fed and fasted mice, P < 0.01), consistent with hemoconcentration. In addition, 18h fasting induced a significant increase in hepatic (735 and 953 µg/g dry, respectively for the fed and fasted mice, P < 0.05) and splenic non-heme iron content (414 and 488 µg/g dry, respectively for the fed and fasted mice, P < 0.001), and elevated hepatic hamp1 mRNA levels (4-fold increase from the fed group, P < 0.001). To elucidate the mechanism of the Hamp1up-regulation, we measured liver Creb-h and pparα mRNA levels, and observed elevated Creb-h (by 4-fold, P < 0.001) and ppara mRNA levels (by 3-fold, P < 0.001) in the fasted mice. To further elucidate the roles of CREB-H, and PPARα in the regulation of Hamp1 during fasting, we performed fasting-refeeding studies in 10-12 week old male C57BL/6 mice. These mice (N = 4-6) were fed with chow ad libitum, fasted overnight, or fasted overnight then re-fed for 4 hours. Fasting at this age also induced increased in liver pparα, creb-h, and hamp1 mRNA levels (by 2.5-, 3- and 6-fold, respectively), and refeeding over this timeframe was associated with decreases in pparα, creb-h, and hamp1 to levels that are similar to fed mice, even though the serum and tissue iron levels were not restored. To determine if PPARα contributes to the regulation of hepcidin, we examined the fasting response of PPARα^-/- mice. The fasting-associated increases in expression of hamp1 and creb-h were dampened in the PPARα-/- mice. In the WT mice, fasting induced a hamp1 increase of 2.6-fold (P = 0.002), whereas in the PPARα^-/- mice, the expression was unchanged (0.8-fold, P = 0.11). Similarly, fasting induced a creb-h increase of 2.8-fold in the WT mice (P = 0.0003) but a 1.1-fold increase in the PPARα^-/- mice (P = 0.004). The magnitude of change in hamp1 (P < 0.05) and in creb-h (P < 0.001) expression between WT and PPARα^-/- mice were statistically significant. These findings indicate that PPARα contributes to creb-h and hamp1 up-regulation during fasting-induced changes in iron metabolism.