The metabolic hormone FGF-21 is mainly produced and released from the liver in response to nutritional stresses such as starvation, alcohol or ketogenic diet consumption. Body weight lowering and insulin signaling sensitization effects of FGF-21 and its analogues have been demonstrated in animal models or in human subjects. We show here that hepatic FGF-21 mRNA and FGF-21 protein levels were reduced in male LTCFDN, a transgenic mouse line in which canonical Wnt signaling cascade is functionally attenuated due to the expression of dominant negative transcription factor TCF7L2 in the liver, and the reduction is not associated with reduced expression of PPARα, a key transactivator of FGF-21. Furthermore, starvation-induced plasma FGF-21 elevation was also attenuated in male LTCFDN mice.
Utilizing mouse primary hepatocytes, we found that FGF-21 mRNA and FGF-21 protein expression can be increased by Wnt-3a or LiCl treatment. Two evolutionarily conserved TCF binding motifs (TCFB) were then located within the mouse FGF-21 gene promoter. Luciferase and ChIP results suggest that one of them is responsible for β-cat/TCF mediated activation on FGF-21 transcription.It has been shown recently that in mouse brain tanycytes, FGF-21 secretion can be induced by palmitate treatment. We found that in mouse primary hepatocytes, palmitate but not oleate treatment increased expression of the Wnt target gene Ccnd1, which encodes cyclin D1.
Our observations hence suggest that Wnt signaling cascade is involved in hepatic FGF-21 production and secretion, and the positive regulation is likely independent of fibrate/PPARα-mediated induction. Investigations on this novel hepatic signaling axis will strengthen our knowledge on the physiologically significant hormone FGF-21, leading to novel therapeutic avenues in treating impaired metabolism.
Y. Badakhshi: None. W. Shao: None. L. Tian: None. T. Jin: None.
Canadian Institutes of Health Research (PJT159735)