The Mechanism Of FGF21 In Regulating Lipid Metabolism Via AMPK Signal In Bovine Hepatocytes

In dairy cows,transition period,also called periparturient period,suffering from a series of physiological changes from pregnancy,parturition to lactation.In addition,due to the conversion of diets and the decreased dry matter intake,most dairy cows experience a negative energy balance(NEB),which is considered as the pathological basis of energy metabolic disorder disease.Fibroblast growth factor 21(FGF21),known as hepatokines,plays essential roles in the regulation of whole body energy metabolism,specially glucose and lipid metabolism.Some findings indicated that serum FGF21 was parallel with non-esterified fatty acids(NEFA)in health cows before and after calving.However,the FGF21 level of cows suffering fatty liver or ketosis was higher than the healthy.And NEFA could enhance expresstion and activity of FGF21 of bovine hepatocyte in vitro,elucidating that NEB stimulated the expression of FGF21.Other researchers found that FGF21 controlled the energy metabolism in rodent via AMP-activated protein kinase(AMPK).However,it is not entirely clear of dairy cows whether FGF21 activates AMPK signal pathway and what is the molecular mechanism of FGF21 regulateing lipid metabolism via AMPK signaling in bovine hepatocytes.The hypothesis of this project were FGF21 regulating lipid metabolism via AMPK signal in bovine hepatocytes.And then imitating the condition on hepatocyte metabolism in transition period by adding bovine recombinant FGF21,the expression,secretion,and localization of key factors regulating lipid oxidation,synthesis and transportation in primary hepatocytes were detected,intending to evaluate the influence and mechanism of lipid metabolism for FGF21 exposure in bovine hepatocytes.1.Bovine hepatocytes were isolated from caudate lobes by using three-step of perfusion and collagenase digestion method.Then cells were treated with physiological level of FGF21(900 pg/mL)which imitated the metabolic circumstance in liver to establish time gradient experiment(0,2,4,8,12 and 24 h).It was 4 hours that the optimal time of FGF21 activates AMPK.2.FGF21 reduced TG in bovine hepatocytes.SREBP-1c,and its target gene such as ACC,FASN and ACLY were inhibited after treatment with FGF21 via AMPK signal.The results had a negative impact on lipogenesis.3.It could be observed that some genes regulating lipid oxidation were strengthened following FGF21 treatment via AMPK signal.In detail,PPAR? was up-regulated and stimulated ACOX1,CPT-1A and CPT-2.Meanwhile,mitochondrial biogenesis was enhanced due to increasing the expression of PGC-1?.4.900 pg/mL concentration of FGF21 promoted VLDL secretion significantly.For the protein expression of APOB 100,A POE and MTTP,which are components of VLDL,were stimulated by FGF21,and so the proteins associated with lipid transportation were,such as LDLR,CD36,L-FABP.In conclusion,FGF21 participated in the adaptive regulation of energy metabolism by inhibiting TG synthesis and promoting VLDL secretion in bovine hepatocytes.Its mechanism involved in AMPK signal,promoting lipid oxidation and transport,while inhibiting lipid synthesis in primary hepatocytes of dairy cows.