Changes Of Lipid Metabolism In Liver Of Laying Hens During Physiological Remodeling Induced By Fasting

Aged laying hens in the late stage of egg production will face many physiological health problems,such as decreased synthesis and transport capacity of body fat,excessive intake of nutrients,which will aggravate the deposition of fat in the liver,and easily lead to fatty liver syndrome and other diseases related to lipid metabolism.Relevant studies on mammals have shown that proper fasting can reduce the deposition of fat in the liver and inhibit the occurrence of fatty liver syndrome and other diseases related to lipid metabolism.Liver is the main place of lipid metabolism in poultry.Whether physiological remodeling induced by fasting can alleviate or even eliminate fatty liver syndrome of laying hens in late laying period is worth our attention.In this study,90 Houdan chicken(500 days of age)with similar body weight in late laying period were selected,and the blood and liver tissues were collected at 6 time points 1 day before feeding cessation(F0),3 days after feeding and water cessation(F3),16 days after feeding cessation(F16),6 days after feeding resumption(R6),15 days after feeding resumption(R15),and 32 days after feeding resumption(R32).It is used for the determination of blood biochemical indexes,the study of liver tissue sections and the study of genes and pathways related to the regulation of lipid metabolism.By evaluating liver morphology,oxidation and antioxidant states,liver tissue fat content and detecting the changes of genes and pathways related to the regulation of lipid metabolism in the process of fasting induced physiological remodeling,To explore the changes of liver function and lipid metabolism in laying hens during fasting induced physiological remodeling.The results are as follows:Experiment 1: Fasting induced physiological remodeling of liver morphology,lipid metabolism and antioxidant function at different periodsOil red O staining,Elisa,q RT-PCR and other techniques were used to evaluate the liver during fasting induced physiological remodeling.The results were as follows: In the late F0 period of laying hens,liver enlargement,lipid accumulation,bleeding spots,brittle and greasy feeling were observed.After fasting induced physiological remodeling,liver color turned red,volume returned to normal,and liver index significantly decreased(P < 0.05).Liver oil red O staining slices and triglyceride analysis showed that lipid accumulation in liver decreased(P < 0.05).It showed that fatty liver was relieved.Serum estradiol(E2)content of laying hens in late laying period(F0)was higher,and E2 content was significantly decreased during fasting period(P < 0.05).Serum T3 and T4 contents were significantly increased during fasting(P < 0.05),and significantly decreased after resuming feeding(P < 0.05),but they were still significantly higher than those in F0 period.The serum alkaline phosphatase activity was significantly decreased during fasting(P < 0.05),and significantly increased after resuming feeding(P < 0.05),and was significantly higher than that before fasting(P< 0.05).The activities of alanine aminotransferase(ALT)and aspartate aminotransferase(AST)in serum were significantly increased during fasting(P < 0.05),and were significantly decreased after resuming feeding(P < 0.05).The activities of ALT and AST in liver were significantly decreased during fasting(P < 0.05),and significantly increased after resuming feeding(P < 0.05).It suggests that the liver recovers from damage during fasting.The content of malondialdehyde(MDA)in liver of laying hens was significantly increased during fasting(P < 0.05),indicating that fasting caused oxidative stress,and MDA content was significantly decreased after resuming feeding(P < 0.05).During fasting,the activities of liver antioxidant enzymes SOD and CAT had an increasing trend but no significant change(P > 0.05),while the activity of GSH-PX was significantly increased compared with that before fasting(P < 0.05).The m RNA expressions of SOD,CAT and GSH-Px in liver during fasting induced physiological remodeling were significantly increased after fasting and resuming feeding(P < 0.05),indicating that fasting did not affect the antioxidant function of liver,and the antioxidant function of liver tended to increase after the end of physiological remodeling.During fasting,the body alleviates the fasting induced oxidative stress by increasing the activity of some antioxidant enzymes,and the antioxidant function is improved after the end of physiological remodeling.Experiment 2: Fasting induced physiological remodeling of liver cell autophagy and apoptosis and the interaction of lipid metabolismBased on the results of liver transcriptome sequencing of laying hens,the genes related to lipid metabolism and autophagy in liver during fasting induced physiological remodeling were combined,and the gene set was analyzed for differential enrichment.The results showed that these genes were significantly enriched in autophagy,lipid metabolism,apoptosis and other pathways(P < 0.05),and the protein network interaction map also indicated that these genes were highly correlated.The related genes were verified by q RT-PCR.Autophagy related differential genes PIK3 CB,ERN1 and PDGFRA were significantly increased during fasting(P < 0.05),and significantly decreased after resuming feeding(P < 0.05),indicating that liver autophagy may occur during fasting.Proapoptotic genes CASP-3,CASP-7 and MDM2 were significantly decreased during fasting(P < 0.05),and significantly increased after resuming feeding(P < 0.05),while apoptosis suppressor gene BCl2 was significantly increased during fasting(P < 0.05).The expressions of CDK1 and CCNB1 genes were significantly increased in fasting period and significantly decreased in fasting period(P < 0.05),but there was no significant difference compared with F0 condition(P > 0.05),indicating that fasting could stimulate cell proliferation.During fasting,the body may protect the liver from faster-induced damage by activating autophagy to inhibit apoptosis.The expression of ACAT2,a gene related to lipid synthesis,was significantly decreased during fasting(P < 0.05),and was significantly increased after resuming feeding(P < 0.05).The expressions of catabolic related genes ACSBG2 and APOB were significantly decreased during fasting period(P < 0.05),and significantly increased after resuming feeding.ACSL1 was significantly increased during fasting period and significantly decreased after resuming feeding period(P < 0.05),indicating that lipid synthesis was decreased during fasting period.But its catabolism is not entirely achieved in one way.Western-Blot analysis of key proteins related to liver autophagy during fasting induced physiological remodeling also showed that: The expressions of key proteins PI3 K,Beclin1,LC3 and PI3 K which activated autophagy pathway were significantly increased during fasting(P < 0.05),while the expression of key protein m TOR which inhibited autophagy was significantly decreased during fasting(P < 0.05),indicating that autophagy occurred in liver during fasting.The part of liver lipid droplets is degraded by lipid autophagy to provide energy for the body.In conclusion,laying rate of laying hens in late laying period is low and fatty liver incidence is high.Physiological remodeling induced by fasting can not only bring the second peak of laying hens,but also effectively alleviate fatty liver caused by metabolic disorders of older laying hens.The enhancement of antioxidant function of liver after fasting induced physiological remodeling is the basis for the second egg production peak of chickens.The mechanism that fasting induced physiologic remodeling can relieve fatty liver is related to liver activation of autophagy protection and inhibition of apoptosis.This experiment enriched the theoretical basis of physiological remodeling induction,provided a basis for prolonging the feeding cycle of laying hens,and had important significance for guiding production.