Attenuation Of The Oxidative Stress In The Ovaries Of The Aging Laying Chickens

After the onset of egg production,the maximal laying rate of commercial hens could reach more than 95%at about 200 days of age.However,there is a fast decline in egg production after the hens reach 480 days of age.The reproductive performance depends on the ovary function and the follicular development.The critical process of chicken follicular development is yolk deposition,which closely relates to the ability to synthesize the yolk precursor of the liver.One of the major factors that induce organ dysfunction is oxidative stress caused by accumulated reactive oxygen species(ROS)levels.In this study,age-related changes of yolk precursor formation in the liver and the ovarian antioxidative capacity in hens from different laying stages were determined.Subsequently,a D-galactose(D-gal)-induced aging model was established to verify the protective effects of grape seed proanthocyanidin extract(GSPE)and Lycopene on ovarian aging and their related mechanisms.From these studies,we expected to provide theoretic guidance for retarding ovarian aging in the laying hens.1.Age-related changes of yolk precursor formation in the liver of laying hensA rapid decline in egg production results predominantly from the ovarian aging,accompanied by endocrine changes,decreased yolk synthesis and accumulation,and the reduction in follicles selected into the preovulatory hierarchy.In this study,hens at different ages(90,150,280 and 580-days old)were compared for yolk precursor formation in the liver to elucidate effects of aging on laying performance.The results showed that liver lipid synthesis increased remarkably in hens from D90 to D150,but decreased sharply at D580 as indicated by the changes in triglyceride(TG)levels.This result was consistent with the age-related changes of the laying performance.The levels of liver antioxidants and total antioxidant capacity decreased significantly in D580 hens and the methane dicarboxylic aldehyde(MDA)in D580 hens was much higher than at other stages.The serum 17?-estradiol(E2)level increased from D90 to D280,but decreased at D580.Expression of estrogen receptor(ER)a and ? mRNAs in liver displayed similar changes to the serum E2 in D580 hens.Expression of the genes related to yolk precursor formation and enzymes responsible for fat acid synthesis were all decreased in the D580 hens.These results indicated that decreased yolk precursor formation in the liver of the aged hens resulted from concomitant decreases of serum E2 level,transcription levels of estrogen receptors and critical genes involved in yolk precursors synthesis,and liver antioxidant status.2.Age-related changes of the antioxidant status in the ovaries of the laying hensThe goal of this study was to examine the age-related changes of the antioxidant status in the ovaries of the laying hens.Hens at different ages(D90,D150,D280 and D580)were compared for the antioxidant status in the ovaries to elucidate effects of aging on laying performance.The results showed that accompanied by the decreased laying performance,the levels of the ovary antioxidants and the activities of antioxidases decreased significantly in D580 hens and the MDA content in D580 was much higher than that of other stages.Meanwhile,transcription levels of genes related to ovary antioxidant capacity in D580 ovary decreased sharply compared with D150 and D280 ovaries.Western blot analyses confirmed that the expression Nuclear factor erythroid 2-related factor 2(Nrf2)and hemeoxygenase-1(HO-1)protein and Nrf2/HO-1 downstream genes were both down-regulated during aging process.Collectively,these results suggest that the antioxidant status of the ovary in laying hens are increased from pullets(D90)to laying hens(D150 and D280),and then decreased sharply with aging approaching.3.Grape seed proanthocyanidin extract prevents ovarian aging by inhibiting oxidative stress in the hensOxidative stress is an important inducement in ovarian aging which results in fecundity decline in human and diverse animals.As a potent antioxidant,GSPE was investigated to ameliorate chicken ovarian aging in this study.Firstly,a D-gal-induced(2.5 mg/mL)aging ovarian model was established and the cultured ovarian tissues were treated with GSPE at 5 ?g/mL for 72 h to evaluate the putative attenuating effects of GSPE on ovarian aging.Meanwhile,ovaries of D280(young)and D580(old)were respectively treated with GSPE for 72 h in culture to verify the protective effects of GSPE on natural aging ovary.The results showed that GSPE could rescue the antioxidant capacity decline by increasing the antioxidase activities and their gene expression in either D-gal-induced or natural aging ovaries.Moreover,GSPE could maintain the homeostasis between cell proliferation and apoptosis in the D-gal-induced and natural aging ovaries,as well as alleviate D-gal-induced nucleus chromatin condensation in the ovarian granulosa cells.In conclusion,GSPE treatment can effectively prevented the ovarian aging process in hens by reducing oxidative stress.4.Lycopene ameliorates oxidative stress in aging ovary of laying hens via activation of Nrf2/HO-1 pathwayAs a well-known antioxidant,Lycopene was investigated to ameliorate chicken ovarian aging in this study.Firstly,the putative attenuating effects of Lycopene(100 ng/mL)was evaluate through the establishment of a D-gal-induced(2.5 mg/mL)aging ovarian model in vitro.Meanwhile,ovaries of D280(young)and D580(old)were treated with Lycopene for 72 h in vitro to verify the protective effects of Lycopene on natural aging ovaries.The results showed that Lycopene rescued the antioxidant capacity by increasing the activities of antioxidases and activating the Nrf2/HO-1 pathway in both D-gal-induced and natural aging ovaries.Mover,Lycopene maintained the balance between cell proliferation and apoptosis in either D-gal-induced or natural aging ovaries.Furthermore,Lycopene alleviate the D-gal-induced mitochondrial damage in the living granulosa cells.In conclusion,Lycopene effectively ameliorates oxidative stress in aging ovary of laying hens via activation of Nrf2/HO-1 pathway.In summary,the results of this study showed that decreased yolk precursor formation triggered by declining E2 level in the serum and increasing oxidative stress in the liver,and ovarian function decline caused by oxidative stress appeared during the aging process of laying hens.Moreover,the protective effects of GSPE and Lycopene against ovarian aging were explored through the establishment of a D-gal-induced aging ovary model in vitro.The results will provide theoretical basis for retarding ovarian aging of laying hens and extending egg production in the elder layers for poultry production.