Effects Of NAC On Alleviating Chronic Heat Stress On Ovarian Injury In Growing Layer Hens

The purpose of this experiment was to explore the effect of dietary NAC on ovarian growth,development and dysfunction in young laying hens mediated by chronic heat stress,which can be used as a reference for the screening of drugs against heat stress injury in clinic.At the age of 12 weeks,120 Hyline brown growing layer hens were randomly divided into a thermoneutral temperature chamber(Con)and a heat stress chamber(HS).Subsequently,the growing pullets in each temperature chamber were then fed one of two diets namely,a basal diet without supplemental NAC(Con group,HS group)and a basal diet supplemented with 1000 mg NAC per kg of diet(CN group,HSN group),for four groups.The experiment lasted for 3 weeks.In the heat stress room,the ambient temperature was controlled between 36 ±1℃ and 50-60% humidity,and the thermoneutral room was controlled between 22 ±1℃.On the 7th,14 th and 21 st day of the formal experiment,ovarian tissues were collected for pathological section preparation,determination of antioxidant indexes,relative expression of inflammatory factor gene,antioxidant gene and AMPK pathway related gene m RNA,and the expression of AMPKα1,NF-κ B,TNF-α,Nrf2 and HO-1 protein in ovarian tissue.The results are as follows:1.Chronic heat stress can cause ovarian interstitial hemorrhage,irregular changes of follicular dysplasia,increase of atretic follicles and disorder of follicular granulosa cells.2.The antioxidant enzyme activities(GSH-Px,T-AOC,SOD,CAT)were significantly lower(P < 0.05)and MDA content was increased(P < 0.05)in the ovarian tissue of the HS group compared with the Con group.Compared with HS group,the content of MDA in ovarian tissue of HSN group decreased,but the activities of SOD,CAT,GST,T-AOC and GSH-Px increased significantly.3.Compared with the Con group,the protein levels of Nrf2 and HO-1 in the HS group were decreased,the relative expression of Nrf2,HO-1,GST and SOD2 m RNA were increased on the 7th day and decreased significantly on the 14 th and 21 st day.Dietary NAC could increase the expression of Nrf2,HO-1 protein and Nrf2,HO-1,GST,SOD2 gene m RNA in ovarian tissue under chronic heat stress.4.Compared with Con group,the protein levels of NF-κB and TNF-α in ovarian tissue of HS group were increased(P < 0.05);The m RNA relative expression levels of NF-κB and downstream related inflammatory factors were significantly increased(P <0.05),the protein expression levels of NF-κB and TNF-α and m RNA expression levels of NF-κB and downstream related inflammatory factors in ovarian tissues were decreased by dietary NAC(HSN group)under chronic heat stress(P < 0.05).5.Compared with the Con group,the phosphorylation level of AMPKα1 protein in ovarian tissue of HS group was decreased(P < 0.05),the m RNA expression levels of AMPKα1,CPT1 and PPARα were significantly decreased(P < 0.05),and the m RNA expression level of ACC was significantly increased(P < 0.05).Supplementation of NAC(HSN group)increased the phosphorylation level of AMPKα1 and the m RNA expressions of AMPKα1,CPT1 and PPARα in ovarian tissues under chronic heat stress,while decreased the m RNA expression of ACC(P < 0.05).Conclusion: chronic heat stress can inhibit the activity of antioxidant enzymes and the expression of Nrf2 pathway and its downstream genes in ovarian tissue,activate NF-κB signal pathway to trigger ovarian inflammatory response,and inhibit the expression of AMPK energy metabolism gene to affect the energy metabolism of ovarian tissue,resulting in ovarian development and dysfunction,resulting in pathological damage of the ovary.NAC can effectively alleviate the oxidative stress and inflammatory damage of ovarian tissue under chronic heat stress,and reduce the damage of chronic heat stress to the body.This study provides a theoretical basis for the protective mechanism of NAC in alleviating ovarian injury caused by chronic heat stress.