Biocharacteristics And ASK-JNK Singling Regulation In The Development Of Femoral Head Necrosis In Broilers

In the past 50 years,commercial poultry production has increased rapidly and feed efficiency and growth rate have been improved to the extent so that the market-age weights of broilers have nearly quadrupled.Femoral head separation(FHS)is a degenerative skeletal problem in fast-growing poultry,which is characterized by the separation of growth plate of the proximal femur from the articular cartilage.At its early phase,FHS may remain asymptomatic but leads to epiphyseal breakage,infection,and femoral head necrosis(FHN).FHN in leg problems is a terrible threat to chicken health becase it can cause serious lameness and lead to a failure for the birds to get food and water.Skeletal biological parameters are often used as characteristic indexes of bone diseases.This experiment investigated the obvious changes of leg bones which supported the body weight by a series of physical examination of the femur and tibia.Pathogenesis of femoral head necrosis is very complex and has not been determined currently.Metaphyseal chondrocyte apoptosis may affect the blood perfusion of the femoral head,which may result in FHN after long-term of a lack of nutrition supply.So this study was designed to try to explore the possible mechanisms of the FHN by investigating the related signal pathways resulting in chondrocyte apoptosis.1.Modeling and biocharacteristics of femoral head necrosis in broilersThe experiment was designed to inject glucocorticoid in order to induce the femoral head necrosis in broilers,and investigated the results and feasibility of this modling method.One hundred broiler chicks of both sexes were used in the present study.The birds were randomly allocated to control and methylprednisolone-treated groups and each group had 50 birds with 5 pens of 10 birds.The treated-group birds were intramuscularly injected daily with methylprednisolone(20mg·kg-1 of body mass·d-1)and the control-group birds were injected daily with sterile saline for a week.The incidence of FHN in broilers at the age of 21 and 42 days was recorded,and feed intake and body weight were also analysed.Blood samples were collected to determine calcium,serum phosphorus,triglyceride,total cholesterol and alkaline phosphatase.The femul and tibia were obtained to measure for biochemical parameters by Raman spectroscopy or radiology.The results showed that after the treatment of glucocorticoid,the incidence rate of the femoral head necrosis in broilers was 36.37%.Food intake and body weight were significantly decreased in treated group.Calcium,phosphorus,triglyceride,total cholesterol(TC)and alkaline phosphatase were increased,and bone index decreased significantly.It indicated that glucocorticoid can induce femoral head necrosis in broilers.Glucocorticoid induced the changes of bone biocharacteristics,which contributed to the development of FHN.2.ASK-JNK signaling pathways in the development of femoral head necrosis in broilersChondrocytes are the main cells of the growth plate and articular cartilage of the femoral head.Because the cartilage has no blood vessels and nerves distribution,the metabolism of chondrocytes can achieved only through osmosis.Therefore,chondrocytes are very sensitive with the lack of nutrients and oxygen,oxide aggregation and mechanical pressure stress.In this experiment,the growth plates of the femoral head were collected carefully for the detection of the mRNA expression of Col-2,Col-10,Bcl-2,Caspases-3,Caspases-9,ASK-1,and JNK-1 by real-time fluorescent quantitative PCR.The protein expression of JNK was identified by immunohistochemistry in order to investigate the regulated roles of ASK-JNK signaling pathway in the pathogenesis of femoral head necrosis and chondrocytes apotosis in broiler chickens.FHN birds had an apparent decrease in the expression of Col-2,Col-10,and Bcl-2 protein compared with normal chickens(P<0.01).There was a significant promotion in the mRNA expression of Caspases-3,Caspases-9,ASK-1 and JNK-1(P<0.01).It showed that glucocorticoids can increase the expression of ASK-1.Furthermore,the up expression of ASK1 activated the caspase and JNK signaling pathways,ultimately led to chondrocytes apoptosis.