Regulation of bone phosphorus retention and bone development possibly by BMP and MAPK signaling pathways in broilers

The bone morphogenetic protein(BMP)and mitogen-activated protein kinase(MAPK)signaling pathways play an important role in regulation of bone formation and development,however,it remains unclear that the effect of dietary different levels of non-phytate phosphorus(NPP)on these signaling pathways and their correlations with bone phosphorus(P)retention and bone development in broilers.Therefore,this experiment was conducted to investigate the effect of dietary P supplementation on BMP and MAPK signaling pathways and their correlations with bone P retention and bone development in broilers.A total of 800 one-day-old Arbor Acres male broilers were randomly allotted to 1 of 5 treatments with 8 replicates in a completely randomized design.The 5 treatments of dietary NPP levels were 0.15,0.25,0.35,0.45 and 0.55%or 0.15,0.22,0.29,0.36 and 0.43%for broilers from 1 to 21 days of age or 22 to 42 days of age,respectively.The results showed that extracellular signal-regulated kinase 1(ERK1)mRNA expression in the tibia of broilers on days 14 and 28,phosphorylated-ERK1(p-ERK1)on day 14,and BMP2 protein expression on days 28 and42 decreased linearly(P<0.04),while c-Jun N-terminal kinase 1(JNK1)mRNA expression on day 42 increased linearly(P<0.02)with the increase of dietary NPP level.At 14 days of age,total P accumulation in tibia ash(TP),bone mineral concentration(BMC),bone mineral density(BMD),bone breaking strength(BBS)and tibia ash were negatively correlated(r=-0.726 to-0.359,P<0.05)with ERK1 and JNK1 mRNA as well as p-ERK1;tibia alkaline phosphatase(ALP)and bone gal protein(BGP)were positively correlated(r=0.405 to 0.665,P<0.01)with ERK1 mRNA and p-ERK1.At 28 days of age,TP,BMC,BMD,BBS and tibia ash were negatively correlated(r=-0.518 to-0.370,P<0.05)with ERK1 mRNA and BMP2 protein,while tibia ALP was positively correlated(r=0.382 to 0.648,P<0.05)with them.The results indicated that TP,BMC,BMD,BBS or tibia ash had negative correlations,while tibia ALP and BGP had positive correlations with ERK1 and JNK1 mRNAs,BMP2 protein and p-ERK1,suggesting that bone P retention and bone development might be regulated by BMP and MAPK signaling pathways in broiler chickens.