Mechanisms Of Manganese Source And Level In Regulations Of Heart MnSOD Gene Expressions In Broilers

An experiment was conducted to investigate the effects of dietary Mn source and level on growth performance,heart Mn concentrations,heart MnSOD mRNA levels,heart MnSOD protein levels,heart MnSOD activities,transcription factor(Sp-1 or AP-2) DNA binding activities and heart MnSOD-BP RNA binding activities in broilers in order to elucidate the mechanisms of different forms of Mn in transcriptional and translational regulations of heart manganese-containing superoxide dismutase (MnSOD) gene expressions in broilers.A total of 500 one day-old Arbor Acres(AA) commercial male broilers were fed a Mn-unsupplemented corn-soybean meal basal diet,which was formulated to meet all nutrient requirements with the exception of Mn for chickens(NRC,1994),to enhance the sensitivity to manganese before the age of 7d.On day 8,432 birds were randomly allotted by bodyweight to one of nine treatments(six cage replicates of eight chicks each) in a completely randomized design involving a 4×3 factorial arrangement of treatments,and fed a Mn-unsupplemented corn-soybean meal basal diet (Control,16.13mg/kg Mn) or basal diets supplemented with 100 or 200 mg/kg Mn as Mn sulfate, Availa-Mn source with the weak complex strength,MnAAB source with the moderate complex strength or Bioplex Mn source with the strong complex strength for a duration of 14 days.The results showed that dietary Mn sources had significant effects on heart Mn concentrations(P＜0.09),heart MnSOD activities(P＜0.02),heart MnSOD mRNA levels(P＜0.0001),heart AP-2 DNA-binding activities(P＜0.0001) and heart MnSOD-BP RNA-binding activities(P＜0.0001),however ADG (P＞0.72),ADFI(P＞0.79),FCR(P＞0.93),heart MnSOD protein levels(P＞0.69) and heart Sp-1 DNA-binding activities(P＞0.38) were not affected by supplemental Mn sources;Dietary Mn level showed the significant(P＜0.0001) effects on the values mentioned above except for ADG(P＞0.44), ADFI(P＞0.96) or FCR(P＞0.11) in broilers;There was significant influence of Mn source and level interaction on AP-2 DNA-binding activities,heart MnSOD mRNA level and heart MnSOD-BP RNA binding activities(P＜0.0006),but no differences were observed in other indices(P＞0.23).Heart Mn concentrations,heart MnSOD activities,heart Sp-1 DNA-binding activities and heart MnSOD protein levels increased linearly as dietary supplemental Mn level increased(P＜0.0001).As for the significant effects of dietary Mn sources on the heart Mn concentration,MnAAB with the moderate complex strength was higher than Availia Mn with the weak complex strength and Mn sulfate(P＜0.06),but it was similar to Bioplex Mn(P＞0.61);Bioplex Mn was higher than Availia Mn(P＜0.10),but it was similar to Mn sulfate(P＞0.14);Availia Mn was similar to Mn sulfate(P＞0.83).Heart MnSOD activities showed that MnAAB and Bioplex Mn were higher than Mn sulfate(P＜0.02),but they were similar to Availia Mn(P＞0.14);Availia Mn was similar to Mn sulfate(P＞0.13).The heart MnSOD mRNA levels showed the highest(P＜0.0001) for MnAAB,but no differences were found between other three Mn sources treatments when supplemented with 100 mg/kg Mn(P＞0.27).MnAAB was the highest(P＜0.0001),and Bioplex Mn was similar to Availia Mn(P＞0.51),while Mn sulfate was the lowest(P＜0.06) at the supplemented level of 200 mg/kg Mn.When the diet was supplemented with 100 mg/kg Mn or 200 mg/kg Mn,the heart AP-2 DNA binding activities showed the lowest for MnAAB (P＜0.0004),then the little high for Availia Mn(P＜0.04) and the highest(P＜0.04) for Bioplex Mn and Mn sulfate;The heart MnSOD-BP RNA binding activities showed the highest(P＜0.004) for MnAAB, followed by Bioplex Mn(P＜0.0001),Availia Mn(P＜0.002) and Mn sulfate(P＜0.0001).The results indicated that transcriptional regulation of heart MnSOD gene by dietary Mn was obtained by transcription factor Sp-1 and AP-2 and translational regulation of heart MnSOD gene by dietary Mn through MnSOD-BP which was a new mechemism of regulation heart MnSOD gene expression by dietary Mn in broilers.Heart AP-2 DNA-binding activities and heart MnSOD-BP RNA-binding activities were two sensitive new indices to estimate the different bioavailabilities of Mn sources.On the base of transcriptional regulation of heart MnSOD gene by dietary Mn or translational regulation of heart MnSOD gene by dietary Mn in broilers,the MnAAB showed the best biological activity,and the Mn sulfate was the worst among different Mn source.These findings deeply showed the new mechanisms of MnSOD gene expressions by manganese and differences among Mn sources,which have not been reported in literature before,they would be of very important theoretical and practical significances for further investigating the signal transfer way of transcription and translation of MnSOD gene expressions in broilers,selecting the most sensitive indices to evaluate the optimal dietary Mn level and bioavailabilities of Mn,developing and applying the new and highly bioavailable organic Mn additive with the moderate complex strength,so as to promote the growth of broilers and minimize the environmental pollution of Mn excreted by the animal.