Effect  of different dietary iron contents on liver transcriptome characteristics in Wujin pigs
Iron is an important trace element that affects the growth and development of animals and regulates  oxygen transport, hematopoiesis, and hypoxia adaptations. Wujin pig  has unique hypoxic adaptability and iron homeostasis; however, the specific regulatory mechanisms have rarely been reported. This study randomly divided 18 healthy Wujin piglets  into three groups: the control group, supplemented with 100 mg/kg iron (as iron glycinate); the low-iron group, no iron supplementation; and the high-iron group, supplemented with 200 mg/kg iron (as iron glycinate). The pre-feeding period was 5 days, and the formal period was 30 days. Serum was collected from empty stomachs before slaughter and at slaughter to detect changes in the serum iron metabolism parameters. Gene expression in the liver was analyzed via transcriptome analysis to determine the effects of low- and high- iron diets on transcriptome levels. Correlation analysis was performed for apparent serum parameters, and transcriptome sequencing was performed using weighted gene co-expression network analysis to reveal the key pathways underlying hypoxia regulation and iron metabolism. The main results are as follows. (1) Except for the hypoxia-inducible factor 1 (HIF-1) content (between the low- and high-iron groups), significant  differences were not observed among the serum iron metabolic parameters. The serum HIF-1 content of the low-iron group was significantly higher than that of the high-iron group (P<0.05). (2) Sequencing analysis of the liver transcriptome revealed 155 differentially expressed genes (DEGs) between the low-iron  and  control groups, 229 DEGs between the high-iron and control groups, and 279 DEGs between the low- and high-iron groups . Bioinformatics analysis showed that the HIF-1 and transforming growth factor-beta (TGF-ß) signaling pathways were the key pathways for hypoxia regulation and iron metabolism.  Four genes were selected for qPCR validation, and the results were consistent with the transcriptome sequencing data. In summary, the serum iron metabolism parameter results showed that under the influence of low- and high-iron diets, Wujin piglets maintain a steady state of physiological and biochemical indices via complex metabolic regulation of the body, which reflects their stress resistance and adaptability. The transcriptome results revealed the effects of low-iron and high-iron diets on the gene expression level in the liver and showed that the HIF-1 and TGF-ß signaling pathways were key for regulating hypoxia adaptability and iron metabolism homeostasis under low-iron and high-iron diets. Moreover, HIF-1a and HEPC  were the key genes. The findings provide a theoretical foundation for exploring the regulatory pathways and characteristics of iron metabolism in Wujin pigs. Overall design: Three groups piglets were fed with three kinds of iron content feed. Assay rna sequence analysis of liver. WGZA2, WGZA3, WGZA7 belongs to low-iron group, WGZB4, WGZB5, WGZB6 belongs to control group, WGZC2, WGZC7, WGZC8 belongs to high-iron group.