Study On The Expression Of Srebp-1 Gene And Its Target Genes

Fat affects the flavor of pork meat, and more importantly is related to people's health. However, fat metabolism process and its regulatory mechanism are complicated and involve many factors, among which, as a critical nuclear transcription factor, sterol regulatory element binding protein 1(SREBP-1) plays an important role. SREBP-1 can bind to sterol response-elements which locats in the promoters/enhancers of target genes, and can activate target genes'transcription. Our study focused on SREBP-1 gene. Firstly, we analyzed a GEO dataset to explore the target genes and pathways regulated by SREBP-1; then by an experiment we analyzed the effects of genetic and nutritional factors on mRNA expression of SREBP-1, and several of its target genes and the pathways.1. Microarray data analysis of fat metabolism regulated by SREBP-1cWe searched and got microarray dataset GSE9132 from NCBI GEO database, which associated with mouse fat metabolism. By significant difference analysis about expression and plathway, we got 460 significantly differently expressed genes related to SREBP-1c over-expression in adipocyte differentiation process, among which 271 genes were up-regulated genes and 189 down-regulated. By further analyses of these genes, we also got the pathways invovled in the fat metabolism progresses regulated by SREBP-1c, including 11 pathways up-regulated by SREBP-1c over expression such as PPAR signaling, fatty acid metabolism, biosynthesis of steroids and so on, and 3 pathways down-regulated by SREBP-1c over expression, including axon guidance, nitrogen metabolism and adipocytokine signaling pathway.2. Analysis of the effects of genetic and nutritional factors on porcine SREBP-1c and the pathways relatedAccording to the results of microarray analysis, we selected SREBP-1 gene, three genes in steroid biosynthsis pathway which are HMGCR, IDI1 and SC4MOL, and two other related genes SCD and LDLR for further studying. 12 Ningxiang and 16 Duroc×Landrace×Yorkshire (DLY) pigs were used as the experimental animals, and diets with different crude protein levels (10.41%CP,12.91%CP,15.43%CP,19.66%CP,15.28%CP+1% Arginine) were taken as experimental factor. Ningxiang pigs were fed with the first three diets, and DLY pigs were fed with the last four diets. Real-time fluorescence quantitative PCR method was used to examine the mRNA expression pattern of these genes in tissues of cerebrum, cerebellum, loin, sebum, ileum, liver and kidney. Results are as follows: (1) Breed has significant effect on gene expression in some tissues, which are SREBP-1 in sebum, HMGCR in loin, IDI1 in cerebellum, loin and liver, SC4MOL in cerebrum, loin and liver, and LDLR in ileum and liver. The expression of SREBP-1 and LDLR in DLY pigs were higher than in Ningxiang pigs, while what of HMGCR, IDI1 and SC4MOL were higher expressed in Ningxiang pigs than in DLY pigs. Breed had no effect on SCD gene expression. In Ningxiang pigs the higher expression of HMGCR, IDI1 and SC4MOL genes related to steroids biosynthesis may indicate a higher level of cholesterol. (2) Dietary nutrition level had significant effect on expression of all genes except for SCD in some tissues. However, effects of the nutrition level on gene expression were various in different tissues. Effect of nutrition was significant in cerebellum, sebum, ileum, liver and kidney for SC4MOL, in liver for IDI1, in loin, liver and kidney for SC4MOL and in ileum for LDLR. The analysis of data from pigs fed with same diet (15.43% CP diet) showed that there was interaction between breed and dietary nutrition level. Comparison result showed that 15.43% CP and 15.28% CP + 1% Arg had different effects on SREBP-1 gene expression in cerebellum and ileum, and SC4MOL gene expression in liver. The aditional 1% Arg reduced the expression of SREBP-1 gene in cerebellum and ileum, but increased SC4MOL gene expression in liver significantly. (3) All genes except for LDLR were significantly differently expressed among vrious tissues. SREBP-1, HMGCR, IDI1 and SC4MOL genes were expressed most highly in liver. (4) There was no significant correlation between SREBP-1 and its five target genes by the correlation analysis between the genes. However, there was a high correlation between each other among HMGCR, IDI1 and SC4MOL genes in cerebellum, loin, ileum and kidney.It is obvious that our study on the expression of SREBP-1 and its target genes is very helpful for better understanding of fat metabolism mechanism and will guide the pig breeding and feeding. It is also very helpful for detecting the mechanism of lipid metabolism of human diseases such as diabetes, hyperlipemia, fatty liver, and obesity.