Study On The Effect Of Gonadectomy On Fat Metabolism And Its Molecular Mechanism In Chickens

Directional deposition of fat and improvement of meat quality is an urgent problem in broiler production. Previous researches have showed that gonadal axis hormones affected fat metabolism and directional deposition. To systematically elucidate effects of gonadal axis hormone on fat metabolism at molecular levels, the change of fat content, meat quality, hormone levels, as well as differentially expressed genes in abdominal fat and breast tissue of gonadectomized male and female chickens were evaluated in current study. The findings provided the theoretical basis for new technique development which could optimizing the intramuscular fat (IMF) content.Trial 1:The changes of fat content and meat quality in gonadectomized chickensFour groups of Beijingyou (BJY) chickens were reared in the same conditions, including gonadectomized male and female groups at 3 weeks of age and another two non-gonadectomized controls. Chickens were slaughtered and samples were collected at 13 weeks (n= 10 for each group),17 weeks (n= 20 for each group) and 22 weeks (n= 10 for each group) respectively. Results showed that: 1) Gonadectomy significantly increased serum triglyceride (TG), total lipid content of liver and abdominal fat percentage (P< 0.05) in male and female chickens.2) Gonadectomy improved meat quality of male and female, and promoted muscle tenderness and flavor, which mainly characterized of increased IMF content (P< 0.05), reduced redness and increased yellowness of meat (P< 0.05), decreased shear force (P< 0.05), finer muscle fibers (P< 0.05), increased inosine monophosphate (IMP) content, and changed fatty acid composition and content.Trial 2:Effects of gonadal hormone changes on fat deposition in gonadectomized chickensSerum testosterone (T), estradiol (E2) and follicle stimulating hormone (FSH) content were determined in four groups of chickens at 13,17 and 22 weeks. T, E2 and FSH content and expression of their receptors in breast muscle and abdominal fat were detected at 17 weeks, and correlation analysis between abdominal fat weight and hormone content were performed. Results showed that:1) Serum testosterone content of capons significantly decreased with the growth of chickens (P< 0.01), as well as the testosterone content in abdominal fat and breast muscle (P< 0.05). Remarkably, abdominal fat weight were negatively correlated with testosterone content in serum and abdominal fat significantly (P < 0.01).2) Serum E2 content significantly decreased in ovariectomized chickens(P< 0.05), while FSH increased (P< 0.05). In abdominal fat, the E2 content and expression of ESR1 receptor significantly decreased(P< 0.05). However, FSH content and FSHR receptor expression tended to increased in abdominal fat. Moreover, abdominal fat weight was negatively correlated with E2 content in abdominal fat significantly (P< 0.01).Trial 3:Molecular regulation mechanism of gonadectomy on lipid metabolism in chickenTissues of abdominal fat and breast muscle were collected from 3 chickens from two gonadectomized groups and two controls at 17 weeks, respectively. An analysis of RNA-seq was used to investigate the differential expressed genes and related signaling pathways involved in lipid metabolism in abdominal fat and breast muscle of gonadectomized chickens. Results showed that:1) Differentially expressed genes in abdominal fat and breast muscle of gonadectomized chickens were significantly enriched in ECM-receptor interaction, focal adhesion and cell adhesion molecules pathways (P< 0.05), indicating that these pathways might play important roles in the regulation of chicken lipid deposition process.2) Gonadal hormone content changed after gonadectomy of chickens, resulting in up-regulation of lipid synthesis genes (SCD, MSMO1, FABP7), down-regulation of lipolysis (MGLL) and steroid synthesis (CYP2D6) gene in abdominal fat, possibly mediated by steroid biosynthesis and lipid metabolism related signaling pathways, and then promoted abdominal fat deposition (P< 0.05).3) Caponization significantly decreased testosterone content and increased IMF content in male chickens, might associated with regulation of genes related to lipid metabolic, such as up-regulation of CD36, down-regulation of ADIPOQ, AKR1D1 and CYP2D6, and mediated by steroid hormone biosynthesis, primary bile acid biosynthesis, and adipocytokine signaling pathway; on the other hand, ovariectomy decreased E2 content and increased FSH content in female chickens, it promoted IMF deposition might through up-regulation of PECR, down-regulation of HSD17B12 and EPHX2(P< 0.05), possibly mediated by biosynthesis of unsaturated fatty acids and arachidonic acid metabolism pathway.