Liver transcriptome response to avian pathogenic Escherichia coli infection in broilers with corticosterone treatment

Avian pathogenic Escherichia coli (APEC) infection has high morbidity and mortality, and multiple stressors encountered during rearing place poultry in a state of stress. However, research on how poultry cope with APEC infection under stress situation is still limited. In this study, we established a broiler stress model by corticosterone (CORT) administration subcutaneously for 7 consecutive days, followed by APEC challenge intramuscularly. CORT treatment significantly reduced body weight (BW) and average daily gain (ADG) while increasing feed conversion ratio (FCR) (P < 0.01). APEC infection significantly decreased ADG (P < 0.01). CORT treatment and APEC infection elevated plasma corticosterone and heterophil to lymphocyte (H/L) ratio (P < 0.05). Additionally, plasma aspartate aminotransferase (AST), AST to alanine aminotransferase (AST/ALT) ratio, and lactate dehydrogenase (LDH) levels increased significantly (P < 0.01). Histopathological analysis revealed structural damage of liver, indicating that CORT treatment and APEC infection induced liver injury. However, CORT pretreatment broilers exhibited a milder histopathological lesions and significantly lower AST, ALT, and LDH levels (P < 0.05) compared to APEC infection alone. CORT treatment and APEC infection increased plasma levels of lysozyme (LZM), total protein (TP), and globulin (GLOB) (P < 0.05), while CORT pretreatment further elevating their concentrations compared to APEC infection alone, suggesting an enhanced innate immune response. Liver transcriptomic analysis identified 768, 335, and 567 differentially expressed genes (DEGs) following CORT, APEC, or both treatments, respectively, enriched in cytokine-cytokine receptor interaction, PPAR signaling pathway, Toll-like receptor signaling pathway, MAPK signaling pathway, steroid hormone biosynthesis pathway, arachidonic acid metabolism, and phagosome pathway, etc., indicating that CORT treatment regulates lipid metabolism and immunity, while APEC infection induces inflammation and disrupts lipid metabolism. Notably, CORT pretreatment may mitigate APEC induced liver injury by enhancing phagosome function. Moreover, glucocorticoid receptor (GR) may regulate DEGs expressions, thus affected broilers response to CORT, APEC, or both treatments. These results suggest that CORT treatment, APEC infection, or both significantly affect the growth performance, immune response and liver function of broilers, while lipid metabolism may play a crucial role.