Regulative Role Of Fish Oil On TLR4and NOD Signaling Pathways In Hypothanlamus-Pituitary-Adrenal-Immune Axis In Piglets After Lipopolysaccharide Challenge

This study was conducted to evaluate the regulative role of n-3PUFA onhypothanlamus-pituitary-adrenal-immune axis after lipopolysaccharide challengethrough toll-like receptor (TLR4) and the nucleotide binding oligomerizationdomain protein (NOD) signaling pathway in piglets.1. This experiment was explored to the expression and distribution of keygenes in TLR4and NOD signaling pathways. Twelve283d (8.98±0.86kg)crossbred (Duroc Large White Landrace) piglets were sacrificed for collectionof hypothalamus, pituitary gland, adrenal gland, thymus gland and spleen. mRNAexpression of TLR4, NOD and their downstream signaling genes were detected.TLR4and its downstream signals myeloid differentiation factor88(MyD88)、IL-1receptor associated kinase1(IRAK1)、TNF receptor associated factor6(TRAF6),p65nuclear factor (NF)-κB, tumor necrosis factor (TNF)-α were highly expressingin immune tissues. NOD1and NOD2and their downsteam signalreceptor-interacting protein (RIP2) were highly expressed in immune tissues.NOD1and NOD2were also highly expressed in hypothalamus. These resultssuggest that: TLR4, NOD and their downstream signaling gene were highlycorrelated with immunologic challenge.2. This experiment was conducted to investigate if fish oil could alleviatesactivation of hypothalamic-pituitary-adrenal axis caused by lipopolysaccharide inweaned pigs via modulating TLR4and NODs signaling pathways. Twenty-fourcrossbred weaned pigs were used in a22factorial design, and the main factorsconsisted of diet (5%corn oil or5%fish oil) and immunological challenge (LPS orsaline). On d24, pigs were injected with LPS or saline. Blood samples werecollected at pre-injection (0h), or2,4h post-injection, and then pigs weresacrificed for samples collection of hypothalamus, pituitary gland, adrenal gland,thymus gland, intestinal lymph node and spleen. At2h post-injection, fish oilsupplementation alleviated the increase of plasma TNF-α and cortisol levels (P < 0.05) caused by LPS. Fish oil supplementation alleviated the increase ofhypothalamic corticotropin releasing hormone (CRH) and pituitaryproopiomelanocortin (POMC) mRNA expressions (P <0.05), and increasedpituitary CRHR1mRNA expressions (P <0.001). Fish oil supplementationdecreased mRNA expresssion of hypothalamus IRAK1, TRAF6, NOD1and TNF-α,pituitary TLR4, IRAK1and TRAF6, adrenal TLR4, MyD88, IRAK1, NOD2, RIP2,p65Nf-κB and TNF-α, splenic TLR4, MyD88, IRAK1, TRAF6, NOD1and TNF-α,thymic TLR4, IRAK1, TRAF6and RIP2, and lymphadenoid TLR4and TRAF6(P <0.05or P <0.10). These results suggest that fish oil attenuates the activation ofHPA axis due to decreasing pro-inflammatory cytokines expression inneuroendocrine-immune network through inhibition of TLR4and NODs signalingpathways.