Effects Of Lipopolysaccharide Challenge On PPARγ Expression Of Weanling Pigs

The study was conducted to investigate the effects of lipopolysaccharide (LPS) challenge on peroxisome proliferators-activated receptor-γ(PPARγ) expression of weanling pigs.12 pigs were divided into two groups(6 replicates/treatment and 1 pig/replicate).The pigs in the treatment group were injected intraperitoneally with 100μg/kg BW LPS,whereas pigs in the control group were injected with an equivalent amount of sterile saline.Blood samples were collected at 1.5 and 3h post-challenge for furthur analysis.Following blood collection at 3h,the pigs were slaughtered to collect thymus,spleens and intestinal lymph node for furthur detection.The results showed that:(1) At 1.5h,LPS reduced white blood cell,monocyte(P＜0.1) and neutrophil(P＜0.05) numbers, and neutrophil proportion(P＜0.05),and LPS increased lymphocyte proportion(P＜0.05).At 3h,LPS reduced white blood cell,lymphocyte,neutrophil(P＜0.05) and monocyte(P＜0.1) numbers,and increased monocyte proportion(P＜0.1).(2) At 1.5h,LPS increased aspartate aminotransferase(GOT),lactate dehydrogenase (LDH) and creatine kinase(CK) activities(P＜0.05).At 3h,LPS reduced glucose and total protein(P＜0.05),and increased GOT,alkaline phosphatase(P＜0.05) and LDH(P＜0.1).(3) At 1.5h,LPS increased interleukin-6(IL-6),tumour necrosis factor-α(TNF-α),cortisol,corticotropin-releasing hormone(CRH), prostaglandin E₂(PGE₂)(P＜0.05) and glucogan(P＜0.1),and reduced insulin(P＜0.1),growth hormone and insulin-like growth factor-1(IGF-1)(P＜0.05).At 3h, LPS increased IL-6,TNF-α,cortisol,adrenocorticotropin and glucogan(P＜0.05), and reduced insulin(P＜0.001) and IGF-1(P＜0.1).(4) LPS challenge induced congestion with blood in the medullas and blood capillary of cortex in thymus, splenic sinusoid of white pulp in spleen,and the medullas of intestinal lymph node. LPS induced karyopyknosis and cavitation of cells in the medullas of thymus and of lymphocytes in thymus-dependent area and germinative center of lymph nodule. LPS induced hemorrhage in the splenic corpuscle of spleen,and medullas of intestinal lymph node.These results indicate that LPS challenge induces the changes of white blood cell differential count,blood biochemical parameters, plasma hormones and pro-inflammatory cytokines of weanling pigs,which suggests LPS induces an acute immunological stress in pigs.In order to investigate whether the expression of PPARγwas altered in the immune system,the experiment was conducted to investigate the effects of immunological stress on PPARγmRNA and protein expression in the peripheral white blood cells,thymus,spleen and intestinal lymphoid node and PPARγdistribution in the thymus,spleen and intestinal lymphoid node of weanling pigs. The results showed that:(1) Immunological stress increased PPARγmRNA expression in the peripheral white blood cells(P＜0.001),thymus(P＜0.05), spleen(P＜0.1) and intestinal lymphoid node(P＜0.05).(2) Immunological stress increased PPARγprotein expression in the peripheral white blood cells(P＜0.05), thymus(P＜0.1),spleen(P＜0.05) and intestinal lymphoid node(P＜0.05).(3) Immunological stress increased PPARγ-positive cell percentage in the medullas of thymus lobule of thymus(P＜0.05),splenic corpuscle and periarterial lymphatic sheath of white pulp(P＜0.05) and red pulp(P＜0.001) of spleen,and in thymus-dependent area of mesenteric lymph node(P＜0.05).These results indicate that immunological stress induces PPARγexpression in the immune systems.In order to investigate whether the expression of PPARγwas altered in the hypothalamus-pituitary gland-adrenal gland(HPA) axis,the experiment was conducted to investigate the effects of immunological stress on PPARγmRNA expression and its distribution in the hypothalamus,pituitary gland,and adrenal gland of weanling pigs.The results showed that:(1) Immunological stress increased PPARγmRNA expression in the hypothalamus(P＜0.001),pituitary gland(P＜0.001) and adrenal gland(P＜0.01).(2) Immunological stress increased PPARγ-positive cell percentage in the hypothalamus(P＜0.05),adenohypophysis (P＜0.05),adrenal cortex(P＜0.05) and adrenal medulla(P＜0.001).These results indicate that immunological stress induces PPARγexpression in the HPA axis.In a conclusion,immunological stress induces PPARγexpression in the immune system and HPA axis of weanling pigs.Additionally,it is possible that PPARγmay play an important role in regulation of immunological stress in pigs, and it may be a new target for alleviating immunological stress of pigs.