Increased expression of the peroxisome proliferator-activated receptor γ in the immune system of weaned pigs after Escherichia coli lipopolysaccharide injection

Peroxisome proliferator-activated receptor γ (PPARγ), a member of the nuclear hormone receptor superfamily, has been implicated in regulation of immunity and inflammation in rodents and humans. The objective of the current study was to investigate whether the expression of PPARγ was altered in the immune system of weaned pigs after Escherichia coli lipopolysaccharide (LPS) injection. PPARγ expression was investigated in the thymus, spleen, mesenteric lymph node and peripheral white blood cells of weaned pigs (8.54 ± 0.24 kg BW) after LPS injection (100 μg/kg BW, n = 6) and controls (sterile saline, n = 6), by using real-time polymerase chain reaction, Western blot analysis, and immunohistochemistry. Plasma pro-inflammatory cytokines and hormones were also assessed. LPS triggered PPARγ mRNA and protein expression in the thymus (P < 0.05, 4.24-fold; P < 0.10, 1.46-fold), spleen (P < 0.10, 2.75-fold; P < 0.05, 1.84-fold), mesenteric lymph node (P < 0.05, 4.32-fold; P < 0.05, 1.96-fold) and peripheral white blood cells (P < 0.001, 24.44-fold; P < 0.001, 1.58-fold). The LPS-injected pigs showed an increase in PPARγ staining in splenic corpuscle and periarterial lymphatic sheath of white pulp (P < 0.05) and red pulp (P < 0.001) of spleen, and in medullas of thymus lobule of thymus (P < 0.05), and in thymus-dependent area of mesenteric lymph node (P < 0.05) compared to the control pigs. Concurrent with up-regulation of PPARγ expression, LPS induced increases in plasma interleukin-6 (P < 0.001), tumor necrosis factor-α (P < 0.001), cortisol (P < 0.001), prostaglandin E2 (P < 0.01) and 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) (P < 0.05), and decreases in plasma insulin (P < 0.10) and insulin-like growth factor-1 (P < 0.001). These results suggest that induction of PPARγ expression in immune system may be associated with the release of the natural PPARγ activating ligand 15d-PGJ2, and play an important role in host response to immunological stress. Additionally, it is possible that PPARγ would be a new therapeutic target in treatment of immunological stress of livestock.