Lipopolysaccharide-induced liver apoptosis is increased in interleukin-10 knockout mice.
Although IL-10 down-regulates pro-inflammatory cytokine secretion by hepatic Kupffer cells, the mechanisms underlying its hepatoprotective effects are not fully clear. This study tested the hypothesis that IL-10 protects the liver against pro-inflammatory cytokines by counteracting their pro-apoptotic effects. Wild type and IL-10 knockout mice were treated with bacterial lipopolysaccharide and sacrificed 1, 4, 8, and 12 h later. Plasma ALT activity was measured as a marker of liver injury. Liver pathology and TUNEL response were assessed by histology. Plasma levels and whole liver mRNA levels were measured for TNF-alpha, IL-1 beta, TGF-beta1, IL-10, and their respective receptors. Hepatic mRNA levels were measured for several pro-apoptotic adaptors/regulators, including FasL, Fas receptor, FADD, TRADD, Bad, Bak, Bax, and Bcl-X(S), and anti-apoptotic regulators, including Bcl-w, Bcl-X(L), Bcl-2, and Bfl-1. Caspase-3 activity in the liver was determined as well as immunohistochemistry for IL-1RII, TGF-betaRII and Fas receptor. At all time points the livers from IL-10 knockout mice displayed a significantly increased number of apoptotic nuclei compared to wild type mice. Changes in plasma cytokine levels and their liver mRNA levels were consistent with suppression by IL-10 of pro-inflammatory cytokine secretion. In addition, pro-inflammatory cytokine receptor mRNA levels (TNF-alpha, TGF-beta, and IL-1 beta) were markedly up-regulated by LPS at all time points in IL-10 knockout mice as compared to wild type mice. Expression of the pro-inflammatory cytokine receptor IL-1RII was similarly increased as shown by immunostaining. The mRNA levels of a typical pro-apoptotic cytokine, TRAIL, were increased and LPS also up-regulated the mRNA expression of other apoptotic factors to a larger extent in IL-10 knockout mice than in their wild type counterparts, suggestive of an IL-10 anti-apoptotic effect. In the livers of knockout mice, markedly increased caspase-3 activity was already evident at the 1-h time point following LPS administration, while in the wild type animals this increase was delayed. Immunostaining also indicated that LPS increased hepatic expression of the pro-apoptotic receptors Fas and TGF-betaRII in IL-10 knockout mice. The data presented in this study show that: (i) IL-10 modulates not only the secretion of pro-inflammatory cytokines, but also the receptors of these cytokines, and ii) IL-10 protects the liver against LPS-induced injury at least in part by counteracting pro-inflammatory cytokine-induced liver apoptosis.
Division of Digestive Diseases and Nutrition, Department of Internal Medicine, University of Kentucky Medical Center, MN649-0298, Lexington, KY 40536, USA.
Jian
J
Zhong
Ion V
IV
Deaciuc
Ravshan
R
Burikhanov
Willem J S
WJ
de Villiers
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D000410:Alanine Transaminase / Q000097:blood; D000818:Animals; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D016207:Cytokines / Q000097:blood / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D020287:In Situ Nick-End Labeling; D016753:Interleukin-10 / Q000235:genetics / Q000502:physiology*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008099:Liver / Q000378:metabolism / Q000473:pathology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D012333:RNA, Messenger / Q000378:metabolism; D018121:Receptors, Cytokine / Q000235:genetics / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; D016207:Cytokines; D008070:Lipopolysaccharides; D012333:RNA, Messenger; D018121:Receptors, Cytokine; D016753:Interleukin-10; D000410:Alanine Transaminase