Increased susceptibility to exacerbated liver injury in hypercholesterolemic ApoE-deficient mice: potential involvement of oxysterols.
The contribution of metabolic factors to the severity of liver disease is not completely understood. In this study, apolipoprotein E-deficient (ApoE-/-) mice were evaluated to define potential effects of hypercholesterolemia on the severity of carbon tetrachloride (CCl4)-induced liver injury. Under baseline conditions, hypercholesterolemic ApoE-/- mice showed increased hepatic oxidative stress (SOD activity/4-hydroxy-2-nonenal immunostaining) and higher hepatic TGF-beta1, MCP-1, and TIMP-1 expression than wild-type control mice. After CCl4 challenge, ApoE-/- mice exhibited exacerbated steatosis (Oil Red O staining), necroinflammation (hematoxylin-eosin staining), macrophage infiltration (F4/80 immunohistochemistry), and fibrosis (Sirius red staining and alpha-smooth muscle actin immunohistochemistry) and more severe liver injury [alanine aminotransferase (ALT) and aspartate aminotransferase] than wild-type controls. Direct correlations were identified between serum cholesterol and hepatic steatosis, fibrosis, and ALT levels. These changes did not reflect the usual progression of the disease in ApoE-/- mice, since exacerbated liver injury was not present in untreated age-paired ApoE-/- mice. Moreover, hepatic cytochrome P-450 expression was unchanged in ApoE-/- mice. To explore potential mechanisms, cell types relevant to liver pathophysiology were exposed to selected cholesterol-oxidized products. Incubation of hepatocytes with a mixture of oxysterols representative of those detected by GC-MS in livers from ApoE-/- mice resulted in a concentration-dependent increase in total lipoperoxides and SOD activity. In hepatic stellate cells, oxysterols increased IL-8 secretion through a NF-kappaB-independent mechanism and upregulated TIMP-1 expression. In macrophages, oxysterols increased TGF-beta1 secretion and MCP-1 expression in a concentration-dependent manner. Oxysterols did not compromise cell viability. Taken together, these findings demonstrate that hypercholesterolemic mice are sensitized to liver injury and that cholesterol-derived products (i.e., oxysterols) are able to induce proinflammatory and profibrogenic mechanisms in liver cells.
Ferré
Natàlia
N
Department of Biochemistry and Molecular Genetics, Liver Unit, Hospital Clínic, Institut d'Investigacions Biomèdiques August Pi i Sunyer, Universitat de Barcelona, Barcelona, Spain.
Martínez-Clemente
Marcos
M
López-Parra
Marta
M
González-Périz
Ana
A
Horrillo
Raquel
R
Planagumà
Anna
A
Camps
Jordi
J
Joven
Jorge
J
Tres
Alba
A
Guardiola
Francesc
F
Bataller
Ramón
R
Arroyo
Vicente
V
Clària
Joan
J
D000818:Animals; D001057:Apolipoproteins E / Q000235:genetics*; D002251:Carbon Tetrachloride / Q000633:toxicity; D056486:Chemical and Drug Induced Liver Injury; D018932:Chemokine CCL2 / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism; D020022:Genetic Predisposition to Disease; D055166:Hepatic Stellate Cells / Q000378:metabolism; D006888:Hydroxycholesterols / Q000378:metabolism; D006937:Hypercholesterolemia / Q000235:genetics* / Q000378:metabolism*; D016209:Interleukin-8 / Q000378:metabolism; D008107:Liver Diseases / Q000235:genetics* / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D016328:NF-kappa B / Q000378:metabolism; D018384:Oxidative Stress / Q000502:physiology*; D013482:Superoxide Dismutase / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000378:metabolism
D001057:Apolipoproteins E; C491768:Ccl2 protein, mouse; D018932:Chemokine CCL2; D006888:Hydroxycholesterols; D016209:Interleukin-8; D016328:NF-kappa B; D053773:Transforming Growth Factor beta1; D002784:Cholesterol; D002251:Carbon Tetrachloride; D013482:Superoxide Dismutase