Calpain activation is required for homocysteine-mediated hepatic degradation of inhibitor I kappa B alpha.
Hepatic steatosis is a clinical feature observed in severe hyperhomocysteinemic patients. In mice, cystathionine beta synthase (CBS) deficiency, the most common cause of severe hyperhomocysteinemia, is also associated with steatosis, fibrosis and inflammation. Proinflammatory cytokines usually induce apoptosis. However, hyperhomocysteinemia does not increase apoptosis in liver of CBS-deficient mice compared to wild type mice. The aim of the study was to analyze the activation state of the NF-kappaB pathway in liver of CBS-deficient mice and to investigate its possible involvement in anti-apoptotic signals. We analyzed the level of I kappaB alpha in liver of CBS-deficient mice. A co-culture of primary hepatocytes and Kupffer cells was also used in order to investigate how I kappaB alpha degradation occurs in response to homocysteine. We found lower I kappaB alpha level not only in liver of CBS-deficient mice but also in hepatocyte/Kupffer cell co-culture. The homocysteine-mediated I kappaB alpha enhanced proteolysis occurred via calcium-dependent calpains, which was supported by an increased level of calpain activity and a reduced expression of calpastatin in liver of CBS-deficient mice. Intraperitoneal administration of the inhibitor PDTC normalized the expression of two genes induced by NF-kappaB activation, heme oxygenase-1 and cellular inhibitor of apoptosis 2. Moreover, PDTC administration induced an increase of caspase-3 activity in liver of CBS-deficient mice. Our results suggest that hyperhomocysteinemia induces calpain-mediated I kappaB alpha degradation which is responsible for anti-apoptotic signals in liver.
Hamelet
Julien
J
Université Paris Diderot-CNRS, Unit of Functional and Adaptive Biology (BFA), Case 7104, 75205 Paris cedex 13, France.
Couty
Jean-Pierre
JP
Crain
Anne-Marie
AM
Noll
Christophe
C
Postic
Catherine
C
Paul
Jean-Louis
JL
Delabar
Jean-Maurice
JM
Viguier
Mireille
M
Janel
Nathalie
N
D000818:Animals; D017209:Apoptosis / Q000235:genetics; D051017:Apoptosis Regulatory Proteins / Q000235:genetics; D002154:Calpain / Q000096:biosynthesis*; D003541:Cystathionine beta-Synthase / Q000172:deficiency / Q000235:genetics; D005234:Fatty Liver / Q000201:enzymology* / Q000209:etiology* / Q000473:pathology; D015870:Gene Expression; D022781:Hepatocytes / Q000201:enzymology / Q000473:pathology; D006710:Homocysteine / Q000378:metabolism; D020138:Hyperhomocysteinemia / Q000150:complications* / Q000201:enzymology / Q000235:genetics; D020672:I-kappa B Proteins / Q000378:metabolism*; D007728:Kupffer Cells / Q000378:metabolism; D008099:Liver / Q000201:enzymology / Q000473:pathology; D051379:Mice; D008817:Mice, Mutant Strains; D000072000:NF-KappaB Inhibitor alpha; D010766:Phosphorylation
D051017:Apoptosis Regulatory Proteins; D020672:I-kappa B Proteins; C000606205:Nfkbia protein, mouse; D006710:Homocysteine; D000072000:NF-KappaB Inhibitor alpha; D002154:Calpain; D003541:Cystathionine beta-Synthase