Proteasome Activity Deregulation in LEC Rat Hepatitis: Following the Insights of Transcriptomic Analysis

Abstract

LEC rats show spontaneous hepatitis and hepatocarcinoma development related to oxidative stress due to abnormal copper accumulation in the liver. We used DNA microarrays bearing 22,012 genes to investigate at the transcriptomic level the progression of the hepatitis in LEC rats in comparison to a control obtained from LEC rats treated with D-penicillamine, a copper chelating agent known to block hepatitis development. Multivariate statistical analyses as partial least square (PLS) regression between transcriptomic data and hepatitis markers in plasma led us to select 483 genes related to hepatitis development in these rats. After a complementary discriminant analysis (PLS-DA), 239 important genes for the separation between the different rat groups were selected. Gene ontology classification revealed an overrepresentation of genes involved in protein metabolism-related functions. More importantly, some genes implicated in proteasome pathway were upregulated. However, analysis of 20S proteasome activity showed that trypsin-like and peptidylglutamyl peptide hydrolase activities were diminished during hepatitis. Because oxidative stress is known to promote the inactivation of the proteasome complex, we propose the deregulation of the proteasome genes expression as a result of oxidative inactivation of proteasome activity during hepatitis in LEC rats. These results bring new insights in the hepatitis and the hepatocarcinogenesis development.

Systems biology approach to Wilson’s disease

“…Another trend reported in the above study of LEC rats was upregulation of protein degradiation machinery along with pathology progression (Marquez-Quinones et al 2007). This observation resonates with the results of Muller and colleagues, who investigated response of cultured hepatocytes HepG2 to high copper load (Muller et al 2007).…”

“…Several groups have investigated molecular mechanisms behind copper-induced pathology by characterizing changes in hepatic mRNA profiles (Ralle et al 2010; Klein et al 2003; Tsubota et al 2010; Huster et al 2007; Marquez-Quinones et al 2007). The precise gene-to-gene comparison of the results is difficult, because studies used different array platforms and the age of animals and the functional state of their liver did not match exactly.…”

“…Nevertheless, overall trends (i.e., the major biological processes affected by copper overload) can be identified and compared. In order to make such comparisons with a minimal bias, we analyzed with the same GeneSifter software the mRNA array data that were relatively similar (Klein et al 2003; Tsubota et al 2010; Marquez-Quinones et al 2007). We specifically focused on the earlier stages of pathology development (i.e., when pathology is not yet apparent or mild) to identify initial, and presumably more specific, effects of copper and to minimize differences between strains that become more apparent with age.…”

“…Additional information was revealed in the mRNA profiling studies where time-dependent progression of hepatitis in the LEC rat was monitored using animals treated with a copper-chelating drug d -penicillamine as a control (Marquez-Quinones et al 2007). This study also included useful evaluation of liver morphology and function.…”

“…Overall, the study has pointed to the upregulation of glutathione-S-transferase P (GSTP) as being characteristic for the stage of hepatitis associated with jaundice development. Among the annotated transcripts the majority (38 out of 59) belong to the “metabolism” category with the most affected metabolic processes being lipid biosynthesis and catabolism, alcohol metabolism and amino-acid biosynthesis (in addition to other less altered pathways) (Marquez-Quinones et al 2007). Altogether, lipid metabolism is emerging as an important pathway to consider in WD pathology.…”