Hepatocytes play a pivotal role in both the synthesis and degradation of numerous endogenous biomolecules, thus maintaining metabolic homeostasis, as well as in the conversion and detoxification of xenobiotic compounds. Based on the location of the blood vessels, the terminal branches of the portal and the hepatic (central) veins and on the direction of the blood flow, hepatocytes of each liver lobule can be divided into two subpopulations, an upstream 'periportal' and a downstream 'perivenous' (pericentral) population. Zonal-specific differences in the metabolic capacities of many enzymes or other proteins, and -to a lesser extent ) of their corresponding messenger RNAs, have been subject to extensive studies throughout the last decades.Many enzymes of intermediary metabolism are not distributed uniformly throughout the liver, but are preferentially expressed in either the periportal or the perivenous hepatocyte subpopulation [1][2][3]. Hence, hepatocytes located in either of the two regions have different, often complementary, functions. Whereas, for example, glycolysis is exclusively active in perivenous hepatocytes, key enzymes of gluconeogenesis, the antagonist pathway, are preferentially expressed in periportal hepatocytes [1]. Zonal-specific expression has also been established for enzymes of amino acid and ammonia metabolism, showing, for example, a higher activity of the urea cycle in periportal cells compared to perivenous hepatocytes [3], whereas glutamine synthesis is exclusively active in the perivenous Hepatocytes located in the periportal and perivenous zones of the liver lobule show remarkable differences in the levels and activities of various enzymes and other proteins. To analyze global gene expression patterns of periportal and perivenous hepatocytes, enriched populations of the two cell types were isolated by combined collagenase ⁄ digitonin perfusion from mouse liver and used for microarray analysis. In total, 198 genes and expressed sequences were identified that demonstrated a ‡ 2-fold difference in expression between hepatocytes from the two different zones of the liver. A subset of 20 genes was additionally analyzed by real-time RT-PCR, validating the results obtained by the microarray analysis. Several of the differentially expressed genes encoded key enzymes of intermediary metabolism, including those involved in glycolysis and gluconeogenesis, fatty acid degradation, cholesterol and bile acid metabolism, amino acid degradation and ammonia utilization. In addition, several enzymes of phase I and phase II of xenobiotic metabolism were differentially expressed in periportal and perivenous hepatocytes. Our results confirm previous findings on metabolic zonation in liver, and extend our knowledge of the regulatory mechanisms at the transcriptional level.Abbreviations GS, glutamine synthetase.

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Acute renal failure from ischemia significantly contributes to cardiovascular morbidity and mortality. Extracellular adenosine has been implicated as an anti-inflammatory metabolite particularly during conditions of limited oxygen availability (e.g., ischemia). Because ecto-5-nucleotidase (CD73) is rate limiting for extracellular adenosine generation, this study examined the contribution of CD73-dependent adenosine production to ischemic preconditioning (

Experimentally induced liver tumors in mice harbor activating mutations in either Catnb (␤-catenin) or Ha-ras, according to the carcinogenic treatment. We have now investigated by microarray analysis the gene expression profiles in tumors of the two genotypes. In total, 364 genes or expressed sequences with aberrant expression relative to normal liver were identified, but only 30 of these demonstrated unidirectional changes in both tumor types. Several functional clusters were identified that involve changes in amino acid utilization and ammonia disposition in Catnb-mutated tumors as opposed to alterations in lipid and cholesterol metabolism in Ha-ras-mutated tumors. Moreover, several genes coding for inhibitory molecules within the Wnt-signaling pathway were upregulated in Catnb-mutated tumors, suggesting induction of a negative feedback loop, whereas Ha-ras-mutated tumors showed alterations in the expression of several genes functional in monomeric G-protein signaling. We conclude that mouse hepatoma cells adopt different evolutionary strategies that allow for their selective outgrowth under variable environmental conditions. Human hepatocellular cancers (HCC) lack RAS mutations but are frequently mutated in CTNNB1, the human Catnb ortholog. The set of genes aberrantly expressed in Catnb-mutated mouse tumors was used to screen, by expression profiling, for dysregulation of orthologous genes within a panel of 25 HCCs, of which 10 were CTNNB1-mutated. HCCs with activated ␤-catenin displayed a gene expression profile that was similar to Catnb-mutated mouse tumors but distinct from the other human HCCs. In conclusion, expression fingerprints may be used for diagnostic purposes and potential new therapeutic intervention strategies. If, however, DEN treatment is combined with subsequent chronic administration of the liver tumor promoter phenobarbital (PB) according to a classical initiation-promotion protocol, tumors predominate that lack ras mutations but show activating mutations in the Catnb (␤-catenin) proto-oncogene instead. 3 On histological examination, liver tumors generated in the absence or presence of the tumor promoter PB demonstrate considerable differences in hematoxylin-eosin-stained sections: the former are often basophilic and are generally composed of comparatively small cells, whereas the latter are often eosinophilic and contain larger cells with enlarged nuclei. 4,5 Several additional differences have been described if individual markers were used for discrimination of tumor types including glutamine synthetase (GS), which is strongly increased in expression in Catnb-mutated but undetectable in ras-mutated mouse hepatocytes. 6 This suggests that mutation in either of the two genes produces divergent phenotypes; however, comparative genome-