Differential gene expression profiles of acute and chronic injury and recovery in rat liver steatosis-fibrosis/cirrhosis model

Abstract

Microarray analyses of RNA from carbon tetrachloride (CCl4)-administered rat livers were performed to establish a global gene expression profile during acute and chronic intoxication regimens. In an acute intoxication model, a single dose of 1 ml/kg of CCl4 was given by i.p. injection, and the liver samples were obtained after 6 h, 24 h, 48 h, and 2 wk. Histopathologic, biochemical, and immunohistochemical studies enabled the classification of the CCl4 effect into injury (6 h and 24 h) and regeneration (48 h and 2 wk) stages. The expression levels of 5,180 clones on a custom rat gene microarray were analyzed and 587 clones yielded changeable gene expression on at least single time point. One hundred seventy nine clones were classified as injury-specific clones, while 38 clones as regeneration-specific clones. Characteristic gene expression profiles could be associated with CCl4-induced gene expression with the disruption of lipid metabolism, which is known to cause the fatty liver induced by CCl4 treatment. In addition, induction of the transcripts for many ribosomal proteins was detected during the injury stage, particularly at the 24 h time point, despite the previous report of decreased protein synthesis rate upon CCl4 treatment. Several genes with known functions were also identified as CCl4-regulated genes. In the chronic intoxication model, rats received 0.5 ml CCl4/kg three times a week, and the liver samples were obtained after 0, 30, 60, and 90 d of injection. Histopathologic studies of liver tissues enabled the classification of the CCl4 effect into mild and severe fatty liver/steatosis (30 and 60 d, respectively) and fibrosis/cirrhosis (90 d) stages. The expression levels of 4,900 clones on a custom rat gene microarray were analyzed and the results were confirmed by semi-quantitative RT-PCR. Four hundred thirty eight clones were differentially expressed with more than a 1.625-fold difference (which equals 0.7 in log2 scale) at one or more time points. Multiple genes involved in lipid metabolism and ribosome biogenesis showed differential transcript levels upon chronic CCl4 administration, which was previously seen in acute rat model as well. In addition, a total of 149 clones were identified as fibrosis/cirrhosis-specific genes by either fold changes or Significance Analysis of Microarrays. In conclusion, we established a global gene expression profile utilizing microarray analysis in rat liver upon acute or chronic CCl4 administration with a full chronological profile that covers injury and regeneration stage or fatty liver/steatosis and fibrosis/cirrhosis, respectively. These data will provide the insight of specific gene expression profiles that is implicated in the multistep process of fatty liver/steatosis and fibrosis/cirrhosis after acute or chronic hepatotoxin exposure.