Comparisons of the chemokines’ and cytokines’ cycle threshold values in the liver and in the isolated cells

While the increases in the levels of mRNA specific to particular chemokines and cytokines were indicative of the alterations in expression of single genes that were upregulated after irradiation of liver tissues and cells that had been isolated from the liver, comparisons of the cycle threshold (Ct) values provided indirect indications of the relative levels of gene expression for the chemokines, chemokine receptors and cytokines in the liver tissue, hepatocytes and in the LMFs before treatment. Furthermore, it may provide additional insights into the reasons underlying the discrepancies between the magnitudes of the changes induced by gamma-irradiation in vivo and those induced by irradiating single cell populations in vitro. The Ct values showed that the relative abundance of specific mRNA in the liver tissue was lower, but that the kinetics of the declines in the Ct values, that is, the increases in the amounts of specific mRNA, were similar.

Figure 19: Changes in the levels of messenger ribonucleic acid (mRNA) expression for (a) the CXC chemokines, (b) the CC chemokines and (c) interleukin (IL)-1 beta and IL-6 in liver myofibroblasts (LMFs) at

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real time-polymerase chain reaction data that are presented as fold changes in the mRNA expression levels were normalised using two housekeeping genes, namely, beta-actin and ubiquitin C, and the control value was set at one. The data are presented as means ± standard errors of the mean from three separate experiments carried out in duplicate, and these were compared with those from sham-irradiated cells at each time point (*P < 0.05, according to a one-way analysis of variance).

Abbreviation: IL, interleukin.

The CXCL2 and CXCL5 genes were constitutively expressed in isolated untreated LMFs with the highest mRNA expression in these cells, followed by hepatocytes and liver tissue. In contrast, the mRNA-level of CXCL1 gene was highest in the untreated hepatocytes, followed by LMFs and the hepatic tissue. The constitutive level of the chemokine genes was low in the liver tissue, and irradiation upregulated the expression of the chemokine genes by about 100-fold in the liver tissue and it upregulated the expression of the chemokine genes by about 10-fold in the LMFs, which was associated with a strong constitutive expression of these genes in isolated LMFs. The transcriptional level of the CXCL1 was higher in the untreated control hepatocytes (35 ± 5.2-fold) and at 3 hours (21 ± 3.1-fold) after the irradiation of the hepatocytes, and it was higher in the untreated control LMFs (11.5 ± 2.2-fold) and at 3 hours (33.4 ± 7.1-2.2-fold) after the irradiation of the LMFs, relative to sham-irradiated livers. The CXCL2 gene was more strongly expressed in the untreated control hepatocytes (15 ± 1.2-fold) and at 3 hours (29 ± 3.1-fold) after the irradiation of the hepatocytes, and it was higher in the untreated control LMFs (98 ± 17-fold) and at 3 hours (565 ± 97.1-fold) after the irradiation of the LMFs compared with the non-irradiated control livers. The mRNA-level of the CXCL5 gene was higher in the untreated control hepatocytes (5 ± 1.2-fold) and at 3 hours (9 ± 3.1-fold) after the irradiation of the hepatocytes, and it was higher in the untreated control LMFs (65.5 ± 8.2-fold) and at 3 hours (668.4 ± 64.6-fold) after the irradiation of the LMFs compared with the non-irradiated control livers (Fig. 20). Of the chemokine genes, the MCP-1/CCL2 gene was constitutively expressed and, compared with the sham-irradiated control livers, its level of expression was highest in the untreated control LMFs (229 ± 18-fold), followed by its expression in the untreated control hepatocytes (2 ± 0.18-fold). The expression of the gene for MCP-1/CCL2 increased in the LMFs at 3 hours after irradiation (982 ± 78-fold) and in the liver (Figs. 15 & 20) after irradiation, compared with the sham-irradiated livers, but no change was evident in the irradiated hepatocytes. The level of CXCR2 gene expression was higher in the isolated hepatocytes than in the sham-

Figure 20: The declines in the cycle threshold (Ct) values for CXCL1, CXCL2, CXCL5, CCL2, CCL7, CXCR2, CCR2, IL-1 beta and IL-6 in irradiated and sham-irradiated control rat livers, hepatocytes and liver myofibroblasts. The data were obtained from real-time polymerase chain reaction analysis of the total ribonucleic acid extracted from control and irradiated livers and from isolated liver cells after gamma irradiation.

The data are representative of three experiments performed in duplicate, and the means ± the standard errors of the means are shown for each time point.

Abbreviations: Ct, cycle threshold; IL, interleukin; Hep, hepatocytes; LMF, liver myofibroblasts.

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irradiated liver tissue whereas no such difference was detected in the expression of the CCR2 gene between the isolated hepatocytes and the sham-irradiated liver tissue. The levels of gene expression within the isolated hepatocytes and within the LMFs differed considerably, but some chemokine genes were constitutively expressed. Moreover, the mRNA-level of these genes induced in hepatic tissue (Fig. 14 & 15) and in the LMFs (Fig. 19) after irradiation, but no considerable increases in the gene expression levels were observed in the isolated hepatocytes (Fig. 18). Similar observations were apparent in relation to mRNA-levels of the IL-1 beta and IL-6 genes. Compared with the sham-irradiated control liver tissue, the untreated control LMFs displayed a high IL-1 beta (3.6 ± 0.7-fold) gene expression level that increased at 3 hours (13.4 ± 1.2-fold) after irradiation, and they showed a very high level of expression of the IL-6 gene (159.6 ± 32-fold) that increased at 3 hours after irradiation (206 ± 51-fold). The CXCR-2 and CCR2 genes were not detected in the control or in the irradiated LMFs (Fig. 20).