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Regulation of TGF beta gene expression in rat liver intoxicated with carbon tetrachloride
J Armendariz-Borunda1, J M Seyer, A H Kang
1Veterans Administration Medical Center, Memphis, Tennessee 38104.
Abstract:
Transforming growth factor beta (TGF beta) has been implicated as having a central role in the postinflammatory tissue regeneration and fibrosis. To test its potential involvement in events that follow hepatotoxin-mediated liver regeneration and fibrosis, we quantitated changes in the steady-state levels of TGF beta mRNA in parenchymal and nonparenchymal cells at various times after an acute treatment with CCl4, and also compared TGF beta gene expression in these two cell types from livers subjected to chronic CCl4 treatment. The parenchymal and nonparenchymal cells from normal liver contained undetectable amounts of TGF beta mRNA. In contrast, we could readily detect TGF beta specific transcripts in both the parenchymal and nonparenchymal cells after acute injury. Nonparenchymal cells from acutely injured liver contained fivefold greater amounts of TGF beta mRNA, which peaked at 48 h and declined thereafter. In chronically treated rat livers (1, 2, 3, and 7 wk after the initiation of CCl4 treatment), increased expression of TGF beta mRNA was found only in nonparenchymal cells obtained after 2-3 wk of treatment. Strikingly large elevations in the steady-state levels of beta-actin mRNA in CCl4-treated liver were also observed, which may be related to the known regenerative processes associated with acute liver toxicity. Changing dynamics of TGF beta gene expression, therefore, appear to be an important attribute of regenerating liver after acute or chronic CCl4 toxicity.
Insights
Transforming growth factor beta (TGF beta) mRNA levels increase in liver cells after CCl4 injury, particularly in nonparenchymal cells during regeneration. This suggests TGF beta plays a key role in liver repair and fibrosis following toxic insult.
Area of Science:
- Hepatology
- Molecular Biology
- Cell Biology
Background:
- Transforming growth factor beta (TGF beta) is linked to tissue regeneration and fibrosis.
- Its role in hepatotoxin-induced liver injury and regeneration requires further investigation.
Purpose of the Study:
- To quantify TGF beta mRNA levels in parenchymal and nonparenchymal liver cells after acute and chronic carbon tetrachloride (CCl4) exposure.
- To understand the dynamics of TGF beta gene expression during liver regeneration.
Main Methods:
- Acute and chronic CCl4 treatments in rats.
- Isolation of parenchymal and nonparenchymal liver cells.
- Quantification of TGF beta mRNA using steady-state levels.
- Measurement of beta-actin mRNA levels.
Main Results:
- TGF beta mRNA was undetectable in normal liver cells.
- Following acute CCl4 injury, TGF beta mRNA was detected in both cell types, with nonparenchymal cells showing a fivefold increase peaking at 48 hours.
- Chronic CCl4 treatment led to increased TGF beta mRNA only in nonparenchymal cells at 2-3 weeks.
- Elevated beta-actin mRNA levels were observed in CCl4-treated livers, indicating regenerative processes.
Conclusions:
- TGF beta gene expression dynamics are crucial in liver regeneration after acute or chronic CCl4 toxicity.
- Nonparenchymal cells are a significant source of TGF beta during liver injury and repair.
- TGF beta likely plays a role in the fibrotic response following liver damage.