Abstract
Zonation of metabolic activities within specific structures and cell types is a phenomenon of liver organization and ensures complementarity of variant liver functions like protein production, glucose homeostasis and detoxification. To analyze damage and regeneration of liver tissue in response to a toxic agent, expression of liver specific enzymes was analyzed by in situ hybridization in mouse over a 6 days time course following carbon tetrachloride (CCl4) injection. CCl4 mixed with mineral oil was administered to BALB/c mice by intraperitoneal injection, and mice were sacrificed at different time points post injection. Changes in the expression of albumin (Alb), arginase (Arg1), glutaminase 2 (Gls2), Glutamine synthetase (Gs), glucose-6-phosphatase (G6pc), glycogen synthase 2 (Gys2), Glycerinaldehyd-3-phosphat-Dehydrogenase (Gapdh), Cytochrom p450 2E1 (Cyp2e1) and glucagon receptor (Gcgr) genes in the liver were studied by in situ hybridization and qPCR. We observed significant changes in gene expression of enzymes involved in nitrogen and glucose metabolism and their local distribution following CCl4 injury. We also found that Cyp2e1, the primary metabolizing enzyme for CCl4, was strongly expressed in the pericentral zone during recovery. Furthermore, cells in the damaged area displayed distinct gene expression profiles during the analyzed time course and showed complete recovery with strong albumin production 6 days after CCl4 injection. Our results indicate that despite severe damage, liver cells in the damaged area do not simply die but instead display locally adjusted gene expression supporting damage response and recovery.
Highlights
Liver is the central metabolic organ in vertebrates and plays key roles in many physiological processes, including detoxification, synthesis of plasma proteins, glucose homeostasis, as well as utilization and cycling of various nutrients
Tissue sections from all time points were arranged on one slide to ensure equal conditions during in situ hybridization
Gene expression of two genes was visualized in one section using complementary digoxigenin and fluorescein labeled riboprobes, yellow staining for fluorescein labeled probes and violet staining for digoxigenin labeled probes
Summary
Liver is the central metabolic organ in vertebrates and plays key roles in many physiological processes, including detoxification, synthesis of plasma proteins, glucose homeostasis, as well as utilization and cycling of various nutrients. Loss of liver function is the consequence of various liver diseases and toxic damage, and is a major health risk factor. Tissue repair mechanisms are initiated, enabling regeneration of the damaged tissue [1]. E.g. severe damage, viral infections and continuous exposure to toxic chemicals, dysfunctional tissue repair can lead to degenerative liver disease, including liver fibrosis, cirrhosis and hepatocellular carcinoma (HCC). In this study we used the well-known hepatotoxin carbon tetrachloride (CCl4) to induce tissue damage [2, 3] and followed the regeneration of the tissue in a 6 days time course analyzing the expression of key enzymes of major metabolic pathways by in situ hybridization (ISH) to elucidate the interplay between damage response and maintenance of liver function in the functional units of the liver
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