Normal liver regeneration in p50/nuclear factor kappaB1 knockout mice.

Nuclear factor kappaB (NF-kappaB) is rapidly activated during liver regeneration following partial hepatectomy or carbon tetrachloride (CCl(4))-mediated liver injury and is felt to be important in the antiapoptotic and regenerative responses. After partial hepatectomy, livers of mice deficient in the p50 subunit of NF-kappaB (p50(-/-)) showed a loss of NF-kappaB and decreased STAT3 transcription factor DNA binding activities. However, nuclear levels of the NF-kappaB p65 subunit were increased and peaked earlier in p50(-/-) livers. Both messenger RNA and cytoplasmic protein levels of the NF-kappaB inhibitor IkappaBalpha were lower in p50(-/-) livers, potentially accounting for the increase in p65 protein. Small effects on gene expression posthepatectomy were observed in p50(-/-) livers, but no effects were seen on hepatocyte DNA synthetic or mitotic responses, serum enzyme levels, or overall liver mass restoration. After CCl(4) treatment, hepatocyte DNA synthesis and mitosis and serum enzyme levels were similar in p50(-/-) and p50(+/+) mice, and histologic analysis indicated a slight decrease in overall damage in p50(-/-) livers. After injection of Fas antibody, p50(-/-) livers showed an earlier onset of nuclear changes consistent with apoptosis. These data indicate that absence of p50 affects certain protein and gene activation pathways following partial hepatectomy, CCl(4), and Fas treatment but does not impair overall liver regeneration. Interleukin 6 (IL-6) levels were reduced but still adequate to support regeneration. We hypothesize that increased levels of the NF-kappaB p65 subunit in p50(-/-) livers may provide compensation for the absence of p50, thereby allowing normal liver regeneration and repair following liver injury.

Increased toxin-induced liver injury and fibrosis in interleukin-6-deficient mice.

Interleukin-6 null (IL-6-/-) mice have impaired liver regeneration and increased liver necrosis following partial hepatectomy that is corrected with IL-6 treatment. Following acute carbon tetrachloride (CCl(4)) treatment, we found that IL-6-/- mice developed increased hepatocellular injury and defective regeneration with significant blunting of signal transducer-and-activator of transcription protein 3 (STAT3) and nuclear factor-kappaB (NF-kappaB) activation and reduced hepatocyte DNA synthetic and mitotic responses. After CCl(4) treatment, unlike partial hepatectomy, increased hepatocyte apoptosis was noted in IL-6-/- livers. Pretreatment with IL-6 before CCl(4) reduced acute CCl(4) injury and apoptosis and accelerated regeneration in both IL-6+/+ and -/- livers. Repetitive doses of CCl(4) in the presence or absence of phenobarbital resulted in increased injury and fibrosis in IL-6 -/- compared with +/+ livers. After acute and chronic injury, IL-6-/- livers showed the protracted presence of alpha-smooth muscle actin associated with activated stellate cells, indicating a disturbed response in wound healing that progressed to fibrosis. These data provide evidence for an important role for IL-6 in reducing CCl(4)-induced acute and chronic liver injury and fibrosis.

Liver-specific and proliferation-induced deoxyribonuclease I hypersensitive sites in the mouse insulin-like growth factor binding protein-1 gene.

The insulin-like growth factor binding protein-1 (IGFBP-1) gene is highly expressed in fetal, perinatal, and regenerating liver. Up-regulation is transcriptionally mediated in regenerating liver and occurs in the first few minutes to hours after partial hepatectomy. In transgenic mice a 970-bp region from -776 to +151 of the IGFBP-1 promoter was sufficient for tissue-specific and induced expression of the gene in fetal and hepatectomized livers. However weak and/or poorly regulated expression in some transgenic lines suggested the existence of other regulatory regions. Here, genomic clones containing large regions 5' of the mouse IGFBP-1 gene sequence were isolated, subcloned, and sequenced. Deoxyribonuclease I (DNaseI) hypersensitivity analyses identified clusters of tissue-specific nuclease-sensitive sites in the promoter region, -100 to -300, -2,300, -3,100, and -5,000 along with other weak sites. After partial hepatectomy, enhanced sensitivity and/or novel sites were detected in the -100/-300, -5,000, and -3,100 regions, the promoter region remaining the most hypersensitive. A subset of these sites was present in fetal and perinatal livers. Novel tissue-specific sites that interacted with C/EBP and hepatic nuclear factor 3 (HNF3) transcription factors were identified in the -3,100 region. A hepatectomy-induced DNA binding complex containing the transcription factor USF1 was identified within the -100 to -300 region of the promoter. These results suggested that a complex array of tissue-specific and hepatic proliferation-induced transcription factors combine to regulate both the proximal promoter and more distal regulatory elements of the IGFBP-1 gene.

Liver failure and defective hepatocyte regeneration in interleukin-6-deficient mice.

Liver regeneration stimulated by a loss of liver mass leads to hepatocyte and nonparenchymal cell proliferation and rapid restoration of liver parenchyma. Mice with targeted disruption of the interleukin-6 (IL-6) gene had impaired liver regeneration characterized by liver necrosis and failure. There was a blunted DNA synthetic response in hepatocytes of these mice but not in nonparenchymal liver cells. Furthermore, there were discrete G1 phase (prereplicative stage in the cell cycle) abnormalities including absence of STAT3 (signal transducer and activator of transcription protein 3) activation and depressed AP-1, Myc, and cyclin D1 expression. Treatment of IL-6-deficient mice with a single preoperative dose of IL-6 returned STAT3 binding, gene expression, and hepatocyte proliferation to near normal and prevented liver damage, establishing that IL-6 is a critical component of the regenerative response.