Reversal of phenobarbital-induced hyperplasia and hypertrophy in the livers of lpr mice

Clones of aging: When better fitness can be dangerous

The biological and clinical significance of aberrant clonal expansions in aged tissues is being intensely discussed. Evidence is accruing that these clones often result from the normal dynamics of cell turnover in our tissues. The aged tissue microenvironment is prone to favour the emergence of specific clones with higher fitness partly because of an overall decline in cell intrinsic regenerative potential of surrounding counterparts. Thus, expanding clones in aged tissues need not to be mechanistically associated with the development of cancer, albeit this is a possibility. We suggest that growth pattern is a critical phenotypic attribute that impacts on the fate of such clonal proliferations. The acquisition of a better proliferative fitness, coupled with a defect in tissue pattern formation, could represent a dangerous mix setting the stage for their evolution towards neoplasia.

Liver fibrosis

Liver damage leads to an inflammatory response and to the activation and proliferation of mesenchymal cell populations within the liver which remodel the extracellular matrix as part of an orchestrated wound-healing response. Chronic damage results in a progressive accumulation of scarring proteins (fibrosis) that, with increasing severity, alters tissue structure and function, leading to cirrhosis and liver failure. Efforts to modulate the fibrogenesis process have focused on understanding the biology of the heterogeneous liver fibroblast populations. The fibroblasts are derived from sources within and out with the liver. Fibroblasts expressing alpha-smooth muscle actin (myofibroblasts) may be derived from the transdifferentiation of quiescent hepatic stellate cells. Other fibroblasts emerge from the portal tracts within the liver. At least a proportion of these cells in diseased liver originate from the bone marrow. In addition, fibrogenic fibroblasts may also be generated through liver epithelial (hepatocyte and biliary epithelial cell)-mesenchymal transition. Whatever their origin, it is clear that fibrogenic fibroblast activity is sensitive to (and may be active in) the cytokine and chemokine profiles of liver-resident leucocytes such as macrophages. They may also be a component driving the regeneration of tissue. Understanding the complex intercellular interactions regulating liver fibrogenesis is of increasing importance in view of predicted increases in chronic liver disease and the current paucity of effective therapies.

No Increase of Apoptosis in Regressing Mouse Liver after Withdrawal of Growth Stimuli or Food Restriction

In short-term in vivo experiments, liver growth and regression in mice with high (C3H/He), intermediate (B6C3F1) or low (C57BL/6J) susceptibility to hepatocarcinogenesis was compared. Liver growth was induced by dietary administration of phenobarbital (PB; 750 ppm) or nafenopin (NAF; 500 ppm). PB or NAF treatment for 7 days produced moderate increases of liver DNA (15% or 25-28%, respectively) along with pronounced hypertrophy. Liver growth was strongest in C3H/He mice. Cessation of PB or NAF treatment led to a rapid regression of liver hypertrophy. However, the enhanced hepatic DNA content persisted for at least 2 weeks in all mouse strains. Apoptosis was not increased at any time after cessation of treatment in all strains. Food restriction to 60% of the ad libitum intake did not amplify either regression of liver hyperplasia or the occurrence of apoptosis. No strain difference in the occurrence of apoptosis was detected. Mouse hepatocytes in liver regressing after mitogen withdrawal do not enter apoptosis as readily as rat hepatocytes.

Regeneração hepática induzida por ressecção segmentar do fígado, em rato

OBJETIVO: Avaliar a regeneração progressiva do parênquima hepatocitário, nos seus aspectos macro e microscópicos, em pós-operatório imediato e tardio de ressecção segmentar do fígado. MÉTODO: Foram estudados 10 ratos machos albinos da raça Wistar, pesando entre 250 e 300 gramas, submetidos à hepatectomia parcial de lobo esquerdo, com retirada de cerca de 20% da massa total do órgão. Os animais foram divididos aleatoriamente em dois grupos (n=5) para estudo no 7º (Grupo 1) e 21º (Grupo 2) dias pós-operatórios. Decorrido o tempo de acompanhamento, avaliou-se o aspecto macroscópico e microscópico do fígado. RESULTADOS: No Grupo 1, após sete dias, os animais apresentavam a cavidade abdominal com poucas aderências. O fígado mostrava reação cicatricial no local da ressecção, porém seu tamanho já era próximo ao normal. O exame histopatológico mostrou freqüentes sinais de poliploidia dos hepatócitos, além de tecido de granulação frouxo e desordenado, acompanhado de escasso infiltrado de células inflamatórias. O Grupo 2, após 21 dias, mostrava poucas aderências na cavidade abdominal, e o fígado com aspecto e dimensões próximos ao normal. A histologia mostrou tecido cicatricial mais denso, ordenado, sem sinais inflamatórios. Observou-se apenas pequeno grau de poliploidia hepatocitária. CONCLUSÃO: Após remoção cirúrgica de 20% do parênquima hepático houve aumento temporário da renovação celular verificado por poliploidia hepatocitária.

Simple epithelium keratins 8 and 18 provide resistance to Fas-mediated apoptosis. The protection occurs through a receptor-targeting modulation

Keratins 8 and 18 belong to the keratin family of intermediate filament (IF) proteins and constitute a hallmark for all simple epithelia, including the liver. Hepatocyte IFs are made solely of keratins 8 and 18 (K8/K18). In these cells, the loss of one partner via a targeted null mutation in the germline results in hepatocytes lacking K8/K18 IFs, thus providing a model of choice for examining the function(s) of simple epithelium keratins. Here, we report that K8-null mouse hepatocytes in primary culture and in vivo are three- to fourfold more sensitive than wild-type (WT) mouse hepatocytes to Fas-mediated apoptosis after stimulation with Jo2, an agonistic antibody of Fas ligand. This increased sensitivity is associated with a higher and more rapid caspase-3 activation and DNA fragmentation. In contrast, no difference in apoptosis is observed between cultured K8-null and WT hepatocytes after addition of the Fas-related death-factors tumor necrosis factor (TNF) alpha or TNF-related apoptosis-inducing ligand. Analyses of the Fas distribution in K8-null and WT hepatocytes in culture and in situ demonstrate a more prominent targeting of the receptor to the surface membrane of K8-null hepatocytes. Moreover, altering Fas trafficking by disrupting microtubules with colchicine reduces by twofold the protection generated against Jo2-induced lethal action in K8-null versus WT hepatocytes. Together, the results strongly suggest that simple epithelium K8/K18 provide resistance to Fas-mediated apoptosis and that this protection occurs through a modulation of Fas targeting to the cell surface.

Hepatic extramedullary granulopoiesis after treatment with liver-stimulatory xenobiotics, in lpr mice

This study demonstrates that extramedullary hematopoiesis occurs in livers of adult lpr mice and, after treatment with each of three xenobiotic compounds--phenobarbital, cyproterone acetate, and nafenopin--it includes granulopoiesis. lpr mice are used as a model of the human disease systemic lupus erythematosus (SLE). The develop a syndrome very similar to that of human sufferers. In untreated lpr mice, mononuclear white blood cells were discernible in hepatic sinusoidal foci; T and B lymphocytes were distinguished from each other by immunocytochemistry at light microscope level. After treatment with any of the xenobiotic compounds, immunolabeling demonstrated the additional presence of granulocytes in foci, and, at electron microscope level neutrophils, eosinophils and their precursors were clearly recognizable.