Liver homeostasis is maintained by midlobular zone 2 hepatocytes

The liver is organized into zones in which hepatocytes express different metabolic enzymes. The cells most responsible for liver repopulation and regeneration remain undefined, because fate mapping has only been performed on a few hepatocyte subsets. Here, 14 murine fate-mapping strains were used to systematically compare distinct subsets of hepatocytes. During homeostasis, cells from both periportal zone 1 and pericentral zone 3 contracted in number, whereas cells from midlobular zone 2 expanded in number. Cells within zone 2, which are sheltered from common injuries, also contributed to regeneration after pericentral and periportal injuries. Repopulation from zone 2 was driven by the insulin-like growth factor binding protein 2–mechanistic target of rapamycin–cyclin D1 (IGFBP2-mTOR-CCND1) axis. Therefore, different regions of the lobule exhibit differences in their contribution to hepatocyte turnover, and zone 2 is an important source of new hepatocytes during homeostasis and regeneration.

Pathomorphologic changes of pigs by the spontaneous ochratoxicosis

Today, the actual environmental problem of the agro-industrial complex is the damage to the fodder of vegetable origin, as well as livestock production by mycotoxins – secondary metabolites of mold fungi. Owing to the widespread spread and severe toxic effects on animals and humans, the study of ochratoxins, the main producers of Aspergillus ochraceus and Pennicilium viridicatum, is intensively studied. The pigs are very sensitive to ochratoxins, the effects of which the most pronounced changes develop in the organs of the urinary system, as well as in the gastrointestinal tract, the liver, the immune and nervous systems. Diagnosis of ochratoxicosis should be comprehensive, based on anamnestic data, clinical, pathologoanatomical and chemico-toxicological studies. In the course of the study, the pathoanatomical changes that are developing in the body of sows for ochratoxicosis are studied in detail. Also, a mycological and mycotoxicological study was conducted in which the producer of ochertoxins Aspergillus ochraceus was detected in feeds. The content of ochratoxin A in feed fed to sows varied from 8.32 mg/kg to 85.72 mg/kg, and in the kidneys its concentration was 4.34–48.33 mg/kg. In a pathologoanatomical study in the kidneys, there was a discovery of gialinosis and sclerosis of renal glomeruli, as well as hyaline droplets degeneration, necrotic changes in epithelial proximal tubule, infiltration of interstitium by lymphocytes, macrophages, fibroblasts, focal growth of connective tissue, which was accompanied by the appearance of cystic cavities in 21.4% of animals. In the gastrointestinal tract, acute catarrhal or catarrhal-hemorrhagic inflammation was detected, and in 28.57% of sows the ulcers of the fundus zone of the mucous membrane of the stomach, the development of which was accompanied by massive hemorrhage in the gastrointestinal tract and posthemorrhagic anemia. Alterative (necrotic and degenerative changes) of hepatocytes, which were most pronounced in the periportal zone of the liver lobes, as well as acute congestive hyperemia, stasis in vessels of the microcirculatory bed, focal infiltration of the stroma by lymphocytes and histiocytes, were recorded in the liver. In the peripheral organs of the immune system, necrotic changes in lymphoid cells were recorded, indicating an immunosuppressive effect of ochratoxins.

Obstructive cholestasis induces TNF-α- and IL-1β-mediated periportal downregulation of Bsep and zonal regulation of Ntcp, Oatp1a4, and Oatp1b2

Inverse acinar regulation of Mrp2 and 3 represents an adaptive response to hepatocellular cholestatic injury. We studied whether obstructive cholestasis (bile duct ligation) and LPS treatment affect the zonal expression of Bsep (Abcb11), Mrp4 (Abcc4), Ntcp (Slc10a1), and Oatp isoforms (Slco1a1, Slco1a4, and slco1b2) in rat liver, as analyzed by semiquantitative immunofluorescence. Contribution of TNF-α and IL-1β to transporter zonation in obstructive cholestasis was studied by cytokine inactivation. In normal liver Bsep, Mrp4, Ntcp, and Oatp1a1 were homogeneously distributed in the acinus, whereas Oatp1a4 and Oatp1b2 expression increased from zone 1 to 3. Glutamine synthetase-positive pericentral hepatocytes exhibited markedly lower Oatp1a4 expression than the remaining zone 3 hepatocytes. In cholestatic liver Bsep and Ntcp immunofluorescence in periportal hepatocytes significantly decreased to 66 ± 4% ( P < 0.01) and 67 ± 7% ( P < 0.05), whereas it was not altered in pericentral hepatocytes. Oatp1a4 was significantly induced in hepatocytes with a primarily low expression, i.e., in periportal hepatocytes and in glutamine synthetase-positive pericentral hepatocytes. Likewise, Oatp1b2 was upregulated in periportal hepatocytes. Mrp4 zonal induction was homogeneous. Inactivation of TNF-α and IL-1β prevented periportal downregulation of Bsep. Recruitment of neutrophils and polymorphonuclear cells mainly occurred in the periportal zone. Likewise, IL-1β induction was largely found periportally. No significant transporter zonation was seen following LPS treatment. In conclusion, zonal downregulation of Bsep in obstructive cholestasis is associated with portal inflammation and is mediated by TNF-α and IL-1β. Periportal downregulation of Ntcp and induction of Oatp1a4 and Oatp1b2 may represent adaptive mechanisms to reduce cholestatic injury in hepatocytes with profound downregulation of Bsep and Mrp2.

Assessment of rate of O2 release from single hepatic sinusoids of rats

Characteristics of O2 release from single hepatic sinusoids are described in relation to the sinusoidal O2 inflow for the first time. Microspectroscopic measurement of the rate of O2 release (RO2) from single sinusoids to surrounding hepatocytes was carried out at the edge of the liver of anesthetized rats. The oxyhemoglobin inflow ([HbO2] inflow) into sinusoids, which is a product of sinusoidal blood flow rate and inflowing oxyhemoglobin concentration ([HbO2]), was varied by exchange transfusion of blood with physiological saline. 1) RO2 from single hepatic sinusoids of control rats was fairly constant [0.66 +/- 0.14 (SD) nmol.cm-2.s-1, with 18 sinusoids of 9 rats] over a wide range of [HbO2] inflow (50-200 fmol/s). 2) In the cases of mild anemia, [HbO2] inflow scarcely decreased but RO2 increased, probably because of the increased metabolism of hepatocytes. 3) In the cases of severe anemia, [HbO2] inflow decreased below 50 fmol/s and RO2 decreased accordingly. 4) In all cases no difference was observed between the RO2 values obtained from periportal zone and those from pericentral zone. These results are discussed on the bases of the vascular structure and function of hepatic sinusoids and on the animal model of hemorrhagic shock.

Acinar zonation of the hormonal regulation of cytosolic aspartate aminotransferase in the liver

The zonation of the expression and regulation of the cytosolic aspartate aminotransferase (cAspAT) mRNAs in the liver acinus was investigated in diabetic and/or adrenalectomized rats. Dexamethasone increased cAspAT activity two- to threefold alone and up to sixfold in combination with streptozotocin-induced diabetes. Northern blot analysis showed that the cAspAT mRNAs were increased by those treatments; the effect of streptozotocin was reversed by the administration of insulin. In situ hybridization experiments showed that basal cAspAT mRNAs were uniformly distributed within the liver acinus. However, cAspAT mRNAs were induced by glucocorticoids specifically in the periportal zone and by streptozotocin in a larger area including the periportal and intermediary zone. The alpha 2u-globulin mRNAs which are specifically expressed in the perivenous hepatocytes are also induced by glucocorticoids in this zone, suggesting that the specific regulation of the cAspAT gene by glucocorticoids in the periportal zone is not due to the absence of functional glucocorticoid receptors in the other zones. We conclude that the regulation of the cAspAT housekeeping gene is zone specific in the liver. Furthermore, this zonation depends on the gene and on the type of hormonal or pharmacological treatment.

Lobular patterns of the immunocytochemical localization of enzymes involved in hepatic carbohydrate metabolism

A heterogeneous distribution of many of the enzymes involved in carbohydrate metabolism has been demonstrated within the lobules of the liver. Biochemical studies have demonstrated that hepatocytes in the periportal zone exhibit higher activities of gluconeogenic enzymes, whereas higher activities of glycolytic enzymes are found in cells surrounding the central vein (pericentral). These studies were undertaken to determine the lobular distribution of phosphoenolpyruvate carboxykinase (PEPCK), glycogen synthase (GS) and glycogen phosphorylase (GP) in fed and fasted rats with an immunocytochemical technique using a gold conjugated secondary antibody.

Distribution of hepatic glutaminase activity and mRNA in perivenous and periportal rat hepatocytes

Perivenous and periportal hepatocytes were isolated by the digitonin/collagenase perfusion technique. The specific activity of phosphate-activated glutaminase was 2.33-fold higher in periportal cells than in perivenous cells. Similarly, the relative abundance of glutaminase mRNA was 2.6-fold higher in samples from periportal cells. The distribution of glutaminase activity and mRNA was compared with those for glutamine synthetase (predominantly perivenous) and phosphoenolpyruvate carboxykinase (predominantly periportal). The results suggest that phosphate-activated glutaminase is predominantly expressed in the periportal zone of the liver acinus.