Importance of cell aggregation for expression of liver functions and regeneration demonstrated with primary cultured hepatocytes

Adult rat hepatocytes aggregated to form floating multicellular spheroids when cultured in Primaria dishes, which have a positively charged surface, in serum-free Williams' medium E (WE) supplemented with insulin and epidermal growth factor (EGF). These hormones were essential for maintenance of the spheroids, whereas the size of the spheroids depended on the inoculum cell density. The spheroids retained in vivo levels of expressions of albumin and glucokinase and synthesized scarcely any DNA even in the presence of insulin and EGF. On transfer to type I collagen-coated dishes, the spheroids gradually disaggregated and the cells formed monolayers, in which the expressions of albumin and glucokinase were suppressed and DNA synthesis and hexokinase activity were increased. DNA synthesis of hepatocytes in monolayer culture was maximal 24 hr after transfer of the spheroids, ～80% of the hepatocyte nuclei were labelled with bromodeoxyuridine during culture for 48 hr, and the mitotic index was ～70% after 60 hr. These results suggest that, in spheroids, hepatocytes remained in the G₀ phase, but that when they formed monolayers, they progressed to the G₁ phase and proceeded through the cell cycle in the presence of insulin and EGF. This work shows that the cell cycle of hepatocytes in culture can be manipulated by providing conditions for quiescence as spheroids or growth as monolayers and that the shape of hepatocytes is important for regulating their growth and liver-specific functions. © 1993 Wiley-Liss, Inc.     

Increase of transferrin receptors in hepatocytes during rat liver regeneration

Transferrin receptor in hepatocytes was studied by iron-saturated[125I]transferrin binding. In regenerating rat liver, the receptor was increased 18 hr after partial hepatectomy and decreased at 8 days. The increase of transferrin receptor in hepatocytes may be a marker of proliferation of the cells.     

Expression of the rat prothymosin alpha gene during T-lymphocyte proliferation and liver regeneration.

Prothymosin alpha (ProT alpha) is a widely distributed acidic protein whose function has been related to cell proliferation. We have analyzed the expression of the rat ProT alpha gene in several proliferative systems: concanavalin A (ConA)/interleukin-2-stimulated thymocytes, ConA-stimulated splenic T-lymphocytes, and hepatocytes proliferating during liver regeneration. In these systems, ProT alpha mRNA was detected in all stages of the cell cycle, with maximal increments (2-4-fold) at the beginning of the S phase. By contrast, the mRNAs for proliferating cell nuclear antigen/cyclin and histone H3, two cell-cycle-regulated proteins, were hardly detected in resting cells but increased notably at the G1/S boundary and in the S phase, respectively. Treatment of T-cells with the calcium ionophore A23187 increased ProT alpha mRNA levels 2.5-fold, whereas phorbol 12-myristate 13-acetate, a protein kinase C activator, had no effect on ProT alpha gene expression. Incubation of ConA-stimulated T-cells with hydroxyurea, a DNA synthesis inhibitor, did not decrease the levels of ProT alpha mRNA, indicating that its expression is independent of DNA synthesis. These findings suggest that ProT alpha is required throughout all the stages of the cell cycle, resembling a constitutively expressed gene rather than one strictly involved in cell proliferation.     

Expression of neuritin during liver maturation and regeneration

Cell surface molecules are not only important for cell-cell interactions but also useful for a marker to define cell types and differentiation stages. Unlike hematopoietic system in which numerous such antigens have been identified, only a few cell surface molecules have been used to define differentiation stage of hepatocytes. In order to identify such cell surface molecules, we performed DNA microarray analysis using mRNA from fetal hepatocytes in E12.5 and E17.5 mice and cDNAs encoding a membrane protein were selected. Northern blot analysis was employed to confirm the genes upregulated during maturation of fetal hepatocytes and neuritin, a GPI-anchored protein, was found as a membrane protein expressed in hepatocytes, but not in nonparenchymal cells. Its expression increased along with liver development and the maximum expression was achieved from the neonatal to adult stage. The neuritin protein was localized in sinusoidal lumen of hepatocytes in adult liver. Partial hepatectomy transiently downregulated the expression of neuritin. The expression of neuritin mRNA in C/EBPalpha deficient liver was reduced to about 50% of that of wild type mice. Thus, neuritin expression is well correlated to the maturation of hepatocytes and can be a useful tool to define the differentiation stage of hepatocytes.     

Changes in lipoprotein binding and uptake by hepatocytes during rat liver regeneration

The binding and uptake of cholesterol enriched lipoproteins by isolated hepatocytes was decreased at 16 hours after partial hepatectomy, with a tendency to return to control values as the regeneration proceeds. The number of lipoprotein binding sites of total cellular membranes remained similar to control at 16 and 24 hours. The plasma lipoprotein pattern, determined by electrophoretic analysis, showed a lower per cent of very low density lipoproteins (VLDL) and a higher per cent of low density lipoproteins (LDL) at 16 and 24 hours post-partial hepatectomy. At these times, plasma lecithin: cholesterol acyltransferase (LCAT) activity was decreased. It is intriguing to suggest that the regenerating liver could regulated the blood lipoprotein pattern and the uptake of lipoproteins by modulating the surface expression of the receptors.     

STAT3 contributes to the mitogenic response of hepatocytes during liver regeneration

STAT3 is rapidly induced during liver regeneration in an interleukin 6 (IL-6)-dependent fashion, and IL-6 is required for normal liver regeneration. We wanted to know whether STAT3 was also required for liver regeneration but disruption of the STAT3 gene during embryonic stages causes lethality. Therefore, an albumin promoter-driven Cre-loxP recombination system was used to create a STAT3 deletion in the adult mouse liver to study the role of STAT3 in liver regeneration. After partial hepatectomy, there was virtually no STAT3 RNA or protein induction in Alb(+) STAT3(fl/fl) livers. STAT3 DNA binding activity was also absent in Alb(+) STAT3(fl/fl) livers. Unlike in control livers, STAT1 was activated in STAT3 conditional-mutant livers posthepatectomy. Hepatocyte DNA synthesis at 40 h posthepatectomy in Alb(+) STAT3(fl/fl) livers was reduced to approximately one-third of the control. Alb(+) STAT3(fl/fl) livers had abnormalities in immediate-early gene activation that largely correlated with but were not identical to those seen in IL-6-/- livers. G(1) phase cyclins including cyclins D1 and E had lower expression levels in Alb(+) STAT3(fl/fl) livers, indicating an abnormal G(1) to S phase transition. Therefore, STAT3 accounts for part of the DNA synthetic response of the hepatocytes during liver regeneration, which cannot be compensated for by induction of STAT1. Normal activation of the MAPK pathway in Alb(+) STAT3(fl/fl) livers reinforces the fact that at least part of the effect of IL-6 on hepatocyte proliferation is not mediated by STAT3. This study provides the first in vivo evidence that STAT3 promotes cell cycle progression and cell proliferation under physiological growth conditions.     

Molecular dissection of gp130-dependent pathways in hepatocytes during liver regeneration

Interleukin-6 (IL-6) via its signal transducer gp130 is an important mediator of liver regeneration involved in protecting from lipopolysaccharide (LPS)-induced liver injury after partial hepatectomy (PH). Here we generated mice either defective (Delta) in hepatocyte-specific gp130-dependent Ras or STAT activation to define their role during liver regeneration. Deletion of gp130-dependent signaling had major impact on acute phase gene (APG) regulation after PH. APG expression was blocked in gp130-DeltaSTAT animals, whereas gp130-DeltaRas mice showed an enhanced APG response and stronger SOCS3 regulation correlating with delayed hepatocyte proliferation. To define the role of SOCS3 during hepatocyte proliferation, primary hepatocytes were co-stimulated with IL-6 and hepatocyte growth factor. Higher SOCS3 expression in gp130-DeltaRas hepatocytes correlated with delayed hepatocyte proliferation. Next, we tested the impact of LPS, mimicking bacterial infection, on liver regeneration. LPS and PH induced SOCS3 and APG in all animal strains and delayed cell cycle progression. Additionally, IL-6/gp130-dependent STAT3 activation in hepatocytes was essential in mediating protection and thus required for maximal proliferation. Unexpectedly, oncostatin M was most strongly induced in gp130-DeltaSTAT animals after PH/LPS-induced stress and was associated with hepatocyte proliferation in this strain. In summary, gp130-dependent STAT3 activation and concomitant SOCS3 during liver regeneration is involved in timing of DNA synthesis and protects hepatocyte proliferation during stress conditions.     

Analysis of the role of the integrin signaling pathway in hepatocytes during rat liver regeneration

To explore the role of the integrin signaling pathway in hepatocytes during rat liver regeneration, the integrin signaling pathway-related gene expression profile in hepatocytes of regenerative liver was detected using Rat Genome 230 2.0 array. The chip data showed that 265 genes of the integrin signaling pathway were included by Rat Genome 230 2.0 array and 132 genes showed significant expression changes in hepatocytes of regenerative liver. The numbers of up-, down- and up/down-regulated genes were 110, 15 and 7 respectively. In addition, bioinformatics and systems biology methods were used to analyze the role of the integrin signaling pathway in hepatocytes. The analysis of gene synergy value indicated that paths 1, 8, 12, and 15 promoted hepatocyte proliferation at the priming phase of liver regeneration; paths 1, 3, 8, and 12–15 enhanced hepatocyte proliferation at the progressing phase; paths 11 and 14 promoted hepatocyte proliferation, while paths 12 and 13 reduced hepatocyte proliferation at the terminal phase. Additionally, the other 8 paths (2, 4, 5–7, 9–10, and 16) were not found to be related to liver regeneration. In conclusion, 132 genes and 8 cascades of the integrin signaling pathway participated in regulating hepatocyte proliferation during rat liver regeneration.     

Change in the number of epidermal growth factor receptors of hepatocytes during liver regeneration in rats

The number of epidermal growth factor (EGF) receptors was determined for rat's hepatocytes under condition of their regeneratory proliferation, following a partial hepatectomy. In the normal hepatocytes two classes of EGF-receptors are distinguished, with high and low affinity, respectively. As early as 2 hours after the partial hepatectomy the total number of EGF-receptors sharply decreases, those with high affinity being not determined at all. The patterns of autophosphorylation of EGF-receptors with low affinity, examined in regenerating liver hepatocytes, remained the same as in the intact liver: their kinase activity was EGF-dependent, tyrosine residues of receptor molecules, with molecular mass equal to 150-170 kDa, underwent phosphorylation.     

Age-related decline of inducible nitric oxide synthase gene expression in primary cultured rat hepatocytes

Hepatocytes exhibit a non-specific immune response by expressing the enzyme inducible nitric oxide (NO) synthase (iNOS, NOS2) through the stimulation of a mixture of cytokines, or a single cytokine such as interleukin-1beta. We examined the age-dependent inducibility of the iNOS gene expression and the capacity of NO production in response to lipopolysaccharide (LPS) or interleukin-1beta (IL-1beta) in primary cultured rat hepatocytes that were isolated from the livers of rats, 3 (young) and 24 (aging) months of age. NO production (NO2-), indicating iNOS activity, was much higher in the young rat hepatocytes following stimulation with LPS or IL-1beta. Likewise, in the young hepatocytes, Western blot analyses showed much higher protein levels in the iNOS expression; it was also a little higher in mRNA levels that were analyzed by RT-PCR. Furthermore, after stimulation with IL-1beta, the levels of transactivation of nuclear factor-KB (NF-kappaB) that were involved in the induction of the iNOS gene were reduced without a significant difference in the aged cells. Therefore, the decrease of NO formation in the aged hepatocytes was due to the belated and incomplete inducibility of the iNOS protein expression, together with a minor contribution of the reduced-transactivation of NF-kappaB. These results suggest that the age-related decline of the iNOS gene expression in primary rat hepatocytes may be associated with the increased incidence of many infective diseases with aging.     

细胞外基质相关基因在大鼠肝再生中表达模式分析

细胞外基质具有维持细胞极性、调节细胞粘附、增殖、组织器官形态、发生、分化等功能。为了进一步在基因转录水平了解细胞外基质在大鼠肝再生中变化和作用, 用搜集网站资料和查阅相关论文等方法获得细胞外基质基因, 用Rat Genome 230 2.0芯片检测它们在大鼠再生肝中表达情况, 用真、假手术比较方法确定肝再生相关基因。初步证实上述97个基因与肝再生相关。其中, 肝再生启动(部分肝切除(parital hepatectomy, PH)后0.5~4 h)、G0/G1过渡(PH后4~6 h)、细胞增殖(PH后6~66 h)、细胞分化和组织结构功能重建(PH后72~168 h)等4个阶段起始表达的基因数为49、19、73、5, 基因总表达的次数为84、51、369、144, 表明相关基因主要在肝再生启动阶段起始表达, 在不同阶段发挥作用。它们表达的相似性分为均上调、上调占优势、均下调、下调占优势、上调和下调相近等5类, 涉及38、21、21、10和7个基因, 共上调411次, 下调186次, 分为24种表达模式, 表明肝再生中细胞生理生化活动具有阶段性、多样性和复杂性。根据细胞外基质相关基因在肝再生中表达变化推测, 肝再生前期纤粘连蛋白形成相关基因表达增强, 肝再生中期胶原形成相关基因表达增强。     

Expression and localization of regenerating gene I in a rat liver regeneration model

Regenerating gene (Reg) I has been identified as a regenerative/proliferative factor for pancreatic islet cells. We examined Reg I expression in the regenerating liver of a rat model that had been administered 2-acetylaminofluorene and treated with 70% partial hepatectomy (2-AAF/PH model), where hepatocyte and cholangiocyte proliferation was suppressed and the hepatic stem cells and/or hepatic progenitor cells were activated. In a detailed time course study of activation of hepatic stem cells in the 2-AAF/PH model, utilizing immunofluorescence staining with antibodies of Reg I and other cell-type-specific markers, we found that Reg I-expressing cells are present in the bile ductules and increased during regeneration. Reg I-expressing cells were colocalized with CK19, OV6, and AFP. These results demonstrate that Reg I is significantly upregulated in the liver of the 2-AAF/PH rat model, accompanied by the formation of bile ductules during liver regeneration.     

Expression profiles of the organic acid metabolism-associated genes during rat liver regeneration

In this study, 55 of the organic acid metabolism-involved genes were primarily confirmed to be associated with liver regeneration (LR) by bioinformatics and gene expression profiling analysis. Number of the initially and totally expressed genes occurring in initiation phase of LR, G₀/G₁, cell proliferation, cell differentiation and liver tissue structure-function reconstruction were 21, 5, 33, 1 and 40, 20, 174, 44, respectively, illustrating that genes were initially expressed mainly in initiation stage, and worked in different phases. 151 times up-regulation and 114 times down-regulation as well as 14 types of expression patterns showed the diversification and complication of genes expression changes. It is inferred from the above gene expression changes and patterns that acetate biosynthesis enhanced at forepart, propionate biosynthesis at forepart, prophase and early metaphase, pyruvate biosynthesis at forepart, metaphase and anaphase, succinate biosynthesis at forepart and anaphase; malate biosynthesis in metaphase and N-acetylneuraminate biosynthesis at 36, 66 and 96 h. Whereas, carnitine biosynthsis attenuates at forepart and prophase, enhancement at middle metaphase; isocitrate in the forepart, quinolinate at forepart and early metaphase, creatine at early metaphase and fumarate at anaphase perform the restrained biosynthesis, respectively; catabolisms of propionate and pyruvate were depressed in metaphase.     

Prolactin influences the circadian rhythm of lipogenesis in primary cultured hepatocytes

Hepatocytes from male Syrian hamsters were cultured in the presence of insulin and assayed for lipogenesis by following (14C)acetate incorporation into total cell lipid at 4 hourly intervals over a 48-h period. Circadian rhythms of lipogenic activity were observed on days 2 and 3 of culture. Although the phases of the rhythms were similar, the amplitude of the peak levels of lipogenesis declined from day 2 to 3. Addition of prolactin to the culture reversed this decline when introduced at specific times relative to the lipogenic peaks. Prolactin more than doubled lipogenesis only at the daily peaks of lipogenic activity and only when added to culture 20 h before the times of peak lipogenesis. The results are the first to demonstrate important roles for circadian rhythms and a direct prolactin stimulation in the regulation of lipogenesis in primary hepatocyte culture.