High Responsiveness to Thyroid Hormone of Adult Rat Primary Hepatocytes Cultured on EHS-Gel

The induction of malic enzyme gene expression by triiodothyronine and insulin was severely blunted in rat monolayer hepatocytes cultured on type I collagen compared with that in spherical hepatocytes cultured on a reconstituted basement membrane gel (EHS-gel). Although the mRNA level of thyroid hormone receptor β (TRβ) gradually decreased in the monolayer hepatocytes during culture, the mRNA level in the hepatocytes on EHS-gel was maintained at around the in vivo level. Our results suggest that the maintenance of TRβ mRNA on EHS-gel is responsible for the high responsiveness to thyroid hormone in a hepatocyte culture.     

Growth induction of hepatic stimulator substance in hepatocytes through its regulation on EGF receptors

The cytosolic liver-specific growth factor-hepatic stimulator substance (HSS) has been shown to be able to amplify the rat hepatkocyte proliferation responded to BGF.In order to get more insight into the mechanism,the regulatory effect of HSS on EGF-receptor (EGF-R) and the receptor phosphorylation at molecular level was studied.HSS partially purified from weanling rat liver was given to cultured hepatocytes and its influence on EGF-R specific binding and internalization as well as mRNA expression were investigated.The results showed that preincubation of hepatocytes with HSS could lead to an increase in [^125I]-EGF binding to its receptors and inhibit EGF-induced receptor down-regulation.Furthermore,the overexpression of EGF-R mRNA stimulated by HSS was seen during 2-12 h after the incubation.Additionally,it was demonstrated with human hepatoma SMMC-7721 cells in Western blot that the EGF-R expression and the receptor autophosphorylation were increased with dose/timedependency after HSS treatment.These results strongly suggest that the mechanism of HSS action on hepatocyte growth might be related to its modulation on EGF-R and receptor-mediated signaling transfuction.     

Formation of bile canaliculi in long-term primary cultures of adult rat hepatocytes on permeable membrane: an ultrastructural study

Adult rat hepatocytes were cultured for 15 days on type I collagen-coated permeable membranes in a hormonally defined Waxman's modified medium supplemented with very low concentrations of insulin, glucagon and dexamethasone. Phase contrast examination showed that 15-day-old cultures still formed a regular monolayer of polygonal cells. In similarly aged cultures, intracellular glycogen was abundant and evenly distributed, while steatosis remained very limited. Scanning and transmission electron microscopy showed that well developed bile canaliculi could be observed on the lateral side of the hepatocyte membrane after 4 days of incubation and persisted for 2 weeks. These canalicular structures probably originated from coalescence of membrane invaginations observed in 1-day-old cultures. Transmission electron microscopy showed that the ultrastructure of the cells was very close to that of normal rat hepatocytes in the intact liver. These results suggest that rat hepatocytes cultured under these experimental conditions are able to develop and maintain tissue-specific cytochemical and morphological properties for at least 15 days.     

Lipid accumulation impairs adiponectin-mediated induction of activin A by increasing TGFbeta in primary human hepatocytes

Fatty liver is commonly detected in obesity and has been identified as a risk factor for the progression of hepatic fibrosis in a wide range of liver diseases. Transforming growth factor beta (TGFβ) and activin A, both members of the TGFβ superfamiliy, are central regulators in liver fibrosis and regeneration, and the effect of hepatocyte lipid accumulation on the release of these proteins was studied. Primary human hepatocytes (PHH) were incubated with palmitic acid or oleic acid to increase lipid storage. Whereas activin A and its natural inhibitor follistatin were not affected, TGFβ was 2-fold increased. The hepatoprotective adipokine adiponectin dose-dependently induced activin A while lowering follistatin but did not alter TGFβ. Activin A was markedly reduced in hepatocyte cell lines compared to PHH and was not induced upon adiponectin incubation demonstrating significant differences of primary and transformed cells. In free fatty acid (FFA)-incubated PHH adiponectin-mediated induction of activin A was impaired. Inhibition of TGFβ receptors ALK4/5 and blockage of SMAD3 phosphorylation rescued activin A synthesis in FFA and in TGFβ incubated cells suggesting that FFA inhibit adiponectin activity by inducing TGFβ. To evaluate whether serum levels of activin A and its antagonist are altered in patients with hepatic steatosis, both proteins were measured in the serum of patients with sonographically diagnosed fatty liver and age- and BMI-matched controls. Systemic adiponectin was significantly reduced in patients with fatty liver but activin A and follistatin were not altered. In summary the current data demonstrate that lipid accumulation in hepatocytes induces TGFβ which impairs adiponectin bioactivity, and thereby may contribute to liver injury.     

Rb蛋白功能缺陷降低肝细胞对TGF-β的敏感性

目的：探讨肝细胞内视网膜母细胞瘤（Rb）基因缺陷对转化生长因子-β（TGF-β）诱导的细胞周期静止的影响。方法：分离并培养原代肝细胞,特异性siRNA腺病毒封闭细胞内Rb基因表达后加入TGF-β诱导,然后MTT法检测细胞生长变化,流式细胞仪检测细胞周期变化,并用Western blot和荧光定量逆转录聚合酶反应（FQ-RT-PCR）法检测细胞中pRb、E2F、c-MYC和p16的表达变化。结果：原代培养肝细胞感染Rb-siRNA重组腺病毒后,正常对照肝细胞抑制率高于Rb基因封闭的肝细胞（69.76%,p<0.01）,流式细胞检测可见对照组TGF-β诱导后处于G1期的肝细胞数明显增多（99.80%,p<0.05）,而在Rb基因封闭组中,TGF-β诱导后各细胞周期分布与未诱导的正常肝细胞基本一致。Western blotting检测可见48h时对照组TGF-β诱导后,E2F和c-MYC蛋白表达减少而p16高表达,Rb基因封闭组TGF-β诱导后c-MYC表达减少而p16表达增高。结论：TGF-β可诱导肝细胞静止于G1期,而Rb基因功能缺陷的肝细胞对TGF-β的诱导敏感性显著降低。     

The importance of physiological oxygen concentrations in the sandwich cultures of rat hepatocytes on gas‐permeable membranes

Oxygen supply is a critical issue in the optimization of in vitro hepatocyte microenvironments. Although several strategies have been developed to balance complex oxygen requirements, these techniques are not able to accurately meet the cellular oxygen demand. Indeed, neither the actual oxygen concentration encountered by cells nor the cellular oxygen consumption rates (OCR) was assessed. The aim of this study is to define appropriate oxygen conditions at the cell level that could accurately match the OCR and allow hepatocytes to maintain liver specific functions in a normoxic environment. Matrigel overlaid rat hepatocytes were cultured on the polydimethylsiloxane (PDMS) membranes under either atmospheric oxygen concentration [20%‐O₂ (+)] or physiological oxygen concentrations [10%‐O₂ (+), 5%‐O₂ (+)], respectively, to investigate the effects of various oxygen concentrations on the efficient functioning of hepatocytes. In parallel, the gas‐impermeable cultures (polystyrene) with PDMS membrane inserts were used as the control groups [PS‐O₂ (?)]. The results indicated that the hepatocytes under 10%‐O₂ (+) exhibited improved survival and maintenance of metabolic activities and functional polarization. The dramatic elevation of cellular OCR up to the in vivo liver rate proposed a normoxic environment for hepatocytes, especially when comparing with PS‐O₂ (?) cultures, in which the cells generally tolerated hypoxia. Additionally, the expression levels of 84 drug‐metabolism genes were the closest to physiological levels. In conclusion, this study clearly shows the benefit of long‐term culture of hepatocytes at physiological oxygen concentration, and indicates on an oxygen‐permeable membrane system to provide a simple method for in vitro studies. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:1401–1410, 2014     

两种原代树鼩肝细胞的分离和培养方法的研究

目的 探讨体外原代培养树嗣肝细胞的分离方法.方法 以成年树鼩和新生树鼦做为肝供体,分别采用体外两步灌流法和Percoll梯度液离心方法获取肝细胞并进行体外培养;以台盼蓝染色法测细胞存活率,在相差倒置显微镜下观察细胞形态变化,MTT法测培养细胞活性,并采用PAS染色法鉴定.结果 分离收获成年树鼩肝细胞较新生树鼩肝细胞存活率高;培养过程中,新生树胸肝细胞较成年树鼩肝细胞生长快,增殖能力强,具有统计学意义;PAS染色观察,新生树鼩和成年树鼩的肝细胞中充满大量糖原颗粒,两者差异无显著性.结论 两种方法均可用于原代树鼩肝细胞的体外培养.     

Structural modeling and biochemical studies reveal insights into the molecular basis of the recognition of β‐2‐microglobulin by antibody BBM.1

Human β‐2‐microglobulin (β2m) is the light chain of human leucocyte antigen‐I (HLA‐I). It can disassociate from HLA‐I and accumulate to cause serious dialysis‐related amyloidosis (DRA) in long‐term hemodialysis patients. Monoclonal antibody (mAb) BBM.1 can recognize both free‐form and HLA‐I associated β2m. It can be used for specific elimination of β2m from serum and can induce apoptosis of several types of tumor cells, and thus has great therapeutic potential. In this study, we constructed structural models of the BBM.1 Fv (fragment of the variable domain) and the BBM.1 Fv‐β2m complex, followed by biochemical evaluation. Analysis of the optimal complex model reveals that the previously identified immunodominant residues Glu⁴⁴ and Arg⁴⁵ of β2m have direct interactions with BBM.1, while Asp³⁸ exerts its function mainly via stabilization of Arg⁴⁵. In addition, Arg⁸¹ of β2m is a newly identified immunodominant residue to have direct interaction with BBM.1. Further modeling study shows no steric conflict between the antibody and the HLA‐I heavy chain. These results provide insights into the molecular basis of the recognition of β2m by BBM.1 and explain why BBM.1 can bind both free‐form and HLA‐1 associated β2m. This information could be exploited in the engineering and improvement of BBM.1 and the development of other β2m‐targeting mAbs for therapeutic purposes. Copyright © 2009 John Wiley & Sons, Ltd.     

hβ2m/HLA-B2704双转基因小鼠的制备及β2m对HLA-B2704表达的影响

制备hβ2m HLA B2 70 4双转基因小鼠 ,研究hβ2m对HLA B2 70 4表达的影响 .通过hβ2m转基因小鼠和HLA B2 70 4转基因小鼠交配 ,出生动物及后代经PCR初步筛选 ,采用Southern杂交对经PCR初步筛选的hβ2m HLA B2 70 4双转基因阳性小鼠基因组DNA标本作进一步鉴定 .阳性者进行RT PCR和流式细胞光度术检测其在mRNA和蛋白水平的表达 .hβ2m阳性小鼠和HLA B2 70 4阳性小鼠交配 ,生仔鼠 6 7只 ,其中 2 8只仔鼠同时整合hβ2m和HLA B2 70 4基因 .Southern杂交证实 ,阳性鼠同时都含有hβ2m和HLA B2 70 4基因 .阳性小鼠的皮肤、结肠、睾丸和脾脏组织中均有HLA B2 70 4和hβ2m基因的mRNA表达 ,其外周血淋巴细胞膜上HLA B2 70 4基因的蛋白表达为 35 87% ,在HLA B2 70 4单转基因小鼠外周血淋巴细胞膜上HLA B2 70 4基因的蛋白表达为 7 87% (Histogramsta tistics) .成功地制备了hβ2m HLA B2 70 4双转基因小鼠 .在hβ2m HLA B2 70 4双转基因小鼠的外周血淋巴细胞膜上 ,HLA B2 70 4基因在蛋白水平表达较高 ,而在HLA B2 70 4单转基因小鼠中则表达不明显 .hβ2m可与HLA B2 70 4重链分子结合 ,稳定和增高其在淋巴细胞膜上的表达     

Engineering hepatocyte functional fate through growth factor dynamics: the role of cell morphologic priming.

We have reported previously that cellular stimulation induced by variable mechanochemical properties of the extracellular microenvironment can significantly alter liver-specific function in cultured hepatocytes (Semler et al., Biotech Bioeng 69:359-369, 2000). Cell activation via time-invariant presentation of biochemical growth factors was found to either enhance or repress cellular differentiation of cultured hepatocytes depending on the mechanical properties of the underlying substrate. In this work, we investigated the effects of dynamic growth factor stimulation on the cell growth and differentiation behavior of hepatocytes cultured on either compliant or rigid substrates. Specifically, hepatotrophic growth factors (epidermal and hepatocyte) were either temporally added or withdrawn from hepatocyte cultures on Matrigel that was crosslinked to yield differential degrees of mechanical compliance. We determined that the functional responsiveness of hepatocytes to fluctuations in GF stimulation is substrate specific but only in conditions in which the initial mechanochemical environment induced significant cell morphogenesis. Our studies indicate that in conditions under which hepatocytes adopted a "rounded" phenotype, they exhibited increased levels of differentiated function upon soluble stimulation and markedly decreased function upon the depletion of GF stimulation. In contrast, hepatocytes that assumed a "spread" phenotype exhibited slightly increased function upon the depletion of GF stimulation. By examining the functional responsiveness of hepatocytes of differential morphology to varied fluctuations in GF activation, insights into the ability of cell shape to "prime" hepatocyte behavior in dynamic microenvironments were elucidated. We report on the possibility of uncoupling and, thus, selectively manipulating, the concerted contributions of GF-induced cellular activation and substrate- and GF-induced cell morphogenesis toward induction of cell function.     

Development of hepatocyte spheroids immobilization technique using alternative encapsulation method

Primary hepatocytes of small animals such as rat and rabbit were often used for the study of extracorporeal liver support systems. Freshly isolated rat hepatocytes form spheroids within two days when cultivated as suspension in spinner vessels. These spheroids showed enhanced liver specific functions and more differentiated morphology compared to hepatocytes cultured as monolayers. However, shear stress caused by continuous agitation deteriorated spheroids gradually. In this work we immobilized spheroids to prolong liver specific activities. First, hepatocyte spheroids were suspended in collagen solution containing calcium chloride and then dropped into alginate solution. A thin layer of calcium alginate was formed around the droplet and then was removed after the inner collagen was gelled by treatment of sodium citrate buffer. Spheroids embedded in collagen-gel bead maintained liver specific functions such as albumin secretion rate longer than hepatocyte spheroids exposed to shear stress. Therefore, we suggest that this immobilization technique may offer an effective long-term hepatocyte cultivation and facilitate the development of a bioartificial liver support device.     

Gas‐permeable membranes and co‐culture with fibroblasts enable high‐density hepatocyte culture as multilayered liver tissues

To engineer reliable in vitro liver tissue equivalents expressing differentiated hepatic functions at a high level and over a long period of time, it appears necessary to have liver cells organized into a three‐dimensional (3D) multicellular structure closely resembling in vivo liver cytoarchitecture and promoting both homotypic and heterotypic cell–cell contacts. In addition, such high density 3D hepatocyte cultures should be adequately supplied with nutrients and particularly with oxygen since it is one of the most limiting nutrients in hepatocyte cultures. Here we propose a novel but simple hepatocyte culture system in a microplate‐based format, enabling high density hepatocyte culture as a stable 3D‐multilayer. Multilayered co‐cultures of hepatocytes and 3T3 fibroblasts were engineered on collagen‐conjugated thin polydimethylsiloxane (PDMS) membranes which were assembled on bottomless frames to enable oxygen diffusion through the membrane. To achieve high density multilayered co‐cultures, primary rat hepatocytes were seeded in large excess what was rendered possible due to the removal of oxygen shortage generally encountered in microplate‐based hepatocyte cultures. Hepatocyte/3T3 fibroblasts multilayered co‐cultures were maintained for at least 1 week; the so‐cultured cells were normoxic and sustained differentiated metabolic functions like albumin and urea synthesis at higher levels than hepatocytes monocultures. Such a microplate‐based cell culture system appears suitable for engineering in vitro miniature liver tissues for implantation, bioartificial liver (BAL) development, or chemical/drug screening. © 2011 American Institute of Chemical Engineers Biotechnol. Prog., 2011.     

Primary rat hepatocyte culture on 3D nanofibrous polymer scaffolds for toxicology and pharmaceutical research

Primary rat hepatocytes are a widely used experimental model to estimate drug metabolism and toxicity. In currently used two‐dimensional (2D) cell culture systems, typical problems like morphological changes and the loss of liver cell‐specific functions occur. We hypothesize that the use of polymer scaffolds could overcome these problems and support the establishment of three‐dimensional (3D) culture systems in pharmaceutical research. Isolated primary rat hepatocytes were cultured on collagen‐coated nanofibrous scaffolds for 7 days. Cell loading efficiency was quantified via DNA content measurement. Cell viability and presence of liver‐cell‐specific functions (albumin secretion, glycogen storage capacity) were evaluated. The activity of liver‐specific factors was analyzed by immunofluorescent staining. RNA was isolated to establish quantitative real‐time PCR. Our results indicate that primary rat hepatocytes cultured on nanofibrous scaffolds revealed high viability and well‐preserved glycogen storage. Albumin secretion was existent during the entire culture period. Hepatocytes remain HNF‐4 positive, indicating highly preserved cell differentiation. Aggregated hepatocytes re‐established positive signaling for Connexin 32, a marker for differentiated hepatocyte interaction. ZO‐1‐positive hepatocytes were detected indicating formation of tight junctions. Expression of cytochrome isoenzymes was inducible. Altogether the data suggest that nanofibrous scaffolds provide a good in vitro microenvironment for neo tissue regeneration of primary rat hepatocytes. Biotechnol. Bioeng. 2011; 108:141–150. © 2010 Wiley Periodicals, Inc.     

Generating low immunogenic pig pancreatic islet cell clusters for xenotransplantation

Xenotransplantation of pancreatic islets offers a promising alternative to overcome the shortage of allogeneic donors. Despite significant advances, either immune rejection or oxygen supply in immune protected encapsulated islets remains major bottlenecks for clinical application. To decrease xenogeneic immune responses, we generated tissue engineered swine leucocyte antigen (SLA)‐silenced islet cell clusters (ICC). Single‐cell suspensions from pancreatic islets were generated by enzymatic digestion of porcine ICCs. Cells were silenced for SLA class I and class II by lentiviral vectors encoding for short hairpin RNAs targeting beta2‐microglobulin or class II transactivator, respectively. SLA‐silenced ICCs‐derived cells were then used to form new ICCs in stirred bioreactors in the presence of collagen VI. SLA class I silencing was designed to reach a level of up to 89% and class II by up to 81% on ICCs‐derived cells. Xenogeneic T cell immune responses, NK cell and antibody‐mediated cellular‐dependent immune responses were significantly decreased in SLA‐silenced cells. In stirred bioreactors, tissue engineered islets showed the typical 3D structure and insulin production. These data show the feasibility to generate low immunogenic porcine ICCs after single‐cell engineering and post‐transduction islet reassembling that might serve as an alternative to allogeneic pancreatic islet cell transplantation.     

Stable hepatocyte transplantation using fibrin matrix

Fibrin matrix, a naturally derived biodegradable polymer matrix, was evaluated as a scaffold for hepatocyte transplantation in an athymic mouse model. One week after transplantation, opaque conglomerates of the transplanted hepatocytes and fibrin matrix were found on the intestinal mesentery, whereas no transplanted hepatocytes were observed in control groups (transplantation of hepatocytes suspended in culture medium). The hepatocytes in the conglomerates retained hepatocyte-specific functions, as examined with histochemical and immunohistochemical stainings. Stable hepatocyte engraftment may thus be achieved by hepatocyte transplantation using fibrin matrix.     

DE-loop mutations affect ��2 microglobulin stability, oligomerization, and the low-pH unfolded form

β2 microglobulin (β2m) is the light chain of class‐I major histocompatibility complex (MHC‐I). Its accumulation in the blood of patients affected by kidney failure leads to amyloid deposition around skeletal joints and bones, a severe condition known as Dialysis Related Amyloidosis (DRA). In an effort to dissect the structural determinants of β2m aggregation, several β2m mutants have been previously studied. Among these, three single‐residue mutations in the loop connecting strands D and E (W60G, W60V, D59P) have been shown to affect β2m amyloidogenic properties, and are here considered. To investigate the biochemical and biophysical properties of wild‐type (w.t.) β2m and the three mutants, we explored thermal unfolding by Trp fluorescence and circular dichroism (CD). The W60G mutant reveals a pronounced increase in conformational stability. Protein oligomerization and reduction kinetics were investigated by electrospray‐ionization mass spectrometry (ESI‐MS). All the mutations analyzed here reduce the protein propensity to form soluble oligomers, suggesting a role for the DE‐loop in intermolecular interactions. A partially folded intermediate, which may be involved in protein aggregation induced by acids, accumulates for all the tested proteins at pH 2.5 under oxidizing conditions. Moreover, the kinetics of disulfide reduction reveals specific differences among the tested mutants. Thus, β2m DE‐loop mutations display long‐range effects, affecting stability and structural properties of the native protein and its low‐pH intermediate. The evidence presented here hints to a crucial role played by the DE‐loop in determining the overall properties of native and partially folded β2m.