Endothelial nitric oxide synthase and caveolin-1 are co-localized in sinusoidal endothelial fenestrae.

BACKGROUND/AIMS: Nitric oxide is synthesized in diverse mammalian tissues by a family of calmodulin-dependent nitric oxide synthases (NOS). Caveolin, the principal structural protein in caveolae, interacts with endothelial NOS leading to enzyme inhibition in a reversible process modulated by Ca++-calmodulin. The aim of the present study was to clarify the ultrastructural localization of eNOS and caveolin-1 in hepatic sinusoidal endothelium by an electron immunogold method. METHODS: Male Wistar rats were used. Liver tissues and hepatic sinusoidal endothelial cells isolated from rat livers by collagenase infusion were studied. For immunohistochemistry, liver specimens were reacted with anti-eNOS or anti-caveolin-1 antibody. The ultrastructural localization of eNOS or caveolin-1 was identified by electron microscopy using an immunogold post-embedding method. RESULTS: Immunohistochemical studies using liver tissues localized endothelial NOS in hepatic sinusoidal lining cells, portal veins and hepatic arteries; and caveolin-1 in sinusoidal lining cells, bile canaliculi, portal vein and hepatic arteries. Immunogold particles indicating the presence of eNOS and caveolin-1 were demonstrated on the plasma membrane of sinusoidal endothelial fenestrae in liver tissue and also in isolated sinusoidal endothelial cells. CONCLUSION: Endothelial NOS and caveolin are co-localized on sinusoidal endothelial fenestrae, suggesting that interaction of the two may modulate cellular regulation of NO synthesis.     

Enhanced expression of endothelial nitric oxide synthase and caveolin‐1 in human cirrhosis

Abstract: Background/aims: Nitric oxide is synthesized in diverse mammalian tissues by a family of calmodulin‐dependent nitric oxide synthases (NOS). Caveolin, the principal structural protein in caveolae, interacts with endothelial NOS (eNOS) leading to enzyme inhibition by a reversible process modulated by Ca⁺⁺ ‐calmodulin. The aim of the present study was to examine the localizations of eNOS and caveolin‐1 at protein level in normal human liver tissue, and how the expressions are altered in cirrhotic liver. Methods: Fresh liver specimens were obtained from hepatic surgeries. Normal portions resected from cases of carcinoma metastasized to the liver were used as control specimens, and cirrhotic portions resected from cases of hepatocellular carcinoma with hepatitis C‐related cirrhosis were used as cirrhotic specimens. Anti‐eNOS and anticaveolin‐1 antibodies were used for immunohistochemistry and Western blotting. Immunoelectron microscopy was conducted on ultra thin sections using immunoglobulin–gold combined with silver staining. Results: Immunohistochemistry revealed that both eNOS and caveolin‐1 were sparsely expressed on hepatic sinusoidal lining in normal liver specimens, and these findings were confirmed by Western blot. Both immunohistochemistry and Western blotting demonstrated over‐expression of eNOS and caveolin‐1 in cirrhotic liver specimens. Morphometric analysis of immunogold particle labeling for eNOS and caveolin‐1 was performed on immunoelectron micrographs. In normal liver tissue, hepatic stellate cells and sinusoidal endothelial cells (SEC) expressed low levels of caveolin‐1, and SEC expressed a very low level of eNOS. In cirrhotic liver, both caveolin‐1 and eNOS expressions were significantly increased by approximately four‐fold on SEC compared to normal liver. Conclusion: In cirrhotic human liver, marked increase of caveolin‐1 in perisinusoidal cells may promote caveolin‐eNOS binding and reduce the activity of eNOS despite an increased eNOS expression, leading to impaired NO production and increased hepatic microvascular tone.     

Elevated expression of caveolin-1 at protein and mRNA level in human cirrhotic liver: relation with nitric oxide

Background. Caveolin, the principal structural protein of caveolae, binds with endothelial nitric oxide synthase (eNOS) leading to enzyme inhibition. This study examined the expression of caveolin and eNOS at the protein and mRNA levels in patients with hepatocellular carcinoma and hepatitis C-related cirrhosis, and in control noncirrhotic liver specimens obtained from patients with metastatic liver carcinoma. Methods. Anti-eNOS, anti-caveoin-1, and anti-calmodulin antibodies were used for Western blotting. For in situ hybridization (ISH), human eNOS and caveolin-1 peptide nucleic acid probes were used with a catalyzed signal amplification system. Results. Western blotting showed marked overexpression of caveolin-1 protein in cirrhotic liver, while caveolin-1 was almost undetectable in control liver tissue. Endothelial NOS was expressed at a slightly higher level in cirrhotic liver than in control liver tissue. Calmodulin was expressed abundantly in control liver tissue and at a low level in cirrhotic liver tissue. By ISH, eNOS mRNA was localized on portal vein and hepatic lining cells, and caveolin-1 mRNA was almost undetectable in normal liver tissue. In cirrhotic liver tissue, caveolin-1 mRNA was overexpressed on hepatic sinusoidal lining cells, while eNOS mRNA expression was similar to that in normal liver. Conclusions. Enhanced caveolin-1 expression may be associated with a significant reduction in NO catalytic activity in cirrhosis.     

Vascular endothelial growth factor increases fenestral permeability in hepatic sinusoidal endothelial cells

Abstract: Vascular endothelial growth factor (VEGF) is an important regulator of vasculogenesis and vascular permeability. Hepatic sinusoidal endothelial cells (SECs) possess sieve‐like pores that form an anastomosing labyrinth structure by the deeply invaginated plasma membrane. Caveolin is the principal structural protein in caveolae. In this study, we examined the role of VEGF on the fenestration and permeability of SECs and the relation with caveolin‐1. SECs isolated from rat livers by collagenase infusion method were cultured for 24 h with (10 or 100 ng/ml) or without VEGF. The cells were then examined by transmission and scanning electron microscopy (EM). The expression of caveolin was investigated by confocal immunofluorescence, immunogold EM, and Western blot. Endocytosis and intracellular traffic was studied using horseradish peroxidase (HRP) reaction as a marker of fluid phase transport in SECs. Both transmission and scanning EM showed an increased number of sinusoidal endothelial fenestrae (SEF) in SECs cultured with VEGF. By confocal immunofluorescence, SECs cultured with VEGF displayed prominent caveolin‐1‐positive aggregates in the cytoplasm, especially surrounding the nucleus region. Immunogold EM depicted increased caveolin‐1 reactivity on vesicles and vacuoles of VEGF‐treated SECs compared with VEGF‐nontreated cells. However, there was no change in the level of caveolin‐1 protein expression on Western blot. After HRP injection, an increase of electron‐dense tracer filled the SEF in cells treated with VEGF. Our results suggested that VEGF induced fenestration in SECs, accompanied by an increased number of caveolae‐like vesicles. Increased caveolin‐1 might be associated with vesicle formation but not with fenestration. Increased fenestration may augment hepatic sinusoidal permeability and trans‐endothelial transport.     

Hepatic sinusoidal endothelial fenestrae express plasma membrane Ca++pump and Ca++Mg++‐ATPase

Abstract: Background/Aim: In general, intracytoplasmic free calcium ions (Ca⁺⁺) are maintained at a very low concentration in mammalian tissue by extruding Ca⁺⁺ against a high concentration of extracellular Ca⁺⁺, mainly through the activity of the plasma membrane Ca⁺⁺pump‐ATPase. The aim of the present study was to demonstrate by electron cytochemical and immunogold methods the ultrastructural localization of two different types of plasma membrane Ca⁺⁺‐ATPase, i.e. Ca⁺⁺Mg⁺⁺‐ATPase and Ca⁺⁺pump‐ATPase in the hepatic sinusoidal endothelium. Methods: Liver tissues and the isolated hepatic sinusoidal endothelial cell (SEC)s were subjected to the following procedures. The ultrastructural localizations of Ca⁺⁺Mg⁺⁺‐ATPase were examined by an electron cytochemical method. The ultrastructural localization of Ca⁺⁺pump‐ATPase was identified by an electron immunogold method. Results: The cytochemical reaction of Ca⁺⁺Mg⁺⁺‐ATPase was found to be localized on the outer sites of the plasma membrane of sinusoidal endothelial fenestrae (SEF). The immunogold particles indicating the presence of Ca⁺⁺ pump‐ATPase were identified on the inner sites (cytoplasmic) of the invaginated plasma membrane of SEF. Conclusions: Both Ca⁺⁺Mg⁺⁺‐ATPase and Ca⁺⁺pump‐ATPase demonstrated on the SEF plasma membrane may be involved in the regulation of intracytoplasmic Ca⁺⁺ concentration.     

Caveolin‐1 and Rac regulate endothelial capillary‐like tubular formation and fenestral contraction in sinusoidal endothelial cells

Background/Aims: Rho guanidine triphosphatases (GTPases) are major regulators of cell migration. We investigated the cytoskeleton and Rho GTPases during cell migration and morphogenesis processes in isolated rat liver sinusoidal endothelial cells (LSECs) cultured on Matrigel while stimulated by the vascular endothelial growth factor (VEGF). Methods: To obtain primary monolayers, LSECs were cultured on Matrigel for 5–17 h with or without VEGF. Sinusoidal endothelial fenestrae (SEF) morphology was observed using scanning electron microscopy and transmission electron microscopy. RhoA, Rac1 and phosphorylated myosin light‐chain kinase, Rho‐binding domain of Rhotekin and the p21‐binding domain of p21‐activated protein kinase were analysed using Western blotting. Results: The LSECs showed cellular protrusions and or cords of aligned cells resembling primitive capillary‐like structures, with SEF contraction. Time course analyses of Rac1 activation matched specific morphological changes. Rac1 activity increased progressively to 17 h in cells cultured without VEGF, but markedly increased at 7 h in the presence of VEGF. RhoA activity was slightly elevated at 5 h. The levels of endogenous caveolin‐1 (CAV‐1) expression increased in a time‐dependent manner, reaching a peak at 7 h. CAV‐1 expression occurred immediately before the formation of the capillary‐like tube. Moreover, treatment with VEGF regulated CAV‐1 expression in LSECs. Conclusions: Spatial activation of Rac1 is involved in the formation of a capillary‐like tubular network accompanying SEF contraction in LSECs, implying that endothelial migration and adhesion are necessary for LSECs tubular formation in the liver. CAV‐1 might play an important positive role in the regulation of LSEC tubular formation.     

Enhanced expression of endothelial nitric oxide synthase and caveolin-1 in human cirrhosis

BACKGROUND/AIMS: Nitric oxide is synthesized in diverse mammalian tissues by a family of calmodulin-dependent nitric oxide synthases (NOS). Caveolin, the principal structural protein in caveolae, interacts with endothelial NOS (eNOS) leading to enzyme inhibition by a reversible process modulated by Ca++ -calmodulin. The aim of the present study was to examine the localizations of eNOS and caveolin-1 at protein level in normal human liver tissue, and how the expressions are altered in cirrhotic liver. METHODS: Fresh liver specimens were obtained from hepatic surgeries. Normal portions resected from cases of carcinoma metastasized to the liver were used as control specimens, and cirrhotic portions resected from cases of hepatocellular carcinoma with hepatitis C-related cirrhosis were used as cirrhotic specimens. Anti-eNOS and anticaveolin-1 antibodies were used for immunohistochemistry and Western blotting. Immunoelectron microscopy was conducted on ultra thin sections using immunoglobulin-gold combined with silver staining. RESULTS: Immunohistochemistry revealed that both eNOS and caveolin-1 were sparsely expressed on hepatic sinusoidal lining in normal liver specimens, and these findings were confirmed by Western blot. Both immunohistochemistry and Western blotting demonstrated over-expression of eNOS and caveolin-1 in cirrhotic liver specimens. Morphometric analysis of immunogold particle labeling for eNOS and caveolin-1 was performed on immunoelectron micrographs. In normal liver tissue, hepatic stellate cells and sinusoidal endothelial cells (SEC) expressed low levels of caveolin-1, and SEC expressed a very low level of eNOS. In cirrhotic liver, both caveolin-1 and eNOS expressions were significantly increased by approximately four-fold on SEC compared to normal liver. CONCLUSION: In cirrhotic human liver, marked increase of caveolin-1 in perisinusoidal cells may promote caveolin-eNOS binding and reduce the activity of eNOS despite an increased eNOS expression, leading to impaired NO production and increased hepatic microvascular tone.     

Physiological role of sinusoidal endothelial cells and Kupffer cells and their implication in the pathogenesis of liver injury

We reviewed the morphological characteristics and physiological functions of hepatic sinusoidal endothelial cells (SECs) and Kupffer cells (KCs), both of which are major components of the hepatic sinusoid, and we showed the implication of these hepatic sinusoidal lining cells in the pathophysiology of the liver, based on our experimental studies. The most outstanding feature of SECs is that they are provided with numerous fenestrae, thereby allowing direct communication between the sinusoidal lumen and the space of Disse. Physiologically, SECs play a role in filtration function, endocytic function, and putative participation in the regulation of sinusoidal blood flow. As for KCs, they account for major portion of fixed macrophages in the entire body, and exhibit vigorous activity for phagocytosis, and produce many kinds of soluble mediators such as cytokines, prostanoids, oxygen radicals, and proteases. To determine whether these cells are implicated in pathophysiological processes in the liver we directed our attention to liver injury associated with sepsis and cold‐preservation injury of liver tissue. In a septic rat model, we found that when KCs that included hepatic macrophages were activated, they released excess tissue‐toxic mediators, probably leading to SEC damage. In the cold‐preserved liver, we demonstrated that KCs were functionally activated and that the morphology of SECs was destroyed. When the liver was reperfused with plasma and a leucocyte suspension, hypercoagulability and increased leucocyte adherence occurred. In both experimental models, we demonstrated that KC blockade ameliorated the liver injury, and this was associated with the morphological improvement of SECs. Thus, we showed the pathogenetic implication of KCs and SECs, due possibly to microcirculatory disturbance in the hepatic sinusoid, and further emphasized the involvement of activated KCs in SEC impairment.     

Three‐dimensional organization of fenestrae labyrinths in liver sinusoidal endothelial cells

Background/Aims: Liver sinusoidal endothelial cell (LSEC) fenestrae are membrane‐bound pores that are grouped in sieve plates and act as a bidirectional guardian in regulating transendothelial liver transport. The high permeability of the endothelial lining is explained by the presence of fenestrae and by various membrane‐bound transport vesicles. The question as to whether fenestrae relate to other transport compartments remains unclear and has been debated since their discovery almost 40 years ago. Methods: In this study, novel insights concerning the three‐dimensional (3D) organization of the fenestrated cytoplasm were built on transmission electron tomographical observations on isolated and cultured whole‐mount LSECs. Classical transmission electron microscopy and atomic force microscopy imaging was performed to accumulate cross‐correlative structural evidence. Results and Conclusions: The data presented here indicate that different arrangements of fenestrae have to be considered: i.e. open fenestrae that lack any structural obstruction mainly located in the thin peripheral cytoplasm and complexes of multifolded fenestrae organized as labyrinth‐like structures that are found in the proximity of the perinuclear area. Fenestrae in labyrinths constitute about one‐third of the total LSEC porosity. The 3D reconstructions also revealed that coated pits and small membrane‐bound vesicles are exclusively interspersed in the non‐fenestrated cytoplasmic arms.     

Impaired endothelial nitric oxide synthase activity associated with enhanced caveolin binding in experimental cirrhosis in the rat.

BACKGROUND & AIMS: A reduction in nitric oxide (NO) has been implicated as a cause of intrahepatic vasoconstriction in cirrhosis, but the regulatory mechanisms remain undefined. The aim of this study was to examine a contributory role for caveolin-1, a putative negative regulator of endothelial NO synthase, in mediating deficient intrahepatic NO production in the intact cirrhotic liver. METHODS: Cirrhosis was induced by carbon tetrachloride inhalation. Flow regulation of NO production and perfusion pressure was examined in the perfused rat liver. Protein expression of endothelial NO synthase (eNOS), caveolin, and calmodulin was examined by Western blotting and immunohistochemistry. NOS activity and NO production were assessed by citrulline generation and chemiluminescence, respectively. Protein-protein interactions were examined using whole tissue protein immunoprecipitation. RESULTS: In response to incremental increases in flow, cirrhotic animals produced significantly less NO(x) than control animals. NOS activity was significantly reduced in liver tissue from cirrhotic animals compared with control animals in the presence of similar eNOS protein levels. Deficient eNOS activity was associated with a severalfold increase in binding of eNOS with caveolin. Protein levels of caveolin-1 were markedly increased in the cirrhotic liver. CONCLUSIONS: These studies provide evidence that enhanced expression and interaction of caveolin with eNOS contribute to impaired NO production, reduced NOS activity, and vasoconstriction in the intact cirrhotic liver.     

整合素α6在肝窦毛细血管化中的表达

目的探讨整合素α6在肝窦毛细血管化时的表达情况. 方法皮下注射四氯化碳制备大鼠肝纤维化模型,进行层粘连蛋白(LN)及其整合素受体α6免疫组织化学检测及整合素α6斑点免疫印迹研究. 结果动态观察了LN在肝纤维化时沿肝窦在Disse间隙沉积形成肝窦毛细血管化;正常时整合素α6局限于汇管区血管内皮和胆管内皮细胞膜上,窦内皮细胞(SEC)上无表达,肝窦毛细血管化时,SEC出现整合素α6阳性表达沿肝窦连续分布,整合素α6在纤维化时组织中含量明显高于正常(P＜0.05). 结论肝窦毛细血管化时SEC出现整合素α6亚基的诱导表达.     

Sinusoidal endothelial cell injury by superoxide anion and iron in the Propionibacterium acnes‐pretreated and lipopolysaccharide‐stimulated rat liver

Abstract: Aims/Background: We attempted to measure the generation of superoxide anion, examine its site of release and determine its pathological role in Propionibacterium acnes‐lipopolysaccharide‐induced liver injury in the rat. Methods: The P. acnes‐pretreated (16 mg/kg i.v.) rat liver was perfused with buffer containing lipopolysaccharide (2.5 μg/ml). Chemiluminescence enhanced with Cypridina luciferin analog, MCLA, and reduction of nitro blue tetrazolium were used for detecting superoxide anion. Leakage of enzymes and release of cytokines into the perfusate, and histological specimens were also examined. Results: Superoxide dismutase‐inhibitable chemiluminescence peaked at 30 min of lipopolysaccharide infusion and blue formazan precipitate was histochemically deposited mainly on hepatic macrophages. Purine nucleoside phosphorylase (PNP) activity in the perfusate, as a marker of sinusoidal endothelial cell injury, reached its maximum at 50 min and aspartate aminotransferase (AST) activity, as a marker of hepatocyte injury, reached a plateau at 90 min. Simultaneous treatment with superoxide dismutase and deferoxamine mesylate significantly suppressed the leakage of PNP and AST. Release of tumor necrosis factor‐α and growth‐related oncogene/cytokine‐induced neutrophil chemoattractant‐1 lagged behind PNP leakage. Light microscopy showed destruction of the sinusoids followed by hepatocyte necrosis. Electron microscopy revealed adherence of hepatic macrophages to sinusoidal endothelial cells. Conclusion: These results indicate that superoxide anion released from hepatic macrophages may induce sinusoidal endothelial cell injury via interaction with iron in the P. acnes‐lipopolysaccharide‐treated liver.     

Localization of hyaluronan in human liver sinusoids: a histochemical study using hyaluronan-binding protein

Abstract: Circulating hyaluronan is mostly derived from lymph, fibroblast and Ito cells in the liver, and more than 90% of hyaluronan is degraded in hepatic sinusoidal endothelial cells. Thus, elevated serum hyaluronan is regarded as an indication of hepatic fibrosis with activated Ito cells and dysfunctional sinusoidal endothelial cells. We studied the distribution of hyaluronan in human liver sinusoids to determine the influences on elevated hyaluronan levels in sera. Histochemical examination was made using hyaluronan-binding protein (HABP) and serial sections of liver tissue for staining of alpha-smooth muscle actin (ASMA) (an indicator of activated Ito cells) and of ulex europaeus agglutinin I lectin (UEA-1) (closely related to hepatic sinusoidal capillarization). Positive staining, indicating the presence of hyaluronan, was noted in fibrous regions around the portal tracts, areas of focal necrosis in the liver parenchyma, and walls of the sinusoids in chronic hepatitis. In this group, hyaluronan-positive areas corresponded to positive ASMA staining and faint staining of UEA-1. On the contrary, in liver cirrhosis, UEA-1-positive areas were essentially identical to hyaluronan-positive areas and to ASMA-negative areas in sinusoidal walls. Hyaluronan and ASMA could be detected in the same areas of sinusoidal walls in chronic hepatitis, but not in liver cirrhosis. Hyaluronan appears to be mainly related to the staining of activated Ito cells in chronic hepatitis. Therefore, we concluded that in chronic hepatitis, the production of hyaluronan was accelerated in Ito cells; however, degradation of hyaluronan by sinusoidal endothelial cells continued. On the contrary, in liver cirrhosis, hyaluronan production decreased in Ito cells, and a marked transformation of sinusoidal endothelial cells with hepatic sinusoidal capillarization indicated loss of the ability to degrade hyaluronan. These different mechanisms in chronic hepatitis and liver cirrhosis may operate in the sinusoidal walls and may cause the elevation of hyaluronan in sera.     

Lecithin: retinol acyltransferase protein is distributed in both hepatic stellate cells and endothelial cells of normal rodent and human liver

Background: To determine the extent to which hepatic stellate cell (HSC) activation contributes to liver fibrosis, it was found necessary to develop an alternative structural and functional stellate cell marker for in situ studies. Although several HSC markers have been reported, none of those are associated with particular HSC functions. Aim: The present study was undertaken to examine whether lecithin:retinol acyltransferase (LRAT), the physiological retinol esterification enzyme of the liver, is a potential and relevant tissue marker for HSC. Methods: An antibody specific to mouse and human LRAT was prepared based on the amino acid sequences. Antibodies to LRAT were used for immunohistochemical studies to assess the distribution of LRAT‐positive cells in the liver with the aid of fluorescence and immunogold electron microscopy. Results: LRAT‐positive cells were found to be confined in the space of Disse, corresponding with the location of desmin‐positive HSC in rodent liver, also in human liver. Interestingly, LRAT‐positive staining was also observed along the liver sinusoidal endothelial lining. Furthermore, immune electron microscopic studies revealed that LRAT was mainly distributed in HSC within the rough‐endoplasmic reticulum (RER) and multivesicular bodies, whereas LRAT staining within the endothelial cells was largely confined to the perinuclear area and to some extent to the RER. Conclusion: Evidence has been accumulated that LRAT might serve as an excellent alternative HSC marker for future structural and functional studies. Furthermore, the presence of LRAT in endothelial cells might suggest a currently unknown function of this enzyme in liver endothelial biology.     

The mechanisms of hepatic sinusoidal endothelial cell regeneration: A possible communication system associated with vascular endothelial growth factor in liver cells

Vascular endothelial growth factor (VEGF) has been shown to induce proliferation of sinusoidal endothelial cells in primary culture. To elucidate the mechanisms of sinusoidal endothelial cell regeneration in vivo, mRNA expression of VEGF and its receptors, flt-1 and KDR/flk-1, were studied in rat livers. Northern blot analysis revealed that VEGF-mRNA was expressed in hepatocytes immediately after isolation from normal rats. In contrast, non-parenchymal cells, including sinusoidal endothelial cells, expressed VEGF receptor-mRNA. Vascular endothelial growth factor-mRNA expression in hepatocytes was decreased during primary culture, but increased following a peak of DNA synthesis, induced by addition of epidermal growth factor or hepatocyte growth factor to the culture medium at 24 h of plating. In a 70% resected rat liver, VEGF-mRNA expression increased with a peak at 72 h after the operation, and mRNA expression of VEGF receptors between 72 and 168 h. In such a liver, mitosis was maximal in hepatocytes at 36 h and in sinusoidal endothelial cells at 96 h. Also, mRNA expression of both VEGF and its receptors was significantly increased in carbon tetrachloride-intoxicated rat liver compared with normal rat liver. Vascular endothelial growth factor expression was minimal in Kupffer cells isolated from normal rats, but marked in activated Kupffer cells and hepatic macrophages from the intoxicated rats. Vascular endothelial growth factor-mRNA expression was also increased in activated stellate cells from these rats and in the cells activated during primary culture compared with quiescent cells. We conclude that increased levels of VEGF expression in regenerating hepatocytes may contribute to the proliferation of sinusoidal endothelial cells in partially resected rat liver, probably through VEGF receptors up-regulated on the cells. Also, VEGF derived from activated Kupffer cells, hepatic macrophages and stellate cells may be involved in this proliferation in injured rat liver.     

Endothelial cell heterogeneity in the normal human liver acinus: in situ immunohistochemical demonstration

While a certain degree of structural and functional intra-lobular heterogeneity of sinusoidal endothelial cells has been observed in rodents, little information is available about the zonal characteristics of sinusoidal endothelial cells in the human liver acinus. We have therefore examined the intra-acinar distribution of a panel of endothelial markers in the normal human liver, including: (a) structural markers of continuous and sinusoidal endothelia (PECAM-1, CD-34 protein, VE-cadherin, 1F10 antigen), (b) functional markers specific for sinusoidal endothelial cells, as previously determined in the laboratory (CD4 protein, the lipo-polysaccharide-binding protein receptor (CD 14), aminopeptidase N, ICAM-1, receptors II and III for the Fc fragment of immunoglobulins G), (c) endothelial cell-matrix adhesion proteins and leukocyte-endothelial cell adhesion molecules. We observed a heterogeneous distribution for: (a) the 1F10 antigen, whose distribution in the human liver acinus was restricted to vessels situated along the axis of acinar zone 1, (b) the lipopolysaccharide-binding protein receptor and the receptor III for the Fc fragment of IgG, not expressed or only barely expressed in acinar zone 1. The distribution of the other markers tested did not display significant intra-lobular variation. Our in situ results suggest the existence of a degree of zonal heterogeneity in the structural and functional characteristics of sinusoidal endothelial cells in the human liver acinus. This might contribute to the constitution of distinct microenvironments within the human liver parenchyma.     

四氯化碳诱导的肝纤维化大鼠肝窦毛细血管化的形成

目的：观察四氯化碳（CCl4）诱导的大鼠肝纤维化过程中肝窦毛细血管化的形成过程,探讨其与肝纤维化的关系。方法32只清洁级雄性SD大鼠,随机分为正常对照组,肝纤维化模型组,正常对照组大鼠腹腔注射0．9％氯化钠溶液2 mL/kg ,模型组大鼠腹腔注射50％ CCl4-蓖麻油混合液2 mL/kg ,每周2次,共8周;分别于造模第2、4、6、8周处死大鼠,观察肝组织炎症及纤维化程度,放射免疫法检测血清中透明质酸（HA）的含量,透射电镜观察肝窦窦壁结构,S-P 免疫组织化学检测各组大鼠肝组织CD31、层黏连蛋白（LN）、IV型胶原（Col-IV）的表达。结果肝脏组织学证实CCl4诱导的大鼠肝纤维化模型构建成功,6周可见纤维间隔形成;透射电镜显示,CCl4诱导2周时,部分肝窦内皮细胞（liver sinusoidal endothelial cells ,LSEC）窗孔减少,内皮下未见基底膜（Basement membrane,BM）,随着造模的进程,LSEC 窗孔进一步减少,部分甚至消失,第6、8周时局部肝窦内皮下形成连续的BM。同时,随着肝纤维化的进程,HA浓度逐渐升高,肝窦内皮细胞表面标志物CD31及基底膜主要成分Col-IV、LN表达逐渐增强。结论在CCl4诱导大鼠肝纤维化过程中,肝窦毛细血管化是逐渐形成的,LSEC失窗孔早于纤维间隔的形成,而肝窦内皮下基底膜出现在纤维间隔形成以后。     

Hepatic sinusoidal endothelial fenestrae express plasma membrane Ca++pump and Ca++Mg++-ATPase

BACKGROUND/AIM: In general, intracytoplasmic free calcium ions (Ca++) are maintained at a very low concentration in mammalian tissue by extruding Ca++ against a high concentration of extracellular Ca++, mainly through the activity of the plasma membrane Ca++pump-ATPase. The aim of the present study was to demonstrate by electron cytochemical and immunogold methods the ultrastructural localization of two different types of plasma membrane Ca++-ATPase, i.e. Ca++Mg++-ATPase and Ca++pump-ATPase in the hepatic sinusoidal endothelium. METHODS: Liver tissues and the isolated hepatic sinusoidal endothelial cell (SEC)s were subjected to the following procedures. The ultrastructural localizations of Ca++Mg++-ATPase were examined by an electron cytochemical method. The ultrastructural localization of Ca++pump-ATPase was identified by an electron immunogold method. RESULTS: The cytochemical reaction of Ca++Mg++-ATPase was found to be localized on the outer sites of the plasma membrane of sinusoidal endothelial fenestrae (SEF). The immunogold particles indicating the presence of Ca++pump-ATPase were identified on the inner sites (cytoplasmic) of the invaginated plasma membrane of SEF CONCLUSIONS: Both Ca++Mg++-ATPase and Ca++pump-ATPase demonstrated on the SEF plasma membrane may be involved in the regulation of intracytoplasmic Ca++ concentration.     

An endothelin A receptor antagonist induces dilatation of sinusoidal endothelial fenestrae: implications for endothelin-1 in hepatic microcirculation

Background Sinusoidal endothelial fenestrae (SEF) regulate the sinusoidal circulation by altering their diameter and number. This study documented the effects of endothelin (ET) receptor antagonists on SEF and hepatic microcirculation. Methods The portal pressure and hepatic tissue blood flow were measured with a hydromanometer and a laser Doppler blood flow meter, respectively. BQ-123 (ET_A receptor antagonist) or BQ-788 (ET_B receptor antagonist) was continuously infused into normal rats at the rate of 10 nmol/min for 10 min. The sinusoids were observed at 60 min after the infusion by scanning electron microscopy. The localization of ET-1 and ET_A and ET_B receptors was examined by the indirect immunoperoxidase method. Results When BQ-123 was infused, the portal pressure gradually decreased with time, and it showed a significant reduction compared with the control groups. On the other hand, a decrease in portal pressure was not evident in the BQ-788-infused groups. Hepatic tissue blood flow was maintained at the value prior to the infusion in both groups. BQ-123 also caused a marked dilatation of the SEF. The diameters of the SEF after BQ-123 infusion were almost three times those of normal SEF. ET-1 was evenly present along the sinusoidal walls, and the reaction products of the ET_A receptors were recognized along the portal vein and in the sinusoidal cells, that is, the hepatic stellate cells and endothelial cells. Conclusions Action of ET-1 via the ET_A receptors may regulate the size of SEF in addition to hepatic microcirculation.     

Endothelial,but not the inducible,nitric oxide synthase is detectable in normal and portal hypertensive rats

Abstract: Background: Chronic portal hypertension is accompanied by a nitric oxide (NO) dependent vasodilation. Three isoforms of NO producing synthases (NOS) are characterized: neuronal NOS (nNOS), endothelial NOS (eNOS) and inducible NOS (iNOS). Sources of increased NO levels in chronic hypertension is disputed. Methods: To determine eNOS and iNOS expression in different organs of portal hypertensive and control rats, we divided Sprague-Dawley rats in 6 groups: (1) Partial portal vein ligated rats, (2) Bile duct ligated rats, (3) Carbon tetrachloride treated rats, (4) Sham operated rats, (5) Untreated control rats, and (6) LPS treated rats. Immunohistochemistry (IHC) and immunoblotting (IB) using antibodies against eNOS or iNOS were carried out on samples from thymus, aorta, heart, lung, oesophagus, liver, spleen, kidney, pancreas, small and large intestine. Results: IHC revealed an even eNOS expression in all groups. Expression of iNOS was restricted to macrophages in organs of LPS treated and the thymus of rats. IB mirrored these results. Conclusion: In chronic portal hypertension, the main source for NO production depends on eNOS activity.