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Extremely rapid endocytosis mediated by the mannose receptor of sinusoidal endothelial rat liver cells.

ABSTRACT: Isolated sinusoidal endothelial rat liver cells (EC) in suspension bound and internalized ovalbumin, a mannose-terminated glycoprotein, in a saturable manner. The binding and uptake were Ca2+-dependent and were effectively inhibited by alpha-methyl mannoside and yeast mannan, but not by galactose or asialoglycoproteins. This corresponds to the binding specificity described for the mannose receptor of macrophages and non-parenchymal liver cells. Binding studies indicated a surface pool of 20,000-25,000 mannose receptors per cell, with a dissociation constant of 6 x 10(-8) M. Uptake and degradation of ovalbumin by isolated EC were inhibited by weak bases and ionophores which inhibit acidification of endocytic vesicles and dissociation of receptor-ligand complexes. Cycloheximide had no effect on uptake or degradation. Degradation, but not uptake, was inhibited by leupeptin. We conclude that ovalbumin dissociates from the mannose receptors in the endosomal compartment and the receptors are recycled to the cell surface, while the ovalbumin is directed to the lysosomes for degradation. A fraction of the internalized ovalbumin was recycled intact to the cell surface and escaped degradation (retroendocytosis). The rate of internalization of ovalbumin by isolated EC was very fast, with a Ke (endocytotic rate constant) of 4.12 min-1, which corresponds to a half-life of 10 s for the surface pool of receptor-ligand complexes. To our knowledge, this is the highest Ke reported for a receptor-mediated endocytosis system.

SUBMITTER: Magnusson S

PROVIDER: S-EPMC1135637 | biostudies-other | 1989 Feb

REPOSITORIES: biostudies-other

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Project description:Liver sinusoidal endothelial cells (LSECs) play an essential role in systemic waste clearance by effective endocytosis of blood-borne waste macromolecules. We aimed to study LSECs' scavenger function during aging, and whether age-related morphological changes (eg, defenestration) affect this function, in F344/BN F1 rats. Endocytosis of the scavenger receptor ligand formaldehyde-treated serum albumin was significantly reduced in LSECs from old rats. Ligand degradation, LSEC protein expression of the major scavenger receptors for formaldehyde-treated serum albumin endocytosis, stabilin-1 and stabilin-2, and their staining patterns along liver sinusoids, was similar at young and old age, suggesting that other parts of the endocytic machinery are affected by aging. Formaldehyde-treated serum albumin uptake per cell, and cell porosity evaluated by electron microscopy, was not correlated, indicating that LSEC defenestration is not linked to impaired endocytosis. We report a significantly reduced LSEC endocytic capacity at old age, which may be especially important in situations with increased circulatory waste loads.

| S-EPMC2920583 | biostudies-literature

Proteomic Analysis Reveals Dab2 Mediated Receptor Endocytosis Promotes Liver Sinusoidal Endothelial Cell Dedifferentiation.

Project description:Sinusoidal dedifferentiation is a complicated process induced by several factors, and exists in early stage of diverse liver diseases. The mechanism of sinusoidal dedifferentiation is poorly unknown. In this study, we established a NaAsO2-induced sinusoidal dedifferentiation mice model. Liver sinusoidal endothelial cells were isolated and isobaric tag for relative and absolute quantitation (iTRAQ) based proteomic approach was adopted to globally examine the effects of arsenic on liver sinusoidal endothelial cells (LSECs) during the progression of sinusoidal dedifferentiation. In all, 4205 proteins were identified and quantified by iTRAQ combined with LC-MS/MS analysis, of which 310 proteins were significantly changed in NaAsO2 group, compared with the normal control. Validation by western blot showed increased level of clathrin-associated sorting protein Disabled 2 (Dab2) in NaAsO2 group, indicating that it may regulate receptor endocytosis, which served as a mechanism to augment intracellular VEGF signaling. Moreover, we found that knockdown of Dab2 reduced the uptake of VEGF in LSECs, furthermore blocking VEGF-mediated LSEC dedifferentiation and angiogenesis.

| S-EPMC5647404 | biostudies-literature

Endocytosis of ricin by rat liver cells in vivo and in vitro is mainly mediated by mannose receptors on sinusoidal endothelial cells.

Project description:Upon intravenous injection into rats, the plant toxin ricin was rapidly cleared from the circulation by the liver. Among the different liver cell populations, most of the injected ricin associated with the sinusoidal endothelial cells (EC), whereas the liver parenchymal cells (PC) and Kupffer cells (KC) yielded minor contributions to the total liver uptake in vivo. Co-injection of mannan strongly inhibited ricin uptake by the EC, showing that it was mediated by mannose receptors. On the other hand, co-injection of lactose, which inhibits the galactose-specific association of ricin with cells, enhanced ricin uptake by the EC. The carbohydrate-dependency of the EC contribution to the uptake of ricin in vivo was reflected in the carbohydrate-dependency of the uptake in vivo by whole liver. In vitro, the EC also endocytosed ricin more efficiently than did the PC or KC. Whereas uptake in vitro in the EC was mainly mannose-specific, uptake in the two other cell types was mainly galactose-specific. Western blotting showed that the mannose receptors of liver non-parenchymal cells are identical with the mannose receptor previously isolated from alveolar macrophages. The mannose receptors are expressed at a higher level in EC than in KC. Ligand blotting showed that, in the presence of lactose, the mannose receptor is the only protein in the EC that binds ricin, and the binding is mannose-specific and Ca(2+)-dependent.

| S-EPMC1132432 | biostudies-other

Mannose 6-phosphate receptor and sortilin mediated endocytosis of α-galactosidase A in kidney endothelial cells.

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| S-EPMC3386966 | biostudies-literature

Uptake of mannose-terminated glycoproteins in isolated rat liver cells. Evidence for receptor-mediated endocytosis in hepatocytes.

Project description:Even though most of the hepatic binding capacity for mannose-terminated glycoproteins has previously been shown to reside in the hepatocytes (not in the non-parenchymal cells), detailed evidence for the specific uptake of mannose-terminated ligands has been lacking. In the present studies, yeast invertase, a large glycoprotein (Mr 270 000) containing about 50% mannose, was shown to be taken up into hepatocytes by receptor-mediated endocytosis. The uptake was saturable and could be specifically inhibited by mannosides or by a Ca2+ chelator. The asialo-glycoprotein receptor was not involved. The low-Mr (13 000) ligand ribonuclease B, which contains a single high-mannose glycan, was not taken up by hepatocytes; however, it was taken up as fast as invertase by non-parenchymal liver cells. After injection of 131I-invertase into a rat in vivo, about one-half of the labelled protein was recovered in the hepatocytes. On a per-cell basis, each endothelial cell contained 3-4 times as much radioactivity as did the hepatocytes. On fractionation of hepatocytes in sucrose gradients, invertase showed a different intracellular distribution from that of asialo-fetuin, in that invertase moved much faster into that region of the gradient where the lysosomes were recovered. This indicates that invertase and asialo-fetuin are not transported intracellularly by identical mechanisms.

| S-EPMC1144275 | biostudies-other

Insulin promotes sinusoidal endothelial cell proliferation mediated by upregulation of vascular endothelial growth factor in regenerating rat liver after partial hepatectomy.

Project description:AimTo determine whether insulin could promote sinusoidal endothelial cell (SEC) proliferation mediated by upregulation of vascular endothelial growth factor (VEGF) in regenerating rat liver after partial hepatectomy (PHx).MethodsAdult male Sprague-Dawley rats undergoing 70% PHx were injected with insulin (300 MU/kg) or saline via the tail veins every 8 h after surgery for 7 d and killed at 0, 24, 48, 72, 96, 120, 144, and 168 h after surgery. Proliferation of both hepatocytes and SECs was monitored by evaluating the proliferating cell nuclear antigen (PCNA) labeling index (LI). The expression of VEGF protein was evaluated by immunohistochemistry. The mRNA expressions of VEGF and its receptors Flt-1 and Flk-1 were evaluated by semi-quantitative reverse transcription-PCR.ResultsInsulin markedly increased the expression of VEGF mRNA between 24 and 120 h after hepatectomy compared to controls. Similarly, insulin significantly increased the expression of Flt-1 between 24 and 96 h. However, insulin had no significant effect on Flk-1. Furthermore, the immunohistochemical staining revealed that expression of VEGF protein increased in the insulin groups. Insulin significantly increased the PCNA LI of hepatocytes and SECs compared to controls.ConclusionExogenous insulin may promote SEC proliferation with an enhanced expression of VEGF and its receptor Flt-1 in regenerating rat liver after PHx.

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Advanced glycation end products are eliminated by scavenger-receptor-mediated endocytosis in hepatic sinusoidal Kupffer and endothelial cells.

Project description:Long-term incubation of proteins with glucose leads to the formation of advanced glycation end products (AGE). Physiological aspects of the catabolism of non-enzymically glycated proteins were studied in vivo and in vitro. AGE-modified BSA (AGE-BSA) was a mixture of high-Mr (cross-linked), monomeric and low-Mr (fragmented) AGE-BSA. After intravenous administration in rat, all three fractions of AGE-BSA accumulated extremely rapidly and almost exclusively in liver. Uptake in liver endothelial, Kupffer and parenchymal cells accounted for approx. 60%, 25% and 10-15% respectively of hepatic elimination. Both cross-linked and monomeric AGE-BSA were efficiently taken up and degraded in cultures of purified liver endothelial and Kupffer cells. Endocytosis of AGE-BSA by these cells was inhibited by several ligands for the scavenger receptor. Although 125I-Hb was not endocytosed in vitro, 125I-AGE-Hb was effectively endocytosed by a mechanism that was subject to inhibition by AGE-BSA. Endocytosis of N-terminal propeptide of type I procollagen, a physiological ligand for the scavenger receptor, was effectively inhibited by AGE-Hb and AGE-BSA. We conclude that AGE-modification renders macromolecules susceptible for elimination via the scavenger receptor of both liver endothelial and Kupffer cells.

| S-EPMC1218227 | biostudies-other

Scavenger receptor B1, the HDL receptor, is expressed abundantly in liver sinusoidal endothelial cells.

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