Plasma clearance of rat bikunin: evidence for receptor-mediated uptake.
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ABSTRACT:
SUBMITTER: Sjoberg EM
PROVIDER: S-EPMC1136806 | biostudies-other | 1995 Jun
REPOSITORIES: biostudies-other
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Project description:BackgroundThe liver-derived plasma protein fetuin A is a systemic inhibitor of ectopic calcification. Fetuin-A stabilizes calcium phosphate mineral initially as ion clusters to form calciprotein monomers (CPM), and then as larger multimeric consolidations containing amorphous calcium phosphate (primary CPP, CPP 1) or more crystalline phases (secondary CPP, CPP 2). CPM and CPP mediate excess mineral stabilization, transport and clearance from circulation.MethodsWe injected i.v. synthetic fluorescent CPM and studied their clearance by live two-photon microscopy. We analyzed organ sections by fluorescence microscopy to assess CPM distribution. We studied cellular clearance and cytotoxicity by flow cytometry and live/dead staining, respectively, in cultured macrophages, liver sinusoidal endothelial cells (LSEC), and human proximal tubule epithelial HK-2 cells. Inflammasome activation was scored in macrophages. Fetuin A monomer and CPM charge were analyzed by ion exchange chromatography.ResultsLive mice cleared CPP in the liver as published previously. In contrast, CPM were filtered by kidney glomeruli into the Bowman space and the proximal tubules, suggesting tubular excretion of CPM-bound calcium phosphate and reabsorption of fetuin A. Fetuin-A monomer clearance was negligible in liver and low in kidney. Anion exchange chromatography revealed that fetuin A monomer was negatively charged, whereas CPM appeared neutral, suggesting electrochemical selectivity of CPM versus fetuin A. CPM were non-toxic in any of the investigated cell types, whereas CPP 1 were cytotoxic. Unlike CPP, CPM also did not activate the inflammasome.ConclusionsFetuin-A prevents calcium phosphate precipitation by forming CPM, which transform into CPP. Unlike CPP, CPM do not trigger inflammation. CPM are readily cleared in the kidneys, suggesting CPM as a physiological transporter of excess calcium and phosphate. Upon prolonged circulation, e.g., in chronic kidney disease, CPM will coalesce and form CPP, which cannot be cleared by the kidney, but will be endocytosed by liver sinusoidal endothelial cells and macrophages. Large amounts of CPP trigger inflammation. Chronic CPM and CPP clearance deficiency thus cause calcification by CPP deposition in blood vessels and soft tissues, as well as inflammation.
| S-EPMC8116800 | biostudies-literature
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
Project description:Native human carcinoembryonic antigen is rapidly removed from the circulation by the rat liver Kupffer cell after intravenous injection. The molecule is subsequently transferred to the hepatocyte in an immunologically identifiable form. Carcinoembryonic antigen has a circulatory half-life of 3.7 (+/- 0.8) min, and cellular entry is by receptor-mediated endocytosis. Non-specific fluid pinocytosis and phagocytosis can be excluded as possible mechanisms by the kinetics of clearance and failure of colloidal carbon to inhibit uptake. Substances with known affinity for the hepatic receptors for mannose, N-acetylglucosamine, fucose and galactose all fail to inhibit carcinoembryonic antigen clearance. After two cycles of the Smith degradation, carcinoembryonic antigen is still able to inhibit clearance of the native molecule. Receptor specificity is apparently not dependent on those non-reducing terminal sugars of the native molecule. Performic acid-oxidized carcinoembryonic antigen also inhibits clearance of carcinoembryonic antigen in vivo. Receptor binding is not dependent on tertiary protein conformation. Non-specific cross-reacting antigen, a glycoprotein structurally similar to carcinoembryonic antigen, is cleared by the same mechanism.
| S-EPMC1158362 | biostudies-other
Project description:Background and purposeCalcitonin gene-related peptide (CGRP) is widely distributed in the trigeminovascular system and released from sensory fibres of the cranial dura mater upon noxious stimulation. Such release may be a mechanism underlying migraine headache. Based on data from guinea pig basilar artery preparations, we have here studied CGRP release and uptake in an organ preparation of the hemisected rat skull.Experimental approachCGRP release from the cranial dura was quantified by a commercial enzyme-linked immunoassay. CGRP was depleted using repetitive challenges of capsaicin. After incubating the tissue with CGRP for 20?min and extensive washing, another capsaicin challenge was performed. Immunohistochemistry was used to visualize CGRP immunofluorescence in dural nerve fibres.Key resultsCapsaicin-induced CGRP release was attenuated by the transient receptor potential vanilloid receptor type I antagonist capsazepine or by Ca(2+)-free solutions. After the CGRP-depleted preparation had been exposed to exogenous CGRP, capsaicin-induced CGRP release was increased compared to the challenge just prior to incubation. CGRP uptake was not influenced by Ca(2+)-free solutions. Olcegepant and CGRP(8-37) (CGRP receptor antagonists) did not affect uptake of CGRP. However, a monoclonal CGRP-binding antibody decreased CGRP uptake significantly. Release of CGRP after incubation was attenuated by Ca(2+)-free solutions and by capsazepine. Immunohistochemical assays indicated a weak trend towards CGRP uptake in rat dura mater.Conclusion and implicationsWe have presented evidence for CGRP uptake in nerves and its re-release in rat dura mater. This may have implications for the pathophysiology and treatment of migraine.
| S-EPMC3010590 | biostudies-literature
Project description:Erythropoietin (Epo) is the primary hormone that stimulates erythroid proliferation and differentiation through its cell surface receptor (EpoR) on erythroid progenitor cells. Previous studies have suggested that the bone marrow plays an important role in Epo's elimination. The changes in the EpoR mRNA levels and Epo's clearance in the bone marrow of 11 newborn lambs were studied to elucidate the role of EpoR in Epo's clearance under anemic conditions. Epo mRNA levels were measured by real-time polymerase chain reaction, and relative expression of EpoR was calculated by using the comparative CT method. The glyceraldehyde-3-phosphate dehydrogenase housekeeping gene was chosen as a control gene for the calculations. All lambs showed significant increase in bone marrow EpoR mRNA levels after phlebotomy-induced anemia. Epo's clearance determined from simultaneous pharmacokinetic studies with 125I-recombinant human Epo showed a significant increase after phlebotomy-induced anemia that was similar to the increase in EpoR. By day 28 after phlebotomy, EpoR mRNA levels and Epo clearance had returned toward baseline. These results indicate that the changes in Epo's clearance are not caused by body growth but result from significant changes in the pool of EpoR. A linear mixed-effect model was used to evaluate the quantitative relationship between EpoR and Epo's clearance. This analysis demonstrated a highly significant positive linear correlation between EpoR and Epo clearance. Together, these findings provide strong evidence that receptor-mediated Epo clearance is an important route for Epo's elimination.
| S-EPMC2872962 | biostudies-literature
Project description:Iron is essential for the proliferation of fungal pathogens during infection. The availability of iron is limited due to its association with host proteins. Fungal pathogens have evolved different mechanisms to acquire iron from host; however, little is known regarding how Paracoccidioides species incorporate and metabolize this ion. In this work, host iron sources that are used by Paracoccidioides spp. were investigated. Robust fungal growth in the presence of the iron-containing molecules hemin and hemoglobin was observed. Paracoccidioides spp. present hemolytic activity and have the ability to internalize a protoporphyrin ring. Using real-time PCR and nanoUPLC-MSE proteomic approaches, fungal growth in the presence of hemoglobin was shown to result in the positive regulation of transcripts that encode putative hemoglobin receptors, in addition to the induction of proteins that are required for amino acid metabolism and vacuolar protein degradation. In fact, one hemoglobin receptor ortholog, Rbt5, was identified as a surface GPI-anchored protein that recognized hemin, protoporphyrin and hemoglobin in vitro. Antisense RNA technology and Agrobacterium tumefaciens-mediated transformation were used to generate mitotically stable Pbrbt5 mutants. The knockdown strain had a lower survival inside macrophages and in mouse spleen when compared with the parental strain, which suggested that Rbt5 could act as a virulence factor. In summary, our data indicate that Paracoccidioides spp. can use hemoglobin as an iron source most likely through receptor-mediated pathways that might be relevant for pathogenic mechanisms.
| S-EPMC4022528 | biostudies-literature
Project description:Transferrin receptor (TFRC) is the major mediator for iron entry into a cell. Under excessive iron conditions, TFRC is expected to be reduced to lower iron uptake and toxicity. However, the mechanism whereby TFRC expression is maintained at high levels in iron-enriched cancer cells and the contribution of TFRC to cancer development are enigmatic. Here the work shows TFRC is induced by adenomatous polyposis coli (APC) gene loss-driven β-catenin activation in colorectal cancer, whereas TFRC-mediated intratumoral iron accumulation potentiates β-catenin signaling by directly enhancing the activity of tankyrase. Disruption of TFRC leads to a reduction of colonic iron levels and iron-dependent tankyrase activity, which caused stabilization of axis inhibition protein 2 (AXIN2) and subsequent repression of the β-catenin/c-Myc/E2F Transcription Factor 1/DNA polymerase delta1 (POLD1) axis. POLD1 knockdown, iron chelation, and TFRC disruption increase DNA replication stress, DNA damage response, apoptosis, and reduce colon tumor growth. Importantly, a combination of iron chelators and DNA damaging agents increases DNA damage response and reduces colon tumor cell growth. TFRC-mediated iron import is at the center of a novel feed-forward loop that facilitates colonic epithelial cell survival. This discovery may provide novel strategies for colorectal cancer therapy.
| S-EPMC10074045 | biostudies-literature
Project description:Sotuletinib (BLZ945), a CSF1-R specific kinase inhibitor developed for the treatment of Amyotrophic Lateral Sclerosis, induced liver enzyme elevation in absence of hepatocellular lesions in preclinical rat and monkey studies. The monocytic cell family, including Kupffer cells, e.g., the liver-resident macrophages, are dependent upon CSF1 pathway activation for their survival, proliferation, and differentiation. Kupffer cells act as the main body compartment responsible for elimination of some blood-borne proteins, like ALT, AST, and few others. The depletion of Kupffer cells through CSF1 pathway inhibition has already been hypothesized as responsible for apparent liver enzyme elevation without detectable corresponding liver damage. However, a release of these biomarkers from unseen hepatic lesions or from other organs cannot be excluded. In order to eliminate a potential contribution of ALT elevation from an internal organ source, we injected recombinant his-Tagged ALT1 into rats pretreated with Sotuletinib. The elimination rate of the exogenous ALT1 was significantly lower in treated animals, demonstrating a delayed clearance independently of any potential organ lesions.
| S-EPMC9637862 | biostudies-literature
Project description:In this study, a novel IR-binding protein (IRBP) from Momordica charantia, named as mcIRBP, was identified by analyzing the physical and functional interactions between mcIRBP and IR. The hypoglycemic effect and mechanism of mcIRBP were further evaluated in normal and streptozotocin-induced diabetic mice. Normal and diabetic mice were treated without or with mcIRBP and RNAs from muscle tissues were extracted for microarray analysis. Number of replicate was three.
2016-06-25 | E-GEOD-48274 | biostudies-arrayexpress
Project description:Transcranial focused ultrasound (FUS) delivers highly focused acoustic energy to a small region of the brain in a noninvasive manner. Recent studies have revealed that FUS, which is administered either in pulsed or continuous waves, can elicit or suppress neural tissue excitability. This neuromodulatory property of FUS has been demonstrated via direct motion detection, electrophysiological recordings, functional magnetic resonance imaging (fMRI), confocal imaging, and microdialysis sampling of neurotransmitters. This study presents new evidence of local increase in glucose metabolism induced by FUS to the rat brain using FDG (18-fludeoxyglucose) positron emission tomography (PET).Sprague-Dawley rats underwent sonication to a unilateral hemispheric area of the brain prior to PET scan. The pulsed sonication (350 kHz, tone burst duration of 0.5 ms, pulse repetition frequency of 1 kHz, and duration of 300 ms) was applied in 2 s intervals for 40 min immediately after the FDG injection via tail vein. Subsequently, the PET was acquired in dynamic list-mode to image FDG activity for an hour, and reconstructed into a single volume representing standardized uptake value (SUV). The raw SUV as well as its asymmetry index (AI) were measured from five different volume-of-interests (VOIs) of the brain for both hemispheres, and compared between sonicated and unsonicated groups.Statistically significant hemispheric changes in SUV were observed only at the center of sonication focus within the FUS group [paired t-test; t(7) = 3.57, p < 0.05]. There were no significant hemispheric differences in SUV within the control group in any of the VOIs. A statistically significant elevation in AI (t-test; t(7) = 3.40, p < 0.05) was observed at the center of sonication focus (7.9 ± 2.5%, the deviations are in standard error) among the FUS group when compared to the control group (-0.8 ± 1.2%).Spatially distinct increases in the glucose metabolic activity in the rat brain is present only at the center of sonication focus, suggesting localized functional neuromodulation mediated by the sonication.
| S-EPMC3585755 | biostudies-other