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Results for “Extracellular vesicles”

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At least 631 records · Page 35Linked to original sources

PubMed1995

Full-length and truncated Alzheimer amyloid precursors in chromaffin granules: solubilization of membrane amyloid precursor is mediated by an enzymatic mechanism.

The amyloid beta peptide (A beta) of Alzheimer disease is derived from the proteolytic processing of the amyloid precursor proteins (APPs), which are considered type I transmembrane proteins. Here we report that the soluble fraction of isolated adrenal medullary chromaffin granules (CG), a model neuronal secretory vesicle system, contains an antigen that immunochemically and on sodium dodecyl sulfate-polyacrylamide gel electrophoresis was indistinguishable from full-length APP. A truncated APP fragment with intact A beta sequence was also detected in the soluble fraction of CG. In vitro experiments showed that full-length APP was solubilized from CG membranes at 37 degrees C as a function of pH, with a peak of activity between pH 8.5 and pH 9.0. Solubilization of full-length APP was inhibited by several protease inhibitors, including aprotinin, cystatin, and iodoacetamide, by the divalent cations Ca2+ and Zn2+, and by preheating of the membranes. These results are consistent with and suggest the involvement of an enzymatic mechanism in the solubilization of potentially amyloidogenic full-length APP. Production of A beta from a transmembrane APP predicts a proteolytic cleavage within the lipid bilayer, a site relatively inaccessible to proteases. Thus, the detected soluble, potentially amyloidogenic, full-length APP may be a substrate for the proteases producing A beta. The detection of soluble APP with intact A beta sequence in secretory vesicles is consistent with the extracellular topology of amyloid depositions.

Adrenal Medulla↗

PubMed2005

Characteristic localisation of denatured high-density lipoprotein (HDL) at the periphery of a lipid core in human atherosclerotic lesions.

AIMS: High-density lipoprotein (HDL) has been reported to efflux cholesterol (Chl) from the cell membrane, and the physiological balance between the influx and efflux of Chl is important in the formation of atherosclerotic lesions. METHODS: In order to clarify these mechanisms in atherosclerotic lesions, the ratios of areas of apoprotein A-I (apo A-I)-positive areas were determined using a fluorescence polarisation microscope coupled to a spectrometer. RESULTS: According to the staining patterns of apo A-I, atherosclerotic lesions are classified into three types, namely, focal dense area (FA), diffuse dense area (DA) and shading area (SA). In FA, protein was prominent and lipid was minimal in the intercellular space of degenerated cells in the thickened intima. In DA, the protein and lipid were co-localised. In SA, at the periphery of lipid core, more lipids were present than protein. In the developed lesions, FA and SA were statistically bigger than those in the early lesions. CONCLUSIONS: These results suggest that an effective micro-solubilisation mechanism in FA may result in a low lipid content. Moreover, accumulated HDL may alter the relationship between various lipid vesicles and crystals in the extracellular matrix, and be an additional factor for the fragility of atheromatous plaques at the periphery of the lipid core.

Adult↗

PubMed1998

Juvenile hyaline fibromatosis: ultrastructural study.

Juvenile hyaline fibromatosis is a multisystemic disorder characterized by a triad of cephalic fibrous outgrowths, gingival hyperplasia, and flexion contractures. The aim of this study was to find new ultrastructural features that could be useful for differentiating this entity from other types of fibromatosis. Mucosal lesions processed for light and electron microscopy by routine techniques showed hyperactive-appearing spindle-shaped fibroblasts and dysplastic mesenchymal cells. Dilated rough endoplasmic reticulum, prominent Golgi complexes, and multivesicular bodies as well as single membrane vesicles filled with fibrillogranular material were seen within the cytoplasm of dysplastic mesenchymal cells. Many fibrillogranular vesicles contained smaller vesicles. There were also invaginations of the cell membrane that contained fibrillogranular material similar to that seen in the single membrane vesicles, suggesting engulfment of an extracellular substance. The stroma contained both normal and serrated collagen fibrils, microfibrils, and two types of fibrillogranular material, one of them with a characteristic banding pattern. Our clinical and histopathologic findings resemble those previously described in cases of infantile systemic hyalinosis and juvenile hyaline fibromatosis. So many features of these two conditions overlap that it is difficult not to consider them as parts of a spectrum of the same disorder.

Fibroma↗

PubMed1983

Ultrastructural aspects after cryoultramicrotomy of bone tissue and sutural cartilage in neonatal mice calvaria.

Using transmission electron microscopy after cryoultramicrotomy, mineralized as well as unmineralized bone tissues and sutural cartilage were observed in neonatal mice calvaria. A good definition of osteoblasts (nucleus, membranes, organelles) and extracellular constituents (collagen fibrils, matrix vesicles, mineral substance) was obtained. The sutural zone was composed of an unmineralized cartilaginous tissue with more or less hypertrophic cells surrounded by a finely fibrillar matrix.

Animals↗

PubMed2002

Multivesicular bodies and multivesicular endosomes: the "ins and outs" of endosomal traffic.

Multivesicular endosomes (MVEs) are complex intracellular organelles that function in endocytosis. A major function of the endocytic pathway is to sort internalized macromolecules and membrane proteins. Appropriately sorted proteins, such as epidermal growth factor (EGF) receptor (EGFR), are incorporated into MVEs before transport to the lysosomal compartment, where degradation occurs. Thus, MVEs operate in the endosome-to-lysosome portion of the pathway. In yeast cells, where MVE formation has been extensively studied, the pathway terminates in the yeast vacuole, which is equivalent to the vertebrate lysosome. MVEs arise by invagination of the limiting membrane of an endosomal vesicle such that many small internal vesicles are formed, hence the term "multivesicular endosome." In part, the internalization and targeting of membrane proteins to the MVE involves ubiquitin, a small protein associated with protein degradation. In reticulocytes and certain antigen-presenting cells, MVEs are routed to the plasma membrane rather than the lysosome, releasing small vesicles called "exosomes" back into the extracellular space.

Animals↗

PubMed2002

Problem-based writing with peer review improves academic performance in physiology.

The aim of this study was to determine whether problem-based writing with peer review (PW-PR) improves undergraduate student performance on physiology exams. Didactic lectures were replaced with assignments to give students practice explaining their reasoning while solving qualitative problems, thus transferring the responsibility for abstraction and generalization to the students. Performance on exam items about concepts taught using PW-PR was compared with performance on concepts taught using didactic lectures followed by group work. Calibrated Peer Review, a Web-delivered program, was used to collect student essays and to manage anonymous peer review after students "passed" three calibration peer reviews. Results show that the students had difficulty relating concepts. Relationship errors were categorized as (1) problems recognizing levels of organization, (2) problems with cause/effect, and (3) overgeneralizations. For example, some described cells as molecules; others thought that vesicles transport materials through the extracellular fluid. With PW-PR, class discussion was used to confront and resolve such difficulties. Both multiple-choice and essay exam results were better with PW-PR instead of lecture.

Educational Measurement↗

PubMed1983

The morphology of the calcification front in articular cartilage. Its significance in joint function.

Biochemical and histochemical studies have indicated that there is specific cellular activity in the region of the calcification front of articular cartilage implying that a regulation process takes place there. Using scanning and transmission electron microscopy and light microscopy to examine tissue sections of both undecalcified and decalcified articular cartilage in the region of the calcification front, we have looked at its morphology with particular reference to its cellular control. Our observations show that physiological calcification is an active process under cellular control and is related to the presence of extracellular membrane-bound matrix vesicles.

Animals↗

PubMed2006

Low density lipoprotein aged in plasma forms clusters resembling subendothelial droplets: aggregation via surface sites.

In early phases of atherogenesis, droplets and vesicles accumulate in the subendothelial extracellular space of arterial intima. There is much evidence to suggest that these droplets, ranging between 100 and 400 nm, derive from modified low-density lipoprotein (LDL). In investigations of the formation mechanism of these droplets, LDL fusion was previously induced in vitro by proteolysis, lipolysis, oxidation, and vigorous shaking, but all treatments failed to reproduce the size distribution range of in vivo droplets, mostly resulting, instead, in particles with a diameter intermediate between that of one and two LDL. Our approach was meant to mimic LDL aging in plasma. LDL isolated from plasma that was incubated overnight at 37 degrees C is slightly modified in the secondary structure of its protein component and is primed to form very large aggregates according to a reaction-limited mechanism. This mechanism requires interactions between selected surface sites, whereas massive fusion is ruled out. In the frame of the general theory for colloids, the aggregation of LDL aged in plasma fulfills all the requirements of the reaction-limited mechanism, encompassing 1), exponential growth; 2), fractal structure, with the dimension of elementary constituent still consistent with a single LDL; and 3), extreme polydispersity of aggregates, with shape and dimension very close to that of droplets observed in vivo.

Circular Dichroism↗

PubMed1995

Japanese encephalitis virus-specific proliferative responses of human peripheral blood T lymphocytes.

The T lymphocytes play an important role in prevention and recovery from viral infections. To characterize T lymphocyte responses to Japanese encephalitis (JE) virus infections, we analyzed JE virus-specific T lymphocytes in peripheral blood mononuclear cells (PBMC) obtained from seven JE patients and 10 vaccinees who had received a formalin-inactivated, purified JE virus vaccine (Biken vaccine). These PBMC were examined for proliferative responses against live JE virus, a glutaraldehyde-fixed lysate of cells infected with JE virus, and extracellular particles (EPs; subviral membrane vesicles released from cells infected with recombinant vaccinia viruses encoding the JE virus premembrane and envelope proteins). Japanese encephalitis virus-specific T cell proliferation was demonstrated with PBMC from both patients and vaccinees after stimulation with infectious JE virus or the lysate of JE virus-infected cells. Proliferating PBMC included CD4+ T lymphocytes and CD8+ T lymphocytes in responses to either form of JE viral antigens. Responses to EPs were observed only with PBMC from some American vaccinees whose PBMC also responded to the virus and lysate. These results indicate that JE virus infection and immunization with an inactivated JE vaccine induce JE virus-specific CD4+ and CD8+ T memory lymphocytes that can be induced to proliferate by infectious JE virus and noninfectious JE antigens.

Antibodies, Viral↗

PubMed2003

Neuronal glutamate uptake Contributes to GABA synthesis and inhibitory synaptic strength.

Neurons must maintain a supply of neurotransmitter in their presynaptic terminals to fill synaptic vesicles. GABA is taken up into inhibitory terminals by transporters or is synthesized from glutamate by glutamic acid decarboxylase. Here we report that glutamate transporters supply GABAergic terminals in the hippocampus with glutamate, which is then used to synthesize GABA for filling synaptic vesicles. Glutamate transporter antagonists reduced IPSC and miniature IPSC (mIPSC) amplitudes, consistent with a reduction in the amount of GABA packaged into each synaptic vesicle. This reduction occurred rapidly and independently of synaptic activity, suggesting that modulation of vesicular GABA content does not require vesicle release and refilling. Raising extracellular glutamate levels increased mIPSC amplitudes by enhancing glutamate uptake and, consequently, GABA synthesis. These results indicate that neuronal glutamate transporters strengthen inhibitory synapses in response to extracellular glutamate. This modulation appears to occur under normal conditions and may constitute a negative feedback mechanism to combat hyperexcitability.

Amino Acid Transport System X-AG↗

PubMed1975

Synthesis of type I collagen by human smooth muscle cells in vitro.

Human vascular smooth muscle cells, derived from explants of medial smooth muscle of a fetal aorta, were grown in vitro and examined with phase and electron microscopy for characteristic morphologic features of smooth muscle cells and for the biosynthesis of connective tissue proteins. Their patterns of growth and ultrastructure were similar to those described for other species of cultured arterial smooth muscle cells. Most cells contained varying amounts of myofilaments interpersed with dense bodies, rough and smooth endoplasmic reticulum, mitochondria, various sized vesicles, lysosomes, and lipid droplets. Extracellularly, small amounts of electron-dense material and microfilaments were observed adjacent to or between the cells. The over-all morphology suggested that the smooth muscle cells were actively engaged in protein synthesis. Although we could not identify banded collagen fibrils in 10- to 14-day-old cultures by electron microscopy, the cells synthesized and secreted a collagen characterized as type I collagen. A hydroxyproline-containing protein composed of two alpha-1 and one alpha-2 chains was extracted from the cell layer. The triple helical precursor of type I collagen, procollagen, was secreted into the medium.

Aorta↗

PubMed1988

Localization of vitamin D3-responsive alkaline phosphatase in cultured chondrocytes.

Alkaline phosphatase activity appears to be altered when chondrocyte cultures are incubated with 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3). This study examined whether the hormone-responsive enzyme activity is associated with alkaline phosphatase-enriched extracellular membrane organelles called matrix vesicles. Confluent, third passage cultures of rat costochondral growth cartilage (GC) or resting zone chondrocytes (RC) were incubated with 1,25-(OH)2D3 or 24,25-dihydroxyvitamin D3 (24,25-(OH)2D3) and enzyme specific activity was assayed in the cell layer or in isolated matrix vesicle and plasma membrane fractions. Alkaline phosphatase-specific activity in the matrix vesicles was enriched at least 2-fold over that of the plasma membrane and 10-fold over that of the cell layer. Matrix vesicle alkaline phosphatase was stimulated by 1,25-(OH)2D3 in GC cultures and by 24,25-(OH)2D3 in RC cultures. The cell layer failed to reveal these subtle differences. 1,25-(OH)2D3 increased GC enzyme activity but the effect was one-half that observed in the matrix vesicles alone. No effect of 1,25-(OH)2D3 on enzyme activity of the RC cell layer or of 24,25-(OH)2D3 on either GC or RC cell layers was detected. Thus, response to the metabolites is dependent on chondrocytic differentiation and is site specific: the matrix vesicle fraction is targeted and not the cells per se.

24,25-Dihydroxyvitamin D 3↗

PubMed1985

Acetylcholinesterase in human thymus cells.

Acetylcholinesterase (AChE) was long thought to be an enzyme found specifically at the sites of nerve synapses and neuromuscular junctions. It has also been found to occur, however, in cells that are not involved with neurotransmission. This study presents the ultrastructural localization of AChE activity in human thymus cells, using the indirect thiocholine method. Cytochemical demonstration of the enzyme was based on the coupling of acetylthiocholine iodide hydrolysis to the precipitation of heavy metal salts. AChE activity was selectively revealed in the perinuclear cisternae, within the endoplasmic reticulum, and in the Golgi complex of thymic lymphocytes and epithelial cells. Evidence of the presence of reaction product in the latter cells was also found in vesicles that opened into the extracellular space. This is the first demonstration of AChE in human thymus cells. Its possible physiologic role in the thymus gland is discussed.

Acetylcholinesterase↗

PubMed1983

[Calcification of the arterial wall in the aging process. Electron microscopic and biochemical studies of a model of vitamin D3 overdose].

The following mechanisms for inactivating excessive Ca++ are found in the vessel wall (e.g. in old age, arteriosclerosis, hypertension, or overdosage with Vitamin D3): 1. The production of Matrix Vesicles, which reduce biologically active extracellular Ca++ by precipitating it during the initial stage of calcification. 2. An increase in the number of muscle cells changed from the "k" to the "m" form. These also possess a mechanism for reducing the intracellular Ca++ level. If in spite of these mechanisms the extracellular Ca++ concentration remains raised, this can result in calcification of the interzellular substance, particularly the elastic material.

Aged↗

PubMed2001

Amphetamine distorts stimulation-dependent dopamine overflow: effects on D2 autoreceptors, transporters, and synaptic vesicle stores.

Amphetamine (AMPH) is known to raise extracellular dopamine (DA) levels by inducing stimulation-independent DA efflux via reverse transport through the DA transporter and by inhibiting DA re-uptake. In contrast, recent studies indicate that AMPH decreases stimulation-dependent vesicular DA release. One candidate mechanism for this effect is the AMPH-mediated redistribution of DA from vesicles to the cytosol. In addition, the inhibition of stimulation-dependent release may occur because of D2 autoreceptor activation by DA that is released via reverse transport. We used the D2 receptor antagonist sulpiride and mice lacking the D2 receptor to address this issue. To evaluate carefully AMPH effects on release and uptake, we recorded stimulated DA overflow in striatal slices by using continuous amperometry and cyclic voltammetry. Recordings were fit by a random walk simulation of DA diffusion, including uptake with Michaelis-Menten kinetics, that provided estimates of DA concentration and uptake parameters. AMPH (10 microm) promoted the overflow of synaptically released DA by decreasing the apparent affinity for DA uptake (K(m) increase from 0.8 to 32 microm). The amount of DA released per pulse, however, was decreased by 82%. This release inhibition was prevented partly by superfusion with sulpiride (47% inhibition) and was reduced in D2 mutant mice (23% inhibition). When D2 autoreceptor activation was minimal, the combined effects of AMPH on DA release and uptake resulted in an enhanced overflow of exocytically released DA. Such enhancement of stimulation-dependent DA overflow may occur under conditions of low D2 receptor activity or expression, for example as a result of AMPH sensitization.

Amphetamine↗

PubMed2004

Lysophospholipid regulates release and activation of latent TGF-beta1 from chondrocyte extracellular matrix.

Transforming growth factor beta-1 (TGF-beta1) is released from the extracellular matrix of rat growth plate chondrocytes and activated by stromelysin-1 (matrix metalloproteinase 3, MMP-3), an enzyme that is stored in matrix vesicles. MMP-3 is released from these extracellular organelles by the direct action of 1alpha,25(OH)2D3 via activation of phospholipase A2 (PLA2), resulting in local production of lysophospholipids and matrix vesicle membrane destabilization. This effect of 1alpha,25(OH)2D3 is greater in matrix vesicles from growth zone chondrocyte cultures and PLA2 activity is higher in the growth zone in vivo, suggesting that it may depend on chondrocyte maturation state in the endochondral lineage. Previous studies have shown that latent TGF-beta1 can be activated by mild detergents in vitro, suggesting that lysophospholipids may act in vivo in a similar manner. To test this hypothesis, we determined if rat costochondral growth plate cartilage cells produce lysophosphatidylcholine (LPC) and lysophosphatidylethanolamine (LPE) in a maturation state-dependent manner and if LPC or LPE could release and activate latent TGF-beta1 from the extracellular matrix produced by these cells. Rat growth plate chondrocytes produced both lysophospholipids, with growth zone cells producing higher levels of LPE via PLA1, and resting zone cells producing higher levels of LPC via PLA2. LPC and LPE directly increased activation of recombinant human latent TGF-beta1 in a biphasic manner with a peak at 2 microg/ml. Phosphatidylcholine, phosphatidylethanolamine, and LPE plasmalogen (LPEP), but not choline, also activated TGF-beta1. Latent TGF-beta1 incubated with LPC or LPE, but neither lysophospholipid alone, stimulated [3H]-thymidine incorporation of resting zone cells, indicating the TGF-beta1 released was biologically active. LPC and LPE also released TGF-beta1 in a dose- and time-dependent manner when incubated with cell-free extracellular matrices produced by the cells. These results indicate that LPC and LPE have important roles as regulators of rat growth plate chondrocytes by directly and indirectly activating TGF-beta1 stored in the extracellular matrix.

Animals↗

PubMed1988

Endogenous lectin secretion into the extracellular matrix of early embryos of Xenopus laevis.

An endogenous galactoside-binding lectin with subunit molecular weight of 43,000-45,000, previously detected in unfertilized eggs of Xenopus laevis, persists at high levels in embryos through gastrulation. During embryonic development the lectin is found in cytoplasmic vesicles, and then is secreted into extracellular matrix which is prominent around the blastopore and on the roof of the blastocoel. The lectin is also found in the extracellular material in the developing neural fold. The presence of lectin at sites of active morphogenetic movements raises the possibility that it participates in the formation of an extracellular matrix that influences these processes.

Animals↗

PubMed1988

Ultrastructure of odontogenic cells during enameloid matrix synthesis in tooth buds from an elasmobranch, Raja erinacae.

The ultrastructure of the inner dental epithelial cells (IDE) and odontoblasts in elasmobranch (Raja erinacae) tooth buds was investigated by transmission electron microscopy to determine what contribution each cell type makes to the forming enameloid matrix. Row II, early stage, IDE cells contained few organelles associated with protein synthesis, whereas preodontoblasts appeared competent to initiate extracellular matrix production. Row III IDE cells are also devoid of organelles related to secretory protein synthesis, although these IDE cells accumulated large pools of intracellular glycogen. The glycogen appeared to be packaged into vesicles and exocytosed into the lateral extracellular space toward the forming enameloid matrix. Row III odontoblasts had a morphology consistent with an active protein secretory cell. No procollagen granules were present within the odontoblasts, however, nor were many collagen fibers observed in the enameloid matrix. Instead, non-collagenous "giant" fibers having 17.5-nm periodic cross striations were associated with the invaginations of odontoblast cell processes. Giant fibers, which spanned a clear zone adjacent to the odontoblasts, terminated within the enameloid matrix. Smaller 25-nm-wide "unit" fibers emanated from the giant fiber tips to form the bulk of the enameloid matrix. The clear zone, which separated the odontoblasts from the enameloid matrix at early stages, diminished in size at later stages until the odontoblast processes were completely embedded in the enameloid matrix. Nascent enameloid crystallites were observed only after a layer of unmineralized predentin was deposited beneath fully formed enameloid matrix. The results suggest that the major constituent of the enameloid matrix in skates is a non-collagenous protein derived from the odontoblasts. The inner dental epithelial cells appear to contribute large quantities of carbohydrates to the forming enameloid matrix.

Animals↗