SEARCH · PubMed Health

Results for “Cell Aggregation”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14Linked to original sources

PubMed2004

Gap junction communication between cells aggregated on a cellulose-coated polystyrene: influence of connexin 43 phosphorylation.

The appropriate functioning of tissues and organ systems depends on intercellular communication such as gap junctions formed by connexin (Cx) protein channels between adjacent cells. We have previously shown that Swiss 3T3 cells aggregated on hydrophilic cellulose substratum Cuprophan (CU) establish short linear gap junctions composed of Cx 43 in cell surface plaques. This phenomenon seems to depend on the high intracellular cyclic AMP (cAMP) concentration triggered by attachment of the cells to CU. We have now used a cellulose-coated polystyrene inducing the same cell behaviour to analyse the gap junction communication between aggregated cells. The transfer of the dye Lucifer Yellow (LY) between cells showed that cells aggregated on cellulose substratum rapidly (within 90 min) establish functional gap junctions. Inhibitors of cAMP protein kinase (PKI) or protein kinase C (GF109203X) both inhibited the diffusion of LY between neighbouring cells. Western blot analysis showed that this change in permeability was correlated with a decrease in Cx 43 phosphorylation. Thus, cellulose substrata seem to induce cell-cell communication through Cx 43 phosphorylation modulated by PKA and PKC. To understand the mechanisms by which a substratum regulates gap junctional communication is critically important for the emerging fields of tissue engineering and biohybrid devices.

Animals↗

PubMed1979

The lipid composition of rat brain aggregating cell cultures during development.

The lipid and fatty acid composition of rat brain was studied during its development both in vivo and in an aggregating cell culture system. Although the amount of lipid present in the cultures was very low, the increase in glycolipid content corresponded closely to the period of intense myelin formation. Very long chain fatty acids (hydroxylated and unsubstituted) were present in 41-day cultures. In comparison to the in vivo situation, myelination was delayed in vitro and, after 40 days in culture, cholesterol esters were 5-fold higher than in vivo, indicating that demyelination was occurring.

Animals↗

PubMed1970

A fine structural study of adhesive cell junctions in heterotypic cell aggregates.

Mixed suspensions of cells obtained by dissociation of 7 day chicken embryo heart and pigmented retina were allowed to reaggregate in tissue culture. The reaggregates which resulted contained both kinds of cells. Establishment of homogeneous tissues by cell sorting out in these reaggregates was advanced by 20 hr in culture and was complete within 2 days. When sorting out was advanced, heterotypic aggregates were fixed, sectioned, and examined in the electron microscope. Particular attention was paid to the morphology of regions of contact between cells. No qualitative differences were observed in the contact junctions between like cells (heart-heart or pigmented retina-pigment retina junctions) and unlike cells (heart-pigmented retina junctions). Broad areas of undifferentiated cell contact with cell membranes separated by a 100-200 A gap were formed regardless of cell type. Specialized junctions of the fascia and macula adherens type were also present, not only between like cells but also between unlike cells.

Animals↗

PubMed1989

Production of interleukin-6 by folliculo-stellate cells of the anterior pituitary gland in a histiotypic cell aggregate culture system.

Reaggregate cell cultures of mouse or rat anterior pituitary were found to produce interleukin-6 (IL-6), a cytokine known for its multiple actions in the immune system. Studies on aggregates prepared from differentially enriched pituitary cell populations revealed the presence of folliculo-stellate (FS) cells to be essential for IL-6 production. Aggregates that contained only hormone-secreting, but no FS cells, failed to produce IL-6. Furthermore, the yield of IL-6 increased with increasing proportions of FS cells present in the aggregates. It is suggested that IL-6 participates in the local regulation of the secretory function of the hypophysis and may constitute a link between events in the immune system and those in the endocrine system.

Animals↗

PubMedDate not supplied

Effect of the bombesin receptor blockers [Leu13, psi CH2NH-Leu14]bombesin and N-pivaloyl GRP(20-25) alkylamide (L 686,095-001C002) on basal and neuromedin C-stimulated PRL and GH release in pituitary cell aggregates.

Perifusion of rat anterior pituitary cell aggregates, cultured in estrogen-supplemented serum-free medium with 1 nM of the bombesin (BBN)-like peptide, neuromedin C (NMC), significantly stimulates GH and PRL release. This effect is dose-dependently inhibited by the BBN receptor blocker L 686,095-001C002 [an N-pivaloyl-gastrin-releasing-peptide(20-25) alkylamide]. The IC50 was 0.20 nM in the case of the GH response and 0.16 nM in the case of the PRL response. The antagonist has no effect on basal PRL or GH release. [Leu13, psi CH2NH-Leu14]BBN (psi BBN) displays an IC50 of 0.41 microM for inhibiting the GH response and 0.36 microM for inhibiting the PRL response to NMC. At a concentration of 0.5 microM or 5 microM, however, the latter antagonist stimulates PRL and GH release when perifused alone. This stimulatory effect is dose dependent, augments when aggregates are cultured in 1 nM E2 (as is the case for NMC) and is abolished by 2 nM L 686,095-001C002. It is concluded that L 686,095-001C002 is a potent and pure antagonist of pituitary BBN receptors mediating PRL and GH release, whereas psi BBN is a relatively weak antagonist with considerable partial agonist activity.

Amides↗

PubMed1990

NASPE young investigator awardee-1990. Complex rhythms resulting from overdrive suppression in electrically stimulated heart cell aggregates.

Spontaneously beating embryonic chick heart cell aggregates were stimulated with current pulses delivered either as periodic trains, or at a fixed delay after each action potential. Following stimulation at fixed rates faster than the intrinsic rate, there was a transient slowing of the spontaneous rhythm. This response, called overdrive suppression, can lead to a complex evolution of rhythms. During periodic stimulation there is a continuum of dropped beat patterns, and during fixed delay stimulation bursting activity appears. This study provides a conceptual basis for understanding analogous rhythms in the intact heart.

Action Potentials↗

PubMed1983

Stimulation of prolactin release by angiotensin II in superfused rat anterior pituitary cell aggregates.

Superfusion of rat anterior pituitary cell aggregates with 10-min pulses of 0.1-10 nM angiotensin II (AII) resulted in a prompt and concentration-dependent rise of PRL release. The effect could be blocked by saralasin, an AII receptor antagonist. The response to AII, but not that to TRH, was rapidly desensitized: a 10 nM AII pulse caused an 80% depression of the response to a subsequent 10 nM pulse given 50 min later. The data provide a possible functional significance for the renin-angiotensin system recently demonstrated in the anterior pituitary.

Angiotensin II↗

PubMed1994

Cell aggregation in a Chinese hamster ovary cell microcarrier culture affects the expression rate and N-linked glycosylation of recombinant mouse placental lactogen-1.

A microcarrier culture of Chinese hamster ovary (CHO) cells, expressing the N-glycosylated recombinant protein mouse placental lactogen I (mPL-I), was found to form large cellular aggregates (400 to 600 microns in diameter). There was increased accumulation of lower molecular sized mPL-I glycoforms in cultures containing the large cellular aggregates at pH 7.3, but not at pH 7.6. Specific rates of mPL-I expression were found in the cultures with cellular aggregates at both pH values (7.3 and 7.6). These findings are interpreted in the light of our earlier studies that showed that extracellular pH and elevated ammonia concentrations affect both the glycosylation and the expression rates of mouse placental lactogen I.

Ammonia↗

PubMed2001

Novel cyclic peptide inhibits intercellular adhesion molecule-1-mediated cell aggregation.

Leukocyte adherence mediated by intercellular adhesion molecule-1 (ICAM-1) binding to leukocyte function-associated antigen (LFA-1) is required for proper inflammatory and immune function. Inhibition of ICAM-1\LFA-1 binding using monoclonal antibodies (mAb) has been shown to be efficacious at inhibiting lymphoma metastasis as well as leukocyte emigration into tissue in a number of inflammatory diseases such as ischemia-reperfusion injury, septic shock and rheumatoid arthritis. In this report, we describe the development and characterization of a small peptide antagonist of ICAM-1-dependent cell aggregation. By using repeated selection of a cyclic nonapeptide phage display library on purified ICAM-1, we identified phage that were competitively eluted with anti-ICAM-1 mAb. The peptide sequences were determined by nucleotide sequencing, and the peptide sequence (C*LLRMRSIC*) (IP01) that occurred most frequently was chosen for further study. Phage expressing this peptide sequence specifically bound ICAM-1 over a range of 5 x 10(6) to 1 x 10(8) phage/microL. A cyclic IP01 peptide, linear IP01 peptide, a cyclic nonapeptide with a scrambled IP01 sequence, and a random, cyclic nonapeptide were synthesized. The cyclic and linear IP01 peptides were able to inhibit ICAM-1-mediated cell aggregation at a concentration of 1 mM, whereas the random and scrambled peptide sequences did not alter aggregation. Cyclic IP01 had a half-maximal inhibitory concentration of approximately 970 microM. Cyclic IP01 did not inhibit cellular aggregation that was dependent on ICAM-2 or ICAM-3. Alanine substitutions in the cyclic IP01 identified at least four amino acids necessary for inhibition of ICAM-1 dependent cell aggregation; leucine 2, leucine 3, methionine 5, and arginine 6. Finally, we showed that cyclic IP01 can inhibit firm adhesion of neutrophils to endothelium, a critical event in inflammatory diseases, in an assay that recapitulates physiologic flow conditions. Homology of IP01 with the primary amino acid sequences of the alpha or beta subunit of LFA-1 was not identified. Thus, we identified a unique molecule that inhibits ICAM-1 dependent cell adhesion, but is not related to the primary sequence of the ICAM-1 ligand LFA-1. Due to the small size and ability to block cell-cell adhesion, IP01 may serve as a useful tool for study of ICAM-1 and LFA-1 biology as well as for the development of small molecule therapeutics.

Alanine↗

PubMed1983

Cell position regulates endodermal differentiation in embryonal carcinoma cell aggregates.

It has been suggested that cell position regulates endodermal differentiation in mouse embryo inner cell masses and in aggregates of embryonal carcinoma (EC) cells. This hypothesis states that cells at the interface between the cell mass and blastocoel fluid or culture medium differentiate into endoderm, whereas internally located cells follow alternative developmental pathways. To test the cell position hypothesis, pluripotent PSA-1 cells were aggregated with hypoxanthine phosphoribosyltransferase-deficient, parietal-like, endodermal cells. The resulting aggregates consisted of cores of PSA-1 cells surrounded by endodermal cells. Autoradiography was used to distinguish between endodermal cells that were the products of EC cell differentiation and the exogenous endoderm. Alkaline phosphatase staining was used to distinguish EC cells from endodermal cells. As predicted by the cell position hypothesis, the PSA-1 EC cells, all of which were internally located, did not differentiate into endodermal cells. Nonspecific inhibition of differentiation did not account for the lack of PSA-1-derived endoderm since the PSA-1 cells in such aggregates did differentiate into columnar ectodermal-like cells. Similar experiments were also conducted with F9 cells. In this case, aggregation cultures contained retinoic acid to induce F9 cells to differentiate into visceral endoderm. In cultures containing F9 cells surrounded by parietal-like endodermal cells, no F9-derived endoderm was detected either autoradiographically or by assaying for alpha-fetoprotein production, a visceral endoderm marker. Thus, retinoic acid-induced endodermal differentiation was also regulated by cell position. Collectively, the above results provide strong evidence for the hypothesis that cell position regulates endodermal differentiation in aggregates of EC cells.

Alkaline Phosphatase↗

PubMed2001

Engagement of CD147 molecule-induced cell aggregation through the activation of protein kinases and reorganization of the cytoskeleton.

CD147 is a broadly expressed cell surface molecule of the immunoglobulin superfamily whose expression is up-regulated upon T cell activation. Engagement of CD147 by CD147 monoclonal antibodies (mAbs) has been shown to induce homotypic aggregation of U937 cells. To study intracellular signal transduction induced by the engagement of CD147 molecules, protein kinase C (PKC) and protein tyrosine kinase (PTK) inhibitors were used to inhibit cell aggregation. The results indicated that a PKC inhibitor, sphingosine, and a PTK inhibitor, herbimycin A, inhibited CD147 mAb-induced cell aggregation in a dose-dependent manner. In contrast to herbimycin A, a PTK inhibitor, genistein, enhanced cell aggregation. This discrepancy may be due to the differential effect of herbimycin A and genistein on the target cells. Effect of actin filament polymerization blocking agent, cytochalasin B, was also studied and it was found that cytochalasin B completely inhibited CD147 mAb-induced cell aggregation. This result implied that U937 cell aggregation induced by CD147 mAbs is associated with cytoskeleton reorganization. Thus, our observations suggest that cell aggregation induced by the engagement of CD147 with specific mAbs depend upon the activation of protein kinases and a functional cytoskeleton.

Antibodies, Monoclonal↗

PubMed1988

Enhanced ANG II activity in anterior pituitary cell aggregates from hypertensive rats.

Pituitary cell reaggregates from 14-day-old and adult spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) were cultured in serum-free, chemically defined medium supplemented with the thyroid hormone triiodothyronine and the glucocorticoid dexamethasone. After 1 wk in culture, aggregates were transferred into a perifusion system, and the effect of angiotensin II (ANG II) on prolactin (PRL) and growth hormone (GH) release was studied. In aggregates from adult SHR, ANG II displayed a significant and dose-dependent GH releasing activity, whereas a negligible effect or no effect was seen in aggregates from adult WKY. In contrast, no difference in the stimulation of PRL release by ANG II was found. To exclude the possibility that the enhanced GH responsiveness was secondary to longstanding hypertension, aggregates from animals in the prehypertensive stage were studied. Both the GH and PRL responses to ANG II were significantly higher in aggregates from 14-day-old SHR than in aggregates from 14-day-old WKY. These data indicate that abnormal GH and PRL responses to ANG II exist in pituitary cell aggregates from SHR long before hypertension develops. Because these differences were found in pituitary cells maintained in culture for 1 wk, they do not seem to be secondary to changes in brain regulation of pituitary function but rather are caused by factors intrinsic to the pituitary.

Angiotensin II↗

PubMedDate not supplied

[Cell aggregation in cultures of Micrococcus luteus studied by dynamic light scattering].

Cell aggregation was studied using the method of dynamic light scattering in the course of growth of Micrococcus luteus cultures in a liquid medium. The method detects particles ranging in size from 0.5 to 1000 microm in samples containing no more than 10(5) cells/ml. When grown in liquid media, M. luteus forms aggregates; during the lag phase, 80% of the cells are found in aggregates of 10 to 1000 microm, only minor amounts being represented by single cells. With the onset of exponential growth, the aggregates were decomposed, and single cells became prevalent in the culture liquid. This observation confirms that the aggregation of the cells during the lag phase is prerequisite to the initiation of bacterial growth. The method may be used in biotechnology for monitoring the state of bacterial cultures.

Culture Media↗

PubMed2000

Dynamics of cell aggregation during in vitro neurogenesis by immortalized neuroectodermal progenitors.

Early events of in vitro neuronal development were studied by inducing neuron formation in a neuroectodermal cell line, NE-4C/A3, derived from the embryonic forebrain vesicles of p53-deficient mice. Neuronal differentiation was initiated by treating the cells with all-trans retinoic acid (RA). By the second day of RA treatment compact cell aggregates were formed. The first signs of neuronal cell fate decision were revealed inside the aggregates. To elucidate the process of aggregate formation, the dynamics of cell clustering and the migration of individual cells were investigated by a novel computer-controlled videomicroscopic system. Besides real-time observation of cell motility, the system allowed statistical analysis of large sets of data providing quantitative evaluation of cell locomotion during an early, critical phase of RA induced neuron formation. The results showed that chemoattractants did not play a principal role in cell aggregation. Retinoic acid, on the other hand, was found to cause a rapid decrease in the average migratory velocity without changing the randomness of migratory routes. The data indicated that aggregation was facilitated by increased cohesion upon incident collision of randomly encountering cells. The resulting compact cell clusters provided the structural conditions for contact communication apparently needed for the neuronal differentiation of NE-4C/A3 cells.

Animals↗

PubMed1987

In vitro culture of Drosophila imaginal disc cells: aggregation, sorting out, and differentiative abilities.

This paper describes the aggregation in vitro of cells dissociated from imaginal discs and demonstrates the sorting out of undifferentiated cells from different imaginal discs and from differently determined regions of the same imaginal disc, as well as the abilities of such cells to undergo pattern reconstruction when injected into larvae. Dissociated cells begin to aggregate by 1.5 hr of rotation. By 5 hr of rotation, large aggregates of loosely associated cells appear. By 18 hr the aggregates have condensed and taken on a characteristic epithelial structure. To study sorting out in undifferentiated cells, we combined a histochemical stain for acid phosphatase with the use of the acid phosphatase null mutant acphn-11. We performed cell mixing experiments with 0-2 (prospective notum) and 2-8 (prospective wing) fragments, with the A and P (prospective anterior and posterior) fragments of the dorsal mesothoracic disc and with mixtures of cells from ventral prothoracic and dorsal mesothoracic discs. We found that prospective anterior and posterior dorsal mesothoracic cells do not sort out, but that prospective notum and wing and leg and wing cells do. The results from differentiated implants are consistent with those from undifferentiated mixes.

Acid Phosphatase↗

PubMed1996

PC12 cell aggregation and neurite growth in gels of collagen, laminin and fibronectin.

PC12 cells form aggregates when suspended within three-dimensional, self-assembled, type I collagen gels; these aggregates increase in size over time. In addition, when the cells are cultured in the presence of nerve growth factor, they express neurites, which extend through the three-dimensional matrix. In this report, the roles of fibronectin, laminin and nerve growth factor in PC12 cell aggregation and neurite growth following suspension in collagen matrices were evaluated. Single cells and small clusters of cells were suspended in collagen gels; the kinetics of aggregation were determined by measurement of the projected area of each aggregate, and neurite lengths were determined by measurement of end-to-end distance. Fibronectin and laminin inhibited the aggregation of PC12 cells at 50 micrograms/ml, and fibronectin, but not laminin, inhibited the growth of neurites at 100 micrograms/ml. In the absence of serum, the aggregation of cells cultured with nerve growth factor was almost completely inhibited, but the average neurite length was unaffected. In the presence of nerve growth factor, the extent of cell aggregation could not be explained simply by an increase in cell number, suggesting the presence of two separate mechanisms for aggregate growth: one dependent on cell motility and another dependent on cell proliferation.

Animals↗

PubMed1999

Infection of rat brain cell aggregates with neurovirulent and nonneurovirulent strains of herpes simplex virus type 1.

Rat brain cell aggregates represent a three-dimensional tissue culture system of brain tissue in the form of small, multicellular spheroids. In the present work, we have infected these "minibrains" with neurovirulent, nonneurovirulent, and nonreplicating strains of HSV-1. The neurovirulent strains 17(+) and KOS(M) spread rapidly through the aggregates, while the nonreplicating ICP4 deletion mutant KD6 infected cells only at the periphery of the aggregates. Spread and replication of the nonneurovirulent strains RE6 and tk-7, and to some extent also of R13/1, were restricted. The interaction between different strains of HSV-1 and the rat brain cell aggregates is thus comparable to that seen in the brain, suggesting that the aggregates represent a useful tool for studying HSV-1 infection of brain tissue in vitro.

Animals↗

PubMed1995

Roles of hematocrit and fibrinogen in red cell aggregation determined by ultrasonic scattering properties.

Parameters of the power spectrum of backscattered echoes were applied to quantitatively evaluate red cell aggregation in vitro. Human red cell suspensions were circulated in a closed loop of tubing, and ultrasonic, radiofrequency, echo-signal data were obtained using a 10-MHz transducer. Data acquisition was performed at 30-s to 1-min intervals for 5 min after flow stoppage. Two parameters of the normalized power spectrum of the echo signals, spectral slope and Y-intercept, were computed, and estimates of two scattering properties, the scatterer size and acoustic concentration were calculated from these parameters using equations based on scattering theory. Size and acoustic concentration were observed as they changed over time after the stoppage of flow. The key findings were that hematocrit affected the rate of cell aggregation while fibrinogen controlled aggregate size and acoustic concentration.

Adult↗