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H Geerts

Publications and source records attributed to H Geerts.

At least 37 records · Page 2Linked to original sources
PubMed1998

Annexin V binding assay as a tool to measure apoptosis in differentiated neuronal cells.

We describe a rapid and reliable method to quantitate the extent of apoptosis in neuronal cell cultures. Based on their annexin V-affinity, resulting from phosphatidylserine (PS) exposure at the outer leaflet of the plasma membrane, apoptotic cells can be distinguished from annexin V-negative living cells, by using microscopic and flow cytometric procedures. When combined with propidium iodide (PI) the double labeling procedure allows a further distinction of necrotic (annexin V+/PI+), apoptotic (annexin V+/PI-) cells. Furthermore, when the cells are incubated with annexin V prior to harvesting, the former cell populations can be separated from cells damaged during isolation (annexin V-/PI+). In the present paper, we show that the annexin V-binding assay is also applicable to differentiated neuronal cells with fragile neurite outgrowths.

Annexin A5↗
PubMed1998

Altered [Ca2+] homeostasis in PC12 cells after nerve growth factor deprivation.

[Ca2+]i homeostasis in individual PC12 cells after elevated [K+]o was studied by ratiometric microscopy, during nerve growth factor (NGF) deprivation. A significantly lower number of cells responded with an increased [Ca2+]i in the NGF deprived condition. Moreover, the responding cells were more deficient in regulating their [Ca2+]i back to control levels, after the transient peak. This suggests that differentiated neurons do not traverse the apoptotic program homogeneously with regard to their [Ca2+]i regulation and that NGF deprived PC12 cells have more difficulties to reduce their [Ca2+]i after influx of [Ca2+]o.

Animals↗
PubMed1998

Neuronal differentiation is accompanied by NSP-C expression.

Neuroendocrine-specific protein (NSP) reticulons are expressed in neural and neuroendocrine tissues and cell cultures derived therefrom, while most other cell types lack NSP-reticulons. Three major subtypes have been identified so far, designated NSP-A, NSP-B, and NSP-C. We have investigated the correlation between the degree of neuronal differentiation, determined by morphological and biochemical criteria, and NSP-reticulon subtype expression. For this purpose, several human neuroblastoma cell lines, exhibiting different degrees of neuronal differentiation, were examined immuno(cyto)chemically. It became obvious that the expression of NSP-C, as detected by immunofluorescence microscopy and Western blotting, is most prominent in cell lines with a high degree of neuronal differentiation, such as LA-N-5. Such highly differentiated cells also express other neural and neuroendocrine markers, such as neural cell adhesion molecule (NCAM), neurofilament proteins, synaptophysin, and chromogranin. NSP-A was observed in all cell lines to a different extent. However, no clear correlation was observed with the degree of neuronal differentiation as defined by other neuronal and neuroendocrine markers or morphology. NSP-B could not be detected. The induction of neuronal differentiation with nerve growth factor, dbcAMP, and retinoic acid in the rat pheochromocytoma cell line PC12 and the human teratocarcinoma cell line hNT2, respectively, induced the expression of NSP-A and NSP-C in these cell lines parallel to the induction of neurofilament protein expression. It is concluded that NSP-C expression, in particular, is strongly correlated with neuronal differentiation.

Animals↗
PubMed1998

Okadaic acid-induced apoptosis in neuronal cells: evidence for an abortive mitotic attempt.

There is increasing evidence that apoptosis in postmitotic neurons is associated with a frustrated attempt to reenter the mitotic cycle. Okadaic acid, a specific protein phosphatase inhibitor, is currently used in models of Alzheimer's research to increase the degree of phosphorylation of various proteins, such as the microtubule-associated protein tau. Okadaic acid induces programmed cell death in the human neuroblastoma cell lines TR14 and NT2-N, as evidenced by fragmentation of DNA and attenuation of this process by protein synthesis inhibitors. In differentiated TR14 cells, okadaic acid increases the fraction of cells in the S phase, induces the appearance of cyclin B1 and cyclin D1 markers of the cell cycle, and triggers a time-dependent increase in DNA fragmentation after release of a thymidine block. Fully differentiated NT2-N cells are forced to enter the mitotic cycle as shown by DNA staining. Chromatin condensation and chromosome formation are initiated, but the cells fail to complete their mitotic cycle. These data suggest that okadaic acid forces differentiated neuronal cells into the mitotic cycle. This pattern of cyclin up-regulation and cell cycle shift is compared with apoptosis induced by neurotrophic factor deprivation in differentiated rat pheochromocytoma PC12 cells.

Anaphase↗
PubMed1997

Aberrant tau phosphorylation and neurite retraction during NGF deprivation in PC12 cells.

Recently apoptotic markers have been found in Alzheimer's Disease (AD) brain. To investigate the relation between tau phosphorylation and apoptosis, immunocytochemistry of AT8 (indicating the degree of phosphorylation at the tau Ser202/Thr205 site) was quantitatively determined the degree of tau phosphorylation at the Ser202 site was monitored during neuronal apoptosis in differentiated PC12 cells after nerve growth factor (NGF) deprivation. During this programmed cell death a prominent retraction of neurites took place that was associated with a clear increase in the level of AT8 signalaberrant phosphorylated tau at the Ser202 site. The broad spectrum kinase inhibitor staurosporine attenuated both this increase in tau phosphorylation, neurite retraction, and apoptosis. We suggest that at some point during programmed cell death, kinases with tau as substrate become activated and that the resulting loss of cytoskeletal integrity leads to neurite instability.

Animals↗
PubMed1995

Sodium butyrate induces aberrant tau phosphorylation and programmed cell death in human neuroblastoma cells.

Paired helical filaments, one of the major hallmarks of Alzheimer's disease brains at autopsy, consist mainly of aberrantly phosphorylated tau. This aberrant tau phosphorylation can be induced in the human neuroblastoma cell line TR14 by a hyperstimulating mixture, consisting of nerve growth factor (NGF), db-cAMP, gangliosides and sodium butyrate (NaBut) [20,23]. Evidence is presented that exposing these cells to increasing concentrations of NaBut alone in the 0.5-2 mM dose-range is sufficient to induce aberrant tau phosphorylation within 24 h, measured by AT-8 immunocytochemistry and Western blotting. This process is associated with increased morphological differentiation. Furthermore, the aberrant tau phosphorylation is followed by neurotoxicity. This neurotoxicity has features of programmed cell death, such as fragmentation on a DNA agarose gel, fragmented nuclei and chromatin condensation and inhibition by the protein synthesis inhibitor cycloheximide. The mechanism by which NaBut induces these modified tau proteins and neurotoxicity are largely unknown but the data suggest an involvement of cytoskeletal proteins.

Antibodies, Monoclonal↗
PubMed1993

The fast axonal transport in hippocampal neurones is acutely enhanced by db-cAMP.

It has been observed that neurones have a certain capacity for the upregulation of fast axonal transport, for instance during nerve regeneration or reactive sprouting. However, the molecular regulation of this transport system is largely unknown. We show here by quantitative video-microscopy of endogenous organelles that application of 1 mM db-cAMP increases the velocity of fast axonal transport maximally by 32% within 60 minutes in neonatal hippocampal cells. At the same time, the jump length of the saltatory motions remains largely unchanged. The data suggest that activation of protein kinase A plays a role in the immediate upregulation of axonal transport.

Animals↗
PubMed1992

Sabeluzole, a memory-enhancing molecule, increases fast axonal transport in neuronal cell cultures.

Morphological rearrangements, such as synapse number changes, have been observed in the adult mammalian brain after various experimental paradigms of learning and behavioral experience. The role of axonal transport in the physical translocation of material during this form of brain plasticity has not been fully appreciated. We show here by quantitative video microscopy that sabeluzole (R58735), a new memory-enhancing drug in humans, effectively increases fast axonal transport in rat neuronal cell cultures. Long-term incubation (24 hr) with sabeluzole in the concentration range between 0.1 and 1 microM increases both velocity and jump length of saltatory movements maximally by 20-30% in embryonic hippocampal neurons. Acute treatment only increases the velocity by 15-20%. Furthermore, the inhibition of axonal transport by 0.1 mM vanadate in N4 neuroblastoma cells is reversed by 1 microM sabeluzole. Observations on the kinesin-induced microtubule mobility in a reconstituted system show a 10% enhancement by sabeluzole at an optimal concentration of 2 microM, but no increase in kinesin ATPase activity. To our knowledge, this is the first pharmacological compound shown to increase fast axonal transport. The mechanism of fast axonal transport enhancement is discussed as a rationale for new therapeutic treatment in neuropathology.

Animals↗
PubMed1992

Lysophosphatidylcholine-induced Ca(2+)-overload in isolated cardiomyocytes and effect of cytoprotective drugs.

It has been previously demonstrated that lysophosphatides accumulate rapidly in ischaemic tissue, and may play a key role in the genesis of ischaemia-reperfusion injury. The present study investigated the effects of exogenously added lysophosphatidylcholine (1-20 microM) on single isolated cardiomyocytes from adult rabbit hearts. Quiescent cells exposed to > or = 8 microM lysophosphatidylcholine dose-dependently displayed irreversible hypercontraction, whereas after 60 min at 3 microM lysophosphatidylcholine, most cells remained rod-shaped (87.2 +/- 2.0%, mean +/- S.E.M.). However, when combined with electrical field stimulation (1 Hz), exposure to 3 microM lysophosphatidylcholine resulted in irreversible hypercontracture of most cells after 60 min: only 27.5 +/- 7.5% of the cells remained rod-shaped. Contracture depended upon the presence of extracellular Ca2+, and coincided with a significant rise in the median intracellular free Ca2+ level from 72.2 to 352.1 nM (P = 0.0001), suggesting intracellular Ca(2+)-overload. Pretreatment with 10(-6) M flunarizine or R 56865 significantly reduced the fraction of damaged cells when exposed to 3 microM lysophosphatidylcholine and electrical stimulation: 78.3 +/- 12.2% and 56.3 +/- 13.1% respectively of the cells remained rod-shaped. No protection was observed when quiescent cells were exposed to 10 microM lysophosphatidylcholine. Cytochemical localization of Ca2+ showed that lysophosphatidylcholine induced a loss of sarcolemma-bound Ca2+ precipitate and an accumulation of Ca2+ clusters in mitochondria of damaged cells in a dose and time dependent way. These results suggest that lysophosphatidylcholine induces functional and structural damage (Ca(2+)-overload) in isolated cardiomyocytes and that this can be prevented by cytoprotective drugs.

Animals↗
PubMed1991

Nanovid microscopy.

By combining small colloidal gold probes with video-enhanced quantitative microscopy, the intracellular dynamics of specific proteins in living cells can now be studied.

Axonal Transport↗
PubMed1991

Lateral diffusion and retrograde movements of individual cell surface components on single motile cells observed with Nanovid microscopy.

A recently introduced extension of video-enhanced light microscopy, called Nanovid microscopy, documents the dynamic reorganization of individual cell surface components on living cells. 40-microns colloidal gold probes coupled to different types of poly-L-lysine label negative cell surface components of PTK2 cells. Evidence is provided that they bind to negative sialic acid residues of glycoproteins, probably through nonspecific electrostatic interactions. The gold probes, coupled to short poly-L-lysine molecules (4 kD) displayed Brownian motion, with a diffusion coefficient in the range 0.1-0.2 micron2/s. A diffusion coefficient in the 0.1 micron2/s range was also observed with 40-nm gold probes coupled to an antibody against the lipid-linked Thy-1 antigen on 3T3 fibroblasts. Diffusion of these probes is largely confined to apparent microdomains of 1-2 microns in size. On the other hand, the gold probes, coupled to long poly-L-lysine molecules (240 kD) molecules and bound to the leading lamella, were driven rearward, toward the boundary between lamelloplasm and perinuclear cytoplasm at a velocity of 0.5-1 micron/min by a directed ATP-dependent mechanism. This uniform motion was inhibited by cytochalasin, suggesting actin microfilament involvement. A similar behavior on MO cells was observed when the antibody-labeled gold served as a marker for the PGP-1 (GP-80) antigen. These results show that Nanovid microscopy, offering the possibility to observe the motion of individual specific cell surface components, provides a new and powerful tool to study the dynamic reorganization of the cell membrane during locomotion and in other biological contexts as well.

Adenosine Triphosphate↗
PubMed1991

The effect of cyclosporine on electrically paced isolated rat cardiomyocytes.

The acute cardiotoxicity of cyclosporine was investigated in isolated cardiomyocytes from adult rats. In a first study, myocytes were incubated with CsA ranging from 1 to 10 micrograms/ml and paced by electrical-field stimulation. After 30 min of stimulation the number of surviving rod-shaped myocytes was significantly reduced at 2.5 micrograms/ml (77.9%) and 5 micrograms/ml CsA (64.2%) as compared with the drug vehicle methanol (88.8%, P less than 0.05) with a further decrease at 10 micrograms/ml CsA (30.1% vs. 81.2%, P less than 0.005). In a second study, with the use of digital image processing of fura-2 fluorescence, the mean intracellular free calcium concentration, integrated over 1 sec, of single myocytes in the presence of 5 micrograms/ml CsA, the solvent methanol, or pure Krebs Ringer Hepes buffer was measured. Starting 2 Hz field stimulation increased the intracellular free calcium concentration from 100.1 to 177.9 nM in buffer and from 145.7 to 200.6 nM calcium with methanol. In contrast, there was a 3-fold increase of the intracellular free calcium concentration with 5 micrograms/ml CsA from 128.8 to 376.1 nM calcium. The intracellular free calcium during electrical stimulation was significantly higher with CsA than with the solvent (376.1 nM vs. 200.6 nM, P less than 0.001). In a further study, myocytes were incubated with calcium ranging from 0.5 to 8 mM calcium in the presence of 5 micrograms/ml CsA or the solvent methanol and electrically stimulated. Here, with increasing extracellular calcium the number of rod-shaped myocytes decreased significantly with CsA as compared with the solvent (P less than 0.02). The data suggest that CsA exerts a dose-dependent toxic effect on isolated rat cardiomyocytes that depends on the extracellular calcium concentration. There is direct evidence that CsA increases the intracellular free calcium concentration in rat cardiomyocytes.

Animals↗
PubMed1990

Automatic quantification of fast axonal transport in neuronal cell cultures.

A method is presented which allows the automatic quantification of the fast axonal transport of endogenous organelles in neurites of cultured neuronal cells. Stretches of videotape recordings from Allen video enhanced contrast (AVEC) microscopy are digitized by currently available image processor hardware and analysed off-line on a MicroVAX II. Movements along the axon are calculated in great detail, allowing statistically significant changes to be detected. Interaction from the operator is minimised, thereby bypassing tedious manual analysis. This paper further reports the application of this system to the effect of vanadate treatment on axonal transport in cultures of rat embryonic hippocampal neurons.

Animals↗
PubMed1989

The effect of flunarizine on intracellular calcium in isolated rat cardiomyocytes. A digital image processing study.

The molecular mechanisms associated with the effects of various pathological stimuli on myocardial tissue, as well as the mechanisms by which Ca2+ antagonists exert their protective effect, are poorly understood. With the use of digital image processing of Fura-2 fluorescence, we have shown that the mean intracellular free Ca2+ concentration of single isolated rat cardiomyocytes is increased upon exposure to various pathological stimuli (high extracellular Ca2+, veratrine). This increased Ca2+ content coincided with an increased number of hypercontracted cells. Pretreatment with flunarizine under these experimental conditions lowered the free intracellular Ca2+ concentration, thereby reducing the number of hypercontracted cells. Verapamil had no effect. The kinetics of changes in intracellular Ca2+ in electrically paced cardiomyocytes were not affected by flunarizine, but were significantly altered by the beta agonist isoprenaline. In addition, isoprenaline increased the mean diastolic intracellular free Ca2+ concentration of paced cardiomyocytes, whereas it remained unchanged in flunarizine treated cells. We conclude that flunarizine reduces intracellular free Ca2+ levels in isolated cardiomyocytes under pathological conditions, but does not affect physiological processes mediated by Ca2+. The report also illustrates the possibilities of digital imaging microscopy in the study of ion distributions in living cells.

Animals↗
PubMed1988

Dynamic behavior of the transferrin receptor followed in living epidermoid carcinoma (A431) cells with nanovid microscopy.

Transferrin receptors labeled with the B3/25 monoclonal antibody-gold complexes were followed in living A431 cells by using video-enhanced contrast microscopy. Initially, the antibody-gold complexes bind to receptors which are freely mobile on the upper cell surface; they then become trapped at the inner margins of the peripheral lamellae and internalize. During endocytosis discrete gold-loaded vesicular elements first appear, and then, as they fuse, a heterogenous peripheral endosomal compartment forms. The endosomes from this compartment then begin to migrate centripetally through the cytoplasm in a saltatory way so that within 15 min gold label accumulates in a juxtanuclear endosome compartment. This compartment, which consists mainly of multivesicular bodies, is thus formed by the influx and retention of peripheral endosomal elements and their continued fusion in the juxtanuclear area. Although their overall migration is inward, saltating endosomes frequently reverse their direction of movement. As label builds up in the juxtanuclear area, small vesicles containing gold label continuously pinch off from the larger elements and migrate toward the cell periphery. Experiments with nocodazole and sodium azide show that the saltatory movements, the accumulation and retention of endosomes in the juxtanuclear area, and the separation of vesicles from endosomes are driven by a microtubule-associated, ATP-dependent, motility-generating mechanism. Analysis of the movements shows that although each individual vesicle saltation can occur unpredictably toward the centre or the periphery of the cell, a net centripetal flux is observed. Moreover, it is evident that the probability of migration toward and maintenance in the juxtanuclear area is related to the diameter of the vesicles. We propose a mechanism by which bidirectional saltation along microtubules forming a radial network may be instrumental in the selective concentration of large endosomes in the juxtanuclear area while small vesicles are left free to return to the periphery. This process may be responsible for the sorting of receptors and ligands destined either for intracellular degradation in juxtanuclear lysosomes or, alternatively, for recycling to the plasma membrane.

Alkaloids↗
PubMed1987

Nanovid tracking: a new automatic method for the study of mobility in living cells based on colloidal gold and video microscopy.

We describe a new automatic technique for the study of intracellular mobility. It is based on the visualization of colloidal gold particles by video-enhanced contrast light microscopy (nanometer video microscopy) combined with modern tracking algorithms and image processing hardware. The approach can be used for determining the complete statistics of saltatory motility of a large number of individual moving markers. Complete distributions of jump time, jump velocity, stop time, and orientation can be generated. We also show that this method allows one to study the characteristics of random motion in the cytoplasm of living cells or on cell membranes. The concept is illustrated by two studies. First we present the motility of colloidal gold in an in vitro system of microtubules and a protein extract containing a kinesin-like factor. The algorithm is thoroughly tested by manual tracking of the videotapes. The second study involves the motion of gold particles microinjected in the cytoplasm of PTK-2 cells. Here the results are compared to a study using the spreading of colloidal gold particles after microinjection.

Animals↗