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D Popp

Publications and source records attributed to D Popp.

At least 19 recordsLinked to original sources
PubMed2001

Preferential labeling of glial and meningial brain tumors with [2-(14)C]acetate.

UNLABELLED: Acetate is preferentially transported into and metabolized by astrocytes, rather than synaptosomes or neurons, and labeled acetate is used as a glial reporter molecule to assess glial metabolism and glial-neuronal interactions. Because monocarboxylic acid transporter specificity might confer a phenotype to help localize, detect, and characterize brain tumors of glial origin, use of [2-(14)C]acetate and [(14)C]deoxyglucose (a glucose analog metabolized by all brain cells) was compared in rat and human brain tumors. METHODS: Cultured C6 glioma or U-373 glioblastoma/astrocytoma tumor cells were injected into the caudate nucleus of anesthetized CDF Fisher rats; 2--3 wk later, an intravenous pulse of [2-(14)C]acetate or [(14)C]deoxyglucose was given, and timed blood samples were drawn during the 5- or 45-min experiment, respectively. Local (14)C levels in the brain were assayed by quantitative autoradiography, and acetate uptake or glucose use was calculated. Uptake and metabolism of the [(14)C]acetate was also assayed in C6 glioma and human surgical tumor samples in vitro. RESULTS: [(14)C]Acetate uptake into rat brain C6 tumors was 9.9 +/- 2.1 mL/100 g/min, compared with 3.9 +/- 1.0 mL/100 g/min in contralateral tissue (n = 6; P < 0.001), and was much higher than that into other brain structures (e.g., 5:1 for white matter and 2:1 for cortical gray matter). Glucose use in C6 tumors was 111 +/- 34 micromol/100 g/min, versus 81 +/- 5 micromol/100 g/min in contralateral tissue (n = 6; P = 0.08); no left-right differences in glucose use or acetate uptake were seen in other brain structures. The tumor-to-contralateral-tissue ratio for acetate (2.3 +/- 0.3) exceeded that for deoxyglucose (1.4 +/- 0.5) (P < 0.05), indicating that acetate is a sensitive C6 glioma marker. [(14)C]Acetate uptake also demarcated a few 3-wk-old C6 tumors that had unlabeled necrotic cores. U-373 tumors were smaller than C6 tumors in rat brain and were detected equally well with [(14)C]acetate and [(14)C]deoxyglucose. In vitro uptake of [(14)C]acetate into human glioblastoma or meningioma tumors was higher than uptake into pituitary adenoma. Rat C6 and human tumors with high uptake metabolized acetate to acidic compounds and amino acids. CONCLUSION: Tumor imaging with radiolabeled acetate can help to localize and classify brain tumors. Transporter and metabolic substrate specificity are traits that can be exploited further for in vivo imaging of brain glial tumors.

Acetic Acid↗
PubMed2000

Malignant osteopetrosis obscured by maternal vitamin D deficiency in a neonate.

UNLABELLED: A neonate presented with clinical, biochemical, endocrine and radiographic features consistent with vitamin D deficiency rickets of maternal origin. Persistent hypocalcemia and subsequent development of pancytopenia, hemolysis and hepatosplenomegaly prompted further studies that led to the diagnosis of infantile osteopetrosis. CONCLUSION: Osteopetrosis is an important differential diagnosis of neonatal rickets and is not excluded by low vitamin D levels.

Female↗
PubMed1998

[Volumetric brain findings in late depression. A study with quantified magnetic resonance tomography].

A number of observations including clinical manifestation, course, outcome, and family history, support the view that patients presenting with a major depression occurring first in late life should be treated as a nosological subgroup. In this study quantitative magnetic resonance imaging (MRI) was used to investigate volumes of different brain structures in 19 patients with late onset major depression (age of onset > 50) and 13 age matched controls. 3-D MRI sequences were acquired using a Siemens 1.5T scanner. Whole brain volume, CSF volume, volume of the frontal and temporal lobes and the volume of the amygdala-hippocampus complex were assessed using the software NMRWin. Compared to the controls, depressed patients showed a significantly lower whole brain volume and a significantly higher CSF volume, whereas volumes of the frontal and temporal lobes as well as the amygdala-hippocampus complex volumes were not significantly decreased. In addition, depressed patients exhibited a higher ventricle-brain ratio suggesting a higher degree of central atrophy compared to healthy individuals. Our results indicate that cerebral changes involving subcortical structures are of relevance in the pathogenesis of late-onset depression. Defining the aetiology of these lesions may be important for the development of preventive treatment of depression in the elderly.

Aged↗
PubMed1997

Quantitative magnetic resonance imaging in geriatric depression and primary degenerative dementia.

Quantitative magnetic resonance imaging (MRI) was used to investigate volumes of different brain structures in 19 patients with late-onset major depression (DSM-III-R), 27 patients with Alzheimer's disease (NINCDS-ADRDA criteria) and 13 age matched controls. 3-D MRI sequences were acquired using a Siemens 1.5 T scanner. Whole brain volume, CSF volume, volume of the frontal and temporal lobes and the volume of the amygdala-hippocampus complex were assessed using the software NMR Win. Compared to the controls, depressed patients showed a significantly lower whole brain volume and a significantly higher CSF volume, whereas volumes of the frontal and temporal lobes as well as the amygdala-hippocampus complex volumes were not significantly decreased. In addition, depressed patients exhibited a higher ventricle-brain ratio suggesting a higher degree of central atrophy compared to healthy individuals. In contrast, Alzheimer patients showed significantly lower volumes than depressed patients and controls with respect to all volumetric parameters. Although the findings indicate the presence of brain atrophy in patients with late-onset depression, the pattern of volumetric changes in these patients differs markedly from that observed in patients with primary degenerative dementia.

Aged↗
PubMed1997

Emergence of undifferentiated rat tracheal cell carcinomas, but not squamous cell carcinomas, is associated with a loss of expression of E-cadherin and of gap junction communication.

A series of cells representing normal, non-tumorigenic cell lines, as well as differentiating neoplastic and undifferentiated neoplastic rat tracheal epithelial cell populations were evaluated for their ability to establish homologous and/or heterologous cell-cell gap junction communication in culture. Gap junction communication was evaluated by flow cytometric quantitation of the transfer of the fluorescent dye calcein from a donor to a recipient cell population via gap junctions. The data indicate that normal primary cultures of rat tracheal epithelial cells, as well as non-tumorigenic cell lines and squamous cell carcinomas cell populations, retain the ability to establish both homologous and heterologous gap junction communication. In all cases an average of >48% of recipient cells had acquired calcein label during a 5-h interval of co-culture of donor and recipient cells at confluent densities. Cells harvested directly from squamous cell carcinoma tumors exhibited similar levels of cell-cell communication. In contrast, cells giving rise to undifferentiated carcinomas, as well as cells harvested from undifferentiated carcinomas, exhibited very low levels or no homologous or heterologous cell-cell communication. Cell populations exhibiting distinctly different communication phenotypes were evaluated by Northern blot analysis for expression of connexins (Cx 26, 32 and 43) and E-cadherin. Neither communicating nor non-communicating cells expressed connexin 32. Those cell populations, which established functional gap junctions, expressed E-cadherin as well as connexin 26 and/or 43. In contrast, those cell populations that lacked the ability to communicate universally lacked expression of E-cadherin, and a quarter also lacked expression of detectable levels of connexin.

Animals↗
PubMed1996

Interleukin-3 increases the incidence of 5-azacytidine-induced thymic lymphomas in pBOR-Il-3 mice.

Interleukin-3 (Il-3) is a glycoprotein produced by a CD4+CD8- subpopulation of T-lymphocytes. Il-3 has been associated with the proliferation of bone marrow stem cells and their differentiation to granulocytes, macrophages, basophil/mast cells, megakaryocytes, erythroid cells, and neutrophils. The pBOR-Il-3 transgenic mice were developed by pronuclear microinjection to study how chemical insults modulate transcription of the Il-3 gene driven by a long-terminal repeat (LTR) of an endogenous retrovirus and to determine the biological consequences of interleukin-3 expression. We injected 5-azacytidine, a demethylating agent, to increase the LTR-driven expression of Il-3. Upon 5-azacytidine treatment, both the pBOR-Il-3 and the FVB/N nontransgenic controls developed thymic lymphomas. The pBOR-Il-3 mice developed thymic lymphomas at a higher frequency than the FVB/N mice. The thymic lymphoma cells were of a T-cell origin, as determined by T-cell receptor gene rearrangement analysis, and, in most cases, were of monoclonal origin. According to flow cytometric analysis of CD3, CD4, and CD8 cell surface markers, the thymic lymphoma cells did not lose their ability to differentiate, but the differentiation process was aberrant. Flow cytometric analyses also revealed that in pBOR-Il-3 mice the thymic lymphomas are mostly of a CD8+CD4- origin, whereas in the FVB/N group, the predominant type of thymic lymphoma is of a CD4+CD8- origin.

Animals↗
PubMed1995

An atomic model of the unregulated thin filament obtained by X-ray fiber diffraction on oriented actin-tropomyosin gels.

We present a model of the actin-tropomyosin complex in which the radial and azimuthal position of tropomyosin was adjusted to fit the X-ray fiber diffraction patterns from oriented actin-tropomyosin gels at a resolution of 1/8 A-1. We used the recently published atomic F-actin model for the calculations. The atomic model of tropomyosin was obtained by model-building a coiled coiled-coil structure from the tropomyosin sequence. The resulting atomic model is strongly preferred and shows strong electrostatic interactions between charged side-chains of tropomyosin residues and actin residues in subdomain 3 and subdomain 4. Furthermore, calculations of enthalpies based upon electrostatic interactions indicate that there is a favored rotational position of the tropomyosin core at the calculated azimuthal and radial position given by the X-ray refinement. Rotations of the tropomyosin strand out of this position turn strongly attractive electrostatic interactions into repulsive forces. The resulting binding radius of 39 A and the determined azimuthal position of tropomyosin are in good agreement with electron microscopy reconstructions and neutron diffraction experiments. Furthermore, the calculated position of tropomyosin would still partly block the rigor interaction of myosin cross-bridges with actin, whereas it very likely allows undisturbed binding of the cross-bridges in a weak binding state.

Actins↗
PubMed1994

Ultrastructure of skeletal muscle fibers studied by a plunge quick freezing method: myofilament lengths.

We have set up a system to rapidly freeze muscle fibers during contraction to investigate by electron microscopy the ultrastructure of active muscles. Glycerinated fiber bundles of rabbit psoas muscles were frozen in conditions of rigor, relaxation, isometric contraction, and active shortening. Freezing was carried out by plunging the bundles into liquid ethane. The frozen bundles were then freeze-substituted, plastic-embedded, and sectioned for electron microscopic observation. X-ray diffraction patterns of the embedded bundles and optical diffraction patterns of the micrographs resemble the x-ray diffraction patterns of unfixed muscles, showing the ability of the method to preserve the muscle ultrastructure. In the optical diffraction patterns layer lines up to 1/5.9 nm-1 were observed. Using this method we have investigated the myofilament lengths and concluded that there are no major changes in length in either the actin or the myosin filaments under any of the conditions explored.

Actin Cytoskeleton↗
PubMed1993

Refinement of the F-actin model against X-ray fiber diffraction data by the use of a directed mutation algorithm.

The F-actin model has been refined by a Directed Mutation Algorithm, a reiterative procedure which combines a Monte-Carlo method of selecting subdomains to be refined at each cycle with a non-linear least-squares routine to get the best fit for the particular selected domains. The G-actin crystal structure was used as a starting model. The experimental data were obtained by X-ray fiber diffraction patterns from oriented F-actin gels. After 250 cycles we were able to obtain an almost perfect fit of the calculated diffraction pattern to the experimental diffraction pattern as well as a reasonable stereochemistry including intermolecular interactions of the actin monomers with an r.m.s. shift in the C alpha-positions of 3.2 A from the crystal coordinates. The stereochemistry of the intersubunit packing was calculated by molecular dynamics using the program X-PLOR. In addition, the binding site of phalloidin, a cyclic heptapeptide from the mushroom Amanita phalloides, could be determined. Furthermore, we were able to determine differences in the structures of F-actin with and without phalloidin. The method proved itself robust and showed a high degree of convergence.

Actins↗
PubMed1993

Calcium ions and the structure of muscle actin filament. An X-ray diffraction study.

In order to investigate the effects of Ca(2+)-binding to troponin on the conformation of the muscle thin filament (consisting of actin, tropomyosin and troponin) in the absence of actomyosin interaction, two series of X-ray diffraction experiments were undertaken. Firstly, the small angle X-ray scattering from filaments in solution indicate the tropomyosin strands are centred at about 3.5 nm from the filament axis and this distance is calcium independent. Secondly, X-ray fibre diffraction patterns from the filaments orientated in glass capillaries were studied. The X-ray intensity of the 2nd actin layer-line increased in a highly co-operative manner at a concentration of free calcium ions [Ca2+] of 10(-6.8) M, which is the range in which muscle contraction is physiologically regulated. However, this intensity increase accounted for some 30% of the total increase observed in diffraction patterns from muscle on activation, suggesting that the Ca(2+)-binding alters the state of the thin filament, which then undergoes further changes upon interaction with myosin.

Actins↗
PubMed1993

A comparison of the atomic model of F-actin with cryo-electron micrographs of actin and decorated actin.

We compare the atomic model calculated from the crystal structure and the X-ray fiber diagram of orientated F-actin1) with the 3-D reconstructions produced from cryo-electron microscopy of actin2). Out to 30A resolution the two structures are essentially identical. Furthermore, by combining the atomic model with the reconstruction of S1-decorated actin filaments2) one can establish the nature of the actin binding site for myosin in the rigor complex. Each myosin head binds to two actin molecules on two distinct sites. Some of the actin residues involved in each of these binding sites can be identified. Furthermore, the atomic model of actin may be combined with the reconstruction of the S1 decorated thin filament to establish the tropomyosin binding site in the rigor complex. This result is compared with the model of tropomyosin-actin derived from an analysis of the X-ray fibre diagram of a reconstituted thin filament and are shown to be very similar.

Actins↗
PubMed1992

X-ray diffraction studies on oriented gels of vertebrate smooth muscle thin filaments.

The ATPase activity of acto-myosin subfragment 1 (S1) at low ratios of S1 to actin in the presence of tropomyosin is dependent on the tropomyosin source and ionic conditions. Whereas skeletal muscle tropomyosin causes a 60% inhibitory effect at all ionic strengths, the effect of smooth muscle tropomyosin was found to be dependent on the ionic strength. At low ionic strength (20 mM) smooth muscle tropomyosin inhibits the ATPase activity by 60%, while at high ionic strength (120 mM) it potentiates the ATPase activity three- to five-fold. Therefore, the difference in the effect of smooth muscle and skeletal muscle tropomyosin on the acto-S1 ATPase activity was due to a greater fraction of the tropomyosin-actin complex being turned on in the absence of S1 with smooth muscle tropomyosin than with skeletal muscle tropomyosin. Using well-oriented gels of actin and of reconstituted specimens from vertebrate smooth muscle thin filament proteins suitable for X-ray diffraction, we localized the position of tropomyosin on actin under different levels of acto-S1 ATPase activity. By analysing the equatorial X-ray pattern of the oriented specimens in combination with solution scattering experiments, we conclude that tropomyosin is located at a binding radius of about 3.5 nm on the f-actin helix under all conditions studied. Furthermore, we find no evidence that the azimuthal position of tropomyosin is different for smooth muscle tropomyosin at various ionic strengths, or vertebrate tropomyosin, since the second actin layer-line intensity (at 17.9 nm axial and 4.3 nm radial spacing), which was shown in skeletal muscle to be a sensitive measure of this parameter, remains strong and unchanged. Differences in the ATPase activity are not necessarily correlated with different positions of tropomyosin on f-actin. The same conclusion is drawn from our observations that, although the regulatory protein caldesmon inhibits the ATPase activity in native and reconstituted vertebrate smooth muscle thin filaments at a molar ratio of actin/tropomyosin/caldesmon of 28:7:1, the second actin layer-line remains strong. Only adding caldesmon in excess reduces the intensity of the second actin layer-line, from which the binding radius of caldesmon can be estimated to be about 4 nm. The lack of predominant meridional reflections in oriented specimens, with caldesmon present, suggests that caldesmon does not project away from the thin filament as troponin molecules in vertebrate striated muscle in agreement with electron micrographs of smooth muscle thin filaments. In freshly prepared native smooth muscle thin filaments we observed a Ca(2+)-sensitive reversible bundling effect.(ABSTRACT TRUNCATED AT 400 WORDS)

Actins↗
PubMed1992

Time-resolved x-ray diffraction study of the troponin-associated reflexions from the frog muscle.

The vertebrate skeletal muscle gives rise to a series of x-ray reflexions indexed as orders (n) of 77 nm, the even orders being meridional whereas the odd orders being near-meridional. The diffraction intensities associated with these reflexions originate from the axial period of 39 nm attributable to the repeat of troponin-tropomyosin on the thin filament. In the present study, the x-ray intensities of the furthest inner reflexions, A2 (n = 2) reflexion at an axial spacing of 1/39 nm-1 and A4 (n = 4) reflexion at 1/19 nm, of this series were measured with a time resolved manner. Upon activation of the frog striated muscle, the two reflexions underwent biphasic time courses of the intensity changes. With A2 reflexion, a rapid intensity increase by 16%, being completed by the time when tension rises to 5%, was followed by a slow intensity decrease down to 50%, which was associated with the tension rise. In both phases, lateral widths remained unchanged. A4 reflexion also behaves in the same way, although the first phase (the intensity increase) was not clear due to unsatisfactory statistics. We interpret phase one as being caused by conformational change of the troponin-tropomyosin complex upon binding of Ca2+ to troponin, whereas phase two being due to direct contribution of the mass of the myosin heads bound to the thin filament, although possible contribution of conformational changes of the regulatory proteins to phase two is not excluded. The results indicated that the calcium activation of the thin filament leads the onset of the actomyosin interaction.

Animals↗
PubMed1991

X-ray diffraction studies on muscle regulation.

Using the intensity of the outer part of the second actin layer line as an indicator of thin filament conformation in vertebrate muscle we were able to identify the four different states of rest, and the three states induced by the presence of Ca2+ ions, rigor bridge attachment and actively cycling bridges, respectively. These findings are in qualitative agreement with a number of biochemical studies by Eisenberg and Greene and others, indicating that activation of the thin filament depends both on Ca2+ ions and crossbridge binding. Yet quantitatively, the biochemical data and our structural data are contradictory. Whereas the biochemical studies suggest a strong coupling between structural changes of the thin filament and the ATPase activity, the structural studies indicate that this is not necessarily the case. Troponin molecules also change their conformation upon activation depending on both Ca2+ ions and crossbridge binding as demonstrated by the early part of the time course of the thin filament meridional reflections in contracting frog muscle. Low ionic strength which has been shown by Brenner and collaborators to increase weakly binding crossbridges in relaxed rabbit psoas muscle does not influence the intensity of the second actin layer line in this muscle. Yet in contracting frog muscle the increase of the second actin layer line increases very rapidly in one step, suggesting that weak binding bridges which are attached to actin prior to force production may indeed influence the thin filament conformation. It therefore appears that weakly bound bridges in the low ionic strength state do not have the same effect on the thin filament conformation as weakly bound bridges in an actively contracting muscle. Arthropod muscles like the thin filament regulated lobster muscles differ from vertebrate muscle in not showing an increase of the second layer line during contraction, which may have to do with differences in crossbridge attachment. The myosin-regulated molluscan muscle ABRM shows a large increase on the second actin layer line upon phasic contraction and a much smaller increase in catch or rigor, indicating that actively cycling bridges influence the thin filament conformation differently than catch or rigor bridges. Several pieces of evidence which we have briefly outlined in this paper suggest that the thin filament conformational changes we have observed do not arise solely from tropomyosin movements and that conformational changes of actin domains should be considered.

Animals↗
PubMed1991

X-ray studies of order-disorder transitions in the myosin heads of skinned rabbit psoas muscles.

Using x-rays from a laboratory source and an area detector, myosin layer lines and the diffuse scattering between them in the moderate angle region have been recorded. At full overlap, incubation of rigor muscles with S-1 greatly reduces the diffuse scattering. Also, three of the four actin-based layer lines lying close to the meridian (Huxley, H. E., and W. Brown, 1967. J. Mol. Biol. 30:384-434; Haselgrove, J. C. 1975. J. Mol. Biol. 92:113-143) increase, suggesting fuller labeling of the actin filaments. These results are consistent with the idea (Poulsen, F. R., and J. Lowy, 1983. Nature [Lond.]. 303:146-152) that some of the diffuse scattering in rigor muscles is due to a random mixture of actin monomers with and without attached myosin heads (substitution disorder). In relaxed muscles, regardless of overlap, lowering the temperature from 24 to 4 degrees C practically abolishes the myosin layer lines (a result first obtained by Wray, J.S. 1987. J. Muscle Res. Cell Motil. 8:62 (a). Abstr.), whilst the diffuse scattering between these layer lines increases appreciably. Similar changes occur in the passage from rest to peak tetanic tension in live frog muscle (Lowy, J., and F.R. Poulsen. 1990. Biophys. J. 57:977-985). Cooling the psoas demonstrates that the intensity relation between the layer lines and the diffuse scattering is of an inverse nature, and that the transition occurs over a narrow temperature range (12-14 degrees C) with a sigmoidal function. From these results it would appear that the helical arrangement of the myosin heads is very temperature sensitive, and that the disordering effect does not depend on the presence of actin. Measurements along the meridian reveal that the intensity of the diffuse scattering increases relatively little and does so in a nearly linear manner: evidently the axial order of the myosin heads is much less temperature sensitive. The combined data support the view (Poulsen, F. R., and J. Lowy. 1983. Nature [Lond.]. 303:146-152) that in relaxed muscles a significant part of the diffuse scattering originates from disordered myosin heads. The observation that the extent of the diffuse scattering is greater in the equatorial than in the meridional direction suggests that the disordered myosin heads have an orientation which is on average more parallel to the filament axis.

Actins↗
PubMed1990

Atomic model of the actin filament.

The F-actin filament has been constructed from the atomic structure of the actin monomer to fit the observed X-ray fibre diagram from oriented gels of F-actin. A unique orientation of the monomer with respect to the actin helix has been found. The main interactions are along the two-start helix with a contribution from a loop extending across the filament axis provided by the molecule in the adjacent strand. There are also contacts along the left-handed genetic helix.

Actins↗
PubMed1990

Supercoiling of f-actin filaments.

In the X-ray diffraction pattern from oriented gels of actin-containing filaments sampling of layer lines indicating the development of a well-ordered pseudo-hexagonal lattice within the gels at interfilament spacings as large as 13 nm is observed. This value exceeds by 3 nm the largest estimate of an external diameter of pure f-actin. The development of layer line sampling is always accompanied by: (i) the appearance of strong forbidden meridional reflections on the 5.9- and 5.1-nm layer lines; (ii) a drastic intensification of the first (expected) 2.75-nm meridional reflection by a factor of about 4; (iii) the appearance of streaks, connecting near-meridional reflections on the 5.9-, 5.1-, and 37-nm layer lines; and (iv) a slight decrease in the number of subunits per turn of the basic f-actin helix. All these features strongly indicate that f-actin filaments are supercoiled and make regular local contacts between themselves, which may lead to periodic distortions of the mobile external domain in the actin subunits.

Actins↗