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M Simons

Publications and source records attributed to M Simons.

At least 91 records · Page 5Linked to original sources
PubMed1997

Enhancement of migration by protein kinase Calpha and inhibition of proliferation and cell cycle progression by protein kinase Cdelta in capillary endothelial cells.

Activation of protein kinase C (PKC) induces angiogenesis, migration, and proliferation of endothelial cells (EC), but can also prevent growth factor-induced EC proliferation. To determine whether these disparate effects are mediated by substrates of individual PKC isoenzymes, PKCalpha and PKCdelta were overexpressed in rat microvascular EC. Basal and stimulated migration were enhanced in PKCalpha EC compared with either PKCdelta or control EC. Serum-induced growth of PKCdelta EC was decreased, while that of PKCalpha cells was similar to control EC. Phorbol ester markedly inhibited PKCdelta EC growth but enhanced growth of PKCalpha and control EC. To determine possible causes for this altered proliferation, the effect of PKCdelta on adhesion, mitogen-activated protein kinase activity, and cell cycle progression was measured. Adherence of PKCdelta EC to vitronectin was significantly enhanced. Serum-induced extracellular signal-regulated kinase-2 activity was increased equally in both PKCalpha and PKCdelta EC above that of control, while extracellular signal-regulated kinase-1 activity was similar in all EC. Cell cycle analysis suggested that PKCdelta EC entered S phase inappropriately and were delayed in passage through S phase. Thus, PKCalpha may mediate some proangiogenic effects of PKC activation; conversely, PKCdelta may direct antiangiogenic aspects of overall PKC activation, including slowing of the cell cycle progression.

Animals↗
PubMed1997

Antisense oligonucleotide inhibition of PDGFR-beta receptor subunit expression directs suppression of intimal thickening.

BACKGROUND: The elucidation of molecular mechanisms of vascular cell biology has markedly influenced our thinking on the pathophysiology of vascular disease. Antisense oligonucleotide gene therapy has helped identify proteins critical to cell-cycle progression and proliferation and possible therapeutic strategies to combat human disease. This approach, however, has not yet been used to examine the contribution of chemotactic proteins and/or their receptors. Platelet-derived growth factor-BB (PDGF-BB) released from activated platelets adherent to subendothelial connective tissue is a principal smooth muscle cell chemotactic factor. METHODS AND RESULTS: A series of experiments was performed to assess the capacity of antisense oligonucleotides to reduce PDGF-beta receptor subunit (PDGFR-beta) expression and the contribution of PDGFR-beta in neointimal formation. Sustained, direct, and local perivascular administration of two different antisense oligonucleotide sequences complementary to PDGFR-beta mRNA almost completely abolished the expression of PDGFR-beta protein in the intima and media of injured carotid arteries and decreased neointimal formation by 80% and 60%, respectively. Furthermore, neointimal formation correlated precisely with PDGFR-beta expression in an exponential fashion. CONCLUSIONS: Thus, myointimal proliferation depends on both PDGFR-beta overexpression and its activation by PDGF-BB. Removal of either of these two elements can suppress neointimal formation.

Animals↗
PubMed1997

c-Myb function in fibroblasts.

The protooncogene c-myb is a nuclear transcription factor that shares significant sequence homology with two other myb family members, A-myb and B-myb. Recent studies have suggested that c-myb is involved in regulation of the cell cycle via control of intracellular calcium [Ca2+]i concentration. Given the limited cell type expression of the c-myb gene, we set out to investigate whether myb-dependent cell cycle regulation occurs in cells not known to express the c-myb protein. NIH 3T3 fibroblasts were stably transfected with an inducible c-myb dominant negative construct composed of a myb DNA binding domain linked to the Drosophila engrailed transcription suppresser (pGREMEn) and a full-length murine c-myb cDNA sequence. Induced expression of the dominant negative construct was associated with a G1 cell cycle arrest and a failure to increase late G1 intracellular calcium levels. Similar expression studies in mouse embryonic fibroblasts derived from the c-myb knockout mouse have demonstrated lower baseline [Ca2+]i levels than in normal mice fibroblasts that were not further lowered by MEn expression. We conclude that regulation of calcium homeostasis and cell cycle progression via myb-dependent transcription may play an important role in cells not possessing detectable levels of c-myb protein.

3T3 Cells↗
PubMed1997

Extent of myocardial collateralization: determination with three-dimensional elastic-subtraction spiral CT.

RATIONALE AND OBJECTIVES: This study was undertaken to develop a standard that can be used to assess new high-resolution collateral zone imaging methods. MATERIALS AND METHODS: The authors performed ex vivo helical CT in seven pig hearts after microsphere studies of blood flow and coronary angiography. They compared the zones of collateralization depicted at CT and at microsphere studies. RESULTS: The extent of the collateral zone at CT, computed by using elastic subtraction, correlated well with the coronary blood flow distribution determined with microsphere analysis (r = .95). The root-mean-square error was 6.5%, which indicates good agreement. CONCLUSION: Accurate assessment of collateralization extent has become an important goal because of the discovery of agents that stimulate the growth of coronary collateral vessels. The precision of elastic-subtraction CT and its validation with respect to the blood flow distribution at microsphere analysis indicate that elastic-subtraction CT can serve as a standard for the measurement of collateralization extent.

Animals↗
PubMed1997

How accurate is the assessment of thyroid volume by palpation? A prospective study of 316 patients.

Goitre is the cardinal symptom of most thyroid diseases and treatment is often influenced by the evaluation of thyroid size. Quantitative palpation of the thyroid gland could offer a quick and easy initial examination method for discovering most thyroid diseases. However, this clinical technique is frequently underestimated and its accuracy is not evaluated. Therefore, we examined the question whether thyroid volume can be determined with sufficient precision by manual palpation. 316 patients with suspected thyroid diseases were selected at random at our hospital and prospectively studied. Thyroid volume of each patient was assessed by palpation followed by ultrasonically scanning. The examinations were performed by two physicians: an endocrinologist (A) and a resident (B) who had undergone a structured palpation training. Ultrasonic scanning of 99 thyroid glands revealed a high level of agreement (r2 = 0.87) between both physicians. Examiner A evaluated 111 patients by palpation and ultrasonic scanning. The mean volume determined by ultrasound was 35.9 ml (SD = 27.1 ml) with a range of 4-152 ml. This correlated well with the results of palpation (r2 = 0.872). Examiner B evaluated 215 patients. These ultrasonically determined volumes had a mean value of 37.3 ml (SD = 24.2 ml; range 4-145 ml) and correlated well with the results obtained by palpation (r2 = 0.856). A total of 53 patients were examined by both physicians. The interobservers' comparison of the palpation results yielded an excellent correspondence (r2 = 0.893). We conclude that the manual palpation technique yields sufficiently precise quantitative results for clinical purposes and can be taught. Clinical assessment of thyroid size on a routine basis should result in better diagnostic strategies for thyroid diseases and in cost savings.

Adolescent↗
PubMed1997

Aseptic necrosis. A scintigraphic imitator of osseous involvement in Ga-67 avid lymphoma.

Based on the data by Armas et al, avascular necrosis, a not uncommon treatment-associated complication in patients with lymphoma, it should be easily distinguishable from osseous lymphomatous involvement in patients with Ga-67 avid lymphoma. In avascular necrosis, Ga-67 uptake will be either absent, decreased, or normal, whereas in lymphoma Ga-67 uptake will be increased. The authors present a patient with Hodgkin's disease who had new foci of simultaneously increased Ga-67 and Tc-99m MDP uptake because of avascular necrosis as proven by biopsy and long-term follow-up. The authors hypothesize that a possible-explanation for the discrepancy between this patient report and the series by Armas et al may be that increased Ga-67 is a delayed phenomenon related to healing.

Adult↗
PubMed1997

Differential renal function measured by 99Tcm-DTPA and 99Tcm-DMSA in a complete unilateral renal obstruction rat model.

We performed a prospective study to determine whether 99Tcm-DTPA differential renal function (DRF) in the case of acute obstruction in a unipapillary kidney rat model shows a similar pattern of results as 99Tcm-DMSA in a multipapillary kidney model, and to exclude recirculation or a block of tubular transport of DMSA which might explain the discrepancy reported by Kelleher et al. In 15 male and 4 female Wistar rats (weight 300-350 g), 99Tcm-DMSA renal uptake was measured 24 h before complete obstruction of the right ureter, which served as reference values. Twenty-four hours after obstruction, 99Tcm-DTPA (18.5 MBq) renography and 99Tcm-DMSA (111 MBq) non-depth-corrected renal uptake measurements were performed in the 15 male rats; in the 4 female rats, 740 MBq of 99Tcm-DMSA were injected and absolute, non-depth-corrected renal uptake measured at 24, 48 and 72 h. 99Tcm-DMSA DRF of the right kidney ranged from 48 to 55% (mu: 51%; sigma: 2%) before obstruction and from 14 to 35% (mu: 24%; sigma: 6%) after obstruction, whereas 99Tcm-DTPA DRF ranged from 16 to 30% (mu: 25%; sigma: 4%). No significant differences were found between DRF measured by 99Tcm-DMSA and 99Tcm-DTPA (P = 0.18), or between DRF of the obstructed kidney as measured by 99Tcm-DMSA at 24, 48 and 72 h (P > 0.2). Hypothetically, the discrepancy between our findings and those of Kelleher et al. may be due to intratubular pressure. In conclusion, the present findings and those of Kelleher et al. suggest the differences in DRF following complete unilateral renal obstruction, as determined by DTPA and DMSA, are probably species-specific. Furthermore, recirculation and block of tubular transport are unlikely to contribute significantly to differences in DRF as measured by the two radiopharmaceuticals.

Animals↗
PubMed1997

Regulation of vascular smooth muscle cell proliferation by plasma membrane Ca(2+)-ATPase.

We have previously shown that reductions in c-Myb-dependent transcription inhibit cell cycle progression and decrease intracellular Ca2+ concentrations in vascular smooth muscle cells (VSMC). We now report that these effects are largely mediated by a 4- to 10-fold increased rate of La(3+)-sensitive 45Ca extrusion, which is associated with 2- to 4-fold increased levels of plasma membrane Ca(2+)-ATPase 1 (PMCA1) mRNA and protein. PMCA4 mRNA, present at much lower concentrations, undergoes similar changes during suppression of c-Myb activity. We also report that PMCA1 expression is regulated during VSMC cell cycle progression, such that levels of PMCA1 are 40% lower at the G1/S interface than at G0. Moreover, transient overexpression of PMCA1a in VSMC elevates the 45Ca efflux rate by approximately 2-fold, decreases resting and peak thapsigargin-releasable Ca2+ concentrations at G1/S by 43% (68 nM) and 52% (160 nM), respectively, and reduces the rate of cell proliferation by over 2.5-fold. These data define a mechanism for c-Myb-dependent Ca2+ homeostasis and support a critical role for PMCA in the regulation of VSMC growth.

Animals↗
PubMed1997

Hemodynamic effects of intracoronary VEGF delivery: evidence of tachyphylaxis and NO dependence of response.

Vascular endothelial growth factor (VEGF) has been utilized to improve blood flow in the setting of myocardial or peripheral vascular ischemia. In this investigation we studied the hemodynamic effects of intracoronary VEGF administration. Hemodynamic parameters and Doppler flow wire recordings from the left anterior descending coronary artery were measured after intracoronary infusion of VEGF (1, 10, and 100 micrograms) in 28 intubated pigs. Additional studies were performed using an in vitro isolated microvessel preparation. VEGF produced a highly significant dose-dependent increase in coronary blood flow (maximal 3.51 +/- 0.85-fold) in the absence of significant changes in epicardial artery diameter, a decline in mean arterial pressure (maximal 43%), and a decrease in left ventricular end-diastolic pressure (maximal 52%), all of which could be inhibited by pretreatment with NG-nitro-L-arginine. The increase in coronary flow seen with 10 or 100 micrograms VEGF was significantly greater than the maximal vasodilation achieved with serotonin or nitroglycerin and was equivalent to a maximal adenosine response. In summary, VEGF stimulates nitric oxide (NO)-dependent dilation of coronary microvessels, and repeat administrations of VEGF resulted in rapid development of tachyphylaxis to VEGF as well as serotonin, but not to nitroglycerin or adenosine, which appeared to be secondary to impaired NO production.

Adenosine↗
PubMed1997

c-Myb-dependent cell cycle progression and Ca2+ storage in cultured vascular smooth muscle cells.

Considerable controversy surrounds the role of the c-myb proto-oncogene in vascular smooth muscle cells (VSMCs). Previous investigations using antisense approaches have suggested a relationship between c-myb expression, cell cycle progression, and cytoplasmic Ca2+ concentration ([Ca2+]cyt). However, the ability of certain antisense oligonucleotides to bind and inactivate growth factors allows alternative explanations. To define more specifically the role of c-Myb in cultured VSMCs (SVE and A10 cell lines), we have generated stable cell clones expressing a dominant-negative c-Myb lacking critical elements of the DNA binding domain (delta5-SVE) and transiently transfected cell populations (GRE-MEn-SVE and GRE-MEn-A10) expressing a glucocorticoid-inducible chimeric protein that targets the Drosophila Engrailed repressor domain to c-Myb-responsive promoters. The delta5-SVE clones and GRE-MEn cell populations exhibit a 60% reduction in mean intracellular c-Myb activity, as measured by cotransfection assays with a c-Myb-responsive reporter, a 42% decrease in the mean S phase entry of growth-arrested (G[0]) cells after serum stimulation, and a 36% inhibition of mean cell proliferation over 4 days. These cells also display 28% (34-nmol/L) and 30% (42-nmol/L) reductions in mean [Ca2+]cyt at G(0) and at the G1/S interface, respectively, as well as significant reductions in the peak [Ca2+]cyt responses to thapsigargin (5 micromol/L) and caffeine (10 mmol/L). These latter reductions in operationally defined Ca2+ pools were observed both at different stages of the cell cycle and after transient induction of the dominant-interfering construct, suggesting that c-Myb regulates these releasable Ca2+ stores independent of its effects on cell cycle progression.

Animals↗
PubMed1997

Macrophage-dependent regulation of syndecan gene expression.

Heparan sulfates in the extracellular matrix are required for a variety of biological processes, including cellular response to heparin-binding growth factors. However, little is known regarding the regulation of their expression and composition under pathophysiological conditions. In the present study, we have investigated the regulation of expression of two key heparan sulfate chain-carrying core proteins, syndecan-1 and syndecan-4, in a mouse/rat infarct model of tissue injury and repair. Induction of myocardial infarction was associated with a prompt increase in expression of both syndecan genes. Although infiltrating macrophages accounted for a substantial increase in syndecan expression, increased expression was noted in the levels of syndecan-1 mRNA in endothelial cells and syndecan-4 mRNA in cardiac myocytes. This increase in expression was limited to the immediate peri-infarct region and was absent from remote areas of the left or right ventricles. The influx of blood-derived macrophages in the heart correlated with the appearance of PR-39 peptide, which has previously been shown to increase syndecan expression in vitro. Studies in the op/op mice strain (which demonstrates sharply reduced levels of circulating monocytes) showed that myocardial infarction was associated with markedly reduced levels of macrophage influx and corresponding reduction in the expression of PR-39 and both syndecan genes. Pretreatment of op/op mice with granulocyte macrophage colony-stimulating factor restored myocardial macrophage content with corresponding restoration of PR-39/syndecan expression. In summary, myocardial infarction is associated with a distinct spatial and temporal pattern of syndecan-1 and -4 gene expression, which is induced by an influx of blood-derived macrophages.

Animals↗
PubMed1997

Basic fibroblast growth factor in a porcine model of chronic myocardial ischemia: a comparison of angiographic, echocardiographic and coronary flow parameters.

Recently, a number of growth factors including basic fibroblast growth factor (bFGF) have been shown to promote angiogenesis in vivo. In this study, we evaluated dose-dependent effect of bFGF administration in the setting of chronic myocardial ischemia. A total of 18 Yorkshire pigs subjected to ameroid occluder placement on the left circumflex artery were randomized to treatment with 10 (n = 6) or 100 microg (n = 5) of bFGF incorporated into heparin-alginate microspheres or inactive control pellets (n = 7). Eight weeks later, all animals underwent angiographic evaluation of collateral development as well as studies of coronary flow and global and regional left ventricular function. Both bFGF groups had significantly higher angiographic collateral index, TIMI flow scores and coronary flow in the ameroid-compromised territory compared with controls. Left ventricular function studies demonstrated improved global and regional function in both fibroblast growth factor groups with significantly better preservation of regional wall motion in high dose (100 microg) bFGF animals. We conclude that local perivascular delivery of bFGF results in significant improvement in myocardial function in the setting of chronic myocardial ischemia.

Animals↗
PubMed1997

Bone scintigraphy of the hands in early stage lupus erythematosus and rheumatoid arthritis.

OBJECTIVE: To evaluate retrospectively the discriminatory value of bone scintigraphy, especially spot images of the hands, in differentiating early stage systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). METHODS: Data from 19 patients with SLE (3 men, 16 women) and 20 patients with RA (6 men, 14 women), presenting with early stage articular disease (arbitrarily defined as articular complaints for no longer than 3 mo), were reviewed. At this stage, radiographs were normal in all patients. In all 39 patients, total body bone scintigraphy with spot images of the hands was performed as part of a complete diagnostic investigation. For differentiation between SLE and RA in early disease stage, less extensive semiquantitative description in 3 categories (normal, diffuse mildly increased, and (multi)focal moderately to markedly increased tracer accumulation) proved to be sufficient. Locations of bone scintigraphic findings were correlated to clinical findings. RESULTS: In RA, bone scintigraphy revealed foci of moderate to markedly increased tracer accumulation, corresponding to the sites of clinical synovitis in all patients. In 10 patients with SLE, bone scintigraphy images of the hands were normal, and in 9 patients diffuse mildly increased tracer accumulation was observed. CONCLUSION: The data suggest bone scintigraphy may be useful to differentiate SLE from RA in early stage disease.

Adolescent↗
PubMed1996

The beta-amyloid domain is essential for axonal sorting of amyloid precursor protein.

We have analysed the axonal sorting signals of amyloid precursor protein (APP). Wild-type and mutant versions of human APP were expressed in hippocampal neurons using the Semliki forest virus system. We show that wild-type APP and mutations implicated in Alzheimer's disease and another brain beta-amyloidosis are sorted to the axon. By analysis of deletion mutants we found that the membrane-inserted APP ectodomain but not the cytoplasmic tail is required for axonal sorting. Systematic deletions of the APP ectodomain identified two regions required for axonal delivery: one encoded by exons 11-15 in the carbohydrate domain, the other encoded by exons 16-17 in the juxtamembraneous beta-amyloid domain. Treatment of the cells with the N-glycosylation inhibitor tunicamycin induced missorting of wild-type APP, supporting the importance of glycosylation in axonal sorting of APP. The data revealed a hierarchy of sorting signals on APP: the beta-amyloid-dependent membrane proximal signal was the major contributor to axonal sorting, while N-glycosylation had a weaker effect. Furthermore, recessive somatodendritic signals, most likely in the cytoplasmic tail, directed the protein to the dendrites when the ectodomain was deleted. Analysis of detergent solubility of APP and another axonally delivered protein, hemagglutinin, demonstrated that only hemagglutinin formed CHAPS-insoluble complexes, suggesting distinct mechanisms of axonal sorting for these two proteins. This study is the first delineation of sorting requirements of an axonally targeted protein in polarized neurons and indicates that the beta-amyloid domain plays a major role in axonal delivery of APP.

Alzheimer Disease↗
PubMed1996

Amyloidogenic processing of the human amyloid precursor protein in primary cultures of rat hippocampal neurons.

The aim of this study was to investigate the proteolytic processing of the amyloid precursor protein (APP) in polarized primary cultures of hippocampal neurons. We have used the Semliki Forest virus (SFV) vector to express human APP695 in hippocampal neurons, sympathetic ganglia, and glial cells. The latter two cells secrete little or no APP, whereas hippocampal neurons secrete two forms of APP695, which differ in sialic acid content and in their kinetic appearance in the culture medium. In addition, rat hippocampal neurons expressing human APP produced significant amounts of the 4 kDa peptide beta A4. After 3 hr of metabolic labeling, the relative amount of beta A4 peptide to total cellular APP was 5.3%. Fibroblasts expressing APP695 using the same SFV vector mainly produced a related 3 kDa p3 peptide, a nonamyloidogenic fragment. Remarkably, the hippocampal neurons also produced significant amounts of beta A4-containing C-terminal fragments (10-12 kDa) intracellularly. Radiosequencing showed that these fragments were created at a previously described beta-secretase cleavage site and at a cleavage site 12 residues from the N terminus of the beta A4 domain (Thr584 of APP695), which we named delta-cleavage. Based on the observation that mature hippocampal neurons produce two potentially amyloidogenic fragments and secrete substantial amounts of beta A4 when expressing human APP, our results strengthen the hypothesis that neurons play a central role in the process of beta A4 deposition in cases of Alzheimer's disease and in aged primates.

Amino Acid Sequence↗