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Biomedical subjects

M R Freeman

Publications and source records attributed to M R Freeman.

At least 19 recordsLinked to original sources
PubMed2006

Dynamics of an Ising chain under local excitation: a scanning tunneling microscopy study of Si(100) dimer rows at 5 K.

An extension of the classical Ising model to a situation including a source of spin-flip excitations localized on the scale of individual spins is considered. The scenario is realized by scanning tunneling microscopy of the Si(100) surface at low temperatures. Remarkable details, corresponding to the passage of phasons through the tunnel junction, are detected by the STM within the short span between two atoms comprising an individual Si dimer.

Journal Article↗
PubMed2005

Nonequilibrium domain pattern formation in mesoscopic magnetic thin film elements assisted by thermally excited spin fluctuations.

The dynamic behavior in the evolving pattern of thermally assisted, nonequilibrium domains in magnetic thin-film elements undergoing ultrafast 180 degrees magnetization reversal was studied. Magnetization reversal enters a fully dynamic regime when the external field conditions are changed much faster than the sample is able to respond. The dynamic pathway develops a complexity not seen in quasistatic reversal but still retains a high level of order with well-developed dynamic domain patterns formed in response to subnanosecond transitions of the external applied magnetic field.

Journal Article↗
PubMed2004

Mechanical strain delivers anti-apoptotic and proliferative signals to gingival fibroblasts.

Physical forces play a critical role in the survival and proliferation of many cell types, including fibroblasts. Gingival fibroblasts are exposed to mechanical stress during mastication, orthodontic tooth movement, and wound healing following periodontal surgery. The aim of this study was to examine the effect of mechanical strain on human gingival fibroblasts (hGF). Cells were subjected to short-term (up to 60 min) and long-term (up to 48 hrs) 20% average elongation at 0.1 Hz. We monitored survival signaling by evaluating the phosphorylation status and localization of Forkhead box (FoxO) family members, which are mediators of apoptosis. We also examined strain-induced proliferation by measuring the level of proliferating cell nuclear antigen (PCNA). We observed that cyclic strain caused the phosphorylation and retention in the cytoplasm of FoxO family members. Moreover, mechanical strain resulted in increased ERK kinase phosphorylation and PCNA expression. In conclusion, cyclic strain delivers anti-apoptotic and proliferative stimuli to hGF.

Apoptosis↗
PubMed2001

Advances in magnetic microscopy.

A remarkable number of methods for direct, real-space imaging in magnetic microscopy have been demonstrated over the past decade and a half, and the pace of development shows no sign of slowing. Our understanding of magnetism increases as each striking new image of surface and thin-film magnetization is obtained. The continued development of high-performance magnetic information technologies also requires detailed study of the magnetostatics and dynamics of microscopic magnetic structures. Both fundamental curiosity and practical interest now drive us toward innovations in magnetic microscopy for nanometer-length scale and femtosecond temporal resolutions, which are beyond the limits of traditional imaging techniques. This survey is intended to provide an overview of the motivations, accomplishments, and future prospects for this discipline.

Journal Article↗
PubMed2001

BAG-1 is a novel cytoplasmic binding partner of the membrane form of heparin-binding EGF-like growth factor: a unique role for proHB-EGF in cell survival regulation.

Several cell functions related to growth and survival regulation have been attributed specifically to the membrane form of heparin-binding EGF-like growth factor (proHB-EGF), rather than to the diffusible, processed HB-EGF isoform. These findings suggest the existence of a functional binding partner specifically for the membrane form of the growth factor. In this study we have identified the prosurvival cochaperone, BAG-1, as a protein that interacts with the cytoplasmic tail domain of proHB-EGF. Interaction between BAG-1 and the 24-amino acid proHB-EGF cytoplasmic tail was initially identified in a yeast two-hybrid screen and was confirmed in mammalian cells. The proHB-EGF tail bound BAG-1 in an hsp70-independent manner and within a 97-amino acid segment that includes the ubiquitin homology domain in BAG-1 but does not include the hsp70 binding site. Effects of BAG-1 and proHB-EGF co-expression were demonstrated in cell adhesion and cell survival assays and in quantitative assays of regulated secretion of soluble HB-EGF. Because the BAG-1 binding site is not present on the mature, diffusible form of the growth factor, these findings suggest a new mechanism by which proHB-EGF, in isolation from the diffusible form, can mediate cell signaling events. In addition, because effects of BAG-1 on regulated secretion of soluble HB-EGF were also identified, this interaction has the potential to alter the signaling capabilities of both the membrane-anchored and the diffusible forms of the growth factor.

Animals↗
PubMed2001

CaT1 expression correlates with tumor grade in prostate cancer.

Ca(2+) signaling is important for growth and survival of prostatic carcinoma (PCa) cells. Here we report that the gene for CaT1, a channel protein highly selective for Ca(2+), is expressed at high levels in human PCa and in the LNCaP PCa cell line. CaT1 mRNA levels were elevated in PCa specimens in comparison to benign prostatic hyperplasia (BPH) specimens and positively correlated with Gleason grade in a PCa series. CaT1 mRNA was suppressed by androgen and was induced by a specific androgen receptor antagonist in LNCaP cells, suggesting that the gene is negatively regulated by androgen. These findings are the first to implicate a Ca(2+) channel in PCa progression and suggest that CaT1 may be a novel target for therapy.

Androgen Antagonists↗
PubMed2001

Ultrafast magnetization reversal dynamics investigated by time domain imaging.

Spatiotemporal magnetization reversal dynamics in a Ni(80)Fe(20) microstructure is studied using ps time scale scanning Kerr microscopy. Time domain images reveal a striking change in the reversal associated with the reduction in switching time when a transverse bias field is applied. Magnetization oscillations subsequent to reversal are observed at two resonance frequencies, which sensitively depend on the bias field strength. The oscillation at f = 2 GHz is caused by the damped precession of M, while the lower frequency approximately 0.8 GHz mode is interpreted in terms of domain wall oscillation.

Journal Article↗
PubMed2001

Vascular endothelial growth factor-mediated autocrine stimulation of prostate tumor cells coincides with progression to a malignant phenotype.

Vascular endothelial growth factor (VEGF), which is often produced at high levels by tumor cells, is a well-known mediator of tumor angiogenesis. VEGF receptor tyrosine kinases, KDR/Flk-1 and Flt-1, have been thought to be expressed exclusively by endothelial cells. In this study, we have used a prostate tumor progression series comprised of a differentiated rat prostate epithelial cell line, NbE-1, and its highly motile clonal derivative, FB2. Injection of NbE-1 cells into the inferior vena cava of syngeneic rats indicated that these cells are nontumorigenic. Using the same model, FB2 cells generated rapidly growing and well-vascularized tumors in the lungs. NbE-1 expressed marginal levels of VEGF, whereas high levels of VEGF protein were detected in FB2-conditioned medium and in FB2 tumors in vivo. Analysis of (125)I-VEGF(165) binding to NbE-1 and FB2 cells indicated that only motile FB2 cells expressed the VEGF receptor Flt-1. Consistent with this finding, physiological concentrations of VEGF induced chemotactic migration in FB2 but not in NbE-1 cells. This is the first documentation of a functional Flt-1 receptor in prostate tumor cells. Our results suggest two roles for VEGF in tumor progression: a paracrine role as an angiogenic factor and a previously undescribed role as an autocrine mediator of tumor cell motility.

Animals↗
PubMed2001

Male partner screening before in vitro fertilization: preselecting patients who require intracytoplasmic sperm injection with the sperm penetration assay.

OBJECTIVES: To determine the diagnostic accuracy of the sperm penetration assay (SPA) and standard semen parameters for subsequent fertilization in in vitro fertilization-embryo transfer (IVF-ET). DESIGN: Prospective study. SETTING: Andrology Laboratory, and university research laboratory. PATIENTS: Two hundred sixteen couples undergoing male-partner screening before IVF-ET (265 cycles). INTERVENTION(S): Male-partner screening (semen analyses [SA] and SPA), standard IVF-ET procedures, follow-up of fertilization in IVF-ET. MAIN OUTCOME MEASURE(S): Diagnostic accuracy of SA and SPA for prediction of fertilization in IVF-ET. RESULT(S): The SPA predicted IVF fertilization with high negative (84%) and positive (98%) predictive rates, and correct prediction in 88% of cycles. In contrast, sperm concentration, motility, morphology, and complete SA showed poor diagnostic accuracy, with correct prediction of IVF fertilization in 64%, 65%, 45%, and 68% of cycles, respectively. CONCLUSION(S): Very low sperm concentration and/or motility were good predictors of poor IVF fertilization, however, low to normal semen parameters were not predictive of successful IVF fertilization. The SPA is a useful screening tool that predicts IVF fertilization with high diagnostic accuracy. The SPA may be useful to discriminate between those couples with a high probability of normal fertilization in IVF and those with a low probability of normal fertilization that may benefit from assisted fertilization by intracytoplasmic sperm injection (ICSI).

Animals↗
PubMed2001

Partial ureteral obstruction dysregulates the renal renin-angiotensin system in the fetal sheep kidney.

OBJECTIVES: To investigate whether partial ureteral obstruction (PUO) in the fetus induces dysregulation of the renin-angiotensin system (RAS) and of transforming growth factor-beta 1 (TGF-beta1) and tissue inhibitors of metalloproteinase (TIMP1) expression. Previous studies have indicated that renal and urinary tract development depend on an intact renal RAS. Fetal urinary obstruction is distinct from postnatal obstruction. It has been suggested in postnatal animal studies that dysregulation of the RAS, and subsequent increased expression of TGF-beta1 and TIMP1, leads to changes in extracellular matrix composition. METHODS: Bilateral PUO was created in 4 fetal sheep. Seven animals (four obstructed and three controls) were killed at birth and their kidneys removed. Semiquantitative reverse transcriptase-polymerase chain reaction was used to quantify the levels of renin, angiotensinogen, angiotensin receptor type 1 (AT1 receptor), angiotensin receptor type 2 (AT2 receptor), TGF-beta1, and TIMP1. These messages were normalized to glyceraldehyde-3-phosphate dehydrogenase mRNA. RESULTS: All obstructed animals had moderate to severe hydronephrosis with enlarged kidneys (mean weight 22.0 g versus 9.4 g for the control animals; P <0.05). The increase in the levels of renin, angiotensinogen, AT1 receptor, TGF-beta1, and TIMP1 mRNA was significant in the PUO group compared with the control group (P <0.05). AT2 receptor levels did not increase, but the AT1/AT2 mRNA ratio was significantly increased over normal (P <0.005). Also, a significant linear correlation was found between the increased renal weight and increased TGF-beta1 mRNA levels (P <0.005). CONCLUSIONS: Our findings suggest that fetal PUO can cause upregulation of the renal RAS and increased expression of TGF-beta1 and TIMP1, which may alter the balance between the generation and degradation of the extracellular matrix. The coordinate increases in renin, angiotensinogen, and AT1 receptor mRNA levels in chronic fetal PUO may represent a maladaptive response that contributes to interstitial fibrosis and prolonged vasoconstriction. RAS components and growth factors, particularly TGF-beta1, may be considered relevant targets in the prevention and treatment of congenital obstructive nephropathy.

Angiotensinogen↗
PubMed2001

Heparin-binding epidermal growth factor-like growth factor is an autocrine mediator of human prostate stromal cell growth in vitro.

PURPOSE: The physiological mechanisms by which soluble mediators of cell proliferation and survival alter expansion of the prostatic stroma in benign prostatic hyperplasia are poorly understood. We recently identified heparin-binding epidermal growth factor like growth factor (HB-EGF) as a product predominantly of the smooth muscle cell compartments of the adult human prostate. We assess the potential role of this growth factor as a stromal cell regulator. MATERIALS AND METHODS: Primary cultures of desmin and alpha-actin positive human prostate stromal cells were shown to express several cell associated HB-EGF isoforms as well as the primary cognate HB-EGF receptor, ErbB1/HER1, suggesting the existence of an autocrine or juxtacrine regulatory loop. The related receptor tyrosine kinase, ErbB2/HER2, was also expressed as assessed by reverse transcriptase (RT) polymerase chain reaction (PCR). HB-EGF messenger RNA levels in human prostate stromal cells increased modestly (70%) in response to a repetitive mechanical stimulus, a lower response than has been reported for neonatal rat bladder smooth muscle cells, in which HB-EGF was originally identified as a mechanically responsive gene. RESULTS: HB-EGF, epidermal growth factor and basic fibroblast growth factor stimulated human prostate stromal cell growth, while a specific antagonist of HB-EGF, [Glu52]-diphtheria toxin/CRM197, inhibited human prostate stromal growth in serum-free medium by a mechanism that did not involve increased apoptosis. A function blocking antibody against CD9/DRAP27/MRP-1, a cell surface binding partner of the membrane form of HB-EGF, also stimulated human prostate stromal cell proliferation. CONCLUSIONS: HB-EGF is an endogenously produced human prostate stromal cell growth factor and, thus, may have a role as a physiologically relevant autocrine or juxtacrine mediator of stromal expansion in benign prostatic hyperplasia.

Adult↗
PubMed2001

Asymmetric Prospero localization is required to generate mixed neuronal/glial lineages in the Drosophila CNS.

In many organisms, single neural stem cells can generate both neurons and glia. How are these different cell types produced from a common precursor? In Drosophila, glial cells missing (gcm) is necessary and sufficient to induce glial development in the CNS. gcm mRNA has been reported to be asymmetrically localized to daughter cells during precursor cell division, allowing the daughter cell to produce glia while precursor cell generates neurons. We show that (1) gcm mRNA is uniformly distributed during precursor cell divisions; (2) the Prospero transcription factor is asymmetrically localized into the glial-producing daughter cell; (3) Prospero is required to upregulate gcm expression and induce glial development; and (4) mislocalization of Prospero to the precursor cell leads to ectopic gcm expression and the production of extra glia. We propose a novel model for the separation of glia and neuron fates in mixed lineages in which the asymmetric localization of Prospero results in upregulation of gcm expression and initiation of glial development in only precursor daughter cells.

Animals↗
PubMed2001

Effects of rhythm regularization and rate control in improving left ventricular function in atrial fibrillation patients undergoing atrioventricular nodal ablation.

OBJECTIVES: To assess the relative contributions of rate control and rhythm regularization to left ventricular function in atrial fibrillation (AF) patients undergoing atrioventricular nodal ablation. This was performed by assessing the effect of ventricular rhythm regularization on left ventricular function during AF, and the effect of varying heart rate on left ventricular function after ablation. PATIENTS AND METHODS: Eleven patients with continuous AF and V/VI-R pacemakers undergoing therapeutic atrioventricular nodal ablation were studied. Preablation patients underwent two 30 min observation periods in a randomized, blinded fashion during which they were either in baseline AF (pacer set to default V/VI 50/min) or being paced using a rhythm stabilizing algorithm (RSA) designed to regularize rhythm without changing baseline ventricular rate. Six weeks after ablation, patients were again observed during the two following 30 min periods: pacing at a low clinically indicated rate (69+/-9 beats/min), and pacing at the rapid, mean preablation rate. During all observation periods, left ventricular function was measured continuously using a nuclear vest that provided validated measures of heart rate, ejection fraction, and normalized end-systolic volume (ESV) and end-diastolic (EDV) volume. RESULTS: Before ablation, RSA successfully regularized rhythm, decreasing the coefficient of variation of interbeat intervals 20+/-5% to 10+/-4% (P<0.001). The heart rate with RSA (105+/-19 beats/min) was not significantly different from the baseline AF rate (102+/-21 beats/min). Increased rhythm regularity achieved by RSA significantly improved left ventricular function, decreasing ESV from 62+/-12 units to 57+/-11 units (P=0.03), and increasing the ejection fraction from 31+/-11% to 36+/-11% (P=0.03). After ablation, at the clinically indicated low pacing rate of 69+/-9 beats/min, a much greater improvement in ejection fraction was observed, increasing to 44+/-13% (P=0.005 compared with preablation). However, rapid regular pacing at the mean preablation rate of 110+/-18 beats/min eradicated this improvement, decreasing the ejection fraction to 31+/-8% (P=0.003), and increasing ESV from 53+/-13 units to 62+/-8 units (P=0.006). CONCLUSIONS: Rhythm regularity achieved by a regularizing pacing algorithm can significantly, albeit modestly, improve left ventricular function in AF. However, more marked improvements in left ventricular function seen after ablation are primarily due to rate reduction alone.

Aged↗
PubMed2000

Heparin-binding EGF-like growth factor is up-regulated in the obstructed kidney in a cell- and region-specific manner and acts to inhibit apoptosis.

The expression of certain growth factors in the epidermal growth factor (EGF) family is altered in response to renal injury. Recent studies have demonstrated that heparin binding EGF-like growth factor (HB-EGF) expression may be cytoprotective in response to apoptotic signals. The purpose of this study was to investigate the potential role of HB-EGF in the upper urinary tract following unilateral ureteral obstruction. We present evidence that: i) ureteral obstruction induced cell-specific but transient activation of HB-EGF gene expression; ii) HB-EGF expression in renal epithelial cells increased under conditions where mechanical deformation, such as that caused by hydronephrotic distension, induces apoptosis, but HB-EGF expression did not increase in renal pelvis smooth muscle cells under identical conditions; and iii) enforced expression of HB-EGF served to protect renal epithelial cells from stretch-induced apoptosis. These results suggest a potential mechanism by which the kidney protects itself from apoptosis triggered by urinary tract obstruction.

Actins↗
PubMed2000

Cyclic stretch activates p38 SAPK2-, ErbB2-, and AT1-dependent signaling in bladder smooth muscle cells.

Cyclic mechanical stretch of bladder smooth muscle cells (SMC) increases rates of DNA synthesis and stimulates transcription of the gene for heparin-binding epidermal growth factor-like growth factor (HB-EGF), an ErbB1/EGF receptor ligand that has been linked to hypertrophic bladder growth. In this study we sought to clarify the signaling pathways responsible for mechanotransduction of the stretch stimulus. HB-EGF mRNA levels, DNA synthesis, and AP-1/Ets DNA binding activities were induced by repetitive stretch of primary culture rat bladder SMC. Inhibitors of the p38 SAPK2 pathway, the angiotensin receptor type 1 (AT1), and the ErbB2 tyrosine kinase reduced each of these activities, while an inhibitor of the extracellular signal-regulated kinase mitogen-activated protein kinase (Erk-MAPK) pathway had no effect. Stretch rapidly activated stress-activated protein kinase 2 (p38 SAPK2) and Jun NH(2)-terminal kinase (JNK)/SAPK pathways but not the Erk-MAPK pathway and induced ErbB2 but not ErbB1 phosphorylation. Angiotensin II (ANG II) a bladder SMC mitogen previously linked to the stretch response, did not activate ErbB2, and ErbB2 activation occurred in response to stretch in the presence of an ANG receptor inhibitor, indicating that activation of the AT1-mediated pathway and the ErbB2-dependent pathway occurs by independent mechanisms. p38 SAPK2 and JNK/SAPK signaling also appeared to be independent of the ErbB2 and AT1 pathways. These findings indicate that stretch-stimulated DNA synthesis and gene expression in normal bladder SMC occur via multiple independent receptor systems (e.g., AT1 and ErbB2) and at least one MAPK pathway (p38 SAPK2). Further, we show that the Erk-MAPK pathway, which in most systems is linked to receptor-dependent cell growth responses, is not involved in progression to DNA synthesis or in the response of the HB-EGF gene to mechanical forces.

Angiotensin II↗
PubMed2000

A nontoxic diphtheria toxin analogue inhibits neonatal bladder smooth muscle cell proliferation.

PURPOSE: The response of the neonatal bladder to infravesical obstruction, such as posterior urethral valves or detrusor-sphincter dyssynergia, may result in structural and functional changes that persist well after obstruction is treated. A pharmacological means of inhibiting smooth muscle cell proliferation would likely serve to halt or reverse this deleterious process. Heparin binding (HB) epidermal growth factor (EGF) is a known smooth muscle cell mitogen, while its membrane bound precursor serves as the diphtheria toxin receptor. We report the effects of the nontoxic diphtheria toxin analogue cross reacting material (CRM) 197 on neonatal sheep bladder smooth muscle cell proliferation. MATERIALS AND METHODS: Neonatal sheep smooth muscle cell cultures were obtained from whole bladder explants. Immunohistochemical staining was performed for desmin and alpha-smooth muscle actin. HB-EGF messenger RNA was detected by reverse transcriptase polymerase chain reaction using primers to the human sequence, while pro-HB-EGF peptide was confirmed using a diphtheria toxin sensitivity assay with incorporation of tritiated leucine. Cells grown in 96 well plates were exposed to 1, 10 and 100 microg./ml. CRM 197 for 5 days, after which relative cell number was determined using an 3-[4,5-dimethylthiazol-2-yl] -2,5-diphenyltetrazolium bromide; thiazolyl blue based assay read at a wavelength of 550 nm. Statistical analysis was performed using Student's t test. RESULTS: Primary cell cultures stained positive for desmin and alpha-smooth muscle actin, confirming a smooth muscle origin. Reverse transcriptase polymerase chain reaction yielded a 453 bp product with 88% homology to human HB-EGF. Total protein synthesis significantly decreased when cells were incubated with diphtheria toxin, confirming the presence of membrane bound pro-HB-EGF. CRM 197 inhibited bladder smooth muscle cell growth in a dose dependent fashion at a concentration of 10 microg./ml., resulting in a 40% decrease in proliferation (p <0.0001). CONCLUSION: CRM 197 inhibits bladder smooth muscle cell proliferation in a dose dependent, nontoxic fashion through its interaction with HB-EGF. These data suggest that molecular strategies designed to inhibit HB-EGF mediated cell growth may prove beneficial for the prevention and/or treatment of detrusor hypertrophy secondary to anatomical or functional bladder outlet obstruction.

Animals↗