Biomedical subjects

D A Harris

Publications and source records attributed to D A Harris.

At least 37 records · Page 2Linked to original sources

PubMed2001

A transmembrane form of the prion protein contains an uncleaved signal peptide and is retained in the endoplasmic Reticulum.

Although there is considerable evidence that PrP(Sc) is the infectious form of the prion protein, it has recently been proposed that a transmembrane variant called (Ctm)PrP is the direct cause of prion-associated neurodegeneration. We report here, using a mutant form of PrP that is synthesized exclusively with the (Ctm)PrP topology, that (Ctm)PrP is retained in the endoplasmic reticulum and is degraded by the proteasome. We also demonstrate that (Ctm)PrP contains an uncleaved, N-terminal signal peptide as well as a C-terminal glycolipid anchor. These results provide insight into general mechanisms that control the topology of membrane proteins during their synthesis in the endoplasmic reticulum, and they also suggest possible cellular pathways by which (Ctm)PrP may cause disease.

Animals↗

PubMed2001

Pott's puffy tumour: an unusual presentation and management.

Pott's puffy tumour is a rare clinical entity in this era of antibiotics. It is usually seen as a complication of frontal sinusitis. This is the first report of Pott's puffy tumour presenting as a complication of maxillary sinusitis. This is also the first reported case of Pott's puffy tumour treated with debridement and gentamicin beads. We discuss the clinical presentation and successful treatment of this rare disease.

Abscess↗

PubMed2000

Most pathogenic mutations do not alter the membrane topology of the prion protein.

The prion protein (PrP), a glycolipid-anchored membrane glycoprotein, contains a conserved hydrophobic sequence that can span the lipid bilayer in either direction, resulting in two transmembrane forms designated (Ntm)PrP and (Ctm)PrP. Previous studies have shown that the proportion of (Ctm)PrP is increased by mutations in the membrane-spanning segment, and it has been hypothesized that (Ctm)PrP represents a key intermediate in the pathway of prion-induced neurodegeneration. To further test this idea, we have surveyed a number of mutations associated with familial prion diseases to determine whether they alter the proportions of (Ntm)PrP and (Ctm)PrP produced in vitro, in transfected cells, and in transgenic mice. For the in vitro experiments, PrP mRNA was translated in the presence of murine thymoma microsomes which, in contrast to the canine pancreatic microsomes used in previous studies, are capable of efficient glycolipidation. We confirmed that mutations within or near the transmembrane domain enhance the formation of (Ctm)PrP, and we demonstrate for the first time that this species contains a C-terminal glycolipid anchor, thus exhibiting an unusual, dual mode of membrane attachment. However, we find that pathogenic mutations in other regions of the molecule have no effect on the amounts of (Ctm)PrP and (Ntm)PrP, arguing against the proposition that transmembrane PrP plays an obligate role in the pathogenesis of prion diseases.

Amino Acid Substitution↗

PubMed2000

Accumulation of protease-resistant prion protein (PrP) and apoptosis of cerebellar granule cells in transgenic mice expressing a PrP insertional mutation.

We have generated lines of transgenic mice that express a mutant prion protein (PrP) containing 14 octapeptide repeats whose human homologue is associated with an inherited prion dementia. These mice develop a neurological illness with prominent ataxia at 65 or 240 days of age, depending on whether the transgene array is, respectively, homozygous or hemizygous. Starting from birth, mutant PrP is converted into a protease-resistant and detergent-insoluble form that resembles the scrapie isoform of PrP, and this form accumulates dramatically in many brain regions throughout the lifetime of the mice. As PrP accumulates, there is massive apoptosis of granule cells in the cerebellum. Our analysis provides important insights into the molecular pathogenesis of inherited prion disorders in humans.

Animals↗

PubMed2000

Brain copper content and cuproenzyme activity do not vary with prion protein expression level.

Prion diseases are neurodegenerative disorders that result from conformational transformation of a normal cell surface glycoprotein, PrP(C), into a pathogenic isoform, PrP(Sc). Although the normal physiological function of PrP(C) has remained enigmatic, the recent observation that the protein binds copper ions with micromolar affinity suggests a possible role in brain copper metabolism. In this study, we have used mice that express 0, 1, and 10 times the normal level of PrP to assess the effect of PrP expression level on the amount of brain copper and on the properties of two brain cuproenzymes. Using mass spectrometry, we find that the amount of ionic copper in subcellular fractions from brain is similar in all three lines of mice. In addition, the enzymatic activities of Cu-Zn superoxide dismutase and cytochrome c oxidase in brain extracts are similar in these groups of animals, as is the incorporation of (64)Cu into Cu-Zn superoxide dismutase both in cultured cerebellar neurons and in vivo. Our results differ from those of another set of published studies, and they require a re-evaluation of the role of PrP(C) in copper metabolism.

Animals↗

PubMed2000

Reversion of prion protein conformational changes by synthetic beta-sheet breaker peptides.

BACKGROUND: Transmissible spongiform encephalopathies are associated with a structural transition in the prion protein that results in the conversion of the physiological PrPc to pathological PrP(Sc). We investigated whether this conformational transition can be inhibited and reversed by peptides homologous to the PrP fragments implicated in the abnormal folding, which contain specific residues acting as beta-sheet blockers (beta-sheet breaker peptides). METHODS: We studied the effect of a 13-residue beta-sheet breaker peptide (iPrP13) on the reversion of the abnormal structure and properties of PrP(Sc) purified from the brains of mice with experimental scrapie and from human beings affected by sporadic and variant Creutzfeldt-Jakob disease. In a cellular model of familial prion disease, we studied the effect of the peptide in the production of the abnormal form of PrP in intact cells. The influence of the peptide on prion infectivity was studied in vivo by incubation time assays in mice with experimental scrapie. FINDINGS: The beta-sheet breaker peptide partly reversed in-vitro PrP(Sc) to a biochemical and structural state similar to that of PrPc. The effect of the peptide was also detected in intact cells. Treatment of prion infectious material with iPrP13 delayed the appearance of clinical symptoms and decreased infectivity by 90-95% in mice with experimental scrapie. INTERPRETATION: Beta-sheet breaker peptides reverse PrP conformational changes implicated in the pathogenesis of spongiform encephalopathies. These peptides or their derivatives provide a useful tool to study the role of PrP conformation and might represent a novel therapeutic approach for prion-related disorders.

Animals↗

PubMed2000

A transgenic model of a familial prion disease.

We have generated lines of transgenic mice that express a mutant prion protein containing 14 octapeptide repeats whose human homologue is associated with an inherited prion dementia. These mice develop an ataxic illness that begins at 65 days of age when the transgene array is homozygous, and results in death by 115-138 days. Starting from birth, mutant PrP is converted into a protease-resistant and detergent-insoluble form that resembles PrP(Sc), and this form accumulates dramatically in many brain regions throughout the lifetime of the mice. As PrP accumulates, there is massive apoptosis of cerebellar granule cells, as well as astrocytosis and deposition of PrP in a punctate pattern. These results establish a new transgenic animal model of an inherited human prion disease, and provide important insights into the molecular pathogenesis of these disorders.

Animals↗

PubMed2000

Oxidative degradation of bilirubin produces vasoactive compounds.

Subarachnoid haemorrhage is often followed by haemolysis and concomitant oxidative stress, and is frequently complicated by pathological vasoconstriction or cerebral vasospasm. It is known that upregulation of haem oxygenase (HO-1) is induced by oxidative stress and results in release of biliverdin and bilirubin (BR), which are scavengers of reactive oxygen species (ROS). Here we report biomimetic studies aimed at modelling pathological conditions leading to oxidative degradation of BR. Oxidative degradation products of BR, formed by reaction with hydrogen peroxide (an ROS model system), demonstrated biological activity by stimulating oxygen consumption and force development in vascular smooth muscle from porcine carotid artery. Analogous biological activity was observed with vasoactive cerebrospinal fluid from subarachnoid haemorrhage patients. Three degradation products of BR were isolated: two were assigned as isomeric monopyrrole (C9H11N2O2) derivatives, 4-methyl-5-oxo-3-vinyl-(1, 5-dihydropyrrol-2-ylidene)acetamide and 3-methyl-5-oxo-4-vinyl-(1, 5-dihydropyrrol-2-ylidene)acetamide and the third was 4-methyl-3-vinylmaleimide (MVM), a previously isolated photodegradation product of biliverdin. Possible mechanisms of oxidative degradation of BR are discussed. Tentative assignment of these structures in the cerebrospinal fluid (CSF) of cerebral vasospasm patients has been made. It is proposed that one or more of the degradation products of biliverdin or bilirubin are involved in complications such as vasospasm and or pathological vasoconstriction associated with haemorrhage.

Bilirubin↗

PubMed2000

Nerve growth factor-induced differentiation does not alter the biochemical properties of a mutant prion protein expressed in PC12 cells.

Insertional and point mutations in the gene encoding the prion protein (PrP) are responsible for familial prion diseases. We have previously generated lines of Chinese hamster ovary cells that express PrP molecules carrying pathogenic mutations, and found that the mutant proteins display several biochemical properties reminiscent of PrP(Sc), the infectious isoform of PrP. To analyze the properties and effects of mutant PrP molecules expressed in cells with a neuronal phenotype, we have constructed stably transfected lines of PC12 cells that synthesize a PrP molecule carrying a nine-octapeptide insertion. We report here that this mutant PrP acquires scrapie-like properties, including detergent insolubility, protease resistance, and resistance to phospholipase cleavage of its glycolipid anchor. A detergent-insoluble and phospholipase-resistant form of the mutant protein is also released spontaneously into conditioned medium. These scrapie-like biochemical properties are quantitatively similar to those seen in Chinese hamster ovary cells and are not affected by differentiation of the PC12 cells into sympathetic neurons by nerve growth factor. Moreover, there is no detectable effect of mutant PrP expression on the morphology or viability of the cells in either the differentiated or undifferentiated state. These results indicate that conversion of mutant PrP into a PrP(Sc)-like form does not depend critically on the cellular context, and they suggest that mutant PrP expressed in cultured cells, even those having the phenotype of differentiated neurons, is not neurotoxic.

Animals↗

PubMed2000

Four earplugs in search of a rating system.

OBJECTIVE: The performance of four insert earplugs was evaluated by determining the Noise Reduction Rating (NRR) and the Subject-Fit Noise Reduction Rating [NRR(SF)]. The NRR and NRR(SF) were calculated from real-ear attenuation at threshold (REAT) data collected using the experimenter-fit protocol described in the now-rescinded ANSI S3.19-1974 (American National Standards Institute, 1974) and the subject-fit protocol of the recently revised ANSI S12.6-1997 (American National Standards Institute, 1997) standards for REAT measurement. DESIGN: A comparison of the experimenter-fit and subject-fit REAT performance was conducted using four pools of subjects, one pool per protector. Each device was tested with at least 20 subjects, the minimum size necessary to estimate the NRR(SF) for an earplug. The REAT was measured with third-octave narrowband noise stimuli for center frequencies at 0.125, 0.25,0.5, 1, 2, 3.15, 4, 6.3, and 8 kHz. The REAT means and standard deviations were compared with the manufacturer data. RESULTS: This study showed that the NRR(SF) is typically lower than the NRR and that the NRR(SF) is not well-predicted by the NRR derating schemes recommended by the National Institute for Occupational Safety and Health and required by the Occupational Safety and Health Administration. CONCLUSION: The difference between the present NRR on hearing protector labels and the NRR(SF) is sufficiently large and unpredictable enough to render the application of derating schemes meaningless even though these schemes attempt to account for the difference between the laboratory and real-world outcomes. The only way to provide a protector noise rating that is predictive of a real-world outcome is to retest the protector according to the subject-fit method of ANSI S12.6-1997 (American National Standards Institute, 1997).

Auditory Threshold↗

PubMed2000

Successful transmission of three mouse-adapted scrapie strains to murine neuroblastoma cell lines overexpressing wild-type mouse prion protein.

Propagation of the agents responsible for transmissible spongiform encephalopathies (TSEs) in cultured cells has been achieved for only a few cell lines. To establish efficient and versatile models for transmission, we developed neuroblastoma cell lines overexpressing type A mouse prion protein, MoPrP(C)-A, and then tested the susceptibility of the cells to several different mouse-adapted scrapie strains. The transfected cell clones expressed up to sixfold-higher levels of PrP(C) than the untransfected cells. Even after 30 passages, we were able to detect an abnormal proteinase K-resistant form of prion protein, PrP(Sc), in the agent-inoculated PrP-overexpressing cells, while no PrP(Sc) was detectable in the untransfected cells after 3 passages. Production of PrP(Sc) in these cells was also higher and more stable than that seen in scrapie-infected neuroblastoma cells (ScN2a). The transfected cells were susceptible to PrP(Sc)-A strains Chandler, 139A, and 22L but not to PrP(Sc)-B strains 87V and 22A. We further demonstrate the successful transmission of PrP(Sc) from infected cells to other uninfected cells. Our results corroborate the hypothesis that the successful transmission of agents ex vivo depends on both expression levels of host PrP(C) and the sequence of PrP(Sc). This new ex vivo transmission model will facilitate research into the mechanism of host-agent interactions, such as the species barrier and strain diversity, and provides a basis for the development of highly susceptible cell lines that could be used in diagnostic and therapeutic approaches to the TSEs.

Animals↗

PubMed1999

Prion proteins carrying pathogenic mutations are resistant to phospholipase cleavage of their glycolipid anchors.

Familial prion diseases are linked to mutations in the gene encoding PrP, a protein of unknown function that is attached to the plasma membrane of neurons and several other cell types by a phosphatidylinositol-containing, glycolipid anchor. We have previously found that PrP molecules carrying disease-associated mutations display several biochemical attributes of PrPSc, the pathogenic isoform of PrP, when expressed in cultured Chinese hamster ovary cells. One of the distinctive properties of these mutant PrPs is their abnormal association with cell membranes, as revealed by their retention on the cell surface after treatment with a bacterial phospholipase that normally cleaves the glycolipid anchor. We demonstrate here that mutant PrP molecules, either expressed on intact cells or solubilized in nondenaturing detergents, are partially resistant to phospholipase cleavage. The anchor becomes fully susceptible to the enzyme when the proteins are denatured in SDS. These results suggest that the mutant PrP conformation, state of aggregation, or association with other molecules renders the glycolipid anchor physically inaccessible to cleavage. This conclusion stands in contrast to our previous suggestion that mutant PrP molecules are poorly released from the cell surface because they possess a secondary mechanism of membrane attachment in addition to the glycolipid anchor. Since PrPSc from scrapie-infected brain and cultured cells is also inefficiently released from membranes by phospholipase, resistance to this enzyme may be a molecular marker of the scrapie state.

Animals↗

PubMed1999

Cell-lysate conversion of prion protein into its protease-resistant isoform suggests the participation of a cellular chaperone.

A conformational transition between the normal cellular prion protein (PrPC) and the beta-sheet-rich pathological isoform (PrPSc) is a central event in the pathogenesis of spongiform encephalopathies. The prion infectious agent seems to contain mainly, if not exclusively, PrPSc, which has the ability to propagate its abnormal conformation by transforming the host PrPC into the pathological isoform. We have developed an in vitro system to induce the PrPC --> PrPSc conversion by incubating a cell-lysate containing mouse PrPC with partially purified mouse PrPSc. After 48 h of incubation with a 10-fold molar excess of PrPSc, the cellular protein acquired PK-resistance resembling a PrPSc-like state. Time course experiments suggest that the conversion follows a stepwise mechanism involving kinetic intermediates. The conversion was induced by PrPSc extracted from mice infected with two different prion strains, each propagating its characteristic Western blot profile. The latter results and the fact that all the cellular components are present in the conversion reaction suggest that PrPC-PrPSc interaction is highly specific and required for the conversion. No transformation was observed under the same conditions using purified proteins without cell-lysate. However, when PrPC-depleted cell-lysate was added to the purified proteins the conversion was recovered. These findings provide direct evidence for the participation of a chaperone-like activity involved in catalyzing the conversion of PrPC into PrPSc.

Animals↗

PubMed1999

Cellular biology of prion diseases.

Prion diseases are fatal neurodegenerative disorders of humans and animals that are important because of their impact on public health and because they exemplify a novel mechanism of infectivity and biological information transfer. These diseases are caused by conformational conversion of a normal host glycoprotein (PrPC) into an infectious isoform (PrPSc) that is devoid of nucleic acid. This review focuses on the current understanding of prion diseases at the cell biological level. The characteristics of the diseases are introduced, and a brief history and description of the prion hypothesis are given. Information is then presented about the structure, expression, biosynthesis, and possible function of PrPC, as well as its posttranslational processing, cellular localization, and trafficking. The latest findings concerning PrPSc are then discussed, including cell culture systems used to generate this pathogenic isoform, the subcellular distribution of the protein, its membrane attachment, proteolytic processing, and its kinetics and sites of synthesis. Information is also provided on molecular models of the PrPC-->PrPSc conversion reaction and the possible role of cellular chaperones. The review concludes with suggestions of several important avenues for future investigation.

3T3 Cells↗

PubMed1999

Lispro or regular insulin for multiple injection therapy in adolescence. Differences in free insulin and glucose levels overnight.

OBJECTIVE: Regular insulin given with the evening meal could contribute to the risk of nocturnal hypoglycemia in adolescents with type 1 diabetes using a multiple injection regimen. To test this hypothesis, we compared glucodynamics and free insulin levels on two separate study nights. RESEARCH DESIGN AND METHODS: A total of 14 adolescents were recruited. On both nights, identical doses of regular insulin or insulin lispro were administered 30 min or 10 min, respectively, before the evening meal, using a double-blind randomized crossover study design. Doses of NPH insulin and carbohydrate content of the evening meal and snack were kept identical. Blood samples were taken every 15 min for blood glucose and every 60 min for free insulin and ketones. RESULTS: After insulin lispro administration, glucose levels were significantly lower between the evening meal and the bedtime snack (analysis of variance [ANOVA] P = 0.02), and four hypoglycemic episodes were recorded. This corresponded to a higher (458 +/- 48 vs. 305 +/- 33 pmol/l, P = 0.02), earlier (64 +/- 4.6 vs. 103 +/- 12 min, P = 0.01), and shorter-lasting (245 +/- 21 vs. 365 +/- 39 min, P = 0.01) insulin peak in contrast to regular insulin. After the bedtime snack, glucose levels increased dramatically during the lispro night and stayed higher, up to 0300 in the morning (ANOVA P = 0.01), corresponding to lower mean insulin levels (146 +/- 20 vs. 184 +/- 27 pmol/l, P = 0.04). No differences were seen in glucose and insulin levels between 0300 and 0800. Four episodes of nocturnal hypoglycemia were documented after the bedtime snack during the regular insulin night, in contrast to one episode after insulin lispro. No differences in ketone levels were observed. CONCLUSIONS: The replacement of regular insulin with insulin lispro may reduce the risk of late hypoglycemia, but redistribution of the evening carbohydrate may be needed to ensure good metabolic control and prevent early postprandial hypoglycemia.

Activity Cycles↗

PubMed1999

Cell biological studies of the prion protein.

Studying PrPC and PrPSc in cell culture systems is advantageous because such systems contain all the organelles, membranes, and molecular cofactors that are likely to play an important role in the biology of the proteins. Using cultured cells expressing PrPC, we have discovered that this isoform constitutively cycles between the cell surface and an endocytic compartment, a process that is mediated by clathrin-coated pits and a putative PrPC receptor. We have also constructed stably transfected lines of CHO cells that express PrP molecules carrying mutations that are associated with familial prion diseases. The mutant PrP molecules in these cells are spontaneously converted to the PrPSc state, a phenomenon which has allowed us to analyze several key features of prion formation.

Animals↗

PubMed1998

Copper stimulates endocytosis of the prion protein.

Prion diseases result from conformational alteration of PrPC, a cell surface glycoprotein expressed in brain, spinal cord, and several peripheral tissues, into PrPSc, a protease-resistant isoform that is the principal component of infectious prion particles. Although a great deal is known about the pathogenic role of PrPSc, the physiological function of PrPC has remained a mystery. Several lines of evidence have recently suggested the possibility that PrPC may play a role in the metabolism of copper. To further investigate the interaction of PrPC and copper, we have analyzed the effect of this metal ion on the endocytic trafficking of PrPC in cultured neuroblastoma cells. We report here that copper rapidly and reversibly stimulates endocytosis of PrPC from the cell surface. This effect may be physiologically relevant and suggests the hypothesis that PrPC could serve as a recycling receptor for uptake of copper ions from the extracellular milieu.

Animals↗

PubMed1998

Effects of low-dose recombinant human insulin-like growth factor-I on insulin sensitivity, growth hormone and glucagon levels in young adults with insulin-dependent diabetes mellitus.

Despite recent interest in the therapeutic potential of recombinant human insulin-like growth factor-I (rhIGF-I) in the treatment of diabetes mellitus, its mechanism of action is still not defined. We have studied the effects of low-dose bolus subcutaneous rhIGF-I (40 microg/kg and 20 microg/kg) on insulin sensitivity, growth hormone (GH) and glucagon levels in seven young adults with insulin-dependent diabetes mellitus (IDDM) using a randomized double-blind placebo-controlled crossover study design. Each was subjected to a euglycemic clamp (5 mmol/L) protocol consisting of a variable-rate insulin infusion clamp (6:00 PM to 8:00 AM) followed by a two-dose hyperinsulinemic clamp (insulin infusion of 0.75 mU x kg(-1) x min(-1) from 8 to 10 AM and 1.5 mU x kg(-1) x min(-1) from 10 AM to 12 noon) incorporating [6,6 2H2]glucose tracer for determination of glucose production/utilization rates. Following rhIGF-I administration, the serum IGF-I level (mean +/- SEM) increased (40 microg/kg, 655 +/- 90 ng/mL, P < .001; 20 microg/kg, 472 +/- 67 ng/mL, P < .001; placebo, 258 +/- 51 ng/mL). Dose-related reductions in insulin were observed during the period of steady-state euglycemia (1 AM to 8 AM) (40 microg/kg, 48 +/- 5 pmol/L, P = .01; 20 microg/kg, 58 +/- 8 pmol/L, P = .03; placebo, 72 +/- 8 pmol/L). The mean overnight GH level (40 microg/kg, 9.1 +/- 1.4 mU/L, P = .04; 20 microg/kg, 9.6 +/- 2.0 mU/L, P = .12; placebo, 11.3 +/- 1.7 mU/L) and GH pulse amplitude (40 microg/kg, 18.8 +/- 2.9 mU/L, P = .04; 20 microg/kg, 17.0 +/- 3.4 mU/L, P > .05; placebo, 23.0 +/- 3.7 mU/L) were also reduced. No differences in glucagon, IGF binding protein-1 (IGFBP-1), acetoacetate, or beta-hydroxybutyrate levels were found. During the hyperinsulinemic clamp conditions, no differences in glucose utilization were noted, whereas hepatic glucose production was reduced by rhIGF-I 40 microg/kg (P = .05). Our data demonstrate that in subjects with IDDM, low-dose subcutaneous rhIGF-I leads to a dose-dependent reduction in the insulin level for euglycemia overnight that parallels the decrease in overnight GH levels, but glucagon and IGFBP-1 levels remain unchanged. The decreases in hepatic glucose production during the hyperinsulinemic clamp study observed the following day are likely related to GH suppression, although a direct effect by rhIGF-I cannot be entirely discounted.

3-Hydroxybutyric Acid↗