Plasmodium falciparum domain mediating adhesion to chondroitin sulfate A: A receptor for human placental infection

Malaria during the first pregnancy causes a high rate of fetal and neonatal death. The decreasing susceptibility during subsequent pregnancies correlates with acquisition of antibodies that block binding of infected red cells to chondroitin sulfate A (CSA), a receptor for parasites in the placenta. Here we identify a domain within a particular Plasmodium falciparum erythrocyte membrane protein 1 that binds CSA. We cloned a var gene expressed in CSA-binding parasitized red blood cells (PRBCs). The gene had eight receptor-like domains, each of which was expressed on the surface of Chinese hamster ovary cells and was tested for CSA binding. CSA linked to biotin used as a probe demonstrated that two Duffy-binding-like (DBL) domains (DBL3 and DBL7) bound CSA. DBL7, but not DBL3, also bound chondroitin sulfate C (CSC) linked to biotin, a negatively charged sugar that does not support PRBC adhesion. Furthermore, CSA, but not CSC, blocked the interaction with DBL3; both CSA and CSC blocked binding to DBL7. Thus, only the DBL3 domain displays the same binding specificity as PRBCs. Because protective antibodies present after pregnancy block binding to CSA of parasites from different parts of the world, DBL-3, although variant, may induce cross-reactive immunity that will protect pregnant women and their fetuses.

A mouse model for X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is a peroxisomal disorder with impaired β-oxidation of very long chain fatty acids (VLCFAs) and reduced function of peroxisomal very long chain fatty acyl-CoA synthetase (VLCS) that leads to severe and progressive neurological disability. The X-ALD gene, identified by positional cloning, encodes a peroxisomal membrane protein (adrenoleukodystrophy protein; ALDP) that belongs to the ATP binding cassette transporter protein superfamily. Mutational analyses and functional studies of the X-ALD gene confirm that it and not VLCS is the gene responsible for X-ALD. Its role in the β-oxidation of VLCFAs and its effect on the function of VLCS are unclear. The complex pathology of X-ALD and the extreme variability of its clinical phenotypes are also unexplained. To facilitate understanding of X-ALD pathophysiology, we developed an X-ALD mouse model by gene targeting. The X-ALD mouse exhibits reduced β-oxidation of VLCFAs, resulting in significantly elevated levels of saturated VLCFAs in total lipids from all tissues measured and in cholesterol esters from adrenal glands. Lipid cleft inclusions were observed in adrenocortical cells of X-ALD mice under the electron microscope. No neurological involvement has been detected in X-ALD mice up to 6 months. We conclude that X-ALD mice exhibit biochemical defects equivalent to those found in human X-ALD and thus provide an experimental system for testing therapeutic intervention.

Elevated free nitrotyrosine levels, but not protein-bound nitrotyrosine or hydroxyl radicals, throughout amyotrophic lateral sclerosis (ALS)-like disease implicate tyrosine nitration as an aberrant in vivo property of one familial ALS-linked superoxide dismutase 1 mutant

Mutations in superoxide dismutase 1 (SOD1; EC 1.15.1.1) are responsible for a proportion of familial amyotrophic lateral sclerosis (ALS) through acquisition of an as-yet-unidentified toxic property or properties. Two proposed possibilities are that toxicity may arise from imperfectly folded mutant SOD1 catalyzing the nitration of tyrosines [Beckman, J. S., Carson, M., Smith, C. D. & Koppenol, W. H. (1993) Nature (London) 364, 584] through use of peroxynitrite or from peroxidation arising from elevated production of hydroxyl radicals through use of hydrogen peroxide as a substrate [Wiedau-Pazos, M., Goto, J. J., Rabizadeh, S., Gralla, E. D., Roe, J. A., Valentine, J. S. & Bredesen, D. E. (1996) Science 271, 515–518]. To test these possibilities, levels of nitrotyrosine and markers for hydroxyl radical formation were measured in two lines of transgenic mice that develop progressive motor neuron disease from expressing human familial ALS-linked SOD1 mutation G37R. Relative to normal mice or mice expressing high levels of wild-type human SOD1, 3-nitrotyrosine levels were elevated by 2- to 3-fold in spinal cords coincident with the earliest pathological abnormalities and remained elevated in spinal cord throughout progression of disease. However, no increases in protein-bound nitrotyrosine were found during any stage of SOD1-mutant-mediated disease in mice or at end stage of sporadic or SOD1-mediated familial human ALS. When salicylate trapping of hydroxyl radicals and measurement of levels of malondialdehyde were used, there was no evidence throughout disease progression in mice for enhanced production of hydroxyl radicals or lipid peroxidation, respectively. The presence of elevated nitrotyrosine levels beginning at the earliest stages of cellular pathology and continuing throughout progression of disease demonstrates that tyrosine nitration is one in vivo aberrant property of this ALS-linked SOD1 mutant.

Toll-like receptor-2 mediates mycobacteria-induced proinflammatory signaling in macrophages

The recognition of mycobacterial cell wall components causes macrophages to secrete tumor necrosis factor α (TNF-α) and other cytokines that are essential for the development of a protective inflammatory response. We show that toll-like receptors are required for the induction of TNF-α in macrophages by Mycobacterium tuberculosis. Expression of a dominant negative form of MyD88 (a signaling component required for toll-like receptor signaling) in a mouse macrophage cell line blocks TNF-α production induced by M. tuberculosis. We identify toll-like receptor-2 (TLR2) as the specific toll-like receptor required for this induction by showing that expression of an inhibitory TLR2 (TLR2-P681H) blocks TNF-α production induced by whole M. tuberculosis. Further, we show that TLR2-dependent signaling mediates responses to mycobacterial cell wall fractions enriched for lipoarrabinomannan, mycolylarabinogalactan–peptidoglycan complex, or M. tuberculosis total lipids. Thus, although many mycobacterial cell wall fractions are identified to be inflammatory, all require TLR2 for induction of TNF-α in macrophages. These data suggest that TLR2 is essential for the induction of a protective immune response to mycobacteria.

Identification of a Plasmodium falciparum intercellular adhesion molecule-1 binding domain: A parasite adhesion trait implicated in cerebral malaria

Binding of infected erythrocytes to brain venules is a central pathogenic event in the lethal malaria disease complication, cerebral malaria. The only parasite adhesion trait linked to cerebral sequestration is binding to intercellular adhesion molecule-1 (ICAM-1). In this report, we show that Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) binds ICAM-1. We have cloned and expressed PfEMP1 recombinant proteins from the A4tres parasite. Using heterologous expression in mammalian cells, the minimal ICAM-1 binding domain was a complex domain consisting of the second Duffy binding-like (DBL) domain and the C2 domain. Constructs that contained either domain alone did not bind ICAM-1. Based on phylogenetic criteria, there are five distinct PfEMP1 DBL types designated α, β, γ, δ, and ɛ. The DBL domain from the A4tres that binds ICAM-1 is DBLβ type. A PfEMP1 cloned from a distinct ICAM-1 binding variant, the A4 parasite, contains a DBLβ domain and a C2 domain in tandem arrangement similar to the A4tres PfEMP1. Anti-PfEMP1 antisera implicate the DBLβ domain from A4var PfEMP1 in ICAM-1 adhesion. The identification of a P. falciparum ICAM-1 binding domain may clarify mechanisms responsible for the pathogenesis of cerebral malaria and lead to interventions or vaccines that reduce malarial disease.

Oocytes are a source of catecholamines in the primate ovary: Evidence for a cell–cell regulatory loop

Catecholamines, thought to derive from the extrinsic innervation of the ovary, participate in the regulation of ovarian development and mature gonadal function. Recently, intraovarian neurons containing tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis, were described in the ovary of nonhuman primates. We now show that the primate ovary expresses both the genes encoding TH and dopamine β-hydroxylase (DBH), the key enzymes in norepinephrine (NE) biosynthesis. Ovarian neurons were identified as a site of TH and DBH gene expression, and surprisingly, oocytes were identified as an exclusive site of DBH synthesis. Oocytes contain neither TH mRNA nor protein, indicating that they are unable to synthesize dopamine (DA). They did, however, express a DA transporter gene identical to that found in human brain. The physiological relevance of this transporter system and DBH in oocytes was indicated by the ability of isolated oocytes to metabolize exogenous DA into NE. Isolated follicles containing oocytes—but not those from which the oocytes had been removed—responded to DA with an elevation in cAMP levels; this elevation was prevented by propranolol, a β-adrenoreceptor antagonist. The results suggest that oocytes and somatic cells are linked by a neuroendocrine loop consisting of NE synthesized in oocytes from actively transported DA and cAMP produced by somatic follicular cells in response to NE-induced β-adrenoreceptor activation.

Applications of informatics in veterinary medicine

This study used the peer-reviewed biomedical literature to define the veterinary informatics knowledgebase and associated subspecialties, and assesses the level of activity in the field over the thirty-year period from 1966 through 1995. Grateful Med was used to search the MEDLINE bibliographic database for articles that shared one or more Medical Subject Headings (MeSH) keywords from the veterinary and medical informatics subject headings. Each of ninety-five MeSH medical informatics terms was assigned to one of twelve veterinary informatics subspecialties. The number of articles retrieved by each MeSH keyword and subspecialty was calculated. A total of 611 articles were retrieved, representing the contributions of 1,338 authors published in 153 journals. The field experienced slow growth over the twenty-year period from 1966 through 1985. In the following decade, the cumulative number of veterinary informatics articles almost tripled and the percentage of veterinary-related articles that included an informatics component increased almost two-and-one-half fold. Despite this recent growth, the number of veterinary-related articles with an informatics component has never exceeded 1% of either the veterinary or medical informatics literature over the past thirty years, and representation of veterinary subspecialties in the literature varied widely.

Direct measurement of oligonucleotide binding stoichiometry of gene V protein by mass spectrometry.

The binding stoichiometry of gene V protein from bacteriophage f1 to several oligonucleotides was studied using electrospray ionization-mass spectrometry (ESI-MS). Using mild mass spectrometer interface conditions that preserve noncovalent associations in solution, gene V protein was observed as dimer ions from a 10 mM NH4OAc solution. Addition of oligonucleotides resulted in formation of protein-oligonucleotide complexes with stoichiometry of approximately four nucleotides (nt) per protein monomer. A 16-mer oligonucleotide gave predominantly a 4:1 (protein monomer: oligonucleotide) complex while oligonucleotides shorter than 15 nt showed stoichiometries of 2:1. Stoichiometries and relative binding constants for a mixture of oligonucleotides were readily measured using mass spectrometry. The binding stoichiometry of the protein with the 16-mer oligonucleotide was measured independently using size-exclusion chromatography and the results were consistent with the mass spectrometric data. These results demonstrate, for the first time, the observation and stoichiometric measurement of protein-oligonucleotide complexes using ESI-MS. The sensitivity and high resolution of ESI-MS should make it a useful too] in the study of protein-DNA interactions.

Cytochrome P450 1A1 promoter as a genetic switch for the regulatable and physiological expression of a plasma protein in transgenic mice.

Transgenic and gene knockout techniques allow for in vivo study of the consequences of adding or subtracting specific genes. However, in some instances, such as the study of lethal mutations or of the physiological consequences of changing gene expression, turning on and off an introduced gene at will would be advantageous. We have used cytochrome p450 1A1 promoter to drive expression of the human apolipoprotein E (apoE) gene in transgenic mice. In six independent lines, robust expression of the transgene depended upon injection of the inducer beta-naphthoflavone, whereas the seventh line had high basal expression that was augmented further by the inducer. The low level of basal expression in an inducer-dependent line was confirmed upon breeding the transgene onto the hypercholesterolemic apoE-deficient background. In the basal state transgene expression was physiologically insignificant, as these mice were as hypercholesterolemic as their nontransgenic apoE-deficient littermates. When injected with the inducer, plasma cholesterol levels of the transgenic mice decreased dramatically as apoE expression was induced to yield greater than physiological levels in plasma. The inducer could pass transplacentally from an injected mother to her fetuses with concomitant induction of fetal transgene mRNA. Inducer could also pass via breast milk from an injected mother to her suckling neonatal pups, giving rise to the induction of human apoE in neonate plasma. These finding suggest a strategy to temporarily ameliorate genetic deficiencies that would otherwise lead to fetal or neonatal lethality.

Decreased atherosclerosis in mice deficient in both macrophage colony-stimulating factor (op) and apolipoprotein E.

To develop a murine model system to test the role of monocyte-derived macrophage in atherosclerosis, the osteopetrotic (op) mutation in the macrophage colony-stimulating factor gene was bred onto the apolipoprotein E (apoE)-deficient background. The doubly mutant (op/apoE-deficient) mice fed a low-fat chow diet had significantly smaller proximal aortic lesions at an earlier stage of progression than their apoE-deficient control littermates. These lesions in the doubly mutant mice were composed of macrophage foam cells. The op/apoE-deficient mice also had decreased body weights, decreased blood monocyte differentials, and increased mean cholesterol levels of approximately 1300 mg/dl. Statistical analysis determined that atherosclerosis lesion area was significantly affected by the op genotype and gender. The confounding variables of body weight, plasma cholesterol, and monocyte differential, which were all affected by op genotype, had no significant additional effect on lesion area once they were adjusted for the effects of op genotype and gender. Unexpectedly, there was a significant inverse correlation between plasma cholesterol and lesion area, implying that each may be the result of a common effect of macrophage colony-stimulating factor levels. The data support the hypothesis that macrophage colony-stimulating factor and its effects on macrophage development and function play a key role in atherogenesis.