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Biomedical subjects

M Aikawa

Publications and source records attributed to M Aikawa.

At least 55 records · Page 3Linked to original sources
PubMed1999

Plasmodium falciparum: detection of a novel asparagine-rich protein on the surface of sporozoite.

We had previously cloned and characterized a gene for a novel asparagine-rich protein from P. falciparum (PfARP), a target of natural human immune response. The antibodies to PfARP were localized to the surface of parasitized red blood cells and reacted with intracellular components in all erythrocytic asexual and sexual stages of the parasite. We here describe reactivity of antibodies against this novel PfARP on the surface of mosquito stage sporozoite of P. falciparum by indirect immunofluorescence assay and immunoelectron microscopy, the latter revealing a highly periodic punctate pattern of distribution of PfARP on the surface of sporozoite. These results suggest a possibility that PfARP might represent yet another sporozoite surface protein.

Amino Acid Sequence↗
PubMed1999

Cloning and characterization of a new asparagine-rich protein in Plasmodium falciparum.

A cDNA clone that encodes a Plasmodium falciparum asparagine (N)-rich protein (PfARP) was isolated through immunoscreening of an expression library. A 9.4 kb PfARP transcript was identified by Northern blot hybridization and the gene was localized on chromosome 1. The complete coding sequence (6666 bp) revealed a protein that contains clustered as well as randomly distributed N residues (24.3%), seven copies of a repeat sequence [DNT(D/N)(K/N)(V/L/M)] and multiple copies of tripeptide repeats within a 101 amino acid region containing 89 D/E residues. The PfARP was immunogenic in inbred and outbred mice and endemic sera revealed the presence of low-titer antibodies against PfARP. Anti-PfARP sera showed cytoplasmic and surface localization of apparently cross-reactive malarial antigens in different life-cycle stages (ring, trophozoite, schizont, and gametocytes). Although the biological function(s) of PfARP are not known, the observation that it is present in multiple parasite stages and that it is a target of natural immune response warrants further study of PfARP as an immune target.

Adolescent↗
PubMed1999

The Plasmodium falciparum translationally controlled tumor protein: subcellular localization and calcium binding.

Artemisinin derivatives are endoperoxide antimalarials widely used to treat falciparum malaria in areas where drug resistance is common. In Plasmodium falciparum-infected erythrocytes, radiolabeled artemisinin derivatives have been shown to react with malarial proteins, one of which is the Translationally Controlled Tumor Protein (TCTP). The P. falciparum TCTP was found by immunofluorescence to be located in both the cytoplasm and food vacuoles. Immunoelectron microscopy shows that it is present in the parasite cytoplasm as well as in its food vacuolar and limiting membranes. Like other TCTPs, the P. falciparum protein binds to calcium. Further studies on the physiological role of TCTP may aid in understanding the mechanism of action of endoperoxide antimalarials.

Animals↗
PubMed1999

Echocardiography-derived left ventricular end-systolic regional wall stress and matrix remodeling after experimental myocardial infarction.

OBJECTIVES: We tested the hypothesis that regional end-systolic left ventricular (ESLV) wall stress is associated with extracellular matrix remodeling activity after myocardial infarction (MI). BACKGROUND: Increased left ventricular (LV) wall stress is a stimulus for LV enlargement, and echocardiography can be used to estimate regional wall stress. A powerful validation of a noninvasive method of estimating wall stress would be predicting cellular responses after a MI. METHODS: Echocardiographic images were obtained in rats 1, 7, 14 or 21 days after coronary ligation (n = 11) or sham surgery (n = 5). End-systolic left ventricular wall stress was calculated by finite element analysis in three regions (infarcted, noninfarcted and border) from short-axis images. Matrix metalloproteinase-9 (MMP-9) and macrophage density were determined by immunohistochemistry, and positive cells were counted in high power fields (hpf). RESULTS: Average ESLV wall stress was higher in rats with MI when compared to shams irrespective of time point (p < 0.01), and ESLV wall stress in the infarcted regions increased with time (25.1 +/- 5.9 vs. 69.9 +/- 4.4 kdyn/cm2, day 1 vs. 21; p < 0.01). Matrix metalloproteinase-9 expression was higher in infarcted and border regions when compared to noninfarcted regions (22.1 vs. 25.7 vs. 0.10 cells/hpf, respectively; p < 0.01). Over all regions, ESLV wall stress was associated with MMP-9 (r = 0.76; p < 0.001), macrophage density (r = 0.72; p < 0.001) and collagen content (r = 0.67; p < 0.001). End-systolic left ventricular wall stress was significantly higher when MMP-9 positive cell density was greater than 10 cells/hpf (45+/-20 vs. 14+/-10 kdyn/cm2; p < 0.001). CONCLUSIONS: Regional increases in ESLV wall stress determined by echocardiography-based structural analysis are associated with extracellular matrix degradation activity.

Animals↗
PubMed1999

Disruption of the Pfg27 locus by homologous recombination leads to loss of the sexual phenotype in P. falciparum.

Transmission of malaria depends upon the differentiation and development of the sexual stages of the parasite. In Plasmodium falciparum, it is a complex, multistage process, involving the expression of a large number of sexual stage-specific proteins. Pfg27 is one such protein, abundantly expressed at the onset of gametocytogenesis. We report successful disruption of the Pfg27 locus using homologous recombination and show that it is essential for the maintenance of the sexual phenotype. Transfectants lacking Pfg27 abort early in sexual development, resulting in vacuolated, highly disarranged, and disintegrating parasites. This suggests a critical role for Pfg27 in the sexual development of the parasite.

Animals↗
PubMed1999

Influence of hemoglobin E trait on the severity of Falciparum malaria.

To determine if hemoglobin E trait influences the course of acute malaria, adults hospitalized for the treatment of symptomatic infection with Plasmodium falciparum were studied retrospectively. Forty-two patients with hemoglobin E trait were compared with 175 reference subjects who did not have hemoglobin E, beta-thalassemia, glucose-6-phosphate dehydrogenase deficiency, or alpha-thalassemia. One patient (2.4%) with hemoglobin E trait had a severe complication of malaria by World Health Organization criteria (cerebral malaria), while 32 subjects in the reference group (18.3%) had one or more severe complications: cerebral malaria (n=18), hyperparasitemia (n=16), renal failure (n=10), and severe anemia (n=1) (P=.044 after adjustment for ethnic categories). The estimated odds of severe complications in the reference subjects were 6.9 times the odds in patients with hemoglobin E trait (95% confidence interval, 1.2-146. 4). These results suggest that hemoglobin E trait may ameliorate the course of acute falciparum malaria.

Acute Disease↗
PubMed1999

Electrophysiologic and blood-flow responses in the endocardium and epicardium to disopyramide and MS-551 during myocardial ischemia in the dog.

The aim of this study was to determine whether a quantitative relation exists between changes in regional myocardial blood flow (RMBF) and those in electrophysiologic determinants recorded via left ventricular endocardial and epicardial bipolar electrograms after administration of disopyramide (DP) and a class III antiarrhythmic drug, MS-551 (MS), during myocardial ischemia in the dog. Dogs were given DP (1 mg/kg, i.v., n = 14), MS (1 mg/kg, i.v., and 0.1 mg/kg/min, d.i.v., n = 13), or saline (n = 12). The effective refractory period (ERP) was determined by an S1-S2 extrastimulus method, and RMBF by a nonradioactive microsphere technique. The duration of regional electrograms (DRE) was measured as an indicator of conduction time in the myocardium. DP blunted ischemia-induced shortening of ERPs and lengthened DREs at the endocardial and epicardial sites, with a greater effect seen epicardially (p < 0.01 each). DP reduced RMBF, especially at the endocardial surfaces of the ischemic zone (p < 0.05). MS prolonged ERPs at the endocardial and epicardial sites in the ischemic and normal zones (p < 0.05-0.01), but there were no significant differences between the two sites. MS prolonged DREs (p < 0.05), but the magnitude of the prolongation of the DREs was similar to the values in the control group. MS had no effects on RMBF. DP treatment prolonged DREs at both sites in the ischemic zone more markedly than MS or saline treatment (p < 0.01 each). DP reduced RMBF at the endocardial site of the ischemic zone more markedly than MS or saline (p < 0.05 in each). Accordingly, MS prolonged ERPs, but did not increase disparities between endocardial and epicardial sites in the ischemic myocardium, whereas DP had a greater ERP-prolonging effect at the epicardial site than at the endocardial site. DP reduced endocardial RMBF more markedly than epicardial RMBF. These observations suggest that differences in ERPs between endocardial and epicardial ischemic myocardium caused by DP treatment are not due to the difference in RMBF reduction between the two tissue layers, and that DP and MS do not affect the same population of ion channel(s) when ERPs are prolonged.

Animals↗
PubMed1999

MRI of rabbit atherosclerosis in response to dietary cholesterol lowering.

Direct imaging of the atherosclerotic plaque, rather than the angiographic lumen, may provide greater insight into the response of atherosclerosis to cholesterol-lowering therapy. Aortic plaque was studied in vivo by MRI in rabbits undergoing dietary cholesterol intervention. Thirty-one rabbits underwent aortic balloon injury and high-cholesterol diet for 4 months and then were assigned to low-cholesterol versus continued high-cholesterol diet for up to an additional 16 months. High-resolution (310 micrometer) fast spin-echo MRI of the abdominal aorta was performed at 4, 12, and 20 months and compared with histology. MRI demonstrated a significant reduction in % area stenosis in rabbits placed on low-cholesterol diet (44.6+/-2. 1% at 20 months versus 55.8+/-1.5% at 4 months, P=0.0002). In contrast, % area stenosis increased in rabbits maintained on high-cholesterol diet (69.8+/-3.8% at 20 months versus 55.8+/-1.5% at 4 months, P=0.001). Similarly, plaque thickness decreased significantly in the low-cholesterol group (0.60+/-0.05 mm at 20 months versus 0.85+/-0.06 mm at 4 months, P=0.006), with a trend toward increase in the high-cholesterol group (1.02+/-0.08 mm at 20 months versus 0.85+/-0.06 mm at 4 months, P=0.1). Thus, in rabbits undergoing dietary cholesterol lowering, MRI detected regression of aortic atherosclerotic plaque in vivo. Plaque progression was seen with maintenance of high-cholesterol diet. MRI is a promising noninvasive technology for directly imaging atherosclerosis and its response to therapeutic interventions.

Animals↗
PubMed1999

A secreted frizzled related protein, FrzA, selectively associates with Wnt-1 protein and regulates wnt-1 signaling.

The Wnt gene family encodes proteins that serve key roles in differentiation and development. Wnt proteins interact with seven transmembrane receptors of the Frizzled family and activate a signaling pathway leading to the nucleus. A primary biochemical effect of Wnt-1 signaling is the stabilization of cytoplasmic (beta)-catenin which, in association with transcription factors of the Lef/tcf family, regulates gene expression. The recent identification of a new class of secreted proteins with similarity to the extracellular, ligand-binding domain of Frizzled proteins, soluble Frizzled related proteins (sFRP), suggested that additional mechanisms could regulate Wnt signaling. Here we demonstrate that FrzA, a sFRP that is highly expressed in vascular endothelium and a variety of epithelium, specifically binds to Wnt-1 protein, but not Wnt-5a protein, and modulates Wnt-1 signaling. FrzA associated with Wnt-1 either when expressed in the same cell or when soluble FrzA was incubated with Wnt-1-expressing cells. FrzA efficiently inhibited the Wnt-1 mediated increase in cytoplasmic (beta)-catenin levels as well as the Wnt-1 induction of transcription from a Lef/tcf reporter gene. The effects of FrzA on (beta)-catenin levels could be demonstrated when co-expressed with Wnt-1 or when individual cells expressing FrzA and Wnt-1 were co-cultured. These data demonstrate the existence of a negative regulatory mechanism mediated by the selective binding of FrzA to Wnt-1 protein.

Blotting, Western↗
PubMed1999

Embryonic smooth muscle myosin heavy chain SMemb is expressed in pressure-overloaded cardiac fibroblasts.

Left ventricular hypertrophy (LVH) is a secondary adaptation to increased external load. Various qualitative and quantitative changes in myocytes and extracellular components occur during the development of LVH. It has recently been demonstrated that alpha-smooth muscle actin (alpha-SMA)-expressing myofibroblasts appear in the interstitium of the heart subjected to increased workload suggesting that cardiac fibroblasts as well as myocytes alter their phenotype in response to pressure overload. In the present study, to explore the load-induced response and phenotypic modulation of cardiac fibroblasts, the localization of embryonic smooth muscle myosin heavy chain (SMemb) and alpha-SMA in thoracic aorta-constricted rat hearts was investigated by immunohistochemistry, and the morphology of the SMemb-expressing cells was examined by electron microscopy. In addition, to clarify the mechanisms by which SMemb is induced in pressure-overloaded hearts, mRNA expression of SMemb in aorta-constricted rat hearts and in transforming growth factor-beta1 (TGF-beta1)-treated or mechanically-stretched cultured cardiac fibroblasts was investigated. Enhanced staining of SMemb and alpha-SMA was detected in the interstitial spindle-shaped cells in the fibrotic lesions of the pressure-overloaded left ventricles by immunohistochemistry. These cells were demonstrated by electron microscopy to have features specific for activated fibroblasts such as serrated nuclei or prominent rough endoplasmic reticulum. These cells also had characteristic features of myofibroblasts, i.e. irregularly arranged actin filaments and scattered dense bodies. Northern blot analysis revealed increased mRNA levels of SMemb both in aorta-constricted rat hearts and in cultured cardiac fibroblasts stimulated by TGF-beta1 or by mechanical stretch. These results suggest that SMemb may be a molecular marker both for the detection of activated cardiac fibroblasts that may play important roles in the remodeling of pressure-overloaded cardiac interstitium, and for the identification of the regu latory mechanisms that control the phenotypic modulation of cardiac fibroblasts in response to pressure overload.

Actins↗
PubMed1998

Lipid lowering promotes accumulation of mature smooth muscle cells expressing smooth muscle myosin heavy chain isoforms in rabbit atheroma.

Smooth muscle cells (SMCs) in the atherosclerotic intima characteristically differ from those in the arterial media, for example, by reduced expression of SMC differentiation/maturation markers such as smooth muscle myosin heavy chain isoforms (SM1 and SM2). This study tested the hypothesis that lipid lowering promotes maturation of intimal SMCs in 33 rabbits subjected to balloon injury and cholesterol feeding (0.3%) for 4 months (Baseline group, n=15); some of which then were switched to a low-cholesterol diet for 8 months (Low group at 8 months, n=3) or 16 months (Low group at 16 months, n=10). The remaining rabbits continued to consume a high-cholesterol diet for 16 months (High group, n=5). We monitored SMC phenotype by expression of immunoreactive alpha-smooth muscle actin, SM1, and SM2. alpha-Actin is an early marker, and SM1 and SM2 are late markers for SMC differentiation/maturation. Only fully differentiated or mature SMCs express SM2. Data are reported as the percentage of the alpha-actin-positive intimal area occupied by smooth muscle myosin-positive SMCs determined by color image analysis of immunostained sections. Levels of SM1 and SM2, highly expressed by SMCs in the normal aortic media (n=5) decreased in the aortic intima of the Baseline and High groups, indicating a less mature phenotype. In contrast, SM1 and SM2 increased in the Low (16 months) group, indicating that intimal SMCs exhibit a more mature phenotype after lipid lowering. Electron microscopy also showed the presence of mature intimal SMCs with abundant myofilaments. Furthermore, lipid lowering reduced levels of platelet-derived growth factor-B in the arterial intima, a factor known to suppress smooth muscle myosin expression. These data demonstrate that lipid lowering favors accumulation of mature SMCs in the atherosclerotic intima in association with reduced levels of platelet-derived growth factor-B expression. Intimal SMCs in the Low group also displayed reduced expression of matrix metalloproteinases-3 and -9 compared with the Baseline and High groups. These findings shed new light on the effects of lipid lowering at the level of the vascular wall, which may influence the biology of the atheroma.

Actin Cytoskeleton↗
PubMed1998

Immunocytochemical colocalization of specific immunoglobulin A with sendai virus protein in infected polarized epithelium.

Immunoglobulin (Ig)A provides the initial immune barrier to viruses at mucosal surfaces. Specific IgA interrupts viral replication in polarized epithelium during receptor-mediated transport, probably by binding to newly synthesized viral proteins. Here, we demonstrate by immunoelectron microscopy that specific IgA monoclonal antibodies (mAbs) accumulate within Sendai virus-infected polarized cell monolayers and colocalize with the hemagglutinin- neuraminidase (HN) viral protein in a novel intracellular structure. Neither IgG specific for HN nor irrelevant IgA mAbs colocalize with viral protein. Treatment of cultures with viral-specific IgA but not with viral-specific IgG or irrelevant IgA decreases viral titers. These observations provide definitive ultrastructural evidence of a subcellular compartment in which specific IgA and viral envelope proteins interact, further strengthening our hypothesis of intracellular neutralization of virus by specific IgA antibodies. Our results have important implications for intracellular protein trafficking, viral replication, and viral vaccine development.

Animals↗
PubMed1998

A subtilisin-like protein in secretory organelles of Plasmodium falciparum merozoites.

In the vertebrate host, the malaria parasite invades and replicates asexually within circulating erythrocytes. Parasite proteolytic enzymes play an essential but poorly understood role in erythrocyte invasion. We have identified a Plasmodium falciparum gene, denoted pfsub-1, encoding a member of the subtilisin-like serine protease family (subtilases). The pfsub-1 gene is expressed in asexual blood stages of P. falciparum, and the primary gene product (PfSUB-1) undergoes post-translational processing during secretory transport in a manner consistent with its being converted to a mature, enzymatically active form, as documented for other subtilases. In the invasive merozoite, the putative mature protease (p47) is concentrated in dense granules, which are secretory organelles located toward the apical end of the merozoite. At some point following merozoite release and completion of erythrocyte invasion, p47 is secreted from the parasite in a truncated, soluble form. The subcellular location and timing of secretion of p47 suggest that it is likely to play a role in erythrocyte invasion. PfSUB-1 is a new potential target for antimalarial drug development.

Amino Acid Sequence↗
PubMed1998

WNT-1 and HGF regulate GSK3 beta activity and beta-catenin signaling in mammary epithelial cells.

Wnt-1, a secreted glycoprotein, participates in development of the nervous system and contributes to mammary oncogenesis when overexpressed. We show that GSK3 activity is decreased in mouse mammary cells transformed by Wnt-1. These cells also exhibit a substantial Wnt-1 dependent increase in the uncomplexed population of beta-catenin. Wnt-1 signaling does not change the steady state level of either GSK3 alpha or GSK3 beta but instead leads to an increased association between GSK3 beta and beta-catenin. HGF/SF treatment of mouse mammary cells also leads to a transient decrease in GSK3 activity and a parallel, selective increase in the uncomplexed pool of beta-catenin. Both Wnt-1 and HGF/SF lead to nuclear accumulation of beta-catenin and activation of a LEF/Tcf responsive reporter gene. This study defines a pivotal signal transduction pathway, activated by both Wnt-1 and HGF/SF, leading to decreased GSK3 beta activity and consequently an increase in the free pool and nuclear accumulation of beta-catenin and changes in gene expression.

Amino Acid Sequence↗
PubMed1998

Lipid lowering by diet reduces matrix metalloproteinase activity and increases collagen content of rabbit atheroma: a potential mechanism of lesion stabilization.

BACKGROUND: Proteolytic enzyme activity in lipid-rich atheroma may promote plaque rupture and precipitate acute coronary syndromes. This study tested the hypothesis that lipid lowering stabilizes plaques by reducing proteolytic activity. METHODS AND RESULTS: We produced experimental atheroma in 33 rabbits by balloon injury and an atherogenic diet (0.3% cholesterol and 4.7% coconut oil) for 4 months. At that time, 15 rabbits were killed (baseline group). The remaining animals were divided into two groups: a hyperlipemic group continued to consume a cholesterol-enriched diet (0.05% to 0.2%) for 16 more months (n=5) and a lipid-lowering group consumed a purified chow diet with no added cholesterol or fat for 8 (n=3) or 16 months (n=10). Macrophage accumulation and interstitial collagenase (matrix metalloproteinase-1, MMP-1) expression in the lesion were measured by quantitative image analysis of standardized sections of immunostained aortas. Baseline lesions expressed high levels of MMP-1 and contained many macrophages. These features of plaque instability persisted in the hyperlipemic group. However, the lipid-lowering group showed progressive reduction in both macrophage content and MMP- 1 immunoreactivity with time. Aortic rings of the baseline and hyperlipemic groups elaborated gelatinolytic, caseinolytic, and elastinolytic activity attributable to MMP-2, MMP-3, or MMP-9, monitored by SDS-PAGE zymography. Proteolytic activity decreased markedly in the lipid-lowering group. Aortic content of interstitial collagen, determined by sirius red staining, increased in the lipid-lowering group compared with the baseline or continued hyperlipemic groups, indicating that lipid lowering reinforced the fibrous skeleton of the atheroma. CONCLUSIONS: These results establish a mechanism by which lipid lowering may stabilize vulnerable plaques by reduced expression and activity of enzymes that degrade the arterial extracellular matrix and render atheroma less susceptible to disruption and thrombosis by favoring collagen accumulation in the fibrous cap.

Animals↗
PubMed1998

Age-related degeneration of the serotoninergic fibers in the zitter rat brain.

The serotonin neuron system was studied using immunohistochemical and neurochemical techniques in zitter mutant rats aged 1-14 months, which are characterized by abnormal metabolism of superoxides. The morphology of the serotoninergic neuron system and the serotonin level in the zitter rat were compared to those of age-matched Sprague-Dawley (SD) rats. Up to age 4 month, the density and distribution of serotoninergic fibers in the zitter rat brain were similar to those of control rats. However, several serotoninergic fibers with abnormal morphology, characterized by swollen varicosities, were observed in the cerebral cortex and caudate putamen of 6-month-old zitter rats. The density and distribution of these fibers in other regions of the brain were similar to those of control rats. The abnormal serotoninergic fibers increased in number and extended into other regions of the brain such as the thalamus, hippocampus, and vestibular nucleus. On the other hand, the density of normal serotoninergic fibers decreased throughout the brain of the 14-month-old zitter rat. Abnormal serotoninergic fibers have also been reported in the brain of normal older (24 months) SD rats. Neurochemical analysis revealed lower levels of serotonin, and 5-hydroxyindoleacetic acid, in all cortical areas (prefrontal, parietal, and occipital cortices), the caudate putamen, and the hippocampus of 12-month-old zitter rats. Levels differed significantly in the parietal cortex and hippocampus between the zitter and SD rats. Based on the morphological and neurochemical similarities, the present results suggest that age-related degeneration of serotoninergic fibers occurs in the zitter rat brain. Furthermore, degeneration of serotoninergic fibers appears to be induced by superoxide species. Thus, the zitter rat may provide a good model for studying the neurotoxic effects of superoxide species on the serotoninergic neuron system.

Aging↗