Biomedical subjects

J Saarinen

Publications and source records attributed to J Saarinen.

At least 37 records · Page 2Linked to original sources

PubMed1999

Activation of interstitial collagenase, MMP-1, by Staphylococcus aureus cells having surface-bound plasmin: a novel role of plasminogen receptors of bacteria.

Plasmin, the enzymatically active form of plasminogen, can activate several matrix metalloproteinases (MMPs). In this study, we investigated the activation of MMP-1, one of the major interstitial collagenases, by plasmin which was generated on the surface of Staphylococcus aureus cells. Plasmin bound to plasminogen receptors on S. aureus degraded the major (125)I-labeled 55-kDa proMMP-1 into the 42-kDa form corresponding to the size of active MMP-1. MMP-1 formed by S. aureus-bound plasmin was also enzymatically active as judged by digestion of the synthetic collagenase substrate, DNP-Pro-Leu-Gly-Leu-Trp-Ala-D-Arg-NH(2). The finding that, in MMP-1 molecules generated either by soluble plasmin or by S. aureus-bound plasmin, the amino-terminal amino acid sequences were identical indicated that the activation mechanisms of the two plasmin forms do not differ from each other. The present observations emphasise and broaden the physiological importance of bacterial plasminogen receptors. In addition to direct proteolytic effects on components of the extracellular matrix, receptor-bound plasmin is also capable of initiating an MMP-1-dependent matrix-degrading enzymatic cascade.

Bacterial Proteins↗

PubMed1999

A novel function for a ubiquitous plant enzyme pectin methylesterase: the host-cell receptor for the tobacco mosaic virus movement protein.

Plant virus-encoded movement proteins promote viral spread between plant cells via plasmodesmata. The movement is assumed to require a plasmodesmata targeting signal to interact with still unidentified host factors presumably located on plasmodesmata and cell walls. The present work indicates that a ubiquitous cell wall-associated plant enzyme pectin methylesterase of Nicotiana tabacum L. specifically binds to the movement protein encoded by tobacco mosaic virus. We also show that pectin methylesterase is an RNA binding protein. These data suggest that pectin methylesterase is a host cell receptor involved in cell-to-cell movement of tobacco mosaic virus.

Base Sequence↗

PubMed1999

Matrix metalloproteinases-3, -7, and -12, but not -9, reduce high density lipoprotein-induced cholesterol efflux from human macrophage foam cells by truncation of the carboxyl terminus of apolipoprotein A-I. Parallel losses of pre-beta particles and the high affinity component of efflux.

Matrix metalloproteinases (MMPs) have been suggested to function in remodeling of the arterial wall, but no information is available on their possible role in early atherogenesis, when cholesterol accumulates in the cells of the arterial intima, forming foam cells. Here, we incubated the major component responsible for efflux of cholesterol from foam cells, high density lipoprotein 3 (HDL(3)), with MMP-1, -3, -7, -9, or -12 at 37 degrees C before adding it to cholesterol-loaded human monocyte-derived macrophages. After incubation with MMP-3, -7, or -12, the ability of HDL(3) to induce the high affinity component of cholesterol efflux from the macrophage foam cells was strongly reduced, whereas preincubation with MMP-1 reduced cholesterol efflux only slightly and preincubation with MMP-9 had no effect. These differential effects of the various MMPs were reflected in their differential abilities to degrade the small pre-beta migrating particles present in the HDL(3) fraction. NH(2)-terminal sequence and mass spectrometric analyses of the apolipoprotein (apo) A-I fragments generated by MMPs revealed that those MMPs that strongly reduced cholesterol efflux (MMPs-3, -7, and -12) cleaved the COOH-terminal region of apoA-I and produced a major fragment of about 22 kDa, whereas MMPs-1 and -9, which had little and no effect on cholesterol efflux, degraded apoA-I only slightly and not at all, respectively. These results show, for the first time, that some members of the MMP family can degrade the apoA-I of HDL(3), so blocking cholesterol efflux from macrophage foam cells. This expansion of the substrate repertoire of MMPs to include apoA suggests that these proteinases are directly involved in the accumulation of cholesterol in atherosclerotic lesions.

Apolipoprotein A-I↗

PubMed1999

Kallidin- and bradykinin-degrading pathways in human heart: degradation of kallidin by aminopeptidase M-like activity and bradykinin by neutral endopeptidase.

BACKGROUND: Since kinins kallidin (KD) and bradykinin (BK) appear to have cardioprotective effects ranging from improved hemodynamics to antiproliferative effects, inhibition of kinin-degrading enzymes should potentiate such effects. Indeed, it is believed that this mechanism is partly responsible for the beneficial effects of angiotensin-converting enzyme (ACE) inhibitors. In the heart, enzymes other than ACE may contribute to local degradation of kinins. The purpose of this study was to investigate which enzymes are responsible for the degradation of KD and BK in human heart tissue. METHODS AND RESULTS: Cardiac membranes were prepared from the left ventricles of normal (n=5) and failing (n=10) hearts. The patients had end-stage congestive heart failure as the result of coronary heart disease or idiopathic dilated cardiomyopathy. Heart tissue was incubated with KD or BK in the presence or absence of enzyme inhibitors. We found no difference in the enzymes responsible for kinin metabolism or their activities between normal and failing hearts. Thus KD was mostly converted into BK by the aminopeptidase M-like activity. When BK was used as substrate, it was converted into an inactive metabolite BK-(1-7) mostly (80% to 90%) by the neutral endopeptidase (NEP) activity, with ACE unexpectedly playing only a minor role. The low enzymatic activity of ACE in the cardiac membranes, compared with that of NEP, was not due to chronic ACE inhibitor therapy, because the cardiac ACE activities of patients, whether receiving ACE inhibitors or not, and of normal subjects were all equal. CONCLUSIONS: The present in vitro study shows that in human cardiac membranes, the most critical step in kinin metabolism, that is, inactivation of BK, appears to be mediated mostly by NEP. This observation suggests a role for NEP in the local control of BK concentration in heart tissue. Thus inhibition of cardiac NEP activity could be cardioprotective by elevating the local concentration of BK in the heart.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1999

The incidence and cardiovascular risk indicators of deep venous thrombosis.

BACKGROUND: To estimate the incidence and associated risk indicators of deep venous thrombosis (DVT) in the lower extremities. PATIENTS AND METHODS: A population-based 5-year follow-up study with self-administered questionnaire. The study included 5568 persons at the beginning, with a follow-up of 17,005 person-years. A questionnaire was sent to all residents in the city of Tampere, Finland, born in 1929, 1939 and 1949. In the first survey the number of participants was 5568 and in the second questionnaire 4903. The participation rates were 83% and 88%. RESULTS: The incidence of DVT was 140 per 100,000 person-years. The life-time prevalence of DVT was 3.1%. In a univariate analysis, the appearance of a new DVT during the follow-up time (incidence) was statistically significantly associated with pre-existing varicose veins, sex-steroid therapy, heart failure and arterial insufficiency in the lower limbs. In multivariate analysis varicose veins, arterial insufficiency in the lower limbs and sex-steroid therapy remained as significant risk factors associated with DVT. CONCLUSIONS: The study confirms that the incidence of DVT in Finland is close to the estimates in other Western populations. Pre-existing varicose veins, sex-steroid therapy and arterial insufficiency in the lower limbs are independent risk factors for DVT in our population-based study.

Adult↗

PubMed1999

N-glycan structures of matrix metalloproteinase-1 derived from human fibroblasts and from HT-1080 fibrosarcoma cells.

Matrix metalloproteinase-1 (MMP-1) is a collagenolytic metalloproteinase capable of cleaving native triple-helical forms of several collagen subtypes, as well as a number of non-collagenous substrates. The role of MMP-1 in various diseases affecting the connective tissue is well characterized. MMP-1 is secreted as both glycosylated and unglycosylated species, and the two forms have been shown to be identical with respect to substrate specificity, specific activity and inhibitory profile. No function for the glycan moiety of the enzyme has been ascribed to date. In the present study, we report on the detailed characterization of MMP-1-derived oligosaccharides. Using strategies based on sequential exoglycosidase digestion combined with matrix-assisted laser desorption ionization-time of flight MS and electrospray tandem MS, we have characterized the N-glycan structures of MMP-1, derived from human dermal fibroblasts and from the HT-1080 fibrosarcoma cell line. MMP-1 derived from fibroblasts was found to carry mainly alpha 2,3-sialylated complex-type diantennary glycans. On the other hand, HT-1080 cells produce MMP-1 that has a heterogeneous glycosylation pattern, comprising diantennary glycans carrying Lewis X, LacdiNAc, sialylated LacdiNAc and GalNAc beta 1,4 (Fuc alpha 1,3)GlcNAc (LacdiNAc analogue of Lewis X) as terminal elements. We also show that, of the two potential glycosylation sites in the MMP-1 sequence, only Asn120 is used.

Carbohydrate Sequence↗

PubMed1999

The effect of contour closure on shape perception.

We studied psychophysically whether 'contour closure' enhances the accuracy of shape perception. Stimulus configurations (presented on a blank background) always consisted of identical pattern elements, but the positions of the local elements were varied: the global contour shape either contained closure or not. In the first two stimulus conditions (Closure), the oriented pattern elements (Gabor patches) formed a 'closed' rectangular shape composed of either four long lines or four corners. In the third condition (No closure), the global shape was composed of the four corners, but they were outward oriented, and hence they did not form the outline of a closed contour. We measured the precision of shape perception using a discrimination task in which observers judged the aspect ratio of the outline shape i.e. whether the rectangular shape was tall or wide. We found that: (i) shape discrimination was better (more precise) for Closed contours than for Non-closed contours, i.e. the aspect ratio discrimination thresholds were lower for the Closed than Non-closed configurations. The improved performance could not be explained by differences in visibility of the local elements in the two conditions. (ii) For closed contours, shape discrimination was more precise when the local elements were aligned with the global shape, than when the local elements were orthogonal to it.

Form Perception↗

PubMed1998

Cortactin-Src kinase signaling pathway is involved in N-syndecan-dependent neurite outgrowth.

N-syndecan (syndecan-3) was previously isolated as a cell surface receptor for heparin-binding growth-associated molecule (HB-GAM) and suggested to mediate the neurite growth-promoting signal from cell matrix-bound HB-GAM to the cytoskeleton of neurites. However, it is unclear whether N-syndecan would possess independent signaling capacity in neurite growth or in related cell differentiation phenomena. In the present study, we have transfected N18 neuroblastoma cells with a rat N-syndecan cDNA and show that N-syndecan transfection clearly enhances HB-GAM-dependent neurite growth and that the transfected N-syndecan distributes to the growth cones and the filopodia of the neurites. The N-syndecan-dependent neurite outgrowth is inhibited by the tyrosine kinase inhibitors herbimycin A and PP1. Biochemical studies show that a kinase activity, together with its substrate(s), binds specifically to the cytosolic moiety of N-syndecan immobilized to an affinity column. Western blotting reveals both c-Src and Fyn in the active fractions. In addition, cortactin, tubulin, and a 30-kDa protein are identified in the kinase-active fractions that bind to the cytosolic moiety of N-syndecan. Ligation of N-syndecan in the transfected cells by HB-GAM increases phosphorylation of c-Src and cortactin. We suggest that N-syndecan binds a protein complex containing Src family tyrosine kinases and their substrates and that N-syndecan acts as a neurite outgrowth receptor via the Src kinase-cortactin pathway.

Amino Acid Sequence↗

PubMed1998

Human cortical-evoked fields during detection, localisation, and identification of 'pop-out' targets.

We investigated human cortical activity during four 'effortless-pop-out' visual search tasks with the use of magnetoencephalography. The search display, which was identical across all the tasks, consisted of vertical line segments, one of which was rotated abruptly 45 degrees clockwise or counterclockwise. In the passive-viewing task the observers gave no response to the search display. In the target-detection task they responded to the onset of the target motion irrespective of its location and direction. In the target-localisation task the observers reported whether the line rotation appeared above or below the fixation point while ignoring the direction of the rotation. In contrast, in the target-identification task they indicated the direction of the line rotation, and the location of the rotation in the array was irrelevant. Cortical activity was recorded with a whole-scalp magnetometer while the observers were performing each task. In addition to the expected activation of the occipital and somatomotor cortical regions, two other active cortical areas were consistently identified in both hemispheres: one in the occipito-temporal area, probably corresponding to the motion-specific V5 complex, and another in the parieto-temporal region. The activation of the right occipito-temporal source depended on the task. The maximum amplitude was smallest for the passive viewing, increased for the detection task, and was largest for the localisation and identification.

Adult↗

PubMed1998

Angiotensin II formation in the human heart: an ACE or non-ACE-mediated pathway?

The enzymatic pathways for local angiotensin II (Ang II) formation in the heart have been studied both in vivo and in vitro, but the results of these experiments have been discrepant. Thus, the experiments in vivo with intact hearts, both in humans and in animal models, have unequivocally demonstrated that the major Ang II-forming enzyme is angiotensin-converting enzyme (ACE). In contrast, the experiments in vitro with both human or animal heart preparations, have unequivocally demonstrated that the major Ang II-forming enzyme is chymase, a mast cell-derived chymotrypsin-like serine protease. The in vitro approach, however, seems to involve several pitfalls, which tend to overestimate the contribution of chymase as compared to that of ACE. It seems evident that in vivo the chymase-mediated Ang II formation is subjected to local inhibition, a fact that has been overlooked in most of the studies performed in vitro. Accordingly, human chymase, even in its natural form as a protease-proteoglycan complex, is highly sensitive to the protease inhibitors naturally present in the interstitial fluid (IF). We found that if human heart tissue preparations are incubated in vitro in the presence of IF, the chymase-mediated Ang II formation is almost totally suppressed. As the heart interstitium is constantly bathed by IF with its protease inhibitors in concentrations sufficiently high to ensure efficient inhibition of this enzyme, the protease inhibitor-mediated suppression of chymase should also be effective in vivo. Thus, the local production of Ang II in the human heart appears to be regulated by ACE rather than by chymase.

Angiotensin II↗

PubMed1997

Purified HrpA of Pseudomonas syringae pv. tomato DC3000 reassembles into pili.

Pseudomonas syringae pv. tomato DC3000 produces Hrp pili under inducing in vitro conditions. A preparation of partially purified extracellular filaments contains HrpA, flagellin and some minor contaminants. HrpA was separated from the major contaminant, the flagellin, by gel filtration to a fraction containing HrpA as well as its three N-terminally truncated forms. These were further separated by two steps of reversed phase chromatography. HrpA and its degradation products were each shown to reassemble into filament structures after denaturation and renaturation showing that HrpA alone is sufficient for formation of filament structures.

Amino Acid Sequence↗

PubMed1997

Integration of local pattern elements into a global shape in human vision.

The spatial extent of the cortical filters selective for different spatial frequencies and orientations is limited. We studied psychophysically how information from the local filters is integrated into global pattern shapes, i.e., whether performance in the identification of a global pattern consisting of small, locally oriented Gabor elements depends on the orientations of those elements. The observer was presented with an E-like stimulus pattern shape comprised of oriented Gabor patches on a blank background, and the performance measure was the threshold contrast for identifying the orientation of the E pattern (four possible rotated orientations). The results showed that contrast thresholds were significantly lower when the local elements all shared the same orientation (e.g., all horizontal) compared with the condition in which the elements had mixed orientations (both horizontal and vertical). The enhancement effect due to uniform local orientations can be explained by two factors: One is local facilitatory interactions between the orientation selective filters, and the other is second-order information integration across the filters.

Humans↗

PubMed1997

Regulation of local angiotensin II formation in the human heart in the presence of interstitial fluid. Inhibition of chymase by protease inhibitors of interstitial fluid and of angiotensin-converting enzyme by Ang-(1-9) formed by heart carboxypeptidase A-like activity.

BACKGROUND: Data from in vitro studies suggest that both chymase and ACE contribute to the local generation of angiotensin (Ang) II in the heart. The enzyme kinetics under in vivo conditions are unclear. We thus studied the generation of Ang II by cardiac tissue in the presence of interstitial fluid (IF) that contains a variety of naturally occurring protease inhibitors. METHODS AND RESULTS: Ang I was incubated with heart homogenate in the presence of IF. IF obtained from human skin contained substantial amounts of protease inhibitors and ACE activity, the concentration of alpha 1-antitrypsin being 35% and the activity of ACE 24% of the corresponding serum values. When heart homogenate was incubated with Ang I, three enzymes were responsible for its metabolism: heart chymase and heart ACE converted Ang I to Ang II, and heart carboxypeptidase A (CPA)-like activity degraded Ang I to Ang-(1-9). Incubation of heart homogenate in the presence of IF led to practically full inhibition of heart chymase-mediated Ang II formation by the natural protease inhibitors present in IF. In contrast, heart CPA-like activity was not blocked, as reflected by the continued generation of Ang-(1-9). In addition, both heart ACE- and IF ACE-mediated Ang II formation were strongly inhibited. This inhibition was shown to be due to the Ang-(1-9) formed. CONCLUSIONS: The present experimental study defines two novel inhibitory mechanisms of Ang II formation in the human heart interstitium. Heart chymase-mediated Ang II formation is strongly inhibited by the natural protease inhibitors present in the IF. Similarly, both heart ACE- and IF ACE-mediated Ang II formation appear to be inhibited by the endogenous inhibitor Ang-(1-9) formed by heart CPA-like activity. These inhibitory mechanisms provide additional information about how the Ang II concentration in the heart interstitium may be controlled.

Angiotensin II↗

PubMed1997

The speed of visual search in the absence of sensory effects.

The purpose of this study was to investigate the efficiency or speed of the frequently used L versus T visual search when sensory effects were controlled, ie 'set size' was not defined as the number of distractor patterns, but the number of distractors in the display was kept constant and the number of possible target positions varied. A search display consisted of an L-target among T-distractors, and the observer's task was to report the presence or absence of the target (experiment 1) or to identify it (whether the L-target was left-facing or right-facing; experiment 2). The observer was instructed prior to each stimulus block, about the display locations in which the target could appear. In both experiments, search time increased significantly with an increasing number of possible target locations, thus indicating that L versus T search is not 'serial' owing to sensory effects. Because, in the first two experiments, a search display was visible until the observer gave a response, 'serial' search might have resulted just from eye movements. Therefore, a control experiment was run in which display duration was limited to 150 ms. The results of this experiment showed that, even when eye movements were prevented, the search still occurred 'serially', ie response time increased as a function of the number of possible target positions.

Eye Movements↗

PubMed1996

Visual awareness of objects correlates with activity of right occipital cortex.

In the search for human neural correlates of visual awareness, cortical magnetic responses to coherent and meaningful objects were compared with responses to disorganized and meaningless non-objects when observers tried to detect the coherent objects. Three brief stimulus durations were included to vary the detection rate of the objects. Of the multiple brain regions activated, only the right lateral occipital cortex showed signals correlating with the proportion of correct object detections. The results suggest an important role for this area in visual awareness of objects.

Adult↗

PubMed1996

Predictive minimum description length criterion for time series modeling with neural networks.

Nonlinear time series modeling with a multilayer perceptron network is presented. An important aspect of this modeling is the model selection, i.e., the problem of determining the size as well as the complexity of the model. To overcome this problem we apply the predictive minimum description length (PMDL) principle as a minimization criterion. In the neural network scheme it means minimizing the number of input and hidden units. Three time series modeling experiments are used to examine the usefulness of the PMDL model selection scheme. A comparison with the widely used cross-validation technique is also presented. In our experiments the PMDL scheme and the cross-validation scheme yield similar results in terms of model complexity. However, the PMDL method was found to be two times faster to compute. This is significant improvement since model selection in general is very time consuming.

Algorithms↗

PubMed1996

Localization and discrimination of "pop-out" targets.

In parallel visual search, a target pattern "pops out" among distractors rapidly, requiring no effort, regardless of distractor numbers. The localization and discrimination of "pop-out" targets was investigated for this research note using similar multiple displays to those used in Sagi and Julesz's [(1985a) Science, 228, 1217-1219] and Folk and Egeth's [(1989) Journal of Experimental Psychology: Human Perception & Performance, 15, 97-110] studies. The stimulus display contained 2, 5 or 10 oblique target line segments embedded in vertical distractor lines. In the first localization task, the observer indicated whether all the targets were in other positions. The second localization task was otherwise identical to the first one, except that the number of critical inside-corner positions was four. In the discrimination task, the observer reported whether all the target lines had the same orientation, or whether one of them differed in orientation from the others. Reaction times for correct responses were measured in all three tasks. The results showed that target discrimination took place in parallel, but target localization was a "serial" process, i.e. the localization time depended on the number of targets and critical locations to be checked.

Discrimination, Psychological↗

PubMed1996

Target localisation and identification in rapid visual search.

In recent models of visual search in has been proposed that, in rapid parallel search, information about the location of a target pattern among distractors and information about its identity would not be available simultaneously, but that target location is represented at earlier stages of visual processing than target identity. In the present study, the priority of location information over identity information in parallel visual search was investigated by means of one identification and two localisation tasks of different levels of difficulty. In all three tasks, the stimulus display was identical An oblique line segment, randomly 45 degrees or 135 degrees in orientation, was presented randomly at one quadrant of the display. In the identification task, the observer reported the orientation of the oblique line irrespective of its location. In the easy localisation task, the observer indicated whether the oblique line was at the left or right side of the display, and in the difficult localisation task whether it was in the upper or lower part of the display. In both localisation tasks, the observer ignored the orientation of the target line. The oblique line was accompanied by one, five, seventeen, or thirty-nine vertical distractor line segments in all tasks. The results showed that the response speed in the left vs right localisation was faster than in the identification task, whereas performance in the up vs down localisation was inferior. When the response factors (stimulus-response compatibility) in the left vs right localisation were taken into account, there were no performance differences between localisation and identification. Thus, these results demonstrated that direct performance comparisons between localisation and identification may be somewhat arbitrary, and they do not solve the issue of priority of location or identity information in rapid visual search.

Adult↗