Biomedical subjects

H Schnittler

Publications and source records attributed to H Schnittler.

7 recordsLinked to original sources

PubMed1992

Structure and assembly of hemagglutinin mutants of fowl plague virus with impaired surface transport.

Five temperature-sensitive mutants of influenza virus A/FPV/Rostock/34 (H7N1), ts206, ts293, ts478, ts482, and ts651, displaying correct hemagglutinin (HA) insertion into the apical plasma membrane of MDCK cells at the permissive temperature but defective transport to the cell surface at the restrictive temperature, have been investigated. Nucleotide sequence analysis of the HA gene of the mutants and their revertants demonstrated that with each mutant a single amino acid change is responsible for the transport block. The amino acid substitutions were compared with those of mutants ts1 and ts227, which have been analyzed previously (W. Schuy, C. Will, K. Kuroda, C. Scholtissek, W. Garten, and H.-D. Klenk, EMBO J. 5:2831-2836, 1986). With the exception of ts206, the changed amino acids of all mutants and revertants accumulate in three distinct areas of the three-dimensional HA model: (i) at the tip of the 80-A (8-nm)-long alpha helix, (ii) at the connection between the globular region and stem, and (iii) in the basal domain of the stem. The concept that these areas are critical for HA assembly and hence for transport is supported by the finding that the mutants that are unable to leave the endoplasmic reticulum at the nonpermissive temperature do not correctly trimerize. Upon analysis by density gradient centrifugation, cross-linking, and digestion with trypsin and endoglucosaminidase H, two groups can be discriminated among these mutants: with ts1, ts227, and ts478, the HA forms large irreversible aggregates, whereas with ts206 and ts293, it is retained in the monomeric form in the endoplasmic reticulum. With a third group, comprising mutants ts482 and ts651 that enter the Golgi apparatus, trimerization was not impaired.

Amino Acid Sequence↗

PubMed1991

Adenosine diphosphate-ribosylation of G-actin by botulinum C2 toxin increases endothelial permeability in vitro.

The endothelial cytoskeleton is believed to play an important role in the regulation of endothelial permeability. We used botulinum C2 toxin to perturb cellular actin and determined its effect on the permeability of endothelial cell monolayers derived from porcine pulmonary arteries. The substrate for botulinum C2 toxin is nonmuscle monomeric actin which becomes ADP-ribosylated. This modified actin cannot participate in actin polymerization and, in addition, acts as a capping protein. Exposure of endothelial cell monolayers to botulinum C2 toxin resulted in a dose- (3-100 ng/ml) and time-dependent (30-120 min) increase in the hydraulic conductivity and decrease in the selectivity of the cell monolayers. The effects of C2 toxin were accompanied by a time- and dose-dependent increase in ADP-ribosylatin of G-actin. G-Actin content increased and F-actin content decreased time- and dose-dependently in C2 toxin-treated endothelial cells. Phalloidin which stabilizes filamentous actin prevented the effects of botulinum C2 toxin on endothelial permeability. Botulinum C2 toxin induced interendothelial gaps. The effects occurred in the absence of overt cell damage and were not reversible within 2 h. The data suggest that the endothelial microfilament system is important for the regulation of endothelial permeability.

Actins↗

PubMed1990

Effects of Escherichia coli hemolysin on endothelial cell function.

Escherichia coli hemolysin is considered an important virulence factor in extraintestinal E. coli infections. The present study demonstrates that cultured pulmonary artery endothelial cells are susceptible to attack by low concentrations of E. coli hemolysin (greater than or equal to 0.05 hemolytic units/ml; greater than or equal to 5 ng/ml). Sublytic amounts of hemolysin increased the permeability of endothelial cell monolayers in a time- and dose-dependent manner. The hydraulic conductivity increased approximately 30-fold and the reflection coefficient for large molecules dropped from 0.71 to less than 0.05, indicating a toxin-induced loss of endothelial barrier function. The alterations of endothelial monolayer permeability were accompanied by cell retraction and interendothelial gap formation. In addition, E. coli hemolysin stimulated prostacyclin synthesis in endothelial cells. This effect was strictly dependent on the presence of extracellular Ca2+ but not of Mg2+. An enhanced passive influx of 45Ca2+ and 3H-sucrose but not of tritiated inulin and dextran was noted in toxin-treated cells, indicating that small transmembrane pores comparable to those detected in rabbit erythrocytes had been generated in endothelial cell membranes. These pores may act as nonphysiologic Ca2+ gates, thereby initiating different Ca2+-dependent cellular processes. We conclude that endothelial cells are highly susceptible to E. coli hemolysin and that two major endothelial cell functions are altered by very low concentrations of hemolysin.

Animals↗

PubMed1990

Ultrastructural organization of contractile proteins in rat glomerular mesangial cells.

Glomerular mesangial cells of the rat kidney contain actin, nonmuscle myosin, tropomyosin, and the muscular Z-line protein, alpha-actinin. This was shown for actin, myosin, and alpha-actinin by immunoblotting as well as by immunoelectron microscopy. Tropomyosin was localized in mesangial cells by immunofluorescence. In cultured mesangial cells, actin, myosin, and alpha-actinin constitute a considerable amount of the total cellular protein contents. In mesangial cells in situ actin, myosin and alpha-actinin were found to be colocalized within conspicuous microfilament bundles that traverse the cell body or major processes in various directions and project into either the tonguelike pericapillary processes, which run toward mesangial angles, or into the microvilluslike lateral extensions that abut on the perimesangial portion of the glomerular basement membrane (GBM). Thereby, the GBM of opposing mesangial angles as well as of opposing portions of the perimesangial GBM are regularly interconnected by filament bundles within mesangial cells that contain actin, myosin, and alpha-actinin. The authors suggest that the major function of actin-, myosin-, and alpha-actinin-containing filament bundles in mesangial cells is to create an isometric tension (or minute isotonic contractions) to counteract the distending forces of the rather high intracapillary hydraulic pressure and its resulting pressure gradients across the capillary wall and across the perimesangial GBM.

Animals↗

PubMed1989

Role of the endothelial actin filament cytoskeleton in rheology and permeability.

We have provided evidence for the existence of two distinct sets of actin filaments in endothelial cells, the stress fibers, and the peripheral filament band. Both sets of actin filaments also contain myosin, alpha-actinin, and other associated proteins of the contractile apparatus in muscle. We have shown that both systems of actin filaments in endothelial cells can contract. Stress fibers probably serve to prevent the endothelium from hydrodynamic injury and detachment, whereas the peripheral band of actin filaments appears to be important for the regulation of certain aspects of endothelial permeability.

Actin Cytoskeleton↗

PubMed1987

[Endothelial function and arteriosclerosis].

Elevated levels of plasma LDL have been correlated with morphological endothelial damages, e.g. reduced antithrombogenity of endothelial cells. Numerical and functional defects of endothelial cells probably influence the necessary separation of blood fractions from subendothelial tissues in a negative sense. In order to describe an imaginable endothelial dysfunction with respect to LDL transport we examined human umbilical venous endothelial cells (HUVEC) in culture under physiological flow conditions. HUVEC in culture after incubation with a LDL concentration of 100 micrograms/ml medium were exposed to defined levels of physiological shear stress, fixed with formalin and stained with oil-red-O. After documentation of oil-red-O staining with a photomicroscope, the amount of stain has been characterized semiquantitatively with the help of an image-analysis system (IBAS II/Zeiss). HUVEC not exposed to shear stress only showed a marginal oil-red-O staining at the cell surface. If they were exposed to shear stress of 0.5 dyn/cm2 they showed in orthogonal view an average increase of 1.3%, in cross-sectional view an average increase of 0.3%. HUVEC exposed to shear stress of 2.5 dyn/cm2 showed in orthogonal view an average increase of 4.6%, in cross-sectional view an average increase of 8.7%.

Arteriosclerosis↗

PubMed1986

Stress fibres (SF) in human endothelial cells (HEC) under shear stress.

Human umbilical veinous endothelial cells are cultured on artificial substrates precoated with extracellular matrix from bovine corneal endothelial cells. These cultural conditions help cells to keep an elevated maintenance level for otherwise unusual time intervals. Integrity of endothelial cell layers is of special interest for nondisturbed blood circulation. Therefore we look after mechanisms of cell--cell and cell--substrate--adherence. Here we focus on stress fibres, microfilaments, which seem to play an important part in cellular adherence phenomena. Since endothelial cells in vivo are constantly shear stressed by the blood stream we investigated cell--substrate interactions in vitro under dynamical conditions with the help of a modified cone--plate rheometer originally designed for hemorheology. It can be demonstrated in these shearing experiments that toxical substances influence the organization of stress fibres.

Actin Cytoskeleton↗