CD47 is necessary for inhibition of nitric oxide-stimulated vascular cell responses by thrombospondin-1

CD36 is necessary for inhibition of some angiogenic responses by the matricellular glycoprotein thrombospondin-1 and is therefore assumed to be the receptor that mediates its anti-angiogenic activities. Although ligation of CD36 by antibodies, recombinant type 1 repeats of thrombospondin-1, or CD36-binding peptides was sufficient to inhibit nitric oxide (NO)-stimulated responses in both endothelial and vascular smooth muscle cells, picomolar concentrations of native thrombospondin-1 similarly inhibited NO signaling in vascular cells from wild-type and CD36-null mice. Ligation of the thrombospondin-1 receptor CD47 by recombinant C-terminal regions of thrombospondin-1, thrombospondin-1 peptides, or CD47 antibodies was also sufficient to inhibit NO-stimulated phenotypic responses and cGMP signaling in vascular cells. Thrombospondin-1 did not inhibit NO signaling in CD47-null vascular cells or NO-stimulated vascular outgrowth from CD47-null muscle explants in three-dimensional cultures. Furthermore, the CD36-binding domain of thrombospondin-1 and anti-angiogenic peptides derived from this domain failed to inhibit NO signaling in CD47-null cells. Therefore, ligation of either CD36 or CD47 is sufficient to inhibit NO-stimulated vascular cell responses and cGMP signaling, but only CD47 is necessary for this activity of thrombospondin-1 at physiological concentrations.     

Rapid intrachain binding of histidine-26 and histidine-33 to heme in unfolded ferrocytochrome C.

Time-resolved spectroscopic studies of unfolded horse iron(II) cytochrome c have suggested that the imidazole side chains of His26 and His33 bind transiently to the heme iron on microsecond time scales, after photodissociation of a carbon monoxide ligand from the heme. Our studies of four variants of cytochrome c (horse wild type, horse H33N, horse H33N/H26Q, and tuna wild type), unfolded in guanidine hydrochloride at pH 6.5, demonstrate that these side chains are responsible for the observed microsecond spectral changes. As His33 and then His26 are eliminated from the horse wild-type sequence, transient optical absorption spectra show systematic suppression of a rapid (approximately 10-100 micros) Soret absorbance change that follows photolysis of CO. Transient binding of these histidine side chains to the heme therefore generates one of the fast kinetic phases observed in previous photochemically triggered spectroscopic studies of dynamics in unfolded iron(II) cytochrome c. Furthermore, both His33 and His26 appear to contribute to a similar extent in these early kinetics. Thus, the stiffness of the polypeptide chain creates a deviation from Gaussian chain behavior by impeding, although not preventing, the formation of short (<10 peptide bonds) intrachain loops around the heme group.     

Aquatic Habitat Dynamics along a Braided Alpine River Ecosystem (Tagliamento River, Northeast Italy)

Aquatic habitat change caused by flooding was quantified along the Fiume Tagliamento, a morphologically intact gravel-bed river ecosystem in northeast Italy. Five different geomorphic reaches (each around 1.5 km), ranging from near the headwaters at 800 m above sea level (a.s.l.) to near the mouth at 5 m a.s.l., were studied over a 1-year period. All floodplain water bodies in each reach were delineated in August 1999 using a differential global positioning system. Each reach was remapped twice (in December 1999 and August 2000) to investigate the impact of autumn and spring flood seasons on aquatic habitat composition and configuration. A high degree (nearly 62%) of aquatic habitat turnover was documented in a braided headwater floodplain. The degree of aquatic habitat turnover decreased with decreasing elevation to approximately 20% turnover in a meandering reach at 5 m a.s.l. In contrast to turnover, braiding, sinuosity, and aquatic habitat composition changed little in response to flooding in all reaches. Location of aquatic habitats in floodplains changed considerably (turnover), whereas habitat configuration and composition remained relatively stable. These results support the applicability of the shifting mosaic steady-state model to riverine floodplain environments.     

Inundation Dynamics in Braided Floodplains: Tagliamento River, Northeast Italy

The relationships among water level, inundated area, and shoreline dynamics were investigated in a bar-braided and an island-braided floodplain of the Tagliamento River in northeast Italy. Ground-based surveys with a differential global positioning system (aGPS) unit were used to delineate all aquatic-terrestrial interfaces (shorelines) in the active floodplain at different water levels. Despite complex inundation patterns, a highly significant (P < 0.00001) linear relationship between water level and arcsine square root of inundated area was found in both reaches (y = 0.49x + 0.07). A highly significant (P < 0.00009) second-order polynomial relationship occurred between water level and shoreline length (y = 87.83 − 65.85x² + 169.83x). Using these relationships as simple predictive models, we converted several years of water-level data into predictions for degree of inundation and shoreline length. The plot of the simulated degree of inundation strongly resembled the actual hydrograph. Complete inundation of the active floodplains occurred one or two times per year; however, the degree of inundation at lower water levels was highly dynamic during most of the year. Simulated shoreline length averaged 171 m ha⁻¹ (13.6 km km⁻¹), with a maximum of 197 m ha⁻¹ (15.6 km km⁻¹) occurring during periods with intermediate water levels. The corresponding values determined with GPS were somewhat higher, with an average value of 181 m ha⁻¹ (14.4 km km⁻¹) and a maximum of 214 m ha⁻¹ (16.3 km km⁻¹). During major flood events, actual shoreline length decreased to 28 m ha⁻¹ (2.1 km km⁻¹). Braiding index and upstream surface hydrologic connectivity were positively related to water level, whereas total area of isolated water bodies was negatively related to water level. The number of nodes remained high most of the time during the 2-year study period.     

Carbohydrate-dependent sulfur respiration in halo(alkali)philic archaea

Archaea are environmentally ubiquitous on Earth, and their extremophilic and metabolically versatile phenotypes make them useful as model systems for astrobiology. Here, we reveal a new functional group of halo(natrono)archaea able to utilize alpha-d -glucans (amylopectin, amylose and glycogen), sugars, and glycerol as electron donors and carbon sources for sulfur respiration. They are facultative anaerobes enriched from hypersaline sediments with either amylopectin, glucose or glycerol as electron/carbon sources and elemental sulfur as the terminal electron acceptor. They include 10 strains of neutrophilic haloarchaea from circum pH-neutral lakes and one natronoarchaeon from soda-lake sediments. The neutrophilic isolates can grow by fermentation, although addition of S⁰ or dimethyl sulfoxide increased growth rate and biomass yield (with a concomitant decrease in H₂). Natronoarchaeal isolate AArc-S grew only by respiration, either anaerobically with S⁰ or thiosulfate as the terminal electron acceptor, or aerobically. Through genome analysis of five representative strains, we detected the full set of enzymes required for the observed catabolic and respiratory phenotypes. These findings provide evidence that sulfur-respiring haloarchaea partake in biogeochemical sulfur cycling, linked to terminal anaerobic carbon mineralization in hypersaline anoxic habitats. We discuss the implications for life detection in analogue environments such as the polar subglacial brine-lakes of Mars.     

Die physiologische Bedeutung des Golgi-Apparats im Lichte der Vitalfärbungsmethode

Ohne ZusammenfassungDie gegenwärtige Arbeit ist im Laboratorium für vergleichende Histologie am Peterhofschen Naturwissenschaftlichen Institute verfertigt worden.