Soil frost enhances stream dissolved organic carbon concentrations during episodic spring snow melt from boreal mires

Changes in winter time conditions at high‐latitude ecosystems could severely affect the carbon exchange processes. Using a 15 year stream record combined with winter field measurements and laboratory experiment, we studied the regulation of dissolved organic carbon (DOC) concentration in stream water draining boreal mire during snow melt. The most unanticipated finding was that cold soils with deep soil frost resulted in increased snow melt DOC concentrations in the stream runoff. Wintertime field measurements of DOC concentrations below the mire soil frost showed that this phenomenon could be explained by freeze‐out of DOC giving higher levels of DOC in the soil water below the ice as the soil frost developed downwards in the mire. Experimental freezing of water with a certain DOC concentration in the laboratory further corroborated the freeze‐out of DOC. In this experiment, as much as 96% of the DOC was excluded from the ice, whereas the freeze‐out in the mire was less effective (60%). The difference between the proportion of DOC retained in pure water relative to the proportion retained in peat water during freezing is probably due to trapped DOC in the solid peat soil matrix. A simple mass‐balance model showed that to explain the higher stream DOC concentrations during a winter with deep soil frost, approximately 0.5% of the mire area needed to be hydrologically connected to the stream discharge. In the stream records, we also found that the DOC concentrations during snow melt episodic runoff were negatively related to increasing intensity of the snow melt episodes (dilution by low DOC snow melt water) and higher previous export of DOC.     

Release profiles of tricalcium phosphate nanoparticles from poly(L-lactic acid) electrospun scaffolds with single component, core-sheath, or porous fiber morphologies: effects on hASC viability and osteogenic differentiation

Functional PLA scaffolds are created with single component, core-sheath, or porous fiber morphology and doped with TCP nanoparticles to study the release profiles for use in bone tissue engineering applications. Pharmacokinetic analyses are performed for the three different nanofibrous structures after doping with TCP. Results indicate that single component and porous fiber scaffolds exhibit an initial-burst release profile whereas core-sheath fibers show a steady release. All scaffolds are then seeded with human adipose-derived stem cells (hASC), which remain viable and continue proliferation on all nanofibrous morphologies for up to 21 d. Osteogenic differentiation of hASC and cell-mediated calcium accretion are largest on porous fibers.     

Shear stress influences spatial variations in vascular Mn-SOD expression: implication for LDL nitration

Fluid shear stress modulates vascular production of endothelial superoxide anion (O2*-) and nitric oxide (*NO). Whether the characteristics of shear stress influence the spatial variations in mitochondrial manganese superoxide dismutase (Mn-SOD) expression in vasculatures is not well defined. We constructed a three-dimensional computational fluid dynamics model simulating spatial variations in shear stress at the arterial bifurcation. In parallel, explants of arterial bifurcations were sectioned from the human left main coronary bifurcation and right coronary arteries for immunohistolocalization of Mn-SOD expression. We demonstrated that Mn-SOD staining was prominent in the pulsatile shear stress (PSS)-exposed and atheroprotective regions, but it was nearly absent in the oscillatory shear stress (OSS)-exposed regions and lateral wall of arterial bifurcation. In cultured bovine aortic endothelial cells, PSS at mean shear stress (tau ave) of 23 dyn/cm2 upregulated Mn-SOD mRNA expression at a higher level than did OSS at tau ave = 0.02 dyn/cm2 +/- 3.0 dyn.cm(-2).s(-1) and at 1 Hz (PSS by 11.3 +/- 0.4-fold vs. OSS by 5.0 +/- 0.5-fold vs. static condition; P < 0.05, n = 4). By liquid chromatography and tandem mass spectrometry, it was found that PSS decreased the extent of low-density lipoprotein (LDL) nitration, whereas OSS increased nitration (P < 0.05, n = 4). In the presence of LDL, treatment with Mn-SOD small interfering RNA increased intracellular nitrotyrosine level (P < 0.5, n = 4), a fingerprint for nitrotyrosine formation. Our findings indicate that shear stress in the atheroprone versus atheroprotective regions regulates spatial variations in mitochondrial Mn-SOD expression with an implication for modulating LDL nitration.     

Beyond attachment: Roles of DC‐SIGN in dengue virus infection

Dendritic cell‐specific intercellular adhesion molecule‐3‐grabbing non‐integrin (DC‐SIGN), a C‐type lectin expressed on the plasma membrane by human immature dendritic cells, is a receptor for numerous viruses including Ebola, SARS and dengue. A controversial question has been whether DC‐SIGN functions as a complete receptor for both binding and internalization of dengue virus (DENV) or whether it is solely a cell surface attachment factor, requiring either hand‐off to another receptor or a co‐receptor for internalization. To examine this question, we used 4 cell types: human immature dendritic cells and NIH3T3 cells expressing either wild‐type DC‐SIGN or 2 internalization‐deficient DC‐SIGN mutants, in which either the 3 cytoplasmic internalization motifs are silenced by alanine substitutions or the cytoplasmic region is truncated. Using confocal and super‐resolution imaging and high content single particle tracking, we investigated DENV binding, DC‐SIGN surface transport, endocytosis, as well as cell infectivity. DC‐SIGN was found colocalized with DENV inside cells suggesting hand‐off at the plasma membrane to another receptor did not occur. Moreover, all 3 DC‐SIGN molecules on NIH3T3 cells supported cell infection. These results imply the involvement of a co‐receptor because cells expressing the internalization‐deficient mutants could still be infected.      

Polyethylenimine: A new differentiation factor to endothelial/cardiac tissue

Among different tissues, endothelial/cardiac types require specific factors to promote myocardial regeneration after occurred injuries. Herein, cardiac stem cells (CSCs) as the major cell population that involved in cardiovascular repair were selected to study the role of polyethyleneimine (PEI) agent on endothelial differentiation. After preparation of electrospun network of PEI with polyacrylonitrile, the related characterizations were carried out including scanning electron microscope (SEM), field-emission SEM, water contact angle, Fourier transform infrared spectroscopy and mechanical properties. Also, the release kinetic of the corresponding agent was studied up to 7 days. The cell differentiation studies were done in the following with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay, Real-time polymerase chain reaction and immunostaining method. The whole obtained results approved the higher differentiation of CSCs into endothelial/cardiac cells. Finally, it is recommended that the PEI delivering increases the healing potency of CSCs and accordingly the regeneration speed of damaged cardiovascular tissue would be improved.     

Endothelins and their receptors in embryo implantation

As a critical stage of pregnancy, the implantation of blastocysts into the endometrium is a progressive, excessively regulated local tissue remodeling step involving a complex sequence of genetic and cellular interplay executed within an optimal time frame. For better understanding the causes of infertility and, more importantly, for developing powerful strategies for successful implantations and combating infertility, an increasing number of recent studies have been focused on the identification and study of newly described substances in the reproductive tree. The endothelins (ET), a 21-aminoacidic family of genes, have been reported to be responsible for the contraction of vascular and nonvascular smooth muscles, including the smooth muscles of the uterus. Therefore, this review aims to comprehensively discuss the physiological role of endothelins and signaling through their receptors, as well as their probable involvement in the implantation process.     

Mitotic recombination and segregation of satellites in Bloom's syndrome

Mitotic recombination in satellite stalks — a phenomenon often difficult to distinguish from satellite association — was studied in a sister and a brother with Bloom's syndrome. Segregation after recombination was analyzed in the lymphocytes of the sister who had Q-bright satellites. Her cells varied greatly both in regard to the acrocentrics which displayed Q-bright satellites and the number of such satellites per cell. In 58 cells a total of 31 different patterns were seen. In 83 cells of 6 controls who also had Q-bright satellites on at least one acrocentric chromosome, not one cell was found in which the pattern differed from that characteristic of the person. Obviously exchanges between satellite stalks in patients with Bloom's syndrome are fairly frequent (estimated lower limit 6/1000) and very rare in persons who do not have this syndrome (estimated 0.1/1000).