Sildenafil attenuates pulmonary inflammation and fibrin deposition, mortality and right ventricular hypertrophy in neonatal hyperoxic lung injury

Background

Phosphodiesterase-5 inhibition with sildenafil has been used to treat severe pulmonary hypertension and bronchopulmonary dysplasia (BPD), a chronic lung disease in very preterm infants who were mechanically ventilated for respiratory distress syndrome.

Methods

Sildenafil treatment was investigated in 2 models of experimental BPD: a lethal neonatal model, in which rat pups were continuously exposed to hyperoxia and treated daily with sildenafil (50–150 mg/kg body weight/day; injected subcutaneously) and a neonatal lung injury-recovery model in which rat pups were exposed to hyperoxia for 9 days, followed by 9 days of recovery in room air and started sildenafil treatment on day 6 of hyperoxia exposure. Parameters investigated include survival, histopathology, fibrin deposition, alveolar vascular leakage, right ventricular hypertrophy, and differential mRNA expression in lung and heart tissue.

Results

Prophylactic treatment with an optimal dose of sildenafil (2 × 50 mg/kg/day) significantly increased lung cGMP levels, prolonged median survival, reduced fibrin deposition, total protein content in bronchoalveolar lavage fluid, inflammation and septum thickness. Treatment with sildenafil partially corrected the differential mRNA expression of amphiregulin, plasminogen activator inhibitor-1, fibroblast growth factor receptor-4 and vascular endothelial growth factor receptor-2 in the lung and of brain and c-type natriuretic peptides and the natriuretic peptide receptors NPR-A, -B, and -C in the right ventricle. In the lethal and injury-recovery model we demonstrated improved alveolarization and angiogenesis by attenuating mean linear intercept and arteriolar wall thickness and increasing pulmonary blood vessel density, and right ventricular hypertrophy (RVH).

Conclusion

Sildenafil treatment, started simultaneously with exposure to hyperoxia after birth, prolongs survival, increases pulmonary cGMP levels, reduces the pulmonary inflammatory response, fibrin deposition and RVH, and stimulates alveolarization. Initiation of sildenafil treatment after hyperoxic lung injury and continued during room air recovery improves alveolarization and restores pulmonary angiogenesis and RVH in experimental BPD.     

Cell cycle specific induction of apoptosis and necrosis by paclitaxel in the leukemic U937 cells

Induction of cell apoptosis and necrosis by paclitaxel was investigated in human leukemic U937 cells. To explore whether paclitaxel induces both apoptosis and necrosis in different cell cycle stages, we synchronized the cells in G1, S and G2/M stages by counterflow centrifugal elutriation (CCE). The Annexin V and PI analysis revealed that, after paclitaxel treatment, the cells in G1 and S stages died predominantly through apoptosis, whereas G2/M-stage cells died through both apoptosis and necrosis. These phenomena were verified by a trypan blue exclusion assay and by detection of the release of lactose dehydrogenase (LDH). Paclitaxel treatment significantly decreased viability in G2/M cells and led these cells to release more LDH than other cells. These treated cells also released certain substances that inhibited cell growth. These results strongly suggest that the cell membrane of the treated G2/M-cells is disrupted, leading to the leakage of LDH and cell growth inhibitory substances out of cell. Furthermore, the typical events of apoptosis, such as the release of cytochrome c and the decrease of mitochondria membrane potential, occur primarily in S stage rather than in the G2/M stages. These results suggest that paclitaxel induces typical apoptosis in the G1- and S- cells, but it induces both apoptosis and necrosis in G2/M-phase cells.     

Differential membrane potential and ion current responses to different types of shear stress in vascular endothelial cells

Vascular endothelial cells (ECs) distinguish among and respond differently to different types of fluid mechanical shear stress. Elucidating the mechanisms governing this differential responsiveness is the key to understanding why early atherosclerotic lesions localize preferentially in arterial regions exposed to low and/or oscillatory flow. An early and very rapid endothelial response to flow is the activation of flow-sensitive K⁺ and Cl^– channels that respectively hyperpolarize and depolarize the cell membrane and regulate several important endothelial responses to flow. We have used whole cell current- and voltage-clamp techniques to demonstrate that flow-sensitive hyperpolarizing and depolarizing currents respond differently to different types of shear stress in cultured bovine aortic ECs. A steady shear stress level of 10 dyn/cm² activated both currents leading to rapid membrane hyperpolarization that was subsequently reversed to depolarization. In contrast, a steady shear stress of 1 dyn/cm² only activated the hyperpolarizing current. A purely oscillatory shear stress of 0 ± 10 dyn/cm² with an oscillation frequency of either 1 or 0.2 Hz activated the hyperpolarizing current but only minimally the depolarizing current, whereas a 5-Hz oscillation activated neither current. These results demonstrate for the first time that flow-activated ion currents exhibit different sensitivities to shear stress magnitude and oscillation frequency. We propose that flow-sensitive ion channels constitute components of an integrated mechanosensing system that, through the aggregate effect of ion channel activation on cell membrane potential, enables ECs to distinguish among different types of flow. ion channels; atherosclerosis; mechanotransduction     

The origin of GSKIP,a multifaceted regulatory factor in the mammalian Wnt pathway

GSK3β interacting protein (GSKIP) is a naturally occurring negative regulator of GSK3β and retains both the Protein Kinase A Regulatory subunit binding (PKA-RII) domain and GSK3β interacting domain. Of these two domains, we found that PKA-RII is required for forming a working complex comprising PKA/GSKIP/GSK3β/Drp1 to influence phosphorylation of Drp1 Ser637. In this study, bioinformatics and experimental explorations re-analyzing GSKIP's biofunctions suggest that the evolutionarily conserved Domain of Unknown Function (DUF727) is an ancestral prototype of GSKIP in prokaryotes, and acquired the C-terminal GSK3β binding site (tail) in invertebrates except for Saccharomyces spp., after which the N-terminal PKA-RII binding region (head) evolved in vertebrates. These two regions mutually influence each other and modulate GSKIP binding to GSK3β in yeast two-hybrid assays and co-immunoprecipitation. Molecular modeling showed that mammalian GSKIP could form a dimer through the L130 residue (GSK3β binding site) rather than V41/L45 residues. In contrast, V41/L45P mutant facilitated a gain-of-function effect on GSKIP dimerization, further influencing binding behavior to GSK3β compared to GSKIP wild-type (wt). The V41/L45 residues are not only responsible for PKA RII binding that controls GSK3β activity, but also affect dimerization of GSKIP monomer, with net results of gain-of-function in GSKIP-GSK3β interaction. In addition to its reported role in modulating Drp1, Ser637 phosphorylation caused mitochondrial elongation; we postulated that GSKIP might be involved in the Wnt signaling pathway as a scavenger to recruit GSK3β away from the β-catenin destruction complex and as a competitor to compete for GSK3β binding, resulting in accumulation of S675 phosphorylated β-catenin.     

What type of glutamine synthetase is important forStreptomyces coelicolor A3(2) under nitrogen-limited growth conditions?

Summary Glutamine synthetase I activity ofStreptomyces coelicolor was strongly repressed by ammonia and was induced 56.8 fold in a nitrogen-free medium. Glutamine synthetase II activity was not induced even by a long-term nitrogen starvation. Therefore, glutamine synthetase I is the only active enzyme ofStreptomyces coelicolor.     

Mitochondrial gene divergence of Colombian Drosophila pseudoobscura

Isolated populations of drosophila pseudoobscura, separated from North American populations by about 2,400 km, were found in Colombia in 1960. We compared for sequences of the small ribosomal RNA (srRNA) gene on the mitochondria between North American and Colombian D. pseudoobscura in order to clarify the age of the Colombian isolates. The North American populations were not genetically different from each other but were genetically different from the Colombian populations. The Mexican strains represent the area from which the Colombian founders might have come. The estimated net nucleotide divergence between Mexican and Colombian D. pseudoobscura indicates that the Colombian population is not an ancient lineage. Phylogenies using both distance and parsimony methodologies reinforced this conclusion. The Colombian samples group together with both methods but, according to the bootstrap analysis, not significantly. It appears that the populations have not been separated long enough for their DNA sequences to show much divergence.      

I-Ag7-mediated antigen presentation by B lymphocytes is critical in overcoming a checkpoint in T cell tolerance to islet beta cells of nonobese diabetic mice.

B cell-deficient nonobese diabetic (NOD) mice are protected from the development of spontaneous autoimmune diabetes, suggesting a requisite role for Ag presentation by B lymphocytes for the activation of a diabetogenic T cell repertoire. This study specifically examines the importance of B cell-mediated MHC class II Ag presentation as a regulator of peripheral T cell tolerance to islet beta cells. We describe the construction of NOD mice with an I-Ag7 deficiency confined to the B cell compartment. Analysis of these mice, termed NOD BCIID, revealed the presence of functionally competent non-B cell APCs (macrophages/dendritic cells) with normal I-Ag7 expression and capable of activating Ag-reactive T cells. In addition, the secondary lymphoid organs of these mice harbored phenotypically normal CD4+ and CD8+ T cell compartments. Interestingly, whereas control NOD mice harboring I-Ag7-sufficient B cells developed diabetes spontaneously, NOD BCIID mice were resistant to the development of autoimmune diabetes. Despite their diabetes resistance, histologic examination of pancreata from NOD BCIID mice revealed foci of noninvasive peri-insulitis that could be intentionally converted into a destructive process upon treatment with cyclophosphamide. We conclude that I-Ag7-mediated Ag presentation by B cells serves to overcome a checkpoint in T cell tolerance to islet beta cells after their initial targeting has occurred. Overall, this work indicates that the full expression of the autoimmune potential of anti-islet T cells in NOD mice is intimately regulated by B cell-mediated MHC class II Ag presentation.