Flow limitation in liquid-filled lungs: effects of liquid properties

Flow limitation in liquid-filled lungs is examined in intact rabbit experiments and a theoretical model. Flow limitation ("choked" flow) occurs when the expiratory flow reaches a maximum value and further increases in driving pressure do not increase the flow. In total liquid ventilation this is characterized by the sudden development of excessively negative airway pressures and airway collapse at the choke point. The occurrence of flow limitation limits the efficacy of total liquid ventilation by reducing the minute ventilation. In this paper we investigate the effects of liquid properties on flow limitation in liquid-filled lungs. It is found that the behavior of liquids with similar densities and viscosities can be quite different. The results of the theoretical model, which incorporates alveolar compliance and airway resistance, agrees qualitatively well with the experimental results. Lung compliance and airway resistance are shown to vary with the perfluorocarbon liquid used to fill the lungs. Surfactant is found to modify the interfacial tension between saline and perfluorocarbon, and surfactant activity at the interface of perfluorocarbon and the native aqueous lining of the lungs appears to induce hysteresis in pressure-volume curves for liquid-filled lungs. Ventilation with a liquid that results in low viscous resistance and high elastic recoil can reduce the amount of liquid remaining in the lungs when choke occurs, and, therefore, may be desirable for liquid ventilation.     

Mutagenesis of Individual Pentatricopeptide Repeat Motifs Affects RNA Binding Activity and Reveals Functional Partitioning of Arabidopsis PROTON GRADIENT REGULATION3

Pentatricopeptide repeat (PPR) proteins bind RNA and act in multiple eukaryotic processes, including RNA editing, RNA stability, and translation. Here, we investigated the mechanism underlying the functional versatility of Arabidopsis thaliana PROTON GRADIENT REGULATION3 (PGR3), a chloroplast protein harboring 27 PPR motifs. Previous studies suggested that PGR3 acts in (1) stabilization of photosynthetic electron transport L (petL) operon RNA, (2) translation of petL, and (3) translation of ndhA. We showed here that replacement of the 4th amino acid of the 12th PPR with nonpolar or charged amino acids abolished functions (1) and (2) but not (3) of PGR3 by compromising the function of this specific PPR. This discovery enabled us to knock out the RNA binding ability of individual PPR motifs. Consequently, we showed that the 16 N-terminal PPRs were sufficient for function (1) via sequence-specific RNA binding, whereas the 11 C-terminal motifs were essential for functions (2) and (3) by activating translation. We also clarified that the 14th amino acid of the 12th PPR should be positively charged to make the PPR functionally active. Our finding opens up the possibility of selectively manipulating the functions of PPR proteins.     

Mitochondrial density contributes to the immune response of macrophages to lipopolysaccharide via the MAPK pathway

We investigated the role of mitochondrial reactive oxygen species (ROS) in the response of macrophages to lipopolysaccharide (LPS) using RAW 264.7 cells and their ρ(o) cells lacking mitochondria. Mitochondrial density, respiratory activity and related proteins in ρ(o) cells were significantly lower than those in RAW cells. LPS rapidly stimulated mitochondrial ROS prior to cytokine secretion, such as TNF-α and IL-6, from RAW 264.7 cells by activating the MAPK pathway, while the response was attenuated in ρ(o) cells. Exposure of ρ(o) cells to H(2)O(2) partially restored the secretion of cytokines induced by LPS. These results suggest that mitochondrial density and/or the respiratory state contribute to intracellular oxidative stress, which is responsible for the stimulation of LPS-induced MAPK signaling to enhance cytokine release from macrophages.     

Purification and characterization of a lethal toxin from the venom of Heloderma horridum horridum

A lethal toxin was isolated from the venom of Heloderma h. horridum by gel filtration and ion-exchange chromatography. Molecular weight of the purified toxin was determined to be 28 kDa under reducing and nonreducing conditions. Biological activity, assayed by i.v. routes of injection, shows an LD50 for this preparation of 0.135 micrograms/g. Additionally, the toxin possesses an inhibitory effect on direct electrical stimulation of the isolated mouse hemi-diaphragm. However, neither hemorrhagic nor hemolytic activities were detected. Phospholipase A2 activity, proteolytic activity and arginine esterolytic activity were absent. The amino acid composition of the lethal toxin and the NH2-terminal sequence up to residue number 33 were determined. Neither show similarities to other components from H. h. horridum venom.     

Deficiency of Oncostatin M Receptor β (OSMRβ) Exacerbates High-fat Diet-induced Obesity and Related Metabolic Disorders in Mice

Oncostatin M (OSM) belongs to the IL-6 family of cytokines and has diverse biological effects, including the modulation of inflammatory responses. In the present study we analyzed the roles of OSM signaling in obesity and related metabolic disorders. Under a high-fat diet condition, OSM receptor β subunit-deficient (OSMRβ^−/−) mice exhibited increases in body weight and food intake compared with those observed in WT mice. In addition, adipose tissue inflammation, insulin resistance, and hepatic steatosis were more severe in OSMRβ^−/− mice than in wild-type (WT) mice. These metabolic phenotypes did not improve when OSMRβ^−/− mice were pair-fed with WT mice, suggesting that the effects of OSM signaling on these phenotypes are independent of the increases in the body weight and food intake. In the liver of OSMRβ^−/− mice, the insulin-induced phosphorylation of p70 S6 kinase remained intact, whereas insulin-induced FOXO1 phosphorylation was impaired. In addition, OSMRβ^−/− mice displayed a higher expression of genes related to de novo lipogenesis in the liver than WT mice. Furthermore, treatment of genetically obese ob/ob mice with OSM improved insulin resistance, adipose tissue inflammation, and hepatic steatosis. Intraportal administration of OSM into ob/ob mice activated STAT3 and increased the expression of long-chain acyl-CoA synthetase (ACSL) 3 and ACSL5 with decreased expression of fatty acid synthase in the liver, suggesting that OSM directly induces lipolysis and suppresses lipogenesis in the liver of obese mice. These findings suggest that defects in OSM signaling promote the deterioration of high-fat diet-induced obesity and related metabolic disorders.     

Augmentation of 11beta-hydroxysteroid dehydrogenase type 1 in LPS-activated J774.1 macrophages--role of 11beta-HSD1 in pro-inflammatory properties in macrophages

Macrophage infiltration in obese adipose tissue provokes local inflammation and insulin resistance. Evidence has accumulated that activation of 11beta-HSD1 in adipocytes is critically involved in dysfunction of adipose tissue. However, the potential role of 11beta-HSD1 in macrophages still remains unclear. We here demonstrate that a murine macrophage cell line, J774.1 cells expressed 11beta-HSD1 mRNA and reductase activity, both of which were augmented by lipopolysaccharide (LPS)-induced cell activation. Three kinds of pharmacological inhibition of 11beta-HSD1 in LPS-treated macrophages significantly suppressed the expression and secretion of interleukin 1beta, tumor necrosis factor alpha or monocyte chemoattractant protein 1, thereby highlighting a novel role of 11beta-HSD1 in pro-inflammatory properties of activated macrophages.