Identification of bronchioalveolar stem cells in normal lung and lung cancer

Injury models have suggested that the lung contains anatomically and functionally distinct epithelial stem cell populations. We have isolated such a regional pulmonary stem cell population, termed bronchioalveolar stem cells (BASCs). Identified at the bronchioalveolar duct junction, BASCs were resistant to bronchiolar and alveolar damage and proliferated during epithelial cell renewal in vivo. BASCs exhibited self-renewal and were multipotent in clonal assays, highlighting their stem cell properties. Furthermore, BASCs expanded in response to oncogenic K-ras in culture and in precursors of lung tumors in vivo. These data support the hypothesis that BASCs are a stem cell population that maintains the bronchiolar Clara cells and alveolar cells of the distal lung and that their transformed counterparts give rise to adenocarcinoma. Although bronchiolar cells and alveolar cells are proposed to be the precursor cells of adenocarcinoma, this work points to BASCs as the putative cells of origin for this subtype of lung cancer.

Strategy and tactics in protein chemistry

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Calphostin C (UCN-1028C), a novel microbial compound, is a highly potent and specific inhibitor of protein kinase C

Calphostin C (UCN-1028C), a newly isolated compound from Cladosporium cladosporioides, is a potent and specific inhibitor of protein kinase C, because it was 1000 times more inhibitory to protein kinase C (IC50, 0.05 microM) than other protein kinases such as cAMP-dependent protein kinase and tyrosine-specific protein kinase (IC50, greater than 50 microM). Calphostin C did not inhibit calcium activated neutral protease (calpain)-digested protein kinase C, indicating that it interacts with the regulatory domain of protein kinase C. In addition this compound showed inhibitory effects on the binding of [3H]PDBu to protein kinase C. The potent cytotoxic activity and antitumor activity of calphostin C might be due to the inhibition of protein kinase C, and thus it may be potentially useful for the therapeutic application.

Histochemical and ultrastructural demonstration of gamma-glutamyl transpeptidase activity

A simultaneous coupling azo dye method for the histochemical demonstration of γ-glutamyl transpeptidase activity using the new substrate γ-glutamyl-4-methoxy-2-naphthylamide has been described. The method appears superior to previously reported methods for γ-glutamyl transpeptidase activity and can easily be modified for the electron microscopic localization of the enzyme by bridging osmium to the copper chelate of the azo dye via thiocarbohydrazide. The optimum conditions for the histochemical reaction were developed and the distribution of enzymatic activity in the tissues of the rat is described for light microscopy and with rat pancreas for electron microscopy. The electron-opaque deposits were seen in the endoplasmic reticulum in the vicinity of the zymogen granules in the apical portion of the acinar cell.

Neuronal cell loss accompanies the brain tissue response to chronically implanted silicon microelectrode arrays

Implantable silicon microelectrode array technology is a useful technique for obtaining high-density, high-spatial resolution sampling of neuronal activity within the brain and holds promise for a wide range of neuroprosthetic applications. One of the limitations of the current technology is inconsistent performance in long-term applications. Although the brain tissue response is believed to be a major cause of performance degradation, the precise mechanisms that lead to failure of recordings are unknown. We observed persistent ED1 immunoreactivity around implanted silicon microelectrode arrays implanted in adult rat cortex that was accompanied by a significant reduction in nerve fiber density and nerve cell bodies in the tissue immediately surrounding the implanted silicon microelectrode arrays. Persistent ED1 up-regulation and neuronal loss was not observed in microelectrode stab controls indicating that the phenotype did not result from the initial mechanical trauma of electrode implantation, but was associated with the foreign body response. In addition, we found that explanted electrodes were covered with ED1/MAC-1 immunoreactive cells and that the cells released MCP-1 and TNF-alpha under serum-free conditions in vitro. Our findings suggest a potential new mechanism for chronic recording failure that involves neuronal cell loss, which we speculate is caused by chronic inflammation at the microelectrode brain tissue interface.

Role of prostacyclin in the cardiovascular response to thromboxane A2

Thromboxane (Tx) A2 is a vasoconstrictor and platelet agonist. Aspirin affords cardioprotection through inhibition of TxA2 formation by platelet cyclooxygenase (COX-1). Prostacyclin (PGI2) is a vasodilator that inhibits platelet function. Here we show that injury-induced vascular proliferation and platelet activation are enhanced in mice that are genetically deficient in the PGI2 receptor (IP) but are depressed in mice genetically deficient in the TxA2 receptor (TP) or treated with a TP antagonist. The augmented response to vascular injury was abolished in mice deficient in both receptors. Thus, PGI2 modulates platelet-vascular interactions in vivo and specifically limits the response to TxA2. This interplay may help explain the adverse cardiovascular effects associated with selective COX-2 inhibitors, which, unlike aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs), inhibit PGI2 but not TxA2.

Reduction of lipofuscin-like autofluorescence in fluorescently labeled tissue

The fluorescent pigment lipofuscin accumulates with age in the cytoplasm of cells of the CNS. Because of its broad excitation and emission spectra, the presence of lipofuscin-like autofluorescence complicates the use of fluorescence microscopy (e.g., fluorescent retrograde tract tracing and fluorescence immunocytochemistry). In this study we examined several chemical treatments of tissue sections for their ability to reduce or eliminate lipofuscin-like autofluorescence without adversely affecting other fluorescent labels. We found that 1-10 mM CuSO4 in 50 mM ammonium acetate buffer (pH 5) or 1% Sudan Black B (SB) in 70% ethanol reduced or eliminated lipofuscin autofluorescence in sections of monkey, human, or rat neural tissue. These treatments also slightly reduced the intensity of immunofluorescent labeling and fluorescent retrograde tract tracers. However, the reduction of these fluorophores was far less dramatic than that for the lipofuscin-like compound. We conclude that treatment of tissue with CuSO4 or SB provides a reasonable compromise between reduction of lipofuscin-like fluorescence and maintenance of specific fluorescent labels.

Astrocytes promote myelination in response to electrical impulses

Myelin, the insulating layers of membrane wrapped around axons by oligodendrocytes, is essential for normal impulse conduction. It forms during late stages of fetal development but continues into early adult life. Myelination correlates with cognitive development and can be regulated by impulse activity through unknown molecular mechanisms. Astrocytes do not form myelin, but these nonneuronal cells can promote myelination in ways that are not understood. Here, we identify a link between myelination, astrocytes, and electrical impulse activity in axons that is mediated by the cytokine leukemia inhibitory factor (LIF). These findings show that LIF is released by astrocytes in response to ATP liberated from axons firing action potentials, and LIF promotes myelination by mature oligodendrocytes. This activity-dependent mechanism promoting myelination could regulate myelination according to functional activity or environmental experience and may offer new approaches to treating demyelinating diseases.

Divalent ions and the surface potential of charged phospholipid membranes

Phospholipid bilayer membranes were bathed in a decimolar solution of monovalent ions, and the conductance produced by neutral carriers of these monovalent cations and anions was used to assess the electric potential at the surface of the membrane. When the bilayers were formed from a neutral lipid, phosphatidylethanolamine, the addition of alkaline earth cations produced no detectable surface potential, indicating that little or no binding occurs to the polar head group with these ions. When the bilayers were formed from a negatively charged lipid, phosphatidylserine, the addition of Sr and Ba decreased the magnitude of the surface potential as predicted by the theory of the diffuse double layer. In particular, the potential decreased 27 mv for a 10-fold increase in concentration in the millimolar-decimolar range. A 10-fold increase in the Ca or Mg concentration also produced a 27 mv decrease in potential in this region, which was again due to screening, but it was necessary to invoke some specific binding to account for the observation that these cations were effective at a lower concentration than Ba or Sr. It is suggested that the ability of the alkaline earth cations to shift the conductance-voltage curves of a nerve along the voltage axis by 20-26 mv for a 10-fold increase in concentration may be due to essentially a screening rather than a binding phenomenon.

The inhibitory effects of peripheral administration of peptide YY3–36 and glucagon-like peptide-1 on food intake are attenuated by ablation of the vagal–brainstem–hypothalamic pathway

The vagus nerve forms a neuro-anatomical link between the gastrointestinal tract and the brain. A number of gastrointestinal hormones, including cholecystokinin and ghrelin, require an intact vagal-brainstem-hypothalamic pathway to affect CNS feeding circuits. We have shown that the effects of peripheral administration of both peptide YY(3-36) (PYY(3-36)) and glucagon-like peptide-1 (GLP-1) on food intake and activation of hypothalamic arcuate feeding neurones are abolished following either bilateral sub-diaphragmatic total truncal vagotomy or brainstem-hypothalamic pathway transectioning in rodents. These findings suggest that the vagal-brainstem-hypothalamic pathway may also play a role in the effects of circulating PYY(3-36) and GLP-1 on food intake.

Crystal structure of naphthalene dioxygenase: side-on binding of dioxygen to iron

Binding of oxygen to iron is exploited in several biological and chemical processes. Although computational and spectroscopic results have suggested side-on binding, only end-on binding of oxygen to iron has been observed in crystal structures. We have determined structures of naphthalene dioxygenase that show a molecular oxygen species bound to the mononuclear iron in a side-on fashion. In a complex with substrate and dioxygen, the dioxygen molecule is lined up for an attack on the double bond of the aromatic substrate. The structures reported here provide the basis for a reaction mechanism and for the high stereospecificity of the reaction catalyzed by naphthalene dioxygenase.

Use of the fluorescent probe 1-N-phenylnaphthylamine to study the interactions of aminoglycoside antibiotics with the outer membrane of Pseudomonas aeruginosa

The mode of interaction of the polycationic aminoglycoside antibiotics with the surface of Pseudomonas aeruginosa cells was studied with the hydrophobic fluorescent probe 1-N-phenylnaphthylamine (NPN). The addition of the aminoglycoside gentamicin to intact cells in the presence of NPN led to a shift in the fluorescence emission maximum from 460 to 420 nm. At the same time the NPN fluorescence intensity increased fourfold. Gentamicin caused no such effects when added to outer membrane vesicles, suggesting that the increased fluorescence resulted from the interaction of gentamicin with intact cells. Gentamicin-promoted NPN uptake was inhibited by the divalent cations Mg2+ and Ca2+, but occurred in the absence of gentamicin transport across the inner membrane. Low concentrations of gentamicin (2 micrograms/ml) caused NPN fluorescence to increase over a period of 4 min in a sigmoidal fashion. At higher concentrations (50 micrograms/ml) the increase occurred within a few seconds. The final fluorescence intensity was almost independent of the gentamicin concentration. A centrifugation technique was used to demonstrate that gentamicin caused actual uptake of NPN from the supernatant. The initial rate of NPN uptake varied according to the gentamicin concentration in a sigmoidal fashion. Similar data were obtained for seven other aminoglycoside antibiotics. The data, when reanalyzed as a Hill plot, gave a series of lines with a mean slope (the Hill number) of 2.26 +/- 0.26, suggesting that the interaction of aminoglycosides with the cell surface to permeabilize it to NPN involved at least three sites and demonstrated positive cooperativity. There was a statistically significant relationship between the pseudoassociation constant K, from the Hill plots and the minimal inhibitory concentrations for the eight antibiotics. These results are consistent with the concept that aminoglycosides interact as a divalent cation binding site on the P. aeruginosa outer membrane and permeabilize it to the hydrophobic prove NPN.

H+- and Ca2+-induced fusion and destabilization of liposomes

A new liposome fusion assay has been developed that monitors the mixing of aqueous contents at neutral and low pH. With this assay we have investigated the ability of H+ to induce membrane destabilization and fusion. The assay involves the fluorophore 1-aminonaphthalene-3,6,8-trisulfonic acid (ANTS) and its quencher N,N'-p-xylylenebis(pyridinium bromide) (DPX). ANTS is encapsulated in one population of liposomes and DPX in another, and fusion results in the quenching of ANTS fluorescence. The results obtained with the ANTS/DPX assay at neutral pH give kinetics for the Ca2+-induced fusion of phosphatidylserine large unilamellar vesicles (PS LUV) that are very similar to those obtained with the Tb3+/dipicolinic acid (DPA) assay [Wilschut, J., & Papahadjopoulos, D. (1979) Nature (London) 281, 690-692]. ANTS fluorescence is relatively insensitive to pH between 7.5 and 4.0. Below pH 4.0 the assay can be used semiquantitatively by correcting for quenching of ANTS due to protonation. For PS LUV it was found that, at pH 2.0, H+ by itself causes mixing of aqueous contents, which makes H+ unique among the monovalent cations. We have shown previously that H+ causes a contact-induced leakage from liposomes composed of phosphatidylethanolamine and the charged cholesteryl ester cholesteryl hemisuccinate (CHEMS) at pH 5.0 or below, where CHEMS becomes protonated. Here we show that H+ causes lipid mixing in this pH range but not mixing of aqueous contents. This result affirms the necessity of using both aqueous space and lipid bilayer assays to comprehend the fusion event between two liposomes.

Photoproduction of Proton Gradients with π-Stacked Fluorophore Scaffolds in Lipid Bilayers

Rigid p-octiphenyl rods were used to create helical tetrameric pi-stacks of blue, red-fluorescent naphthalene diimides that can span lipid bilayer membranes. In lipid vesicles containing quinone as electron acceptors and surrounded by ethylenediaminetetraacetic acid as hole acceptors, transmembrane proton gradients arose through quinone reduction upon excitation with visible light. Quantitative ultrafast and relatively long-lived charge separation was confirmed as the origin of photosynthetic activity by femtosecond fluorescence and transient absorption spectroscopy. Supramolecular self-organization was essential in that photoactivity was lost upon rod shortening (from p-octiphenyl to biphenyl) and chromophore expansion (from naphthalene diimide to perylene diimide). Ligand intercalation transformed the photoactive scaffolds into ion channels.

Live-cell imaging of alkyne-tagged small biomolecules by stimulated Raman scattering

Sensitive and specific visualization of small biomolecules in living systems is highly challenging. We report stimulated Raman-scattering imaging of alkyne tags as a general strategy for studying a broad spectrum of small biomolecules in live cells and animals. We demonstrate this technique by tracking alkyne-bearing drugs in mouse tissues and visualizing de novo synthesis of DNA, RNA, proteins, phospholipids and triglycerides through metabolic incorporation of alkyne-tagged small precursors.