Biomedical subjects

Y S Edwards

Publications and source records attributed to Y S Edwards.

9 recordsLinked to original sources

PubMed2001

Stretch stimulation: its effects on alveolar type II cell function in the lung.

Mechanical stimuli regulate cell function in much the same way as chemical signals do. This has been studied in various cell types, particularly those with defined mechanical roles. The alveolar type II cell (ATII) cell, which is part of the alveolar epithelium of the lung, is responsible for the synthesis and secretion of pulmonary surfactant. It is now widely believed that stretch of ATII cells, which occurs during breathing, is the predominant physiological trigger for surfactant release. To study this, investigators have used an increasingly sophisticated array of in vitro and in vivo models. Using various stretch devices and models of lung ventilation and expansion, it has been shown that stretch regulates multiple activities in ATII cells. In addition to surfactant secretion, stretch triggers the differentiation of ATII to alveolar type I cells, as well as ATII cell apoptosis. In doing so, stretch modulates the proportion of these cells in the lung epithelium during both development and maturation of the lung and following lung injury. From such studies, it appears that mechanical distortion plays an integral part in maintaining the overall structure and function of the lung.

Animals↗

PubMed2001

Alveolar type II cell apoptosis.

The alveolar type II cells have many important metabolic and biosynthetic functions including the synthesis and secretion of the lipid-protein complex, surfactant. Alveolar type II cells are also considered to be the progenitor cell type of the alveolar epithelium by their ability to both proliferate and to differentiate into alveolar type I cells. Recently, increasing evidence has suggested a role for programmed cell death, or apoptosis, in the maintenance of the alveolar epithelium under normal and pathological conditions. Apoptosis is a form of cell death serving physiologic and homeostatic functions, and is important in the development and progression of various disease states. Alveolar type II cells undergo apoptosis during normal lung development and maturation, and as a consequence of acute lung injury. This review offers an overview of apoptotic signalling pathways in alveolar type II cells and describes the biological and physiological functions of alveolar type II cell apoptosis in the normal and diseased lung. A better understanding of the signalling transduction pathways leading to alveolar type II cell apoptosis may provide new approaches to the treatment of acute lung injury and other pulmonary disorders.

Animals↗

PubMed2000

NO protects alveolar type II cells from stretch-induced apoptosis. A novel role for macrophages in the lung.

We have previously shown that mechanical distortion or stretch of alveolar type II (ATII) cells induces both surfactant release and the induction of apoptosis. We hypothesize that nitric oxide (NO) secreted from alveolar macrophages (AMs) prevents cyclic stretch-induced apoptosis. We show that S-nitroso-N-acetyl-D, L-penicillamine (SNAP), a chemical donor of NO, protects cells against nuclear condensation and DNA fragmentation induced by stretch (30% at 60 cycles/min) as well as by sorbitol. SNAP depleted of NO had no protective effect, and the NO scavenger 2-phenyl-4,4,5, 5-tetramethylimidazoline-1-oxyl 3-oxide blocked the antiapoptotic effect of SNAP. We also show that AMs isolated from rat lung lavage fluid actively synthesize and secrete NO. Using a novel technique in which AMs were cocultured with ATII cells while adhered to floating membrane rafts, we found that NO released from AMs was effective in protecting ATII cells from undergoing apoptosis. We therefore propose that NO secreted by AMs may function as part of a physiological antiapoptotic mechanism that prevents ATII cells from undergoing stretch-induced cell death in the lung.

Animals↗

PubMed1999

Cyclic stretch induces both apoptosis and secretion in rat alveolar type II cells.

We examined the effects of short-term cyclic stretch on both phosphatidylcholine (PC) secretion and apoptosis in primary cultures of rat alveolar type II cells. A 22% cyclic stretch (3 cycles/min) was applied to type II cells cultured on silastic membranes using a Flexercell strain unit. This induced, after a lag period of about 1 h, a small, but significant release of [3H]PC from prelabelled cells. In addition, stretch increased nuclear condensation, the generation of oligosomal DNA fragments and the activation of caspases. Similar responses were triggered by sorbitol-induced osmotic shock, but not by the secretagogue ATP. We conclude that stretch can induce both apoptosis and PC secretion in alveolar type II cells and propose that these diverse responses occur within the lung as a consequence of normal respiratory distortion of the alveolar epithelium.

Animals↗

PubMed1998

Osmotic stress induces both secretion and apoptosis in rat alveolar type II cells.

The aim of this study was to analyze the effects of osmotic shock and secretagogues such as ATP and 12-O-tetradecanoylphorbol 13-acetate (TPA) on various intracellular signaling pathways in primary cultures of alveolar type II cells and examine their potential role in regulating events such as secretion and apoptosis in these cells. Sorbitol-induced osmotic stress caused the sustained release of [3H]phosphatidylcholine ([3H]PC) from primary cultures of rat alveolar type II cells prelabeled with [3H]choline chloride. This release was not dependent on protein kinase C because downregulation of the major protein kinase C isoforms (alpha, betaII, delta, and eta) expressed in alveolar type II cells had no effect on [3H]PC secretion. Sorbitol, as well as the known secretagogues TPA and ATP, activated extracellular signal-regulated kinase. Although an inhibitor of the extracellular signal-regulated kinase cascade, PD-98059, blocked this activation, it had no effect on the release of [3H]PC. Sorbitol and ultraviolet C radiation, but not TPA or ATP, were also found to activate both p38 and stress-activated protein kinase/c-Jun NH2-terminal kinase. Furthermore, both sorbitol and ultraviolet C radiation induced apoptosis in alveolar type II cells as demonstrated by Hoechst 33258 staining of the condensed nuclei, the generation of DNA ladders, and the activation of caspases. The data indicate that multiple signaling pathways are activated by traditional secretagogues such as TPA and ATP and by cellular stresses such as osmotic shock and that these may be involved in regulating secretory and apoptotic events in alveolar type II cells.

Adenosine Triphosphate↗

PubMed1995

Accumulation of phosphatidylalcohol in cultured cells: use of subcellular fractionation to investigate phospholipase D activity during signal transduction.

Phosphatidylalcohol accumulates as a product of a phospholipase D (PLD)-catalysed transphosphatidylation reaction in cells incubated in the presence of a primary alcohol. In the presence of ethanol the phorbol ester, phorbol 12-myristate 13-acetate (PMA), stimulated the accumulation of [3H]phosphatidylethanol (PEth) in HeLa cells prelabelled with [3H]palmitic acid. Radioactivity associated with PEth increased linearly during a 30 min incubation, indicating that a sustained activation of PLD is caused by PMA in these cells. This was accompanied by the membrane association of protein kinase C-alpha (PKC-alpha), the PKC isoform that recent studies indicate is involved in the activation of PLD. In similar experiments, the neuropeptide bradykinin stimulated an accumulation of PEth in 3T3 Li cells. The radioactivity associated with PEth increased to a maximal level at 30 s and plateaued after this time, suggesting that bradykinin induces only a transient activation of PLD in these cells. This is consistent with the effects of bradykinin on PKC-alpha, which underwent a rapid and transient association with cell membranes. The subcellular localization of PEth was examined using the technique of subcellular fractionation on Percoll density gradients to isolate organelle-enriched fractions from HeLa and 3T3 Li cells. An accumulation of [3H]PEth was measured in the plasma-membrane (PM)-enriched fractions of both HeLa and 3T3 Li cells after incubation with PMA and bradykinin respectively. This was accompanied by a time-dependent accumulation of [3H]PEth in the combined mitochondrial and endoplasmic reticulum (MER)-enriched fractions of both cell lines. PMA was also found to cause translocation of PKC-alpha to both the PM- and MER-enriched fractions in HeLa cells. However, bradykinin stimulated the translocation of PKC-alpha to the PM-enriched fractions only of 3T3 Li cells. The results show that PLD activation leads to the accumulation of PEth in both the PM and MER fractions. We therefore propose that either bradykinin activates a PM-associated PLD and the PLD reaction product is rapidly translocated to other membrane systems or it activates an MER-associated PLD by a mechanism that does not involve PKC-alpha.

3T3 Cells↗

PubMed1995

Activation of mitogen-activated protein kinase by arachidonic acid in rat liver epithelial WB cells by a protein kinase C-dependent mechanism.

Arachidonic acid (20:4(n-6)), which is released by cells responding to a wide range of stimuli, may play an important role in intracellular signaling. We now report that incubation of WB cells with 20:4(n-6) resulted in the appearance of several tyrosine-phosphorylated cytosolic proteins. Two of the phosphotyrosine-containing proteins, migrating in SDS-polyacrylamide gels of approximately 43 and 45 kDa, corresponded in mobility to phosphorylated species of the 42- and 44-kDa mitogen-activated protein kinase (MAPK) isoforms. Immunoblots of soluble fractions from unstimulated WB cells with anti-MAPK antibodies revealed the presence of the 42- and 44-kDa isoforms of MAPK. Upon incubation with 20:4(n-6), the mobility of both isoforms was retarded, consistent with their activation by phosphorylation. Chromatography of soluble fractions from these cells on Mono Q columns revealed early and late eluting peaks of myelin basic protein kinase activity, which contained the 42- and 44-kDa MAPK isoforms, respectively. Activation of MAPK was transient, peaking at 5 min, and was detectable at 5 microM 20:4(n-6). Further studies into the mechanisms by which MAPK was activated by 20:4(n-6) strongly suggested the involvement of protein kinase C (PKC). Not only did incubation of WB cells with 20:4(n-6) result in the translocation of PKC alpha, delta, and epsilon to a particulate fraction, it was found that the fatty acid failed to activate MAPK in cells pretreated for 26 h with phorbol 12-myristate 13-acetate, which depleted WB cells of PKC alpha, delta and epsilon. In addition, fatty acids of the n-3 series were effective activators of MAPK. The present study, to our knowledge, is the first to report that polyunsaturated fatty acids can cause the activation of MAPK.

Animals↗

PubMed1992

Basal and phorbol-ester-stimulated turnover of phosphatidylcholine in HeLa cells involve different pathways.

HeLa cells prelabelled with [3H]lysoplatelet-activating factor (lyso-PAF) accumulated phosphatidic acid (PtdOH) when incubated in the presence of either propranolol (an inhibitor of PtdOH phosphohydrolase) or phorbol ester. In the presence of ethanol, phorbol ester but not propranolol stimulated the accumulation of phosphatidylethanol, an index of phospholipase D activity. Incubation of cells with [3H]lyso-PAF led to a rapid accumulation of label in diacylglycerol (DG) followed by a delayed accumulation in PtdOH. It is concluded that propranolol-induced PtdOH accumulation is derived from DG by DG kinase and does not involve phospholipase D.

Cell Membrane↗

PubMed1991

Phorbol ester-stimulated hydrolysis of phosphatidylcholine and phosphatidylethanolamine by phospholipase D in HeLa cells. Evidence that the basal turnover of phosphoglycerides does not involve phospholipase D.

12-O-Tetradecanoylphorbol-13-acetate (TPA) stimulated the release of [3H]ethanolamine from HeLa cells prelabeled with [3H]ethanolamine within 2 min, and of [3H]choline from cells prelabeled with [3H]choline after a lag of 10-20 min. This result suggests that TPA activates phospholipase D. Propranolol alone or propranolol plus TPA stimulated phosphatidic acid (PA) labeling in cells prelabeled with [3H]hexadecanol. In the presence of ethanol, TPA stimulated the accumulation of labeled phosphatidylethanol (PEth); no PEth was formed in the absence of TPA. TPA-dependent PEth accumulation was not observed in cells pretreated with TPA to down-regulate protein kinase C, whereas propranolol-induced accumulation of PA was unaffected by TPA pretreatment. Incubation of prelabeled cells with propranolol alone caused a rapid loss of label and phospholipid mass from both phosphatidylethanolamine and phosphatidylcholine (PC) together with an accumulation of PA and phosphatidylinositol plus phosphatidylserine. When [3H]hexadecanol-prelabeled cells were pulse labeled with 32P to label nucleotide pools, propranolol induced the accumulation of both 3H- and 32P-labeled PA. When cells were prelabeled with lyso-PC double labeled with 3H and 32P, and incubated with propranolol, only 3H-labeled PA accumulated, indicating that the pathways involved in the basal turnover of PC resulted in the loss of 32P from the lipid. These results suggest that the basal turnover of phosphatidylethanolamine and PC involves the sequential actions of phospholipase C, diglyceride kinase, and PA phosphohydrolase.

Choline↗