Morphological aspects of type II alveolar pneumocytes following treatment with puromycin in vivo

Ultrastructural modifications of type II pneumocytes (PNM-II) in mice were analysed 125 and 155 minutes after puromycin treatment (12 mg/100 gm at 0, 30, 60 and 90 minutes). A quantitative evaluation of the cell compartments was carried out and the inhibition of protein synthesis in PNM-II was monitored by light microscopic radioautography, following 3H-leucine injection. In electron micrographs, following a 125-minute puromycin treatment, the number and size of lamellar bodies, the precursors of lung surfactant material appeared markedly reduced. The multivesicular bodies (MVB), which are normally very frequent in PNM-II, had almost completely disappeared, as had composite bodies. Golgi saccules were dilated, while the area occupied by Golgi vesicles was enlarged. Observations following the 155-minute puromycin treatment showed a strong enhancement of these modifications. Smooth and coated vesicles of the Golgi area, as well as peroxisomes, did not appear modified by puromycin. Elongated zones of autophagy were more prevalent after 125-minute treatment than after the 155-minute one. Small bodies were frequently observed in the cytoplasm, near the Golgi zone. They were bounded by a smooth membrane and contained tiny vesicles and/or electron-dense lamellae similar to those present within the lamellar bodies. Parallel membranes formed folds, some of them in continuity with lamellar bodies, thus encircling portions of cytoplasm. These structures, which were few in number in controls, were very frequently observed in treated cells, mainly after the 125-minute treatment. These extensive alterations of PNM-II morphology appeared to be related to a disturbed production of pulmonary surfactant.     

Spatio-temporal aspects, pathways and actions of Ca(2+) in surfactant secreting pulmonary alveolar type II pneumocytes

The type II cell of the pulmonary alveolus is a polarized epithelial cell that secretes surfactant into the alveolar space by regulated exocytosis of lamellar bodies (LBs). This process consists of multiple sequential steps and is correlated to elevations of the cytoplasmic Ca(2+) concentration ([Ca(2+)](c)) required for extended periods of secretory activity. Both chemical (purinergic) and mechanical (cell stretch or exposure to an air-liquid interface) stimuli give rise to complex Ca(2+) signals (such as Ca(2+) peaks, spikes and plateaus) that differ in shape, origin and spatio-temporal behavior. This review summarizes current knowledge about Ca(2+) channels, including vesicular P2X4 purinoceptors, in type II cells and associated signaling cascades within the alveolar microenvironment, and relates stimulus-dependent activation of these pathways with distinct stages of surfactant secretion, including pre- and postfusion stages of LB exocytosis.     

The effect of anti-oxidants and medium composition on isolation and culture of alveolar type II pneumocytes

Alveolar type II pneumocytes were isolated from adult male rabbits and were placed in primary culture. The presence of anti-oxidants throughout the isolation procedure, particularly ascorbic acid and glutathione, was found to enhance in vitro attachment efficiency of cells. The use of a culture medium substituting D-valine for L-valine also significantly enhanced attachment efficiency. Although these cells do not ordinarily proliferate in culture, a low-serum medium containing insulin, transferrin, selenium and hydrocortisone allowed limited proliferation in addition to promoting dome formation in culture.     

The alveolar pores of Kohn in young postnatal rat lungs and their relation with type II pneumocytes.

In order to obtain more information on the development, morphology and function of the pores of Kohn, the lungs of Wistar rats are studied during their early postnatal period, up to 3 weeks of age, by scanning and transmission electron microscopy. The substantial development of the interalveolar pores on days 14 and 21 coincides with the period of septal rearrangement when secondary interalveolar septa become lengthened and thinner. The high frequency of transseptal type II pneumocytes from day 7 onwards, and their typical localization near the pores of Kohn at this period of lung development especially suggests that type II pneumocytes are engaged in the formation of the pores of Kohn. During early lung development, the pores of Kohn seem to serve as passageways for alveolar macrophages.     

Biochemical evidence for the presence of an amiloride binding protein in adult alveolar type II pneumocytes.

An amiloride binding protein in adult rat and rabbit alveolar type II (ATII) cells was characterized using three different antibodies against epithelial Na+ channel proteins. We found that 1) polyclonal antibodies raised against epithelial Na+ channel proteins from bovine kidney cross-react with a 135-kDa protein in ATII membrane vesicles on Western blots; 2) using the photoreactive amiloride analog, 2'-methoxy-5'-nitrobenzamil (NMBA), in combination with anti-amiloride antibodies, we found that NMBA specifically labeled the same M(r) protein; and 3) monoclonal anti-idiotypic antibodies directed against anti-amiloride antibodies also recognized this same M(r) protein on Western blots. We also demonstrated a low benzamil affinity binding site (apparent Kd = 370 nM) in rabbit ATII cell membranes and both high and low benzamil affinity binding sites (apparent Kd = 6 nM and 230 nM) in bovine kidney membranes using [3H]Br-benzamil as a ligand. Pharmacological inhibitory profiles for displacing bound [3H]Br-benzamil were also different between ATII cells and bovine kidneys. These observations indicate that adult ATII pneumocytes express a population of epithelial Na+ channels having a low affinity to benzamil and amiloride and a pharmacological inhibitory profile different from that in bovine kidney.     

Acetaminophen decreases intracellular glutathione levels and modulates cytokine production in human alveolar macrophages and type II pneumocytes in vitro

Recent epidemiological observations suggest that acetaminophen (paracetamol) may contribute to asthma morbidity. Impaired endogenous antioxidant defences may have a role in the pathogenesis of a number of inflammatory pulmonary diseases, including asthma. We studied the effect of acetaminophen on the intracellular level of reduced glutathione (GSH) with and without inhibitors of cytochrome P450 or prostaglandin H synthetase, and TNF-alpha, IL-6 and IL-8 protein production in human alveolar macrophages and type II pneumocytes in vitro. Following a 20 h incubation with acetaminophen, cytotoxicity was apparent from > or = 5 and > or = 10 mM in macrophages and type II pneumocytes, respectively. A time- and concentration-dependent decrease of intracellular GSH occurred after acetaminophen (0.05-1 mM) exposure (1-4 h) in pulmonary macrophages (up to 53%) and type II pneumocytes (up to 34%). Diethyldithiocarbamic acid, potassium ethyl xanthate, and indomethacin decreased significantly acetaminophen-induced GSH depletion in the two cell types tested, suggesting the involvement of cytochrome P450 (mainly CYP2E1) and/or prostaglandin H synthetase. In macrophages, acetaminophen decreased the secretion of TNF-alpha (at 4 and 24 h, concentration-related) and IL-6 (at 24 h, at 0.1 mM), and did not affect significantly IL-8 production. These in vitro observations demonstrate that clinically relevant concentrations of acetaminophen decreased: (i) intracellular GSH in human pulmonary macrophages and type II pneumocytes and (ii) the secretion of TNF-alpha and possibly IL-6 by human pulmonary macrophages. These findings provide experimental plausibility to the challenging observations that frequent use of APAP may be a risk factor for asthma morbidity.     

VEGF causes pulmonary hemorrhage, hemosiderosis, and air space enlargement in neonatal mice

To determine whether increased levels of VEGF disrupt postnatal lung formation or function, conditional transgenic mice in which VEGF 164 expression was enhanced in respiratory epithelial cells were produced. VEGF expression was induced in the lungs of VEGF transgenic pups with doxycycline from postnatal day 1 through 2 and 6 wk of age. VEGF levels were higher in bronchoalveolar lavage fluid (BALF) and lung homogenates of VEGF transgenic mice compared with endogenous VEGF levels in controls. Neonatal mortality was increased by 50% in VEGF transgenic mice. Total protein content in BALF was elevated in VEGF transgenic mice. Surfactant protein B protein expression was unaltered in VEGF transgenic mice. Although postnatal alveolar and vascular development were not disrupted by VEGF expression, VEGF transgenic mice developed pulmonary hemorrhage, alveolar remodeling, and macrophage accumulation as early as 2 wk of age. Electron microscopy demonstrated abnormal alveolar capillary endothelium in the VEGF transgenic mice. In many locations, the endothelium was discontinuous with segments of attenuated endothelial cells. Large numbers of hemosiderin-laden macrophages and varying degrees of emphysema were observed in adult VEGF transgenic mice. Overexpression of VEGF in the neonatal lung increased infant mortality and caused pulmonary hemorrhage, hemosiderosis, alveolar remodeling, and inflammation.     

Phospholipid-transfer activities in cytosols from lung, isolated alveolar type II cells and alveolar type II cell-derived adenomas.

We have examined phospholipid-transfer activities in cytosols from rat and mouse whole lung, isolated rat alveolar type II cells and alveolar type II cell-derived mouse pulmonary adenomas. We report an enrichment in phosphatidylcholine and phosphatidylglycerol (but not phosphatidylinositol) protein-catalysed transfer in the type II cell and adenoma cytosols compared with the whole-lung cytosols. The activities from these cytosols were resolved using column chromatofocusing, which clearly demonstrated the presence of a phosphatidylcholine-specific transfer protein in each of the four tissues. In addition, two proteins (rat) or three proteins (mouse) catalysing both phosphatidylcholine and phosphatidylglycerol transfer were resolved from whole lung, whereas in both the rat isolated alveolar type II cells and the mouse type II cell-derived adenomas one of these less specific proteins is not present.     

The effect of asbestos and stone-wool fibres on some chemokines and redox system of pulmonary alveolar macrophages and pneumocytes type II

The in vitro effect of stone-wool has been studied in primary cultures of pulmonary alveolar macrophages (AM) and type II pneumocytes (T2) by morphological, biochemical and immunological methods. UICC crocidolite was applied as a positive control. Although stone-wool brought about frustrated phagocytosis, it did not induce serious membrane damage, whereas crocidolite gave rise to very severe membrane alterations. Stone-wool significantly reduced the activity of Cu,Zn/superoxide dismutase (SOD) in alveolar macrophages and significantly decreased the activity of gamma-glutamyl transpeptidase (GGT) in pneumocytes type II. Crocidolite, on the other hand, decreased the activity of all enzymes (glutathione peroxidase - GSH-Px, glutathione reductase - GSH-Rd) of glutathione metabolism in alveolar macrophages. It decreased the activity of all enzymes in pneumocytes type II except for Cu,Zn/SOD. After exposure to stone-wool, the production of inflammatory proteins, macrophage chemoattractant protein-1 (MCP-1) and macrophage inhibitory protein-1alpha (MIP-1alpha) increased in both cultured cells but did not reach the level induced by crocidolite. Although this study provided a useful insight in the toxicity of the stone-wool, we can not draw the conclusions how the intact pulmonary tissue may respond on the exposure to these fibres, exclusively based on the in vitro tests.     

Expression of an epidermal keratin protein in liver of transgenic mice causes structural and functional abnormalities

To examine the role of keratin intermediate filament proteins in cell structure and function, transgenic mice were isolated that express a modified form of the human K14 keratin protein in liver hepatocytes. A modified K14 cDNA (K14.P) sequence was linked downstream of the mouse transthyretin (TTR) gene promoter and enhancer elements to achieve targeted expression in hepatocytes. Hepatocytes expressing high levels of the transgene were found to have abnormal keratin filament networks as detected by indirect immunofluorescence using an antibody specific for the transgene product. Light and electron microscopic level histological analysis of isolated liver tissue showed in many cases degenerative changes that included inflammatory infiltration, ballooning degeneration, an increase in fat containing vacuoles, and glycogen accumulation. These changes were most evident in older mice over four months of age. No indication of typical Mallory body structures were identified at either the light or electron microscopic level. To evaluate secretory function in transgenic livers, bile acid secretion rates were measured in isolated perfused liver and found to be approximately twofold lower than aged-matched controls. These findings indicate that expression of an abnormal keratin in liver epithelial cells in the in vivo setting can alter the structure and function of a tissue and suggest a role of the keratin network in cellular secretion.     

Expression of N-deacetylase/sulfotransferase and 3-O-sulfotransferase in rat alveolar type II cells

Basal laminae beneath alveolar type I cells are suggested to contain highly sulfated heparan sulfate-containing proteoglycans (PGs), and cultured type II cells accumulate highly sulfated matrices. To characterize the regulation of PG synthesis during the transition from type II cells to type I cells, we examined mRNA expression of N-deacetylase/sulfotransferase (NST) and 3-O-sulfotransferase (3-OST), two enzymes specific for heparan sulfate synthesis. We found that both freshly isolated and cultured type II cells expressed NST and 3-OST as shown by in situ hybridization. Expression of surfactant-associated protein A, B, and C mRNAs, determined by semiquantitative PCR, decreased during culture. Expression of type I cell marker T1alpha mRNA increased except in cells cultured on an Engelbrecht-Holm-Swarm gel. Expression of NST was dependent on cell density and matrix and was intense in conditions where cells spread fully, whereas 3-OST expression was unchanged in the conditions examined. The PG sulfation inhibitor sodium chlorate significantly inhibited cultured type II cell spreading, and this inhibition was reversed by sodium sulfate. These results suggest that highly sulfated PGs modified by NST are necessary for the spreading of cells during transdifferentiation of type II cells to mature type I cells.     

Estrogen regulates pulmonary alveolar formation, loss, and regeneration in mice

Lung tissue elastic recoil and the dimension and number of pulmonary gas-exchange units (alveoli) are major determinants of gas-exchange function. Loss of gas-exchange function accelerates after menopause in the healthy aged and is progressively lost in individuals with chronic obstructive pulmonary disease (COPD). The latter, a disease of midlife and later, though more common in men than in women, is a disease to which women smokers and never smokers may be more susceptible than men; it is characterized by diminished lung tissue elastic recoil and presently irremediable alveolar loss. Ovariectomy in sexually immature rats diminishes the formation of alveoli, and estrogen prevents the diminution. In the present work, we found that estrogen receptor-alpha and estrogen receptor-beta, the only recognized mammalian estrogen receptors, are required for the formation of a full complement of alveoli in female mice. However, only the absence of estrogen receptor-beta diminishes lung elastic tissue recoil. Furthermore, ovariectomy in adult mice results, within 3 wk, in loss of alveoli and of alveolar surface area without a change of lung volume. Estrogen replacement, after alveolar loss, induces alveolar regeneration, reversing the architectural effects of ovariectomy. These studies 1) reveal estrogen receptors regulate alveolar size and number in a nonredundant manner, 2) show estrogen is required for maintenance of already formed alveoli and induces alveolar regeneration after their loss in adult ovariectomized mice, and 3) offer the possibility estrogen can slow alveolar loss and induce alveolar regeneration in women with COPD.     

GM-CSF mediates alveolar epithelial type II cell changes, but not emphysema-like pathology, in SP-D-deficient mice

Surfactant protein D (SP-D) is a member of the collectin subfamily of C-type lectins, pattern recognition proteins participating in the innate immune response. Gene-targeted mice deficient in SP-D develop abnormalities in surfactant homeostasis, hyperplasia of alveolar epithelial type II cells, and emphysema-like pathology. Granulocyte/macrophage colony-stimulating factor (GM-CSF) is required for terminal differentiation and subsequent activation of alveolar macrophages, including the expression of matrix metalloproteinases and reactive oxygen species, factors thought to contribute to lung remodeling. Type II cells also express the GM-CSF receptor. Thus we hypothesized GM-CSF might mediate some or all of the cellular and structural abnormalities in the lungs of SP-D-deficient mice. To test this, SP-D (D-G+) and GM-CSF (D+G-) single knockout mice as well as double knockout mice deficient for both SP-D and GM-CSF (D-G-) were analyzed by design-based stereology. Compared with wild type, D-G+ as well as D+G- mice showed decreased alveolar numbers, increased alveolar sizes, and decreased alveolar epithelial surface areas. These emphysema-like changes were present to a greater extent in D-G- mice. D-G+ mice developed type II cell hyperplasia and hypertrophy with increased intracellular surfactant pools, whereas D+G- mice had smaller type II cells with decreased intracellular surfactant pools. In contrast to the emphysematous changes, the type II cell alterations were mostly corrected in D-G- mice. These results indicate that GM-CSF-dependent macrophage activity is not necessary for emphysema development in SP-D-deficient mice, but that type II cell metabolism and proliferation are, either directly or indirectly, regulated by GM-CSF in this model.     

GM-CSF mediates alveolar macrophage proliferation and type II cell hypertrophy in SP-D gene-targeted mice

Mice deficient in surfactant protein (SP) D develop increased surfactant pool sizes and dramatic changes in alveolar macrophages and type II cells. To test the hypothesis that granulocyte-macrophage colony-stimulating factor (GM-CSF) mediates alveolar macrophage proliferation and activation and the type II cell hypertrophy seen in SP-D null mice, we bred SP-D and GM-CSF gene-targeted mice to obtain littermate double null, single null, and wild-type mice. Bronchoalveolar lavage levels of phospholipid, protein, SP-D, SP-A, and GM-CSF were measured from 1 to 4 mo. There was an approximately additive accumulation of phospholipid, total protein, and SP-A at each time point. Microscopy showed normal macrophage number and morphology in GM-CSF null mice, numerous giant foamy macrophages and hypertrophic type II cells in SP-D null mice, and large but not foamy macrophages and mostly normal type II cells in double null mice. These results suggest that the mechanisms underlying the alveolar surfactant accumulation in the SP-D-deficient and GM-CSF-deficient mice are different and that GM-CSF mediates some of the macrophage and type II cell changes seen in SP-D null mice.     

Investigation of the transport of intact glutathione in human and rat type II pneumocytes

The aim of the study was to investigate whether there is transmembrane transport of intact glutathione ([³H]-GSH, 0.1 μCi) in rat and human type II pneumocytes (T2P), and if this transport might be dependent on the redox state of the extracellular fluid. The T2P were pretreated with acivicin (250 μM) to inhibit γ-glutamyl-transferase activity and with L-buthionine-[SR]-sulfoximine (1 mM) to inhibit intracellular GSH synthesis. After 48 h in culture, initial GSH influx rate was 0.70 ± 0.20 nmol/min/mg protein (37°C) and 0.35 ± 0.04 nmol/min/mg protein (4°C) during the first 5 min in rat T2P. In human T2P, the initial GSH influx rate was 0.36 ± 0.30 nmol/min/mg protein (37°C) and 0.32 ± 0.06 nmol/min/mg protein (4°C) during the first 10 min. Thereafter no further influx was found. The influx of 1 mM GSH in freshly isolated rat and human T2P in suspension was 2.3 ± 0.3 and 1.2 ± 0.3 nmol/mg protein after 15 min at 37°C, and 2.8 ± 0.2 and 1.0 ± 0.3 nmol/mg protein at 4°C, respectively. When GSH influx was studied at different concentrations between 0 and 40 mM, a linear increase without saturation or difference between 37°C and 4°C was found. Preexposure to ouabain had no effect on GSH influx. Efflux of GSH was stimulated and influx inhibited by preexposure of the cells to reduced thiols, while disulphides inhibited efflux and favoured inward uptake. Thus, in human and rat T2P a GSH-carrier exists which operates as an effluxer. At GSH concentrations in the physiological range no uptake is seen, but some uptake can be observed at GSH concentrations above normal physiological levels. The uptake appears to be energy-independent and non-saturable. Efflux of GSH is stimulated and influx inhibited by reduced thiols, while disulphides inhibit the efflux and favour inward uptake. GSH uptake in T2P thus may depend on concentration gradients and driving forces, such as the redox state of the extracellular fluid.     

Differences in basement membrane-associated microdomains of type I and type II pneumocytes in the rat and rabbit lung

The basement membrane-associated microdomains of type I pneumocytes in rat and rabbit pulmonary alveoli were found to be uniquely different from those of type II pneumocytes in the specific distribution of cytochemically detectable sulfate esters as demonstrated with the high iron diamine (HID) technique at the electron microscopic level. Aldehyde-fixed frozen or Vibratome sections of neonatal and adult lungs were treated with a mixture of the meta and para isomers of N,N-dimethyl-phenylenediamine-HCl in the presence of ferric chloride, which at low pH (1.0) has been previously shown to be highly specific for sulfate esters of glycosaminoglycans and glycoproteins. Reaction product was subsequently enhanced with a thiocarbohydrazide-silver proteinate, postembedding sequence for electron microscopy. Samples of lung parenchyma treated in this fashion were observed to have discrete, electron-dense silver grains associated with the various microanatomical components of pulmonary basement membranes. In the region of the alveolar basement membrane, the lamina rara externa associated with type I cells was observed to contain an abundance of regularly disposed, cytochemically detectable sulfate esters, while the lamina densa and lamina rara interna were diffusely and sparsely reactive by comparison. Quantitatively, 62% of all reactive sites found in the basement membrane region of type I cells were localized in the lamina rara externa. By contrast, the lamina rara externa of type II cells had less than half as many reactive foci indicative of sulfate esters as the same region of type I cell basement membranes. HID-reactive sulfate esters were found evenly distributed within the laminae associated with the basement membrane of type II cells. This cytochemically detectable difference in the sulfate ester composition of basement membrane-associated sulfate ester composition of basement membrane-associated microdomains of type I compared with that of type II pneumocytes may be highly significant when considering known patterns of epithelial renewal in pulmonary alveoli. Since type II cells are known to divide and either remain type II cells or differentiate into type I cells, regional differences in the molecular composition of the alveolar basement membranes and their associated structures may be key determinants of cell-specific processes of cytodifferentiation in the pulmonary alveolus.     

Association of chlorphentermine with phospholipids in rat alveolar lavage materials, alveolar macrophages and type II cells

Administration of chlorphentermine to rats leads to an increase in the phospholipid content of pulmonary surfactant materials and alveolar macrophages. It is known that this drug binds to pure phospholipids and prevents their degradation by phospholipases. Therefore, experiments were carried out to determine if chlorphentermine binds to surfactant phospholipids in vitro and to measure the in vivo association of drug with phospholipids in alveolar lavage materials from rats injected with [14C]chlorphentermine. The presence of chlorphentermine in alveolar macrophages, type II cells and other small pneumocytes (a population of lung cells which does not include alveolar macrophages or type II cells) from treated animals was also assessed. Binding of the drug to surfactant phospholipids, as measured with the fluorescent probe, 1-anilino-8-naphthalene sulfonate, occurs in vitro and does not differ in various subfractions of alveolar lavage materials isolated by differential centrifugation. Following daily administration of chlorphentermine to rats for 3 days, the drug appears to be associated with surfactant phospholipids such that the molar ratio is 1:100 (chlorphentermine/phospholipid). Chlorphentermine is also associated with alveolar macrophages (molar ratio, 1:18) and type II cells (molar ratio, 1:33). Not much drug is associated with the population of other lung cells (molar ratio, 1:333). In alveolar macrophages, approx. 70% of the drug seems to be bound to phospholipid and/or sequestered in subcellular organelles. However, only 20% of the chlorphentermine is bound and/or sequestered in type II cells. The results of these experiments suggest that following chlorphentermine administration, the drug is associated with phospholipids in acellular pulmonary lavage materials, alveolar macrophages and type II cells. This drug-phospholipid interaction may impair phospholipid degradation and lead to a phospholipidosis in surfactant materials and alveolar macrophages.     

Ultrastructural immunogold localization of prostaglandin endoperoxide synthase (cyclooxygenase) to non-membrane-bound cytoplasmic lipid bodies in human lung mast cells, alveolar macrophages, type II pneumocytes, and neutrophils.

Lipid bodies are non-membrane-bound, lipid-rich cytoplasmic inclusions that occur in many mammalian cell types. Because lipid bodies are more prominent in cells associated with inflammation and are repositories of arachidonyl-phospholipids, a role for lipid bodies in the oxidative metabolism of arachidonic acid to form eicosanoids has been suggested. To evaluate further whether lipid bodies, in addition to serving as non-membranous sources of substrate arachidonate, are involved in eicosanoid formation, we used cells isolated from human lung to investigate the intracellular localization of prostaglandin endoperoxide (PGH) synthase (cyclooxygenase), the key initial, rate-limiting enzyme in the formation of prostaglandins and thromboxanes. Isolated lung cells containing a mixture of mast cells, alveolar macrophages, Type II alveolar pneumocytes, and neutrophils from short-term cultures were fixed in suspension in a dilute aldehyde mixture, post-fixed in osmium tetroxide, stained en bloc with uranyl acetate, dehydrated in a graded series of alcohols, and embedded in Epon. A post-embedding immunogold procedure was used with a primary PGH synthase monoclonal antibody and 20-nm gold-conjugated secondary antibody to demonstrate enzyme locations. Specificity controls were also done. We found PGH synthase in lipid bodies of human lung mast cells, alveolar macrophages, Type II alveolar pneumocytes, and neutrophils. Specific secretory and lysosomal granules and plasma membranes did not express PGH synthase. Specificity controls, including omission of the primary antibody or substitution with an irrelevant antibody, were negative. Absorption of the specific PGH synthase antibody with purified solid-phase PGH synthase resulted in a marked reduction of label in lipid bodies of all four cell types. These findings establish the presence of PGH synthase in lipid bodies of human lung mast cells, alveolar macrophages, Type II alveolar pneumocytes, and neutrophils and, in concert with previous studies, suggest that these cytoplasmic lipid-rich organelles may be non-membrane sites of eicosanoid formation.     

Phenotype of palmitic acid transport and of signalling in alveolar type II cells from E/H-FABP double-knockout mice: contribution of caveolin-1 and PPARgamma

Based on the assumption that fatty-acid-binding proteins (FABPs) of the epidermal-type (E-FABP) and heart-type (H-FABP) in murine alveolar type II (TII) cells mediate the synthesis of dipalmitoyl phosphatidylcholine (DPPC), the main surfactant phospholipid, we analysed TII cells isolated from wild-type (wt) and E/H-FABP double-knockout (double-ko) mice. Application of labelled palmitic acid to these cells revealed a drop in uptake, beta-oxidation, and incorporation into neutral lipids and total phosphatidylcholine (PC) of TII cells from double-ko mice. Whereas incorporation of labelled palmitic acid into DPPC remained unchanged, degradation studies demonstrated a substantial shift in DPPC synthesis from de novo to reacylation. In addition, increased expression of mRNAs and proteins of caveolin-1 and PPARgamma, and an increase of the mRNA encoding fatty acid translocase (FAT) was observed in the double-ko phenotype. As caveolin-1 interacted with PPARgamma, we assumed that FAT, caveolin-1, and PPARgamma form a signalling chain for fatty acid or drug. Consequently, PPARgamma-selective pioglitazone was added to the diet of double-ko mice. We found that further activation of PPARgamma could 'heal' the E/H-FABP double-ko effect in these TII cells as transport and utilisation of labelled palmitic acid restored a wt phenocopy. This indicated that E-FABP and/or H-FABP are involved in the mediation of DPPC synthesis in wt TII cells.