Heide Wissel

HDL is the major source of vitamin E for type II pneumocytes.

The alveolar surfactant is a prime target of reactive oxygen species present in air. Alveolar surfactant is supplemented with vitamin E during its assembly in type II pneumocytes. However, it is unknown which of the lipoproteins supply type II pneumocytes with vitamin E. The measurement of the uptake kinetics indicates that HDL might be the primary source of the vitamin E uptake by type II pneumocytes. Vitamin E depletion of rats caused an increase of vitamin E uptake by isolated type II pneumocytes from HDL but not from LDL or VLDL. We demonstrated that type II pneumocytes express the scavenger receptor class B type 1 (SR-B1), an HDL-specific receptor. Vitamin E depletion caused an increased expression of SR-B1 by a post-transcriptional mechanism. The increased vitamin E uptake from HDL and the increased expression of the SR-B1 were reversed by refeeding the vitamin. We propose that HDL is the primary source of vitamin E for type II pneumocytes. The rate of uptake of vitamin E by this cell type might be regulated by the expression of SR-B1.

Intratracheal perfluorocarbons diminish LPS-induced increase in systemic TNF-α

Perfluorocarbons (PFC) reduce the production of various inflammatory cytokines, including TNF-alpha. The anti-inflammatory effect is not entirely understood. If anti-inflammatory properties are caused by a mechanical barrier, PFC in the alveoli should have no effect on the inflammatory response to intravenous LPS administration. To test that hypothesis, rats (n=31) were administered LPS intravenously and were either spontaneously breathing (Spont), conventionally ventilated (CMV), or receiving partial liquid ventilation (PLV). Serum concentration of TNF-alpha was measured. The pulmonary expressions of TNF-alpha and TNF-alpha receptor 1 protein and of TNF-alpha and ICAM-1 mRNA were determined. LPS caused a significant (P<0.001) increase in serum TNF-alpha. Serum TNF-alpha concentration was similar in LPS/Spont (525+/-180 pg/ml) and LPS/CMV (504+/-154 pg/ml) but was significantly (P<0.001) lower in animals of the LPS/PLV group (274+/-101 pg/ml). Immunohistochemical data on TNF-alpha protein expression showed a LPS-induced increase in TNF-alpha and TNF-alpha receptor 1 expression that was diminished by partial liquid ventilation. PCR measurements revealed a lower expression of TNF-alpha and ICAM-1 mRNA in LPS/PLV than in LPS/CMV or LPS/Spont animals. Semiquantitative histological evaluation revealed only minor alveolar inflammation with no significant differences between the groups. Low serum TNF-alpha concentration in PFC-treated animals is most likely explained by a decreased production of TNF-alpha in the lung.

Perfluorocarbons are taken up by isolated type II pneumocytes and influence its lipid synthesis and secretion.

ObjectiveBecause alveoli fill with perfluorocarbons during liquid ventilation, an uptake of perfluorocarbons by type II pneumocytes can be postulated that might affect synthesis and secretion of pulmonary surfactant. The study was performed to answer the following questions: Do isolated type II pneumocytes take up perfluorocarbons? Do perfluorocarbons affect lipid synthesis of type II cells? Do perfluorocarbons change surfactant secretion of type II pneumocytes? DesignControlled experiments that used isolated type II pneumocytes. SettingExperimental laboratory of a university hospital. SubjectsMale Wistar rats. InterventionsTo study perfluorocarbon uptake, isolated type II cells were incubated with fluorescence-labeled perfluorocarbons and examined with a laser scanning microscope. The effect of perfluorocarbons on biosynthesis of phospholipids and triglycerides was measured by incubating cells that were pulse-labeled with [H]-palmitic acid for 30 secs, with two different perfluorocarbons (PF 5080 or RM 101) for 10 mins. The effect of perfluorocarbon incubation on lipid secretion was studied by transmission electron microscopy. To quantify secretion, adherent type II pneumocytes (containing radioactively labeled phospholipids) were incubated with perfluorocarbons, and extra- and intracellular radioactivity was measured. Measurements and Main ResultsWe found a significant uptake of labeled perfluorocarbons into lamellar bodies within 10 mins. Both perfluorocarbon species significantly (p < .05) reduced the biosynthesis of phospholipids when compared with control. Perfluorocarbon incubation did not affect mitochondrial activity, tested by MitoTracker staining. Transmission electron microscopy revealed changes that suggest an increased secretion of surfactant by type II cells. Studies with radioactively labeled surfactant revealed a significantly (p < .01) higher amount of extracellular lipids after RM 101 and PF 5080 treatment (RM 101, 17 ± 7.9%; PF 5080, 9 ± 1.9%) compared with control (5.3 ± 1.9%). ConclusionsOur results suggest that perfluorocarbons are taken up by type II pneumocytes and cause an increased secretion of surfactant, despite a relative reduction in the synthesis of phospholipids.

Perfluorocarbons Decrease Chlamydophila pneumoniae –Mediated Inflammatory Responses of Rat Type II Pneumocytes In Vitro

Chlamydophila pneumoniae alter the expression of Toll-like receptor (TLR) 4 in alveolar type II (ATII)-cells. Subsequently nuclear factor kappaB (NF-κB) is activated and tumor necrosis factor-α (TNF-α) and macrophage inflammatory protein 2 (MIP-2) are produced. Perfluorocarbons (PFC) are beneficial in animals with bacterial pneumonia and reduce production of TNF-α. Using isolated ATII-cells, it was studied whether PFC prevent C. pneumoniae-induced TNF-α and MIP-2 release and what the underlying pathway is. PF5080 preincubation prevented C. pneumoniae-induced secretion of TNF-α (43 ± 10 versus 661 ± 41 pg/mL) and MIP-2 (573 ± 41 versus 4786 ± 502 pg/mL). The C. pneumoniae-induced 2.2-fold increase of TNF-α Receptor 1 expression was reduced by PF5080. C. pneumoniae reduced cytoplasmatic IκBα (3.7 ± 0.3 versus 14 ± 1) and increased NF-κB p65 (31 ± 7.5 versus 3.6 ± 1.1) compared with control. PF5080 prevented NF-κB activation. TLR4 expression was 1.5-fold higher after C. pneumoniae incubation, but remained at control levels after PF5080 pretreatment. After 24 h of C. pneumoniae incubation, in 88 ± 6% of cells bacteria were found in the perinuclear region and in 50% of these cells bacteria adhered to cellular surface. After PF5080 preincubation, C. pneumoniae were in 32 ± 4% attached to and in 5 ± 1% internalized in ATII-cells. Since PF5080 was found in ATII-cell membranes, PF5080 effect could be explained by an alteration of the cellular membrane, preventing activation of the inflammatory cascade.

Kinetics of Surfactantprotein A-specific surfactantresecretion by type II pneumocytes

Background: Surfactant components can be recycled (= reuptake resecretion) by alveolar type II cells. Surfactant protein A is involved in this process.

GTP Binding Proteins are Involved in Receptor Mediated SP-A Transport in Rat Type II Pneumocytes 151

Background: We have identified a 55 kDa membrane protein of rat type II pneumocytes that is involved in SP-A mediated surfactant uptake and recycling.

219 MECHANISM OF SP-A-MEDIA TED SURFACTANT ENDOCYTOSIS BY TYPE II CELLS

AIM: Surfactant protein A (SP-A) enhances surfactant lipid uptake by type II pneumocytes. In the presence of SP-A internalized surfactant lipids are reported to bypass the degradative pathway and are recycled towards lamellar bodies. We wanted to further clarify the role of SP-A in surfactant lipid endocytosis.METHODS: A previously described antibody (2H5) against a type II cell membrane protein which stimulates surfactant lipid uptake by type II cells (Pediatr. Res. 1994, 35: 278) was used in parallel with SP-A to study uptake and intracellular fate of liposomes with surfactant-like composition in rat type II cells.RESULTS: In the presence of 2H5 or SP-A significantly more labeled lipid is internalized in a time- and concentration-dependent fashion by type II cells than in their absence (2H5 2-fold, SP-A 3-fold above control). In cells in solution no difference in the distribution of label in phospholipid classes between control cells and cells incubated with either 2H5 on SP-A was found. In adherent 24 hour-old cells after one hour of incubation 82% of the internalized 3H-label is still associated with PC in control cells vs. 87% in the presence of 2H5 and 94% with SP-A. Surprisingly, inhibition of coated pit formation (uptake pathway for SP-A) by K+-depletion enhanced lipid uptake by type II cells significantly. Also, inhibition of protein kinase C (PKC) (staurosporine 100 nM) enhanced lipid uptak^ by type II cells in the presence of SP-A.CONCLUSIONS: SP-A and 2H5 do quantitatively enhance lipid uptake in type II cells. The subsequent intracellular fate of the PC molecule may depend on the type of assay used. Uptake via coated pits and PKC activation are involved in these processes.