GCN5L1 regulates pulmonary surfactant production by modulating lamellar body biogenesis and trafficking in mouse alveolar epithelial cells

BACKGROUND

The pulmonary surfactant that lines the air-liquid surface within alveoli is a protein-lipid mixture essential for gas exchange. Surfactant lipids and proteins are synthesized and stored in the lamellar body (LB) before being secreted from alveolar type II (AT2) cells. The molecular and cellular mechanisms that regulate these processes are incompletely understood. We previously identified an essential role of general control of amino acid synthesis 5 like 1 (GCN5L1) and the biogenesis of lysosome-related organelle complex 1 subunit 1 (BLOS1) in surfactant system development in zebrafish. Here, we explored the role of GCN5L1 in pulmonary surfactant regulation.

METHOD

GCN5L1 knockout cell lines were generated with the CRISPR/Cas9 system. Cell viability was analyzed by MTT assay. Released surfactant proteins were measured by ELISA. Released surfactant lipids were measured based on coupled enzymatic reactions. Gene overexpression was mediated through lentivirus. The RNA levels were detected through RNA-sequencing (RNA-seq) and quantitative reverse transcription (qRT)- polymerase chain reaction (PCR). The protein levels were detected through western blotting. The cellular localization was analyzed by immunofluorescence. Morphology of the lamellar body was analyzed through transmission electron microscopy (TEM), Lysotracker staining, and BODIPY phosphatidylcholine labeling.

RESULTS

Knocking out GCN5L1 in MLE-12 significantly decreased the release of surfactant proteins and lipids. We detected the downregulation of some surfactant-related genes and misregulation of the ROS-Erk-Foxo1-Cebpα axis in mutant cells. Modulating the activity of the axis or reconstructing the mitochondrial expression of GCN5L1 could partially restore the expression of these surfactant-related genes. We further showed that MLE-12 cells contained many LB-like organelles that were lipid enriched and positive for multiple LB markers. These organelles were smaller in size and accumulated in the absence of GCN5L1, indicating both biogenesis and trafficking defects. Accumulated endogenous surfactant protein (SP)-B or exogenously expressed SP-B/SP-C in adenosine triphosphate-binding cassette transporterA3 (ABCA3)-positive organelles was detected in mutant cells. GCN5L1 localized to the mitochondria and LBs. Reconstruction of mitochondrial GCN5L1 expression rescued the organelle morphology but failed to restore the trafficking defect and surfactant release, indicating specific roles associated with different subcellular localizations.

CONCLUSIONS

In summary, our study identified GCN5L1 as a new regulator of pulmonary surfactant that plays a role in the biogenesis and positioning/trafficking of surfactant-containing LBs.

Borage Oil Enhances Lamellar Body Content and Alters Fatty Acid Composition of Epidermal Ceramides in Essential Fatty Acid-Deficient Guinea Pigs

Borage oil [BO: 40.9% linoleic acid (LNA) and 24.0% γ-linolenic acid (GLA)] reverses disrupted epidermal lipid barrier in essential fatty acid deficiency (EFAD). We determined the effects of BO on lamellar body (LB) content and LNA and GLA incorporation into epidermal ceramide 1 (CER1) and epidermal ceramide 2 (CER2), major barrier lipids. EFAD was induced in guinea pigs by a diet of 6% hydrogenated coconut oil (HCO) for 10 weeks (group HCO) or 8 weeks followed by 6% BO for 2 weeks (group HCO + BO). LB content and LNA and GLA incorporation into CER1 were higher in group HCO + BO than in group HCO. Small but significant levels of LNA, GLA, and their C20-metabolized fatty acids [dihomo-γ-linolenic acid (DGLA) and arachidonic acid (ARA)] were incorporated into CER2, where ARA was detected at a level lower than LNA, but DGLA incorporation exceeded that for GLA in group HCO + BO. Dietary BO enhanced LB content and differential incorporation of GLA into CER1 and DGLA into CER2.

Trafficking of newly synthesized surfactant protein B to the lamellar body in alveolar type II cells

Lung surfactant accumulates in the lamellar body (LB) via not only the secretory (anterograde) pathway but also the endocytic (retrograde) pathway. Our previous studies suggested that the major surfactant components, phosphatidylcholine and surfactant protein A take independent trafficking routes in alveolar type II cells. Thus, trafficking of surfactant protein B (SP-B), a major hydrophobic surfactant apoprotein, should be re-evaluated by a straightforward method. Radiolabeling of cells and subsequent cell fractionation were employed to pursue the sequential trafficking of newly synthesized SP-B in rabbit alveolar type II cells. The LB fraction was prepared by gradient ultracentrifugation. Immunoprecipitation from the culture medium, total cells, and LB fraction was carried out with anti-SP-B antibody. Newly synthesized [³⁵S]-pro-SP-B (~ 42 kDa) was detected in the cells after 1 h. An ~ 8-kDa mature form of [³⁵S]-SP-B was detected in the cells after 3 h and in the LB after 6 h. Mature [³⁵S]-SP-B was predominant in the cells after 24 h, and the dominant portion was present in the LB. In contrast, only a small amount of mature [³⁵S]-SP-B was present in the culture medium. Molecular processing of ~ 42 kDa [³⁵S]-pro-SP-B and transport to the LB was inhibited by brefeldin A, which disassembles the Golgi apparatus. These results suggest that newly synthesized SP-B is sorted to the LB via the Golgi and stored until exocytosis. This pathway is distinct from the pathways reported for phosphatidylcholine and surfactant protein A.

The rate of neonatal respiratory distress syndrome/transient tachypnea in the newborn and the amniotic lamellar body count in twin pregnancies compared with singleton pregnancies

BACKGROUND

Whether or not the period of fetal lung maturity differs between twin and singleton pregnancies has not been clarified. We examined whether or not fetal lung maturity and fetal lung absorption are achieved earlier in twin fetuses than in singleton fetuses.

METHODS

We registered 454 singleton pregnancies and 398 twin pregnancies with no congenital abnormalities affecting the respiratory function or neonatal deaths. All patients were delivered by Caesarean section without labor between 24 and 38 gestational weeks. The amniotic fluid samples were analyzed immediately without centrifugation. A multiple logistic regression analysis was performed to explore the relationship between twin pregnancy and neonatal respiratory distress syndrome and transient tachypnea of the newborn (RDS/TTN).

RESULTS

The rate of RDS/TTN in infants was significantly higher and the lamellar body counts (LBCs) significantly lower in singleton pregnancies than that in twin pregnancies (P < .001). According to a multivariate logistic regression analysis, twin pregnancy (odds ratio, 0.34; 95% confidence interval, 0.22-0.55) was a significant preventive factor for neonatal RDS/TTN.

CONCLUSIONS

We showed that twin fetuses experience more rapid lung maturation and lung fluid absorption than singleton fetuses, as confirmed by the higher LBC values in twin fetuses.

The impact of fertility treatment on the neonatal respiratory outcomes and amniotic lamellar body counts in twin pregnancies

BACKGROUND

To elucidate the impact of fertility treatment on neonatal respiratory outcomes and amniotic lamellar body counts (LBCs) in twin pregnancies.

METHODS

One hundred ninety twin pairs, including 99 dichorionic twin (DCT) and 91 monochorionic twin (MCT) pairs were registered at our institutions. All amniotic fluid samples were obtained from each sac at cesarean section. Samples were analyzed immediately after arrival at the laboratory without centrifugation. We divided the patients into 3 groups: the no therapy group (natural conception), the induced ovulation group (with or without intrauterine insemination), and the assisted reproductive technology (ART) group (in vitro fertilization or intracytoplasmic sperm injection).

RESULTS

No statistically significant associations between the fertility treatment and the rates of neonatal RDS/TTN were observed in the whole study population (odds ratio [OR], 0.95; 95% confidence interval [CI], 0.45-2.00), DCT (OR, 0.86; 95%CI, 0.30-2.47), and MCT (OR, 1.45; 95%CI, 0.41-5.11). In addition, there was no association between the fertility treatment and neonatal RDS/TTN in the propensity score analysis of the whole study population (OR, 1.25; 95%CI, 0.57-2.74).

CONCLUSIONS

None of the individual types of fertility treatment had a direct impact on respiratory disorders such as RDS and TTN in twin infants.

A lamellar body mimetic system for the treatment of oxazolone-induced atopic dermatitis in hairless mice

BACKGROUND

Atopic dermatitis is a common skin disease characterized by a Th2 cell-dominant inflammatory infiltrate, elevated serum IgE levels and impaired epidermal barrier function. It is associated to abnormal epidermal lamellar body secretion, producing alteration in lipid composition and extracellular lamellar membrane organization.

OBJECTIVES

The oxazolone-induced atopic dermatitis in hairless mice was used to evaluate in vivo the effect of the application of a lipid system that mimics the morphology, structure and composition of epidermal lamellar bodies.

METHODS

The skin barrier function was evaluated measuring TEWL and skin hydration in vivo. Inflammation was assessed by analysis of serum IgE levels and histological analysis. The microstructure of the intercellular lipid region was also evaluated before and after treatment.

RESULTS

The skin condition was improved after 10 days of treatment indicated by decreased TEWL, decreased serum IgE levels, reduced epidermal thickness and reduced lymphocyte-dominated infiltrate. However, the treatment did no improve skin hydration.

CONCLUSIONS

The treatment with this lipid system seems to improve the skin condition by reinforcing the barrier function and reducing the skin inflammation. Therefore, the present study provides evidence that this lipid system combining appropriate lipid composition and morphology could be of interest for the development of future treatments for atopic dermatitis.

Risk assessment for neonatal RDS/TTN using gestational age and the amniotic lamellar body count in twin pregnancies

BACKGROUND

The amniotic lamellar body count (LBC) is useful for predicting respiratory distress syndrome (RDS) and transient tachypnea of the newborn (TTN) in twin pregnancies. However, the risk of neonatal respiratory complications varies with gestational age (GA). We herein created a model to predict the risk for RDS and TTN using GA and the LBC in twin pregnancies.

METHODS

Six hundred thirty-two amniotic fluid samples, comprising 169 dichorionic twin (DCT) and 147 monochorionic twin (MCT) gestations, were obtained at Cesarean section. The samples were analyzed immediately without centrifugation. A logistic regression model including the LBC and GA was used to develop the prediction model for RDS/TTN.

RESULTS

There were 101 neonates (16.0%) with RDS/TTN. The GA and LBC were significant independent factors affecting RDS/TTN. According to the logistic regression model, we determined the probability of RDS/TTN given the values of GA and the LBC. The overall diagnostic accuracy for predicting neonatal RDS/TTN using GA and the LBC was higher than the use of the LBC alone.

CONCLUSIONS

GA-specific LBC cutoffs for the risk assessment of neonatal RDS/TTN have been considered to be more accurate in twin pregnancies. Our findings provide valuable, new information for the management of twin pregnancies.

Actin depolymerisation and crosslinking join forces with myosin II to contract actin coats on fused secretory vesicles

In many secretory cells actin and myosin are specifically recruited to the surface of secretory granules following their fusion with the plasma membrane. Actomyosin-dependent compression of fused granules is essential to promote active extrusion of cargo. However, little is known about molecular mechanisms regulating actin coat formation and contraction. Here, we provide a detailed kinetic analysis of the molecules regulating actin coat contraction on fused lamellar bodies in primary alveolar type II cells. We demonstrate that ROCK1 and myosin light chain kinase 1 (MLCK1, also known as MYLK) translocate to fused lamellar bodies and activate myosin II on actin coats. However, myosin II activity is not sufficient for efficient actin coat contraction. In addition, cofilin-1 and α-actinin translocate to actin coats. ROCK1-dependent regulated actin depolymerisation by cofilin-1 in cooperation with actin crosslinking by α-actinin is essential for complete coat contraction. In summary, our data suggest a complementary role for regulated actin depolymerisation and crosslinking, and myosin II activity, to contract actin coats and drive secretion.

Synaptotagmin-7 links fusion-activated Ca²⁺ entry and fusion pore dilation

Ca(2+)-dependent regulation of fusion pore dilation and closure is a key mechanism determining the output of cellular secretion. We have recently described 'fusion-activated' Ca(2+) entry (FACE) following exocytosis of lamellar bodies in alveolar type II cells. FACE regulates fusion pore expansion and facilitates secretion. However, the mechanisms linking this locally restricted Ca(2+) signal and fusion pore expansion were still elusive. Here, we demonstrate that synaptotagmin-7 (Syt7) is expressed on lamellar bodies and links FACE and fusion pore dilation. We directly assessed dynamic changes in fusion pore diameters by analysing diffusion of fluorophores across fusion pores. Expressing wild-type Syt7 or a mutant Syt7 with impaired Ca(2+)-binding to the C2 domains revealed that binding of Ca(2+) to the C2A domain facilitates FACE-induced pore dilation, probably by inhibiting translocation of complexin-2 to fused vesicles. However, the C2A domain hampered Ca(2+)-dependent exocytosis of lamellar bodies. These findings support the hypothesis that Syt7 modulates fusion pore expansion in large secretory organelles and extend our picture that lamellar bodies contain the necessary molecular inventory to facilitate secretion during the exocytic post-fusion phase. Moreover, regulating Syt7 levels on lamellar bodies appears to be essential in order that exocytosis is not impeded during the pre-fusion phase.

Effect of placenta previa on neonatal respiratory disorders and amniotic lamellar body counts at 36-38weeks of gestation

BACKGROUND

Pregnancies with placenta previa are significantly associated with preterm delivery and cesarean section. Therefore particular attention should be paid to the incidence of neonatal respiratory disorders in pregnancies with placenta previa.

AIMS

The purpose of this study is to examine the relationship between placenta previa and neonatal respiratory disorders, including respiratory distress syndrome (RDS) and transient tachypnea of the newborn (TTN), and to evaluate the impact of placenta previa on the amniotic lamellar body count (LBC) values.

METHODS

We analyzed the data from 186 registered elective cesarean cases without fetal or maternal complications at 36-38weeks of gestation. Amniotic fluid samples were analyzed immediately without centrifugation, and the LBC was measured using a platelet channel on the Sysmex XE-2100.

RESULTS

RDS was present in four neonates (2.2%) and TTN in 12 neonates (6.5%). The rate of TTN was significantly higher and the LBC values were significantly lower in the placenta previa group than in the control group (P=0.002 and P=0.024). The adjusted odds ratio for neonatal TTN was 7.20 (95% confidence interval: 6.58-7.88) among females with placenta previa. In placenta previa, warning bleeding was a significant factor protecting against neonatal respiratory disorders (P=0.046).

CONCLUSIONS

Placenta previa in itself is a risk factor for neonatal TTN. When an elective cesarean section is performed in cases with uncomplicated placenta previa, special care should be taken to monitor for neonatal TTN even at 36-38weeks of gestation.

Role of lipids in the formation and maintenance of the cutaneous permeability barrier

The major function of the skin is to form a barrier between the internal milieu and the hostile external environment. A permeability barrier that prevents the loss of water and electrolytes is essential for life on land. The permeability barrier is mediated primarily by lipid enriched lamellar membranes that are localized to the extracellular spaces of the stratum corneum. These lipid enriched membranes have a unique structure and contain approximately 50% ceramides, 25% cholesterol, and 15% free fatty acids with very little phospholipid. Lamellar bodies, which are formed during the differentiation of keratinocytes, play a key role in delivering the lipids from the stratum granulosum cells into the extracellular spaces of the stratum corneum. Lamellar bodies contain predominantly glucosylceramides, phospholipids, and cholesterol and following the exocytosis of lamellar lipids into the extracellular space of the stratum corneum these precursor lipids are converted by beta glucocerebrosidase and phospholipases into the ceramides and fatty acids, which comprise the lamellar membranes. The lipids required for lamellar body formation are derived from de novo synthesis by keratinocytes and from extra-cutaneous sources. The lipid synthetic pathways and the regulation of these pathways are described in this review. In addition, the pathways for the uptake of extra-cutaneous lipids into keratinocytes are discussed. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

Fatty aldehyde and fatty alcohol metabolism: review and importance for epidermal structure and function

Normal fatty aldehyde and alcohol metabolism is essential for epidermal differentiation and function. Long-chain aldehydes are produced by catabolism of several lipids including fatty alcohols, sphingolipids, ether glycerolipids, isoprenoid alcohols and certain aliphatic lipids that undergo α- or ω-oxidation. The fatty aldehyde generated by these pathways is chiefly metabolized to fatty acid by fatty aldehyde dehydrogenase (FALDH, alternately known as ALDH3A2), which also functions to oxidize fatty alcohols as a component of the fatty alcohol:NAD oxidoreductase (FAO) enzyme complex. Genetic deficiency of FALDH/FAO in patients with Sjögren-Larsson syndrome (SLS) results in accumulation of fatty aldehydes, fatty alcohols and related lipids (ether glycerolipids, wax esters) in cultured keratinocytes. These biochemical changes are associated with abnormalities in formation of lamellar bodies in the stratum granulosum and impaired delivery of their precursor membranes to the stratum corneum (SC). The defective extracellular SC membranes are responsible for a leaky epidermal water barrier and ichthyosis. Although lamellar bodies appear to be the pathogenic target for abnormal fatty aldehyde/alcohol metabolism in SLS, the precise biochemical mechanisms are yet to be elucidated. Nevertheless, studies in SLS highlight the critical importance of FALDH and normal fatty aldehyde/alcohol metabolism for epidermal function. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.