ABSTRACT
The P4-ATPases ATP11A and ATP11C function as flippases at the plasma membrane to translocate phosphatidylserine from the outer to the inner leaflet. We herein demonstrated that Atp11a-deficient mouse embryos died at approximately E14.5 with thin-walled heart ventricles. However, the cardiomyocyte- or epiblast-specific Atp11a deletion did not affect mouse development or mortality. ATP11C may have compensated for the function of ATP11A in most of the cell types in the embryo. On the other hand, Atp11a, but not Atp11c, was expressed in the mouse placenta, and the Atp11a-null mutation caused poor development of the labyrinthine layer with an increased number of TUNEL-positive foci. Immunohistochemistry and electron microscopy revealed a disorganized labyrinthine layer with unfused trophoblasts in the Atp11a-null placenta. Human placenta-derived choriocarcinoma BeWo cells expressed the ATP11A and ATP11C genes. A lack of ATP11A and ATP11C eliminated the ability of BeWo cells to flip phosphatidylserine and fuse when treated with forskolin. These results indicate that flippases at the plasma membrane play an important role in the formation of syncytiotrophoblasts in placental development.
Subject(s)
Placenta , Trophoblasts , ATP Binding Cassette Transporter 1 , Adenosine Triphosphatases/metabolism , Animals , Cell Membrane/metabolism , Female , Mice , Phosphatidylserines/metabolism , Placenta/metabolism , Pregnancy , Trophoblasts/metabolismABSTRACT
ATP11A translocates phosphatidylserine (PtdSer), but not phosphatidylcholine (PtdCho), from the outer to the inner leaflet of plasma membranes, thereby maintaining the asymmetric distribution of PtdSer. Here, we detected a de novo heterozygous point mutation of ATP11A in a patient with developmental delays and neurological deterioration. Mice carrying the corresponding mutation died perinatally of neurological disorders. This mutation caused an amino acid substitution (Q84E) in the first transmembrane segment of ATP11A, and mutant ATP11A flipped PtdCho. Molecular dynamics simulations revealed that the mutation allowed PtdCho binding at the substrate entry site. Aberrant PtdCho flipping markedly decreased the concentration of PtdCho in the outer leaflet of plasma membranes, whereas sphingomyelin (SM) concentrations in the outer leaflet increased. This change in the distribution of phospholipids altered cell characteristics, including cell growth, cholesterol homeostasis, and sensitivity to sphingomyelinase. Matrix-assisted laser desorption ionization-imaging mass spectrometry (MALDI-IMS) showed a marked increase of SM levels in the brains of Q84E-knockin mouse embryos. These results provide insights into the physiological importance of the substrate specificity of plasma membrane flippases for the proper distribution of PtdCho and SM.
Subject(s)
ATP Binding Cassette Transporter 1/genetics , ATP-Binding Cassette Transporters/genetics , ATP-Binding Cassette Transporters/metabolism , Neurodegenerative Diseases/genetics , Neurodegenerative Diseases/metabolism , Phosphatidylcholines/metabolism , Point Mutation , ATP Binding Cassette Transporter 1/deficiency , ATP Binding Cassette Transporter 1/metabolism , ATP-Binding Cassette Transporters/chemistry , Adult , Amino Acid Sequence , Amino Acid Substitution , Animals , Brain/diagnostic imaging , Cell Membrane/metabolism , Female , Genes, Lethal , Heterozygote , Humans , Male , Membrane Lipids/metabolism , Mice , Mice, Inbred C57BL , Mice, Inbred ICR , Mice, Mutant Strains , Molecular Dynamics Simulation , Neurodegenerative Diseases/diagnostic imaging , Phospholipid Transfer Proteins/genetics , Phospholipid Transfer Proteins/metabolism , PregnancyABSTRACT
Terahertz (THz) wave detectors are increasingly expected to serve as key components of powerful nondestructive and noncontact inspection tools in a large variety of fields. In contrast to conventional THz detectors based on rigid solid materials, we previously developed an uncooled and bendable THz camera based on the THz-induced photothermoelectric effect of carbon nanotube (CNT) array devices and demonstrated omnidirectional THz imaging of three-dimensional curved samples. Although this development opened a pathway to flexible THz electronics, the physical parameters that determine the performance of the CNT THz camera have not been fully investigated. As a result, the thermal device design has not been optimized in terms of the camera sensitivity and spatial resolution. In this work, we studied the underlying mechanism of the THz-induced photothermoelectric effect of the CNT camera and found physical factors related to the detector performance. Through simulation and experiments, we observed that the detection sensitivity and response time strongly depend on the CNT channel width and film thickness. We further identified that the irradiated wave penetration into the CNT film through the electrode materials deteriorates the detection area, which is directly linked to the camera spatial resolution. By utilizing the improved CNT device design fabricated based on these findings, we eliminated undesired signals generated via thermal diffusion and THz wave penetration and achieved higher-sensitivity THz detection and higher imaging resolution compared to our previously reported THz camera. The presented technologies are expected to contribute to future flexible THz imaging applications and will also be applicable to other types of photothermoelectric devices.
