ABSTRACT
PURPOSE: In the event of failed tracheostomy decannulation, patients might have a tragic course of events. We retrospectively evaluated our stepwise tracheostomy decannulation program and examined its safety. METHODS: A 12-year retrospective study of pediatric patients was conducted. The decannulation program was performed on patients who had airway patency by laryngobronchoscopy and whose cannula could be capped during the day. A stepwise decannulation program was performed: continuous 48-h capping trial during hospitalization (Phase 1), removal of the tracheostomy tube for 48 h during hospitalization (Phase 2), and outpatient observation (Phase 3). If a persistent tracheocutaneous fistula existed, the fistula was closed by surgery (Phase 4). RESULTS: The 77 patients in the study underwent 86 trials. The age at the first time of the decannulation program was 6.5 ± 3.6 years. Sixteen trials failed (18.6%): 8 trials in Phase 1, 2 trials in Phase 2, 4 trials in Phase 3, and 2 trials in Phase 4. Most decannulation failures were due to desaturation in Phase 1/2 and dyspnea in Phase 3/4. The time to reintubation after decannulation was 15-383 days in Phase 3/4. CONCLUSIONS: Patients could fail at every phase of the program, suggesting that a stepwise decannulation program contributes to safety.
Subject(s)
Outpatients , Tracheostomy , Child , Child, Preschool , Humans , Hospitalization , Retrospective Studies , Trachea , Tracheostomy/adverse effects , Clinical Trials as Topic , CatheterizationABSTRACT
Using our newly developed ultrafast camera described in the companion paper, we reduced the data acquisition periods required for photoactivation/photoconversion localization microscopy (PALM, using mEos3.2) and direct stochastic reconstruction microscopy (dSTORM, using HMSiR) by a factor of ≈30 compared with standard methods, for much greater view-fields, with localization precisions of 29 and 19 nm, respectively, thus opening up previously inaccessible spatiotemporal scales to cell biology research. Simultaneous two-color PALM-dSTORM and PALM-ultrafast (10 kHz) single fluorescent-molecule imaging-tracking has been realized. They revealed the dynamic nanoorganization of the focal adhesion (FA), leading to the compartmentalized archipelago FA model, consisting of FA-protein islands with broad diversities in size (13-100 nm; mean island diameter ≈30 nm), protein copy numbers, compositions, and stoichiometries, which dot the partitioned fluid membrane (74-nm compartments in the FA vs. 109-nm compartments outside the FA). Integrins are recruited to these islands by hop diffusion. The FA-protein islands form loose ≈320 nm clusters and function as units for recruiting FA proteins.
Subject(s)
Focal Adhesions , Molecular Dynamics Simulation , Diffusion , Focal Adhesions/metabolism , Integrins/metabolism , Single Molecule Imaging , Cell BiologyABSTRACT
The number and subunit compositions of AMPA receptors (AMPARs), hetero- or homotetramers composed of four subunits GluA1-4, in the synapse is carefully tuned to sustain basic synaptic activity. This enables stimulation-induced synaptic plasticity, which is central to learning and memory. The AMPAR tetramers have been widely believed to be stable from their formation in the endoplasmic reticulum until their proteolytic decomposition. However, by observing GluA1 and GluA2 at the level of single molecules, we find that the homo- and heterotetramers are metastable, instantaneously falling apart into monomers, dimers, or trimers (in 100 and 200 ms, respectively), which readily form tetramers again. In the dendritic plasma membrane, GluA1 and GluA2 monomers and dimers are far more mobile than tetramers and enter and exit from the synaptic regions. We conclude that AMPAR turnover by lateral diffusion, essential for sustaining synaptic function, is largely done by monomers of AMPAR subunits, rather than preformed tetramers.
Subject(s)
Neuronal Plasticity , Neurons/metabolism , Receptors, AMPA/metabolism , Synapses/metabolism , Animals , CHO Cells , Cell Membrane/metabolism , Cricetulus , Dendrites/metabolism , Diffusion , HEK293 Cells , Humans , Mice , Microscopy, Fluorescence , Patch-Clamp Techniques , Single Molecule ImagingABSTRACT
Prion proteins (PrPc) are receptors for amyloid ß 1-42 (Aß1-42) oligomers, but we do not know the impact of Aß1-42 binding to PrPc on the interaction of membrane-bound PrPc with molecules that regulate downstream biological pathways. Stability of the PrPc dimeric complex and subsequent intermolecular interactions with membranous or cytoplasmic molecules are important for physiological functions of PrPc including neuroprotection. The principal aim of this study was to determine whether homodimer lifetime of PrPc is affected by the presence of Aß1-42 oligomers. Single-molecule imaging analysis was carried out by total internal reflection fluorescence microscopy in PrPc-transfected CHO-K1 cells in the absence or presence of characterized Aß1-42 oligomers. The contribution of different Aß1-42 oligomer conformations to Alzheimer's disease pathophysiology and to the associated neurotoxicity is unknown. To be precise, with the oligomeric species used in our study, we biochemically analyzed the molecular weight of oligomers formed from Aß1-42 monomers under our experimental conditions. The lifetime of PrPc homodimers was 210 ms, and in the presence of Aß1-42 oligomers, the lifetime was significantly reduced (to 92 ms). The reduction of PrPc homodimer lifetime by Aß1-42 oligomers may impair PrPc-mediated downstream neuroprotective signaling.
Subject(s)
Amyloid beta-Peptides/metabolism , Peptide Fragments/metabolism , PrPC Proteins/metabolism , Amyloid beta-Peptides/chemistry , Animals , CHO Cells , Cell Membrane/metabolism , Cell Membrane/pathology , Cell Survival/physiology , Cricetulus , Microscopy, Fluorescence , Molecular Imaging , Molecular Weight , Neuroprotection/physiology , Peptide Fragments/chemistry , PrPC Proteins/chemistry , Protein Binding , Protein Multimerization , Protein StabilityABSTRACT
The central mechanism for the transmission of the prion protein misfolding is the structural conversion of the normal cellular prion protein to the pathogenic misfolded prion protein, by the interaction with misfolded prion protein. This process might be enhanced due to the homo-dimerization/oligomerization of normal prion protein. However, the behaviors of normal prion protein in the plasma membrane have remained largely unknown. Here, using single fluorescent-molecule imaging, we found that both prion protein and Thy1, a control glycosylphosphatidylinositol-anchored protein, exhibited very similar intermittent transient immobilizations lasting for a few seconds within an area of 24.2 and 3.5 nm in diameter in CHO-K1 and hippocampal neurons cultured for 1- and 2-weeks, respectively. Prion protein molecules were immobile during 72% of the time, approximately 1.4× more than Thy1, due to prion protein's higher immobilization frequency. When mobile, prion protein diffused 1.7× slower than Thy1. Prion protein's slower diffusion might be caused by its transient interaction with other prion protein molecules, whereas its brief immobilization might be due to temporary association with prion protein clusters. Prion protein molecules might be newly recruited to prion protein clusters all the time, and simultaneously, prion protein molecules in the cluster might be departing continuously. Such dynamic interactions of normal prion protein molecules would strongly enhance the spreading of misfolded prion protein.
Subject(s)
Cell Membrane/metabolism , Glycosylphosphatidylinositols/chemistry , Prion Proteins/metabolism , Thy-1 Antigens/metabolism , Animals , CHO Cells , Cell Membrane/chemistry , Cells, Cultured , Cricetinae , Cricetulus , Diffusion , Fluorescent Dyes/chemistry , Glycosylphosphatidylinositols/metabolism , Hippocampus/cytology , Hippocampus/metabolism , Microscopy, Fluorescence , Prion Proteins/chemistry , Rats , Rats, Wistar , Thy-1 Antigens/chemistryABSTRACT
The location and number of neurotransmitter receptors are dynamically regulated at postsynaptic sites. However, currently available methods for visualizing receptor trafficking require the introduction of genetically engineered receptors into neurons, which can disrupt the normal functioning and processing of the original receptor. Here we report a powerful method for visualizing native α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors (AMPARs) which are essential for cognitive functions without any genetic manipulation. This is based on a covalent chemical labelling strategy driven by selective ligand-protein recognition to tether small fluorophores to AMPARs using chemical AMPAR modification (CAM) reagents. The high penetrability of CAM reagents enables visualization of native AMPARs deep in brain tissues without affecting receptor function. Moreover, CAM reagents are used to characterize the diffusion dynamics of endogenous AMPARs in both cultured neurons and hippocampal slices. This method will help clarify the involvement of AMPAR trafficking in various neuropsychiatric and neurodevelopmental disorders.
Subject(s)
Hippocampus/metabolism , Neurons/metabolism , Receptors, AMPA/metabolism , Animals , HEK293 Cells , Hippocampus/cytology , Humans , In Vitro Techniques , Indicators and Reagents/chemistry , Mice , Mice, Inbred ICR , Rats , Rats, Sprague-DawleyABSTRACT
The mechanisms by which the diffusion rate in the plasma membrane (PM) is regulated remain unresolved, despite their importance in spatially regulating the reaction rates in the PM. Proposed models include entrapment in nanoscale noncontiguous domains found in PtK2 cells, slow diffusion due to crowding, and actin-induced compartmentalization. Here, by applying single-particle tracking at high time resolutions, mainly to the PtK2-cell PM, we found confined diffusion plus hop movements (termed "hop diffusion") for both a nonraft phospholipid and a transmembrane protein, transferrin receptor, and equal compartment sizes for these two molecules in all five of the cell lines used here (actual sizes were cell dependent), even after treatment with actin-modulating drugs. The cross-section size and the cytoplasmic domain size both affected the hop frequency. Electron tomography identified the actin-based membrane skeleton (MSK) located within 8.8 nm from the PM cytoplasmic surface of PtK2 cells and demonstrated that the MSK mesh size was the same as the compartment size for PM molecular diffusion. The extracellular matrix and extracellular domains of membrane proteins were not involved in hop diffusion. These results support a model of anchored TM-protein pickets lining actin-based MSK as a major mechanism for regulating diffusion.
Subject(s)
Actin Cytoskeleton , Cell Membrane/metabolism , Phospholipids/chemistry , Receptors, Transferrin/chemistry , Animals , Cell Line , Diffusion , Humans , Models, Biological , Potoroidae , RatsABSTRACT
Advanced single-molecule fluorescent imaging was applied to study the dynamic organization of raft-associated glycosylphosphatidylinositol-anchored proteins (GPI-APs) in the plasma membrane and their stimulation-induced changes. In resting cells, virtually all of the GPI-APs are mobile and continually form transient (~200 ms) homodimers (termed homodimer rafts) through ectodomain protein interactions, stabilized by the presence of the GPI-anchoring chain and cholesterol. Heterodimers do not form, suggesting a fundamental role for the specific ectodomain protein interaction. Under higher physiological expression conditions , homodimers coalesce to form hetero- and homo-GPI-AP oligomer rafts through raft-based lipid interactions. When CD59 was ligated, it formed stable oligomer rafts containing up to four CD59 molecules, which triggered intracellular Ca(2+) responses that were dependent on GPI anchorage and cholesterol, suggesting a key part played by transient homodimer rafts. Transient homodimer rafts are most likely one of the basic units for the organization and function of raft domains containing GPI-APs.
Subject(s)
Glycosylphosphatidylinositols/metabolism , Membrane Microdomains , CD59 Antigens/metabolism , Dimerization , Fluorescence Resonance Energy TransferABSTRACT
The focal adhesion (FA) is an integrin-based structure built in/on the plasma membrane, mechanically linking the extracellular matrix with the termini of actin stress fibers, providing key scaffolds for the cells to migrate in tissues. The FA was considered as a micron-scale, massive assembly of various proteins, although its formation and decomposition occur quickly in several to several 10 s of minutes. The mechanism of rapid FA regulation has been a major mystery in cell biology. Here, using fast single fluorescent-molecule imaging, we found that transferrin receptor and Thy1, non-FA membrane proteins, readily enter the FA zone, diffuse rapidly there, and exit into the bulk plasma membrane. Integrin ß3 also readily enters the FA zone, and repeatedly undergoes temporary immobilization and diffusion in the FA zone, whereas approximately one-third of integrin ß3 is immobilized there. These results are consistent with the archipelago architecture of the FA, which consists of many integrin islands: the membrane molecules enter the inter-island channels rather freely, and the integrins in the integrin islands can be rapidly exchanged with those in the bulk membrane. Such an archipelago architecture would allow rapid FA formation and disintegration, and might be applicable to other large protein domains in the plasma membrane.