In-Distribution and Out-of-Distribution Self-Supervised ECG Representation Learning for Arrhythmia Detection.

This paper presents a systematic investigation into the effectiveness of Self-Supervised Learning (SSL) methods for Electrocardiogram (ECG) arrhythmia detection. We begin by conducting a novel analysis of the data distributions on three popular ECG-based arrhythmia datasets: PTB-XL, Chapman, and Ribeiro. To the best of our knowledge, our study is the first to quantitatively explore and characterize these distributions in the area. We then perform a comprehensive set of experiments using different augmentations and parameters to evaluate the effectiveness of various SSL methods, namely SimCRL, BYOL, and SwAV, for ECG representation learning, where we observe the best performance achieved by SwAV. Furthermore, our analysis shows that SSL methods achieve highly competitive results to those achieved by supervised state-of-the-art methods. To further assess the performance of these methods on both In-Distribution (ID) and Out-of-Distribution (OOD) ECG data, we conduct cross-dataset training and testing experiments. Our comprehensive experiments show almost identical results when comparing ID and OOD schemes, indicating that SSL techniques can learn highly effective representations that generalize well across different OOD datasets. This finding can have major implications for ECG-based arrhythmia detection. Lastly, to further analyze our results, we perform detailed per-disease studies on the performance of the SSL methods on the three datasets.

L-alanyl-L-glutamine modified perfusate improves human lung cell functions and extend porcine ex vivo lung perfusion.

BACKGROUND: The clinical application of normothermic ex vivo lung perfusion (EVLP) has increased donor lung utilization for transplantation through functional assessment. To develop it as a platform for donor lung repair, reconditioning and regeneration, the perfusate should be modified to support the lung during extended EVLP. METHODS: Human lung epithelial cells and pulmonary microvascular endothelial cells were cultured, and the effects of Steen solution (commonly used EVLP perfusate) on basic cellular function were tested. Steen solution was modified based on screening tests in cell culture, and further tested with an EVLP cell culture model, on apoptosis, GSH, HSP70, and IL-8 expression. Finally, a modified formula was tested on porcine EVLP. Physiological parameters of lung function, histology of lung tissue, and amino acid concentrations in EVLP perfusate were measured. RESULTS: Steen solution reduced cell confluence, induced apoptosis, and inhibited cell migration, compared to regular cell culture media. Adding L-alanyl-L-glutamine to Steen solution improved cell migration and decreased apoptosis. It also reduced cold preservation and warm perfusion-induced apoptosis, enhanced GSH and HSP70 production, and inhibited IL-8 expression on an EVLP cell culture model. L-alanyl-L-glutamine modified Steen solution supported porcine lungs on EVLP with significantly improved lung function, well-preserved histological structure, and significantly higher levels of multiple amino acids in EVLP perfusate. CONCLUSIONS: Adding L-alanyl-L-glutamine to perfusate may provide additional energy support, antioxidant, and cytoprotective effects to lung tissue. The pipeline developed herein, with cell culture, cell EVLP, and porcine EVLP models, can be used to further optimize perfusates to improve EVLP outcomes.

Ischemia-Reperfusion Injury in a Simulated Lung Transplant Setting Differentially Regulates Transcriptomic Profiles between Human Lung Endothelial and Epithelial Cells.

Current understanding of mechanisms of ischemia-reperfusion-induced lung injury during lung preservation and transplantation is mainly based on clinical observations and animal studies. Herein, we used cell and systems biology approaches to explore these mechanisms at transcriptomics levels, especially by focusing on the differences between human lung endothelial and epithelial cells, which are crucial for maintaining essential lung structure and function. Human pulmonary microvascular endothelial cells and human lung epithelial cells were cultured to confluent, subjected to different cold ischemic times (CIT) to mimic static cold storage with preservation solution, and then subjected to warm reperfusion with a serum containing culture medium to simulate lung transplantation. Cell morphology, viability, and transcriptomic profiles were studied. Ischemia-reperfusion injury induced a CIT time-dependent cell death, which was associated with dramatic changes in gene expression. Under normal control conditions, endothelial cells showed gene clusters enriched in the vascular process and inflammation, while epithelial cells showed gene clusters enriched in protein biosynthesis and metabolism. CIT 6 h alone or after reperfusion had little effect on these phenotypic characteristics. After CIT 18 h, protein-biosynthesis-related gene clusters disappeared in epithelial cells; after reperfusion, metabolism-related gene clusters in epithelial cells and multiple gene clusters in the endothelial cells also disappeared. Human pulmonary endothelial and epithelial cells have distinct phenotypic transcriptomic signatures. Severe cellular injury reduces these gene expression signatures in a cell-type-dependent manner. Therapeutics that preserve these transcriptomic signatures may represent new treatment to prevent acute lung injury during lung transplantation.

Context-Dependent and Disease-Specific Diversity in Protein Interactions within Stress Granules.

Stress granules (SGs) are transient ribonucleoprotein (RNP) aggregates that form during cellular stress and are increasingly implicated in human neurodegeneration. To study the proteome and compositional diversity of SGs in different cell types and in the context of neurodegeneration-linked mutations, we used ascorbate peroxidase (APEX) proximity labeling, mass spectrometry, and immunofluorescence to identify ∼150 previously unknown human SG components. A highly integrated, pre-existing SG protein interaction network in unstressed cells facilitates rapid coalescence into larger SGs. Approximately 20% of SG diversity is stress or cell-type dependent, with neuronal SGs displaying a particularly complex repertoire of proteins enriched in chaperones and autophagy factors. Strengthening the link between SGs and neurodegeneration, we demonstrate aberrant dynamics, composition, and subcellular distribution of SGs in cells from amyotrophic lateral sclerosis (ALS) patients. Using three Drosophila ALS/FTD models, we identify SG-associated modifiers of neurotoxicity in vivo. Altogether, our results highlight SG proteins as central to understanding and ultimately targeting neurodegeneration.

DEAD-box RNA helicase Dbp4 is required for small-subunit processome formation and function.

DEAD-box RNA helicase Dbp4 is required for 18S rRNA synthesis: cellular depletion of Dbp4 impairs the early cleavage reactions of the pre-rRNA and causes U14 small nucleolar RNA (snoRNA) to remain associated with pre-rRNA. Immunoprecipitation experiments (IPs) carried out with whole-cell extracts (WCEs) revealed that hemagglutinin (HA)-tagged Dbp4 is associated with U3 snoRNA but not with U14 snoRNA. IPs with WCEs also showed association with the U3-specific protein Mpp10, which suggests that Dbp4 interacts with the functionally active U3 RNP; this particle, called the small-subunit (SSU) processome, can be observed at the 5' end of nascent pre-rRNA. Electron microscopy analyses indicated that depletion of Dbp4 compromised SSU processome formation and cotranscriptional cleavage of the pre-rRNA. Sucrose density gradient analyses revealed that depletion of U3 snoRNA or the Mpp10 protein inhibited the release of U14 snoRNA from pre-rRNA, just as was seen with Dbp4-depleted cells, indicating that alteration of SSU processome components has significant consequences for U14 snoRNA dynamics. We also found that the C-terminal extension flanking the catalytic core of Dbp4 plays an important role in the release of U14 snoRNA from pre-rRNA.

Nucleolar proteins Bfr2 and Enp2 interact with DEAD-box RNA helicase Dbp4 in two different complexes.

Different pre-ribosomal complexes are formed during ribosome biogenesis, and the composition of these complexes is highly dynamic. Dbp4, a conserved DEAD-box RNA helicase implicated in ribosome biogenesis, interacts with nucleolar proteins Bfr2 and Enp2. We show that, like Dbp4, Bfr2 and Enp2 are required for the early processing steps leading to the production of 18S ribosomal RNA. We also found that Bfr2 and Enp2 associate with the U3 small nucleolar RNA (snoRNA), the U3-specific protein Mpp10 and various pre-18S ribosomal RNA species. Thus, we propose that Bfr2, Dbp4 and Enp2 are components of the small subunit (SSU) processome, a large complex of ∼80S. Sucrose gradient sedimentation analyses indicated that Dbp4, Bfr2 and Enp2 sediment in a peak of ∼50S and in a peak of ∼80S. Bfr2, Dbp4 and Enp2 associate together in the 50S complex, which does not include the U3 snoRNA; however, they associate with U3 snoRNA in the 80S complex (SSU processome). Immunoprecipitation experiments revealed that U14 snoRNA associates with Dbp4 in the 50S complex, but not with Bfr2 or Enp2. The assembly factor Tsr1 is not part of the '50S' complex, indicating this complex is not a pre-40S ribosome. A combination of experiments leads us to propose that Bfr2, Enp2 and Dbp4 are recruited at late steps during assembly of the SSU processome.

Retinal patterning by Pax6-dependent cell adhesion molecules.

Long-standing evidence gained from Pax6 mutant embryos pointed to an involvement of Pax6-dependent cell adhesion molecules in patterning the central nervous system and, in particular, the retina. However, direct evidence for such pathways remained elusive. We here present direct evidence that knockdown of Pax6 expression by morpholino antisense molecules in Xenopus embryos and knockdown of maternal N-cadherin (mNcad), N-cadherin (Ncad) and neural cell adhesion molecule (NCAM) produce similar phenotypes. Eye formation is reduced and retinal lamination is heavily disorganized. In Pax6 knockdown embryos, the levels of mRNAs coding for these cell adhesion molecules are markedly reduced. Overexpression of Pax6 efficiently rescues the phenotype of Pax6 knockdown embryos and restores expression of these putative target genes. Rescue of Pax6-deficiency by the putative target gene mNcad moderately rescues eye formation. The promoters of the genes coding for cell adhesion molecules contain several putative Pax6 binding sites, as determined by computer analysis. Chromatin immunoprecipitation shows that, in embryonic heads, Pax6 binds to promoter regions containing such predicted binding sites. Thus, several cell adhesion molecules are direct target genes of Pax6 and cooperate in retinal patterning.