Cardio-Pulmonary Institute

Atrial fibrillation represents the most prevalent cardiac arrhythmia and is associated with substantial morbidity, including an increased risk for stroke and heart failure. The pathophysiology of atrial fibrillation involves electrical and structural remodeling of the atria, often referred to as atrial myopathy, that together increase the risk for arrhythmias. However, a specific approach to target the proarrhythmic substrate of atrial fibrillation is still lacking. Aldosterone and the mineralocorticoid receptor are well-known drivers of cardiac remodeling, and recent clinical and experimental studies indicate that they play a critical role in the pathogenesis of atrial fibrillation. Elevated aldosterone levels, for example, in primary aldosteronism, are associated with a higher risk for atrial fibrillation. Mineralocorticoid receptor antagonists reduce the onset of atrial fibrillation across various patient populations, including patients with hypertension, heart failure, chronic kidney disease, or undergoing cardiac surgery. In patients with preexisting atrial fibrillation, mineralocorticoid receptor antagonists may decrease atrial fibrillation recurrence when added to antiarrhythmic therapies. Experimental studies provide a direct link between aldosterone and atrial remodeling and arrhythmia. Mineralocorticoid receptor activation modulates several key cellular processes involved in atrial inflammation, fibrosis, and arrhythmogenesis, including fibroblast activation, cardiomyocyte dysfunction, and ion channel activity. Here, we review what is currently known about the role of aldosterone and the mineralocorticoid receptor in atrial fibrillation, summarize the mechanistic basis as supported by experimental studies, and discuss the potential of mineralocorticoid receptor antagonists in the prevention and treatment of atrial fibrillation.

The updated S3 guideline on the "Epidemiology, Diagnosis and Treatment of Adult Patients with Nosocomial Pneumonia", published in January 2024, provides evidence- and consensus-based recommendations aimed at improving care for this prevalent hospital-acquired infection. Replacing the 2017 version, the guideline was developed through an interdisciplinary process involving 14 professional societies. It includes 26 recommendations, covering extended diagnostic strategies (including multiplex PCR, biomarkers, and BAL) and tailored antimicrobial therapy. Key innovations include shortened treatment durations, targeted use of combination regimens, integration of viral and fungal pathogens, and a flowchart to guide empirical therapy. Emphasis is placed on antibiotic stewardship, reevaluation strategies, and resistance management. The guideline remains valid until February 2029.

Pulmonary vascular remodelling occurs in the early development of chronic obstructive pulmonary disease (COPD). Cellular/molecular alterations in pulmonary vasculature precede emphysema and may be mechanistically intertwined. In COPD, such alterations have been characterised by hyper-proliferations of pulmonary artery smooth muscle cells (PASMCs) and increased expression of inducible nitric oxide synthase (iNOS) in pulmonary vessels. Treatment with iNOS inhibitor, L-NIL, reverses cigarette smoke (CS)-induced emphysema in a pre-clinical COPD model. However, the mechanisms of alveolar repair driven by iNOS inhibition remain elusive. Here, we explore the therapeutic potential of iNOS-ablation in <italic>Acta2</italic>+ cells, including PASMC, using a transgenic mouse model with Cre/loxP system (<italic>Acta2</italic>-CreERT2/iNos-floxed). The mice were exposed to CS for 8 months to induce emphysema, followed by 3 months of CS cessation after tamoxifen-activated iNOS deletion. Lung function measurements were performed, and lung samples were collected for precision-cut lung slices (PCLS) generation, single-cell transcriptome profiling, and histological/stereological analyses. <italic>Acta2+</italic> cell-specific deletion of iNOS reversed established CS-induced emphysema, showing reduced lung compliance, decreased mean linear intercept, and increased number of alveoli. An increased number of proliferative cells in the proximity of the pulmonary vascular compartment was observed in PCLS from iNOS-deleted mice. Single-cell transcriptome analyses in all <italic>Acta2+</italic> cells revealed that contractile markers were downregulated in vascular <italic>Acta2+</italic> cells from iNOS-knockout mice. Future studies will decipher the molecular landscape of the vascular <italic>Acta2+</italic> cell-mediated reparative process.

Bronchopulmonary dysplasia (BPD) is a neonatal chronic lung disease characterized by failed alveolar and vascular formation, as well as lung matrix remodeling. In a hyperoxia-based model of BPD, we previously described a regulation of the transcription factor Krüppel-like factor 4 (Klf4) in alveolar epithelial type 2 cells (AT2). Since Klf4 is a central regulator of stemness and cellular homeostasis, we now investigated its role in AT2. We employed a tamoxifen inducible mouse model with AT-2 specific ablation of Klf4 [SftpC-Cre-ER(T2)^+/-;Klf4^fl/fl;Yfp^fl/fl] and controls [SftpC-Cre-ER(T2)^-/-;Klf4^fl/fl;Yfp^fl/fl]. Tamoxifen was administered at postnatal day 3 (P3), and mice were exposed to 85% O₂ (HYX) or 21% O₂ (NOX) from birth to P21. Lungs were studied at P21 and after recovery in NOX at P70. The AT2-specific deletion of Klf4 in HYX-exposed mice induced an AT2 to AT1 transition, and attenuated hyperoxia-induced alveolar growth arrest. Transcriptomic profiling of isolated AT2 with Klf4 ablation revealed a dysregulation of processes involved in angiogenesis and ECM formation. Indeed, targeted analysis revealed an upregulation of <italic>Vegfa</italic> and its receptor <italic>Flt1</italic> in AT2 with a Klf4 deletion. Histomorphometric analysis confirmed preserved microvascular formation at P21 as well as later in life at P70 in transgenic mice with a neonatal AT2-specific ablation of Klf4 when compared to controls. In summary, our findings indicate cell-autonomous (i.e. transdifferentiation of AT2) and non-cell autonomous (i.e. promoting angiogenesis-associated alveologenesis) function in AT2 that control neonatal alveolar growth.

Background: Chronic lung allograft dysfunction (CLAD) occurs in up to 50% of patients within the first five years after lung transplantation (LuTX) and represents the main complication and cause of death regarding this surgery. Alveolar septal widening in transbronchial biopsies has shown an association with acute humoral allograft rejection. We aimed to explore histological markers that could predict the development of CLAD before its clinical manifestation. Methods: We retrospectively analyzed transbronchial biopsies taken at three time points from 57 patients who underwent LuTX between February 2010 and July 2019, 26 of whom developed CLAD up to November 2022. The biopsies were analyzed by microscopic morphometry and quantitative reverse transcription PCR to identify predictors of CLAD. Results: CLAD development was associated with increased alveolar septal width (ASW) as early as the first year post-LuTX (5.46 ± 0.76 µm versus 4.59 ± 0.44 µm; p < 0.001). The ASW in later biopsy timepoints predicted survival in multivariate models (last timepoint: hazard ratio 1.885, 95% confidence interval 1.086–3.269). Collagen (COL1A1 and COL3A1) expression was significantly increased in samples from patients who developed CLAD compared with those who did not. The increase in ASW was paralleled by interstitial deposition of COL1A1 and COL3A1 and a decrease in both the carbon monoxide (DLCO) diffusing capacity of the lung and the DLCO/alveolar volume. Conclusions: We report a new histologic approach for early assessment of risk of CLAD in patients who have undergone LuTX. The ASW represents a pre-symptomatic, continuous, and widely distributed change within the lung parenchyma that is accessible to transbronchial biopsy.

Chromatin organization guides gene regulatory mechanisms and has been subject of extensive research using chromatin accessibility assays. ATAC-seq is commonly applied to elucidate regulatory regions of the genome at both bulk and single-cell resolutions. However, the analysis of single-cell ATAC-seq data is particularly challenging due to issues such as data sparsity, low signal-to-noise ratios, and the lack of standardized quality control (QC) protocols. While QC based on the fragment length distribution (FLD) represents common practice for bulk analyses, an algorithmic solution that utilizes the full potential of the FLD at the single-cell level is missing. To address this limitation, we introduce the python package PEAKQC, a novel tool that provides a robust metric for identifying high-quality cells. PEAKQC quantifies the deviation of individual cells’ FLD patterns from the expected distribution using a wavelet transformation-based convolution approach. Benchmarking against alternative metrics revealed favorable selection of high-quality cells, facilitating accurate downstream analysis including cell type identification and cluster separation. PEAKQC is readily installable via the Python Package Index and can be seamlessly integrated into existing single-cell analysis frameworks that utilize Python. By providing a robust and scalable solution for single-cell ATAC-seq QC, PEAKQC addresses a significant knowledge gap in the field and proposes FLD patterns as a novel standard for data quality assessment.