Analysis of Legionella Metabolism by Pathogen Vacuole Proteomics

The causative agent of Legionnaires' disease, Legionella pneumophila, replicates in free-living amoebae as well as in macrophages of the innate immune system within a distinct membrane-bound compartment, the "Legionella-containing-vacuole" (LCV). LCV formation is a complex process and requires the bacterial Icm/Dot type IV secretion system, which translocates approximately 300 different "effector" proteins. Intact LCVs from infected Dictyostelium discoideum amoebae or RAW 264.7 murine macrophages can be purified using a straightforward protocol. In the first step, the LCVs in cell homogenates are tagged with an antibody directed against an L. pneumophila effector protein specifically localizing to the pathogen vacuole membrane and isolated by immunomagnetic separation using a secondary antibody coupled to magnetic beads. In the second step, the LCVs are further enriched by density gradient centrifugation through a Histodenz cushion. LCVs thus purified are analyzed by mass spectrometry-based proteomics and characterized by biochemical and cell biological approaches

Neural mechanisms of atrial arrhythmias

The past 5 years have seen great advances in the knowledge of neural mechanisms of atrial arrhythmogenesis. Direct autonomic nerve recordings demonstrate that simultaneous sympathovagal discharges and intrinsic cardiac nerve activities are common triggers of paroxysmal atrial tachycardia and atrial fibrillation. While activity of the autonomous nervous system (ANS) is crucial in triggering paroxysmal atrial fibrillation, a high incidence of sympathovagal coactivation at baseline is associated with a high vulnerability to pacing-induced sustained atrial fibrillation, suggesting that ANS has a role in the development of persistent atrial fibrillation. Modulation of ANS activity may constitute an important therapeutic strategy for the management of atrial tachyarrhythmias. Specifically, continuous, low-level stimulation of the left cervical vagus nerve effectively suppresses atrial tachyarrhythmias by reducing the nerve activity of the stellate ganglion. Clinically, compared with pulmonary vein isolation alone, the addition of ablation of intrinsic cardiac ganglia may confer better outcomes for patients with paroxysmal atrial fibrillation. These findings suggest that further investigations in the neural mechanisms of atrial arrhythmias might lead to better management of patients with atrial arrhythmias. In this article, we review the role of the ANS in the induction and maintenance of atrial arrhythmias and the role of neural modulation as a treatment strategy for atrial arrhythmias