A striking feature of white-nose syndrome, a fungal infection of hibernating bats, is the difference in infection outcome between North America and Europe. Here we show high WNS prevalence both in Europe and on the West Siberian Plain in Asia. Palearctic bat communities tolerate similar fungal loads of Pseudogymnoascus destructans infection as their Nearctic counterparts and histopathology indicates equal focal skin tissue invasiveness pathognomonic for WNS lesions. Fungal load positively correlates with disease intensity and it reaches highest values at intermediate latitudes. Prevalence and fungal load dynamics in Palearctic bats remained persistent and high between 2012 and 2014. Dominant haplotypes of five genes are widespread in North America, Europe and Asia, expanding the source region of white-nose syndrome to non-European hibernacula. Our data provides evidence for both endemicity and tolerance to this persistent virulent fungus in the Palearctic, suggesting that host-pathogen interaction equilibrium has been established.

Background—: Phosphoinositide 3-kinase γ (PI3Kγ) signaling engaged by β-adrenergic receptors is pivotal in the regulation of myocardial contractility and remodeling. However, the role of PI3Kγ in catecholamine-induced arrhythmia is currently unknown. Methods and Results—: Mice lacking PI3Kγ (PI3Kγ ^−/− ) showed runs of premature ventricular contractions on adrenergic stimulation that could be rescued by a selective β ₂ -adrenergic receptor blocker and developed sustained ventricular tachycardia after transverse aortic constriction. Consistently, fluorescence resonance energy transfer probes revealed abnormal cAMP accumulation after β ₂ -adrenergic receptor activation in PI3Kγ ^−/− cardiomyocytes that depended on the loss of the scaffold but not of the catalytic activity of PI3Kγ. Downstream from β-adrenergic receptors, PI3Kγ was found to participate in multiprotein complexes linking protein kinase A to the activation of phosphodiesterase (PDE) 3A, PDE4A, and PDE4B but not of PDE4D. These PI3Kγ-regulated PDEs lowered cAMP and limited protein kinase A–mediated phosphorylation of L-type calcium channel (Ca _v 1.2) and phospholamban. In PI3Kγ ^−/− cardiomyocytes, Ca _v 1.2 and phospholamban were hyperphosphorylated, leading to increased Ca ²⁺ spark occurrence and amplitude on adrenergic stimulation. Furthermore, PI3Kγ ^−/− cardiomyocytes showed spontaneous Ca ²⁺ release events and developed arrhythmic calcium transients. Conclusions—: PI3Kγ coordinates the coincident signaling of the major cardiac PDE3 and PDE4 isoforms, thus orchestrating a feedback loop that prevents calcium-dependent ventricular arrhythmia.

In underground hibernacula temperate northern hemisphere bats are exposed to Pseudogymnoascus destructans, the fungal agent of white-nose syndrome. While pathological and epidemiological data suggest that Palearctic bats tolerate this infection, we lack knowledge about bat health under pathogen pressure. Here we report blood profiles, along with body mass index (BMI), infection intensity and hibernation temperature, in greater mouse-eared bats (Myotis myotis). We sampled three European hibernacula that differ in geomorphology and microclimatic conditions. Skin lesion counts differed between contralateral wings of a bat, suggesting variable exposure to the fungus. Analysis of blood parameters suggests a threshold of ca. 300 skin lesions on both wings, combined with poor hibernation conditions, may distinguish healthy bats from those with homeostatic disruption. Physiological effects manifested as mild metabolic acidosis, decreased glucose and peripheral blood eosinophilia which were strongly locality-dependent. Hibernating bats displaying blood homeostasis disruption had 2 °C lower body surface temperatures. A shallow BMI loss slope with increasing pathogen load suggested a high degree of infection tolerance. European greater mouse-eared bats generally survive P. destructans invasion, despite some health deterioration at higher infection intensities (dependant on hibernation conditions). Conservation measures should minimise additional stressors to conserve constrained body reserves of bats during hibernation.

Rationale: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a rare disease, manifested by syncope or sudden death in children or young adults under stress conditions. Mutations in the Ca ²⁺ release channel/RyR2 (type 2 ryanodine receptor) gene account for about 60% of the identified mutations. Recently, we found and described a mutation in RyR2 N-terminal domain, RyR2 ^R420Q . Objective: To determine the arrhythmogenic mechanisms of this mutation. Methods and Results: Ventricular tachycardias under stress conditions were observed in both patients with catecholaminergic polymorphic ventricular tachycardia and knock-in mice. During action potential recording (by patch-clamp in knock-in mouse cardiomyocytes and by microelectrodes in mutant human induced pluripotent stem cell-derived cardiomyocytes), we observed an increased occurrence of delayed afterdepolarizations under isoproterenol stimulation, associated with increased Ca ²⁺ waves during confocal Ca ²⁺ recording in both mouse and human RyR2 ^R420Q cardiomyocytes. In addition, Ca ²⁺ -induced Ca ²⁺ -release, as well as a rough indicator of fractional Ca ²⁺ release, were higher and Ca ²⁺ sparks longer in the RyR2 ^R420Q -expressing cells. At the ultrastructural nanodomain level, we observed smaller RyR2 clusters and widened junctional sarcoplasmic reticulum measured by gated stimulated emission depletion super-resolution and electron microscopy, respectively. The increase in junctional sarcoplasmic reticulum width might be due to the impairment of RyR2 ^R420Q binding to JPH2 (junctophilin-2), as there were less junctophilin-2 coimmunoprecipitated with RyR2 ^R420Q . At the single current level, the RyR2 ^R420Q channel dwells longer in the open state at low intracellular Ca ²⁺ ([Ca ²⁺ ] _i ), but there is predominance of a subconductance state. The latter might be correlated with an enhanced interaction between the N terminus and the core solenoid, a RyR2 interdomain association that has not been previously implicated in the pathogenesis of arrhythmias and sudden cardiac death. Conclusions: The RyR2 ^R420Q catecholaminergic polymorphic ventricular tachycardia mutation modifies the interdomain interaction of the channel and weakens its association with JPH2. These defects may underlie both nanoscale disarrangement of the dyad and channel dysfunction.

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a lethal genetic arrhythmia that manifests syncope or sudden death in children and young adults under stress conditions. CPVT patients often present bradycardia and sino-atrial node (SAN) dysfunction. However, the mechanism remains unclear. We analyzed SAN function in two CPVT families and in a novel knock-in (KI) mouse model carrying the RyR ₂ ^R420Q mutation. Humans and KI mice presented slower resting heart rate. Accordingly, the rate of spontaneous intracellular Ca ²⁺ ([Ca ²⁺ ] _i ) transients was slower in KI mouse SAN preparations than in WT, without any significant alteration in the “funny” current ( I _f ). The L-type Ca ²⁺ current was reduced in KI SAN cells in a [Ca ²⁺ ] _i -dependent way, suggesting that bradycardia was due to disrupted crosstalk between the “voltage” and “Ca ²⁺ ” clock, and the mechanisms of pacemaking was induced by aberrant spontaneous RyR ₂ - dependent Ca ²⁺ release. This finding was consistent with a higher Ca ²⁺ leak during diastolic periods produced by long-lasting Ca ²⁺ sparks in KI SAN cells. Our results uncover a mechanism for the CPVT-causing RyR ₂ N-terminal mutation R420Q, and they highlight the fact that enhancing the Ca ²⁺ clock may slow the heart rhythm by disturbing the coupling between Ca ²⁺ and voltage clocks.