Xander Wehrens Lab

Wehrens Lab Projects


Ryanodine receptor regulation in post-operative atrial fibrillation (R01 HL089598)

Postoperative atrial fibrillation (poAF) is a common complication of cardiothoracic surgery with an incidence between 10 and 50 percent. This condition typically peaks two-three days following surgery, and is associated with excessive hospitalization time, increased risk of stroke, and an increase in patient morbidity. Whereas progress has been made towards understanding the pathogenesis of AF in general, very little remains known about the molecular mechanisms underlying poAF. Our preliminary data reveal perturbed intracellular calcium (Ca) handling in atrial biopsies from patients with poAF. Increased activity of the ryanodine receptor Ca release channel was found in atrial myocytes of patients with poAF and a novel mouse model of poAF. Our data suggest that enhanced RyR2 activity is caused by altered levels of `Striated Muscle Preferentially Expressed Protein Kinase' (SPEG) in atria of patients and mice with poAF. The long-term goal of this project is to elucidate the molecular and cellular mechanisms underlying poAF development.

Mechanisms underlying atrial fibrillation associated with chronic kidney disease (R01 HL147108)

Chronic kidney disease (CKD) is a known predictor of cardiovascular morbidity and mortality, and is an important risk factor for atrial fibrillation (AF). Very little remains known about the molecular mechanisms underlying AF associated with CKD. Our preliminary data reveal activation of the NLRP3 inflammasome within atrial myocytes isolated in a mouse model of CKD. The long-term goal of this project is to elucidate the molecular and cellular mechanisms underlying AF development as a result of inflammasome activation in mice with CKD. We will test the hypothesis that enhanced activation of the NLRP3 inflammasome within atrial myocytes enhances the susceptibility to AF by promoting proarrhythmogenic Ca2+ releases via increased SPEG-phosphorylation of RyR2.

Junctophilin-2 cleavage in ischemic heart disease (R01 HL153350)

Ischemic heart disease is a major cause of death in the United States. At the cellular level, myocardial ischemia alters excitation-contraction coupling and promoted the development of HF. Junctophilin-2 (JPH2) is an inter-membrane linker protein that maintains the plasmalemma and sarcoplasmic reticulum (SR) at a fixed distance to facilitate excitation-contraction coupling. Ischemia/reperfusion injury and ischemic heart disease lead to a loss of JPH2 protein levels, which in part is caused by proteolysis by the Ca2+-sensitive enzyme calpain. Our long-term goal of this project is to elucidate the molecular and cellular mechanisms by which calpain causes JPH2 cleavage and how the ensuing JPH2 C-terminal peptide alters myocardial function. We will test the central hypothesis that calpain cleaves JPH2 to release a C-terminal peptide that traffics into the cardiomyocyte nucleus where it alters CaMKII-d splicing which affects myocardial remodeling.

Role of Nucleoside-Diphosphate Kinase signaling in atrial fibrillation (R01 HL160992)

Atrial fibrillation (AF), the most common arrhythmia, is associated with high morbidity and mortality, but remains difficult to treat due to an incomplete understanding of underlying mechanisms. Emerging evidence suggests that nucleoside diphosphate kinases (NDPKs) play an important role in the heart by being able to elevate cAMP levels in a G-protein receptor-independent manner. Our pilot data suggest that increased levels of NDPK-B and NDPK-C isoforms in patients with persistent (chronic) AF are associated with elevated cAMP levels, abnormal sarcoplasmic reticulum Ca2+ releases, ectopic (triggered) activity and inducible AF. The long- term goal of this project is to dissect the molecular and cellular basis of NDPK-dependent arrhythmia mechanisms in AF. The central hypothesis is that enhanced NDPK-B and -C levels promote AF by enhancing cAMP levels in the RyR2 microdomain, resulting in aberrant intracellular Ca2+ signaling that creates a substrate for AF initiation, maintenance, and progression. These studies will be performed in atrial myocytes from patients with AF, a dog model of AF, and various atrial-selective genetic mouse models of AF. Novel targeted cAMP FRET sensors and atrial-selective adeno-associated virus (AAV9)-mediated gene therapy will be utilized to resolve the pro-arrhythmic roles of NDPK-B/C and cAMP within specific cellular microdomains. These studies are expected to establish whether and how NDPK isoforms contributes to AF development and serve as a platform for the validation of NDPKs as novel druggable target for the prevention or treatment of AF.

Genome editing for the treatment of CPVT 

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited cardiac arrhythmia syndrome associated with stress-induced arrhythmias that can cause sudden cardiac death. Current treatment modalities are only partially effective and may cause serious side effects. Our preliminary data reveal that genome editing using CRISPR/Cas9 delivered in vivo using adeno-associated virus can prevent ventricular tachycardia in a mouse model of CPVT. The long-term goal of this project is to elucidate the molecular and cellular mechanisms by which genome editing can normalize intracellular calcium handling and prevent arrhythmias in mouse models and induced pluripotent stem cell-derived cardiomyocytes obtained from CPVT patients. We will test the central hypothesis that CRISPR/Cas9 genome editing can be used to specifically reduce the number of mutant monomers in RyR2 channel complexes or to even correct the disease-causing mutation using prime editing, thereby normalizing SR Ca2+ handling, and preventing ventricular arrhythmias in mice and human iPSC-CMs.

Regulation of sarcoplasmic reticulum calcium release in heart failure

It is well established that altered sarcoplasmic reticulum (SR) Ca handling plays a key role in heart failure (HF) pathogenesis. Whereas altered post-translational modifications (PTM) of the SR Ca release channel/RyR2 have been linked to HF development, it remains highly controversial which kinases and phosphatases underlie these disease-associated changes. Our long-term goal is to define the molecular and cellular mechanisms by which SEPG regulates RyR2 and intracellular Ca handling in normal and failing hearts. The overall hypothesis is that SPEG phosphorylates residue S2367on RyR2, which modulates RyR2 activity and intracellular Ca handling in cardiac myocytes. A better understanding of the molecular mechanisms underlying abnormal RyR2 function in HF could lead to new pharmacological strategies.