Research projects

RESEARCH INTERESTS

Our research is specifically focused on elucidating the functionality of subcellular nanodomains and their role in regulation of proteins responsible for normal and pathophysiological electro-mechanical activity of the heart. We pursue two main directions: determining the cellular and molecular mechanisms underlying normal electrical activity and dysfunction of the sinoatrial node, the heart’s natural pacemaker, and discovering novel strategies for atrial fibrillation treatment and risk stratification.

Microdomain–specific localization of functional ion channels in cardiomyocytes: an emerging concept of local regulation and remodeling

Cardiac excitation involves the generation of action potential by individual cells and the subsequent conduction of the action potential from cell to cell through intercellular gap junctions. Excitation of the cellular membrane results in opening of the voltage-gated L-type calcium ion (Ca2+) channels, thereby allowing a small amount of Ca2+ to enter the cell, which in turn triggers the release of a much greater amount of Ca2+ from the sarcoplasmic reticulum, the intracellular Ca2+ store, and gives rise to the systolic Ca2+ transient and contraction. These processes are highly regulated by the autonomic nervous system, which ensures the acute and reliable contractile function of the heart and the short-term modulation of this function upon changes in heart rate or workload. It has recently become evident that discrete clusters of different ion channels and regulatory receptors are present in the sarcolemma, where they form an interacting network and work together as a part of a macro-molecular signaling complex which in turn allows the specificity, reliability and accuracy of the autonomic modulation of the excitation–contraction processes by a variety of neurohormonal pathways. Disruption in subcellular targeting of ion channels and associated signaling proteins may contribute to the pathophysiology of a variety of cardiac diseases, including heart failure and certain arrhythmias. Recent methodological advances have made it possible to routinely image the topography of live cardiomyocytes, allowing the study of clustering functional ion channels and receptors as well as their coupling within a specific microdomain. Our laboratory is particularly interested in understanding the functionality of distinct subcellular microdomains in cardiac myocytes, such as transversal (t)-tubules, caveolae, and various costamers, and their functional role in the accumulation, neuro-hormonal and mechanical regulation of proteins responsible for normal and pathophysiological electrical activity of the heart.

Caveolae membrane invaginations, mechanotransduction, and cytoprotection

Cardiac excitation involves the generation of action potential by individual cells and the subsequent conduction of the action potential from cell to cell through intercellular gap junctions. Excitation of the cellular membrane results in opening of the voltage-gated L-type calcium ion (Ca2+) channels, thereby allowing a small amount of Ca2+ to enter the cell, which in turn triggers the release of a much greater amount of Ca2+ from the sarcoplasmic reticulum, the intracellular Ca2+ store, and gives rise to the systolic Ca2+ transient and contraction. These processes are highly regulated by the autonomic nervous system, which ensures the acute and reliable contractile function of the heart and the short-term modulation of this function upon changes in heart rate or workload. It has recently become evident that discrete clusters of different ion channels and regulatory receptors are present in the sarcolemma, where they form an interacting network and work together as a part of a macro-molecular signaling complex which in turn allows the specificity, reliability and accuracy of the autonomic modulation of the excitation–contraction processes by a variety of neurohormonal pathways. Disruption in subcellular targeting of ion channels and associated signaling proteins may contribute to the pathophysiology of a variety of cardiac diseases, including heart failure and certain arrhythmias. Recent methodological advances have made it possible to routinely image the topography of live cardiomyocytes, allowing the study of clustering functional ion channels and receptors as well as their coupling within a specific microdomain. Our laboratory is particularly interested in understanding the functionality of distinct subcellular microdomains in cardiac myocytes, such as transversal (t)-tubules, caveolae, and various costamers, and their functional role in the accumulation, neuro-hormonal and mechanical regulation of proteins responsible for normal and pathophysiological electrical activity of the heart.

Functional microdomains in the sinoatrial node

Over the last 20 years, Dr. Glukhov’s research has focused on the role of autonomic imbalance in heart rhythm abnormalities, including sinoatrial node pacemaker dysfunction and atrial arrhythmogenesis. Our groups developed a conceptually innovative approach to study sinoatrial node dysfunction through functional protein-protein interactions within discrete nanodomains. In particular, we focus our research on specialized cardiomyocyte membrane structures, namely caveolae, submicroscopic plasma membrane pits, that organize sinoatrial node pacemaking through complex spatiotemporal cAMP-dependent and Ca2+-mediated crosstalk between sarcoplasmic reticulum and sarcolemmal membrane proteins within the so-called coupled-clock pacemaker system that support a stable, regular sinus rhythm. This pioneering research introduces a novel concept of electrophysiological changes resulting from physical alterations in the subcellular localization of and interactions between signaling complexes following structural remodeling. This extends beyond the classical concept of electrical remodeling, according to which dysfunction can be explained by straightforward increases or decreases in protein expression alone, and adds a new dimension to understanding heart rhythm abnormalities.

Mechano-electro-chemical signal transduction in pathophysiology of atrial fibrillation

Atrial fibrillation often occurs in the setting of hypertension which is associated with atrial dilatation and pathologically increased cardiomyocyte stretch. Ectopic beats, that initiate atrial fibrillation, result from subcellular Ca2+ mishandling in atrial cardiomyocytes triggering aberrant electrical activity, which can be suppressed pharmacologically, or via catheter-based ablation; however, both treatments have limitations and side-effects. We extended the concept of functional cAMP/Ca2+ caveolar nanodomains to the development of atrial fibrillation in the settings of pathological atrial stretch. Our recent findings showed that stretch-mediated downregulation of caveolae structures activates complex mechano-chemical and mechano-electrical signal transduction feedback mechanisms. First, cardiomyocyte stretch disturbs caveolar cAMP nanodomains and leads to cAMP-mediated augmentation of protein kinase A (PKA) activity and associated Ca2+ mishandling, forming a trigger for AF. Second, cardiomyocyte stretch activates caveolar mechano-sensitive ion currents, including mechanosensitive volume-regulated chloride current ICl,swell, leading to heterogeneous conduction slowing throughout the atria and forming a substrate for AF. These findings provide a completely new understanding on cardiac mechanosensing and form a mechanistic basis for development of novel and effective therapeutic approaches to treat AF via modulation of the components of caveolar mechano-electro-chemical signal transduction. More precise approaches could help to avoid common side effects of conventional antiarrhythmic therapies.

The Wisconsin Atrial Fibrillation Initiative: Integrating Novel Technologies to Tackle a Pervasive Disease

In collaboration with Drs. Alejandro Roldán-Alzate (Departments of Mechanical Engineering and Radiology) and Matthew Kalscheur (Department of Medicine), we have shown showed, in both atrial fibrillation patients and animal models, that atrial stretch is heterogeneous in a given subject, creating distinct “vulnerable” regions of the most severe pathophysiological remodeling. These regions are located near venous trunks, including pulmonary veins, superior and inferior vena cava, and coronary sinus, which demonstrate the most common sources of arrhythmogenic atrial ectopy. By utilizing 4D flow magnetic resonance imaging (MRI) combined with computational fluid dynamics, we propose a highly innovative approach for identifying regions of stretch-induced myocardial remodeling and proarrhythmic ectopy as areas of local hypokinetic behavior. This will allow the development of a much-needed non-invasive tool for the assessment of the degree of electro-anatomical remodeling of patient atria and prediction criteria for atrial fibrillation risk stratification in vulnerable cohorts of patients.