Project 12: Remodelling of human atrial cardiomyocytes in response to in vitro tachypacing
PI Göttingen: N. Voigt; PI London: M. Mayr; PhD student: F.E. Fakuade - finished PhD, Double degree
Scientific background and preliminary results
Atrial fibrillation (AF) is the most common sustained arrhythmia in the clinical setting and is associated with significant morbidity and mortality. Currently available AF therapies have limited efficacy and safety, particularly in patients with long-standing persistent (‘chronic’) AF (cAF). A better understanding of the molecular mechanisms promoting AF is expected to facilitate the development of improved anti-AF therapies. We and others have shown that AF is associated with electrical remodeling of various ion currents, resulting in reentry-promoting shortening of atrial repolarization. Increased open probability of the sarcoplasmic reticulum (SR) Ca2+-release channel (ryanodine receptor channel type-2, RyR2) predisposes patients with paroxysmal (pAF) and chronic AF to spontaneous (non-AP-triggered) diastolic SR Ca2+ release events (SCaEs). Resulting excess diastolic [Ca2+]i is handled by Na+/Ca2+ exchanger (NCX), which by transporting three Na+ ions into the cell per single Ca2+ ion extruded, creates a depolarizing transient inward current (“Iti”) that can produce arrhythmogenic membrane depolarizations (DADs). Recent work indicates that SCaEs and DADs may contribute to the pathophysiology of pAF and cAF. CaMKII-mediated hyperphosphorylation of RyR2 has been suggested to contribute to RyR2 dysfunction in cAF.
However, because of concomitant cardiac diseases and patient medication, studies in atrial tissue from patients usually do not allow a clear differentiation between causes and consequences of the AF-related changes. It is unclear whether AF-associated alterations in Ca2+ homeostasis and cellular electrophysiology result from the underlying heart disease that predisposes to AF or are a consequence of AF-induced remodeling per se.
To simulate the effect of atrial tachycardia we propose to develop an in-vitro model of paced human atrial cardiomyocytes (HAM) obtained from patients with sinus rhythm during cardiac surgery. We will investigate whether in-vitro tachypacing (TP) is sufficient to mimic alterations of cellular electrophysiological and Ca2+ handling typically seen in atrial myocytes from patients with cAF. Furthermore, we will assess molecular mechanisms underlying remodeling processes in this model.
We and others have previously shown that 24 h in-vitro tachypacing of canine atrial myocytes leads to a transient Ca2+ overload resulting in development of typical electrophysiological remodeling including shortening of action potential (AP) duration (APD), L-type Ca2+ current (ICa,L) downregulation and development of constitutive activity of acetylcholine-dependent inward-rectifier K+ channels (IK,ACh). To enable 24 h in-vitro pacing of HAM we established a new isolation protocol, which allows us to maintain (“culture”) HAM at 37°C for up to 48 h. Size and shape of these cultured HAM are comparable to freshly isolated HAM. In addition, amplitude of L-type Ca2+ current remained unchanged in comparison to our previously published controls suggesting that basic electrophysiological and Ca2+ handling parameters are unaltered.
Hypotheses of the PhD project
In the proposed project we will test the hypotheses that
1. tachypacing of HAM at high frequencies is sufficient to mimic in-vivo AF-related proarrhythmic alterations of major ion currents and intracellular Ca2+ handling.
2. Ca2+ loading and CaMKII activation in response to in-vitro TP contributes to TP-associated remodelling of intracellular Ca2+ handling.
3. Formation of ROS contributes to increased SR Ca2+ leak and SCaEs in myocytes subjected to in-vitro TP.
Research interests: Atrial fibrillation, cardiomyocyte Ca2+ signalling
Research interests: GPCR signalling, protein kinases/phosphatases, transduction and cardioprotection
PhD student 2nd IRTG 1816 cohort, Double degree
Current Position: Postdoctoral Scientist, University Medical Center Göttingen, Germany