An integrative approach to understanding the pathophysiology of cardiac disease

An integrative approach to understanding the pathophysiology of cardiac disease

The burden of coronary heart disease:


Coronary heart disease (CHD) caused by narrowing or blockage of coronary arteries leads to heart muscle cell death and injury (myocardial infarction) and is the leading cause of premature mortality in many countries around the world. Novel therapeutic strategies are urgently needed to reduce heart muscle cell injury, prevent the progression to heart failure and reduce abnormal heart rhythms associated with CHD which can be fatal. In order to develop more effective prevention and therapies to treat CHD it is important that we understand the mechanisms underlying cardiac dysfunction.


The importance of an integrative approach to study heart disease:


Dr. Loughrey’s laboratory utilises a wide range of experimental techniques to investigate heart function at the level of the molecule, cell, organ and whole animal. This integrative approach provides the opportunity to study abnormal alterations of gene and protein expression/function and in turn how these changes influence whole heart function. The value of integrating scientific research data collected at the molecular and cellular level with whole animal physiology is an increasingly recognised prerequisite to the development of new therapeutic strategies to treat both human and animal diseases.
Dr. Loughrey’s laboratory has practical expertise in a number of methodologies. These include: confocal microscopy, single cell electrophysiology, fluorescence measurements/imaging, Western blotting, PCR, whole heart techniques (Langendorff perfusion and working heart preparations) and in vivo cardiovascular measurements/micro-surgery (e.g. intra-ventricular pressure-volume measurements, electrocardiography and a mouse model of myocardial infarction). These techniques are used in a number of projects which are on-going within Dr. Loughrey’s laboratory:


1. CALCIUM REGULATION IN HEART CELLS:
The spatial-temporal properties of calcium concentration within heart muscle cells– the cardiomyocytes - determine how efficiently the heart pumps. During cardiac disease the process that controls cardiomyocyte calcium concentration is disturbed in such a way as to result in poor cardiac contractile function (leading to heart failure) and heart rhythms (arrhythmias) that lead to sudden cardiac death. A major focus for Dr. Loughrey’s laboratory is the measurement of intracellular calcium and in particular how altered expression of novel cardiac proteins affect intracellular calcium properties thus the ability of the heart to pump blood around the body. By understanding how specific proteins alter cardiomyocyte calcium dynamics under both normal and disease conditions and in turn their influence on heart function, we aim to inform therapeutic strategies for the treatment of heart disease.

2. CATHEPSINS AND ISCHAEMIA- REPERFUSION 
INJURY:
CHD leads to reduced myocardial blood flow (ischaemia) resulting in cardiac pump dysfunction. In order to limit ischaemic-induced damage, restoration of blood flow (myocardial reperfusion) is required but paradoxically this can exacerbate cardiac dysfunction in a phenomenon called ischaemia-reperfusion (I/R) injury. Effective therapeutic strategies to limit I/R injury require identification of novel therapeutic targets. We have identified a novel target called cathepsin-L which is a protease that directly impairs cardiomyocyte function. Our novel ex vivo data demonstrate that cathepsin-L is increased during I/R and when inhibited prior to I/R improves myocardial function. We aim to advance these exciting ex vivo data along the translational pathway to characterise further the mechanisms underlying the effect of cathepsins on the heart in animal models and human patients.

3. AFRICAN TRYPANOSOMES AND THE HEART:
African trypanosomiasis (AT) is caused by blood-borne extracellular protozoans (Trypanosoma brucei subsp.) transmitted by the tsetse fly. AT patients initially display haemolymphatic infection profiles (Stage I disease), but as infection progresses the parasites cross endothelial barriers and migrate into different tissues (Stage II disease). Extravascular T. brucei migration is classically associated with central nervous system (CNS) disorders. However, recent field and post-mortem studies in animals and humans demonstrate widespread cardiac involvement including contractile dysfunction and arrhythmias. The mechanisms underlying these cardiac-related abnormalities remain unclear. Our novel data demonstrate that trypanosomes secrete cathepsin-L which interacts with cardiomyocytes resulting in an increased propensity for abnormal calcium release from an intracellular calcium store called the sarcoplasmic reticulum (SR). Prior to these novel data, the only suggested mechanism for cardiac-related clinical symptoms has been the immune/inflammatory response to the parasite.  Our data demonstrate that this is not the sole mechanism and present a new paradigm for trypanosome-induced cardiac dysfunction.

4. RUNX AND THE HEART:
Runx proteins (Runx 1-3) are involved in processes ranging from blood cell development to bone formation. Recently, Runx1 expression has been found to increase in hearts of human patients who have suffered from a myocardial infarction and we have also demonstrated this within our animal model of myocardial infarction. Despite this observation, the role Runx plays in the heart remains unknown. We have discovered that increased Runx1 expression alters SR function within heart muscle cells. Given the established link between altered SR function and contractile dysfunction and arrhythmias, Dr. Loughrey’s laboratory is investigating the mechanism by which this effect occurs in order to advance our understanding of the role Runx plays in the heart.

5. NOVEL DRUGS TO TREAT HEART FAILURE:
SR-mediated calcium handling (which includes calcium uptake via the sarcoplasmic/endoplasmic calcium ATPase pump, SERCA, and calcium release via the ryanodine receptor, RyR2) is altered in almost all models of heart failure and may lead to abnormal heart contractile function and relaxation. K201 (JTV-519), a 1,4 benzothiazepine derivative structurally distinct from diltiazem, was originally discovered when screening compounds to prevent sudden cardiac cell death in a rat Langendorff model of myofibrillar over-contraction. The beneficial effect of K201 during cardiac disease has been attributed to reducing the open probability of RyR2 thus preventing abnormal RyR2-mediated calcium release. Our work on K201 has revealed several new mechanistic insights into the therapeutic potential of K201. We have shown that K201 significantly alters the spatial-temporal properties of intracellular calcium concentration in such a way as to reduce the detrimental consequences of spontaneous calcium release from the SR. In doing so we revealed a mechanism by which the deleterious arrhythmogenic and mechanical effects of excessive diastolic SR-mediated calcium release can be limited. Our current work in this area revolves around investigating the actions of related compounds on the heart that are similar to K201 and may also benefit patients with heart failure

Publications

  1. Loughrey CM, Craig MA, Seidler T, Smith GL: K201 modulates excitation-contraction coupling and spontaneous Ca2+ release in isolated adult rabbit ventricular cardiomyocytes. Cardiovascular Research 2007;76:236-46.
  2. Toischer K, Lehnart SE, Tenderich G, Milting H, Körfer R, Schmitto JD, Schoendube FA, Kaneko N, Loughrey CM, G.L. Smith GL et al: K201 reduces the calcium leak of the sarcoplasmic reticulum and improves contractile performance in human failing myocardium. Basic Research in Cardiology 2010;105:279-287.
  3. Currie S, Elliott EB, Smith GL & Loughrey CM: Two candidates at the heart of dysfunction: The ryanodine receptor and calcium/calmodulin protein kinase II as potential targets for therapeutic intervention - an in vivo perspective. Pharmacology & Therapeutics 2011;131:204-20.
  4. Elliott EB, Otani N, Hasumi H, Kaneko N, Smith GL, Loughrey CM: K201 (JTV-519) alters the spatiotemporal properties of diastolic Ca(2+) release and the associated diastolic contraction during β-adrenergic stimulation in rat ventricular cardiomyocytes. Basic Research in Cardiology 2011;106:1009-22.
  5. Kelly A, Elliott EB, Kaneko N, Smith GL, Loughrey CM: The effect of K201 on isolated working rabbit heart mechanical function during pharmacologically-induced Ca(2+) overload. British Journal of Pharmacology 2012;165:1068-83.
  6. Elliott EB, Kelly A, Smith GL, Loughrey CM: Isolated rabbit working heart function during progressive inhibition of myocardial SERCA activity. Circulation Research 2012;110:1618-1627.
  7. Loughrey CM, Gray G: Advancing our understanding of the pathophysiology of cardiac disease using in vivo assessment of heart function in rodent models, Experimental Physiology 2013;98:599-600.