Postgraduate Studies Projects

The Experimental Cardiology Laboratory is well equipped with cutting-edge facilities and has been at the forefront of in vivo heart research using mouse models for the last 10 years in Australia. Our research has focussed on mechanisms and novel therapies of pathological components of the failing heart, in particular, contractile dysfunction, myocardial hypertrophy and ischemia, cardiac fibrosis, adrenergic mechanisms and arrhythmias.

We are seeking motivated and enthusiastic Hons and PhD students interested in working with animal models of heart disease. We are currently offering 4 projects, listed below. The nature of these projects would particularly suit students with a background in physiology, biomedical sciences or pharmacology. We have a committed research team experienced in student supervision.

Project 1 - Anti-platelet interventions alleviate post-infarct myocardial inflammation and injury

Supervisors:           Xiao-Jun Du, Xiao-Ming Gao, Anthony M. Dart

Platelet activation and aggregation at atherosclerotic arteries are well known to induce ischemic events to the heart or brain. Current clinical use of anti-platelet drugs is aimed at limiting the ischemic injury or, in the setting of primary stent angioplasty after acute MI, to inhibit re-stenosis. We have conducted a series of studies in mice with myocardial infarction (MI) focusing on regional inflammation and its consequences. These studies have shown an early onset and severe inflammation in the mouse infarcted myocardium leading to acute ventricular remodelling and wall rupture. This is due to leukocyte-derived expression of matrix metalloproteinases (MMPs) that mediate breakdown of collagen fibrils with consequent loss of wall tensile strength.

Platelets are not only implicated in physiological hemostasis and pathological thrombosis, but also in inflammation through platelet-leukocyte interactions mediated by membrane molecules that function either as receptors or ligands, as well as release of numerous pro-inflammatory mediators (cytokines, chemokines) and MMPs. Our very recent experiments have revealed for the first time the regional accumulation of platelets within the infarcted myocardium (Figure) and that inhibition of platelet activation by using the platelet inhibitor clopidogrel largely prevented rupture in this model.

Based on these findings, we propose that platelets play a pivotal role in post-MI regional inflammation directly by contributing to inflammatory process and indirectly by promoting leukocyte infiltration. Thus, pharmacological or genetic interventions inhibiting platelet adhesion, activation and aggregation would be beneficial in the setting of acute MI, efficacy independent of action on arterial thrombosis. Knowledge in this area is vital considering that anti-platelet therapy (clopidogrel plus aspirin) is routinely prescribed to patients with acute MI, albeit with the primary aim to prevent coronary artery thrombosis.

We will test the effects of interventions that inhibit platelet adhesion, activation or aggregation, on inflammatory markers and the degree of myocardial injury of the mouse heart with MI induced surgically by coronary artery occlusion. We will test a few anti-platelet drugs or antibodies for their potential efficacy in mice with surgically induced MI. Parameters include: incidence of rupture;  infarct size, inflammatory cell infiltration of the infarcted myocardium (by immunohistochemistry, IHC), gene expression of cytokines, chemokines and MMPs of the infarcted myocardium (by RT-PCR), MMP abundance and activity of infarcted myocardium (by gelatin zymography or Western blotting) and regional platelet accumulation (by IHC).  In addition, experiments will be conducted on strains of mice with disruption of platelet-specific genes and hence loss of particular function.

Whereas the significance of platelets in thrombosis within atherosclerotic coronary artery has been well appreciated, the role of regional accumulation and activation of platelets in mediating myocardial inflammation and injury remain largely unexplored. The results generated from this project would provide important insights into this aspect and contribute to our understanding on the use and efficacy of anti-platelet therapy in the setting of acute myocardial infarction.

Project 2 - Activation of PI3K signalling pathway in ischemic post-conditioning cardioprotection

Supervisors: Xiao-Ming Gao, Julie McMullen and Xiao-Jun Du

Acute myocardial infarction (AMI) is the largest single cause of death in the industrialised world. After onset of AMI, the current clinical treatment is to restore the blood supply to the ischemic heart, by this way to limit the extent of tissue injury. However, experimental and clinical studies have shown that the initial phase of reperfusion to an ischemic heart can stimulate a vigorous inflammatory response, that will further damage the injured myocardium and lead to heart dysfunction and failure, and 38% patients will ultimately die within one year.

It has been reported that several cycles of brief coronary artery occlusion and reopening prior to sustained ischemia (preconditioning) or started during early reperfusion after prolonged ischemia (post-conditioning) can protect the heart against ischemia-reperfusion (I/R) injury by reducing infarct size, limiting the local inflammatory response and improving cardiac function. This phenomenon is now called as “ischemic pre- or post-conditioning”. Recently, a number of experimental studies have indicated that activation of a pathway via PI3K, a key kinase that mediates survival signalling, may play an important role in fulfilling such cardioprotection. So far, most studies addressing this issue were performed in vitro, and this protective effect has only been shown up to a few hours after ischemia-reperfusion. Importantly, the long-term efficacy has not been demonstrated. In addition, two subtypes of PI3ka  and PI3Kg presented in the heart have distinct biological function and the involvement of the subtype of PI3K remains undefined.

This project will use a number of novel genetic-manipulated mouse strains, such as constitutively activated PI3Ka (caPI3K) with enhanced PI3Ka function, dominant-negative PI3Ka (dnPI3K) with suppressed PI3Ka function or PI3Kg knockout in the heart, to study the long-term effects of different interventions in PI3K on mice with I/R injury and to define the subtype of PI3K responsible for such cardioprotection. The results from this project will bear important significance in improving therapy of AMI. Students would have chance to observe, learn and practice a range of exciting research techniques, including, microsurgery, echocardiography, micro-catheterization and biochemical and molecular assays.

Project 3 - Pivotal role of NADPH oxidases/p38 MAPK in mediating adrenergic signalling in the failing heart

Supervisors: Qi Xu and Xiao-Jun Du

Heart failure (HF) is the leading cause of death in Australia, affecting over 2% of the population.  Although HF represents the endpoint of varying etiologies, a common feature is excessive activation of the β-adrenoceptors (β-AR) in the heart. Drugs that block β-ARs (β-blocker) are commonly used in HF therapy. The consequence of β-AR activation has been described as “double-edged”. On the one hand, increased β-AR stimulation may assist the function of the failing heart by promoting the force of muscle contraction and heart rate. On the other hand, sustained β-AR stimulation leads to detrimental consequences, resulting in deterioration of function and irreversible HF. The mechanism(s) underlying the detrimental effects of chronic β-AR stimulation on the heart are not fully understood. This lab has recently found that it was the production of free oxygen radicals due to activation of NADPH oxidases (enzymes) that plays a pivotal role in mediating β-AR activation-induced adverse effects. In this project, we will use genetic modified mouse models to examine whether disruption of NADPH oxidases, a key source of free oxygen radicals, can prevent the adverse biological consequences while promote the contractile-enhancing effects of β-AR activation in diseased hearts.

Functional changes will be assessed using various physiological procedures, including non-invasive echocardiography and cardiac catheterization. Histological, cellular and molecular changes will be assessed by biochemical, molecular biological and morphological assays, such as electron spin resonance (ESR), gel electrophoresis and High Performance Liquid Chromatography (HPLC).

Project 4 - Cardiac phenotype in a transgenic model of Huntington’s disease

Supervisors: Xiao-Jun Du, Geoff Head (Neuropharmacology Lab)

Huntington's disease (HD) is one of the neurodegenerative diseases due to intracellular accumulation of poly-glutamine (Poly-Q) aggregates with profound interference in gene expression in the brain tissue. HD represents a single gene mediated neuronal disorder with poor quolity of life and shortened life-span. Although heart failure is known as the second leading cause of death in HD patients accounting for >30% mortality, the mechanism of possible cardiac abnormalities remain largely unexplored either clinically or experimentally. 

This proejct will be conducted using a transgenic mouse model of HD, R6/1, due to expression of a human Huntington gene derived from a HD patient. Our recent experiments on this strain of mice have revealed significnat abmormalities in the cardiac regulation by the autonomic nervous system. As the consequence, HD mice showed abbarent levels and regularity in heart rate and contractile function at baseline and during -adrenegic activation. Interestingly, these abnormalities occurs at pre-motor symdrome phase. We will examine the autonomic nervous function by telemetry method in conscious animals and test the cardiac responses to stressors including pressure overload and ischemic insult to fully explore the cardiac phenotype in the HD mice.

This study represents the first to thoroughly investigate cardiac phenotype in a clinically relevant mouse model of HD, an area that has rarely been explored. Whereas HD is not a common disease in Australia, its genetic mechanism is representative of a class of neurodegenerative diseases (e.g. Alzheimer's, Parkinson's, familial amyotrophic lateral sclerosis FALS), recently defined as Poly-Q diseases.

Project 5 - Role of low affinity 1-adrenoceptors in heart disease

Supervisors: Xiao-Jun Du, Helen Kiriazis, Peter Molenaar (Queensland University of Technology)

Although chronic -adrenergic receptors (AR) activation in the diseased heart leads to adverse consequences, the mechanism remains poorly defined. Despite the common use of -blockers, heart failure is still poorly controlled, characterized by poor prognosis, morbidity and mortality. Thus, further research in this area would be important to further our standing in the mechanism and optimize therapy targeting the -AR signalling. Pharmacological studies in vitro have shown that a subgroup of b₁-adrenoceptors exists at high (b_1HAR) or low affinity status (b_1LAR). Whilst the b_1HAR can be effectively blocked by commonly used -blockers, b_1LAR cannot be blocked. Both b_1HAR and b_1LAR share the same signalling mechanism by activating stimulatory Gs-protein and protein kinase A. Thus, b_1LAR is responsible for the continuous -adrenergic signalling in the presence of -blockers. It remains completely unknown regarding the physiological significance of b_1LAR, particularly in the setting of heart disease in which sympathetic nervous activity is known to be activated.  

We have shown for the first time in vivo that chronic stimulation (over 4 weeks) in mice with a b_1LAR agonist caused dose-dependent increments in heart rate and ventricular fractional shortening. This project is designed to explore the role of b_1LAR in the transition from compensatory cardiac hypertrophy to heart failure. We hypotheses that constant activation of b_1LAR would be deleterious in the development and progression fo heart failure in diseased hearts. Experiments will be conducted in a mouse model of pressure overaload hypertrophy and treatment with the b_1LAR agonist will commence at week-5 after full development of ventricular hypertrophy, for a period of 4 weeks. The functional and histopathological changes induced by _1LAR activation will be assessed by techniques including echocardiography and micromanometry. Comprehensive molecular and pharmacological experiments will be performed to explore the mechanism.

This project would document that role of activation of _1LAR in the heart in vivo, thereby paving the way for development of new _1LAR blocking agents. The outcomes would have the potential to change our way of thinking of -blockers for heart failure.