Molecular CardiologyLaboratory

Key Research Areas

• Cardiac regeneration
• Heart failure
• Hypertension
• Spontaneous coronary artery dissection (SCAD)

Research Overview

Heart failure is a leading cause of morbidity and mortality in Australia, with 50% of people dying within 5 years of diagnosis—a prognosis worse than that of almost all forms of cancer. High blood pressure (hypertension) and loss of heart muscle cells after a heart attack (myocardial infarct) predispose patients to this syndrome. No therapies are available that specifically target the underlying causes of heart failure. Current treatments are aimed at relieving symptoms and slowing progression of this syndrome but, even today, the only definitive therapy is heart transplantation; a procedure that is plagued by limited supply of donor organs and by the need for life-long immunosuppressive therapy. Hence, there is an urgent need to develop novel preventative and reparative therapies.

Recent studies suggest that the human heart has a limited capacity for regeneration, albeit that this rapidly wanes in early life. This provides hope that this process can be reactivated in adulthood to affect repair of the heart injured by myocardial infarction of other insults. The Molecular Cardiology Laboratory, therefore, has a major interest in understanding the biology of postnatal heart development, particularly that of its constituent muscle cells (cardiomyocytes), as a prelude to initiating meaningful heart muscle regeneration in the injured adult or mal-developed infant heart.

Other major interests of the laboratory include the genetic and cell biological basis for Spontaneous Coronary Artery Dissection (SCAD), a form of coronary artery disease that causes death or presents as an acute coronary syndrome, predominantly (>95%) affects relatively young (<50 yr) women who lack traditional risk factors, and can recur (~20% of cases), as well as the role of adrenergic receptors in the regulation of cardiac contractile function, both physiologically and in disease settings.

Participate in SCAD research

The Victor Chang Cardiac Research Institute is leading Australian first research into SCAD. If you are a SCAD survivor and would like to be involved in the research program, please email: scad@victorchang.edu.au

There are 3 key projects underway in the Molecular Cardiology Laboratory, led by Professor Bob Graham;

1. Cardiac regeneration

As the body grows and matures, heart muscle cells lose their ability to divide—a process called terminal differentiation. This limits the ability of the heart muscle to regenerate after a heart attack. In collaboration with Prof. Ahsan Husain, Emory University, Atlanta, we shown that contrary to dogma spanning over 100 years, murine cardiomyocytes (CMs) although becoming quiescent by postnatal day 7-10 (P&-10) do not undergo terminal differentiation at this time but retain proliferative competence.

This allows them to re-enter the cell cycle at P14-15, resulting in a temporarily restricted proliferative burst that increase CM number by ~40%; a response triggered by a rapid increase in circulating thyroid hormone (T3) levels on P12 mediated by maturation of the hypothalamic-pituitary-thyroid axis. Maturation of this axis is profoundly influenced by nutrition status and by the presence of congenital heart disease. Thus, these findings may have important ramifications for heart development in children with growth retardation, given that stunting due to malnutrition affects over 209 million children under age 5 in the developing world, and in children with congenital disorders heart disease. Failure to attain the normal complement of CMs during postnatal development may also markedly impair resilience of the adult heart to injury.

Currently, we are dissecting the signalling pathways mediating T3’s mitogenic effects on CMs, as well as determining the transcriptional signatures underpinning postnatal CM development.

2. Spontaneous coronary artery dissection

Cardiovascular diseases remain the leading cause of premature death and disability in our society. To address this issue requires mechanistic insights into disease pathophysiology. One form of cardiovascular disease, which was thought to be rare but recently has been found to be the cause of 2-4% of all cases presenting with acute coronary syndrome (ACS) and to account for up to 24% of cases of myocardial infarction (MI) in women aged 50 yr, is spontaneous coronary artery dissection (SCAD).

SCAD is a non-atherosclerotic disease of coronary arteries that presents as an ACS or sudden death in younger women (45 – 52 yr), who are not overweight and have a low incidence of traditional risk factors, and can occur in families. It has also recently been strongly associated with fibromuscular dysplasia (FMD) with 45-86% of cases having been found to have non-coronary FMD on routine screening. Given that both conditions are uncommon, this suggests that SCAD and FMD are pathophysiologically linked. Of interest, a genetic association study of FMD in patients of European ancestry recently identified an intronic variant in the phosphatase and actin regulator 1 gene (PHACTR1), involved in angiogenesis and cell migration, with higher PHACTR1 expression in primary cultured fibroblasts of FMD risk allele carriers compared to non-carriers. We have recently reported on the outcomes of the first 40 of now almost 200 SCAD patients that we have accumulated, including six families with more than one affected, most of whom were accrued as a result of a social media survey. FMD was identified in 7 (37%) of 19 patients screened.

Interestingly, migraine was identified in 43% of the 40 cases, a prevalence that is similar to previous reports of SCAD (37.5% cases) and FMD (32.2% cases) and considerably higher than in the general population (12%, P0.001). Accordingly, we hypothesise that SCAD is due to a genetic susceptibility resulting from variants in the phosphatase and actin regulator 1 gene (PHACTR1), or in genes in functionally related pathways, involved in angiogenesis and cell migration. Further, we hypothesise these variants result in a systemic vascular process with both structural endothelial vulnerabilities and impaired vasomotor tone as possible mechanisms for both SCAD and migraine development, which is commonly observed in SCAD suffers, via altered functions of PHACTR1 or pathway-related proteins. Accordingly, we are currently undertaking genetic, genomic and cell biology studies to test these hypotheses in our cohort of SCAD patients.

3. Adrenergic receptors and heart failure

Chronic high blood pressure or the loss of CMs after a heart attack places a greater load on the heart. Because of the inability of adult CMs to divide, the heart cannot respond by increasing the number of cells, which would limit the amount of work that each cell has to do. Rather, the cells enlarge (hypertrophy). Although initially beneficial, the chronic effects of hypertrophy over time increase the energy demands of the heart and over many years can lead to impaired cardiac contraction. We are using pharmacological, biophysical and molecular modelling approaches, as well as genetically engineered animal models, to elucidate the molecular mechanisms that underlie hypertrophy and progression to heart failure. We are specifically focusing on alpha₁-adrenergic receptor-mediated signalling pathways, with the long-term aim of developing preventative therapies targetting this signalling pathway.

1. Lorand L, Graham RM. Transglutaminases: crosslinking enzymes with pleiotropic functions. Nature Reviews Mol. Cell Biol. 2003; 4:140-156
2. Nakaoka H, Perez DM, Baek KJ, Das, T, Husain A, Misono K, Im M-J, Graham RM. G_h: A GTP-binding protein with transglutaminase activity and receptor signalling function. Science 1994; 264:1593-1596
3. Semsarian C, Wu M-J, Ju Y-K, Marciniec T, Yeoh T, Allen DG, Harvey RP, Graham, RM. Skeletal muscle hypertrophy is mediated by a Ca²⁺-dependent calcineurin signalling pathway. Nature 1999, 400:576-581
4. Perez DM, Piascik M, Graham RM. Solution-phase library screening for the identification of rare clones: isolation of the a_1D-adrenergic receptor. Mol Pharmacol 1991;40:876-883
5. Graham RM, Perez DM, Hwa J, Piascik MT. a₁-Adrenergic receptor subtypes: molecular structure, function and signalling. Circ Res 1996; 78: 737-749
6. Fatkin D, Graham RM. Molecular mechanisms of inherited cardiomyopathies. Physiol Rev 2002; 82:945-980
7. Perez DM, Hwa J, Gaivin R, Mathur M, Brown F, Graham RM. Constitutive activation of a single effector pathway: Evidence for multiple activation states of a G-protein-coupled receptor. Mol Pharmacol 1996, 49:112-122
8. Nanda N, Iismaa SE, Owens WA, Husain A, Mackay F, Graham RM. Targeted inactivation of G_h/Transglutaminase 2. J Biol Chem 2001; 276:20673-20678
9. Lin F, Owens WA, Chen S, Stevens ME, Kesteven S, Arthur JF, Woodcock EA, Feneley M, Graham RM. Targeted a_1A-Adrenergic receptor overexpression induces enhanced cardiac contractility but not hypertrophy. Circ Res 2001; 89:343-350
10. Lismaa SE, Holman S, Wouters MA, Lorand L, Graham RM, Husain A. Evolutionary specialization of a tryptophan indole group for transition-state stabilization by eukaryotic transglutaminases. Proc Natl Acad Sci (USA) 2003; 22:12636-12641
11. Begg G, Carrington L, Stokes P, Matthews JM, Wouters MA, Husain A, Lorand L, Iismaa SE, Graham RM. Mechanism of allosteric regulation of transglutaminase 2 by GTP. Proc Soc Natl Acad Sci (USA) 2006; 103:19683-19688
12. Liu X, Gu X, Li X, Li H, Chen P, Giu H, Yuan P, Jin J, Jao H, Xi B, Chen D, Lai D, Graham RM, Zhou M. Neuregulin-1/erbB- activation improves cardiac function and survival in models of ischemic, dilated and viral cardiomyopathy. J Am Coll Cardiol 2006; 48: 1438-1447
13. Lismaa SE, Mearns B, Lorand L, Graham RM. Transglutaminases and Disease: Lessons from genetically-engineered mouse models and inherited disorders. Physiol Rev 2009; 89:991-1023
14. Macdiarmid JA, Amaro-Mugridge NB, Madrid-Weiss J, Sedliarou I, Wetzel S, Kochar K, Brahmbhatt V, Phillips L, Pattison ST, Petti C, Stillman B, Graham RM, Brahmbhatt H. Sequential treatment of drug-resistant tumors with targeted minicells containing siRNA or a cytotoxic drug. Nature Biotech 2009; 27:643-651
15. Jabbour A, Hayward CS, Keogh AM, Kotlyar E, McCrohon JA, England JF, Amor R, Liu X, Li XY, Zhou M, Graham RM, Macdonald PS. Parenteral administration of recombinant human neuregulin-1 to patients with stable chronic heart failure produces favourable acute and chronic haemodynamic responses. Eur J Heart Fail 2011; 13:83-92
16. Riek RP and Graham RM. The elusive p-helix. J Struct Biol. 2011; 173:153-60
17. Naqvi N, Li M, Calvert JW, Tejada T, Holman SR, Matsuda T, Lovelock D, Howard W, Iismaa SE, Crawford BH, Wagner MB, Lefer DJ, Graham RM, Ahsan Husain A. A proliferative burst during preadolescence establishes the final cardiomyocyte number. Cell 2014;157:795-807
18. Cannon L, Marciniec T, Mearns B, Iismaa S, Nikolova-Krstevski V, Rainer S, Humphreys D, Preiss T, Feneley MP, Graham RM, Fatkin D. Transient expression of Arg403Gln α-myosin heavy chain is an inductive trigger for sustained left ventricular hypertrophy. J Am Coll Cardiol 2015;65:560-569
19. Dhital K, Iyer A, Connellan M, Chee Chew H, Gao L, Doyle A, Hicks M, Soto C, Dinale A, Cartwright B, Nair P, Granger E, Jansz P, Jabbour A, Kotlyer E, Keogh A, Feneley M, Hayward C, Graham RM, Spratt P, Macdonald P. Adult heart transplantation with distant procurement and ex-vivo preservation of donor hearts after circulatory death: a case series. The Lancet 2015;385:2585-2591
20. Ngo T, Ilatovskiy AV, Stewart AG, Coleman JL, McRobb FM, Riek RP, Graham RM, Abagyan R, Kufareva I, Smith NJ. Orphan receptor ligand discovery by pickpocketing pharmacological neighbors. Nat Chem Biol. 2017 Feb 13(2):235-242