Platelet derived growth factor-A (Pdgf-a) gene transfer modulates scar composition and improves left ventricular function after myocardial infarction
Introduction
Heart failure (HF) is a progressive and debilitating condition, affecting over 37 million people worldwide and costing more than US$100 billion each year [1,2]. The adult myocardium has very limited self-regenerative capacity; previous studies have suggested a small proportion of existing cardiomyocytes can re-enter the cell cycle to proliferate, with a turnover rate estimated at 0.5% – 2% per year [3]. This is insufficient to replace the hundreds of millions of cardiomyocytes lost during and immediately following MI. As a result, the left ventricle undergoes adverse remodelling. Depending on infarct size, the bulk of the infarcted myocardium is replaced by collagen-rich scar tissue. Numerous cytokines and growth factors regulate the activation of cardiac interstitial fibroblasts and therefore extracellular matrix deposition and scar formation during post-infarct wound healing [4].
Platelet derived growth factor (PDGF) is a potent mitogen and chemotactic agent for cardiac fibroblasts. There are multiple PDGF isoforms (A, B, C, and D), which combine to form biologically active dimers. PDGF dimers bind tyrosine kinase receptors, platelet derived growth factor receptor alpha (PDGFRα) and beta (PDGFRβ) to initiate cell signalling [[5], [6], [7]]. We have previously identified a PDGFRα+ cardiac progenitor cell population and have reported on therapeutic effects of transplanting these cells [[8], [9], [10], [11]]. These PDGFRα+/CD90+/CD31- cells demonstrate a clonogenic progenitor phenotype and give rise to cardiac interstitial fibroblasts, vascular smooth muscle and endothelial cells.
PDGF and its receptors have complex timing and context-dependent roles in cardiac development, fibrosis and post-infarct remodelling. Although adverse pro-fibrotic effects in the normal heart after transgenic overexpression of PDGF isoforms have been reported [12], PDGFRα and -β signalling are also known to mediate effective and beneficial wound healing in the infarcted heart, orchestrating collagen deposition and neovessel formation [13]. Intramyocardial and systemic treatment with PDGF-AB enhances angiogenesis and reduces infarct size in small animal models [14,15]. Furthermore, our group recently demonstrated that systemic administration of recombinant human PDGF-AB improves survival and cardiac function in a pre-clinical, large animal model of MI [16]. Mechanistically, these benefits were mediated by increasing collagen anisotropy and neovasculogenesis.
Gene transfer via recombinant adeno-associated virus (rAAV) is a powerful method to overexpress a specific gene directly. Adeno-associated viruses have minimal immunogenicity compared to other vector types and can achieve persistent overexpression with minimal DNA integration in the host genome [17,18]. Here, we use rAAV9 vector-mediated gene transfer to investigate the therapeutic potential of Pdgf-a overexpression in a rat model of MI. We demonstrate that Pdgf-a upregulation in the heart reduces scar size, modulates scar collagen composition and increases vascularity in the peri-infarct region leading to improved post-infarct left ventricular (LV) function. This supports overexpression of PDGF-A after MI as a potential cardiac therapeutic.
Section snippets
Myocardial infarction (ischemia-reperfusion) model and rAAV9 Pdgf-a delivery
Adult male Sprague Dawley rats (8–12 weeks of age) were subjected to myocardial ischemia/reperfusion (I/R) injury by occlusion of the left anterior descending coronary artery (LAD) for 90 min [19]. rAAV9 Pdgf-a (1 × 10^11 vector copies per animal) was injected via the tail vein under anaesthesia, immediately following I/R. The control group was injected with the same dose of rAAV9 Empty. Two experimental time points were set for tissue harvesting; day 14 and day 28 post-I/R. All animal
rAAV9 Pdgf-a induces overexpression of PDGF-A and improves cardiac function after myocardial infarction
After confirming rAAV9 Pdgf-a transduction efficacy and Pdgf-a transgene functionality in vitro (Supplementary Fig. 1) we then evaluated rAAV9 cardiac transduction after systemic administration (tail-vein injection) in rats with induced myocardial infarction (MI). At 7 days post-MI, we quantified rAAV9 Pdgf-a and rAAV9 Empty vector copy numbers in the heart, liver, lung, and kidney (Fig. 1a). Vector copy numbers were detected in all organs, but were significantly higher in the heart and liver.
Discussion
This study demonstrates that systemic administration of rAAV9 Pdgf-a after induction of MI: 1) significantly improves LV function 28 days post-I/R; 2) increases revascularization of the peri-infarct border zone with de novo arterioles and capillaries, and 3) results in upregulation of COL3A1 in the infarct zone.
Recombinant AAV is the most commonly used gene chaperoning system in clinical trials for gene therapy [23]. As AAV serotype 9 (AAV9) has high transduction efficiency for rat myocardium,
Conclusion
This study shows that systemic gene delivery of Pdgf-a using the rAAV9 vector increases neovascularization and modulates scar collagen composition in the infarcted rodent heart, which is accompanied by an improvement in LV systolic function. This highlights the extracellular matrix as a potential target for therapies to improve ventricular function in the post-infarct heart.
Disclosures
The authors declare that there is no conflict of interest regarding the publication of this article.
Funding acknowledgement
This work was supported by the National Health and Medical Research Council [APP1100046]; the National Heart Foundation, Australia [100463]; and a Stem Cells Australia Project Grant.
Declaration of Competing Interest
None.
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Cited by (0)
- 1
FNR, ZEC and MO contributed equally to this work.
- 2
Masahito Ogawa (Present Address): Department of Regenerative Medicine and Tissue Engineering, National Cerebral and Cardiovascular Centre, Osaka, Japan.