Background Modulation of post-ischaemic remodelling is a significant clinical need.¹ Ischaemia results in the loss of millions of living cells as a result of the hypoxic condition.¹ However, our tissue is programmed to compensate for this loss by activating a remodelling program which leads to the formation of a fibrotic scar.¹ Inspired by the natural extracellular matrix, we have developed an injectable elastin-based hydrogel which showed marked functional and biological improvements in the ischaemic hearts by using a large animal model.²

Methods Focal infarcts were induced in male sheep by multiple suture ligations of side branches of the left anterior descending coronary artery. Functional data of ejection fraction and fractional shortening were obtained using transthoracic echocardiography prior to the induction of infarcts, prior to intervention, and at three weeks after intervention. Samples were analysed by bulk RNA-seq, LC-ESI-MS/MS proteomics and N-glycomics. Histology included Masson’s Trichrome, anti-CD31 and lectin histochemistry.

Results ELRs-treated sheep showed less fibrosis and more angiogenesis compared to the untreated ones, as validated by expression, proteomic, glycomic, and histological analyses [3]. Remarkably, the effects of the hydrogel injection were already significant 21 days post-treatment, thus in the acute phase of the disease. Since our ELRs-hydrogel also contained matrix metalloproteinase-responsive motifs (MMP-2 and -9), this study showed that the combination of ELRs sequences together with MMP-2 and -9 responsive motifs in the crosslinked hydrogel network enabled the recruitment of endothelial cells to promote an angiogenic effect (figure 1). The enhancement of a stable angiogenic response resulted in a protective effect towards the cardiomyocytes located in the border zone of the infarct that play a crucial role in the functional recovery of the infarcted heart. Here, an unbiased approach based on RNA-sequencing and proteomic analyses enabled us to identify GATA4 as the most relevant regulator of the improved response in the hydrogel-treated sample. We have validated our molecular analysis by evaluating the preserved mitochondrial integrity in the GATA4+ cardiomyocytes in the border zone of the hydrogel-treated animals.

Conclusions In this up-to-date scenario, our ELRs-hydrogel has a distinct advantage for its translational potential due to its marked benefit despite the absence of any stem cell or growth factor. Our study highlighted the elastin-derived molecular signalling advantages, thus acting as a timely reminder not to underestimate the potential of ECM proteins which were only partially studied when compared with paracrine effect-dependent cellular systems.

Acknowledgements Seventh Framework Programme Grant Agreement no.: 317304; Centre for Microscopy & Imaging funded by NUI Galway and PRTLI, Cycles 4 and 5, National Development Plan 2007–2013; Science Foundation Ireland (SFI) and European Regional Development Fund under Grant Number 13/RC/2073.

References

1. Contessotto P, Pandit A, Therapies to prevent post-infarction remodelling: From repair to regeneration. Biomaterials 2021;275:120906

2. Contessotto P et al. Elastin-like recombinamers-based hydrogel modulates post-ischemic remodeling in a non-transmural myocardial infarction in sheep. Sci. Transl. Med. 2021;13:581

Ethics Approval All experiments in this study were performed following the regulations established by the European Union directive on the protection of animals for scientific research (2010/63/EU). All animal procedures and treatments were approved by the ethics committee at the Lithuanian University of Health Sciences.

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Abstract 42 Figure 1

Modulation of fibrosis and angiogenesisSchematics of the ELRs-hydrogel intervention in focal infarcts. Lower plots show the entity of the effects of the treatment on fibrosis, angiogenesis and cellular stress/integrity compared with the MI-only pathological condition