Developmental age-dependent effects of solubilized cardiac extracellular matrix therapy following myocardial infarction

Introduction: Cardiovascular disease (CVD) remains the leading cause of death worldwide and the primary cause of CVD-related death is myocardial infarction (MI). Patients who experience a moderate-to-severe MI will eventually progress to heart failure where only transplantation is an effective treatment. Therefore, the development of regenerative means to repair the heart is vital. One of the major challenges in heart repair is the limited proliferative capacity of postnatal cardiomyocytes (CMs), which shift from hyperplastic to hypertrophic growth shortly after birth. Studies by our group and others have demonstrated that the cardiac extracellular matrix (cECM) serves as an important factor in promoting cardiac differentiation and CM proliferation and also helps to drive a more regenerative healing response. While there have been significant studies on the use of adult cECM as a therapeutic post-MI, there have been few looking at early developmental aged ECM even though our group and others have shown potentially greater beneficial responses to younger ECM. Here, we investigate the potential of porcine cECM from different ages as a therapeutic method to improve cardiac regeneration post-MI.

Materials and

Methods: MI was induced in rats via permanent left anterior descending artery (LAD) ligation and animals were randomly assigned to one of 3 different groups: fetal, adult cECM from porcine, and non-treatment control. The fetal and adult pig cECM were decellularized as previously described by our lab and others. All treatments were solubilized in phosphate-buffered saline and injected immediately post-MI surgery. Echocardiography was employed to monitor cardiac function for 2 months post-treatment. The left ventricular (LV) pressure-volume (PV) loop measurement was performed on the day of harvest. Following the isolation of the hearts, tissue was analyzed via histology, bulk RNA-seq, and our novel ECM structure-function analysis method.

Results, Conclusions, and Discussions: Our first two cohorts of animals were recently completed, and we analyzed the functional data, including echocardiography and left ventricular pressure-volume (LV PV) loops (Fig. 1, 2). Studies have shown that a low ejection fraction (EF) following myocardial infarction (MI) is associated with an increased risk of heart failure. Our results revealed that rats treated with fetal ECM demonstrated an increase in EF (%) compared to those treated with adult ECM after 2 months, indicating improved cardiac performance (Fig. 1a, p< 0.08). The left ventricular relaxation time constant, Tau, is the most established index to describe left ventricular diastolic function. During the phase of MI, early filling occurs, leading to a reduction of Tau, which supports our results (Fig. 1b).
Additionally, we measured the end-systolic pressure-volume relationship (ESPVR), end-diastolic pressure-volume relationship (EDPVR), and preload recruitable stroke work (PRSW) from the LV PV loop (Fig. 2). A lower ESPVR slope indicates decreased cardiac contractility, while a higher EDPVR slope suggests a stiffer heart, both of which are commonly observed following severe MI. Collectively, fetal ECM emerged as a more promising therapeutic candidate for enhancing the regenerative performance of an infarcted heart, although further cohorts are being carried out to bolster the sample size and allow for more robust statistical comparisons. Other biological results, including histology, ECM structure-function analysis, and mechanical testing of the isolated hearts, are still ongoing to further support our conclusions.

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