Use of heart transplantation is limited by severe shortage in donor organ supply, resulting in death of many heart transplantation candidates before a suitable donor heart becomes available.1, 2 In addition to the scarcity of total donor hearts, national transplant data collected by the Association of Organ Procurement Organizations indicates that nationwide approximately 70% of cardiac allografts were rejected for transplantation during 2009?2011. The majority of these hearts were discarded due to stringent acceptance criteria, one of which is the limited acceptable time between procurement and transplantation. This time correlates with progression of myocardial ischemia/reperfusion (I/R) injury, and constrains the acceptable geographic distance between the sites of donor heart explantation and transplantation. Overall, there is an urgent need to develop effective approaches to increase transplantable grafts by improving the numbers of organs which will fulfill acceptance criteria. Amelioration of I/R injury despite prolonged transport times and in organs felt to be potentially marginal will improve preservation of graft function, thus expanding the donor pool and increasing access. Human adipose-derived stem/stromal cells (hASC) represent a uniquely practical subtype of MSC, due to their abundance, the simplicity of isolation from adipose tissue and their rapid in vitro expansion capacity. We3 and others4 have shown that hASC produce paracrine factors that provide therapeutically beneficial effects in multiple pathological conditions. In the context of myocardial infarction, we have shown that hASC preserve myocardial function, inhibit apoptosis, and stimulate angiogenesis primarily through ASC-secreted factors.5 Moreover, we previously reported that pre-treatment of explanted hearts with hASC improved myocardial functional recovery following acute I/R injury in an ex-vivo heart perfusion system.6 Our preliminary data indicates that pre-ischemic infusion of ASC-derived paracrine factors also improves myocardial function during recovery from cold ischemia, with significant preservation of a normal molecular pattern ?fingerprint? of the myocardial transcriptome, as defined by deep RNA sequencing. These RNASeq experiments specifically indicate that cold ischemia leads to prominent disruption of a set of genes (Arnt/Bmal, Esrra, Per2, Per3, Cry2) governing the circadian clock within the myocardium, which in turn prompts a coordinated increase in transcription directing mitochondrial biogenesis; and that these disruptions are specifically counteracted by hASC factors. Accordingly, we propose the hypothesis that infusion of hASC-derived factors into the cardiac circulation will ameliorate ischemia/reperfusion-induced functional deterioration of model donor hearts ex vivo as well as of human iPS-derived cardiomyocytes in vitro, by mechanisms mediated by soluble growth factors as well as exosomes, which limit damage to cardiomyocytes by preserving a normal pattern of circadian gene expression and mitigating the induction of deleterious mitochondrial biogenesis. To test this hypothesis, we will employ three specific aims:
Aim 1. Evaluate the protective effect of extracorporeal infusion of human adipose stem cell conditioned medium (ASC-CM), fractions, on normal mouse donor heart preservation during cold static storage.
Aim 2. Identify the specific cellular targets protected by ASC-CM as well as its exosomal and extra- exosomal fractions, using human iPS-derived human cardiomyocytes (iCM), iPS-derived endothelial cells (iEC) cultured individually as well as together using a three-dimensional human ?myocardium-on- a-chip? (MOC) model organ.
Aim 3. Determine the relative roles of selected molecular components of the exosomal and extra- exosomal fractions of ASC-CM in protecting the human iEC and iCM in the MOC organ construct.
Cardiac transplantation is the ultimate treatment modality for terminal heart failure, a common disease in Veterans, but its use is limited by the supply of hearts. Despite this lack, more than half of donor hearts available for transplantation are not utilized. For example, progression of ischemic cardiac damage after explantation limits use of donor hearts from geographical areas far from recipients, due to the time required for transportation. We have shown that adipose stem / stromal cells (ASC), which are readily available and cultured, markedly ameliorate ischemia and inflammation in multiple organs, including the heart; that these effects are mediated by paracrine factors and lead to major changes in circadian and mitochondrial gene transcription. We will optimize the ability of ASC-derived conditioned medium to improve cardiac preservation, and obtain novel insight into the molecular mechanisms by which this is effective, thus expanding the donor pool to the hearts obtained from donors at long distances.
