Cardiac Organogenesis: 3D Bioscaffolds, Bioenergetics and Regeneration

Abstract

Each year the Organ Procurement and Transplantation Network (OPTN) reports an increase in patients requiring an organ transplant without an increase in available donor organs, leading to a transplant gap that continues to widen. Over 70% of donor hearts are deemed unsuitable for transplantation each year, and a large number of these organs (~50%) are discarded due to poor organ function, decreased ejection fraction, disease, or cardiac arrest (Scientific Registry of Transplant Recipients (SRTR) Annual Data Report 2011).We therefore set out to improve knowledge in the field of cardiac transplantation in terms of organogenesis, bioenergetics, and regeneration. The main goal through tissue bioengineering is to regenerate and salvage discarded hearts through organogenesis, or to lengthen the total organ preservation time such that organs would not be thrown away while a recipient was waiting to be found. Our first hypothesis was that an optimized acellular extracellular matrix scaffold would allow for cell adherence, growth and proliferation, and could potentially be grown into a clinically transplantable organ. To achieve these goals, an optimized protocol was developed for the total acellularization of a whole porcine heart, leaving behind a 3D bioscaffold. We showed that acellularized matrices could be successfully seeded using endothelial cells for acellular vasculature and stem cells for other acellular tissues, both as a 2D matrix and within a constantly perfused 3D Langendorff setup bioreactor. In order to best understand cell-cell and cell-matrix interactions, cellular bioenergetics were evaluated. We hypothesized that the bioenergetic demand of the type and anatomical origin of stem cells would affect the regeneration potential dependent on intrinsic metabolic demand. We therefore showed a differential of the bioenergetic profiles of human adipose-derived stem cells isolated from various adipose depots, concluding that the physiological microenvironment that supports stem cells in specific anatomic locations can regulate how stem cells participate in tissue regeneration, maintenance and repair, and also will vary based on donor-differences. During organ transplantation, organ preservation solutions are created for use at specific conditions, such as on ice or at room temperature. We hypothesized that hypothermia would slow down cellular metabolism, and that solutions containing a higher content of antioxidants and other protective substrates against ischemic reperfusion injury would create the best organ storage conditions. We tested three organ preservation solutions against control media and normal saline at 4 and 21 degrees C, for 4 to 8 hours, investigating the bioenergetics of organ preservation solution effects on cardiac cells. By simulating clinical conditions, we were able to determine that one of our solutions was ideal and had protective effects for cells for up to 8 hours at 4 degrees C. Finally, we believed that studying existing cardiac patches and optimizing cardiac matrix design would lead to improved cardiac physiological function and would aid in healing and repair during cardiac surgery. Following a clinical case report showing new cardiac tissue growth after implantation of an acellular porcine extracellular matrix, we devised a proof-of-concept study to show that clinical matrices could be easily cultured in vitro. We successfully seeded these clinical matrices using human amniotic stem cells, a commonly used cell type for regeneration and repair after surgery. Our preliminary studies suggest that preconditioned matrices can be potentially used clinically for greater efficacy and tissue regeneration.