Successfully growing heart tissue transplants for valve replacement

Researchers have developed a new high-throughput microarray platform with which the growth and transformation of endothelial to mesenchymal tissue may be better understood, and perhaps even facilitated, according to study results recently published in the journal Biotechnology and Bioengineering.

Congenital heart valve malformations affect roughly 1% of the population, and heart valve replacements with mechanical or biological valves are necessary in many. Both replacement options, however, have drawbacks, and researchers have looked to tissue-engineered heart valves developed from autologous cells as a possible option.

“Science has long been working towards ways to minimize or eliminate the rejection risks faced by tissue transplant patients,” said Keekyoung Kim, MAsc, BEng, PhD, NSERC postdoctoral fellow at Harvard Medical School, Boston, MA, and assistant professor of engineering at UBC’s Okanagan campus.

“While the goal of using a patient’s own genetic material to grow a body tissue is still a long way off, this study has moved us further towards that goal. This new technique essentially allows us to use less material to study the heart-valve regeneration process more quickly and at a lower cost,” he added.

Using a high-throughput combinatorial microarray platform, Dr. Kim and colleagues studied microenvironmental regulation of endothelial-to-mesenchymal transformation (EndMT), which precedes the formation of nascent heart valve leaflets.

For this study, they placed various proteins, growth-influencing biological molecules, and simple cells in a number of different combinations on top of a gel-like substance, hydrogel. They then combined five extracellular matrix proteins (ECMPs) present in the heart valve—collagen I (C1), II (C2) and IV (C4), fibronectin (Fn), laminin (Lm)—with three growth factors: TGF-β1, VEGF, and basic fibroblast growth factor (bFGF).

After seeding mitral valve endothelial cells (MVEC) onto these arrays, they performed immunostaining and high-throughput image analysis to assess how EndMT was affected by the various combinations of ECMPs and GFs, and which cell combinations affected or influenced the metamorphosis of a single cell into the more complex cells necessary to grow heart valves.

In this way, they identified the specific protein and molecule patterns that affected EndMT in MVECs. For example, they found that TGF-ß1 brought about significant upregulation of EndMT, but bFGF or VEGF served to downregulate this process. They also found that ECM proteins have a possible influence on both MVEC attachments and responses to growth factors, and that fibronectin brings about better MVEC adhesion. Overall, collage IV and fibronectin both have a vital part in promoting EndMT process, they concluded.

“We’re confident this process can be used for other types of tissue, so we are currently in the process of building a microarray in the Okanagan so we can continue testing,” he concluded.

Dr. Kim conducted this study with fellow UBC researcher Zongjie Wang, ETH Zurich researcher Blaise Calpe and Prof. Ali Khademhosseini of Harvard’s Medical School.

This study was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant (RGPIN-2014-04010), and funded by the US Army Engineer Research and Development Center, the Institute for Soldier Nanotechnology, the NIH (EB009196; DE019024; EB007249; HL099073; AR057837), and the National Science Foundation CAREER award (AK).