Matters of the Heart
There’s nothing quite like the human body. From ancient Egypt to the modern world, scientists have poked and prodded and marveled at such a feat of engineering and evolution. I often found myself sitting in biology classes, in awe at the power of nature. Such engineering is beyond our abilities. Or is it? As in every other aspect of life, scientists around the world are always pushing further the boundaries of what we know, understand and can recreate ourselves. So why not tackle our own organs?
Professor Doris Taylor (University of Minnesota) and her team are working on producing a bio-artificial heart. Much like the sci-fi concepts of cyborgs, it is a heart developed using both biological and mechanical properties. Although it will be engineered within their lab, the structure and cells will remain completely biological. Still confused? Here’s the basic idea. Take a donor heart, rid it of the cells that tie it to one specific individual, re-cellularise it with cells from the patient and transplant it into the patient without risk of rejection. But how does it work and does it solve the problems other scientists are facing?
Let’s look at basic organ transplants, which are now commonplace when dealing with organ failure and other diseases. Although many are very successful, they are not without complication, the most common of which is organ rejection. You see, your body is very special and unique. The DNA inside each of your cells is particular only to you. So if your body senses something awry, its first reaction is to attack. Research on the immune system has focused on investigating how we can repress parts of it without wiping out the whole defense system. But if the cells in the organ are your own, your body should recognize them and thus not reject them. This would also allow for more organs to be used, helping to solve the problem of organ sourcing. So that’s one thing dealt with, potentially.
Now, how do you get your own cells into a different organ? This is where stem cells and tissue engineering come in. Stem cells are cells within your body that can develop into any cell type, like muscle or brain cells. Some are embryonic stem cells. During the life of an embryo, cells all start off the same and through a series of biological, temporal and positional cues; they differentiate into specialist cells for each area of the body. So if we know what the cues are, we can harvest these cells and grow them in labs into different cells. Furthermore, many organs and tissues have un-differentiated cells within them which can also be used in the same way. So potentially, with a proper source of stem cells and a thorough knowledge of how to grow them, a multitude of cells with your DNA differentiated into the proper type could be used to re-cellularise the organ.
But let’s backtrack one minute. Aren’t all organs and tissues made up of cells in the first place? How do you rid an organ of its cells without destroying it? Organs and tissues are not only composed of cells. Cells secrete products which create the material base for the scaffolds. This is called the extracellular matrix and in certain parts of the body is more important than meets the eye. For instance, a tendon is actually composed of very few cells. When they develop, tendon cells secrete collagen, which accumulates into bigger and bigger fibers that make up the tendon itself. Similarly with a heart, once it is fully formed it is possible to rid it of its cells, leaving a perfectly formed heart matrix. It is notoriously complicated to grow a whole organ from scratch. This method would alleviate the need to produce an organ which has already developed flawlessly.
So that’s the theory, but how far has this research gone? Pioneers in the field, Professor Taylor and her lab have successfully decellularised a living heart, leaving only its matrix as a scaffold and re-perfused it with cardiac cells. Although they have not got to the stage of transplants yet, experiments comparing the bio-artificial heart with an organic heart have been promising. Not only have the cells re-integrated the organ and differentiated into the different types needed, it has been shown the heart is able to propel fluid in the highly regular manner which is necessary to pump blood around a body. Similar results have been established with liver and lung constructs with reports they were successfully re-implanted.
This research has pushed boundaries in a very complex and cutting edge field. Not only does it deal with rejection problems and organ sourcing; it could potentially be much simpler than growing whole organs from scratch. It might just be the future of organ and tissue engineering.