Slashdot Mirror
Growing New Cartilage
bsletten writes "Researchers at the Duke University Medical Center have successfully grown fat cells into cartilage, that they hope to use to repair/create new joints for patients. Normal cartilage does not repair itself well so this should be a boon to people with knee and hip problems." Cartilage doesn't repair at all, and there aren't any good replacements for it. I think teflon disks are the state of the art now, and they wear out eventually, which necessitates more surgery. Creating real cartilage replacements would be a major advance.
Okay, I've actually worked in the Vacanti Tissue Engineering laboratory, the lab that did the Ear-on-the-back-of-the-mouse experiment. I've since moved on doing other work on stem cells.
Cartilage usually doesn't repair appreciably on its own because it is one of the least densely populated tissues in the body. Cartilage is mostly extracellular matrix (ECM) proteins like collagen with a few cells scattered here and there to put out enough protein to maintain the tissue structure. It's also very poorly fed as few blood vessels travel through the cartilage so the few cartilage cells (chondrocytes) present operate at a slow metabolic pace too.
Cartilage has been an early and popular target of tissue engineering efforts. First of all it's a relatively homogenous, simple tissue. Secondly, alot of people have problems with damaged cartilage. What's done is that a porous 'scaffolding' of some material which will break down in the body is molded into the desired shape and then cells are 'seeded' onto the scaffolding with the intention that they will colonize it and grow. The breakdown characteristics are matched as closely as possible to the ECM buildup of proteins released by the cells. Eventually the artificial scaffolding is replaced by tissue. That's what the 'ear' on the back of the mouse is (by implanting it in a mouse, the engineered tissue gets fed in an 'in vivo' environment). Tissue engineered this way has yet to match the physical properties of normally produced cartilage, but there are approaches being investigated to improve these characteristics such as growing the tissue under a physical stress load.
The limiting reagent in this process is the supply of cells for seeding. That's why this story is news. During development, cells take cues from their environment and long range chemical signals to decide where they are and consequently what cell type would be apporpriate to differentiate into. However, not all of the cells in the body move into a final specific cell type. Some of them remain generalized as a pool or reserve of cells. Bone marrow is the easiest example of this. That's what has been taken advantage of here. The chondrocytes in this experiment were developed from stromal cells (not fat cells like the headline states). These are a less specific cell type than either chondrocytes or fat cells (adipocytes). They were grown in a physical environment and fed chemical signals that 'convinced' the cells they needed to become chondrocytes. Figuring out these conditions and signals is a nice piece of work.
There are quite a few pieces of research like this coming to light in the last two years. The direction of research in the stem cell field is moving towards trying to turn 'stem' cells from one particular tissue into developed cells of another tissue. Some labs are even trying to take fully differentiated and presumably committed cells and get them to turn into other cell types, sometimes referred to as 'trans-differentiation'. In that regard, this research isn't earth shattering, it's one more piece of confirmation. Also, if trans-differentiation is confirmed as a general trend, then you could conceivably get chondrocytes from many many different tissues in the body.
As a source for engineered tissue though, this has the practical advantage of being from a readily available source. Nicely done.