CSB #5: Breakthroughs in Tissue Regeneration by Madhu Nori

At companies such as Organogenesis Inc. and ReNeuron, researchers are looking into the field of regenerative medicine, which is the science of growing new human body parts. The typical strategy for regeneration would be through stem cells, because, as they are not set/destined to become one type of cell yet, they have the ability to set apart and mature into many different cell types, including cell types that the adult body cannot normally regenerate. It's a simple enough idea, but it's difficult to implement because it is politically opposed, as it could require the use of embryonic stem cells, which may strike some people as unethical. Also, there would be countless technical challenges. However, so far, stem cells have only been used for bone marrow transplant patients, and more widespread stem cell therapies seem to be possible in the far future. With stem cell therapy, doctors would prescribe a potion that lets patients grow their own stem cells instead of giving a patient a sprinkling of stem cells.

Kostandin V. Pajcini and Jason H. Pomerantz in the Blau lab at Stanford University are examining how certain fish and amphibians can regrow tissue in their muscles, eyes, and hearts, while mammals cannot. Pajcini's team began by noticing an evolutionary pattern: basic organisms are good at growing new muscles, but complex vertebrates are bad at it. The human body cannot grow new skeletal muscles for two reasons. First, skeletal muscles are stuck in interphase, so mitosis does not start. Second, skeletal muscle cells have a strange characteristic that makes mitosis impossible. Pajcini and colleagues hypothesized that the key to regeneration is still carried within the mammalian genome, it's just being blocked by genes that mammals have, and amphibians do not. The ability to regenerate muscle tissue is obviously a great survival skill, so it is perplexing that evolution has subdued it.Studies on newts provide the answer: research shows that genes involved in newt tissue regeneration are also genes involved with how human cancer is caused. An example is the retinoblastoma gene, or Rb. The gene named because of the retinal cancer that results if it is mutated in humans. But in newts, deactivating Rb's protein product gives the signal that it is time to sprout a new muscle.

Pajcini's team looked to nature to try to produce a mammalian version of the newt's awesome limb-sprouting capability. But looking for inspiration in nature is not the only way to get results. Many other methods are being researched currently, such as "reprogramming" mature cells that didn't come from embryos or immature tissue to become stem cells, adopt a different job/function, and "turn off" certain genes that may prove to be harmful or unnecessary in that cell. By the time these methods are safely applied to humans, our stem cell therapies may be advanced enough to safely help people with a variety of conditions, and growing our own cells may no longer be necessary.What are some of the hurdles that need to be overcome before such research findings can be translated into workable therapies? Isn't it always good to have alternative methods if one method proves intractable? In the far future, will we be growing new cells and muscle tissues on our own?

Citations:

Tanenbaum, Jessica. "Breakthroughs in Tissue Regeneration." Science Online. Facts On File, Inc. Web. 7 Mar. 2011. .