What Makes Deer Antlers Unique
For mammals, most body parts stop growing when the animal reaches adulthood. This is unique. These antlers regenerate themselves each year in the late summer/early fall. However, the mechanism that this regeneration process happens through is not always clearly understood. Some studies suggest that the incredibly rapid growth, up to 2 cm per day, that is seen is due to parathyroid hormone-related peptide and retinoic acid (RA). This same chemical substance is essential in in vitro growth, allowing cells to differentiate into chondrocytes, osteoblasts, and osteoclasts.
Simply put, this regeneration process appears to be stem cell-based, and thus, it potentially gives medical hope to thousands of people who have lost limbs and other appendages.
The Medical Problem of Lost Limbs
Statistics suggest that approximately 2 million Americans are affected by limb loss, and the numbers worldwide are even more dramatic. Contrary to the popular opinion that limb loss is primarily driven by trauma, this is in fact not the case, at least not in the United States. Although limb loss related to trauma may be more common in certain war-torn areas of the world. In the United States, on the other hand, limb loss is primarily linked to vascular diseases, including diabetes. As the American population continues to age, coupled with dietary challenges and an increasingly sedentary lifestyle, more people may be impacted by diabetes and run the risk of losing a limb. In addition to trauma and diabetes, other diseases, such as bone cancer, may play a role in limb loss.
In recent decades, technology has led to dramatic improvements in prosthetics. However, prosthetics remain extremely expensive. An artificial leg, for example, may cost up to $50,000. And, it is important to remember that these limbs have a very limited useful lifespan. For example, a limb may last only 3 – 5 years, and this lifespan may be even shorter if it is for a growing child or teenager. Even with state-of-the-art prosthetics, many people still experience limited mobility.
Many of the concerns associated with prosthetics could be alleviated if we were able to scientifically regenerate limbs.
Join our Stem Cell Discussion & Information Facebook Group today!
Stem Cells and Limb Regeneration
We’ve explored in detail the many different areas in which stem cells have transformed the medical sphere. For example, stem cell therapy has proven to be an effective alternative to traditional knee replacement surgeries. Stem cell therapy reduces many of the risks traditionally associated with surgery, such as post-surgical infections, and dramatically shortens the recovery time. Stem cell treatment has also shown promise in treating a wide variety of cancers.
The question remains: Can these advances be applied to limb loss and limb regeneration?
Many animals, including a significant number of amphibians, are able to successfully regenerate limbs that are lost for a variety of reasons. However, mammals, including humans, lack this biological ability, with the exception of the deer antler example that was highlighted and described in greater detail above.
It is important to remember that limb loss generation is complicated. Regrowing a limb does not simply mean regrowing bone. It also requires regenerating a wide range of blood vessels and nerves, as well as skin and muscles. Scientists argue that some parts of the limb will be easier to regenerate than others. For example, human skin is a very durable organ that already undergoes regeneration. The human skin will regenerate after a cut—filling in the damaged tissue. Skin regeneration for the replacement limb would involve the same mechanism, just to a dramatically greater degree.
But, other components of the limb may be harder to grow or regenerate.
Another issue related to limb regeneration is that not only do these components need to grow, but they also need to regrow in the correct place and order. For example, tissue at the fingertips may be very different than tissue at the elbow. Similar concerns exist in the legs as well. Muscles, tissue, and nerves in the feet play a very different role than the same components in a person’s thigh. Simply put, it is not simply regeneration that we are looking for, but controlled regeneration.
The regeneration process in deer antlers, which is based on stem cells, provides one clear example of how technology may eventually be extended to human limb regeneration. There are numerous other examples in the animal kingdom that could be used as a building block moving forward.
For example, salamanders have a strong ability to regenerate, and, research is being conducted to determine what biological and chemical features in the salamanders enable this process. If this can be identified, then it may be possible to apply this to a person (despite the obvious genetic differences between salamanders and humans).
Additional insight has also been gained in studies of mice. In this research, it appears that the Lin28a gene allows mice to regrow tissue at the tips of their ears. However, as mice age, this gene is eventually turned off and re-growth is no longer feasible. Research continues to explore if this concept can be extended to humans, as well.
As this research seems to suggest, human limb regeneration may be feasible by harnessing new stem cell technology, as well as other scientific insights. However, it is not clear what time frame we are talking about, will these innovations happen in the next several years or are we talking about decades? If one thing has been learned about stem cell research, it is that it is difficult to predict the speed of innovations. For example, we regularly highlight insights and breakthroughs that would previously have been unthinkable.
At first glance, deer antlers may not seem to have a lot in common with human limb regeneration. But, in fact, deer antlers, and the process through which they regenerate at rapid rates each year, may be the key for millions of Americans (and others worldwide) who are impacted by limb loss. Deer regrow their antlers via a stem cell process. If this process can be better understood, then it could be applied to human limbs. However, it is important recognize that this process will not be easy. Regenerating a limb requires everything from re-growing bones to generating new muscles, nerves, and blood vessels. And, it also requires organizing this growth.
Human limb regeneration may not be feasible immediately. However, by learning from examples in the animal kingdom, ranging from salamanders to mice to deer antlers, it could be the next wave in how stem cell therapy changes the face of medical care and positively impacts thousands of people.