Regeneration

It's the first official blog post! And what better way to kick it off then to talk about my Master's work. I did my Master of Science (MSc) at the University of Guelph in the Ontario Veterinary College's biomedical sciences department. I joined Dr. Vickaryous' lab in the fall of 2014 with no prior research experience and little expectation. I honestly did not foresee a career in research for myself. Like many students fresh out of undergrad, I was uncertain of my next steps and the opportunity to do an MSc kind of fell into my lap. I did not anticipate how much I'd come to love research.

Look how excited I am about doing science!

Look how excited I am about doing science!

Our lab aimed to answer one question: why are some organisms able to regenerate whereas others cannot? There is a broad spectrum of regenerative ability amongst different organisms. On one end of the spectrum, there are organisms like zebrafish that can regenerate their spinal cord, heart, retina, amputated fins or lesioned regions of the brain. On the other end of the spectrum, there are organisms who have a limited regenerative ability like humans. Of course, a number of species fall in between, including the humble leopard gecko (Eublepharis macularius). As the closest regeneration-competent amniote (an animal that develops in an amnion like humans), it is a great model to explore the underlying biology of regeneration.

Look how cute these baby leopard geckos are! 

Look how cute these baby leopard geckos are! 

Geckos have the ability to drop their tail if they are threatened by a predator. The tail undulates and distracts their would-be captor while they escape. After that it takes just over a month to regenerate a new tail that appears functional, yet structurally distinct from their old tail.

 
 

My project focused on skin regeneration aka wound healing. Broadly speaking, there are two forms of acute wound healing: scar formation and scar-free wound healing. If you injure the skin of a leopard gecko, whether on the body or the tail, it has the ability to replace its skin scar-free. In fact, the wound is indistinguishable from the surrounding uninjured tissue. So why are leopard geckos for example, able to regenerate their skin, but humans on the other hand, scar? 

 

A video of the phases of wound healing. A 3mm biopsy was created in the skin of the gecko and by the end of wound healing, the region that was biopsied was indistinguishable from the surrounding tissue.

 

The events of scar formation and scar-free wound healing are very similar. Generally, there is a phase of hemostasis (aka blood clotting) and inflammation, followed by a phase of cell proliferation (aka cell division), and finally a phase of remodelling. It is thought that the magnitude and duration of these events effect the ultimate outcome of producing either a scar or not. For example, the inflammatory phase is significantly more muted in scar-free wound healing compared to in scar formation. Another difference with scars is the formation of an exuberantly vascularized structure called granulation tissue, which forms during the proliferative phase of wound healing. The analogous structure in scar-free wound healing is a modestly vascularized structure called the blastema

 
This is a mature gecko blood vessel.  The blue indicates the nuclei of cells; the red indicates the blood vessel; and the green indicates support cells. Having the support cells surround the blood vessel indicates that it is a mature blood vessel. 

This is a mature gecko blood vessel.  The blue indicates the nuclei of cells; the red indicates the blood vessel; and the green indicates support cells. Having the support cells surround the blood vessel indicates that it is a mature blood vessel. 

 

The goal of my project was to improve our understanding of the biology of wound healing. I was initially interested in blood vessels and trying to increase their amount to induce granulation tissue formation - a hallmark of scar formation - in a model of scar-free wound healing. I thought that maybe this was the key event responsible for producing scars. Unfortunately, I was unsuccessful in even increasing the number of blood vessels. It turns out geckos are extremely resilient at maintaining their inherent nature to heal scar-free.

I took a step back and re-focused on the epidermis (the outermost layer of your skin) and the process of re-epithelialization (your outermost skin layer reforming following an injury). In organisms that can regenerate, this process occurs significantly faster than in organisms that scar. I looked at several major growth factors (broadly speaking, molecules that stimulate cellular growth) and looked at how their expression changed before, during and after scar-free wound healing in the leopard gecko. These factors that I investigated were for the most part, present throughout the entire process of wound healing.

The presence of two of these growth factors (and their receptors) called vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) respectively, in the epidermis suggested that in addition to helping re-establish homeostasis (maintenance of a stable internal environment, despite changes in the external environment), there could be some protective effects against UV damage. This implication is consistent with studies in mammals looking at these same growth factor families in the epidermis' as well, providing further support for this hypothesis.   

So what is the importance of studying wound healing? First and foremost everyone scars. Obviously not all scars are serious, we all get minor scrapes, but depending on the degree of the scarring and the location (e.g. over a joint), there can be a decrease in tensile strength, thermoregulation and somatosensation. There can also be significant psychological effects on a person. Down the line, this research will be especially important in developing therapies for burn victims and diabetic patients who have a difficult time healing. 

If you want to learn more - check out this one minute video our lab entered into the Natural Sciences and Engineering Research Council (NSERC) Science, Action! video contest narrated by yours truly. We did not win, but we were finalists! If you want to learn even more about the work that I did, click here to read the original academic publication.