Healing Skin Wounds with Modified Proteins
by Elizabeth Burstein
Bioengineering in application - research findings from a bioengineerÕs lab bench have found an exciting new application: wound healing. In collaboration with the Department of Surgery at the Stanford University School of Medicine, Assistant Professor of Bioengineering Jennifer Cochran is working on expediting the process that the body uses to heal skin wounds by delivering a mutated version of a naturally occurring protein.
Natural Wound Healing
Epidermal growth factor (EGF), a naturally occurring protein, is crucial to the process of healing cuts as healthy skin cells gather and multiply in the affected area. By attracting fibroblasts--connective tissue cells that produce collagen--to the area of the wound, EGF helps to build new skin tissue. CochranÕs collaborator Dr. Michael Longaker explains the everyday importance of EGF in a Stanford News Service report by pointing out that Òanimals lick their wounds because their saliva includes a high concentration of EGF.Ó
After initially being attracted by EGF, fibroblasts produce their own EGF. This causes the cells forming the outer layer of skinÑcalled keratinocytesÑto multiply and close the wound. While EGF is one of natureÕs own powerful healing tools, it only exists at the wound site for a short time. The Cochran lab has therefore engineered mutated EGF that should last longer at the wound site to promote enhanced healing.
From the Lab Bench to the Clinic
Although the preclinical work with engineered versions of EGF now occurs at Stanford, Dr. Cochran began creating the mutant EGF proteins several years earlier. As a postdoctoral fellow at the Massachusetts Institute of Technology, Cochran used Òdirected evolutionÓ to modify the DNA that codes for EGF by replicating it tens of millions of times under a mutation-producing process. Then, in order to find modified EGF that would be most helpful in wound healing, she sorted through the mutants with a high-throughput assay to select ones that would associate most strongly with EGF receptors. Since her initial work at MIT, Cochran has found dozens of EGF mutants with approximately 4 - 30 times more receptor-binding strength than the naturally occurring growth factor. Ongoing experiments will determine whether this increase in receptor binding affinity will enable the engineered EGF to stay at a wound site for longer periods of time.
Although Dr. Cochran created these enhanced proteins at MIT, after arriving at Stanford she has been able to collaborate with physicians in the Department of Surgery. Cochran explains in Science News, ÒThe clinical collaboration here with Drs. Michael Longaker and George Yang in the Department of Surgery has now allowed us to take this project to the next level. We can start looking at the therapeutic efficacy of these proteins.Ó
Mutated Epidermal Growth Factor and Potential for in vivo Applications
The engineered EGF proteins were recombinantly expressed in yeast cells for preclinical testing. The group has utilized cell-based Òscratch assaysÓ in which a wound is simulated by scratching a 2-millimeter line through a thin layer of tissue in a Petri dish and engineered EGF proteins are added in a saline solution. Preliminary tests have indicated that certain EGF mutants cause cells to fill this artificial ÒwoundÓ faster than with natural EGF, indicating a potential for in vivo wound healing applications. After the scratch assay tests are complete, the group will test the most promising mutated proteins on mice.
Looking to the future
This past April, the Bioengineering Department granted $100,000 to Cochran, Longaker, Yang and research fellows Dr. Daphne Ly, Dr. Stayce Beck, and Stephen Lee to develop therapeutic applications using these engineered EGF proteins.
The potential therapeutic effect of mutated EGF is not just limited to patients with open wounds. Diabetic patients, for example, could benefit from this research, as they sometimes suffer from chronic skin lesions due to neutrophils clearing healthy tissue in a wound by staying at the wound site for too long. Cochran claims that other potential applications of EGF include Òaccelerate[d] healing in gastric and oral ulcers, skin graft donor sites, corneal epithelial wounds, and ear drum perforations.Ó Additionally, EGF may be used to regulate nerve injury response and regeneration. Currently, Cochran's team strives to develop a form of EGF that will treat chronic wounds that are incurable by natural healing and believes that this new approach will be more effective, cheaper and easier to use than alternative solutions for wound healing.