Wound Healing

Emily Brown

Cellular proliferation is a vital process. Some people automatically have a negative connotation in regards to this matter. Their minds quickly go to the ugly side of cellular proliferation--cancer. In humans and other animals, cellular proliferation is necessary to sustain organs like the skin and hair. Cellular proliferation is also necessary for wound healing.

General Wound Healing Process

The wound repair process is complex and dynamic. The process can be divided into three stages: inflammation, proliferation, and remodeling. In general, the first bodily response is bleeding. Then, vasoconstriction and coagulation occur to stop the bleeding and form a clot. There is an influx of inflammatory cells to the damaged area and a scab forms. This inflammation stage protects the area from infection. As the area heals, new epithelial cells arise. In the following weeks or months, the scar tissue is remodeled.

Proliferation Focus

The inflammation stage of wound healing deposits mediators that promote cell proliferation, the second stage of the healing process. Activated platelets that work to coagulate also interact with the damaged parts of the tissue to release thrombin, which converts soluble, circulating fibrinogen to fibrins. Fibrins and platelets work together to form a plug. Platelets degranulate and attract cytokines and growth factors that pull more inflammatory cells into the area. These mediators also work as mitogens (inducers of mitosis) for fibroblasts and endothelial cells. The fibrin of the plug functions as scaffolding for the proliferation and migration of these cells.
When neutrophils arrive on the scene, they begin to phagocytize the fibrin matrix to prepare for the new tissue formation. The neutrophils secrete cytokines to activate fibroblasts and keratinocytes and attract macrophages. The macrophages debride the wound and secrete growth factors such as fibroblast growth factor and epidermal growth factor. These growth factors initiate angiogenesis. These are the "bridge steps" between the tissue injury and the new cell growth.
As the fibroblasts, epithelial cells and endothelial cells migrate to the injured area, they undergo rapid mitosis. With the synthesis of extracellular proteins and proteoglycans along with collagen lysis and synthesis, the remodeling of new tissue occurs. Within hours of the wound occurring, a new layer consisting of almost solely keratinocytes migrates and begins stratification and differentiation to renew the barrier function of the skin at the injury site. This step is known as epithelialization. After this is complete, many processes slow down to allow the reconstitution of the entire stratified epidermis with a basal lamina. Here, the underlying connective tissue contracts to bring the edges of the wound closer together.
Over the next few days, the fibroblasts that were recruited begin to synthesize and deposit collagen to give the wound tensile strength. The fibroblasts also release proteases to dissolve nonviable tissue and the fibrin barrier from the original clot. These fibroblasts stick around in the tissue for a few weeks to continue the remodeling process.

http://www.nature.com/nrc/journal/v12/n3/images/nrc3217-f1.jpg

Proliferation Pathways Used

Sonic Hedgehog

http://eds.b.ebscohost.com/eds/pdfviewer/pdfviewer?vid=1&sid=c9396c10-4d27-4c5e-bed3-12ecfb1f526c%40sessionmgr114&hid=121

Inhibition of HH in adult skin results in defective hair follicle regeneration. The progeny of GLI1-expressing stem cells provide long-term contribution to regenerated epidermis.

Wnt/Frizzled 

http://eds.b.ebscohost.com/eds/pdfviewer/pdfviewer?vid=1&sid=c9396c10-4d27-4c5e-bed3-12ecfb1f526c%40sessionmgr114&hid=121

Epidermal activation increases stem cell numbers and promote hair follicle differentiation in wounded and unwounded skin. Loss of beta-catenin in wounds results in accelerated wound healing because of the reduced number of fibroblasts. Transgenic mice that overexpress stabalized beta-catenin in fibroblasts exhibit hyperplasia on wounding.

Role of MicroRNAs

Mills and Cowin (2013) reviewed various studies that looked at the role of microRNAs in epithelial proliferation. A table consisting of almost 100 different known miRNAs found in skin explained all of their foreseen roles. miR-21, shown on the left side of the figure below, is found in all structural and inflammatory cells. It works to increase fibroblast proliferation. Studies looking into the complex ways that miRNAs interact with this process are being conducted to better our understanding.

Possible roles of miRNAs in wound healing

http://eds.b.ebscohost.com/eds/pdfviewer/pdfviewer?vid=5&sid=60217b98-8bdd-485d-a0c1-f5959c1e57ad%40sessionmgr120&hid=103

Treatment to Expedite Wound Healing

Antrodia camphorata

Amin, et al. (2015) looked at the effect of Antrodia camphorata, a rare fungus from Taiwan, on wound healing. This fungus was ground into a powder and mixed with a topical vehicle to be applied to a surgical wound on mice. Researchers found that applying this fungus to the wound allowed significantly faster wound healing. The fungus in high concentrations significantly increased fibroblast viability and proliferation in this model. There was also less scar width at the wound closure site in the treated mice. These results led researchers to conclude that wound treatment with Antrodia camphorata should be further researched as a possibility for human treatments.

  

Macroscopic appearance of wound healing at day 14 after surgery: (a) rats treated with 0.2 mL gum acacia show wide wound closure area; (b) rats treated with 100 mg/mL of Antrodia camphorata show remarkably moderate wound closure area compared to vehicle; (c) rats treated with 200 mg/mL of Antrodia camphorata show remarkably smaller wound closure area compared to vehicle.

http://eds.b.ebscohost.com/eds/pdfviewer/pdfviewer?sid=999f1ca3-54ed-48e9-a48e-b57d02013a8e%40sessionmgr114&vid=4&hid=103

Topical Oxygen Treatment (TOT)

When a patient suffers from a disease that hinders or slows blood flow, wounds take a much longer time to heal. Because of ischemia in the tissues, nutrients and oxygen are limited in the area. Diabetic patients or patients with severe burns would both have ischemic tissue injuries. Rao, et al. (2016) looked at the effectiveness of TOT treatment on a hind leg injury in an ischemic mouse model. Overall, the introduction of oxygen topically into the wound sped up the formation of the granular tissue and increased the collagen network more quickly than the control group. TOT is much cheaper and less dangerous than the more common hyperbaric oxygen treatment.

Typical macroscopic results showing that the wounds of the oxygen group healed faster than those of the control group

https://www.jstage.jst.go.jp/article/jpts/28/1/28_jpts-2015-682/_pdf

Collagen fibers in the wounds. On day 7, there were many more collagen fibers in the TOT group

https://www.jstage.jst.go.jp/article/jpts/28/1/28_jpts-2015-682/_pdf

Lit Cited

Amin, Zahra A., et al. "Application Of Antrodia Camphorata 
Promotes Rat’S Wound Healing In Vivo And Facilitates Fibroblast Cell Proliferation In Vitro." Evidence-Based Complementary & Alternative Medicine (Ecam) 2015.(2015): 1-14 14p. CINAHL Complete. Web. 9 Mar. 2016.

Arwert, EN, E Hoste, and FM Watt. "Epithelial Stem Cells, Wound Healing And Cancer." Nature Reviews Cancer 12.3 (2012): 170-180 11p. CINAHL Complete. Web. 10 Mar. 2016.
Hunt, T. K., Hopf, H., & Hussain, Z. (2000). Physiology of wound healing. Advances in Skin & Wound Care, 13, 6. Retrieved from http://search.proquest.com/docview/222251945?accountid=27698
Mills, Stuart J., and Allison K. Cowin. "Micrornas And Their Roles In Wound Repair And Regeneration." Wound Practice & Research 21.1 (2013): 26-40 15p. CINAHL Complete. Web. 9 Mar. 2016.

Rao, Congqiang, et al. "Effects of topical oxygen therapy on ischemic wound healing." Journal of Physical Therapy Science 2016 Jan;28(1):118-23.