Temple University School of Podiatric Medicine Journal Review Club
Editor's note: This post is part of the Temple University School of Podiatric Medicine (TUSPM) journal review club blog series. In each blog post, a TUSPM student will review a journal article relevant to wound management and related topics and provide their evaluation of the clinical research therein.

Article Title: G-Protein–Coupled Receptors and Pro-opiomelanocortin Expression After Light-Emitting Diode Irradiation in Diabetic Wound Healing
Author: Pongsathorn Chotikasemsri, PhD
Journal name and Issue: Wounds 29 Vol. 11 (2017), 311-316.
Reviewed by: Victoria Trovillion, Class of 2020, Temple University School of Podiatric Medicine

Introduction: Light-Emitting Diode Therapy for Chronic Non-Healing Diabetic Wounds

Diabetes mellitus is frequently associated with chronic non-healing wounds, many of which result in amputation. The combination of peripheral vascular disease, neuropathy, and impaired immune function contributes to a higher risk of injury and deficiency in healing. Wound healing is a complex process comprising eight important factors: (1) collagen synthesis, (2) cell migration, (3) cell cycle and differentiation, (4) angiogenesis and growth hormone, (5) blood clotting, (6) extracellular matrix and focal adhesion, (7) calcium ion signaling, and (8) immune and inflammatory response. In the diabetic cell, all these processes malfunction, with the exception of collagen synthesis, cell migration, and cell cycle or differentiation.

Previous studies found an association between diabetes and the precursor protein pro-opiomelanocortin (POMC) gene. POMC is normally expressed in pituitary melanotroph and corticotroph cells and functions to control body weight. Studies have suggested that a mutation in the POMC gene leads to early-onset type 2 diabetes and obesity. This correlation is under investigation for its potential use in diabetic therapy.

Light-emitting diode (LED) phototherapy at 660 and 890nm has been shown to significantly accelerate wound healing in normal, healthy patients. This therapy works through molecules with porphyrin structures that are able to trap photon energy and subsequently activate downstream processes. The current study investigated the results of a range of different LED phototherapies on gene expression and cellular function of diabetic cells compared with normal, healthy cells.

Materials and Methods

A light source was equipped with blue (495nm), green (520nm), and red (635nm) LEDs and was calibrated. A type 2 diabetic fibroblast cell line (DMCL) and a healthy, normal fibroblast cell line (NCL) were cultured and plated in a normal blood glucose level. Artificial wounds were created in both with a 1-mL plastic pipette tip. The treatment groups of DMCLs and NCLs were exposed to light at 0.67 J/cm2 for 10 minutes at different wavelengths, whereas the controls received no light exposure.

Immediately afterward, mRNA was extracted from the cells, and the samples underwent microarray assay. Differential gene expression analysis, gene ontology analysis, and pathway analysis were done on all gene expression profiles, with twofold differences.

Results

There was a significant change in differential gene expression for LED-treated DMCLs and NCLs compared with the respective controls. Red, green, and blue light created a statistically significant change in gene expression and cell function in both treatment groups, with the red and green light having the greatest impact on cellular response to healing. Specifically, the red light was shown to boost cell signaling and response to cytokine stimulus, whereas the green light improved the inflammatory response and increased cell proliferation. Although both DMCLs and NCLs showed molecular and cellular responses to LED phototherapy, the DMCLs had a significantly greater response.

Following pathway analysis, it was determined that the G-protein receptor (GPR) class A, with a rhodopsin-like structure, can directly bind the photons from the light and transfer signals to downstream pathways. Red light on NCLs showed upregulation of antiviral response pathways including Toll-like receptor (TLR) genes and interferon regulatory factors. Red light on DMCLs showed a significant increase in calcium-ion binding, regulation of acute inflammatory response, and blood clot formation genes. Red light also had an effect on POMC and corticotropin-releasing hormone (CRH) genes, which trigger other molecules to activate wound healing. Green light showed activation of genes similar to that observed with red light on both NCLs and DMCLs. Additionally, green light on DMCLs increased cell division and proliferation. Although blue light demonstrated some changes in molecular activities, it did not significantly alter wound healing capability, as previously reported in other studies.

Discussion

LED phototherapy, through activation of GPR class A, affects molecular activation and cellular function in both normal and diabetic cells. The red and green light could improve several factors involved in wound healing, including cell signaling, cell migration, cell proliferation, and inflammatory response. In the context of a chronic diabetic wound, LED phototherapy could promote wound healing by enhancing the ability of cells to proliferate and migrate across the wound defect, as well as enhancing immune system activity at the wound area. Blue light did not seem to improve any wound-healing process, most likely because of the structure of GPR, which may be activated only by photons from red and green lights.

POMC and CRH genes, usually suppressed by mutation in diabetes, increased expression in DMCLs treated with red and green light. This increase in activity could improve cellular homeostasis, cellular metabolism, and immune function in diabetic cells.

Conclusion

This study demonstrated that red and green LED phototherapy can potentially be utilized to accelerate wound healing, especially in diabetic ulcers. Additionally, the surprising improvement of antiviral response following phototherapy should be further investigated as a potential treatment for chronic viral infections such as herpes.

About the Author
Victoria Trovillion is a second-year podiatric medical student at Temple University School of Podiatric Medicine (TUSPM). She graduated from Franklin & Marshall College in Lancaster, PA in 2014 with a major in neuroscience and minor in anthropology. Victoria then received her Master's in Health Sciences at Drexel University in 2016. At TUSPM, she is currently the President-Elect of the student chapter of the American College of Foot and Ankle Orthopedic Medicine.

Dr. James McGuire is the director of the Leonard S. Abrams Center for Advanced Wound Healing and an associate professor of the Department of Podiatric Medicine and Orthopedics at the Temple University School of Podiatric Medicine in Philadelphia.