Participation of the Immune System and Hedgehog Signaling in Neoangiogenesis Under Laser Photobiomodulation

Introduction: This study aimed to characterize immune and endothelial cells, myofibroblasts and pericytes, and positive cells for hedgehog proteins in late tissue repair of rats skin wounds treated with 670 nm photobiomodulation therapy (PBMT). Methods: A blind experimental study was conducted, in order to assess the effect of PBMT in later stages of healing, with emphasis on neoangiogenesis, immune cells and Hedgehog signaling. Forty Wistar rats were allocated randomly in two groups; control and treated with a diode GaAlAs laser (9 mW, 670 nm, 0.031 W/cm², spot size of 0.28 cm², fluence of 4 J/ cm² applied every other day, until a total dose of 16 J/cm² was achieved). Standardized skin wounds were performed and the animals were euthanized at 14, 21, 28 and 35 days. Tissue sections were subjected to hematoxylin-eosin and immunohistochemistry for CD31, NG2, smooth muscle alpha actin, CD8, CD68, Ptch, Gli-2 and Ihh. All histomorphometric data were statistically analyzed and significance level was at P<0.05. Results: At late stages of wound healing, neoangiogenesis persisted as revealed for the number of CD31+ cells (P = 0.016) and NG2+ and smooth muscle alpha actin positive pericytes (P = 0.025), for both experimental groups. By day 21, laser-treated group had decreased CD68+ cells (P = 0.032) and increased CD8+ (P = 0.038). At remodeling stage, there were positive cells for the hedgehog signaling pathway family which seemed to be activated. Conclusion: These data suggest that photobiomodulation therapy was able to modulate extracellular matrix remodelling even at the later stages of wound healing.