Comparative effects of low-level laser therapy pre- and post-injury on mRNA expression of MyoD, myogenin, and IL-6 during the skeletal muscle repair

This study analyzed the effect of pre-injury and post-injury irradiation with low-level laser therapy (LLLT) on the mRNA expression of myogenic regulatory factors and interleukin 6 (IL-6) during the skeletal muscle repair. Male rats were divided into six groups: control group, sham group, LLLT group, injury group; pre-injury LLLT group, and post-injury LLLT group. LLLT was performed with a diode laser (wavelength 780 nm; output power 40 mW' and total energy 3.2 J). Cryoinjury was induced by two applications of a metal probe cooled in liquid nitrogen directly onto the belly of the tibialis anterior (TA) muscle. After euthanasia, the TA muscle was removed for the isolation of total RNA and analysis of MyoD, myogenin, and IL-6 using real-time quantitative PCR. Significant increases were found in the expression of MyoD mRNA at 3 and 7 days as well as the expression of myogenin mRNA at 14 days in the post-injury LLLT group in comparison to injury group. A significant reduction was found in the expression of IL-6 mRNA at 3 and 7 days in the pre-injury LLLT and post-injury LLLT groups. A significant increase in IL-6 mRNA was found at 14 days in the post-injury LLLT group in comparison to the injury group. LLLT administered following muscle injury modulates the mRNA expression of MyoD and myogenin. Moreover, the both forms of LLLT administration were able to modulate the mRNA expression of IL-6 during the muscle repair process. (AU)