Spatial and temporal changes in myogenic protein expression by the microenvironment after freeze injury

Abstract

Skeletal muscle has the remarkable capability to regenerate itself following injury. Adult myogenic stem cells (MSCs) are responsible for the repair and regeneration, and their activity is controlled by intrinsic and extrinsic factors. The aim of this study was to examine and compare the expression levels of Pax3, Pax7, MRF and p38 proteins during the course of regeneration and in different areas of the focal freeze-lesion damaged adult rat TA muscle. Using the focal freeze injury model, immunohistochemistry, laser-capture micro-dissection and Western blot analysis were performed. The results show that (1) in the severely damaged area, the focal freezelesion injury significantly activated Pax7 and myogenin expression within 7 days and down-regulated Pax3, MyoD and Myf-5 within 1 or 3 days, and (2) the level of the p38 protein was strongly and transiently upregulated in the whole muscle on day 7 following injury, whereas the level of the pp38 protein was downregulated within 3 days in the severely damaged and non-damaged areas. These findings indicate that the temporal (e.g. the time course of regeneration) and spatial (e.g. three zones created by the focal freeze-lesion) cues in a regenerating muscle have a significant impact on the activity of the adult MSCs.

Effects of photobiomodulation therapy on regulation of myogenic regulatory factor mRNA expression in vivo: A systematic review

“…Contusion injury in rat models often results in change to MyoD expression within 4 to 8 hours post-injury, which declines by 8 days [5]. In contrast, prior research with cryoinjury models has shown that MyoD and Myf5 initially downregulate for 7 days, after which PAX7 downregulation occurs, enabling SC proliferation through expression of the early MRFs [35]. This may explain why MyoD expression changes were analysed more often from 7 days onwards, and why a significant increase was noted by most of the studies analysing expression at this time.…”

“…Cryoinjury generally exhibits distinct and well-characterized layers of damage, which are known to result in different MRF expression and regulation depending on the extent of tissue damage and should be considered a factor when analysing MRF expression [35]. Given the early expression of MyoD in some cases of skeletal muscle injury, it is unexpected that only one study analysed the effect at day 1 [26].…”

“…Studies of myogenin expression, have shown that it follows a similar pattern as MyoD during contusion injuries, upregulating within 4 to 8 hours and eventually declining at 8 days [5]. Cryoinjuries can differ, exhibiting myogenin upregulation within the severely damaged areas of tissue but only a weak expression at 7 days [35]. Myogenin expression has only been observed in two PBMT in vitro studies by Zhang et al and Mesquita-Ferrari et al, who observed myogenin expression at 24 hours and 24 and 48 hours, respectively [37,39].…”

“…This concurs with this current review's results, showing within the first few days post-injury, myogenin is not notably expressed. As myogenin is responsible for the terminal differentiation and fusion of myoblasts in mature muscle fibres, this may explain why it is not expressed during the early stages of injury [35]. Due to the limited numbers of studies MRF expression in the latter stages of injury at 7, 14 and 21 days, it is difficult to determine whether a trend of upregulation is present towards myotube maturation.…”