P21 Deficiency Delays Regeneration of Skeletal Muscular Tissue

Abstract

The potential relationship between cell cycle checkpoint control and tissue regeneration has been indicated. Despite considerable research being focused on the relationship between p21 and myogenesis, p21 function in skeletal muscle regeneration remains unclear. To clarify this, muscle injury model was recreated by intramuscular injection of bupivacaine hydrochloride in the soleus of p21 knockout (KO) mice and wild type (WT) mice. The mice were sacrificed at 3, 14, and 28 days post-operation. The results of hematoxylin-eosin staining and immunofluorescence of muscle membrane indicated that muscle regeneration was delayed in p21 KO mice. Cyclin D1 mRNA expression and both Ki-67 and PCNA immunohistochemistry suggested that p21 deficiency increased cell cycle and muscle cell proliferation. F4/80 immunohistochemistry also suggested the increase of immune response in p21 KO mice. On the other hand, both the mRNA expression and western blot analysis of MyoD, myogenin, and Pax7 indicated that muscular differentiation was delayed in p21KO mice. Considering these results, we confirmed that muscle injury causes an increase in cell proliferation. However, muscle differentiation in p21 KO mice was inhibited due to the low expression of muscular synthesis genes, leading to a delay in the muscular regeneration. Thus, we conclude that p21 plays an important role in the in vivo healing process in muscular injury.

In vivo analysis of γH2AX+ cells in skeletal muscle from aged and obese humans

“…Plasminogen Activator Inhibitor‐1 is a marker and mediator of cellular senescence, 54 but is induced by TGFβ in muscle, independent of senescence, and contributes to fibrosis 53,55,56 . p21 inhibits cell cycle progression in senescent cells, but also promotes apoptosis, 57,58 assists in maintaining cells in quiescence, 59‐61 is necessary for differentiation of satellite cells to myofibers, 62‐64 and is essential for skeletal muscle regeneration 65,66 . Further, some of the commonly used senescence markers appear to be tissue specific.…”

Development of autoimmune pancreatitis is independent of CDKN1A/p21-mediated pancreatic inflammation

“…In addition to its regulatory effect on cell cycle and consequently regeneration,35 p21 is involved in inflammatory and autoimmune diseases in several models, for example, atherosclerosis, lung inflammation, septic shock, arthritis and lupus 16 19 21 36. Evidence from these studies suggests that p21 influences proliferation, T cell activation, monocyte differentiation, that is, processes that are involved in the pathophysiology of pancreatitis.…”

CDK inhibitors for muscle stem cell differentiation and self-renewal

“…However, upon cardiotoxin (CTX) injury to the muscles, which induces muscle degeneration followed by regeneration, muscle regeneration in the p21 KO mice was greatly decreased compared to the wild-type muscle. There was the case of decreased differentiation of myoblasts as well as increases in cell proliferation, immune cell infiltration and increases in TUNEL-positive apoptotic cells in the p21 KO mice 97,98) . The ultimate regeneration that was detected in the p21 KO mice might be due to possible contributions from p27 and/or p57, indicating that p21 is required for proper skeletal muscle regeneration, and that the lack of the gene abrogates muscle differentiation 97) .…”