Elevated p21 mRNA level in skeletal muscle of DMD patients and mdx mice indicates either an exhausted satellite cell pool or a higher p21 expression in dystrophin-deficient cells per se

Abstract

Abnormalities in proliferation and differentiation of the dystrophin-deficient muscle are a controversial aspect of the pathogenesis of Duchenne muscular dystrophy (DMD). Analyses of molecules involved in cell cycle modulation do not exist in this context. Cells withdrawn from the cell cycle permanently express p21. The fact that p2 1, in contrast to other cell cycle proteins, is not diminished when myotubes are reexposed to growth media, allocates this cyclin-dependent kinase inhibitor a special function. Here we report for the first time statistically increased p21 mRNA levels in dystrophin-deficient muscle tissue. Only 42% of conventional RT-PCRs from six muscle samples of human controls yielded positive results but almost all skeletal muscle biopsy samples (87%) from DMD patients (n=5). For p21 mRNA quantification in murine muscle samples we were able to use the exact real-time TaqMan PCR method due to generally higher p21 mRNA levels than in human muscles. In addition, contamination with fibroblasts can be excluded for the murine samples because they do not demonstrate fibrosis at the age of 350 days but start to lose their regenerative capacity. In accord with the results in humans, we observed p21 mRNA levels in mdx mice that were approx. four times as high as those in control mice. Elevated p21 mRNA level may indicate a shift in cell composition towards differentiated p21 expressing cells as a result of an exhausted pool of undifferentiated, non-p21-expressing satellite cells due to previous cycles of de- and regeneration. Alternatively, dystrophin-deficient cells per se may express higher p21 levels for unknown reasons. Although we cannot distinguish between these possibilities, the eventual transfec tion of a patient's own satellite cells with p21 antisense oligonucleotides may enable the dystrophic process to be influenced.

Systemic Delivery of Allogenic Muscle Stem Cells Induces Long-Term Muscle Repair and Clinical Efficacy in Duchenne Muscular Dystrophy Dogs

“…11,71,72 In parallel to fusion with host fibers and dystrophin recovery, MuStem cells generated satellite cells, an essential feature in the context of satellite cell pool exhaustion in muscular dystrophy. 73,74 This data suggested that MuStem cell injection could have a long-term impact on the regenerative potential of dystrophic fibers by their constant recruitment for the host fiber regeneration. Similar contribution to the satellite cell pool has been demonstrated in injured mouse muscles for muscle SP cells, 21 muscle-derived floating populations, 42 CD133 ϩ cells, 24 and synovial membrane-derived mesenchymal stem cells.…”

Global deletion ofBCATmincreases expression of skeletal muscle genes associated with protein turnover

“…JunB has been shown to increase skeletal muscle hypertrophy and mass by promoting FoxO3 binding to Fbxo32 and MuRF1 promoters and thereby reduces protein breakdown (68). The cyclindependent kinase inhibitor p21 (Cdkn1a), which plays an important role in skeletal muscle regeneration (20,33), was also significantly elevated in BCATm KO mouse muscle (Supplementary Tables S1-S3). Interestingly, eIF4G2 (also known as death-associated protein 5, DAP-5) expression was almost twofold greater in muscle of KO compared with wild-type mice (Fig.…”

CXCL16‐mediated cell recruitment to rheumatoid arthritis synovial tissue and murine lymph nodes is dependent upon the MAPK pathway

“…The final RNA was digested with DNase and with an RNase inhibitor added. Reverse transcription was performed simultaneously using Superscript II reverse transcriptase (Invitrogen, Carlsbad, CA) followed by the PCR reactions and preparation of serial dilutions of the purified PCR products (35). PCR primers and TaqMan fluorogenic probes were designed using the Primer Express program, version 1.01 (Applied Biosystems, Foster City, CA).…”