Premature senescence in primary muscle cultures of myotonic dystrophy type 2 is not associated with p16 induction

Abstract

<jats:p>Myotonic dystrophy type 1 (DM1) and type 2 (DM2) are multisystemic disorders linked to two different genetic loci and characterized by several features including myotonia, muscle weakness and atrophy, cardiac dysfunctions, cataracts and insulin-resistance. In both forms, expanded nucleotide sequences cause the accumulation of mutant transcripts in the nucleus deregulating the activity of some RNAbinding proteins and providing an explanation for the multisystemic phenotype of DM patients. However this pathogenetic mechanism does not explain some histopathological features of DM skeletal muscle like muscle atrophy. It has been observed that DM muscle shares similarities with the ageing muscle, where the progressive muscle weakness and atrophy is accompanied by a lower regenerative capacity possibly due to the failure in satellite cells activation. The aim of our study is to investigate if DM2 satellite cell derived myoblasts exhibit a premature senescence as reported for DM1 and if alterations in their proliferation potential and differentiation capabilities might contribute to some of the histopathological features observed in DM2 muscles. Our results indicate that DM myoblasts have lower proliferative capability than control myoblasts and reach in vitro senescence earlier than controls. Differentely from DM1, the p16 pathway is not responsible for the premature growth arrest observed in DM2 myoblasts which stop dividing with telomeres shorter than controls. During in vitro senescence, a progressive decrease in fusion index is observable in both DM and control myotubes with no significant differences between groups. Moreover, myotubes obtained from senescent myoblasts appear to be smaller than those from young myoblasts. Taken together, our data indicate a possible role of DM2 premature myoblast senescence in skeletal muscle histopathological alterations i.e., dystrophic changes and type 2 fibre atrophy.</jats:p>

Myotonic Dystrophy Type 2: An Update on Clinical Aspects, Genetic and Pathomolecular Mechanism

“…Conversely, recent data demonstrated that DM2 myoblasts are characterized by senescence related features mainly consisting in the early appearance of cytological alterations and impairment of the pre-mRNA maturation pathways [104]. Moreover, Renna et al [105] reported that DM1 and DM2 myoblasts are characterized by a premature proliferative growth arrest compared to healthy myoblasts through a mechanism similar to senescence since both DM1 and DM2 cells expressed biomarkers usually observed in senescent cells. These data suggest that the in vivo regenerative capacity of satellite cells in DM1 and DM2 muscle might be constitutively impaired [105].…”

“…Moreover, Renna et al [105] reported that DM1 and DM2 myoblasts are characterized by a premature proliferative growth arrest compared to healthy myoblasts through a mechanism similar to senescence since both DM1 and DM2 cells expressed biomarkers usually observed in senescent cells. These data suggest that the in vivo regenerative capacity of satellite cells in DM1 and DM2 muscle might be constitutively impaired [105]. Furthermore, contrary to DM1, the p16 pathway is not responsible for the premature growth arrest observed in DM2 myoblasts which stop dividing with telomeres shorter than controls suggesting that CCTG expansion might interfere with the telomere homeostasis in DM2 cells [105–108].…”

“…These data suggest that the in vivo regenerative capacity of satellite cells in DM1 and DM2 muscle might be constitutively impaired [105]. Furthermore, contrary to DM1, the p16 pathway is not responsible for the premature growth arrest observed in DM2 myoblasts which stop dividing with telomeres shorter than controls suggesting that CCTG expansion might interfere with the telomere homeostasis in DM2 cells [105–108]. Hence, it appears that CTG and CCTG expansions trigger in vitro a mechanism of myoblast premature senescence through two different pathways, which could explain the different histological alterations observed between DM1 and DM2 skeletal muscle as for example the selective type 2 fibre atrophy present in DM2 muscle.…”

Semaphorin 3A promotes activation of Pax7, Myf5, and MyoD through inhibition of emerin expression in activated satellite cells

“…D,E). It was reported that myogenic cells in a senescent state are no longer proliferative and their nuclei and cytoplasmic areas were enlarged . Therefore, we propose that Sema3A‐knockdown induced some of the cells into a senescent state.…”

Is there still room for novelty, in histochemical papers?

“…22-42 Here again, multiple immunohistochemical assays have mostly been used to identify pathogenetic factors or to relate the changes in protein expression with tissue remodeling, 22,29-33 or the progression of the disease. 23-28,34,35 Interestingly, cartilage, bone and dentin in different pathologies were especially investigated, 36-41 which demonstrates the unique role of histochemistry in studying these tissues under normal or pathological conditions. 42 …”