Decline of DNA damage response along with myogenic differentiation

Abstract

DNA integrity is incessantly confronted to agents inducing DNA lesions. All organisms are equipped with a network of DNA damage response mechanisms that will repair DNA lesions and restore proper cellular activities. Despite DNA repair mechanisms have been revealed in replicating cells, still little is known about how DNA lesions are repaired in postmitotic cells. Muscle fibers are highly specialized postmitotic cells organized in syncytia and they are vulnerable to age-related degeneration and atrophy after radiotherapy treatment. We have studied the DNA repair capacity of muscle fiber nuclei and compared it with the one measured in proliferative myoblasts here. We focused on the DNA repair mechanisms that correct ionizing radiation (IR)-induced lesions, namely the base excision repair, the nonhomologous end joining, and the homologous recombination (HR). We found that in the most differentiated myogenic cells, myotubes, these DNA repair mechanisms present weakened kinetics of recruitment of DNA repair proteins to IR-damaged DNA. For base excision repair and HR, this decline can be linked to reduced steady-state levels of key proteins involved in these processes.

The DNA damage response relies on the characteristics of ionizing particles in myogenic cells

“…1, A and C vs Fig. S1, A and C), as we previously reported (33). Likewise, we observed that this was also the case upon 10,000 protons irradiation (Fig.…”

“…Thereby, we demonstrated that DSB repair (DSBR) mechanisms in proliferating myogenic cells, myoblasts, switch as a function of energy deposition and time after irradiation, whatever the particle delivered, proton or α-particle. Additionally, we found that myoblasts orchestrate IR-induced DSB repair with dynamics that depend on the type of high LET particle used, proton or α-particle, while differentiated myotubes remained with declined DNA damage response as was previously reported (33).…”

“…To obtain stable and homogenous GFP-tagged protein expressing C2C7 lines, 24 h post-transfection the GFP-expressing cells were enriched under 1mg.mL -1 of geneticin (G418 sulfate; Gibco) selection for 10 consecutive days. Then, the GFP-tagged protein expressing C2C7 cells were isolated by FACs sorting and further expanded (33).…”

“…To assess initial IR-induced DNA damage response of myogenic cells, we used the immortalized murine C2C7 cells stably expressing GFP-tagged repair proteins and the microbeam MIRCOM facility, which allows in situ localized irradiation within the nuclei of living cells (33,39,43). The MIRCOM microbeam can deliver a controlled number of a given particle.…”

“…Previously, it has been reported that adult muscle stem cells have more efficient and accurate DNA repair capacity than their committed progeny (32). Recently, we have also shown that multi-nucleated skeletal myofibers, generated from muscle stem cells of neonatal mice or immortalized myoblasts, have a reduced DNA damage response (DDR) in comparison to their precursors, myoblasts upon x-ray or α-particle irradiation (33). Additionally, our previous findings suggest that repair of DSBs induced either by x-ray or α-particle irradiation in mono and multinuclear myogenic cells is essentially carried out by NHEJ (33) as in their progenitor, muscle stem cells (32,34).…”