591P DNA damage in LMNA-related congenital muscular dystrophy.

Repair of DNA double-strand breaks via the non-homologous end joining (NHEJ) involves several histone modifications, including phosphorylation of H2AX (γH2AX), followed by histone ubiquitylation, deacetylation and methylation, required for 53BP1 recruitment via its BRCT, UDR and Tudor domains. Recent studies show an accumulation of DNA breaks in a group of neuromuscular pathologies linked to mutations in the LMNA gene, and more specifically in its most severe form, LMNA -related congenital muscular dystrophy (L-CMD). The LMNA gene codes for lamins A/C, proteins organized in a network at the nuclear membrane called the nuclear lamina, notably involved in the resistance of nuclei to mechanical stress. Lamin A/C interacts with a number of proteins, including histone acetylases and deacetylases, as well as 53BP1 via its Tudor domain, protecting it from degradation in intact cells and facilitating its recruitment to break sites. We hypothesize that the increase in DNA breaks in L-CMD is linked to defects in the interaction of mutated lamin A/C with its protein partners. Our preliminary data confirm that primary myoblasts from L-CMD patients differentiated into myotubes display a higher number of breaks, marked γH2AX, than controls. Induction of double strand breaks by etoposide phosphate (EP) treatment, followed by 2h without treatment, shows an increase in γH2AX marks during EP treatment followed by a decrease during the 2h without EP signalling DNA repair in controls. EP treatment results in a increase in breaks in L-CMD myotubes, followed by cell death. Under the same conditions, unlike control myotubes, L-CMD myotubes are unable to form 53BP1 foci. This could be due to the stronger interaction of 53BP1 with mutated A/C lamins observed by Proximity Ligation Assay. [ABSTRACT FROM AUTHOR]