Myotonic Dystrophy type 2 (DM2) is caused by a DNA microsatellite expansion within the ZNF9 gene leading to an abnormal splicing pattern largely responsible for the pathological condition. To better define the functional changes occurring in human DM2 myotubes, we performed a quantitative proteome comparison between myotubes of DM2 and control patients using two-dimensional gel electrophoresis followed by mass spectrometry. Our results indicate that the proteins, altered in DM2 cultures, belong to two major functional categories: i) mitochondrial components, with a reduction of Elongation factor Tu (EFTu), Heat Shock Protein 60 (HSP60), Glucose Regulated Protein 75 (GRP75) and Dienoyl-CoA-Isomerase, an enzyme involved in fatty acids degradation; ii) the ubiquitin proteasome system, with increase of the 26S proteasome regulatory subunit 13 and a reduction of Proteasome subunit Apha 6 and of Rad23B homolog. Altered ubiquitin-proteasomal activity is supported by a global reduction of cytosolic ubiquitinated proteins, nonetheless the accumulation of ubiquitin-protein conjugates after proteasomal inhibitor MG-132 treatment is maintained in DM2 and control cells, suggesting a higher degradation rate for the proteasome in myoblasts from patients affected by the disease. Although future work is required to clarify how these changes affect the protein degradation machinery and mitochondrial function and to evaluate if these changes also occur in the biopsies of DM2 patients, these results identify the mitochondrial proteins and the ubiquitin-proteasomal system as candidates potentially relevant to DM2 pathogenesis. Further analysis performed in Human skin fibroblasts primary cultures, obtained from patients biopsies, revealed an Hyperpolaryzation of the mitochondrial membrane potential involving DM2 cells, indicating a putative functional issue for mitochondria. As the evaluation of the Cytocrome c release following hydrogen peroxide treatment showed a differential response to this stress inducing compound, we pointed out a functional involvement of the DM2 mitochondrial-mediated cellular response to oxidative stress
