Proteome profile in Myotonic Dystrophy type 2 myotubes reveals dysfunction in protein processing and mitochondrial pathways

Myotonic Dystrophy type 2 (DM2) is caused by a DNA microsatellite expansion within the Zinc Finger Protein 9 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 EFTu, HSP60, 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 Alfa6 and of Rad23B homolog. Altered ubiquitin-proteasomal activity is supported by a global reduction of cytosolic ubiquitinated proteins. Although future work is required to clarify how these changes affect the 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.