Abstract
Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant genetic disease characterized by a progressive muscle degeneration leading to ptosis (eyelid drooping), dysphagia (swallowing difficulty) and proximal limb weakness. OPMD is due to (GCN) repeat expansion in the gene encoding the poly(A) binding protein nuclear 1 (PABPN1) protein. These mutations result in expansion of an alanine stretch (11 to 18 alanines) at the N-terminus of PABPN1, leading to misfolding and aggregation of mutant PABPN1 in muscle nuclei. PABPN1 has several functions in RNAs biogenesis, including key roles in mRNA polyadenylation and in the turn-over of non-coding RNAs.Several molecular mechanisms involved in OPMD have been discovered such as mitochondrial dysfunction and oxidative stress, as well as increased proteasome activity leading to the degradation of myofibrillar proteins.The aim of my thesis was to identify other molecular pathways deregulated in OPMD. We use Drosophila models of OPMD which express the alanine-expanded PABPN1 (PABPN1-17ala) specifically in Drosophila muscles. These models recapitulate OPMD features such as progressive muscle degeneration and PABPN1 nuclear aggregation.We discovered that the Unfolded Protein Response (UPR) is activated during OPMD pathogenesis. UPR is activated by the endoplasmic reticulum (ER) stress when misfolded proteins accumulate in the ER. Analysis of molecular markers of the UPR shows that this pathway is activated in muscles expressing PABPN1-17ala. In addition, the IFB-088 molecule (developed by Inflectis BioScience), that targets the UPR to maintain its activation and translation inhibition, is beneficial in the Drosophila OPMD model. The genetic approach allowed us to demonstrate the functional role of the UPR in OPMD and the effect of IFB-088 through targeting its known target in the UPR.We also found that ribosomal RNAs (rRNAs) have an increased number of polyadenylation sites and longer poly(A)-tails, indicating a defect in rRNA processing and turn-over. Moreover, small RNA fragments accumulate in muscles of the OPMD Drosophila model, likely resulting from defective rRNA processing and degradation. Our hypothesis is that these rRNA fragments could impede the RNA interference pathway through their loading into Argonaute proteins.Another objective of my thesis was to test new compounds and identify active molecules in Drosophila OPMD models. Positive results were obtained with molecules showing antiaggregation properties and with antioxidant molecules. Further analysis of these molecules could lead to identifying potential candidates for future pharmacological treatments of OPMD.Molecular defects involved in OPMD are also often observed in other proteinopathies. Understanding the mechanisms involved in OPMD allows us to identify new active molecules in OPMD that might also prove to be efficient in other diseases.