Understanding Marinesco-Sjögren Syndrome using Quantitative Proteomics

SIL1 is a nucleotide exchange factor for HSP70 chaperone BiP (GRP78), which is involved in protein processing and protein folding in the endoplasmic reticulum (ER). Mutations in the SIL1 gene cause the Marinesco-Sjögren syndrome (MSS; OMIM 248800), which is a rare autosomal recessive multisystem disorder, affecting in particular skeletal muscle, eye and brain. However, it is not clear why the loss of SIL1 affects only certain tissues/organs. Up regulation of another ER nucleotide exchange factor GRP170 (HYOU1) expression might be one of the compensatory mechanisms in the unaffected tissues. We therefore, utilize quantitative proteomic strategies to identify the differences between healthy and diseased cells/tissues using targeted SRM (screening for GRP170 levels and phosphorylation sites) along with global approaches like label free and stable-isotope labeling (iTRAQ). To achieve this we are developing reproducible sample preparation methods, which will enable us to perform quantitative analysis with minute amounts of tissue samples. Furthermore, the potentially altered translocation of plasma membrane and secreted proteins due to the SIL1 loss will be addressed based on two phase partitioning. This study should lead to a better understanding of genesis and progression of MSS and may help to develop novel therapeutic strategies in the treatment of this disorder.