Project description:The Wiskott-Aldrich Syndrome Protein (WASP) family is known for its participation in cytoskeleton reorganization (Marchand et al., 2001 and Jia et al., 2010). In 2007, the human subtelomeric MGC52000 genes were renamed as Wiskott-Aldrich Syndrome Protein and SCAR Homolog (WASH). Human WASH proteins are part of the WASP protein family and colocalize with actin in cells and promote Arp2/3-dependent actin polymerization in vitro (Linardopoulou et al., 2007). WASH multiprotein complex consists of seven subunits: notable to mention Strumpelin and Was Protein Family Homolog (WASH)-interacting protein (SWIP), which is encoded by KIAA1033/WASHC4 gene, FAM21 and Arp2/3. The Arp2/3 dependent actin polymerization from G-actin to F-actin is an important step in regulation of the cytoskeleton, enabling multiple endosomal transport processes (Kelleher et al., 1995 and Derivery et al., 2010). Linardopoulou and colleagues have also shown in an animal model (Drosophila), that the single WASH ortholog is essential for viability (Linardopoulou et al., 2007), strengthening the concept, that WASHC4 plays a crucial role in muscle cell integrity and function. A link between autosomal recessive intellectual disability (ARID) and mutations in the KIAA1033/WASHC4 gene was first recognized in 2011 by Ropers and colleagues. Very recently, Assoum and colleagues reported three additional patients (from two unrelated families) with syndromic ID. Two of them being sisters (8 and 6 years), both presenting with learning disabilities, macrocephaly, dysmorphic features, skeletal anomalies and subependymal heterotopic nodules due to a compound heterozygous mutation of the KIAA1033/WASHC4 gene (p.[Gln442*] and p.[Asp1048Gly]). In this study, we precisely describe the clinical phenotype of the two siblings and provide additional information (histological and proteomic data) derived from the muscle biopsy of the elder sibling to confirm the pathogenicity of the reported variant and establish the function of WASHC4 as relevant for muscle homeostasis. Which, as far as the authors know, has not yet been described in literature.

Project description:The elucidation of pathomechanisms leading to the manifestation of neuromuscular diseases (NMDs) represents an important step toward the understanding of the genesis of the respective disease and might help to define starting points for (new) therapeutic intervention concepts. However, these “discovery studies” are often limited by the availability of human biomaterial especially regarding the fact that muscle and nerve biopsies became less common in the diagnostic work-up of patients suffering from NMDs. Moreover, given that results of next-generation-sequencing approaches frequently result in the identification of ambiguous variants, testing of their pathogenicity is crucial but also depending on patient-derived material. To systematically address the question if human skin fibroblasts might serve as a valuable biomaterial for (molecular) studies of NMDs, using proteomic profiling we generated a protein library by decreasing protein complexity via pH8-based sample fractionation: cataloguing of 8280 proteins revealed the expression of a variety of such linked to genetic forms of motor neuron diseases, congenital myasthenic syndromes, neuropathies and muscular disorders. In silico-based pathway analyses revealed expression of a variety of proteins involved in muscle contraction and such decisive for neuronal function and maintenance suggesting the suitability of human skin fibroblasts to study the etiology of NMDs. Based on these findings, next we aimed to further demonstrate the suitability of this in vitro model to study NMDs by a use case: utilizing a data independent acquisition (DIA) approach, the proteomic signature of whole protein extracts of fibroblasts derived from an Allgrove-patient was studied. Paradigmatic dysregulated proteins were confirmed in muscle biopsy of the patient and protein-functions could be linked to neurological symptoms known for this disease. Moreover, LC-MS/MS-based investigation of nuclear protein composition allowed the identification of protein-dysregulations which accord with structural perturbations observed in the muscle biopsy.

Project description:Myotonic Dystrophy type 2 (DM2) is an autosomal-dominant, multisystemic disease with a core manifestation of proximal muscle weakness, muscle atrophy, myotonia, and myalgia. The disease-causing CCTG tetranucleotide expansion within the CNBP gene on chromosome 3 leads to an RNA-dominated spliceopathy which is currently untreatable. Research exploring the pathophysiological mechanisms in Myotonic Dystrophy Type 1 resulted in new insights into disease mechanisms and identified mitochondrial dysfunction as promising therapeutic target. It remains unclear whether similar mechanisms underlie DM2 and, if so, whether these might also serve as potential therapeutic targets. In this cross-sectional study, we studied DM2 skeletal muscle biopsy specimens on proteomic, molecular, and morphological including ultrastructural levels in two separate patient cohorts consisting of 8 (explorative cohort) and 40 (confirmatory cohort) patients. Seven muscle biopsy specimens obtained from four female and three male DM2 patients underwent proteomic analysis. We performed immunoblotting of respiratory chain complexes, mitochondrial DNA copy number determination and long-range PCR (LR-PCR) to study mitochondrial deletions on six biopsies. Forty-eight biopsy samples were studied by light and electron microscopy. Proteomic analysis revealed a downregulation of essential mitochondrial proteins, namely of subunits of respiratory chain complexes I, III, and IV (e.g. mt-CO1, mt-ND1, mt-CYB, NDUFB6) and associated translation factors (TACO1). Light microscopy showed an age-inappropriate amount of COX-deficient fibers in most biopsy specimens. Electron microscopy revealed widespread ultrastructural mitochondrial abnormalities including dysmorphic mitochondria with paracrystalline inclusions. Immunoblotting and LR-PCR did not reveal significant differences between patients and controls, while mtDNA-copy number measurement revealed a reduction of mtDNA-copy numbers in the patient group compared to controls. This first multi-level study of DM2 unravels thus far undescribed functional and structural mitochondrial abnormalities. While the molecular link between the tetranucleotide expansion, and mitochondrial dysfunction needs to be further elucidated, these findings may provide an additional route for treatment strategies for DM2.

Dataset Information

Proteome profiling of human myoblastic RCMH cell line

Publications

Proteome Profiling and Ultrastructural Characterization of the Human RCMH Cell Line: Myoblastic Properties and Suitability for Myopathological Studies.

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