In-depth phenotyping of lymphoblastoid cells suggests selective cellular vulnerability in Marinesco-Sjögren syndrome

Abstract

SIL1 is a ubiquitous protein of the Endoplasmic Reticulum (ER) acting as a co-chaperone for the ER-resident chaperone, BiP. Recessive mutations of the corresponding gene lead to vulnerability of skeletal muscle and central nervous system in man (Marinesco-Sjögren syndrome; MSS) and mouse. However, it is still unclear how loss of ubiquitous SIL1 leads to selective vulnerability of the nervous system and skeletal muscle whereas other cells and organs are protected from clinical manifestations. In this study we aimed to disentangle proteins participating in selective vulnerability of SIL1-deficient cells and tissues: morphological examination of MSS patient-derived lymphoblastoid cells revealed altered organelle structures (ER, nucleus and mitochondria) thus showing subclinical vulnerability. To correlate structural perturbations with biochemical changes and to identify proteins potentially preventing phenotypical manifestation, proteomic studies have been carried out. Results of proteomic profiling are in line with the morphological findings and show affection of nuclear, mitochondrial and cytoskeletal proteins as well as of such responsible for cellular viability. Moreover, expression patterns of proteins known to be involved in neuromuscular disorders or in development and function of the nervous system were altered. Paradigmatic findings were confirmed by immunohistochemistry of splenic lymphocytes and the cerebellum of SIL1-deficient mice. Ataxin-10, identified with increased abundance in our proteome profile, is necessary for the neuronal survival but also controls muscle fiber apoptosis, thus declaring this protein as a plausible candidate for selective tissue vulnerability. Our combined results provide first insights into the molecular causes of selective cell and tissue vulnerability defining the MSS phenotype.

Review: Protein misfolding diseases – the rare case of Marinesco‐Sjögren syndrome

“…Lymphoblastoid cells from MSS patients showed UPR activation and morphological alterations of the ER, nucleus and mitochondria (Table ), similar to those reported in SIL1‐KD HEK293 cells . They were less viable than control lymphoblasts, both in basal conditions and under oxidative or ER stress .…”

“…Antibody production was further investigated in patient‐derived lymphoblastoid cells (LCs), which as expected did not express detectable amounts of SIL1 unless treated with the proteasome inhibitor MG132 . These LCs assembled and secreted amounts of IgGs comparable to controls, even though ORP150 was not up‐regulated and the UPR was not activated . In contrast, others have reported clear signs of UPR in MSS patient‐derived LCs , indicating that there may be some SIL1 loss‐related deficits in immune cells (see below).…”

“…Proteomic analysis showed 59 up‐ and 103 down‐regulated proteins compared to controls, suggesting alterations of the secretory pathway, mitochondria, cytoplasm and cytoskeleton. Ataxin‐10 (ATXN10), a gene involved in neuronal degeneration and muscle cell apoptosis, was up‐regulated in MSS LCs . ATXN10 expression was increased in non‐vulnerable vestibulocerebellar but not in vulnerable neocerebellar PCs of woozy mice, suggesting a role in selective tissue vulnerability .…”

Clinical and research strategies for limb‐girdle congenital myasthenic syndromes

“…In light of these facts, we systematically addressed the expression of CMS‐related proteins in the laboratory standard cell lines HeLa, RCMH, and HEK293, as well as in cells that can be minimally invasively (e.g., lymphoblastoid cells) or invasively (e.g., muscle cells) obtained from patients and healthy donors. These data are compiled from proteins identified in previous comparative proteome profiling experiments . In the context of the laboratory standard cell lines, it is worth noting that RCMH cells have already been extensively characterized on the morphological and biochemical level.…”

SIL1 deficiency causes degenerative changes of peripheral nerves and neuromuscular junctions in fish, mice and human

“…However, increased abundance of proteins with protective potential does not only indicate a vulnerability of the PNS against loss of functional SIL1, but also might explain why PNS pathology is subtle compared to cerebellar and skeletal muscle phenotype. In this context, it is worth noting that recently one of our molecular studies on organ vulnerability in MSS suggested that the presence of antagonizing factors modifies the vulnerability of cells/ tissues against loss of functional SIL1 [57].…”