Isolation and identification of ER associated proteins with unique expression changes specific to the V144D SPTLC1 mutations in HSN-I

Axonal degeneration is the final common path in many neurological disorders. Hereditary sensory neuropathies (HSN) are a group of neuropathies involving the sensory neurons. The most common subtype is autosomal dominant hereditary sensory neuropathy type I (HSN-I). Progressive degeneration of the dorsal root ganglion (DRG) neuron with an onset of clinical symptoms between the second or third decade of life characterises HSN-I. Mutations in the serine palmitoyltransferase (SPT) long chain subunit 1 (SPTLC1) gene cause HSN-I. The endoplasmic reticulum (ER) is a dynamic organelle that houses the SPTLC1 protein. Ultra structural analysis has shown the ER in the HSN-I mutant cells to wrap around dysfunctional mitochondria and tethers them to the perinucleus. This investigation establishes that the V144D mutant of SPTLC1 alters the expression of and potentially interacts with a set of proteins within the ER. Using ER protein lysates from HSN-I patient and control lymphoblasts: we have identified a change in regulation of five proteins; Hypoxia Up regulated Protein 1: Chloride intracellular channel protein 1: Ubiqutin-40s Ribosomal protein S27a: Coactosin and Ig Kappa chain C. The expression and regulation of these proteins may help to establish a link between the ER and the ‘dying back’ process of the DRG neuron

Optimal isolation of mitochondria for proteomic analyses

Considering the key role of mitochondria in cellular (dys)functions, we compared a standard isolation protocol, followed by lysis in urea/detergent buffer, with a commercially available isolation buffer that rapidly yields a mitochondrial protein fraction. The standard protocol yielded significantly better overall resolution and coverage of both the soluble and membrane mitochondrial proteomes; although the kit was faster, it resulted in recovery of only approximately 56% of the detectable proteome. The quality of ‘‘omic’’ analysis depends on sample handling; for large-scale protein studies, well-resolved proteomes are highly dependent on the purity of starting material and the rigor of the extraction protocol

Mitochondrial protein alterations in a familial peripheral neuropathy caused by the V144D amino acid mutation in the sphingolipid protein, SPTLC1

Axonal degeneration is the final common path in many neurological disorders. Subsets of neuropathies involving the sensory neuron are known as hereditary sensory neuropathies (HSNs). Hereditary sensory neuropathy type I (HSN-I) is the most common subtype of HSN with autosomal dominant inheritance. It is characterized by the progressive degeneration of the dorsal root ganglion (DRG) with clinical symptom onset between the second or third decade of life. Heterozygous mutations in the serine palmitoyltransferase (SPT) long chain subunit 1 (SPTLC1) gene were identified as the pathogenic cause of HSN-I. Ultrastructural analysis of mitochondria from HSN-I patient cells has displayed unique morphological abnormalities that are clustered to the perinucleus where they are wrapped by the endoplasmic reticulum (ER). This investigation defines a small subset of proteins with major alterations in abundance in mitochondria harvested from HSN-I mutant SPTLC1 cells. Using mitochondrial protein isolates from control and patient lymphoblasts, and a combination of 2D gel electrophoresis, immunoblotting and mass spectrometry, we have shown the increased abundance of ubiquinol-cytochrome c reductase core protein 1, an electron transport chain protein, as well as the immunoglobulin, Ig kappa chain C. The regulation of these proteins may provide a new route to understanding the cellular and molecular mechanisms underlying HSN-I

Proteome alterations associated with the V144D SPTLC1 mutation that causes hereditary sensory neuropathy-I

Background: Hereditary sensory neuropathy type is the most common subtype and presents with clinical onset in the second to third decade of life with progressive degeneration of the dorsal root ganglion neurons. Three different missense mutations in the gene encoding for serine palmitoyltransferase long chain subunit 1 have been linked to HSN-I. Here we quantitatively assess the proteomes and identify marked protein alterations in both mitochondria and endoplasmic reticulum from HSN-I patient lymphoblasts which harbour the V144D mutation. Methods: Mitochondria and endoplasmic reticulum were fractionated and lysed from control and patient-derived lymphoblasts. Protein samples were separated into total soluble and total membrane fractions and analysed using a well-established topdown proteomic protocol. Altered protein species were identified by LC MS/MS. Results: Using a detailed proteomic approach, we identified 36 proteins that were completely altered in abundance in cells harbouring the V144D SPTLC1 mutation relative to normal controls. Conclusion: The data establish that major protein alterations occur in both the endoplasmic reticulum, where the SPTLC1 protein resides, and in the mitochondria from V144D patient lymphoblasts. These proteins potentially play a major role in disease pathogenesis and may thus help to further elucidate the molecular mechanism(s) underlying hereditary sensory neuropathy type I and might also prove to be potential therapeutic targets

Autophagy is up regulated in a neuronal model of Charcot-Marie-Tooth disease that overexpresses dynamin 2 mutant

Dominant-Intermediate Charcot-Marie-Tooth disease is one of the most common inherited disorders affecting the peripheral nervous system. Pleckstrin homology domain mutations in dynamin 2 cause dominant-intermediate Charcot Marie Tooth Syndrome. Autophagy in normal cells helps to maintain homeostasis and degrade damaged or old organelles and proteins. Here we link the pleckstrin homology domain mutants and the disease state to autophagy. Cells over-expressing the K558E mutation in the pleckstrin homology domain of dynamin 2 have shown an increase in expression of ER stress and autophagy markers. Although the exact link between autophagy and peripheral neurodegeneration has yet to be fully elucidated, these results set the foundation for further research into the interactions between dynamin 2 mutations, autophagy, and Dominant-Intermediate Charcot-Marie-Tooth

Identifying unique protein alterations caused by SPTLC1 mutations in a transfected neuronal cell model

Hereditary sensory neuropathy type I is an autosomal dominant disorder that affects the sensory neurons. Three missense mutations in serine palmitoyltransferase long chain subunit 1 cause hereditary sensory neuropathy type I. The endoplasmic reticulum, where the serine palmitoyltransferase long chain subunit 1 protein resides, and mitochondria are both altered in hereditary sensory neuropathy type I mutant cells. Employing a transfected neuronal cell line (ND15), we have identified and confirmed altered protein expression levels of ubiquinol cytochrome C, Hypoxia Up regulated Protein 1, Chloride Intracellular Channel Protein 1, Ubiqutin-40s Ribosomal Protein S27a, and Coactosin. Additionally, further 14 new proteins that exhibited altered expression within V144D, C133W and C133Y mutants were identified. These data have shown that mutations in SPTLC1 alter the expression of a set of proteins that may help to establish a causal link between the mitochondria and ER and the “dying back” process of dorsal root ganglion neurons that occurs in HSN-I

Increased lipid droplet accumulation associated with a peripheral sensory neuropathy

Hereditary sensory neuropathy type 1 (HSN-1) is an autosomal dominant neurodegenerative disease caused by missense mutations in the SPTLC1 gene. The SPTLC1 protein is part of the SPT enzyme which is a ubiquitously expressed, critical and thus highly regulated endoplasmic reticulum bound membrane enzyme that maintains sphingolipid concentrations and thus contributes to lipid metabolism, signalling, and membrane structural functions. Lipid droplets are dynamic organelles containing sphingolipids and membrane bound proteins surrounding a core of neutral lipids, and thus mediate the intracellular transport of these specific molecules. Current literature suggests that there are increased numbers of lipid droplets and alterations of lipid metabolism in a variety of other autosomal dominant neurodegenerative diseases, including Alzheimer's and Parkinson's disease. This study establishes for the first time, a significant increase in the presence of lipid droplets in HSN-1 patient-derived lymphoblasts, indicating a potential connection between lipid droplets and the pathomechanism of HSN-1. However, the expression of adipophilin (ADFP), which has been implicated in the regulation of lipid metabolism, was not altered in lipid droplets from the HSN-1 patient-derived lymphoblasts. This appears to be the first report of increased lipid body accumulation in a peripheral neuropathy, suggesting a fundamental molecular linkage between a number of neurodegenerative diseases