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Thorsten Hornemann - One of the best experts on this subject based on the ideXlab platform.
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subunit composition of the mammalian serine palmitoyltransferase defines the spectrum of straight and methyl branched long chain bases
Proceedings of the National Academy of Sciences of the United States of America, 2020Co-Authors: Museer A Lone, Arnold Von Eckardstein, Andreas J Hulsmeier, Essa M Saied, Gergely Karsai, Christoph Arenz, Thorsten HornemannAbstract:Sphingolipids (SLs) are chemically diverse lipids that have important structural and signaling functions within mammalian cells. SLs are commonly defined by the presence of a long-chain base (LCB) that is normally formed by the conjugation of l-serine and palmitoyl-CoA. This pyridoxal 5-phosphate (PLP)-dependent reaction is mediated by the enzyme serine-palmitoyltransferase (SPT). However, SPT can also metabolize other acyl-CoAs, in the range of C14 to C18, forming a variety of LCBs that differ by structure and function. Mammalian SPT consists of three core subunits: SPTLC1, SPTLC2, and SPTLC3. Whereas SPTLC1 and SPTLC2 are ubiquitously expressed, SPTLC3 expression is restricted to certain tissues only. The influence of the individual subunits on enzyme activity is not clear. Using cell models deficient in SPTLC1, SPTLC2, and SPTLC3, we investigated the role of each subunit on enzyme activity and the LCB product spectrum. We showed that SPTLC1 is essential for activity, whereas SPTLC2 and SPTLC3 are partly redundant but differ in their enzymatic properties. SPTLC1 in combination with SPTLC2 specifically formed C18, C19, and C20 LCBs while the combination of SPTLC1 and SPTLC3 yielded a broader product spectrum. We identified anteiso-branched-C18 SO (meC18SO) as the primary product of the SPTLC3 reaction. The meC18SO was synthesized from anteiso-methyl-palmitate, in turn synthesized from a precursor metabolite generated in the isoleucine catabolic pathway. The meC18SO is metabolized to ceramides and complex SLs and is a constituent of human low- and high-density lipoproteins.
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HSAN1 mutations in serine palmitoyltransferase reveal a close structure-function-phenotype relationship
Human Molecular Genetics, 2015Co-Authors: Heiko Bode, Irina Alecu, Arnold Von Eckardstein, Yu Wei, Florence Bourquin, Saranya Suriyanarayanan, Alaa Othman, Thorsten HornemannAbstract:Hereditary sensory and autonomic neuropathy type 1 (HSAN1) is a rare autosomal dominant inherited peripheral neuropathy caused by mutations in the SPTLC1 and SPTLC2 subunits of serine palmitoyltransferase (SPT). The mutations induce a permanent shift in the substrate preference from L-serine to L-alanine, which results in the pathological formation of atypical and neurotoxic 1-deoxy-sphingolipids (1-deoxySL). Here we compared the enzymatic properties of 11 SPTLC1 and six SPTLC2 mutants using a uniform isotope labelling approach. In total, eight SPT mutants (STPLC1p.C133W, p.C133Y, p.S331F, p.S331Y and SPTLC2p.A182P, p.G382V, p.S384F, p.I504F) were associated with increased 1-deoxySL synthesis. Despite earlier reports, canonical activity with l-serine was not reduced in any of the investigated SPT mutants. Three variants (SPTLC1p.S331F/Y and SPTLC2p.I505Y) showed an increased canonical activity and increased formation of C20 sphingoid bases. These three mutations are associated with an exceptionally severe HSAN1 phenotype, and increased C20 sphingosine levels were also confirmed in plasma of patients. A principal component analysis of the analysed sphingoid bases clustered the mutations into three separate entities. Each cluster was related to a distinct clinical outcome (no, mild and severe HSAN1 phenotype). A homology model based on the protein structure of the prokaryotic SPT recapitulated the same grouping on a structural level. Mutations associated with the mild form clustered around the active site, whereas mutations associated with the severe form were located on the surface of the protein. In conclusion, we showed that HSAN1 mutations in SPT have distinct biochemical properties, which allowed for the prediction of the clinical symptoms on the basis of the plasma sphingoid base profile.
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Sinéad M. Murphy, MD, MRCPI*
2015Co-Authors: Daniela Ernst Msc, Thorsten Hornemann, Henry Houlden, Yu Wei Msc, Matilde Laurà, Yo-tsen Liu, James Polke, Julian Blake Mrcp, Mary M. ReillyAbstract:Supplemental data at www.neurology.org Hereditary sensory and autonomic neuropathy type 1 (HSANI) caused by a novel mutation in SPTLC2 Objective: To describe the clinical and neurophysiologic phenotype of a family with hereditary sensory and autonomic neuropathy type 1 (HSANI) due to a novel mutation in SPTLC2 and to characterize the biochemical properties of this mutation. Methods: We screened 107 patients with HSAN who were negative for other genetic causes for mutations in SPTLC2. The biochemical properties of a new mutation were characterized in cell-free and cell-based activity assays. Results: A novel mutation (A182P) was found in 2 subjects of a single family. The phenotype of the 2 subjects was an ulcero-mutilating sensory-predominant neuropathy as described previously for patients with HSANI, but with prominent motor involvement and earlier disease onset in the firs
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THE SPTLC3 SUBUNIT OF SERINE- PALMITOYLTRANSFERASE GENERATES SHORT CHAIN SPHINGOID BASES
2015Co-Authors: Thorsten Hornemann, Anke Penno, Markus F Rutti, Daniela Ernst, Fatma Kivrak-pfiffnerAbstract:The enzyme serine-palmitoyltransferase (SPT) catalyses the rate limiting step in the de-novo synthesis of sphingolipids. Previously the mammalian SPT was described as a heterodimer composed of two subunits- SPTLC1 and SPTLC2. Recently we identified a novel third SPT subunit (SPTLC3). SPTLC3 shows about 68 % identity to SPTLC2 and also includes a PLP consensus motif. Here we report that the overexpression of SPTLC3 in HEK293 cells leads to the formation of two new sphingoid base metabolites, namely C16-sphinganine and C16-sphingosine. SPTLC
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1042 Hereditary sensory and autonomic neuropathy type 1: correlation of severity and plasma atypical deoxy-sphyngoid bases
Journal of Neurology Neurosurgery & Psychiatry, 2012Co-Authors: L Matilde, Thorsten Hornemann, Sinead M Murphy, James M Polke, F Eichler, K Bull, H. Houlden, Mary M. ReillyAbstract:Hereditary sensory and autonomic neuropathy type 1 (HSAN1) is an inherited peripheral neuropathy characterised by marked sensory loss, variable motor involvement and frequent complications. Mutations in the SPTLC1 gene are responsible for this disorder. Mutant SPTLC1 is associated with the accumulation of two atypical deoxy-sphyngoid bases (dSBs) which produce a toxic effect in cultured sensory neurons. dSB levels are elevated in plasma of patients with HSAN1 and transgenic mice. L-serine is a potential therapy for HSAN1, however the lack of natural history studies and outcome measures are major barriers to a clinical trial. This cross-sectional study has been conducted to fully characterise the phenotype of HSAN1 and to establish correlation of plasma dSBs with disease severity. We obtained detailed clinical data in a cohort of 20 SPTLC1/ HSAN1 patients. Clinical impairment was assessed by the Charcot Marie Tooth Neuropathy score (CMTNS). Onset occurred in the second and third decade in the majority of patients. Males showed a more severe disease course compared to females. Neuropathic pain was present in 70% of patients. Sensory complications were observed in 80% of patients. dSBs were significantly elevated in all patients and correlate with disease severity. This cross-sectional study highlights the role of dSBs as a potential marker for disease severity. A longitudinal study to establish whether dSBs can be used as biomarker of progression of disease is warranted.
Arnold Von Eckardstein - One of the best experts on this subject based on the ideXlab platform.
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subunit composition of the mammalian serine palmitoyltransferase defines the spectrum of straight and methyl branched long chain bases
Proceedings of the National Academy of Sciences of the United States of America, 2020Co-Authors: Museer A Lone, Arnold Von Eckardstein, Andreas J Hulsmeier, Essa M Saied, Gergely Karsai, Christoph Arenz, Thorsten HornemannAbstract:Sphingolipids (SLs) are chemically diverse lipids that have important structural and signaling functions within mammalian cells. SLs are commonly defined by the presence of a long-chain base (LCB) that is normally formed by the conjugation of l-serine and palmitoyl-CoA. This pyridoxal 5-phosphate (PLP)-dependent reaction is mediated by the enzyme serine-palmitoyltransferase (SPT). However, SPT can also metabolize other acyl-CoAs, in the range of C14 to C18, forming a variety of LCBs that differ by structure and function. Mammalian SPT consists of three core subunits: SPTLC1, SPTLC2, and SPTLC3. Whereas SPTLC1 and SPTLC2 are ubiquitously expressed, SPTLC3 expression is restricted to certain tissues only. The influence of the individual subunits on enzyme activity is not clear. Using cell models deficient in SPTLC1, SPTLC2, and SPTLC3, we investigated the role of each subunit on enzyme activity and the LCB product spectrum. We showed that SPTLC1 is essential for activity, whereas SPTLC2 and SPTLC3 are partly redundant but differ in their enzymatic properties. SPTLC1 in combination with SPTLC2 specifically formed C18, C19, and C20 LCBs while the combination of SPTLC1 and SPTLC3 yielded a broader product spectrum. We identified anteiso-branched-C18 SO (meC18SO) as the primary product of the SPTLC3 reaction. The meC18SO was synthesized from anteiso-methyl-palmitate, in turn synthesized from a precursor metabolite generated in the isoleucine catabolic pathway. The meC18SO is metabolized to ceramides and complex SLs and is a constituent of human low- and high-density lipoproteins.
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HSAN1 mutations in serine palmitoyltransferase reveal a close structure-function-phenotype relationship
Human Molecular Genetics, 2015Co-Authors: Heiko Bode, Irina Alecu, Arnold Von Eckardstein, Yu Wei, Florence Bourquin, Saranya Suriyanarayanan, Alaa Othman, Thorsten HornemannAbstract:Hereditary sensory and autonomic neuropathy type 1 (HSAN1) is a rare autosomal dominant inherited peripheral neuropathy caused by mutations in the SPTLC1 and SPTLC2 subunits of serine palmitoyltransferase (SPT). The mutations induce a permanent shift in the substrate preference from L-serine to L-alanine, which results in the pathological formation of atypical and neurotoxic 1-deoxy-sphingolipids (1-deoxySL). Here we compared the enzymatic properties of 11 SPTLC1 and six SPTLC2 mutants using a uniform isotope labelling approach. In total, eight SPT mutants (STPLC1p.C133W, p.C133Y, p.S331F, p.S331Y and SPTLC2p.A182P, p.G382V, p.S384F, p.I504F) were associated with increased 1-deoxySL synthesis. Despite earlier reports, canonical activity with l-serine was not reduced in any of the investigated SPT mutants. Three variants (SPTLC1p.S331F/Y and SPTLC2p.I505Y) showed an increased canonical activity and increased formation of C20 sphingoid bases. These three mutations are associated with an exceptionally severe HSAN1 phenotype, and increased C20 sphingosine levels were also confirmed in plasma of patients. A principal component analysis of the analysed sphingoid bases clustered the mutations into three separate entities. Each cluster was related to a distinct clinical outcome (no, mild and severe HSAN1 phenotype). A homology model based on the protein structure of the prokaryotic SPT recapitulated the same grouping on a structural level. Mutations associated with the mild form clustered around the active site, whereas mutations associated with the severe form were located on the surface of the protein. In conclusion, we showed that HSAN1 mutations in SPT have distinct biochemical properties, which allowed for the prediction of the clinical symptoms on the basis of the plasma sphingoid base profile.
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Cell polarity factor Par3 binds SPTLC1 and modulates monocyte serine palmitoyltransferase activity and chemotaxis.
Journal of Biological Chemistry, 2009Co-Authors: Norimasa Tamehiro, Thorsten Hornemann, Arnold Von Eckardstein, Zahedi Mujawar, Suiping Zhou, Debbie Z. Zhuang, Michael L. FitzgeraldAbstract:Elevated sphingolipids have been associated with increased cardiovascular disease. Conversely, atherosclerosis is reduced in mice by blocking de novo synthesis of sphingolipids catalyzed by serine palmitoyltransferase (SPT). The SPT enzyme is composed of the SPTLC1 and -2 subunits, and here we describe a novel protein-protein interaction between SPTLC1 and the PDZ protein Par3 (partitioning defective protein 3). Mammalian SPTLC1 orthologs have a highly conserved C terminus that conforms to a type II PDZ protein interaction motif, and by screening PDZ domain protein arrays with an SPTLC1 C-terminal peptide, we found it bound the third PDZ domain of Par3. Overlay and immunoprecipitation assays confirmed this interaction and indicate Par3 is able to associate with the SPTLC1/2 holoenzyme by binding the C-terminal SPTLC1 PDZ motif. The physiologic existence of the SPTLC1/2-Par3 complex was detected in mouse liver and macrophages, and short interfering RNA inhibition of Par3 in human THP-1 monocytes significantly reduced SPT activity and de novo ceramide synthesis by nearly 40%. Given monocyte recruitment into inflamed vessels is thought to promote atherosclerosis, and because Par3 and sphingolipids have been associated with polarized cell migration, we tested whether the ability of THP-1 monocytes to migrate toward MCP-1 (monocyte chemoattractant protein 1) depended upon Par3 and SPTLC1 expression. Knockdown of Par3 significantly reduced MCP1-induced chemotaxis of THP-1 monocytes, as did knockdown of SPTLC1, and this Par3 effect depended upon SPT activity and was blunted by ceramide treatment. In conclusion, protein arrays were used to identify a novel SPTLC1-Par3 interaction that associates with increased monocyte serine palmitoyltransferase activity and chemotaxis toward inflammatory signals.
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SPTLC1 binds ABCA1 to negatively regulate trafficking and cholesterol efflux activity of the transporter.
Biochemistry, 2008Co-Authors: Norimasa Tamehiro, Thorsten Hornemann, Arnold Von Eckardstein, Suiping Zhou, Debbie Z. Zhuang, Keiichiro Okuhira, Yair Benita, Cari E. Brown, Eicke Latz, Ramnik J. XavierAbstract:ABCA1 transport of cholesterol and phospholipids to nascent HDL particles plays a central role in lipoprotein metabolism and macrophage cholesterol homeostasis. ABCA1 activity is regulated both at the transcriptional level and at the post-translational level. To explore mechanisms involved in the post-translational regulation of the transporter, we have used affinity purification and mass spectrometry to identify proteins that bind ABCA1 and influence its activity. Previously, we demonstrated that an interaction between β1-syntrophin stimulated ABCA1 activity, at least in part, be slowing the degradation of the transporter. This work demonstrates that one subunit of the serine palmitoyltransferase enzyme, SPTLC1, but not subunit 2 (SPTLC2), is copurified with ABCA1 and negatively regulates its function. In human THP-I macrophages and in mouse liver, the ABCA1−SPTLC1 complex was detected by co-immunoprecipitation, demonstrating that the interaction occurs in cellular settings where ABCA1 activity is critic...
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Is the mammalian serine palmitoyltransferase a high-molecular-mass complex?
Biochemical Journal, 2007Co-Authors: Thorsten Hornemann, Yu Wei, Arnold Von EckardsteinAbstract:SPT (serine palmitoyltransferase) catalyses the rate-limiting step for the de novo synthesis of sphingolipids. Mammalian SPT is believed to be a heterodimer composed of two subunits, SPTLC1 and SPTLC2. We reported previously the identification of a new third SPT subunit, SPTLC3. In the present study, we have investigated the structure of the SPT complex in more detail. Pull-down assays with antibodies against SPTLC3 concomitantly co-precipitated SPTLC1 and SPTLC2 in human placenta extracts and SPTLC3 overexpressing human embryonic kidney-293 cells. By size exclusion chromatography, we determined the molecular mass of the functional SPT complex to be approx. 480 kDa. By Blue-native-PAGE experiments we demonstrated that all three SPT subunits (SPTLC1–3) are co-localized within a single SPT complex. On the basis of these results we conclude that the functional SPT is not a dimer, but a higher organized complex, composed of three distinct subunits (SPTLC1, SPTLC2 and SPTLC3) with a molecular mass of 480 kDa. The stoichiometry of SPTLC2 and SPTLC3 in this complex seems not to be fixed and is probably changed dynamically in dependence of the tissue specific SPTLC2 and SPTLC3 expression levels. Based on our own and earlier published data we propose a model of an octameric SPT structure. The observed dynamic composition of the SPT complex could provide a cellular mechanism to adjust SPT activity to tissue specific requirements in sphingolipid synthesis.
Anke Penno - One of the best experts on this subject based on the ideXlab platform.
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ARTICLE Mutations in the SPTLC2 Subunit of Serine Palmitoyltransferase Cause Hereditary Sensory and Autonomic Neuropathy Type I
2015Co-Authors: Annelies Rotthier, Anke Penno, Michaela Auer-grumbach, Kim Van Hoof, Katrien Janssens, Jonathan Baets, An Jacobs, Els De Vriendt, Leonardo Almeida-souza, Beate Schlotter-weigelAbstract:Hereditary sensory and autonomic neuropathy type I (HSAN-I) is an axonal peripheral neuropathy associated with progressive distal f g ath ie u a ga cts sti tions in the first subunit (SPTLC1 [MIM 605712]) of the methyl-SA) instead of sphinganine (SA). These alterna-The Ameenzyme serine palmitoyltransferase (SPT).4–6 The SPT enzyme is a multisubunit structure, consisting of dimeric subunits of SPTLC1 with either SPTLC2 (MIM 605713) or SPTLC3 (MIM 611120).7 It is associated with the endo-plasmic reticulum (ER), where it catalyzes the pyridoxal
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THE SPTLC3 SUBUNIT OF SERINE- PALMITOYLTRANSFERASE GENERATES SHORT CHAIN SPHINGOID BASES
2015Co-Authors: Thorsten Hornemann, Anke Penno, Markus F Rutti, Daniela Ernst, Fatma Kivrak-pfiffnerAbstract:The enzyme serine-palmitoyltransferase (SPT) catalyses the rate limiting step in the de-novo synthesis of sphingolipids. Previously the mammalian SPT was described as a heterodimer composed of two subunits- SPTLC1 and SPTLC2. Recently we identified a novel third SPT subunit (SPTLC3). SPTLC3 shows about 68 % identity to SPTLC2 and also includes a PLP consensus motif. Here we report that the overexpression of SPTLC3 in HEK293 cells leads to the formation of two new sphingoid base metabolites, namely C16-sphinganine and C16-sphingosine. SPTLC
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oral l serine supplementation reduces production of neurotoxic deoxysphingolipids in mice and humans with hereditary sensory autonomic neuropathy type 1
Journal of Clinical Investigation, 2011Co-Authors: Kevin Garofalo, Thorsten Hornemann, Anke Penno, Arnold Von Eckardstein, Matthew P. Frosch, Robert H. Brown, B P Schmidt, Florian EichlerAbstract:Hereditary sensory and autonomic neuropathy type 1 (HSAN1) causes sensory loss that predominantly affects the lower limbs, often preceded by hyperpathia and spontaneous shooting or lancinating pain. It is caused by several missense mutations in the genes encoding 2 of the 3 subunits of the enzyme serine palmitoyltransferase (SPT). The mutant forms of the enzyme show a shift from their canonical substrate l-serine to the alternative substrate l-alanine. This shift leads to increased formation of neurotoxic deoxysphingolipids (dSLs). Our initial analysis showed that in HEK cells transfected with SPTLC1 mutants, dSL generation was modulated in vitro in the presence of various amino acids. We therefore examined whether in vivo specific amino acid substrate supplementation influenced dSL levels and disease severity in HSAN1. In mice bearing a transgene expressing the C133W SPTLC1 mutant linked to HSAN1, a 10% l-serine–enriched diet reduced dSL levels. l-serine supplementation also improved measures of motor and sensory performance as well as measures of male fertility. In contrast, a 10% l-alanine–enriched diet increased dSL levels and led to severe peripheral neuropathy. In a pilot study with 14 HSAN1 patients, l-serine supplementation similarly reduced dSL levels. These observations support the hypothesis that an altered substrate selectivity of the mutant SPT is key to the pathophysiology of HSAN1 and raise the prospect of l-serine supplementation as a first treatment option for this disorder.
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Characterization of two mutations in the SPTLC1 subunit of serine palmitoyltransferase associated with hereditary sensory and autonomic neuropathy type I.
Human Mutation, 2011Co-Authors: Annelies Rotthier, Anke Penno, Michaela Auer-grumbach, Bernd Rautenstrauss, Georg M. Stettner, Bob Asselbergh, Kim Van Hoof, Heinrich Sticht, Nicholas Levy, Vincent TimmermanAbstract:Hereditary sensory and autonomic neuropathy type I (HSAN-I) is an axonal peripheral neuropathy leading to progressive distal sensory loss and severe ulcerations. Mutations in SPTLC1 and SPTLC2, encoding the two subunits of serine palmitoyltransferase (SPT), the enzyme catalyzing the first and rate-limiting step in the de novo synthesis of sphingolipids, have been reported to cause HSAN-I. Here, we demonstrate that the SPTLC1 mutations p.S331F and p.A352V result in a reduction of SPT activity in vitro and are associated with increased levels of the deoxysphingoid bases 1-deoxy-sphinganine and 1-deoxymethyl-sphinganine in patients' plasma samples. Stably expressing p.S331F-SPTLC1 HEK293T cell lines likewise show accumulation of deoxysphingoid bases, but this accumulation is not observed in HEK293T cells overexpressing p.A352V-SPTLC1. These results confirm that the increased formation of deoxysphingoid bases is a key feature for HSAN-I as it is associated with all pathogenic SPTLC1 and SPTLC2 mutations reported so far, but also warrant for caution in the interpretation of in vitro data.
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mutations in the sptlc2 subunit of serine palmitoyltransferase cause hereditary sensory and autonomic neuropathy type i
American Journal of Human Genetics, 2010Co-Authors: Annelies Rotthier, Anke Penno, Michaela Auergrumbach, Katrien Janssens, Jonathan Baets, Leonardo Almeidasouza, Kim Van Hoof, An Jacobs, Els De Vriendt, Beate SchlotterweigelAbstract:Hereditary sensory and autonomic neuropathy type I (HSAN-I) is an axonal peripheral neuropathy associated with progressive distal sensory loss and severe ulcerations. Mutations in the first subunit of the enzyme serine palmitoyltransferase (SPT) have been associated with HSAN-I. The SPT enzyme catalyzes the first and rate-limiting step in the de novo sphingolipid synthesis pathway. However, different studies suggest the implication of other genes in the pathology of HSAN-I. Therefore, we screened the two other known subunits of SPT, SPTLC2 and SPTLC3, in a cohort of 78 HSAN patients. No mutations were found in SPTLC3, but we identified three heterozygous missense mutations in the SPTLC2 subunit of SPT in four families presenting with a typical HSAN-I phenotype. We demonstrate that these mutations result in a partial to complete loss of SPT activity in vitro and in vivo. Moreover, they cause the accumulation of the atypical and neurotoxic sphingoid metabolite 1-deoxy-sphinganine. Our findings extend the genetic heterogeneity in HSAN-I and enlarge the group of HSAN neuropathies associated with SPT defects. We further show that HSAN-I is consistently associated with an increased formation of the neurotoxic 1-deoxysphinganine, suggesting a common pathomechanism for HSAN-I.
Garth A. Nicholson - One of the best experts on this subject based on the ideXlab platform.
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Mutations in the SPTLC1 Protein Cause Mitochondrial Structural Abnormalities and Endoplasmic Reticulum Stress in Lymphoblasts
DNA and cell biology, 2014Co-Authors: Simon J. Myers, Chandra S. Malladi, Ryan A. Hyland, Tara G. Bautista, Ross A. Boadle, Phillip J. Robinson, Garth A. NicholsonAbstract:Mutations in serine palmitoyltransferase long chain subunit 1 (SPTLC1) cause the typical length-dependent axonal degeneration hereditary sensory neuropathy type 1 (HSN1). Transmission electron microscopy studies on SPTLC1 mutant lymphoblasts derived from patients revealed specific structural abnormalities of mitochondria. Swollen mitochondria with abnormal cristae were clustered around the nucleus, with some mitochondria being wrapped in rough endoplasmic reticulum (ER) membranes. Total mitochondrial counts revealed a significant change in mitochondrial numbers between healthy and diseased lymphocytes but did not reveal any change in length to width ratios nor were there any changes to cellular function. However, there was a notable change in ER homeostasis, as assessed using key ER stress markers, BiP and ERO1-Lα, displaying reduced protein expression. The observations suggest that SPTLC1 mutations cause mitochondrial abnormalities and ER stress in HSN1 cells.
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hereditary sensory neuropathy type 1 is caused by the accumulation of two neurotoxic sphingolipids
Journal of Biological Chemistry, 2010Co-Authors: Anke Penno, MM Reilly, Garth A. Nicholson, M Laura, Henry Houlden, Katharina Rentsch, Vera Niederkofler, Esther T Stoeckli, Florian Eichler, Robert H. BrownAbstract:HSAN1 is an inherited neuropathy found to be associated with several missense mutations in the SPTLC1 subunit of serine palmitoyltransferase (SPT). SPT catalyzes the condensation of serine and palmitoyl-CoA, the initial step in the de novo synthesis of sphingolipids. Here we show that the HSAN1 mutations induce a shift in the substrate specificity of SPT, which leads to the formation of the two atypical deoxy-sphingoid bases (DSBs) 1-deoxy-sphinganine and 1-deoxymethyl-sphinganine. Both metabolites lack the C(1) hydroxyl group of sphinganine and can therefore neither be converted to complex sphingolipids nor degraded. Consequently, they accumulate in the cell, as demonstrated in HEK293 cells overexpressing mutant SPTLC1 and lymphoblasts of HSAN1 patients. Elevated DSB levels were also found in the plasma of HSAN1 patients and confirmed in three groups of HSAN1 patients with different SPTLC1 mutations. The DSBs show pronounced neurotoxic effects on neurite formation in cultured sensory neurons. The neurotoxicity co-occurs with a disturbed neurofilament structure in neurites when cultured in the presence of DSBs. Based on these observations, we conclude that HSAN1 is caused by a gain of function mutation, which results in the formation of two atypical and neurotoxic sphingolipid metabolites.
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Late-onset hereditary sensory neuropathy type I due to SPTLC1 mutation: Autopsy findings
Clinical neurology and neurosurgery, 2005Co-Authors: Andrea J. Lindahl, Garth A. Nicholson, Sam D. Lhatoo, Malcolm J. Campbell, Seth LoveAbstract:There is little published information on the autopsy findings in hereditary sensory neuropathy type I (HSN I), and none in genetically confirmed cases. We report the neuropathological findings in a 93-year-old woman with a disease of unusually late onset, who was part of a large HSN I kindred and in whom genetic analysis confirmed an SPTLC1 T399G mutation.
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HEREDITARY SENSORY NEUROPATHY TYPE I: HAPLOTYPE ANALYSIS SHOWS FOUNDERS IN SOUTHERN ENGLAND AND EUROPE
Journal of the Peripheral Nervous System, 2002Co-Authors: Garth A. Nicholson, Jennifer L Dawkins, Sonal Brahmbhatt, Michaela Auer-grumbach, Ian P. Blair, Dennis J HulmeAbstract:Hereditary sensory neuropathy type I (HSN1) is the most common dominantly inherited degenerative disorder of sensory neurons. The gene mutation was mapped to chromosome 9 in a large Australian family, descended from an ancestor from southern England who was a convict. Dawkins et al. recently reported gene mutations in the SPTLC1 gene, in this and other families. The first description of hereditary sensory neuropathy, by Hicks, was in a family from London and Exeter. To determine if the families in the present study that have SPTLC1 mutations are related to English families with HSN1 and, possibly, to the family studied by Hicks, we performed haplotype analysis of four Australian families of English extraction, four English families, and one Austrian family. Three Australian families of English extraction and three English families (two of whom have been described elsewhere) had the 399TG SPTLC1 mutation, the same chromosome 9 haplotype, and the same phenotype. The Australian and English families may therefore have a common founder who, on the basis of historical information, has been determined to have lived in southern England prior to 1800. The sensorimotor neuropathy phenotype caused by the 399TG SPTLC1 mutation is the same as that reported by Campbell and Hoffman and, possibly, the same as that originally described by Hicks.
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mutations in SPTLC1 encoding serine palmitoyltransferase long chain base subunit 1 cause hereditary sensory neuropathy type i
Nature Genetics, 2001Co-Authors: Jennifer L Dawkins, Sonal Brahmbhatt, Michaela Auergrumbach, Dennis J Hulme, Garth A. NicholsonAbstract:Hereditary sensory neuropathy type I (HSN1) is the most common hereditary disorder of peripheral sensory neurons. HSN1 is an autosomal dominant progressive degeneration of dorsal root ganglia and motor neurons with onset in the second or third decades. Initial symptoms are sensory loss in the feet followed by distal muscle wasting and weakness. Loss of pain sensation leads to chronic skin ulcers and distal amputations1,2. The HSN1 locus has been mapped to chromosome 9q22.1–22.3 (refs. 3,4). Here we map the gene SPTLC1, encoding serine palmitoyltransferase, long chain base subunit-1, to this locus. Mutation screening revealed 3 different missense mutations resulting in changes to 2 amino acids in all affected members of 11 HSN1 families. We found two mutations to be located in exon 5 (C133Y and C133W) and one mutation to be located in exon 6 of SPTLC1 (V144D). All families showing definite or probable linkage to chromosome 9 had mutations in these two exons. These mutations are associated with increased de novo glucosyl ceramide synthesis in lymphoblast cell lines in affected individuals. Increased de novo ceramide synthesis triggers apoptosis5,6 and is associated with massive cell death during neural tube closure7, raising the possibility that neural degeneration in HSN1 is due to ceramide-induced apoptotic cell death.
Robert H. Brown - One of the best experts on this subject based on the ideXlab platform.
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Mutations in the SPTLC1 gene are a cause of amyotrophic lateral sclerosis that may be amenable to serine supplementation [preprint]
2019Co-Authors: Janel O. Johnson, Robert H. Brown, Ruth Chia, John LandersAbstract:Abstract SPTLC1 encodes a critical subunit of serine palmitoyltransferase, the enzyme catalyzing the first and rate-limiting step in de novo sphingolipid biosynthesis, and mutations in this gene are known to cause hereditary sensory autonomic neuropathy, type 1A. Using exome sequencing, we identified a de novo variant in SPTLC1 resulting in a p.Ala20Ser amino acid change in an individual diagnosed with juvenile-onset amyotrophic lateral sclerosis (ALS) and confirmed its pathogenicity by showing elevated plasma levels of neurotoxic deoxymethyl-sphinganine. A second case of juvenile-onset ALS arising again from a p.Ala20Ser mutation was later identified, confirming the association of SPTLC1 with this form of motor neuron disease. We also found SPTLC1 mutations in 0.34% of 5,607 ALS cases, and immunohistochemically confirmed the expression of SPTLC1 in spinal cord motor neurons, supporting their role in the pathogenesis of this fatal neurological disease. We corrected the toxicity of deoxymethyl-sphinganine in HEK293FT cells using L-serine supplementation. Our data broaden the phenotype associated with SPTLC1 and suggest that nutritional supplementation with serine may be beneficial if instituted at an early stage among patients carrying mutations in SPTLC1.
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Brief Communications Overexpression of the Wild-Type SPT1 Subunit Lowers Desoxysphingolipid Levels and Rescues the Phenotype
2015Co-Authors: Of Hsan, Robert H. BrownAbstract:Mutations in the SPTLC1 subunit of serine palmitoyltransferase (SPT) cause an adult-onset, hereditary sensory, and autonomic neurop-athy type I (HSAN1). We previously reported that mice bearing a transgene-expressingmutant SPTLC1 (tgSPTLC1C133W) show a reduc-tion in SPT activity and hyperpathia at 10months of age. Now analyzed at a later age, we find thesemice develop sensory losswith a distal small fiber neuropathy and peripheral myelinopathy. This phenotype is largely reversed when these mice are crossed with transgenic mice overexpressing wild-type SPTLC1 showing that the mutant SPTLC1 protein is not inherently toxic. Simple loss of SPT activity also cannot account for the HSAN1 phenotype, since heterozygous SPTLC1 knock-out mice have reduced SPT activity but are otherwise normal. Rather, the presence of two newly identified, potentially deleterious deoxysphingoid bases in the tgSPTLC1C133W, but not in th
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neurophysiology and intraepidermal nerve fiber density in hereditary sensory and autonomic neuropathy type 1 hsan1 p03 202
Neurology, 2012Co-Authors: William S David, Robert H. Brown, Anne Louise Oaklander, Peter Novak, Florian EichlerAbstract:Objective: To quantify the impact of the SPTLC1 mutation upon neurological outcome measures in HSAN1 patients. Background Hereditary sensory and autonomic neuropathy type 1 (HSAN1) is the most common inherited neuropathy to predominantly affect sensory neurons. The disorder is caused by mutations in SPTCL1, which encodes the enzyme serine palmitoyltransferase. Design/Methods: We studied two HSAN1 families with different mutations (n = 8). Five patients carried the C133Y mutation, three the C133W mutation. The median age was 34 years (range 26-59); the median age of onset was 19 (range 15-54). All eight patients underwent neurological examination and were scored using the CMT symptom score (CMTSS). Nerve conduction studies (NCS) of the upper and lower extremities were conducted in all (including 3 motor NCS and 4 sensory NCS). Six patients had skin biopsies at the distal leg and proximal thigh to assess the intraepidermal nerve fiber density (IENFD). Results: The average CMTSS was 12.38 (SD +/-6.74). All patients complained of neuropathic pain apart from two patients who had the highest CMTSS. Sensory symptoms (average score 2.9) were prominent but motor symptoms (average score 1.2) were present as well. No sensory responses were obtainable in 5/8; lower extremity motor responses were absent in 6/8 patients. None of these 6 patients had epidermal nerve fibers detected at the distal leg, while they were present in the thigh in all patients. The correlation coefficient between CMTSS and IENFD was -0.8 and between CMTSS and median motor amplitudes was -0.75. Conclusions: Beyond sensory there is also motor impairment present in HSAN1 patients. In our limited sample size we found an inverse correlation between both CMTSS and IENFD and CMTSS and nerve conduction studies. This study provides important clinical characterization of both neurophysiology and the IENFD in HSAN1. Disclosure: Dr. David has nothing to disclose. Dr. Oaklander has nothing to disclose. Dr. Pan has nothing to disclose. Dr. Novak has nothing to disclose. Dr. Brown has received personal compensation for activities as an advisory board member. Dr. Eichler has nothing to disclose.
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oral l serine supplementation reduces production of neurotoxic deoxysphingolipids in mice and humans with hereditary sensory autonomic neuropathy type 1
Journal of Clinical Investigation, 2011Co-Authors: Kevin Garofalo, Thorsten Hornemann, Anke Penno, Arnold Von Eckardstein, Matthew P. Frosch, Robert H. Brown, B P Schmidt, Florian EichlerAbstract:Hereditary sensory and autonomic neuropathy type 1 (HSAN1) causes sensory loss that predominantly affects the lower limbs, often preceded by hyperpathia and spontaneous shooting or lancinating pain. It is caused by several missense mutations in the genes encoding 2 of the 3 subunits of the enzyme serine palmitoyltransferase (SPT). The mutant forms of the enzyme show a shift from their canonical substrate l-serine to the alternative substrate l-alanine. This shift leads to increased formation of neurotoxic deoxysphingolipids (dSLs). Our initial analysis showed that in HEK cells transfected with SPTLC1 mutants, dSL generation was modulated in vitro in the presence of various amino acids. We therefore examined whether in vivo specific amino acid substrate supplementation influenced dSL levels and disease severity in HSAN1. In mice bearing a transgene expressing the C133W SPTLC1 mutant linked to HSAN1, a 10% l-serine–enriched diet reduced dSL levels. l-serine supplementation also improved measures of motor and sensory performance as well as measures of male fertility. In contrast, a 10% l-alanine–enriched diet increased dSL levels and led to severe peripheral neuropathy. In a pilot study with 14 HSAN1 patients, l-serine supplementation similarly reduced dSL levels. These observations support the hypothesis that an altered substrate selectivity of the mutant SPT is key to the pathophysiology of HSAN1 and raise the prospect of l-serine supplementation as a first treatment option for this disorder.
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hereditary sensory neuropathy type 1 is caused by the accumulation of two neurotoxic sphingolipids
Journal of Biological Chemistry, 2010Co-Authors: Anke Penno, MM Reilly, Garth A. Nicholson, M Laura, Henry Houlden, Katharina Rentsch, Vera Niederkofler, Esther T Stoeckli, Florian Eichler, Robert H. BrownAbstract:HSAN1 is an inherited neuropathy found to be associated with several missense mutations in the SPTLC1 subunit of serine palmitoyltransferase (SPT). SPT catalyzes the condensation of serine and palmitoyl-CoA, the initial step in the de novo synthesis of sphingolipids. Here we show that the HSAN1 mutations induce a shift in the substrate specificity of SPT, which leads to the formation of the two atypical deoxy-sphingoid bases (DSBs) 1-deoxy-sphinganine and 1-deoxymethyl-sphinganine. Both metabolites lack the C(1) hydroxyl group of sphinganine and can therefore neither be converted to complex sphingolipids nor degraded. Consequently, they accumulate in the cell, as demonstrated in HEK293 cells overexpressing mutant SPTLC1 and lymphoblasts of HSAN1 patients. Elevated DSB levels were also found in the plasma of HSAN1 patients and confirmed in three groups of HSAN1 patients with different SPTLC1 mutations. The DSBs show pronounced neurotoxic effects on neurite formation in cultured sensory neurons. The neurotoxicity co-occurs with a disturbed neurofilament structure in neurites when cultured in the presence of DSBs. Based on these observations, we conclude that HSAN1 is caused by a gain of function mutation, which results in the formation of two atypical and neurotoxic sphingolipid metabolites.