title: Substrate Availability of Mutant SPT Alters Neuronal Branching and Growth Cone Dynamics in Dorsal Root Ganglia.
abstract: Serine palmitoyltransferase (SPT) is a key enzyme in the first step of sphingolipid biosynthesis. Mutations in the SPTLC1 gene that encodes for SPT subunits cause hereditary sensory neuropathy type 1. However, little is understood about how mutant SPT regulates mechanisms of sensory neuron and axonal growth. Using transgenic mice overexpressing the C133W SPT mutant, we found that mutant dorsal root ganglia (DRG) during growth in vitro exhibit increased neurite length and branching, coinciding with elevated expression of actin-cross-linking proteins at the neuronal growth cone, namely phosphorylated Ezrin/Radixin/Moesin. In addition, inhibition of SPT was able to reverse the mutant phenotype. Because mutant SPT preferentially uses l-alanine over its canonical substrate l-serine, we also investigated the effects of substrate availability on DRG neurons. Supplementation with l-serine or removal of l-alanine independently restored normal growth patterns in mutant SPTLC1(C133W) DRG. Therefore, we report that substrate availability and selectivity of SPT influence the regulation of neurite growth in DRG neurons.
  
  
  CONCLUSIONS
  Hereditary sensory neuropathy type 1 is an autosomal-dominant disorder that leads to a sensory neuropathy due to mutations in the serine palmitoyltransferase (SPT) enzyme. We investigated how mutant SPT and substrate levels regulate neurite growth. Because SPT is an important enzyme in the synthesis of sphingolipids, our data are of broader significance to other peripheral and metabolic disorders.
authors.affiliation: Neuroscience Center, Massachusetts General Hospital, Boston, Massachusetts 02114; and Department of Neurology, Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Byung Kyu
authors.initials: BK
authors.lastname: Jun
authors.affiliation: Neuroscience Center, Massachusetts General Hospital, Boston, Massachusetts 02114; and Department of Neurology, Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Ankush
authors.identifier: http://orcid.org/0000-0003-1843-3894
authors.initials: A
authors.lastname: Chandra
authors.affiliation: Neuroscience Center, Massachusetts General Hospital, Boston, Massachusetts 02114; and Department of Neurology, Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Dika
authors.initials: D
authors.lastname: Kuljis
authors.affiliation: Neuroscience Center, Massachusetts General Hospital, Boston, Massachusetts 02114; and Department of Neurology, Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Brian P
authors.identifier: http://orcid.org/0000-0003-3460-0605
authors.initials: BP
authors.lastname: Schmidt
authors.affiliation: Neuroscience Center, Massachusetts General Hospital, Boston, Massachusetts 02114; and Department of Neurology, Harvard Medical School, Boston, Massachusetts 02114 feichler@partners.org.
authors.forename: Florian S
authors.initials: FS
authors.lastname: Eichler
mesh_terms: D000409:Alanine / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005229:Fatty Acids, Monounsaturated / Q000494:pharmacology; D005727:Ganglia, Spinal / Q000166:cytology*; D020439:Growth Cones / Q000187:drug effects / Q000502:physiology*; D007166:Immunosuppressive Agents / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009154:Mutation / Q000235:genetics*; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D017711:Nonlinear Dynamics; D012694:Serine / Q000494:pharmacology; D051102:Serine C-Palmitoyltransferase / Q000235:genetics*; D013379:Substrate Specificity; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; C513242:Etv5 protein, mouse; D005229:Fatty Acids, Monounsaturated; D007166:Immunosuppressive Agents; D009419:Nerve Tissue Proteins; D014157:Transcription Factors; D012694:Serine; C487784:SPTLC1 protein, human; D051102:Serine C-Palmitoyltransferase; D000409:Alanine; C001996:thermozymocidin
keywords: Ezrin/Radixin/Moesin; dorsal root ganglia; l-alanine; l-serine; neurite development; sensory neuropathy