title: Hereditary spastic paraplegia-linked REEP1 modulates endoplasmic reticulum/mitochondria contacts.
abstract: OBJECTIVE
  Mutations in receptor expression enhancing protein 1 (REEP1) are associated with hereditary spastic paraplegias (HSPs). Although axonal degeneration is thought to be a predominant feature in HSP, the role of REEP1 mutations in degeneration is largely unknown. Previous studies have implicated a role for REEP1 in the endoplasmic reticulum (ER), whereas others localized REEP1 with mitochondria. We sought to resolve the cellular localization of REEP1 and further elucidate the pathobiology underlying REEP1 mutations in patients.
  
  
  METHODS
  A combination of cellular imaging and biochemical approaches was used to refine the cellular localization of REEP1. Next, Reep1 mutations associated with HSP were functionally tested in neuritic growth and degeneration assays using mouse cortical culture. Finally, a novel assay was developed and used with wild-type and mutant Reep1s to measure the interactions between the ER and mitochondria.
  
  
  RESULTS
  We found that REEP1 is present at the ER-mitochondria interface, and it contains subdomains for mitochondrial as well as ER localization. Knockdown of Reep1 and expression of pathological Reep1 mutations resulted in neuritic growth defects and degeneration. Finally, using our novel split-RLuc8 assay, we show that REEP1 facilitates ER-mitochondria interactions, a function diminished by disease-associated mutations.
  
  
  CONCLUSIONS
  Our data potentially reconcile the current conflicting reports regarding REEP1 being either an ER or a mitochondrial protein. Furthermore, our results connect, for the first time, the disrupted ER-mitochondria interactions to a failure in maintaining health of long axons in HSPs. Finally, the split-RLuc8 assay offers a new tool to identify potential drugs for multiple neurodegenerative diseases with ER-mitochondria interaction defects.
authors.affiliation: Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA.
authors.forename: Youngshin
authors.initials: Y
authors.lastname: Lim
authors.affiliation: Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA.
authors.forename: Il-Taeg
authors.initials: IT
authors.lastname: Cho
authors.affiliation: Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA.
authors.forename: Leah J
authors.initials: LJ
authors.lastname: Schoel
authors.affiliation: Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA.
authors.forename: Ginam
authors.initials: G
authors.lastname: Cho
authors.affiliation: Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA.
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Golden
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology; D001921:Brain / Q000473:pathology; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects; D004247:DNA / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000235:genetics*; D055785:Gene Knockdown Techniques; D006367:HeLa Cells; D006801:Humans; D026901:Membrane Transport Proteins / Q000235:genetics*; D051379:Mice; D008928:Mitochondria / Q000235:genetics*; D009154:Mutation / Q000235:genetics; D009410:Nerve Degeneration / Q000235:genetics; D009420:Nervous System / Q000254:growth & development / Q000378:metabolism; D016501:Neurites; D015419:Spastic Paraplegia, Hereditary / Q000235:genetics*
chemical_list: D026901:Membrane Transport Proteins; C495318:REEP1 protein, human; D004247:DNA