title: Absence of the ER Cation Channel TMEM38B/TRIC-B Disrupts Intracellular Calcium Homeostasis and Dysregulates Collagen Synthesis in Recessive Osteogenesis Imperfecta.
abstract: Recessive osteogenesis imperfecta (OI) is caused by defects in proteins involved in post-translational interactions with type I collagen. Recently, a novel form of moderately severe OI caused by null mutations in TMEM38B was identified. TMEM38B encodes the ER membrane monovalent cation channel, TRIC-B, proposed to counterbalance IP3R-mediated Ca2+ release from intracellular stores. The molecular mechanisms by which TMEM38B mutations cause OI are unknown. We identified 3 probands with recessive defects in TMEM38B. TRIC-B protein is undetectable in proband fibroblasts and osteoblasts, although reduced TMEM38B transcripts are present. TRIC-B deficiency causes impaired release of ER luminal Ca2+, associated with deficient store-operated calcium entry, although SERCA and IP3R have normal stability. Notably, steady state ER Ca2+ is unchanged in TRIC-B deficiency, supporting a role for TRIC-B in the kinetics of ER calcium depletion and recovery. The disturbed Ca2+ flux causes ER stress and increased BiP, and dysregulates synthesis of proband type I collagen at multiple steps. Collagen helical lysine hydroxylation is reduced, while telopeptide hydroxylation is increased, despite increased LH1 and decreased Ca2+-dependent FKBP65, respectively. Although PDI levels are maintained, procollagen chain assembly is delayed in proband cells. The resulting misfolded collagen is substantially retained in TRIC-B null cells, consistent with a 50-70% reduction in secreted collagen. Lower-stability forms of collagen that elude proteasomal degradation are not incorporated into extracellular matrix, which contains only normal stability collagen, resulting in matrix insufficiency. These data support a role for TRIC-B in intracellular Ca2+ homeostasis, and demonstrate that absence of TMEM38B causes OI by dysregulation of calcium flux kinetics in the ER, impacting multiple collagen-specific chaperones and modifying enzymes.
authors.affiliation: Section on Heritable Disorders of Bone and Extracellular Matrix, NICHD, NIH, Bethesda, Maryland, United States of America.
authors.forename: Wayne A
authors.initials: WA
authors.lastname: Cabral
authors.affiliation: Molecular Biology Section, NIDCR, NIH, Bethesda, Maryland, United States of America.
authors.forename: Masaki
authors.initials: M
authors.lastname: Ishikawa
authors.affiliation: Section on Integrative Biophysics, NICHD, NIH, Bethesda, Maryland, United States of America.
authors.forename: Matthias
authors.initials: M
authors.lastname: Garten
authors.affiliation: Section on Physical Biochemistry, NICHD, NIH, Bethesda, Maryland, United States of America.
authors.forename: Elena N
authors.initials: EN
authors.lastname: Makareeva
authors.affiliation: Section on Heritable Disorders of Bone and Extracellular Matrix, NICHD, NIH, Bethesda, Maryland, United States of America.
authors.forename: Brandi M
authors.initials: BM
authors.lastname: Sargent
authors.affiliation: Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, United States of America.
authors.forename: MaryAnn
authors.initials: M
authors.lastname: Weis
authors.affiliation: Section on Heritable Disorders of Bone and Extracellular Matrix, NICHD, NIH, Bethesda, Maryland, United States of America.
authors.forename: Aileen M
authors.initials: AM
authors.lastname: Barnes
authors.affiliation: School of Clinical and Experimental Medicine, Institute of Biomedical Research, University of Birmingham, Birmingham, United Kingdom.|Department of Endocrinology and Diabetes, Birmingham Children's Hospital, Birmingham, United Kingdom.
authors.forename: Emma A
authors.initials: EA
authors.lastname: Webb
authors.affiliation: Department of Endocrinology and Diabetes, Birmingham Children's Hospital, Birmingham, United Kingdom.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Shaw
authors.affiliation: Connective Tissue Gene Tests, Allentown, Pennsylvania, United States of America.
authors.forename: Leena
authors.initials: L
authors.lastname: Ala-Kokko
authors.affiliation: Department of Medical Genetics, Children's National Medical Center, Washington D.C., United States of America.
authors.forename: Felicitas L
authors.initials: FL
authors.lastname: Lacbawan
authors.affiliation: School of Clinical and Experimental Medicine, Institute of Biomedical Research, University of Birmingham, Birmingham, United Kingdom.|Department of Endocrinology and Diabetes, Birmingham Children's Hospital, Birmingham, United Kingdom.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Högler
authors.affiliation: Section on Physical Biochemistry, NICHD, NIH, Bethesda, Maryland, United States of America.
authors.forename: Sergey
authors.initials: S
authors.lastname: Leikin
authors.affiliation: Section on Integrative Biophysics, NICHD, NIH, Bethesda, Maryland, United States of America.
authors.forename: Paul S
authors.initials: PS
authors.lastname: Blank
authors.affiliation: Section on Integrative Biophysics, NICHD, NIH, Bethesda, Maryland, United States of America.
authors.forename: Joshua
authors.initials: J
authors.lastname: Zimmerberg
authors.affiliation: Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, United States of America.
authors.forename: David R
authors.initials: DR
authors.lastname: Eyre
authors.affiliation: Molecular Biology Section, NIDCR, NIH, Bethesda, Maryland, United States of America.
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Yamada
authors.affiliation: Section on Heritable Disorders of Bone and Extracellular Matrix, NICHD, NIH, Bethesda, Maryland, United States of America.
authors.forename: Joan C
authors.initials: JC
authors.lastname: Marini
mesh_terms: D000328:Adult; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D024042:Collagen Type I / Q000096:biosynthesis* / Q000378:metabolism; D003241:Consanguinity; D004252:DNA Mutational Analysis; D004721:Endoplasmic Reticulum / Q000378:metabolism; D059865:Endoplasmic Reticulum Stress; D005260:Female; D005808:Genes, Recessive; D056726:Genetic Association Studies; D020022:Genetic Predisposition to Disease; D006706:Homeostasis; D006801:Humans; D007223:Infant; D007473:Ion Channels / Q000235:genetics*; D008297:Male; D010013:Osteogenesis Imperfecta / Q000235:genetics*; D010375:Pedigree; D011499:Protein Processing, Post-Translational
chemical_list: D024042:Collagen Type I; D007473:Ion Channels; C578840:TMEM38B protein, human; D002118:Calcium