title: Primary Brain Calcification Causal PiT2 Transport-Knockout Variants can Exert Dominant Negative Effects on Wild-Type PiT2 Transport Function in Mammalian Cells.
abstract: Primary brain calcification (PBC) is a neurodegenerative disorder characterized by calcium-phosphate deposits in the basal ganglia and often also other areas of the brain. The prevalent clinical manifestations are cognitive impairment, neuropsychiatric symptoms, and movement disorders. In recent years, monoallelic variants in SLC20A2, which encodes the type III sodium-dependent inorganic phosphate (Pi) transporter 2 (PiT2), have been linked to the familial form of PBC in 40-50% of the families reported worldwide as well as to sporadic cases of PBC. Further insight into the disease mechanism is, however, needed. Based on co-expression studies of wild-type and variant PiT2 in Xenopus laevis oocytes, the molecular disease mechanism associated with SLC20A2 missense variants has formerly been suggested to be haploinsufficiency. We have here used mammalian cells isolated from a Slc20a2-/-mouse and co-expression of human wild-type and variant PiT2. Two of the variants studied have both been reported twice in unrelated PBC cases: PiT2D28N in two sporadic cases and PiT2E575K in a familial and a sporadic case. We find that in mammalian cells, the analyzed SLC20A2 missense variants can exert their effect in a dominant negative manner resulting in decreased wild-type PiT2 Pitransport. Thus, compared to monoallelic lack of functional PiT2 protein expression, which reasonably points towards haploinsufficiency, certain SLC20A2 missense variants may be more detrimental for cellular Piuptake and potentially contribute to an earlier disease onset and/or a more severe phenotype as observed for Slc20a2-/-mice compared to Slc20a2+/-mice.
authors.affiliation: Department of Molecular Biology and Genetics, Aarhus University, C. F. Møllers Allé 3, Building 1130, 8000, Aarhus, Denmark.
authors.forename: Frederik Tibert
authors.initials: FT
authors.lastname: Larsen
authors.affiliation: Department of Molecular Biology and Genetics, Aarhus University, C. F. Møllers Allé 3, Building 1130, 8000, Aarhus, Denmark.|Department of Clinical Medicine, Aarhus University, Aarhus, Denmark.
authors.forename: Nina
authors.initials: N
authors.lastname: Jensen
authors.affiliation: Department of Molecular Biology and Genetics, Aarhus University, C. F. Møllers Allé 3, Building 1130, 8000, Aarhus, Denmark.
authors.forename: Jacob Kwasi
authors.initials: JK
authors.lastname: Autzen
authors.affiliation: Department of Molecular Biology and Genetics, Aarhus University, C. F. Møllers Allé 3, Building 1130, 8000, Aarhus, Denmark.
authors.forename: Iben Boutrup
authors.initials: IB
authors.lastname: Kongsfelt
authors.affiliation: Department of Molecular Biology and Genetics, Aarhus University, C. F. Møllers Allé 3, Building 1130, 8000, Aarhus, Denmark. LP@mbg.au.dk.|Department of Clinical Medicine, Aarhus University, Aarhus, Denmark. LP@mbg.au.dk.
authors.forename: Lene
authors.identifier: http://orcid.org/0000-0002-3396-1292
authors.initials: L
authors.lastname: Pedersen
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism* / Q000473:pathology; D002114:Calcinosis / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D017136:Ion Transport; D051379:Mice; D008810:Mice, Inbred C57BL; D020125:Mutation, Missense; D010641:Phenotype; D010710:Phosphates / Q000378:metabolism; D050611:Sodium-Phosphate Cotransporter Proteins, Type III / Q000235:genetics* / Q000378:metabolism
chemical_list: D010710:Phosphates; C493589:SLC20A2 protein, human; D050611:Sodium-Phosphate Cotransporter Proteins, Type III
keywords: Oligomerization; Phosphate transporter; PiT2; Primary familial brain calcification; SLC20A2