title: Premutation in the Fragile X Mental Retardation 1 (FMR1) Gene Affects Maternal Zn-milk and Perinatal Brain Bioenergetics and Scaffolding.
abstract: Fragile X premutation alleles have 55-200 CGG repeats in the 5' UTR of the FMR1 gene. Altered zinc (Zn) homeostasis has been reported in fibroblasts from >60 years old premutation carriers, in which Zn supplementation significantly restored Zn-dependent mitochondrial protein import/processing and function. Given that mitochondria play a critical role in synaptic transmission, brain function, and cognition, we tested FMRP protein expression, brain bioenergetics, and expression of the Zn-dependent synaptic scaffolding protein SH3 and multiple ankyrin repeat domains 3 (Shank3) in a knock-in (KI) premutation mouse model with 180 CGG repeats. Mitochondrial outcomes correlated with FMRP protein expression (but not FMR1 gene expression) in KI mice and human fibroblasts from carriers of the pre- and full-mutation. Significant deficits in brain bioenergetics, Zn levels, and Shank3 protein expression were observed in the Zn-rich regions KI hippocampus and cerebellum at PND21, with some of these effects lasting into adulthood (PND210). A strong genotype × age interaction was observed for most of the outcomes tested in hippocampus and cerebellum, whereas in cortex, age played a major role. Given that the most significant effects were observed at the end of the lactation period, we hypothesized that KI milk might have a role at compounding the deleterious effects on the FMR1 genetic background. A higher gene expression of ZnT4 and ZnT6, Zn transporters abundant in brain and lactating mammary glands, was observed in the latter tissue of KI dams. A cross-fostering experiment allowed improving cortex bioenergetics in KI pups nursing on WT milk. Conversely, WT pups nursing on KI milk showed deficits in hippocampus and cerebellum bioenergetics. A highly significant milk type × genotype interaction was observed for all three-brain regions, being cortex the most influenced. Finally, lower milk-Zn levels were recorded in milk from lactating women carrying the premutation as well as other Zn-related outcomes (Zn-dependent alkaline phosphatase activity and lactose biosynthesis-whose limiting step is the Zn-dependent β-1,4-galactosyltransferase). In premutation carriers, altered Zn homeostasis, brain bioenergetics and Shank3 levels could be compounded by Zn-deficient milk, increasing the risk of developing emotional and neurological/cognitive problems and/or FXTAS later in life.
authors.affiliation: Department of Molecular Biosciences, School of Veterinary Medicine Davis, CA, USA.
authors.forename: Eleonora
authors.initials: E
authors.lastname: Napoli
authors.affiliation: Department of Molecular Biosciences, School of Veterinary Medicine Davis, CA, USA.
authors.forename: Catherine
authors.initials: C
authors.lastname: Ross-Inta
authors.affiliation: Department of Molecular Biosciences, School of Veterinary Medicine Davis, CA, USA.
authors.forename: Gyu
authors.initials: G
authors.lastname: Song
authors.affiliation: Department of Molecular Biosciences, School of Veterinary Medicine Davis, CA, USA.
authors.forename: Sarah
authors.initials: S
authors.lastname: Wong
authors.affiliation: Medical Investigations of Neurodevelopmental Disorders Institute, University of California, DavisDavis, CA, USA; Department of Pediatrics, University of California Davis Medical CenterSacramento, CA, USA.
authors.forename: Randi
authors.initials: R
authors.lastname: Hagerman
authors.affiliation: Medical Investigations of Neurodevelopmental Disorders Institute, University of California, Davis Davis, CA, USA.
authors.forename: Louise W
authors.initials: LW
authors.lastname: Gane
authors.affiliation: Department of Food Science and Technology and Foods for Health Institute, University of California, Davis Davis, CA, USA.
authors.forename: Jennifer T
authors.initials: JT
authors.lastname: Smilowitz
authors.affiliation: Medical Investigations of Neurodevelopmental Disorders Institute, University of California, DavisDavis, CA, USA; Department of Biochemistry and Molecular Medicine, School of Medicine, University of California, DavisDavis, CA, USA.
authors.forename: Flora
authors.initials: F
authors.lastname: Tassone
authors.affiliation: Department of Molecular Biosciences, School of Veterinary MedicineDavis, CA, USA; Medical Investigations of Neurodevelopmental Disorders Institute, University of California, DavisDavis, CA, USA.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Giulivi
keywords: FMR1; Shank3; bioenergetics; brain; milk; mitochondria; premutation; zinc