2020 - Fluoride Exposure Affects Glutamine Mobilization

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2020 - Fluoride Exposure Affects Glutamine Mobilization

Postby pfpcnews » Tue Aug 18, 2020 1:06 am

NOTE: Glutamate metabolism is regulated by thryoid hormone. See: Domingues et al., 2018; below.

García-López AL, Hernández-Castillo J, Hernández-Kelly LC, Olivares-Bañuelos TN, Ortega A - "Fluoride Exposure Affects Glutamine Uptake in Müller Glia Cells" Neurotox Res. 2020 Jul 31. doi: 10.1007/s12640-020-00263-4. Epub ahead of print. PMID: 32734566


Fluoride, a pollutant present in contaminated ground water, oral care products, food, and pesticides, has deleterious effects in the structure and function of the central nervous system. Among the established neurological defects described in the exposed population, a reduced score in intelligence quotient tests in children of contaminated areas has gained attention over the past years. Maternal fluoride exposure during gestation decreases learning and memory abilities that correlate with a significant diminution of glutamate receptors expression. Since the involvement of glia cells in the maintenance and regulation of glutamatergic synapses is well-documented, in this contribution, we characterized the effect of fluoride exposure in the regulation of glia glutamine transporters. To this end, we used the Müller glia cell line, Mio-M1, and through the use of [3H]L-Glutamine uptake experiments and a Western blot approach, we demonstrate here the functional expression of system N of glutamine transporters, SNAT3 and SNAT5, in this model of human retina radial glia cells. Furthermore, these transporters interact with the glutamate transporter excitatory amino acid transporter 1, in an activity-dependent manner. Fluoride treatment reduces glutamine uptake and cell membrane [3H]glutamine surface binding, in good correlation with a decrease in SNAT3 and 5 protein levels. These results demonstrate that glia cells respond to the presence of fluoride reducing glutamine mobilization and by these means decreases glutamate turnover suggesting a disruption of glutamatergic transmission.

Domingues JT, Wajima CS, Cesconetto PA, Parisotto EB, Winkelmann-Duarte E, Santos KD, Saleh N, Filippin-Monteiro FB, Razzera G, Mena Barreto Silva FR, Pessoa-Pureur R, Zamoner A - "Experimentally-induced maternal hypothyroidism alters enzyme activities and the sensorimotor cortex of the offspring rats" Mol Cell Endocrinol 478:62-76 (2018) doi: 10.1016/j.mce.2018.07.008. Epub 2018 Jul 18. PMID: 30031104.


In this study, we used an experimental model of congenital hypothyroidism to show that deficient thyroid hormones (TH) disrupt different neurochemical, morphological and functional aspects in the cerebral cortex of 15-day-old offspring. Our results showing decreased glutamine synthetase (GS) activity and Ca2+ overload in the cerebral cortex of hypothyroid pups suggest misregulated glutamate metabolism associated with developmentally induced TH deficiency. The 14C-MeAIB accumulation indicates upregulated System A activity and glutamine uptake by neurons. Energy metabolism in hypothyroid cortical slices was preserved, as demonstrated by unaltered glucose metabolism. We also found upregulated acetylcholinesterase activity, depleting acetylcholine from the synaptic cleft, pointing to disrupted cholinergic system. Increased reactive oxygen species (ROS) generation, lipid peroxidation, glutathione (GSH) depletion, which were associated with glutathione peroxidase, superoxide dismutase and gamma-glutamyltransferase downregulation suggest redox imbalance. Disrupted astrocyte cytoskeleton was evidenced by downregulated and hyperphosphorylated glial fibrillary acidic protein (GFAP). Morphological and structural characterization of the sensorimotor cerebral cortex (SCC) showed unaltered thickness of the SCC. However, decreased size of neurons on the layers II & III and IV in the right SCC and increased NeuN positive neurons in specific SCC layers, suggest that they are differently affected by the low TH levels during neurodevelopment. Hypothyroid pups presented increased number of foot-faults in the gridwalk test indicating affected motor functions. Taken together, our results show that congenital hypothyroidism disrupts glutamatergic and cholinergic neurotransmission, Ca2+ equilibrium, redox balance, cytoskeleton integrity, morphological and functional aspects in the cerebral cortex of young rats.
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