Increased Glutamate Receptor and Transporter Expression in the Cerebral Cortex and Striatum of Gcdh-/- Mice: Possible Implications for the Neuropathology of Glutaric Acidemia Type I

Valeska Lizzi Lagranha,Ursula Matte,Bianca Seminotti,David M Koeller,Diogo Onofre Gomes De Souza,Carolina Coffi Pereira,Moacir Wajner,Stephen I Goodman,Talita Giacomet De Carvalho,Michael Woontner,Stefan Strack

doi:10.1371/journal.pone.0090477

Abstract

We determined mRNA expression of the ionotropic glutamate receptors NMDA (NR1, NR2A and NR2B subunits), AMPA (GluR2 subunit) and kainate (GluR6 subunit), as well as of the glutamate transporters GLAST and GLT1 in cerebral cortex and striatum of wild type (WT) and glutaryl-CoA dehydrogenase deficient (Gchh -/-) mice aged 7, 30 and 60 days. The protein expression levels of some of these membrane proteins were also measured. Overexpression of NR2A and NR2B in striatum and of GluR2 and GluR6 in cerebral cortex was observed in 7-day-old Gcdh -/-. There was also an increase of mRNA expression of all NMDA subunits in cerebral cortex and of NR2A and NR2B in striatum of 30-day-old Gcdh -/- mice. At 60 days of life, all ionotropic receptors were overexpressed in cerebral cortex and striatum of Gcdh -/- mice. Higher expression of GLAST and GLT1 transporters was also verified in cerebral cortex and striatum of Gcdh -/- mice aged 30 and 60 days, whereas at 7 days of life GLAST was overexpressed only in striatum from this mutant mice. Furthermore, high lysine intake induced mRNA overexpression of NR2A, NR2B and GLAST transcripts in striatum, as well as of GluR2 and GluR6 in both striatum and cerebral cortex of Gcdh -/- mice. Finally, we found that the protein expression of NR2A, NR2B, GLT1 and GLAST were significantly greater in cerebral cortex of Gcdh -/- mice, whereas NR2B and GLT1 was similarly enhanced in striatum, implying that these transcripts were translated into their products. These results provide evidence that glutamate receptor and transporter expression is higher in Gcdh -/- mice and that these alterations may be involved in the pathophysiology of GA I and possibly explain, at least in part, the vulnerability of striatum and cerebral cortex to injury in patients affected by GA I.

Highlights

Glutaric acidemia type I (GA I, McKusick 23167; OMIM # 231670) is an autosomal recessive inherited neurometabolic disease caused by deficiency of glutaryl-CoA dehydrogenase activity (GCDH, EC 1.3.99.7), with an estimated incidence of 1:30,000-1:100,000 live-births, reaching a much higher prevalence in some communities (1:300) [1,2,3,4,5]
We initially compared the Messenger RNA (mRNA) expression of subunits of NMDA, amino-3hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and kainate receptors in the striatum and cerebral cortex from wild type (WT) and Gcdh-/- mice (KO)
We observed differences in the expression levels of Glutamate receptors (GLUR) genes between WT and Gcdh-/- mice in both cerebral cortex and striatum at all ages. mRNA levels of the GluR2 (AMPA) and GluR6 subunits were higher (1.4 and 1.7-fold respectively) in cerebral cortex of Gcdh-/- as compared to WT mice at 7 days of life (Figure 1A), whereas in striatum it was the expression of NR2A and NR2B (NMDA) that was much higher (2 to 3.5-fold) (Figure 1A)

Summary

Introduction

Glutaric acidemia type I (GA I, McKusick 23167; OMIM # 231670) is an autosomal recessive inherited neurometabolic disease caused by deficiency of glutaryl-CoA dehydrogenase activity (GCDH, EC 1.3.99.7), with an estimated incidence of 1:30,000-1:100,000 live-births, reaching a much higher prevalence in some communities (1:300) [1,2,3,4,5]. Increased concentrations of glutaric acid (GA, 500–5000 mmol/l) and 3-hydroxyglutaric acid (3-HGA), at lower amounts (40–200 mmol/l), are found in the body fluids and in the brain of GA I patients [1,2,6,7,8]. GA-I is considered a ‘‘cerebral’’ organic aciduria because affected patients present essentially neurological symptoms including diskenesia/ dystonia and spasticity that appear especially after encephalopathic crises, which occur between 6 and 36 months of age and are accompanied by bilateral destruction of caudate and putamen [9,10]. The exact pathomechanisms of the neurological symptoms and brain abnormalities of the affected patients are still obscure. There are in vitro and in vivo experimental evidences indicating that disruption of mitochondrial energy metabolism [15,16,17,18,19], oxidative stress [20,21,22,23,24,25,26] and glutamatergic excitotoxicity [27,28,29,30,31,32,33,34,35,36,37,38,39] are involved in the pathogenesis of this disorder

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