Altered expression of neurotransmitter-receptor subunit and uptake site mRNAs in hemimegalencephaly.
OBJECTIVE
Hemimegalencephaly (HMEG) is characterized by unilateral hemispheric enlargement and severe cytoarchitectural abnormalities that are highly associated with intractable epilepsy. No studies have defined alterations in neurotransmitter-receptor subunit gene expression in HMEG. We hypothesize that a differential expression of excitatory amino acid and gamma-aminobutyric acid (GABA)A-receptor subunit messenger RNAs (mRNAs) exists in HMEG.


METHODS
The expression of mRNAs encoding 20 neurotransmitter-receptor subunits, synthetic enzymes, and uptake sites as well as select additional candidate genes was defined in HMEG samples (n=8) compared with homotopic control cortex specimens by using targeted complementary DNA (cDNA) arrays. Expression of GLT-1 (a glial glutamate transporter), EAAC-1 (neuronal glutamate transporter), and NMDA2B was corroborated by immunohistochemical, Western, and ligand-binding assays.


RESULTS
Differential expression of 11 neurotransmitter-related mRNAs was demonstrated in HMEG compared with control cortex. For example, expression of GLT-1 and GluR6 mRNAs was enhanced, whereas diminished expression of the neuronal glutamate transporter EAAC-1, GABAAalpha2, GABAAgamma2, GABAAgamma3, NMDA2B, GluR1, GluR2, GluR4, and GluR5 subunits occurred. Reduced NMDA2B subunit mRNA expression in HMEG was confirmed by receptor ligand-binding assays by using the NMDA2B-receptor antagonist ifenprodil, which revealed barely detectable levels of NMDA2B binding compared with that in control cortex.


CONCLUSIONS
Selective alterations occur in distinct neurotransmitter-receptor and -uptake sites in HMEG. Differential expression of neurotransmitter-receptor and -uptake sites in HMEG may contribute to epileptogenesis in HMEG.
Baybis
Marianna
M
PENN Epilepsy Center, Department of Neurology, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania 19104, USA.
Lynch
David
D
Lee
Allana
A
Patel
Anita
A
McKhann
Guy
G
Chugani
Diane
D
J Kupsky
William
W
Aronica
Eleonora
E
Crino
Peter B
PB
D000293:Adolescent; D015153:Blotting, Western; D001921:Brain / Q000002:abnormalities* / Q000378:metabolism* / Q000473:pathology; D002452:Cell Count; D002540:Cerebral Cortex / Q000002:abnormalities / Q000378:metabolism; D002648:Child; D002675:Child, Preschool; D027342:Excitatory Amino Acid Transporter 2 / Q000235:genetics / Q000378:metabolism; D005260:Female; D015870:Gene Expression; D006801:Humans; D007223:Infant; D008297:Male; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D042787:Receptor, TIE-2; D011963:Receptors, GABA-A / Q000235:genetics / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000235:genetics / Q000378:metabolism; D017981:Receptors, Neurotransmitter / Q000235:genetics / Q000378:metabolism*
D027342:Excitatory Amino Acid Transporter 2; C121001:NR2B NMDA receptor; D012333:RNA, Messenger; D011963:Receptors, GABA-A; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter; D042787:Receptor, TIE-2