Transcriptomic responses in mouse brain exposed to chronic excess of the neurotransmitter glutamate.
BACKGROUND
Increases during aging in extracellular levels of glutamate (Glu), the major excitatory neurotransmitter in the brain, may be linked to chronic neurodegenerative diseases. Little is known about the molecular responses of neurons to chronic, moderate increases in Glu levels. Genome-wide gene expression in brain hippocampus was examined in a unique transgenic (Tg) mouse model that exhibits moderate Glu hyperactivity throughout the lifespan, the neuronal Glutamate dehydrogenase (Glud1) mouse, and littermate 9 month-old wild type mice.


RESULTS
Integrated bioinformatic analyses on transcriptomic data were used to identify bio-functions, pathways and gene networks underlying neuronal responses to increased Glu synaptic release. Bio-functions and pathways up-regulated in Tg mice were those associated with oxidative stress, cell injury, inflammation, nervous system development, neuronal growth, and synaptic transmission. Increased gene expression in these functions and pathways indicated apparent compensatory responses offering protection against stress, promoting growth of neuronal processes (neurites) and re-establishment of synapses. The transcription of a key gene in the neurite growth network, the kinase Ptk2b, was significantly up-regulated in Tg mice as was the activated (phosphorylated) form of the protein. In addition to genes related to neurite growth and synaptic development, those associated with neuronal vesicle trafficking in the Huntington's disease signalling pathway, were also up-regulated.


CONCLUSIONS
This is the first study attempting to define neuronal gene expression patterns in response to chronic, endogenous Glu hyperactivity at brain synapses. The patterns observed were characterized by a combination of responses to stress and stimulation of nerve growth, intracellular transport and recovery.
Wang
Xinkun
X
Higuchi Biosciences Center, 2099 Constant Ave, The University of Kansas, Lawrence, KS 66047, USA. xwang@ku.edu
Bao
Xiaodong
X
Pal
Ranu
R
Agbas
Abdulbaki
A
Michaelis
Elias K
EK
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D001921:Brain / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D020013:Calcium Signaling / Q000235:genetics; D018925:Chemokines / Q000378:metabolism; D051418:Focal Adhesion Kinase 2 / Q000378:metabolism; D020869:Gene Expression Profiling; D015971:Gene Expression Regulation, Enzymologic; D053263:Gene Regulatory Networks / Q000235:genetics; D023281:Genomics; D005969:Glutamate Dehydrogenase / Q000235:genetics; D018698:Glutamic Acid / Q000378:metabolism*; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism / Q000502:physiology; D006816:Huntington Disease / Q000378:metabolism / Q000473:pathology; D042541:Intracellular Space / Q000378:metabolism; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D016501:Neurites / Q000378:metabolism; D009457:Neuroglia / Q000378:metabolism; D018377:Neurotransmitter Agents / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D010750:Phosphoproteins / Q000378:metabolism; D017510:Protein Folding; D015203:Reproducibility of Results; D015398:Signal Transduction / Q000235:genetics; D013312:Stress, Physiological / Q000235:genetics; D013569:Synapses / Q000378:metabolism; D013997:Time Factors; D051193:Toll-Like Receptors / Q000378:metabolism
D000596:Amino Acids; D018925:Chemokines; D018377:Neurotransmitter Agents; D010750:Phosphoproteins; D051193:Toll-Like Receptors; D018698:Glutamic Acid; D005969:Glutamate Dehydrogenase; D051418:Focal Adhesion Kinase 2; C496053:Ptk2b protein, mouse