DIFFERENTIAL
DISPLAY IDENTIFIES NOVEL TARGETS FOR THE ACTIONS OF MOOD
STABILIZING AGENTS LITHIUM (LI) AND
VALPROATE (VPA)
Husseini K.
Manji, MD* and Guang Chen, MD. Molecular Pathophysiology Program,
WSU School of Medicine
mRNA RT-PCR differential display
(DD) was used to identify changes in gene expression induced by
the chronic administration of the mood stabilizer. Inbred male
Wistar Kyoto rats (selected to reduce potential false positives
due to individual differences) were treated chronically (4 weeks)
with saline, lithium carbonate or sodium valproate, and DD was
conducted using total RNAs isolated from FCx. In total, 150
reactions were performed and we found that 14 bands showed
markedly greater levels in FCx following chronic treatment with both
LI and VPA, whereas 7 bands showed markedly lower levels in both
treatment groups. One sequence of cDNA fragments whose expression
is markedly increased by both chronic lithium and VPA has ~90%
homology to a transcription factor, PEBP2b (polyomavirus
enhancer-binding protein 2b ). Gel mobility shift assays for the
PEBP2 transcription factor revealed that the chronic
administration of both lithium and VPA increased DNA binding
activity of PEBP2 a b in rat frontal cortex; by contrast,
neither chronic amphetamine nor chlordiazepoxide had any effect
on PEBP2 DNA binding activity. We next sought to determine if the
lithium and VPA-induced increases in PEBP2 DNA binding activity
resulted in alterations in the levels of the neuroprotective
protein, bcl-2 (known to be transcriptionally regulated by
PEPP2). Chronic treatment of rats with both LI and VPA resulted
in a doubling of bcl-2 levels in FCx. To further localize
the drug-induced increases in bcl-2 levels, immunohistochemical
studies were conducted. Both treatments resulted in a marked
increase in the number of bcl-2 immunoreactive neurons in layers
2 and 3 of FCx. These novel findings represent the first report
of medication-induced increases in bcl-2 levels in brain, and
suggest that the long term beneficial effects of lithium and VPA
may involve hitherto underappreciated neuroprotective effects.