Differential Display Idnetifies 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.