Long term lithium treatment suppresses p53 and bax expression but increases bcl-2 expression anoxic brain injury

Next section abstract

This study was undertaken to investigate the molecular mechanisms underlying the neuroprotective actions of lithium against

Glutamate excitotoxicity with a focus on the role of proapoptotic and antiapoptotic genes. Long term, but not acute, treatment

Of cultured cerebellar granule cells with licl induces a concentration-dependent decrease in mrna and protein levels of proapoptotic

P53 and bax; conversely, mrna and protein levels of cytoprotective bcl-2 are remarkably increased. The ratios of bcl-2/bax

Protein levels increase by approximately 5-fold after lithium treatment for 5–7 days. Exposure of cerebellar granule cells

To glutamate induces a rapid increase in p53 and bax mrna and protein levels with no apparent effect on bcl-2 expression.Anoxic brain injury recovery

Pretreatment with licl for 7 days prevents glutamate-induced increase in p53 and bax expression and maintains bcl-2 in an

Elevated state. Glutamate exposure also triggers the release of cytochrome c from the mitochondria into the cytosol. Lithium pretreatment blocks glutamate-induced cytochrome c release and cleavage of lamin B1, a nuclear substrate for caspase-3. These results strongly suggest that lithium-induced

Bcl-2 up-regulation and p53 and bax down-regulation play a prominent role in neuroprotection against excitotoxicity. Our results

Further suggest that lithium, in addition to its use in the treatment of bipolar depressive illness, may have an expanded

Use in the intervention of neurodegeneration.Anoxic brain injury recovery

For almost half a century, lithium has been the most widely used treatment for bipolar depressive illness, although its therapeutic

Mechanism of action remains obscure. Among the many biochemical actions of long term lithium treatment in vivo and in vitro are its ability to inhibit phosphoinoside turnover and stimulated levels of calcium, influence signal transduction by modulating

G-proteins and protein kinase C, and regulate gene expression involving AP-1 DNA binding activity ( 1-7). Increasing evidence supports the notion that lithium has neuroprotective effects. We have recently reported that long term

Treatment of cultured neurons from the central nervous system with therapeutically relevant concentrations of lithium robustly

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Protects against apoptotic cell death associated with glutamate excitotoxicity via N-methyl- d-aspartate (NMDA) 1 receptors ( 8). In cerebellar granule cells (cgcs), the protection afforded by lithium is accompanied by an inhibition of NMDA receptor-mediated

Calcium influx that is independent of a loss of receptor binding activity or subunit expression ( 8). In a rat model of ischemia that involves glutamate excitotoxicity, chronic lithium administration was found to markedly

Reduce brain infarction and neurological deficits induced by occlusion of the middle cerebral artery ( 9).

In an attempt to elucidate the molecular mechanisms underlying lithium-induced neuroprotection in cultured cgcs, we examined

anoxic brain injury recovery

The long term effects of lithium on the expression of key genes involved in proapoptosis and cytoprotection, notably p53,

Bax, and bcl-2. P53, a nuclear protein that binds to specific DNA sequences and functions as a transcriptional activator,

Promotes the expression of the proapoptotic gene, bax, but suppresses the expression of the antiapoptotic gene, bcl-2 ( 10). Bax has been shown to bind to mitochondrial membranes and thereby to cause the release of cytochrome c, which in turn leads to activation of caspases and degradation of specific protein substrates ( 11-13). The antiapoptotic action of bcl-2 is mediated, at least in part, by blocking bax-induced cytochrome c release and caspase activation ( 14-16).Anoxic brain injury recovery thus, it has been proposed that the relative amounts of bcl-2 and bax determine the fate of a living cell ( 17, 18). In this study, we determined the levels of these proapoptotic and antiapoptotic gene products in cgcs pretreated with lithium

And/or exposed to glutamate.

In contrast, exposure to 100 μ m glutamate for 4 or 8 h markedly increased the mrna levels of p53 and bax but had little or no effect on bcl-2 mrna (fig.

4, a, c, and e). Pretreatment with licl (3 m m) for 7 days abolished glutamate-induced increase in p53 and bax mrna levels, while maintaining elevated levels of bcl-2 mrna

Even in cells exposed to glutamate. Similar effects on protein levels of p53, bax, and bcl-2 were observed in cgcs exposed

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To 50 or 100 μ m glutamate for 24 h in the absence or presence of lithium pretreatment (fig. 4, b, d, and f). Lithium treatment for 5–7 days was found to cause a 5-fold increase in the bcl-2/bax protein ratio (fig. 4 g). Conversely, the bcl-2/bax ratio was decreased with glutamate exposure for 24 h, and this decrease was prevented by lithium

Pretreatment for 7 days. Under these experimental conditions, lithium pretreatment effectively protected cells from excitotoxicity

(fig. 4 h). It should be mentioned that the effects of glutamate on cell viability and levels of p53, bax, and bcl-2 were completely

Blocked by MK-801 (10 μ m), a selective NMDA receptor antagonist (data not shown), confirming our previous report that glutamate-induced apoptosis

anoxic brain injury recovery

Is entirely mediated by NMDA receptors ( 8, 20).

Previous section next section DISCUSSION

Bcl-2 family plays a prominent antiapoptotic role by acting upstream of caspase activation. Specifically, bcl-2 may inhibit

The bax-mediated release of cytochrome c or AIF ( apoptosis- inducing factor) from mitochondria, thereby preventing caspase activation and cell death ( 14, 22). In addition, bcl-2 may physically interact with apaf-1 ( apoptotic protease- activating factor- 1) to prevent apaf-1-mediated caspase activation ( 23, 24). Lithium-induced neuroprotection against glutamate excitotoxicity is likely mediated in part by bcl-2 up-regulation, whereas

Glutamate-induced apoptosis involves the overexpression of p53 and bax.Anoxic brain injury recovery in support of the role of p53 in mediating glutamate

Excitotoxicity, we found that cultured cgcs derived from p53-deficient mice are resistant to the glutamate insult. 2 we also found that glutamate triggers the release of cytochrome c from mitochondria and the cleavage of lamin B1, a nuclear membrane and substrate of caspase-3. Moreover, these glutamate-induced

Effects are almost completely blocked by long term lithium pretreatment.

Other actions of bcl-2 may also contribute to lithium-induced neuroprotection against excitotoxicity. For example, bcl-2 down-regulates

The activity of transcription factor NF-κb induced during apoptosis ( 25) and inhibits abnormal release of calcium from the endoplasmic reticulum, thus reducing calcium loading to mitochondria and

anoxic brain injury recovery

Subsequent oxidative stress ( 26, 27). Bcl-2 overexpression could also be related to the lithium protection against apoptosis induced by anticonvulsants (carbamazepine

And phenytoin) in cgcs ( 28) and by brain damage resulting from focal ischemia in rats ( 9).

This study shows for the first time that lithium influences the expression of p53 and some bcl-2 family members. Moreover,

We show that these changes in gene expression are associated with neuronal survival. In this context, bcl-2 levels appear

To be increased in the frontal cortex of rats chronically treated with lithium and valproate, another drug used to treat manic

Depressive illness. 3It is well established that p53 positively regulates bax but negatively regulates bcl-2 expression ( 10).Anoxic brain injury recovery thus, lithium-elicited changes in the mrna and protein levels of bax and bcl-2 are likely the results of the inhibition

Of p53 expression. Consistent with this possibility, we found that only 1 day of lithium treatment is needed to observe a

Decrease in p53 levels but 3 days are needed to observe a change in bax and bcl-2 levels. However, it is also possible that

Lithium has a direct regulatory role in the expression of bcl-2 and/or bax. Lithium has been shown to increase basal transcription

Factor binding to AP-1 and CRE sites ( 6, 7) but decreases stimulated binding to the AP-1 site in cultured cells and the brain ( 5). These lithium-induced changes in transcription factor binding may be related to the ability of lithium to inhibit the activity

anoxic brain injury recovery

Of glycogen synthase kinase ( 29), which phosphorylates transcription factors such as c-jun, causing a loss of its DNA binding activity ( 30). Lithium modulation of transcription factor DNA binding activity may underlie the effects of this drug on the expression

Of genes involved in apoptosis. Regardless of the mechanisms involved in lithium-induced gene expression, our results suggest

That lithium, in addition to treating bipolar disorder, may also be useful in the treatment of neurodegenerative diseases,

Particularly those involving glutamate excitotoxicity.