Elsevier

Neuroscience

Volume 149, Issue 1, 12 October 2007, Pages 203-212
Neuroscience

Neuropharmacology
Valproic acid and other histone deacetylase inhibitors induce microglial apoptosis and attenuate lipopolysaccharide-induced dopaminergic neurotoxicity

https://doi.org/10.1016/j.neuroscience.2007.06.053Get rights and content

Abstract

Valproic acid (VPA), a widely prescribed drug for seizures and bipolar disorder, has been shown to be an inhibitor of histone deacetylase (HDAC). Our previous study has demonstrated that VPA pretreatment reduces lipopolysaccharide (LPS)-induced dopaminergic (DA) neurotoxicity through the inhibition of microglia over-activation. The aim of this study was to determine the mechanism underlying VPA-induced attenuation of microglia over-activation using rodent primary neuron/glia or enriched glia cultures. Other histone deacetylase inhibitors (HDACIs) were compared with VPA for their effects on microglial activity. We found that VPA induced apoptosis of microglia cells in a time- and concentration-dependent manner. VPA-treated microglial cells showed typical apoptotic hallmarks including phosphatidylserine externalization, chromatin condensation and DNA fragmentation. Further studies revealed that trichostatin A (TSA) and sodium butyrate (SB), two structurally dissimilar HDACIs, also induced microglial apoptosis. The apoptosis of microglia was accompanied by the disruption of mitochondrial membrane potential and the enhancement of acetylation levels of the histone H3 protein. Moreover, pretreatment with SB or TSA caused a robust decrease in LPS-induced pro-inflammatory responses and protected DA neurons from damage in mesencephalic neuron–glia cultures. Taken together, our results shed light on a novel mechanism whereby HDACIs induce neuroprotection and underscore the potential utility of HDACIs in preventing inflammation-related neurodegenerative disorders such as Parkinson’s disease.

Section snippets

Materials

LPS (strain O111:B4) was purchased from Calbiochem (San Diego, CA, USA). Cell culture ingredients were obtained from Invitrogen (San Diego, CA, USA). [3H]-Dopamine (DA; 28 Ci/mmol) was purchased from PerkinElmer Life Sciences (Boston, MA, USA). The polyclonal antibody against tyrosine hydroxylase (TH) was a kind gift from Dr. John Reinhard of Glaxo Wellcome (Research Triangle Park, NC, USA) and the antibody diluent was a product of DAKO (Carpinteria, CA, USA). Biotinylated horse anti-mouse and

Treatment with VPA or other HDACIs triggers microglial apoptosis

To investigate whether VPA decreases the number of microglia by inducing apoptosis (Peng et al., 2005), we examined multiple parameters of apoptotic cell death in VPA-treated rat microglia-enriched cultures. The VPA-treated microglial cells showed a significant dose-dependent reduction in cell viability in the range of 0.3 mM to 1.2 mM, as determined by the MTT assay (Fig. 1A). Moreover, VPA treatment triggered the externalization of PS, an early hallmark of apoptosis, and increased the

Discussion

In this study, we demonstrated that VPA induce the apoptosis of the cultured rat microglia. The microglial apoptosis is characterized by PS externalization, internucleosomal DNA fragmentation, and appearance of TUNEL-positive cells. The apoptosis of microglia is likely responsible for the reduction in the number of microglia in VPA-treated neuron–glia cultures (Peng et al., 2005). The finding that VPA exerted little effect on the proliferation of microglia further supports this notion. Evidence

Conclusion

In conclusion, the present study provides strong evidence that VPA and other HDACIs markedly induce the apoptosis of the microglia. This apoptosis-inducing effect is associated with a loss of microglial mitochondrial transmembrane potential and an increase in histone hyperacetylation. The HDACI-induced microglial apoptosis likely contributes to their neuroprotective effects in response to pro-inflammatory stimuli. Since microglia could potentially act as both protector and attacker, future in

Acknowledgments

We are grateful to Ms. Belinda Wilson and Mr. Robert N. Wine for their technical assistance, and Drs. Sung-Jen Wei, Ms. Michelle L. Block, and Mr. Chiou-Feng Lin for their invaluable comments regarding this manuscript. This work was also supported in part by the Intramural Research Program of the National Institute of Environmental Health Sciences, NIH.

References (41)

  • G.S. Peng et al.

    Valproate pretreatment protects dopaminergic neurons from LPS-induced neurotoxicity in rat primary midbrain cultures: role of microglia

    Brain Res Mol Brain Res

    (2005)
  • S. Petri et al.

    Additive neuroprotective effects of a histone deacetylase inhibitor and a catalytic antioxidant in a transgenic mouse model of amyotrophic lateral sclerosis

    Neurobiol Dis

    (2006)
  • C.J. Phiel et al.

    Histone deacetylase is a direct target of valproic acid, a potent anticonvulsant, mood stabilizer, and teratogen

    J Biol Chem

    (2001)
  • C.C. Wang et al.

    Microglial distribution and apoptosis in fetal rat brain

    Brain Res Dev Brain Res

    (2002)
  • M.H. Allen et al.

    Linear relationship of valproate serum concentration to response and optimal serum levels for acute mania

    Am J Psychiatry

    (2006)
  • M.L. Block et al.

    Microglia-mediated neurotoxicity: uncovering the molecular mechanisms

    Nat Rev

    (2007)
  • J.E. Bolden et al.

    Anticancer activities of histone deacetylase inhibitors

    Nat Rev Drug Discov

    (2006)
  • A. Chan et al.

    Phagocytosis of apoptotic inflammatory cells by microglia and modulation by different cytokines: mechanism for removal of apoptotic cells in the inflamed nervous system

    Glia

    (2001)
  • A. Chan et al.

    Phagocytosis of apoptotic inflammatory cells by microglia and its therapeutic implications: termination of CNS autoimmune inflammation and modulation by interferon-beta

    Glia

    (2003)
  • P.S. Chen et al.

    Valproate protects dopaminergic neurons in midbrain neuron/glia cultures by stimulating the release of neurotrophic factors from astrocytes

    Mol Psychiatry

    (2006)
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    These two authors contribute equally to this work.

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