Endogenous α-Synuclein Is Induced by Valproic Acid through Histone Deacetylase Inhibition and Participates in Neuroprotection against Glutamate-Induced Excitotoxicity

Abstract

Emerging evidence suggests that ␣-synuclein (␣-syn), which is traditionally thought to have a pathophysiological role in neurodegenerative diseases, can have neuroprotective effects. This study aimed to investigate whether endogenous ␣-syn in neurons can be induced by valproic acid (VPA), a mood-stabilizer, anticonvulsant and histone deacetylase (HDAC) inhibitor, and if so, whether the ␣-syn induction is neuroprotective. VPA treatment of rat cerebellar granule cells caused a robust dose-and time-dependent increase in levels of ␣-syn protein and mRNA and in the intensity of ␣-syn immunostaining. Knockdown of VPA-induced ␣-syn overexpression with ␣-syn antisense oligonucleotides or siRNA completely blocked VPA-induced neuroprotection. ␣-Syn knockdown also exacerbated glutamate neurotoxicity, stimulated the expression of the proapoptotic gene ubiquitin-conjugating enzyme E2N, and downregulated the expression of the anti-apoptotic gene Bcl-2. Induction of ␣-syn by VPA was associated with inhibition of HDAC activity, resulting in hyperacetylation of histone H3 in the ␣-syn promoter and a marked increase in ␣-syn promoter activity. Moreover, VPA-induced ␣-syn induction and neuroprotection were mimicked by HDAC inhibitors sodium 4-phenylbutyrate and trichostatin A (TSA). ␣-syn was also induced by VPA in rat cerebral cortical neurons. Additionally, treatment of rats with VPA, sodium butyrate, or TSA markedly increased ␣-syn protein levels in the cortex and cerebellum. Together, our results demonstrate for the first time that VPA induces ␣-syn in neurons through inhibition of HDAC and that this ␣-syn induction is critically involved in neuroprotection against glutamate excitotoxicity. Clinically, VPA may represent a suitable treatment for excitotoxicity-related neurodegenerative diseases.

Novel One-step Immunoassays to Quantify α-Synuclein

“…An histone deacetylase inhibitor (suberohydroxamic acid, indicated by an arrow) reproducibly increased ␣-synuclein content. This was expected based on a prior study with valproic acid (36).…”

“…Technical replication of the screen indicated good reproducibility, and several compounds, including rapamycin, yielded substantial ␣-synuclein reduction. In contrast, a histone deacetylase inhibitor reproducibly increased cellular ␣-synuclein, presumably by de-repression of its mRNA transcription (36). Critically, the ␣-synuclein TR-FRET immunoassays may now be scaled-up to directly accommodate both large-scale compound and full-genome siRNA screens, which are essential to drug development programs.…”

The mood stabilizers lithium and valproate selectively activate the promoter IV of brain-derived neurotrophic factor in neurons

“…Cortical neurons were prepared from day-18 embryonic (E18) rats as described previously 28 with slight modifications. Briefly, cortical cells were cultured in Neurobasal medium supplemented with B27 (Invitrogen; Carlsbad, CA, USA) in the presence of 0.5 mM L-glutamine.…”

“…25,26 Emerging evidence suggests that inhibition of GSK-3 and HDAC are responsible, at least in part, for the neuroprotective effects of lithium and VPA, respectively. 27,28 The present study was undertaken to investigate whether BDNF exon IV-containing mRNA and promoter IV activity are increased by lithium or VPA treatment in rat cortical neurons, and to determine the BDNF promoter region that confers the sensitivity to either drug. We also investigated whether inhibiting GSK-3 or HDAC mimics the ability of mood stabilizers to induce BDNF transcription in cortical neurons.…”

Protective effect of valproic acid on cultured motor neurons under glutamate excitotoxic conditions. Ultrastructural study

“…It was shown that valproic acid protected cultured cerebellar granule cells against GLU-induced excitotoxicity with concomitant transcriptional activation and induction of α-synuclein. This presynaptic protein was induced by valproic acid through histone deacetylase inhibition and participates in neuroprotection [23].…”