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

Putting the 'HAT' back on survival signalling: the promises and challenges of HDAC inhibition in the treatment of neurological conditions

Decreased histone acetyltransferase activity and transcriptional dysfunction have been implicated in almost all neurodegenerative conditions. Increasing net histone acetyltransferase activity through inhibition of the histone deacetylases (HDACs) has been shown to be an effective strategy to delay or halt progression of neurological disease in cellular and rodent models. These findings have provided firm rationale for Phase I and Phase II clinical trials of HDAC inhibitors in Huntington's disease, spinal muscular atrophy, and Freidreich's ataxia. In this review, we discuss the current findings and promise of HDAC inhibition as a strategy for treating neurological disorders. Despite the fact that HDAC inhibitors are in an advanced stage of development, we suggest other approaches to modulating HDAC function that may be less toxic and more efficacious than the canonical agents developed so far.

Trichostatin A enhances OGD-astrocyte viability by inhibiting inflammatory reaction mediated by NF-kappaB

In this study we investigate the protective effects of Trichostatin A (TSA) on astrocyte injury after oxygen-glucose deprivation (OGD) and further explore its possible protective mechanisms of inhibiting inflammatory reaction mediated by nuclear factor-kappaB (NF-kappaB). In the in vitro model of astrocyte OGD, TSA treatment was used at different doses and time points before deprivation. Astroglial viability was determined by MTT assay. Then tumor necrosis factor-alpha, interleukin-1beta (IL-1beta), and IL-6 mRNA were measured by RT-PCR. Furthermore, the expression of phosphorylated p65, mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinases (ERK), MAPK/c-Jun N-terminal (JNK) and MAPK/p38 was assayed by Western blot. The results showed that TSA at the five doses (12.5, 25, 50, 100, and 200 ng/ml) significantly enhanced the astrocytes viability by 25.3%, 46.1%, 37.5%, 34.9%, and 22% of the vehicle, respectively. The level of TNF-alpha, IL-1beta and IL-6 mRNA in astrocytes was increased after OGD and down-regulated by TSA (p<0.05). In addition, the phosphorylation p65 was markedly activated in the astrocytes after OGD compared to the control (p<0.05). TSA inhibited phosphorylation of p65 but did not affect the MAPK pathway. Our results suggest that TSA protects astrocytes from damage after OGD by the inhibition of the inflammatory reaction and this protection is at least partially through the suppression of phosphorylation of NF-kappaB p65.

Histone deacetylase inhibitors suppress interleukin-1beta-induced nitric oxide and prostaglandin E2 production in human chondrocytes

OBJECTIVE

Overproduction of nitric oxide (NO) and prostaglandin E(2) (PGE(2)) plays an important role in the pathogenesis of osteoarthritis (OA). In the present study, we determined the effect of trichostatin A (TSA) and butyric acid (BA), two histone deacetylase (HDAC) inhibitors, on NO and PGE(2) synthesis, inducible NO synthase (iNOS) and cyclooxygenase (COX)-2 expression, and nuclear factor (NF)-kappaB DNA-binding activity, in interleukin-1beta (IL-1)-stimulated human OA chondrocytes, and on IL-1-induced proteoglycan degradation in cartilage explants.

METHODS

Chondrocytes were stimulated with IL-1 in the absence or presence of increasing concentrations of TSA or BA. The production of NO and PGE(2) was evaluated using Griess reagent and an enzyme immunoassay, respectively. The expression of iNOS and COX-2 proteins and mRNAs was evaluated using Western blotting and real-time reverse transcriptase-polymerase chain reaction (RT-PCR), respectively. Proteoglycan degradation was measured with dimethymethylene blue assay. Electrophoretic mobility shift assay (EMSA) was utilized to analyze the DNA-binding activity of NF-kappaB.

RESULTS

HDAC inhibition with TSA or BA resulted in a dose-dependent inhibition of IL-1-induced NO and PGE(2) production. IL-17- and tumor necrosis factor-alpha (TNF-alpha)-induced NO and PGE(2) production was also inhibited by TSA and BA. This inhibition correlated with the suppression of iNOS and COX-2 protein and mRNA expression. TSA and BA also prevented IL-1-induced proteoglycan release from cartilage explants. Finally, we demonstrate that the DNA-binding activity of NF-kappaB, was induced by IL-1, but was not affected by treatment with HDAC inhibitors.

CONCLUSIONS

These data indicate that HDAC inhibitors suppressed IL-1-induced NO and PGE(2) synthesis, iNOS and COX-2 expression, as well as proteoglycan degradation. The suppressive effect of HDAC inhibitors is not due to impaired DNA-binding activity of NF-kappaB. These findings also suggest that HDAC inhibitors may be of potential therapeutic value in the treatment of OA.

Enhancement of glutamate uptake in 1-methyl-4-phenylpyridinium-treated astrocytes by trichostatin A

Histone deacetylases (HDAC) inhibitors have been emerging as neuroprotective agents by acting on neurons and microglia. In this study, we found trichostatin A (TSA), a HDAC inhibitor, could inhibit the elevation of glutamate in 150 microM 1-methyl-4-phenylpyridinium (MPP+)-treated primary cultured astrocytes medium when its concentration reached 132 nM. TSA of 132 nM or more could promote the uptake of [3H]-D, L-glutamate by astrocytes. Further study showed the downregulation of glutamate transporter 1 and glutamate/aspartate transporter induced by MPP+ were prevented by TSA. Therefore, these findings suggested TSA could alleviate MPP+-induced impairment of astrocytic glutamate uptake, which might be a novel mechanism contributing to neuroprotection by HDAC inhibitors.

Age-dependent epigenetic control of differentiation inhibitors is critical for remyelination efficiency

The efficiency of remyelination decreases with age, but the molecular mechanisms responsible for this decline remain only partially understood. In this study, we show that remyelination is regulated by age-dependent epigenetic control of gene expression. In demyelinated young brains, new myelin synthesis is preceded by downregulation of oligodendrocyte differentiation inhibitors and neural stem cell markers, and this is associated with recruitment of histone deacetylases (HDACs) to promoter regions. In demyelinated old brains, HDAC recruitment is inefficient, and this allows the accumulation of transcriptional inhibitors and prevents the subsequent surge in myelin gene expression. Defective remyelination can be recapitulated in vivo in mice receiving systemic administration of pharmacological HDAC inhibitors during cuprizone treatment and is consistent with in vitro results showing defective differentiation of oligodendrocyte progenitors after silencing specific HDAC isoforms. Thus, we suggest that inefficient epigenetic modulation of the oligodendrocyte differentiation program contributes to the age-dependent decline in remyelination efficiency.

HDAC inhibitor increases histone H3 acetylation and reduces microglia inflammatory response following traumatic brain injury in rats

Traumatic brain injury (TBI) produces a rapid and robust inflammatory response in the brain characterized in part by activation of microglia. A novel histone deacetylase (HDAC) inhibitor, 4-dimethylamino-N-[5-(2-mercaptoacetylamino)pentyl]benzamide (DMA-PB), was administered (0, 0.25, 2.5, 25 mg/kg) systemically immediately after lateral fluid percussion TBI in rats. Hippocampal CA2/3 tissue was processed for acetyl-histone H3 immunolocalization, OX-42 immunolocalization (for microglia), and Fluoro-Jade B histofluorescence (for degenerating neurons) at 24 h after injury. Vehicle-treated TBI rats exhibited a significant reduction in acetyl-histone H3 immunostaining in the ipsilateral CA2/3 hippocampus compared to the sham TBI group (p<0.05). The reduction in acetyl-histone H3 immunostaining was attenuated by each of the DMA-PB dosage treatment groups. Vehicle-treated TBI rats exhibited a high density of phagocytic microglia in the ipsilateral CA2/3 hippocampus compared to sham TBI in which none were observed. All doses of DMA-PB significantly reduced the density of phagocytic microglia (p<0.05). There was a trend for DMA-PB to reduce the number of degenerating neurons in the ipsilateral CA2/3 hippocampus (p=0.076). We conclude that the HDAC inhibitor DMA-PB is a potential novel therapeutic for inhibiting neuroinflammation associated with TBI.

Valproate-dependent transcriptional regulation of GLAST/EAAT1 expression: involvement of Ying-Yang 1

Valproate, a widely used anti-epileptic drug also employed in the treatment of neurological diseases such as bipolar disorder and migraine, regulates the glutamatergic and GABAergic systems, although its effects in cell physiology have not been thoroughly characterized. High concentrations of glutamate reached during abnormal neurotransmission if not removed properly, become neurotoxic. Glutamate clearance is carried out by high affinity Na(+)-dependent glutamate transporter systems. The glutamate/aspartate transporter GLAST/EAAT1 plays the major role in glutamate removal and is regulated at different levels: transcription, post-translational modifications and cytoplasmic trafficking. The aim of this work was to gain insight into a plausible effect of valproate in GLAST function. Using cultured Bergmann glia cells from chick cerebellum we demonstrate here that valproate exposure elicits a dual regulatory effect on GLAST. In the short-term, valproate increases its Na(+)-dependent [(3)H]-d-aspartate uptake activity in a cytochalasin B-sensitive manner. Interestingly, a synergism between valproate and a histone deacetylase inhibitor was observed. Long-term valproate treatment up-regulates chglast promoter activity, GLAST mRNA levels, GLAST molecules at the plasma membrane and its uptake activity. Furthermore, valproate induces histone 3 lysine 14 acetylation and regulates Ying-Yang 1 (YY1) transcriptional repression on the chglast promoter. These results suggest that valproate elicits its effect through its histone deacetylase inhibitor properties.