Transcriptional deregulation and changes in mitochondrial bioenergetics, including pyruvate dehydrogenase (PDH) dysfunction, have been described in Huntington's disease (HD). We previously showed that histone deacetylase inhibitors (HDACi), trichostatin A and sodium butyrate (SB), ameliorate mitochondrial function in cells expressing mutant huntingtin. In this work we investigated the effect of HDACi on regulation of PDH activity in striatal cells derived from HD knock-in mice and YAC128 mice. Mutant cells exhibited decreased PDH activity and increased PDH E1alpha phosphorylation/inactivation, accompanied by enhanced protein levels of PDH kinases (PDK)1/3. Exposure to dichloroacetate, an inhibitor of PDKs, increased mitochondrial respiration and decreased production of reactive oxygen species in mutant cells, emphasizing PDH as an interesting therapeutic target in HD. Treatment with SB and sodium phenylbutyrate, another HDACi, recovered cell viability and overall mitochondrial metabolism in mutant cells. Exposure to SB also suppressed hypoxia-inducible factor-1 (HIF-1α) stabilization, and decreased the transcription of the two most abundant PDK isoforms, PDK2 and PDK3, culminating in increased PDH activation in mutant cells. Concordantly, PDK3 knockdown improved mitochondrial function, emphasizing the role of PDK3 inactivation on the positive effects achieved by SB treatment. YAC128 mouse brain presented higher mRNA levels of PDK1-3 and PDH phosphorylation, as well as decreased energy levels, which were significantly ameliorated following SB treatment. Furthermore, enhanced motor learning and coordination was observed in SB-treated YAC128 mice. These results suggest that HDACi, particularly SB, promote the activity of PDH in HD brain, helping to counteract HD-related deficits in mitochondrial bioenergetics and motor function.
The present work provides a better understanding of mitochondrial dysfunction in HD by evidencing the PDH complex as a promising therapeutic target. In particular, the HDACi SB may indirectly (through reduced HIF1α stabilization) decrease the expression of the most abundant PDK isoforms (e.g. PDK3), ameliorating PDH activity, mitochondrial metabolism and further impacting on motor behavior in HD mice, thus constituting a promising agent for HD neuroprotective treatment.
The authors declare no competing financial interests or other conflicts of interest.
Funding: This work was supported by projects PTDC/SAU-FCF/108056/2008, EXPL/BIM-MEC/2220/2013, PEst-C/SAU/LA0001/2013-2014 and UID/NEU/04539/2013 funded by ‘Fundação para a Ciência e a Tecnologia’ (FCT), Portugal, and co-financed by: “COMPETE- Programa Operacional Factores de Competitividade”, QREN and European Union (FEDER- Fundo Europeu de Desenvolvimento Regional), and by ‘Santa Casa da Misericórdia de Lisboa’ (SCML) — Mantero Belard Neuroscience Prize, 1st edition. T.C.-O. and T.R.R. were supported by the FCT postdoctoral fellowships SFRH/BPD/34711/2007 and SFRH/BPD/44246/2008, respectively; M.R. and L.N. were supported by the PhD fellowships SFRH/BD/41285/2007 and SFRH/BD/86655/2012, respectively, co-financed by POPH- Programa Operacional Potencial Humano, QREN and European Union.