RT Journal Article
SR Electronic
T1 Age-Related Changes in d-Aspartate Oxidase Promoter Methylation Control Extracellular d-Aspartate Levels and Prevent Precocious Cell Death during Brain Aging
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 3064
OP 3078
DO 10.1523/JNEUROSCI.3881-15.2016
VO 36
IS 10
A1 Daniela Punzo
A1 Francesco Errico
A1 Luigia Cristino
A1 Silvia Sacchi
A1 Simona Keller
A1 Carmela Belardo
A1 Livio Luongo
A1 Tommaso Nuzzo
A1 Roberta Imperatore
A1 Ermanno Florio
A1 Vito De Novellis
A1 Ornella Affinito
A1 Sara Migliarini
A1 Giacomo Maddaloni
A1 Maria Josè Sisalli
A1 Massimo Pasqualetti
A1 Loredano Pollegioni
A1 Sabatino Maione
A1 Lorenzo Chiariotti
A1 Alessandro Usiello
YR 2016
UL http://www.jneurosci.org/content/36/10/3064.abstract
AB The endogenous NMDA receptor (NMDAR) agonist d-aspartate occurs transiently in the mammalian brain because it is abundant during embryonic and perinatal phases before drastically decreasing during adulthood. It is well established that postnatal reduction of cerebral d-aspartate levels is due to the concomitant onset of d-aspartate oxidase (DDO) activity, a flavoenzyme that selectively degrades bicarboxylic d-amino acids. In the present work, we show that d-aspartate content in the mouse brain drastically decreases after birth, whereas Ddo mRNA levels concomitantly increase. Interestingly, postnatal Ddo gene expression is paralleled by progressive demethylation within its putative promoter region. Consistent with an epigenetic control on Ddo expression, treatment with the DNA-demethylating agent, azacitidine, causes increased mRNA levels in embryonic cortical neurons. To indirectly evaluate the effect of a putative persistent Ddo gene hypermethylation in the brain, we used Ddo knock-out mice (Ddo−/−), which show constitutively suppressed Ddo expression. In these mice, we found for the first time substantially increased extracellular content of d-aspartate in the brain. In line with detrimental effects produced by NMDAR overstimulation, persistent elevation of d-aspartate levels in Ddo−/− brains is associated with appearance of dystrophic microglia, precocious caspase-3 activation, and cell death in cortical pyramidal neurons and dopaminergic neurons of the substantia nigra pars compacta. This evidence, along with the early accumulation of lipufuscin granules in Ddo−/− brains, highlights an unexpected importance of Ddo demethylation in preventing neurodegenerative processes produced by nonphysiological extracellular levels of free d-aspartate.SIGNIFICANCE STATEMENT The enzyme d-aspartate oxidase (DDO) catalyzes the degradation of the NMDA receptor agonist, d-aspartate. In the brain, DDO is expressed only during postnatal life, thus reducing the embryonic storage of d-aspartate and keeping this d-amino acid at low levels during adulthood. Although the presence of DDO in mammals is long established, its biological role in the brain and the mechanism regulating its expression are still unclear. Here, we found that Ddo promoter demethylation enables the postnatal expression of Ddo. Moreover, persistent suppression of Ddo expression leads to persistent spillover of extracellular d-aspartate and produces precocious cell death in the mouse brain, thus suggesting a key role for DDO in preventing early neurodegeneration triggered by excessive NMDA receptor stimulation.