d -Amino acid oxidase controls motoneuron degeneration through d -serine

Abstract

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder involving an extensive loss of motoneurons. Aberrant excitability of motoneurons has been implicated in the pathogenesis of selective motoneuronal death in ALS. D-Serine, an endogenous coagonist of N-methyl-D-aspartate receptors, exacerbates motoneuronal death and is increased both in patients with sporadic/ familial ALS and in a G93A-SOD1 mouse model of ALS (mSOD1 mouse). More recently, a unique mutation in the D-amino acid oxidase (DAO) gene, encoding a D-serine degrading enzyme, was reported to be associated with classical familial ALS. However, whether DAO affects the motoneuronal phenotype and D-serine increase in ALS remains uncertain. Here, we show that genetic inactivation of DAO in mice reduces the number and size of lower motoneurons with axonal degeneration, and that suppressed DAO activity in reactive astrocytes in the reticulospinal tract, one of the major inputs to the lower motoneurons, predominantly contributes to the D-serine increase in the mSOD1 mouse. The DAO inactivity resulted from expressional down-regulation, which was reversed by inhibitors of a glutamate receptor and MEK, but not by those of inflammatory stimuli. Our findings provide evidence that DAO has a pivotal role in motoneuron degeneration through D-serine regulation and that inactivity of DAO is a common feature between the mSOD1 ALS mouse model and the mutant DAO-associated familial ALS. The therapeutic benefit of reducing D-serine or controlling DAO activity in ALS should be tested in future studies.excitotoxicity | motor neuron disease | neurodegeneration | enzyme histochemistry | 2D-HPLC A myotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder characterized by selective loss of motoneurons in the spinal cord and brain leading to fatal paralysis. Approximately 90% of all cases are sporadic, and the remaining cases are inherited. Of inherited cases, 20% are associated with mutations in superoxide dismutase 1 (SOD1), and 10% involves 43-kDa transactivation response DNA-binding protein (TDP-43) and fused in sarcoma/translocated in liposarcoma (FUS/TLS). Despite extensive studies of previously identified ALS-causing genes, the mechanism underlying the selective motoneuronal loss in ALS remains uncertain. Given that the mechanism is at least, in part, common between sporadic and familial ALS, identification of the common pathology is a clue to conquering ALS. Among numerous etiological hypotheses, motoneuronal vulnerability to excitotoxicity is one of the most intensely investigated targets for the treatment of ALS because it is observed in both sporadic and familial ALS with SOD1 mutations (1, 2). For motoneurons, glutamate is the main excitatory transmitter, and excessive motoneuron excitability by glutamate through ionotropic glutamate receptors has been demonstrated.The N-methyl-D-aspartate (NMDA) receptor (NMDAR) is a subtype of the ionotropic glutamate receptors and exhibits relatively higher permeability to the calcium ion (Ca ...

Characterization of the Enzymatic and Structural Properties of Human D-Aspartate Oxidase and Comparison with Those of the Rat and Mouse Enzymes

“…Total RNA was extracted from the cells using the RNeasy Mini Kit (Qiagen, Hilden, Germany), according to the manufacturer's instructions. For first-strand cDNA synthesis, the RNA samples (5 µg) were reverse-transcribed in a 20 µL reaction mixture containing 200 units of SuperScript III Reverse Transcriptase and 0.5 µg of oligo(dT) [12][13][14][15][16][17][18] primer (Invitrogen, Carlsbad, CA, U.S.A.). After incubation at 50°C for 1 h, 1 µL (2 units) of RNaseH (Invitrogen) was added and the mixture was incubated at 37°C for 20 min.…”

“…Indeed, perturbation of D-Ser levels in the nervous system has recently been implicated in the pathophysiology of various neuropsychiatric disorders, including schizophrenia, [5][6][7][8] Alzheimer's disease, 9,10) and amyotrophic lateral sclerosis. 11,12) Unlike the tissue-specific expression of D-Ser, substantial amounts of free D-Asp are present in a wide variety of mammalian tissues and cells, particularly those of the central nervous, neuroendocrine, and endocrine systems. Several lines of evidence suggest that D-Asp plays an important role in regulating developmental processes, hormone secretion, and steroidogenesis.…”

D-Serine in Neuropsychiatric Disorders: New Advances

“…This neurodegenerative disease targets motor neurons in the spinal cord, brain stem, and cerebral cortex, leading to death within a few years of onset [180,181]. In ALS, DSR may mediate motoneuron cell death caused by excessive NMDAR stimulation [182]. A missense mutation that inactivates DAAO results in increased DSR in the spinal cord of patients and causes a familial form of ALS.…”

Sleep-Awake Profile Related Circadian D-Alanine Rhythm in Human Serum and Urine

“…Relationships between the amounts of free D-amino acids and various diseases have also been clarified [17][18][19][20]. Concerning the protein-bound type D-enantiomers, D-amino acid residues are frequently observed in the "aged" proteins, and the correlation between D-amino acids and aging is a matter of high interest [21][22][23].…”