S-sulfocysteine/NMDA receptor–dependent signaling underlies neurodegeneration in molybdenum cofactor deficiency
Avadh Kumar, … , Guenter Schwarz, Abdel Ali Belaidi
Avadh Kumar, … , Guenter Schwarz, Abdel Ali Belaidi
Published November 6, 2017
Citation Information: J Clin Invest. 2017;127(12):4365-4378. https://doi.org/10.1172/JCI89885.
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Research Article Neuroscience

S-sulfocysteine/NMDA receptor–dependent signaling underlies neurodegeneration in molybdenum cofactor deficiency

Abstract

Molybdenum cofactor deficiency (MoCD) is an autosomal recessive inborn error of metabolism characterized by neurodegeneration and death in early childhood. The rapid and progressive neurodegeneration in MoCD presents a major clinical challenge and may relate to the poor understanding of the molecular mechanisms involved. Recently, we reported that treating patients with cyclic pyranopterin monophosphate (cPMP) is a successful therapy for a subset of infants with MoCD and prevents irreversible brain damage. Here, we studied S-sulfocysteine (SSC), a structural analog of glutamate that accumulates in the plasma and urine of patients with MoCD, and demonstrated that it acts as an N-methyl D-aspartate receptor (NMDA-R) agonist, leading to calcium influx and downstream cell signaling events and neurotoxicity. SSC treatment activated the protease calpain, and calpain-dependent degradation of the inhibitory synaptic protein gephyrin subsequently exacerbated SSC-mediated excitotoxicity and promoted loss of GABAergic synapses. Pharmacological blockade of NMDA-R, calcium influx, or calpain activity abolished SSC and glutamate neurotoxicity in primary murine neurons. Finally, the NMDA-R antagonist memantine was protective against the manifestation of symptoms in a tungstate-induced MoCD mouse model. These findings demonstrate that SSC drives excitotoxic neurodegeneration in MoCD and introduce NMDA-R antagonists as potential therapeutics for this fatal disease.

Authors

Avadh Kumar, Borislav Dejanovic, Florian Hetsch, Marcus Semtner, Debora Fusca, Sita Arjune, Jose Angel Santamaria-Araujo, Aline Winkelmann, Scott Ayton, Ashley I. Bush, Peter Kloppenburg, Jochen C. Meier, Guenter Schwarz, Abdel Ali Belaidi

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Figure 6

NMDA-R antagonist is beneficial for the treatment of MoCD in mice.

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NMDA-R antagonist is beneficial for the treatment of MoCD in mice. (A) C...
(A) Cell viability of cortical neurons with SSC (200 μM) was assessed with propidium iodide staining in the absence and presence of the NMDA-R blocker MK801 (1 μM) or memantine (10 μM) after a 12-hour incubation in culture medium (n = 15). (B) The toxic effect of low levels of SSC (1 and 10 μM) was assessed using propidium iodide staining in cortical neurons after a 5-day incubation in the absence and presence of MK801 (1 μM) or memantine (10 μM) (n = 15). (C) Recordings in the current-clamp mode revealed a dose-dependent effect of SSC on depolarization of the neuronal membrane potential. Graph represents the quantification of SSC-induced depolarization of the membrane potential. Numbers in parentheses represent the number of recorded neurons. (D and E) Efficacy of memantine treatment in the tungsten treatment study was evaluated by body weight (D) and motoric performance using rotarod testing (E) in the different mouse groups (n = 10 mice/group). (F) Immunoblot shows that memantine treatment decreased gephyrin degradation bands in control and tungsten-treated animals, while no degradation was observed with PSD95 (n = 6 mice/group). (G) Proposed sequence of events causing neurodegeneration in MoCD and SOD. Data are presented as the mean ± SEM. **P < 0.01 and ***P < 0.001, by 2-way ANOVA with Dunnett’s multiple comparisons test (A, B, D, and E), 1-way ANOVA with Tukey’s multiple comparisons test (C), or 2-tailed, unpaired Student’s t test (F).