Alexander disease astrocytes uncouple the glycerol-3-phosphate shuttle to keep cytosolic NAD+ when the electron transport chain fails

van Gelder, Hol, Burgering and colleagues separate GFAP dose from the Alexander disease mutation R239C with single-cell proteomics. High wild-type GFAP starts to look like R239C, so accumulation matters, but the mutant specifically raises mitochondrial antioxidant enzymes and retunes the proteasome toward ATP- and ubiquitin-independent disposal of oxidized proteins. Patient cortical organoids add nuclear-encoded mitochondrial proteins and respiratory assembly factors without a matching rise in mitochondrially encoded subunits, which they read as impaired electron transport chain assembly. AxD cells then drop oxygen consumption, raise glycolysis, lean on the cytosolic arm of the glycerol-3-phosphate shuttle, and store triacylglycerides. The named couple is NAD+/NADH: partial G3P-shuttle uncoupling regenerates cytosolic NAD+ so glycolysis can run without sending those reducing equivalents fully into the Q pool. The abstract does not name GPD2, FAD, or which respiratory complex fails assembly.

Verdict. Alexander disease astrocytes look like an ETC-assembly problem with a G3P-shuttle workaround: keep cytosolic NAD+ high, keep glycolysis on, park carbon in droplets. R239C is not only too much GFAP.

Metal sites and redox

Named couple: NAD+/NADH, regenerated in the cytosol by a partially uncoupled glycerol-3-phosphate shuttle. The mitochondrial arm of that shuttle, in standard biochemistry, is GPD2 using FAD to reduce the ubiquinone pool (Q/QH2). This abstract does not name GPD2, FAD, ubiquinone, or a respiratory Fe-S or heme site. ETC dysfunction is inferred from more nuclear-encoded assembly factors without more mtDNA-encoded subunits, plus lower oxygen consumption. Do not invent which complex or which cluster is missing. Mitochondrial antioxidant enzymes rise on the mutant; the species (MnSOD, peroxiredoxins, glutathione enzymes) are not listed.

What the authors report

Single-cell proteomes across GFAP levels split dosage from R239C. Overexpressed wild-type GFAP drifts toward the mutant proteome, so pile-up is pathogenic, but only the mutant brings the mitochondrial antioxidant and oxidized-protein proteasome program. Organoid proteomics look like an ETC that cannot finish assembly. Functionally: less oxygen use, more glycolysis, more cytosolic G3P-shuttle use, more fat. Their model: if the chain cannot take electrons, uncouple the shuttle enough to make NAD+ for glycolysis and send G3P to lipid, maybe still making lactate for neurons.

What was measured

Single-cell proteomics, organoid proteomics, OCR, glycolysis, G3P-shuttle utilization, triacylglycerides, lipid droplets.

Caveats

No named complex on a gel. Shuttle uncoupling is a proposal. Neuron lactate supply is not shown. Cell systems versus leukodystrophy white matter.

What to do with it

Put AxD on the ETC-assembly and cytosolic-NAD+ map. The discriminating experiment is BN-PAGE of supercomplexes plus a GPD1/GPD2 flux measurement, not another GFAP stain.

Bibliographic record

Field	Value
Title	Single Cell Proteomics reveals partial uncoupling of the Glycerol-3-Phosphate shuttle to compensate for Electron Transport Chain dysfunction in Alexander Disease GFAP mutations
DOI	10.64898/2026.10.05.756178
Server	biorxiv
Posted	2026-10-12
Topics	ETC assembly, G3P shuttle, NAD+, astrocytes, Alexander disease, lipid droplets
Mitos score	83/100
Confidence	medium
HTML	https://www.biorxiv.org/content/10.64898/2026.10.05.756178
PDF	https://www.biorxiv.org/content/10.64898/2026.10.05.756178.full.pdf

Abstract-based editorial synthesis by Mitos. Not peer review.

Source preprint

Single Cell Proteomics reveals partial uncoupling of the Glycerol-3-Phosphate shuttle to compensate for Electron Transport Chain dysfunction in Alexander Disease GFAP mutations

10.64898/2026.10.05.756178

van Gelder CA, Daoutsali E, Attour Y, El Baghdadi S, Sobrevals Alcaraz P, van Es RM, Gulersonmez C, Stigter EC, Vos HR, Hol EM, Burgering BM.