GSE133483
TMX2 is a key regulator of cellular redox state and its dysfunction causes severe brain developmental abnormalities
The redox state of the neural progenitors regulates physiological processes such as neuronal differentiation, dendritic and axonal growth. The relevance of ER-associated oxidoreductases in these processes is largely unexplored. We describe a severe neurological disorder caused by biallelic loss of function variants in the Thioredoxin (TRX)-Related Transmembrane-2 (TMX2) gene, detected by exome sequencing in ten affected individuals from seven unrelated families presenting with congenital microcephaly, cortical polymicrogyria and other migration disorders. TMX2 encodes one of the five TMX proteins of the Protein Disulfide Isomerase family and is the first to be linked to human brain disease. Our mechanistic studies on protein function show that TMX2 localizes to the ER Mitochondria-Associated-Membranes (MAMs), is involved in posttranslational modification and protein folding and undergoes physical interaction with the MAM associated and ER folding chaperone calnexin and ER calcium pump SERCA2. These interactions are functionally relevant because TMX2-deficient fibroblasts show decreased mitochondrial respiratory reserve capacity and compensatory increased basal glycolytic activity. Intriguingly, under basal conditions TMX2 occurs in both reduced and oxidized monomeric form, while it forms a stable dimer under treatment with hydrogen peroxide, recently recognized as signaling molecule in neural morphogenesis and axonal pathfinding. Exogenous expression of the pathogenic TMX2 variants or of variants with in vitro mutagenized TRX domain induces a constitutive TMX2 polymerization, mimicking increased oxidative state. Altogether these data uncover TMX2 as a sensor in the MAM-regulated redox state and identify it as a key adaptive regulator of neuronal proliferation, migration and organization in the developing brain. Overall design: RNAseq data of RNA isolated from cultured human fibroblasts of 2 affected individuals vs 4 age and gender matched unaffected individuals.