Metabolic Signature of MELAS/Leigh Overlap Syndrome in Patient-specific Induced Pluripotent Stem Cells Model.

Background: Mitochondrial myopathy, Encephalopathy, Lactic Acidosis, Stroke-like episodes/Leigh overlap syndrome (MELAS) is caused by defects in the mitochondrial respiratory chain. It is still largely unknown how these mitochondrial respiratory chain defects affect cellular metabolisms and lead to variable clinical phenotypes. Here, we analyzed metabolic signatures in a cellular model of MELAS/ Leigh overlap syndrome using untargeted gas chromatography coupled to mass spectrometry (GC-MS). .

Methods: We obtained fibroblasts from a MELAS/Leigh overlap syndrome patient carrying the heteroplasmic m.10191T>C mutation, and generated induced pluripotent stem cells (iPSCs) from these fibroblast. Isogenic iPSC clones carrying two different loads of the heteroplasmic mutation (ND3hig-iPSC, ND3"*w- iPSC-) were subjected to metabolome analysis. Metabolite profiles, which were identified by GC-MS, were analyzed by principal component analysis (PCA).

Results: We were able to identify about 40 metabolites in control fibroblasts and iPSCs. Upon comparative metabolome analysis between fibroblasts and iPSCs, lactic acid and proline were distinct between the two groups. When we compared patient fibroblasts and control fibroblasts, no significant distinct metabolites were found. On the other hand, patient specific iPSC with high mutational load (ND3high_ iPSC) showed a distinct metabolite profile compared with ND3""-iPSC and control-iPSCs. Metabolites that contributed to this distinction were pyruvate, malic acid, palmitic acid, stearic acid, and lactic acid. This metabolomic signature was only seen in the undifferentiated state of iPSCs and was lost upon differentiation

Conclusions: These findings suggest that patient specific iPSC technology is useful to elucidate unique pathogenic metabolic pathways ,6mitochondrial chain diseases.