Exclusive neuronal expression of SUCLA2 in the human brain
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SUCLA2 encodes the ATP-forming β subunit (A-SUCL-β) of succinyl-CoA ligase, an enzyme of the citric acid cycle. Mutations in SUCLA2 lead to a mitochondrial disorder manifesting as encephalomyopathy with dystonia, deafness and lesions in the basal ganglia. Despite the distinct brain pathology associated with SUCLA2 mutations, the precise localization of SUCLA2 protein has never been investigated. Here, we show that immunoreactivity of A-SUCL-β in surgical human cortical tissue samples was present exclusively in neurons, identified by their morphology and visualized by double labeling with a fluorescent Nissl dye. A-SUCL-β immunoreactivity co-localized >99 % with that of the d subunit of the mitochondrial F0–F1 ATP synthase. Specificity of the anti-A-SUCL-β antiserum was verified by the absence of labeling in fibroblasts from a patient with a complete deletion of SUCLA2. A-SUCL-β immunoreactivity was absent in glial cells, identified by antibodies directed against the glial markers GFAP and S100. Furthermore, in situ hybridization histochemistry demonstrated that SUCLA2 mRNA was present in Nissl-labeled neurons but not glial cells labeled with S100. Immunoreactivity of the GTP-forming β subunit (G-SUCL-β) encoded by SUCLG2, or in situ hybridization histochemistry for SUCLG2 mRNA could not be demonstrated in either neurons or astrocytes. Western blotting of post mortem brain samples revealed minor G-SUCL-β immunoreactivity that was, however, not upregulated in samples obtained from diabetic versus non-diabetic patients, as has been described for murine brain. Our work establishes that SUCLA2 is expressed exclusively in neurons in the human cerebral cortex.
KeywordsSuccinate thiokinase Succinyl coenzyme A synthetase Substrate-level phosphorylation mtDNA Neuronal mitochondrial marker
Thanks are expressed to Katalin Zölde for excellent technical assistance.This work was supported by the Országos Tudományos Kutatási Alapprogram (OTKA) grants NNF2 85612, K 100319 to A.D., the Danish National Health Research Council grant 12-127702 to E.O., OTKA 81983 and the Hungarian Academy of Sciences grant 02001 to V. A.-V, TÁMOP 4.2.1./B-09/1/KMR and BIOINF09TÉT_10-1-2011-0058 to MJM, OTKA grants NNF 78905, NNF2 85658, K 100918, and the MTA-SE Lendület Neurobiochemistry Research Division grant 95003 to C.C.
Conflict of interest
The authors declare no conflict of interests.
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