The succinate dehydrogenase (SDH) enzyme complex consisting of four subunits (SDHA, SDHB, SDHC and SDHD) has a dual function in the process of mitochondrial energy generation. It converts succinate to fumarate as part of the TCA cycle and also transfers electrons to ubiquinone as part of the electron transport chain. Mutation in any subunit of the enzyme complex increases the risk for the development of neuroendocrine tumors including paraganglioma (PGL) and pheochromocytoma (PHEO). As the SDH enzyme complex is closely linked to the supply of precursors and the regulation of metabolic processes, the study of the molecular background of SDH deficiency in relation to carcinogenesis, cancer survival and metastasis, must be supplemented by characterizing metabolism, which could open new ways to develop more effective therapeutic methods. While human SDHA, SDHC and SDHD mutations mainly cause benign tumors, those in SDHB are strongly associated with malignant PHEO/PGL. The Arg230His missense mutation in the human SDHB gene causes a familial form of malignant PHEO, representing a serious therapeutical challenge. Therefore we aimed to develop an in vivo model for functional characterization of this mutation using a highly conserved C. elegans ortholog. The human Arg230His mutation corresponds to the Arg244His SDHB-1 mutation in the worm. For our experiments, we used the sdhb-1(gk165) deletional derivative and two transgenic lines carrying the Arg244His mutation and genomic wild-type SDHB-1, which were crossed in sdhb-1(gk165) null mutant background. We found that the Arg244His mutation of the SDHB-1 enzyme significantly delays development, shortens lifespan and changes the metabolic profile of the animals. Characterization of the latter was performed as follows: TCA cycle metabolites were detected by LC-MS, whereas oxygen consumption was measured by Seahorse technique. Interestingly in both the deletional and Arg244His point mutants, succinate level was elevated, suggesting that neither mutant possesses SDH activity. These data are in line with our bioinformatic analysis which suggests that the Arg244His substitution exerts a significant effect on the structure of SDHB-1 and might result in an inactive complex. Interestingly, the metabolic profile of Arg244His mutants was also strongly altered compared to the null mutant, which raises the prospect of a rewired metabolism reminiscent of tumor cells undergoing metabolic reprogramming. Transcriptomic profiles of deletional and point mutants compared to wild-type worms further confirmed these biochemical alterations. Our new model mimics the SDH impairment and it may serve a novel tool in deciphering new insight of SDH-associated human diseases.
18 - 21 May 2019
European Society of Endocrinology