170 Chapter 6 biopsies are required. In contrast, hepatobiliary organoids can also be derived from induced pluripotent stem cells (iPSCs) 20–23. The latter can be obtained from fibroblasts, lymphoblasts, or even urine cells, providing an expandable source of hepatic cells through a minimally invasive procedure24. Several protocols have been developed for differentiating iPSCs into hepatobiliary organoids. Although these organoids remain closer to fetal than to adult tissue25–27, they represent an important organ-specific system to understand not only the disease mechanism but also patient-specific phenotypes and symptomatology. Patient-specific iPSC-derived MCADD hepatobiliary organoids could serve (i) to study the effect of different mutations in the ACADM gene itself and (ii) to study compensatory mechanisms that may depend on genetic variation outside the ACADM gene. To realize this goal, it is important that organoids recapitulate the major disease phenotype. Moreover, pathways that have been hypothesized to play a compensatory role in asymptomatic patients, should be active in the organoids. Putative compensatory enzymes and pathways include short-chain acyl-CoA dehydrogenase28, peroxisomal β-oxidation29 and coenzyme A metabolism28. Whereas the MCAD enzyme is localized in the mitochondria, peroxisomes are single membrane organelles equipped with their own β-oxidation pathway. They are involved in many metabolic processes and highly abundant in liver cells. They are renowned for their ability to oxidize branched-chain and very-long-chain fatty acids30, yet they are also capable of oxidizing medium-chain fatty acids (MCFA)29 31 and fatty dicarboxylic acids32. To the best of our knowledge, there are currently no experimental studies reporting on the role of peroxisomes in any of the deficiencies of mitochondrial dehydrogenases (SCADD, MCADD and VLCADD). The goal of this study was to establish and characterize an iPSC-derived hepatobiliary organoid system for the study of MCADD. iPSCs derived from fibroblasts of symptomatic MCADD patients with the classical c.985A>G (p.K329E) mutation were differentiated into hepatic organoids and compared to organoids from healthy controls. Here we demonstrate that MCADD organoids recapitulate typical diagnostic MCADD markers. Moreover, mature organoids upregulate peroxisomal markers, making them a suitable system to study patient-specific differences in peroxisomal metabolism. Finally, we report a minor regulation of peroxisomal CoA metabolism, already in these organoids of symptomatic MCADD patients.
RkJQdWJsaXNoZXIy MTk4NDMw