Patient-derived iPSCs link elevated mitochondrial respiratory complex I function to osteosarcoma in Rothmund-Thomson syndrome

Author summaryRothmund-Thomson syndrome (RTS) is an autosomal recessive genetic disease characterized by an array of clinical phenotypes affecting multiple tissues. Type 2 RTS is caused by pathogenic variants in the RECQL4 gene encoding the RECQL4 DNA helicase. Type 2 RTS patients are prone to developing multiple primary osteosarcomas and have limited chemotherapy options due to organ toxicities or lifetime limits on active agents such as anthracyclines. There is currently no available RTS model that recapitulates the bone malignancy phenotype in this disease, severely limiting the ability to explore new treatment avenues which are greatly needed for these patients. To overcome this problem, we established a Type 2 RTS disease model using a human induced pluripotent stem cell platform. We then applied an unbiased approach to explore novel molecular mechanisms involved in RECQL4 mutation-induced osteosarcoma to explore therapeutic interventions. Our findings indicate that mitochondrial respiratory complex I is an "Achilles' heel" of RTS osteosarcoma and that cancers harboring RECQL4 mutations/deletions, in general, may be vulnerable to mitochondrial respiratory complex I inhibition. Rothmund-Thomson syndrome (RTS) is an autosomal recessive genetic disorder characterized by poikiloderma, small stature, skeletal anomalies, sparse brows/lashes, cataracts, and predisposition to cancer. Type 2 RTS patients with biallelic RECQL4 pathogenic variants have multiple skeletal anomalies and a significantly increased incidence of osteosarcoma. Here, we generated RTS patient-derived induced pluripotent stem cells (iPSCs) to dissect the pathological signaling leading to RTS patient-associated osteosarcoma. RTS iPSC-derived osteoblasts showed defective osteogenic differentiation and gain of in vitro tumorigenic ability. Transcriptome analysis of RTS osteoblasts validated decreased bone morphogenesis while revealing aberrantly upregulated mitochondrial respiratory complex I gene expression. RTS osteoblast metabolic assays demonstrated elevated mitochondrial respiratory complex I function, increased oxidative phosphorylation (OXPHOS), and increased ATP production. Inhibition of mitochondrial respiratory complex I activity by IACS-010759 selectively suppressed cellular respiration and cell proliferation of RTS osteoblasts. Furthermore, systems analysis of IACS-010759-induced changes in RTS osteoblasts revealed that chemical inhibition of mitochondrial respiratory complex I impaired cell proliferation, induced senescence, and decreased MAPK signaling and cell cycle associated genes, but increased H19 and ribosomal protein genes. In summary, our study suggests that mitochondrial respiratory complex I is a potential therapeutic target for RTS-associated osteosarcoma and provides future insights for clinical treatment strategies.