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.

The therapeutic landscape for the treatment of cancer has evolved significantly in recent decades, aided by the development of effective oncology drugs. However, many cancer drugs are often poorly tolerated by the body and in particular the cardiovascular system, causing adverse and sometimes fatal side effects that negate the chemotherapeutic benefits. The prevalence and severity of chemotherapy-induced cardiotoxicity warrants a deeper investigation of the mechanisms and implicating factors in this phenomenon, and a consolidation of scientific efforts to develop mitigating strategies. Aiding these efforts is the emergence of induced pluripotent stem cells (iPSCs) in recent years, which has allowed for the generation of iPSC-derived cardiomyocytes (iPSC-CMs): a human-based, patient-derived, and genetically variable platform that can be applied to the study of chemotherapy-induced cardiotoxicity and beyond. After surveying chemotherapy-induced cardiotoxicity and the associated chemotherapeutic agents, we discuss the use of iPSC-CMs in cardiotoxicity modeling, drug screening, and other potential applications. Improvements to the iPSC-CM platform, such as the development of more adult-like cardiomyocytes and ongoing advances in biotechnology, will only enhance the utility of iPSC-CMs in both basic science and clinical applications.

The objective of this paper is to modify the topology of the unidirectional non-coupled inductor modified SEPIC converter to a bidirectional topology and applied between the DC bus and the battery energy storage system. To improve the conversion ratio, active switched inductors are employed, eliminating the need for a coupled inductor or transformer. This approach offers several advantages, including continuous input current non-inverting input and output. Furthermore, by increasing the switching frequency and utilizing wide bandgap components such as gallium nitride (GaN) instead of Si-based MOSFETs, the converter's volume can be reduced while achieving high efficiency and excellent high-frequency characteristics. The paper will provide an analysis of the operational principles and present experimental results with the following specifications: low side voltage of 48V, high side voltage of 400V, switching frequency of 500kHz, and output power of 500W. The step-down mode achieves a peak efficiency of 93.7%, while the step-up mode reaches a peak efficiency of 90.9%.

Identifying biomolecules that shape nuclear organization is essential for understanding gene regulation in health and disease. Oncogenic fusion proteins rewire chromosome folding and generate biomolecular condensates, but the cofactors of oncoprotein-driven chromatin regulation remain poorly defined, and whether such factors have analogous functions in fusion-naïve cells is unknown. We find that NSD3 mediates chromosome folding in fusion-positive and fusion-negative cells. NSD3 stabilizes the BRD4-NUT fusion oncoprotein on chromatin, promotes histone H3K36me2, and supports oncogene expression while maintaining BRD4-NUT nuclear condensates. NSD3 loss attenuates distant chromatin interactions between BRD4-NUT megadomains both within and between chromosomes. In cells lacking BRD4-NUT, the short, catalytically inactive isoform of NSD3, NSD3short, promotes chromatin contacts separated by multiple megabases. The ability of NSD3short to promote long-range chromatin contacts requires its PWWP domain. By combining chromatin structural analyses in fusion-positive and fusion-negative cells, we show that interrogating fusion oncoprotein-driven chromosome misfolding reveals the multicomponent basis of nuclear compartmentalization and uncovers an adaptor protein that promotes chromatin contacts independent of enzymatic activity.

Background: Rothmund-Thomson syndrome (RTS) is an autosomal recessive genetic disorder characterized by a rash that progresses to poikiloderma; small stature; skeletal anomalies; sparse hair, eyelashes, and/or eyebrows, juvenile cataracts, and an increased risk to cancer. Type 2 RTS patients with biallelic RECQL4 pathogenic variants have a significantly increased incidence of osteosarcoma. However, there is currently no available RTS model that recapitulates the bone malignancy phenotype in this disease, severely limiting the ability of researchers to explore new treatment avenues. Here, we generated RTS patient-derived induced pluripotent stem cells (iPSCs) to dissect the pathological signaling leading to RTS patient-associated osteosarcoma. Methods: iPSCs were reprogrammed from fibroblasts of four individuals from two RTS families, each with one affected RTS proband with RECQL4 mutations and one unaffected parent. These patient iPSCs were differentiated to mesenchymal stem cells (MSCs) and then to osteoblasts, the cell-of-origin of osteosarcoma. All of these MSCs and osteoblasts were subjected to transcriptome analysis by RNA-seq. Based on enriched mitochondrial respiratory gene signatures, we also systematically analyzed the enzymatic activities of the major mitochondrial respiratory protein complexes including complex I/II/III and citrate synthase enzyme activity in RTS osteoblasts by Seahorse assay. Finally, we tested the potential therapeutic effect of clinical oxidative phosphorylation complex I inhibitor IACS-010759 to treat RTS cells and dissect the pharmacological mechanisms involved. Results: RTS iPSC-derived osteoblasts showed defective osteogenic differentiation and a gain of in vitro tumorigenic ability. Transcriptome analysis of RTS osteoblasts revealed decreased bone morphogenesis gene expression but aberrantly upregulated mitochondrial complex I gene expression. Metabolic assays of RTS osteoblasts demonstrated elevated mitochondrial respiratory complex I function, increased oxidative phosphorylation, but decreased ATP production. Inhibition of mitochondrial respiratory complex I activity by IACS-010759 selectively suppressed cellular respiration and cell viability of RTS osteoblasts. Furthermore, systems analysis of IACS-010759-induced changes to RTS osteoblasts suggested that inhibition of mitochondrial complex I in RTS osteoblasts leads to enhanced cell senescence, decreased MAPK signaling and cell cycle associated genes. Conclusion: In summary, we established an RTS iPSC disease platform to dissect the pathological mechanisms involved in RTS-associated osteosarcoma. Our data suggested that mitochondrial complex I is a potential therapeutic target for RTS-associated osteosarcoma and provides future insights for clinical treatment strategies. Citation Format: An Xu, Brittany E. Jewell, Dandan Zhu, Mo-Fan Huang, Yi-Hung Chen, Linchao Lu, Ruiying Zhao, Lisa L. Wang, Dung-Fang Lee. Patient-derived iPSCs reveal pharmacologic targeting mitochondrial respiratory complex I for treating Rothmund-Thomson syndrome associated osteosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3779.