<i>DIO2</i> Is a Regulator of Mitochondrial Function, Morphology and UPR <sup>mt</sup> in Human Cardiomyocytes

Abstract

Objectives: To elucidate the role of DIO2, member of the fetal-gene-program, in PSC-derived human cardiomyocytes and on mitochondrial dynamics and energetics, specifically. Background: Members of the fetal-gene-program may act as regulatory components to impede deleterious events that occur with cardiac remodeling and constitute potential novel therapeutic heart failure (HF) targets. Mitochondrial energy metabolic derangements occur both during early fetal development and in patients with HF. In HF, metabolic roadblocks and structural damage to mitochondria develop which deplete the heart of energy. Methods: RNA sequencing and pathway enrichment analysis was performed on mouse cardiac tissue at different time points during development, adult age and ischemia-induced HF. To determine the function of DIO2 in cardiomyocytes, a stable human pluripotent stem cell (hPSC)-line with a DIO2 short hairpin knockdown was made and used as the source for cardiomyocyte differentiation and mitochondrial dynamics were assessed. Results: We showed the selenoprotein, type II deiodinase (DIO2): the enzyme responsible for tissue-specific conversion of inactive (T4) into active thyroid hormone (T3), to be a member of fetal gene program. Silencing DIO2 resulted in increased reactive oxygen species, impaired activation of the mitochondrial unfolded protein response, severely impaired mitochondrial respiration and reduced cellular viability. Microscopical 3D reconstruction of the mitochondrial network displayed substantial mitochondrial fragmentation. Conclusion: We identified DIO2 to be a member of the fetal-gene-program and as a key regulator of mitochondrial performance in human cardiomyocytes. Our results suggest a key position of human DIO2 as a regulator of mitochondrial function in human cardiomyocytes.