Abstract 13259: IRX5 Transcription Factor Cooperate With TBX5/GATA4/NKX2-5 Complex to Regulate Several Human Cardiomyocyte Functions

• Published in: Circulation (New York, N.Y.) N.Y.), 2021-11, Vol.144 (Suppl_1), p.A13259-A13259
• Main Authors: Canac, Robin, Cimarosti, Bastien, Girardeau, Aurore, Forest, Virginie, Fourgeux, Cynthia, Poschmann, Jeremie, Lamirault, Guillaume, Lemarchand, Patricia, Gaborit, Nathalie
• Format: Article
• Language: English
• ISSN: 0009-7322; 1524-4539
• DOI: 10.1161/circ.144.suppl_1.13259

IntroductionThe transcription factor (TF) Iroquois homeobox 5 (Irx5) is a key patterning and differentiation regulator. In humans, IRX5 regulates the expression of the main cardiac sodium ion channel gene, SCN5A. However, its global mechanistic role in human cardiomyocytes is still to be fully understood. Hamamy syndrome patients, carrying IRX5 mutations, have defects in various organs including the heart and the limbs. Interestingly, heart and limbs defects are also found in Holt-Oram syndrome patients (TBX5 mutations), suggesting a functional link between TBX5 and IRX5. Moreover, a cooperation of TBX5 with GATA4 and NKX2-5 in cardiac development and functions has already been shown. HypothesisWe hypothesized that IRX5 may cooperate with the TF complex TBX5/GATA4/NKX2-5 to regulate key cardiac functions in humans. Methods & ResultsFirst, immunoprecipitations in HEK293 cells showed that IRX5 can bind to TBX5, GATA4 and NKX2-5, individually and together as a complex. Using five truncated forms of IRX5 protein, its homeodomain was identified as being the essential protein region for these interactions. Second, we showed by luciferase assays, that each combination of these TFs impacted differently SCN5A expressione.g. by itself, NKX2-5 has a strong activator effect (increased activity by 10 fold vs. no TF) that is potentialized by IRX5 (12 fold vs. no TF) but inhibited by TBX5 (8 fold vs. no TF). Third, genes bound by IRX5 (n=2253) were identified by ChIP-Seq on cardiomyocytes derived from induced pluripotent stem cells generated from 2 healthy individuals. Analyzing published ChIP-Seq datasets for TBX5, GATA4 or NKX2-5 in the same cellular model, we identified 2990 genes that were bound by these 3 TFs, and associated with cardiac biological pathways, such as muscle contraction. Among these genes, 848 were also bound by IRX5 and were associated with the function of electrical activity and with the fibrosis signaling, suggesting a specific role for IRX5 in these cardiac processes. ConclusionsOverall, our data show new physical and functional interactions between IRX5 and 3 key cardiac TFs (TBX5, GATA4 and NKX2-5), and suggest an unexpected regulatory role for IRX5 in specific human heart functions.