Transgenic Expression Of Nrf2 Induces A Pro-reductive Stress And Adaptive Cardiac Remodeling In Mice

Background: NFE2L2, nuclear factor, erythroid 2 like 2 (Nrf2), is a transcription factor that protects cells through maintaining a homeostatic redox state during stress. Constitutive expression of Nrf2 (CaNrf2-TG) was previously shown to be pathological to the heart over time. We tested a hypothesis that the cardiac-specific expression of full length Nrf2 (mNrf2-TG) would moderately increase the basal antioxidant defense, triggering a pro-reductive environment leading to adaptive cardiac remodeling. Methods: Cardiac-specific full-length Nrf2 transgenic (mNrf2-TG) and non-transgenic (NTG) mice hearts on the C57/BL6 background at 7-8 months of age were used to analyze the transcriptome and cardiac structure/function. Next generation sequencing (NGS) for RNA profiling (n=3/group) and qPCR-based validation (n=5/group) of the NGS data were accomplished. Myocardial redox levels and imaging (echocardiography) were performed. Results: Transcriptomic analysis revealed that out of 14665 identified mRNAs, 679 were differently expressed (DEG) in TG hearts. Of 679 DEGs, 429 were upregulated and 251 were downregulated significantly (FC>2, P<0.05). Gene Set Enrichment Analysis revealed that the top altered pathways were (a) Nrf2 signaling, (b) glutathione metabolism and (c) ROS scavenging. A comparative analysis of glutathione redox state in the hearts demonstrated significant differences between pro-reductive vs. hyper-reductive conditions (233 ± 36.7 and 380 ± 68.7 vs. 139 ± 8.6 μM/mg protein in mNrf2-TG and CaNrf2-TG vs NTG). Expression of fetal genes and hypertrophic biomarkers, cytoskeletal genes, histone deacetylases (HDACs), and GATA transcription factors were moderately increased in mNrf2-TG compared to CaNrf2-TG hearts. Non-invasive echocardiography analysis revealed an increase in systolic function (Ejection Fraction) in mNrf2-TG, suggesting an adaption, as opposed to pathological remodeling in CaNrf2-TG mice experiencing a hyper-reductive stress, leading to reduced survival (40% at 60 weeks). Conclusion: The effects of excess Nrf2-driven antioxidant transcriptome revealed a pro-reductive condition in the myocardium leading to an adaptive cardiac remodeling. While pre-conditioning the myocardial redox with excess antioxidants (i.e. pro-reductive state) could be beneficial against oxidative stress, a chronic pro-reductive environment in the myocardium might transition the adaptation to pathological remodeling.