Nrf2 Plays a Key Role in Iron-Overload Cardiomyopathy

Cardiomyopathy due to iron-overload is a severe complication of patients undergoing chronic transfusion regimen such as β-thalassemia and myelodysplastic syndromes. Previous studies have shown the key role of Nrf2, a redox-related transcriptional factor, in both β-thalassemia erythropoiesis and iron homeostasis (Matte A et al. ARS 2018, 2019; Lim PJ et al Nat Metab, 2019). Here, we compared Nrf2 knockout male mice (Nrf2 -/-) and C57BL-6J as wild-type (WT) controls, with a focus on cardiac function. Nrf2 -/- mice were characterized by a mild chronic hemolytic anemia associated with ineffective erythropoiesis, similar to what observed in murineβ-thalassemia (Toya SCM et al., Blood, 2019). Aging Nrf2 -/- mice developed systolic and diastolic dysfunction, associated with increased cardiac oxidative stress, degradation of the calcium-dependent SERCA2A transporter and activation of metalloproteinase MMP9, involved in both SERCA2A degradation and heart remodeling. In Nrf2 -/- mice, we observed increased plasma NTBI, heart iron deposition and elevated expression of cardiac ferroportin when compared to WT animals. Moreover, cardiac Hamp mRNA levels were down-regulated in aging Nrf2 -/- mice when compared to WT mice. This pattern was consistent with progressive cardiac iron overload in absence of Nrf2. Interestingly, activation of TGF-b receptor and PDGF-B-related pathway as well as increased collagen deposition were observed in hearts from 12 months old Nrf2 -/- mice. Taken together our data suggest an aging-associated development of iron-overload cardiomyopathy in mice genetically lacking Nrf2. To evaluate the role of Nrf2 in iron overload cardiomyopathy, Nrf2 -/- and WT mice were exposed to dietary iron supplementation (2.5% w/w carbonyl iron for 28 days). Nrf2 -/- mice developed cardiac hypertrophy which was accompanied by a worsening in collagen deposition and persistent activation of PDGF-B pathway. This was associated with inflammatory vasculopathy. The biologic importance of Nrf2 is supported by the cardiac activation of Nrf2, degradation of SERC2A and activation of TGF-b receptor and PDGF-B pathway in a mouse model of beta thalassemia intermedia, the Hbb3th/+ mice. Collectively our data support the crucial role of Nrf2 in the protection of cardiomyocytes against iron cytotoxicity which significantly develops in aging as well as in β-thalassemia.