Myocardial infarction (MI) and subsequent ischemia-reperfusion injury trigger a devastating cascade of oxidative stress and cardiomyocyte death, largely driven by mitochondrial dysfunction and excessive reactive oxygen species (ROS) production. While the nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant pathway has been extensively studied in cardioprotection, the role of its homolog, Nrf3, remains less clear. Emerging evidence now positions Nrf3 not as a protective factor but as a novel pathogenic driver in post-MI cardiac injury. A pivotal study published in Circulation(Chen et al., 2025) revealed that Nrf3 is significantly upregulated in infarcted human and mouse hearts, where it promotes mitochondrial superoxide generation, exacerbates apoptosis, and impairs cardiac function by epigenetically suppressing the transcription factor Pitx2. This finding challenges the traditional view of the Nrf family as uniformly protective and identifies the Nrf3-Pitx2 axis as a promising therapeutic target for mitigating infarct size and adverse remodeling.
The pathophysiological mechanism centers on a finely tuned but maladaptive stress response. Following ischemic insult, Nrf3 expression is induced, likely as part of the unfolded protein response emanating from the endoplasmic reticulum. Contrary to initial expectations, this upregulation proves detrimental. Nrf3 translocates to the nucleus and recruits a complex comprising heterogeneous nuclear ribonucleoprotein K (hnRNPK) and DNA methyltransferase 1 (DNMT1) to the promoter region of the Pitx2gene. This recruitment facilitates local DNA hypermethylation, effectively silencing Pitx2 transcription. The loss of Pitx2 is critical, as Pitx2 is a key regulator of mitochondrial redox homeostasis and antioxidant gene expression. Consequently, Pitx2 suppression leads to a surge in mitochondrial superoxide (O2•−), creating a state of severe oxidative stress that triggers intrinsic apoptotic pathways in cardiomyocytes. This Nrf3-hnRNPK-DNMT1-Pitx2-mtROS pathway represents a previously unrecognized epigenetic-metabolic circuit that amplifies injury during both the initial ischemic phase and the subsequent reperfusion phase.
Functional validation of this axis comes from robust genetic models. In Nrf3-knockout mice subjected to MI or ischemia-reperfusion (I/R) injury, researchers observed a markedly improved phenotype: reduced infarct size, lower acute mortality, diminished mitochondrial ROS production, and attenuated long-term pathological remodeling (including fibrosis and dilation) compared to wild-type controls. Crucially, the cardioprotective effects of Nrf3 ablation were abolished when Pitx2 was concomitantly knocked down in cardiomyocytes, confirming that Pitx2 is the essential downstream effector mediating Nrf3's detrimental actions. Conversely, cardiac-specific overexpression of Nrf3 worsened functional outcomes and increased apoptosis, phenotypes that could be rescued by Pitx2 restoration. These findings were further corroborated in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), where Nrf3 knockdown mitigated oxidative stress-induced cell death, underscoring the translational relevance of this pathway across species.
The clinical implications are substantial. Analysis of human heart tissue from MI patients shows a clear correlation between elevated Nrf3 levels in the infarct border zone and poor cardiac function. This positions Nrf3 as both a potential biomarker for risk stratification and a druggable target. Pharmacological strategies aimed at inhibiting Nrf3 activity or disrupting its interaction with the hnRNPK/DNMT1 complex could, in theory, prevent Pitx2 silencing and preserve mitochondrial integrity. Alternatively, gene therapy approaches to enhance Pitx2 expression in the infarcted heart might bypass the Nrf3 blockade and directly boost antioxidant defenses. Such interventions would complement existing reperfusion therapies by targeting the molecular basis of reperfusion injury—uncontrolled oxidative stress—rather than just restoring blood flow.
This discovery also refines our understanding of redox biology in the heart. It demonstrates a stark functional divergence between Nrf2 and Nrf3; while Nrf2 activation is broadly cytoprotective, Nrf3 activation under ischemic conditions becomes paradoxically harmful. This highlights the context-dependent nature of redox signaling and cautions against broad-spectrum antioxidant approaches that do not discriminate between specific ROS sources and transcriptional regulators. Future research should focus on developing small-molecule inhibitors of Nrf3 and testing their efficacy in large-animal models of MI, with the ultimate goal of translating this mechanistic insight into a novel adjuvant therapy to protect the myocardium and prevent the progression to heart failure.
DOI:10.1007/s11684-025-1194-7