Cuproptosis in iron overload hepatocytes.

A long-standing clinical conundrum is the pronounced phenotypic heterogeneity of hereditary hemochromatosis. Patients with identical HFE genotypes and similar degrees of iron overload can have vastly different clinical outcomes, ranging from being completely asymptomatic to developing severe cirrhosis, diabetes, or cardiomyopathy. This variability strongly implies the existence of genetic or environmental modifiers that dictate disease penetrance. Here, copper may be a compelling disease-modifying candidate, due to its intimately intertwined metabolism with iron. Indeed, profound iron loading in hemochromatosis mice (Hfe knockout) and hemochromatosis Huh7 hepatocytes does not cause overt toxicity. However, the addition of copper, even in trace amounts and harmless on its own, dramatically amplifies adverse effects to induce profound cell toxicity. We find that copper-provoked iron vulnerability is not driven by Fenton chemistry-driven ROS damage, but instead induces a cuproptotic-like mechanism, characterized by proteotoxic stress, loss of iron-sulfur cluster enzyme activity, and severe mitochondrial dysfunction. Remarkably, high-affinity copper chelation rescued Huh7 cells, whereas inhibition of other canonical cell death pathways did not. These findings spotlight copper as a critical modifier in iron overload toxicity, capable of converting largely compensated iron overload into severe cellular injury and death, thereby providing a mechanistic explanation for the phenotypic heterogeneity in hemochromatosis.