Copper and Iron Take Separate Roads to Keep Starving Cells Alive

Two of the most abundant trace metals in biology, copper and iron, have long been viewed as a tightly interlocked pair whose availability rises and falls together. A new study in GeroScience shows that despite this biochemical coupling, the two metals drive cellular survival through strikingly different signaling programs, a finding with implications that stretch from aging research to cancer therapy. Using budding yeast as a model, a team led by Arshia Naaz and Mohammad Alfatah at the National University of Singapore and the Genome Institute of Singapore demonstrated that copper and iron each preserve the viability of nutrient-starved cells, but they do so through distinct metabolic routes that respond differently to the cell’s nutrient-sensing state.

The researchers exploited a classic feature of Saccharomyces cerevisiae biology: the ability to separate proliferative growth from long-term survival. When yeast cells exhaust the nutrients in their medium, they stop dividing and enter a stationary phase in which their fate depends on stress adaptation rather than replication. By supplementing cultures with copper sulfate across a twelve-point concentration range from 0 to 200 micromolar, the team found that copper left growth kinetics completely untouched. Yet when they measured survival days later using outgrowth assays, in which aged cells are reinoculated into fresh medium and their regrowth quantified, the difference was dramatic. By day sixteen, untreated cultures retained less than ten percent viability, while copper-supplemented cultures approached one hundred percent survival at concentrations of 6.25 micromolar and above.

Iron told a similar but not identical story. Iron sulfate also preserved stationary-phase viability without affecting growth, and it did so at even lower effective concentrations, maintaining near-complete survival across a range extending down to roughly 0.39 micromolar. The effects were reproduced with chloride salts of both metals, confirming that the counterion was irrelevant. The convergence was striking: two redox-active metals, both essential cofactors for mitochondrial enzymes, both capable of generating damaging free radicals when mishandled, both extending the lifespan of starving cells. But the similarity ended at the phenotype. When the researchers began pulling apart the mechanisms, copper and iron revealed themselves as agents of two fundamentally different survival strategies.

The first clue came from iron chelation. When the team used bathophenanthrolinedisulfonic acid, or BPS, to sequester ferrous iron, cells showed a pronounced growth defect and a sharp downregulation of genes encoding the mitochondrial electron transport chain, spanning complexes I through V, as well as tricarboxylic acid cycle genes. Iron supplementation restored both growth and respiratory gene expression. Critically, copper could only partially rescue the growth defect, and its pro-survival effect proved entirely dependent on iron availability. Even modest chelation with 6.25 micromolar BPS eliminated the survival benefit of low copper doses, and 12.5 micromolar BPS abolished copper’s benefit across all tested concentrations. Copper, in other words, does not act as an independent survival factor; it works through iron-dependent metabolic and redox machinery.

The most surprising result emerged under severe iron limitation. At 25 micromolar BPS, a concentration that drastically slowed proliferation, cells actually survived better in stationary phase without any added metal at all. This iron-starvation-induced survival state, likely reflecting reduced nutrient signaling and a shift toward stress adaptation, was actively disrupted by low-to-moderate copper supplementation, which reduced viability relative to chelation alone. Only higher copper doses retained pro-survival activity under these conditions. The interaction between the two metals is therefore non-linear and state-dependent: copper can support survival, interfere with an alternative survival program, or do nothing, depending on the metabolic configuration of the cell.

To map these configurations onto known signaling pathways, the team turned to the two master regulators of eukaryotic nutrient response: Target of Rapamycin Complex 1, or TORC1, which promotes anabolic growth when nutrients are plentiful, and AMP-activated protein kinase, known as Snf1 in yeast, which orchestrates adaptation to energy and oxidative stress. The divergence between the metals became unmistakable here. Iron-dependent survival required a TORC1-permissive state. Low-dose rapamycin, a TORC1 inhibitor, attenuated iron’s survival benefit, and iron remained incompatible with TORC1 inhibition even at higher drug concentrations. Genetic deletion of GTR1 or EGO1, upstream activators of TORC1, or of SCH9, a major TORC1 effector, similarly diminished iron’s benefit. Biochemical measurements confirmed the mechanism: iron supplementation sustained phosphorylation of Sch9 through the transition into stationary phase, indicating persistent TORC1 activity, whereas untreated cells showed the normal decline.

Copper behaved in nearly the opposite manner. It retained its pro-survival effect under rapamycin treatment, and at higher rapamycin concentrations the two interventions cooperated, enhancing survival beyond either alone. Copper also preserved its benefit in gtr1, ego1, and sch9 deletion strains, and under calorie restriction, a physiological condition that suppresses TORC1, copper supplementation further extended survival while iron supplementation actually blunted the calorie-restriction benefit. Taken together, these results define two viable metabolic configurations for long-term survival: an iron-supported state linked to sustained TORC1 activity and mitochondrial engagement, and a copper-supported state compatible with, and even favored by, TORC1 restriction.

The copper pathway converged on AMPK/Snf1 and antioxidant defense. Copper’s survival benefit was attenuated in snf1 deletion mutants, and its protection against the respiratory chain inhibitor antimycin A was largely Snf1-dependent. Copper also relied on SOD2, the mitochondrial superoxide dismutase: in sod2 mutants, copper’s benefit was diminished and required higher doses for partial rescue, whereas iron robustly restored survival in the same mutants even at low concentrations. Under acute hydrogen peroxide challenge, low copper doses conferred a hormetic, dose-dependent protection that vanished in snf1 cells, while iron provided broader protection that became Snf1-dependent only under severe stress. Measurements of mitochondrial membrane potential added a temporal dimension: iron produced a strong but transient early boost in mitochondrial activity, whereas copper elicited a more moderate and durable response, consistent with maintenance rather than maximal stimulation. Both metals also rescued survival when vacuolar function was disrupted by concanamycin A, suggesting that metal availability can buffer organelle-level dysfunction.

The authors frame these findings as a framework for understanding how micronutrient homeostasis intersects with nutrient sensing during aging. Aging tissues are characterized by declining AMPK activity, dysregulated iron metabolism, and altered TORC1 signaling, and the study suggests that such shifts could change whether copper or iron availability benefits or harms a cell. The implications extend to cancer as well: iron is increasingly targeted therapeutically through ferroptosis-inducing strategies, yet this work shows iron can also support cellular persistence under the nutrient-limited conditions typical of tumor microenvironments. The authors caution that whether these mechanisms are conserved in mammalian cells remains to be determined, and future work in human systems will be needed. But the core message is already clear: the consequences of micronutrient availability are not fixed properties of the metals themselves. They are dynamically shaped by the metabolic and signaling state of the cell, meaning that any intervention aimed at tweaking copper or iron levels, whether for longevity or disease treatment, must first account for the cellular context in which those metals will act.

Subject of Research: Distinct metabolic and nutrient-signaling pathways by which copper and iron regulate cellular survival under nutrient limitation

Article Title: Copper and iron engage distinct metabolic programs for cellular survival

Article References: Naaz, A., Cheng, T. Y. N., Lin, J. J., Gao, M., Dorajoo, R., Kennedy, B. K., & Alfatah, M. (2026). Copper and iron engage distinct metabolic programs for cellular survival. GeroScience. https://doi.org/10.1007/s11357-026-02527-x

Image Credits: AI Generated

DOI: 10.1007/s11357-026-02527-x

Keywords: copper, iron, TORC1, AMPK, mitochondria, cellular survival, nutrient signaling, oxidative stress, chronological lifespan, yeast, aging, micronutrients