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  • Cuproptosis in Health and Disease: Copper’s Double-Edged Sword

Cuproptosis in Health and Disease: Copper’s Double-Edged Sword

Written by Jeyashree Alagarsamy, PhD Candidate at the University of Cincinnati

Copper is an essential micronutrient that plays a critical role in a variety of physiological functions, including mitochondrial respiration, antioxidant defense, and the production of numerous bio-compounds. However, too much copper can be harmful, making it crucial for the body to maintain a delicate balance of this metal. Recent research has discovered a novel copper-dependent cell death mechanism known as cuproptosis, which differs significantly from other known cell death routes such as apoptosis, ferroptosis, and necroptosis. Let’s explore how copper is managed, how it can cause disease when not properly regulated, and the potential role of cuproptosis in health and diseases.

How is Copper Homeostasis Maintained in Cells?

Copper homeostasis within cells is carefully regulated through a sophisticated network of copper-dependent proteins, consisting of cuproenzymes, copper chaperones, and membrane transporters. These proteins collaborate to manage the import, export, and intracellular utilization of copper, therefore supporting cellular copper levels within a specific range, crucial for preventing the adverse effects of copper overload or deficiency. Copper uptake in cells is mostly supported by the high-affinity transporter CTR1 (SLC31A1), which enables Cu+1 entry. CTR1 expression varies with copper levels, upregulating during deficit and downregulating during excess1,2. Its function is critical for intestinal copper absorption, and its absence causes copper shortage in peripheral organs3. ATOX1 and CCS are chaperones that transport copper intracellularly. ATOX1 transports copper to ATP7A and ATP7B in the trans-Golgi network for cuproenzyme production, whereas CCS transports copper to superoxide dismutase 1 (SOD1) to reduce reactive oxygen species. Copper efflux is controlled by ATP7A and ATP7B, which move from the trans-Golgi network to the plasma membrane to remove excess copper when intracellular levels rise. Mutations in these ATPases can result in illnesses such as Menkes and Wilson's disease, highlighting their importance in copper homeostasis.

 

Figure 1: Cellular Cu metabolism pathway adapted from Chen et al. 2022

 

IF analysis of human liver cancer tissue using SLC31A1 antibody (67221-1-Ig) and CoraLite488-Conjugated AffiniPure Goat Anti-Mouse IgG(H+L).

IHC analysis of FFPE human colon cancer tissue using ATP7B-specific antibody (19786-1-AP). Heat mediated antigen retrieval with Tris-EDTA buffer.

 

What Happens to Cells during Cuproptosis?

Several significant biochemical and morphological changes take place within the cell during cuproptosis. Copper ions accumulate in the cell, causing an increase in reactive oxygen species (ROS) generation and oxidative stress, which damage cellular components like lipids, proteins, and DNA. Copper ions also promote aberrant lipoylation and protein aggregation in the tricarboxylic acid (TCA) cycle, which impairs mitochondrial activity4,5. Furthermore, disruption of iron-sulfur (Fe-S) cluster proteins inhibits electron transport and enzymatic activity, compromising mitochondrial respiration. Copper also inhibits the ubiquitin-proteasome pathway, which leads to the accumulation of damaged proteins and increases cellular stress. Protein aggregation and Fe-S cluster disruption cause considerable structural damage in mitochondria, including swelling and loss of cristae. Oxidative stress and lipid peroxidation cause cell membranes to become more permeable and rupture, and cytoplasmic vacuoles form because of perturbed cellular functions and the accumulation of damaged organelles6,7.

What Defines Cuproptosis and Who Are Its Main Players?

Cuproptosis, a novel form of regulated cell death triggered by excess Cu2+, exhibits distinct characteristics compared to other well-known cell death pathways like apoptosis, ferroptosis, and necroptosis. It is closely associated with alterations in mitochondrial enzymes, with the mitochondrion being a primary target of Cu-induced cell death8,9. Excessive copper exposure leads to oxidative damage to the mitochondrial membrane and impairs the function of enzymes in the tricarboxylic acid (TCA) cycle. In patients with copper overload, inactivation of key TCA cycle enzyme aconitase is linked to reduced cytochrome c oxidase (CCO) activity and inhibition of the TCA cycle. Metabolite profiling of cells treated with copper ionophore demonstrates dysregulation of TCA cycle-associated metabolites over time, with inhibition of electron transport chain complexes I and II significantly reducing copper-induced cell death7. DLAT (Dihydrolipoamide S-Acetyltransferase), FDX1 (Ferredoxin 1), and LIAS (Lipoic Acid Synthetase) are the key genes in regulating cuproptosis. DLAT, a key component of the pyruvate dehydrogenase complex (PDC), is required for lipoylation and the activation of enzymes in the tricarboxylic acid cycle10. During cuproptosis, increased copper levels cause aberrant lipoylation and aggregation of DLAT, resulting in mitochondrial dysfunction and cell death. FDX1, which is required for electron transport in several metabolic pathways, helps in the reduction of iron-sulfur (Fe-S) clusters. In addition, FDX1 regulates copper ion homeostasis and redox processes, which are important in cellular responses to copper-induced stress11. LIAS, which is required for lipoic acid synthesis, ensures that TCA cycle enzymes such as DLAT remain stable and active. Disruption in LIAS function causes lipoylated proteins to aggregate pathologically, contributing to cuproptosis. These genes demonstrate the complex interplay of copper metabolism and mitochondrial function in cell survival. Copper therapy alters metabolic enzymes via lipoylation, affecting TCA cycle proteins such as DLAT, FDX1, and LIAS. These proteins are critical in mitigating copper-induced cell death by restoring appropriate protein lipoylation and metabolite levels12-14.

 

 

IF analysis of HepG2 cells using DLAT antibody (green, 83654-3-RR ) and CoraLite®488-Conjugated Goat Anti-Rabbit IgG(H+L) (SA00013-2), and CL594-Phalloidin (red).

Various lysates were subjected to SDS PAGE followed by western blot with FDX1 antibody (82957-1-RR).

 

Figure 2: Schematic model of cuproptosis adapted from Chen et al. 2022

 

The Implications of Cuproptosis in Diseases and Therapeutic Prospects
Wilson's Disease

In Wilson's Disease (WD), which results from mutations in the ATP7B gene, faulty ATP7B function leads to copper buildup in tissues such as the brain and liver, causing significant damage. Liver-related symptoms include vomiting, weakness, fluid accumulation in the abdomen (ascites), leg swelling, jaundice (yellowish skin), and itchiness. Neurological symptoms encompass tremors, muscle stiffness, difficulty speaking, personality changes, anxiety, and auditory or visual hallucinations15. Treatment typically involves oral zinc to limit copper absorption and chelating agents like D-penicillamine and trientine. While these therapies alleviate liver symptoms, their effectiveness for neurological symptoms varies. Promisingly, clinical trials have indicated that compounds such as tetrathiomolybdate (TTM) and WTX101 can mitigate neurological deterioration in WD patients. Since TTM inhibits the harmful effects of copper ionophores, cuproptosis may contribute to the progression of WD. Compounds targeting cuproptosis, such as α-lipoic acid (metabolite in the cuproptosis pathway), show potential in treating WD16. It would be interesting to investigate whether novel drugs targeting cuproptosis could effectively cure this difficult condition.

Neurological Diseases:

Cuproptosis is linked to several neurodegenerative illnesses, including Alzheimer's disease (AD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS)17. High copper levels are linked to disease progression, with research linking accumulation of copper to the production of harmful protein aggregates in AD and HD. Additionally, mutations affecting copper-binding proteins, such as SOD1, have been related to ALS. Mitochondrial failure appears to be a significant mechanism in copper-induced neurotoxicity, suggesting that cuproptosis could be a therapeutic target for these disorders8. More research is needed to understand the role of cuproptosis in neurodegenerative illnesses and its potential as a therapeutic method.

Cancer:

Cuproptosis has shown promise as a therapeutic target in cancer treatment. Copper has been shown in studies to trigger cancer cell death via apoptosis and ROS accumulation18. Novel approaches include employing Cu-coordination nanoparticles, such as GOx@[Cu(tz)], to limit tumor growth in animal models while minimizing toxicity19. Cu ionophores, such as elesclomol, also exhibit anticancer action via increasing ROS generation. Clinical trials using elesclomol in combination with chemotherapy have yielded promising outcomes, particularly in individuals with low lactate dehydrogenase levels, which indicate a high mitochondrial metabolic state20. More research and clinical trials are needed to determine the efficacy of targeting cuproptosis in cancer treatment.

Conclusion

In summary, the discovery of cuproptosis sheds light on the complex relationship between copper regulation and disease pathogenesis. From Wilson's disease to neurodegenerative disorders and cancer, excess copper can trigger harmful cellular mechanisms, suggesting cuproptosis as a potential therapeutic target. While promising, further research and clinical trials are needed to fully explore the therapeutic implications of targeting cuproptosis in diverse disease contexts.

 

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