Copper is essential for life. Our cells need the metal to make energy and stay healthy, but if it is in the wrong place or present in excess, copper can be deadly. Texas A&M AgriLife Research scientists have identified a key protein that helps maintain copper balance, with implications for treating heart failure and rare diseases.
The study, published in PNAS on June 17, was supported by the National Institutes of Health. It was performed in collaboration with researchers at Auburn University, Alabama; University of Missouri, Columbia; and University of Saskatchewan, Saskatoon, Canada.
For years, scientists have known that copper enters the powerhouses of cells — mitochondria — to help produce the energy our cells need. What remained unclear was how mitochondria keep copper from piling up inside them.
“Copper overaccumulation in mitochondria can damage mitochondria and kill cells,” said Mohammad Zulkifli, Ph.D., an AgriLife Research scientist in the lab of Vishal Gohil, Ph.D., professor and Chancellor EDGES Fellow in the Texas A&M Department of Biochemistry and Biophysics. Zulkifli and Gohil are co-corresponding authors on the study.
“A long-standing question, for two decades, has been how excess copper gets out of mitochondria,” Zulkifli said. “We used a drug to identify the protein that moves copper out, which also lets it be used by an enzyme critical for producing energy.”
A drug becomes a research tool
To resolve the question, the team turned to a drug they knew quite well.
Gohil, Zulkifli and their collaborators have spent years researching treatments for copper deficiency disorders such as Menkes disease by using a copper-transporting drug called elesclomol, which was originally developed as a potential anticancer drug.
In 2023, Zulkifli and Gohil, who is also an affiliate member of the Texas A&M AgriLife Institute for Advancing Health Through Agriculture, described how elesclomol delivers copper directly into mitochondria. Inside mitochondria is a central space called the matrix. The matrix is surrounded by two membranes, including a tightly controlled inner membrane that regulates what enters and leaves. Elesclomol bound to copper, the team found, can slip inside those membranes and release copper in the matrix.
Later, Zulkifli read about research implicating a mitochondrial protein, SLC25A3, in moving copper across the mitochondrial membranes. However, the research could not determine the direction in which SLC25A3 moves the copper.
Zulkifli realized elesclomol gave the team the perfect chance to learn what SLC25A3 does.
What happens when the protein is missing
Working with heart cells, Zulkifli deleted the gene for SLC25A3. His experiments showed that these cells had trouble managing copper, consuming oxygen and generating energy.
Next, he treated these defective heart cells with elesclomol to deliver copper directly into the mitochondrial matrix, bypassing the need to involve SLC25A3 for import. The goal was to see whether that copper could make its way out of the matrix to where it was needed. He found that instead of recovering, the cells got sicker.
“We thought elesclomol was a drug we could use for every copper deficiency disease, but we found that no, it’s not true,” Zulkifli said.
Delivering copper into the mitochondrial matrix was not enough to restore function.
Detailed experiments revealed that without SLC25A3, copper could enter the mitochondrial matrix but could not leave. It became trapped, building up to toxic levels instead of reaching an enzyme that uses it to produce energy.
These results showed that SLC25A3 is the pathway cells use to move copper out of the mitochondrial matrix to prevent copper accumulation and support energy generation.
The team also treated the sick cells with compounds that delivered copper within cells but outside mitochondria.
“That’s not a very efficient route, but some copper can still be delivered to the enzymes that need it via this route,” Zulkifli said. “We found two compounds that were able to partially rescue these defective cells.”
Why copper balance matters for human health
The study may help explain what goes wrong in disease.
For example, mutations in SLC25A3 are linked to heart failure in human patients, Zulkifli said. The heart is one of the most energy-demanding organs in the body, and if the copper balance is off, heart cells can become dysfunctional or even die. This highlights the importance of keeping copper properly distributed inside cells.
“Now, we will look at these mutations to determine whether they have defects in copper import or export or both, and whether they can be corrected,” Zulkifli said.
Long-term, the team hopes this work will help guide how copper-transporting drugs are used — not just to deliver copper, but to ensure it reaches the right place inside cells.