CKLF1 regulates ferroptosis in ischaemic-hypoxic cardiomyocytes through the Keap1/Nrf2/Ho1 signalling pathway

When the heart suffers a sudden blockage, cutting off its supply of oxygen and nutrients, the damage extends far beyond the immediate lack of blood. The body's own defense systems, designed to heal, can sometimes turn destructive. In the hours and days following a heart attack, the heart muscle is flooded with inflammatory signals and unstable molecules that attack the cells from within. Among the various ways heart cells can die, a specific process called ferroptosis has recently come into focus. Unlike the more familiar forms of cell death, ferroptosis is driven by iron. When iron builds up inside a cell, it acts like a spark in a dry forest, triggering a chain reaction that rusts the cell's internal fats until the cell membrane bursts. The heart is particularly vulnerable to this because it works so hard and requires so much energy. Scientists have long known that stopping this rusting process could save heart tissue, but the specific switch that turns it on in a heart attack has remained a mystery.

A team of researchers set out to find that switch, focusing on a protein called CKLF1. This protein is part of the body's chemical signaling system, usually known for recruiting immune cells to sites of injury. The researchers suspected that in the context of a heart attack, CKLF1 might be doing more than just calling for help; it might be actively pushing heart cells toward this iron-driven death. To test this, they looked at two different scenarios: rats that had suffered a real heart attack and heart cells grown in a laboratory dish that were deprived of oxygen and sugar to mimic the conditions of a heart attack.

In the living rats, the team induced a heart attack by tying off a major artery and then injected a neutralizing antibody directly into the heart muscle. This antibody acts like a shield, blocking the CKLF1 protein so it cannot send its signals. The results were striking. The rats that received the antibody had significantly smaller areas of dead heart tissue compared to those that did not. Blood tests showed lower levels of enzymes that leak out when heart cells are damaged, confirming that the heart muscle was better preserved. When the researchers examined the tissue under a microscope, they found that the antibody had successfully lowered the levels of CKLF1 in the injured area. More importantly, the treated tissue showed signs of being protected from ferroptosis. The levels of iron and harmful oxidative molecules were lower, while the levels of the cell's natural antioxidant defenses were higher. The proteins that usually signal a cell to undergo ferroptosis were reduced, while the proteins that protect against it were restored.

To understand exactly how this happened, the researchers turned to the laboratory-grown heart cells. They exposed these cells to oxygen deprivation and then treated them with a small peptide called C19, which acts as a blocker for CKLF1. Just as in the rats, the treated cells survived better. The C19 treatment stopped the cells from accumulating iron and prevented the buildup of toxic byproducts that result from iron reacting with fats. It also reversed the changes in the cell's internal machinery that normally lead to death. The researchers then traced the path of this protection to a specific signaling chain inside the cell. They found that when CKLF1 is active, it disrupts a vital defense system known as the Keap1/Nrf2/HO-1 pathway. This pathway is the cell's primary alarm system for oxidative stress; when it works correctly, it turns on genes that produce antioxidants to clean up the dangerous molecules. In the damaged cells, CKLF1 was keeping this alarm system turned down. By blocking CKLF1 with the antibody or the peptide, the researchers were able to flip the switch back on, allowing the cell to produce the antioxidants it needed to survive.

The study also explored what happens if this defense system is deliberately turned off. When the researchers used a drug to block the Nrf2 protein, a central component of the defense pathway, the protective effects of the CKLF1 blocker disappeared. The cells died regardless of whether CKLF1 was blocked, proving that the protection offered by stopping CKLF1 relies entirely on this specific signaling pathway. This confirmed that CKLF1 drives ferroptosis by suppressing the cell's natural ability to fight off iron-induced damage.

These findings suggest that CKLF1 is a key regulator of cell death in heart attacks, acting as a brake on the heart's natural antioxidant defenses. By interfering with this protein, it is possible to keep the heart cells alive during the critical period after a blockage. While the study was conducted in animals and cell cultures, it provides a clear map of the molecular steps involved, moving beyond general observations to identify a specific target. The research indicates that developing drugs to block CKLF1 could offer a new way to limit the damage caused by heart attacks, potentially saving more heart muscle and improving recovery for patients. The work highlights how a protein known for its role in inflammation can also directly control the metabolic fate of heart cells, offering a new perspective on how to treat one of the world's most common causes of death.