Cathepsin B inhibition attenuates acute cerebral ischemia-reperfusion injury and suppresses associated apoptotic and neuroinflammatory responses
This study demonstrates that inhibiting cathepsin B significantly mitigates acute cerebral ischemia-reperfusion injury in rats and PC12 cells by reducing infarct volume and cell death while simultaneously suppressing apoptosis, neuroinflammation, oxidative stress, and blood-brain barrier disruption, highlighting CTSB as a promising therapeutic target.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
When a stroke strikes, the immediate danger is the sudden cutoff of blood to a part of the brain. Without oxygen, brain cells begin to die. However, the story does not end when doctors restore blood flow. In fact, the moment circulation returns, a second wave of damage often begins. This phenomenon, known as reperfusion injury, occurs because the sudden rush of oxygen and nutrients triggers a chaotic chain reaction inside the cells. It is as if the body's emergency response system malfunctions, launching a series of self-destructive signals that kill more cells than the original lack of blood ever did. Scientists have long known that this secondary damage involves cells turning on themselves through a process called apoptosis, or programmed cell death, and that inflammation plays a major role in spreading the destruction. Yet, the precise switch that flips this destructive sequence remains difficult to pinpoint, leaving doctors with few tools to stop it once the blood flow is restored.
Researchers at Gannan Medical University and the Suzhou Institute of Biomedical Engineering and Technology have now identified a specific molecular player that appears to act as a critical trigger for this secondary damage. They focused on an enzyme called cathepsin B, which normally lives safely inside a cell's recycling centers, known as lysosomes. Under normal conditions, this enzyme helps break down waste. But when brain cells are starved of oxygen and then suddenly flooded with blood, these recycling centers can rupture, spilling the enzyme into the rest of the cell. The team investigated what happens when this spill occurs and whether stopping it could save the brain.
To test this, the scientists created a model of stroke in rats by temporarily blocking the main artery that supplies blood to one side of the brain, then removing the blockage to simulate the return of blood flow. They also used a laboratory model of nerve cells that were deprived of oxygen and glucose before being returned to normal conditions. In the rats, the team introduced a chemical inhibitor designed to block cathepsin B just before the artery was blocked and again before blood flow was restored. They compared these animals to others that received no treatment and a group that received a different drug known to block a separate stress signal in the cell. The results were striking. In the untreated rats, the area of dead brain tissue, known as the infarct, accounted for roughly 43 percent of the affected hemisphere. In the rats where cathepsin B was blocked, this area shrank dramatically to just 15 percent. The animals treated with the cathepsin B inhibitor also showed significantly better recovery in their ability to move and function compared to the untreated group.
The study went deeper than just measuring the size of the damaged area. The researchers looked at the molecular events happening inside the brain cells during the first few hours after blood flow returned. They found that when cathepsin B leaked out, it seemed to coordinate a team of other proteins that drive cell death. Specifically, they observed a strong connection between cathepsin B, a stress-signaling protein called JNK3, and a molecule named Bid that helps open the door to cell death. In the injured brains, these three molecules were found in the same places and were physically interacting with one another much more frequently than in healthy brains. When the researchers blocked cathepsin B, the activity of the other two proteins dropped significantly, suggesting that cathepsin B acts as a leader that rallies the others to cause damage.
Beyond stopping cell death, the inhibition of cathepsin B appeared to calm the broader inflammatory storm that follows a stroke. The treatment reduced the activation of the brain's immune cells, lowered levels of harmful inflammatory chemicals, and helped restore the brain's natural antioxidant defenses. Crucially, it also helped preserve the blood-brain barrier, the tight seal that keeps harmful substances in the bloodstream from leaking into the brain tissue. In the untreated rats, this barrier was compromised, allowing dye injected into the blood to leak into the brain, but in the treated rats, the barrier remained much more intact. The team also confirmed these findings using genetic techniques to silence the gene for cathepsin B in the lab-grown cells, which produced the same protective effect as the chemical inhibitor, ruling out the possibility that the drug was simply acting on a different target.
While the study points to cathepsin B as a promising target, the researchers are careful to note that their work is still in the early stages. The experiments were conducted on young male rats, and the drugs were delivered directly into the brain's fluid spaces, a method not currently feasible for human patients. The team suggests that future work must determine if this approach can be delivered safely through the bloodstream and if it works in older animals or those with other health conditions. Nevertheless, the findings offer a clear and detailed map of how a single enzyme can orchestrate a complex network of cell death and inflammation after a stroke. By identifying cathepsin B as a central node in this destructive network, the study provides a new potential avenue for therapies that could one day limit the devastation of a stroke, not just by restoring blood flow, but by preventing the brain from turning against itself when that flow returns.
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