Endothelial-to-mesenchymal transition contributes to blood vessel loss and fibrosis during chronic GVHD
This study demonstrates that endothelial-to-mesenchymal transition (EndMT), driven by elevated TGF-β signaling, contributes to microvascular loss and fibrosis in chronic graft-versus-host disease (cGVHD), and that targeting this pathway with pirfenidone offers a promising non-immunosuppressive therapeutic strategy.
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 patient receives a life-saving transplant of healthy blood stem cells from a donor, the goal is to replace a failing immune system or cure a blood cancer. However, this procedure carries a significant risk of a complication called chronic graft-versus-host disease. In this condition, the new immune cells, while fighting the disease, mistakenly attack the patient's own healthy tissues. This attack often leads to a slow, damaging process where the body's tissues become stiff and scarred, a condition known as fibrosis. For decades, doctors have observed that this scarring is frequently accompanied by a mysterious disappearance of the tiny blood vessels that supply those tissues with oxygen and nutrients. While the loss of these vessels and the buildup of scar tissue are well-known hallmarks of the disease, the biological link connecting them has remained a blind spot in medical science. Without understanding how the blood vessels vanish, researchers have struggled to develop treatments that can stop or reverse the damage.
A team of researchers at Charité Universitätsmedizin Berlin and other institutions has now uncovered a hidden mechanism that explains this dual destruction. By examining tissue samples from patients and conducting detailed experiments in mice, they discovered that the cells lining the blood vessels do not simply die and disappear. Instead, they undergo a dramatic transformation. These vessel cells change their identity, shifting from a structure designed to carry blood into a different type of cell that builds scar tissue. This process, known as endothelial-to-mesenchymal transition, acts as a bridge between the loss of blood flow and the formation of fibrosis. The researchers found that a specific protein signal, which is elevated in the blood of patients with the disease, triggers this change. When the vessel cells receive this signal, they lose their ability to function as healthy blood vessels and instead begin to behave like the cells that create scars, effectively turning the body's plumbing into a wall of tissue.
To prove this connection, the scientists looked closely at skin biopsies from patients suffering from chronic graft-versus-host disease. They searched for cells that carried the markers of both blood vessel linings and scar-building cells simultaneously. In patients with the disease, they found a significant number of these hybrid cells, whereas healthy controls showed almost none. This observation suggested that the blood vessels were actively changing their nature rather than just being destroyed. To confirm this, the team turned to advanced genetic sequencing of tissue from mice that had undergone similar transplants. They mapped the developmental path of individual cells and found a clear trajectory: cells started as blood vessel linings, moved through an intermediate stage where they held traits of both types, and finally settled into a scar-building state. This genetic roadmap provided strong evidence that the transition was a real, ongoing process driving the disease.
The researchers also investigated why this transition happens. They measured levels of a signaling protein called transforming growth factor beta in the blood of patients and found it was significantly higher in those with the disease compared to those without. When they took blood vessel cells from mice with the condition and exposed them to this protein in a lab dish, the cells rapidly changed shape and began producing scar-related proteins. These transformed cells lost their ability to form tight, protective barriers and could no longer create new blood vessel structures. In the living mice, this breakdown in the vessel lining led to leaky blood vessels and a failure to maintain proper blood flow, mirroring the damage seen in human patients. The study showed that the disease environment makes these cells uniquely vulnerable to this transformation, turning a protective system into a source of tissue damage.
Recognizing that this process was the key to the problem, the team tested a potential solution. They used a drug already approved by the US Food and Drug Administration for treating a different type of lung scarring. This drug works by blocking the very signaling pathway that triggers the cell transformation. When they administered this treatment to mice with chronic graft-versus-host disease, the results were striking. The drug reduced the number of cells undergoing the harmful transition, preserved the density of blood vessels in the liver and colon, and significantly lowered the amount of scar tissue. Unlike many current treatments that broadly suppress the immune system and cause severe side effects, this approach targeted the specific mechanism of tissue damage. The findings suggest that by stopping this cellular identity shift, it may be possible to protect blood vessels and prevent the fibrosis that currently has no effective cure.
This research offers a new perspective on a decades-old medical challenge. It moves the focus from simply trying to calm the immune system to understanding the specific biological changes that destroy tissue architecture. By identifying that blood vessel cells can transform into scar-building cells, the study provides a concrete target for future therapies. While the drug tested in the mice is not yet a standard treatment for this condition in humans, the results indicate that targeting this specific transition could offer a path forward. It suggests that the loss of blood vessels and the buildup of scars are not separate problems, but two sides of the same coin, driven by a single cellular event that can potentially be stopped.
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