PRL-1-Enhanced PD-MSCs Promote Liver Regeneration by Improving Endothelial Barrier Function via HGF/c-Met Signaling in Liver Injury

The liver is a resilient organ, capable of repairing itself after acute damage by growing new tissue to replace what was lost. However, when injury becomes chronic and repetitive, this healing process can go awry. Instead of restoring healthy tissue, the liver begins to scar, a condition known as fibrosis that eventually hardens the organ and disrupts its ability to function. A critical, yet often overlooked, part of this failure involves the liver's blood vessels. In a healthy liver, the tiny vessels that carry blood and nutrients are lined with a tight, protective layer of cells that controls what passes through. When chronic injury strikes, this lining becomes leaky and dysfunctional, allowing fluids and proteins to escape into the surrounding tissue. This leakage fuels inflammation and scarring, creating a vicious cycle that prevents the liver from regenerating. To break this cycle, scientists are exploring ways to help the liver's blood vessels heal, hoping that stabilizing the vascular network will allow the organ to recover its function.

In a study published in Stem Cell Research & Therapy, researchers investigated a specific strategy to repair this damaged vascular lining using a type of stem cell derived from the placenta. These cells, known as placenta-derived mesenchymal stem cells, are already known for their ability to reduce inflammation and promote healing. The team, led by scientists at CHA University in South Korea, wondered if they could make these cells even more effective by engineering them to produce higher levels of a specific protein called PRL-1. This protein is naturally found in the liver during regeneration and is known to help cells move and divide. The researchers hypothesized that boosting PRL-1 in these stem cells would not only help the liver cells themselves but would also send stronger signals to the damaged blood vessels, helping them seal up and function correctly again.

To test this idea, the team created a model of chronic liver injury in rats. They induced liver damage over twelve weeks by administering a chemical called thioacetamide, which causes the liver to become scarred and inflamed, mimicking the human condition of cirrhosis. Once the injury was established, they divided the animals into groups. Some received no treatment, while others were given an intravenous injection of either the standard placenta-derived stem cells or the engineered cells enhanced with PRL-1. The researchers tracked the cells using a fluorescent marker and found that the engineered cells stayed in the liver more effectively than the standard ones. More importantly, the rats that received the PRL-1 enhanced cells showed significantly better signs of recovery. Their blood tests indicated less liver damage, and their liver tissue showed higher levels of proteins associated with healthy liver function and regeneration.

The study then looked closely at what was happening inside the liver to cause this improvement. The researchers discovered that the engineered stem cells were secreting much higher amounts of a growth factor called hepatocyte growth factor, or HGF. This molecule is a powerful signal that tells cells to grow and survive. In the rats that received the enhanced stem cells, the levels of HGF were higher, and the receptors on the liver cells that detect this signal were more active. This activation appeared to trigger a chain reaction that helped stabilize the blood vessels. The researchers observed that the blood vessels in the treated rats were less dilated and, crucially, less leaky. They measured this by injecting a fluorescent dye into the rats' veins; in the untreated animals, the dye leaked out of the vessels into the surrounding tissue, but in the rats treated with the engineered cells, the dye stayed tightly contained within the blood vessels, indicating that the barrier function had been restored.

To understand how the stem cells were communicating with the blood vessels, the team moved their experiments to a laboratory setting using human cells grown in a dish. They exposed human blood vessel cells to the same damaging chemical used in the rats, which caused the cells to lose their ability to form a tight network and become overly permeable. When they added the PRL-1 enhanced stem cells to these damaged vessel cells, the network began to repair itself. The cells reconnected, forming a more organized structure, and the leakage of fluid through the cell layer decreased significantly. The researchers also tested a drug that blocks the HGF signal to see if this pathway was essential. When they blocked the signal, the stem cells could not fully repair the damage, confirming that the HGF signal was the key mechanism driving the recovery. The study suggests that by boosting the production of PRL-1, the stem cells become more potent at releasing HGF, which in turn helps the blood vessel lining seal up and function properly.

This work highlights a specific pathway where stem cells can aid liver recovery not just by replacing damaged tissue, but by fixing the environment in which the liver cells live. The findings suggest that the engineered stem cells work by strengthening the liver's vascular barrier, which reduces the inflammation and scarring that usually follow chronic injury. While the study was conducted in animals and cell cultures, the results provide a clear mechanism for how these cells might be used to treat liver disease. The researchers conclude that enhancing stem cells with PRL-1 is a promising strategy to improve their therapeutic power, offering a potential new approach to help the liver heal by first repairing its blood supply.