Knockdown of CDCP1 Inhibits ox-LDL-Induced Phenotypic Transition and Lipid Accumulation in Vascular Smooth Muscle Cells via Downregulating the ITGB4/PI3K/AKT Pathway

The arteries that carry blood throughout the body are lined with a layer of smooth muscle cells. Under normal conditions, these cells act like the sturdy, flexible walls of a garden hose, maintaining the vessel's shape and helping to regulate blood flow. However, when the body is exposed to high levels of bad cholesterol or chronic inflammation, these cells can undergo a dramatic change. They lose their structural role and begin to behave more like immune cells, specifically macrophages. In this new state, they start to gobble up fatty particles, swell with lipid droplets, and release signals that promote inflammation. This transformation is a critical step in the development of atherosclerosis, the hardening and narrowing of arteries that leads to heart attacks and strokes. While doctors have long known that this shift happens, the specific molecular switches that flip the cells from a protective state to a dangerous one have remained largely a mystery.

A team of researchers at the Southern University of Science and Technology Hospital has now identified one of these switches. By studying human tissue samples and conducting experiments on mice and cells in the lab, they found that a protein called CDCP1 plays a central role in driving this harmful transformation. Their work suggests that when CDCP1 is present in high amounts, it encourages smooth muscle cells to change their identity and accumulate fat, accelerating the formation of arterial plaques. The study, published recently, traces the path of this protein from the surface of the cell down to the genetic instructions inside, revealing a chain of events that could offer a new way to think about treating cardiovascular disease.

The investigation began with a search for clues hidden in existing data. The researchers analyzed genetic information from human arterial plaque tissues, comparing them to healthier tissue samples. They were looking for genes that were consistently turned on in diseased arteries. This digital screening pointed to CDCP1 as a gene that was significantly more active in the plaques than in normal tissue. To confirm this finding in a living system, the team fed mice a high-fat diet to induce atherosclerosis. After twelve weeks, the mice developed significant fatty deposits in their arteries, much like the human condition. When the researchers examined the arteries of these mice, they found that CDCP1 levels were indeed much higher in the plaque areas compared to the healthy sections. This confirmed that the protein is not just a bystander but is closely associated with the disease process in both humans and animals.

Next, the scientists wanted to see exactly what CDCP1 was doing inside the cells. They grew mouse vascular smooth muscle cells in a dish and exposed them to oxidized low-density lipoprotein, a form of bad cholesterol that triggers the disease. As expected, the cells began to change. They stopped acting like muscle and started behaving like fat-eating immune cells, taking up more cholesterol and accumulating lipid droplets. Crucially, the cells also produced more CDCP1 during this process. To test if CDCP1 was actually causing these changes, the researchers used a technique to silence the gene responsible for making the protein. When they reduced the amount of CDCP1 in the cells, the harmful changes stopped. The cells retained their muscle-like characteristics, produced fewer inflammatory signals, and, most importantly, absorbed far less fat. The lipid droplets that usually fill the cells were significantly reduced, suggesting that without CDCP1, the cells were protected from the toxic effects of the cholesterol.

To understand how this protein exerts such control, the team looked deeper into the cell's internal signaling network. They sequenced the RNA from the cells with and without CDCP1 to see which other genes were affected. The analysis revealed that when CDCP1 was silenced, a specific pathway known as the PI3K/AKT pathway became less active. This pathway is a well-known communication line inside cells that often drives growth and survival. The researchers found that CDCP1 works by keeping another protein, called ITGB4, stable and active. ITGB4 acts as a trigger for the PI3K/AKT pathway. In the presence of high CDCP1, ITGB4 remains stable, the pathway stays switched on, and the cells transform into fat-laden, inflammatory cells. However, when CDCP1 is removed, ITGB4 breaks down more quickly, the pathway turns off, and the cells remain healthy.

The team then investigated exactly how CDCP1 keeps ITGB4 stable. They discovered that CDCP1 does not change how much ITGB4 is made by the cell's genetic machinery. Instead, it acts like a shield that prevents the ITGB4 message from being destroyed too soon. In cells where CDCP1 was silenced, the ITGB4 message degraded rapidly, leading to a drop in the protein levels needed to drive the disease. This mechanism explains why the cells behave differently: without the protective effect of CDCP1, the signal to change into a harmful cell type fades away. To prove this connection, the researchers performed a rescue experiment. They silenced CDCP1 but then artificially added back high levels of ITGB4 or activated the downstream pathway directly. In these cases, the cells changed back into the harmful, fat-accumulating type, even without CDCP1. This confirmed that CDCP1's main job in this context is to maintain ITGB4 levels, which in turn activates the pathway that drives the disease.

The findings offer a clearer picture of how atherosclerosis progresses at the cellular level. While the study was conducted in mice and cell cultures, and the researchers note that further work is needed to confirm these results in larger groups of patients, the mechanism they uncovered is specific and direct. They have shown that CDCP1 is a key regulator that helps smooth muscle cells transition into a dangerous state by stabilizing a specific protein and keeping a critical signaling pathway active. By identifying this chain of events, the study highlights CDCP1 as a potential target for future therapies. If scientists can find a way to block CDCP1 or disrupt its ability to stabilize ITGB4, it might be possible to prevent the cells from changing their identity and accumulating the fat that leads to heart disease, offering a new strategy to protect the arteries from the inside out.