Cellular adhesion protein E-cadherin plays unexpected role in clearing dead cells from tissues

Protein's Hidden Function Revealed

Researchers have discovered that E-cadherin, a protein long known for binding epithelial cells together into protective tissue barriers, performs a second crucial function: helping cells engulf and remove dead cellular material. The finding emerged from studies of living zebrafish and mouse embryos, published in Nature Communications. Scientists led by Verena Ruprecht at the University of Liverpool found that the same molecular machinery responsible for cementing cells into continuous sealed layers throughout the body — lining skin, gut, and airways — also mobilizes at sites where dying cells contact healthy tissue.

The E-cadherin complex consists of E-cadherin itself plus three additional proteins working in concert. In their experiments, researchers tested whether E-cadherin actually needed to bind to dying cells the same way it attaches to neighboring living cells. They presented epithelial tissues with dying cells stripped of E-cadherin — the tissues removed them as effectively as normal. When researchers introduced fat droplets containing no protein but displaying the chemical signal normally found on dead cells, epithelial cells engulfed those as well. These results demonstrated that E-cadherin and its partners repurpose their adhesion machinery to recognize and consume cellular debris without directly attaching to it.

Mechanical Elegance of the Cleanup Process

Engulfing an object roughly the size of another cell while maintaining a sealed tissue barrier presents a significant mechanical challenge. Live imaging revealed an elegant solution: epithelial cells perform this feat through asymmetrical behavior. The upper surface of the cell — facing the external environment or internal spaces — remains relatively unchanged and continues protecting the tissue barrier. Meanwhile, the lower surface stretches and bends around the dying cell during engulfment. Measurements taken throughout the process showed minimal change to the upper surface area, while the lower surface underwent substantial deformation.

Ruprecht uses a striking analogy: the cells behave like a row of dancers standing arm-in-arm, with their upper bodies remaining steady while their feet execute increasingly complicated choreography when a dying cell appears. This compartmentalized flexibility allows cleanup without compromising tissue integrity.

The research identified two key mechanical components within the E-cadherin complex. One protein functioned like a rope, connecting the molecular assembly to the cell's internal skeleton and transmitting force across the material being engulfed. When this tethering protein or its skeletal attachment point was absent, cells lost their ability to swallow dead material. Another component acted as a brake on the cell's contractile machinery. Surprisingly, removing this brake did not enhance cleanup efficiency; instead, cells became too rigid and lost their capacity to properly remove dying cells. This unexpected finding suggests that the process requires precise mechanical balance rather than maximum force.

Conservation Across Vertebrates and Unanswered Questions

The team extended their investigation to mammalian systems, testing whether this mechanism extends beyond zebrafish. In early mouse embryos, blocking E-cadherin prevented the clearance of dying cells, mirroring results from zebrafish. This suggests the mechanism is conserved among vertebrates, building on Ruprecht's earlier work showing that embryonic epithelial tissues cooperatively remove dying cells as an early form of innate immune defense.

Embryos proved particularly valuable for these studies because their transparency allows researchers to observe living cells and tissues at detail levels impossible to achieve in living human bodies. However, a critical question remains unresolved: whether this E-cadherin-dependent mechanism operates in adult zebrafish, mice, or human tissues. Several factors suggest it could. Adult epithelial tissues are known to remove dying cells in the retina, colon, airways, and mammary gland. E-cadherin is distributed throughout epithelial tissues across the body, and its molecular structure has remained remarkably conserved across species — characteristics that make it a strong candidate for broad-based use.

Implications for Understanding Chronic Inflammation

The medical significance of this discovery centers on what occurs when dead cell removal fails. When dying cells remain in tissues, they eventually rupture and release their contents, contributing to chronic inflammatory responses. Understanding how tissues efficiently clear cellular debris may illuminate why this cleanup process fails in certain disease states. The research demonstrates that successful debris removal depends on more than receiving the correct chemical signal to engulf apoptotic material; cells must also possess the physical capability to change shape, apply force, and wrap around dead material without compromising themselves or surrounding tissue integrity. As Ruprecht concludes, studying the mechanisms of efficient dead cell removal from tissues carries very high relevance to human health.