A protein best known for helping cells and tissues stay connected has revealed an unexpected secondary role that could reshape our understanding of how the human body manages cellular waste. Recent findings show that this molecular machinery, traditionally understood as structural cellular glue, also helps epithelial cells engulf nearby dead cells. These continuous, sealed layers of cells form linings throughout the body, and their ability to clear away debris without compromising barrier integrity represents a fundamental insight into tissue homeostasis.
The discovery, published in Nature Communications, carries significant implications for chronic inflammation and human pathology. Debris left behind by dying cells is a major contributor to inflammatory responses within tissues. Consequently, understanding the precise mechanical and molecular pathways that tissues use to remove that material may reveal new clues about what happens when the cleanup process fails, potentially opening avenues for future therapeutic interventions.
The study centers on the E-cadherin complex, a sophisticated molecular system that includes E-cadherin alongside three additional proteins. Together, these components bind epithelial cells lining vital areas such as the skin, gut, and airways. This interconnected network gives tissues the structural strength they need to remain intact under physical stress. Within these biological architectures, each individual cell securely connects to E-cadherin molecules expressed on the surfaces of neighboring cells, forming a resilient sheet of tissue.
Cellular Glue Takes on a Cleanup Role
A research team led by ICREA Research Professor Verena Ruprecht examined epithelial tissues in living zebrafish and mouse embryos to better understand their developmental dynamics. During these observations, the researchers noticed that the exact molecular machinery responsible for intercellular adhesion also gathers at the precise location where a dying cell comes into contact with the tissue.
Intrigued by this unexpected localization, the research team wanted to determine whether E-cadherin and its molecular partners were attaching to the dying cell in the same manner they normally use to anchor adjacent epithelial cells. To test this hypothesis, the scientists designed two distinct experimental setups.
First, the team presented the epithelial tissue with dying cells that had been intentionally stripped of E-cadherin. Remarkably, the epithelial tissue removed those altered cells just as effectively as it removed normal dying cells. Next, the researchers introduced synthetic fat droplets containing zero protein whatsoever, but carrying a specific biochemical signal normally displayed on the outer surface of dying cells. To the surprise of the observers, the epithelial cells successfully engulfed those protein-free droplets as well, proving that the uptake mechanism relies on recognizing specific clearance cues rather than mutual E-cadherin binding between cells.
"We were intrigued to find out that epithelial cells repurpose their molecular adhesion machinery—the ‘glue’ that normally holds them together—to engulf dying cells," says Verena Ruprecht, the senior author of the study.
How Cells Eat Without Breaking the Barrier
Engulfing an object roughly the size of another cell presents a formidable mechanical problem for any biological system. Epithelial cells are tightly packed into continuous barriers that often need to remain strictly sealed, protecting the organism from external threats even while individual cells undergo drastic shape changes to remove internal debris.
Advanced live imaging revealed the ingenious physical mechanism by which tissues accomplish this feat. The upper and lower surfaces of the same epithelial cell can behave in completely different ways simultaneously. While the lower surface stretches, bends, and actively wraps around the dead cell, the opposite side remains relatively stable and unchanged.
That upper surface, which may face the outside environment of the organism or an open space such as the internal lumen of an organ, continues maintaining the structural integrity of the tissue barrier uninterrupted. Quantitative measurements taken before, during, and after the engulfment process demonstrated that the surface area of the upper boundary changed very little. By contrast, the lower surface underwent substantial deformation throughout the entire "eating" process.
Ruprecht compares this remarkable cellular behavior to a row of dancers standing firmly with their arms linked together. Their upper bodies remain steady and composed while their feet perform increasingly complicated, dynamic movements whenever a dying cell appears nearby. "It’s the same dancer with a different choreography," she notes.
A Molecular Rope and Brake
To understand the mechanics that empower cells to perform this cleanup without failing, the researchers delved deeper into the intracellular components of the E-cadherin complex. Their analyses uncovered distinct roles for individual proteins within the molecular assembly.
One specific protein in the complex acts much like a sturdy rope. It connects the primary molecular assembly directly to the cell’s internal skeleton, allowing mechanical force to be transmitted efficiently across the surface of the material being engulfed. When cells lacked this vital tethering protein, or when they lacked the precise molecular region responsible for attaching it to the cytoskeleton, they completely lost their ability to swallow dead cells.
Conversely, another component within the assembly behaved more like a biological brake on the cell’s contractile machinery. Surprisingly, removing this regulatory brake did not make the cellular cleanup process faster or more efficient. Instead, removing the brake caused the cell to become overly stiff, which paradoxically destroyed its capacity to properly remove dying cells from the tissue environment.
The Same Mechanism Appears in Mammals
Following their observations in zebrafish, the research team investigated whether this specialized clearance process extends to higher vertebrates and mammals.
By analyzing early mouse embryos, the scientists discovered that experimentally blocking E-cadherin caused dying cells to remain uncleared within the tissue. This outcome matched the results previously recorded in zebrafish, providing strong evidence that the mechanism is conserved among vertebrates.
This new work builds directly upon earlier research from Ruprecht’s laboratory demonstrating that embryos can utilize epithelial tissues to cooperatively eliminate dying cells. That collective tissue behavior represents an evolutionarily ancient form of early innate immune defense, operating long before specialized immune cells like macrophages take over those duties in fully developed organisms.
Embryos are particularly valuable models for studying these complex cellular events because they are optically transparent. This transparency allows researchers to observe living cells and tissues directly in real time at a level of spatial and temporal detail that cannot currently be achieved inside adult human bodies.
Could the Same Process Work in Adult Tissues?
Despite these breakthrough insights, an important question remains unanswered. Researchers do not yet know whether this exact E-cadherin-dependent mechanism operates in adult zebrafish, adult mice, or any type of human tissue.
Nevertheless, there are compelling reasons to believe it does. Epithelial tissues in adult organisms are already well known to actively remove dying cells in diverse anatomical locations, including the retina, colon, airways, and mammary gland. Furthermore, E-cadherin is abundantly expressed throughout epithelial tissues across the animal kingdom, and its molecular structure has remained remarkably conserved throughout evolutionary history. Those characteristics make it a strong candidate for a more broadly utilized, universal cleanup mechanism.
The potential medical relevance of these findings stems directly from the pathological consequences of inefficient cellular clearance. Dying cells that remain unremoved within tissues will eventually undergo secondary necrosis, rupturing and spilling their toxic intracellular contents into the surrounding microenvironment. This uncontrolled release is a major driver of chronic inflammation.
The study indicates that successful tissue cleanup depends on much more than a cell simply receiving the correct chemical signal to engulf apoptotic debris. Cells must also possess the precise mechanical capabilities required to change shape, generate and transmit physical force, and wrap around dead material safely without compromising their own structural integrity or that of the surrounding tissue barrier.
"Studying the mechanisms of how dying cells can be removed efficiently from tissues is of very high relevance to human health," concludes Ruprecht.
The study was led by joint first authors Hanna-Maria Häkkinen, Marta Batet Palau, and Laura F. Bianchi, and supervised by Verena Ruprecht. Financial support was provided by the Spanish Ministry of Science and Innovation, the Human Frontier Science Program, the European Union’s Horizon Europe program, and the "la Caixa" Foundation, with additional assistance from the European Social Fund. The research also utilized advanced infrastructure from the CRG Core Facilities for Advanced Light Microscopy, Tissue Engineering, and Protein Technologies.
