Does a Foodborne Pathogen Trigger Blood Clots?...Unveiling the "Hidden Toxin" of Enterohemorrhagic E. coli [Reading Science]

New pathway revealed by which RTX toxin converts red blood cells into a procoagulant state

A new explanation has been identified for why infection with enterohemorrhagic Escherichia coli (EHEC), widely known as a common cause of food poisoning, can lead to fatal thrombotic complications in some patients. While Shiga toxin, which induces vascular injury, has long been regarded as the main culprit, a Korean research team has now identified a toxin pathway that converts red blood cells themselves into a "procoagulant state," expanding our understanding of infection-associated thrombotic diseases.

The National Research Foundation of Korea announced that a joint research team led by Professor Jung Hanyoung of the College of Pharmacy at Chungnam National University and Professor Bae Oknam of the College of Pharmacy at Hanyang University has identified a new mechanism underlying thrombotic complications that occur during EHEC infection.

Schematic of the process by which erythrocytes are converted to a procoagulant state and venous thrombosis forms. When the RTX family toxin EhxA, secreted by enterohemorrhagic Escherichia coli (EHEC), forms pores in the erythrocyte membrane, Ca2+ influx increases, leading to exposure of the phospholipid phosphatidylserine (PS) on the erythrocyte surface. This process is accompanied by microvesicle formation and morphological changes of erythrocytes; PS-exposed erythrocytes display enhanced procoagulant activity, promoting thrombin generation and erythrocyte aggregation. When these responses accumulate, intravascular coagulation is amplified, potentially resulting in venous thrombosis. Figure legend and provided by: Jeong Hanyoung, Professor, College of Pharmacy, Chungnam National University

Thrombosis unexplained by Shiga toxin alone...focus on red blood cell changes

Although EHEC is a representative foodborne pathogen that causes severe bloody diarrhea and abdominal pain, in some patients it can progress to life-threatening complications such as hemolytic uremic syndrome (HUS) or thrombotic microangiopathy (TMA). Previous studies have focused on the pathway by which Shiga toxin damages the vascular endothelium, but this alone has been insufficient to explain all of the thrombotic responses observed in actual infected patients.

The research team focused on the possibility that thrombus formation is linked not only to vascular injury but also directly to changes in blood cells, particularly red blood cells. Under pathological conditions, red blood cells can expose the phospholipid phosphatidylserine (PS) on their surface and thereby amplify coagulation responses, but in the context of EHEC infection it had not been clearly identified which toxin induces this change.

RTX toxin EhxA turns red blood cells into a "thrombus generator"

The joint research team experimentally demonstrated that EhxA, an RTX (Repeats in ToXin) family toxin secreted by EHEC, forms pores in the red blood cell membrane, increasing calcium influx and thereby inducing exposure of phosphatidylserine (PS) on the red blood cell surface. Red blood cells with exposed PS promote thrombin generation and enhance red blood cell aggregation and adhesion to vascular endothelial cells, amplifying intravascular coagulation responses.

In this process, red blood cells undergo morphological changes from a disc shape to a spiculated and then spherical shape, and microvesicles are formed, effectively converting them into a "procoagulant state." In animal experiments, EHEC infection led to increased red blood cell alterations and venous thrombus formation, whereas infection with an EhxA-deficient strain resulted in concurrent reductions in red blood cell shape changes and thrombotic markers. This demonstrates that the RTX toxin EhxA-red blood cell pathway can be directly linked to in vivo thrombus formation.

This study is significant in that it moves beyond the conventional view of infectious thrombotic complications centered on the "Shiga toxin-vascular injury" axis and proposes a new axis of "RTX-family toxin (EhxA)-red blood cells-coagulation amplification." The researchers expect that these findings could be expanded into neutralization strategies targeting EhxA or RTX-family toxins, as well as into thrombotic risk assessment and response strategies that utilize cellular change markers such as red blood cell PS exposure.

This research was supported by the Individual Basic Research Program and the Medical Research Center (MRC) Program funded by the Ministry of Science and ICT and the National Research Foundation of Korea, and the results were published online in the international journal Science Advances on February 7.