How Enterovirus A71 Breaches the Blood-Brain Barrier in Hand, Foot, and Mouth Disease

Researchers in China have discovered how the enterovirus A71 pathogen breaches the blood-brain barrier during severe cases of hand, foot, and mouth disease, using tiny cellular packages to weaken blood vessels from a distance. The study, published in Nature Communications, shows that infected cells release extracellular vesicles filled with specific microRNAs that travel through the bloodstream to loosen tight junctions in cerebral blood vessels.

Cellular Vesicles Disrupt Brain Protection Mechanisms

Hand, foot, and mouth disease is a common childhood illness that usually causes mild fever, mouth sores, and a rash on the hands and feet before resolving within days. In rare instances involving enterovirus A71, however, the pathogen can trigger meningitis or encephalitis. A collaborative team from Jinan University in Guangzhou, Guangzhou Medical University, and Zhengzhou University investigated how the virus crosses the dense barrier of endothelial cells lining the brain’s microvessels without directly infecting them at first.

The research team observed that cells infected with enterovirus A71 produce significantly higher amounts of extracellular vesicles than healthy cells. These membrane-bound packets act as a cellular postal system, carrying genetic material between cells. Inside the vesicles from infected cells, the scientists identified elevated concentrations of microRNAs miR-30 and miR-34. When these vesicles reach the brain’s blood vessels, they release their cargo, which suppresses a protein switch called Notch1 that is required to maintain tight cell-to-cell connections.

Laboratory Tests and Animal Model Findings

To test this mechanism, the investigators constructed an in vitro model of the human blood-brain barrier using cerebral vessel cells. Introducing vesicles from infected cells reduced the barrier’s density and allowed a test dye to pass through more easily. Supplying only the miR-30 and miR-34 microRNAs produced the same weakening effect, whereas artificially stimulating the Notch1 signal with the messenger substance JAG1 restored the barrier tightness.

Newborn mice infected with enterovirus A71 demonstrated the same pathway, as the pathogen penetrated the brain while the barrier became permeable. Activating the Notch1 signal with JAG1 kept the protective wall tighter and reduced the amount of virus entering the brain. The treatment did not alter the viral load in the gut, indicating that the substance stabilized the vascular barrier rather than acting as a direct antiviral agent.

Clinical Blood Samples Reveal Biomarker Potential

To evaluate relevance in humans, the researchers examined blood serum samples from 68 pediatric patients at a children’s hospital in Zhengzhou. The cohort included 24 healthy children, 23 patients with mild illness, and 21 patients with severe disease, nearly half of whom suffered from encephalitis. The circulating vesicles of the severely ill children showed markedly elevated levels of microRNAs miR-30 and miR-34.

Remaining Uncertainties and Clinical Outlook

The study authors noted clear boundaries to their findings, pointing out that the laboratory barrier model utilized a single layer of vessel cells and that the animal trials involved newborn mice with developing nervous systems. Furthermore, the human data relied on a relatively small group of blood samples, and no treatment was tested. The identified microRNA elevation points to an association with severe progression rather than a definitive sole cause, though the laboratory and animal data independently support the mechanism.

The findings point toward two potential applications for future medical management. The vesicle microRNAs miR-30 and miR-34 could serve as biomarkers to identify patients at risk for severe neurological complications before symptoms appear. Additionally, the Notch1 signaling pathway provides a potential target for stabilizing the blood-brain barrier when central nervous system involvement threatens.