Hand-foot-mouth disease (HFMD) is a common acute febrile and eruptive infectious disease caused by enterovirus and more common in children under 5 years old. Its main symptoms are blisters on the palms, soles of the feet, cheek mucosa, tongue, and buttocks (Zhang et al., 2022). Meanwhile, acute flaccid paralysis, myocarditis, pulmonary oedema, and encephalitis are common and severe clinical symptoms of HFMD. Enterovirus 71 (EV71), a single-stranded ribonucleic acid virus belonging to the small ribonucleic acid virus family, is one of the main pathogens causing HFMD in young children and leading to neurological syndrome (You et al., 2023). At present, there are no antiviral drugs available for treating EV71 infection, and existing EV71 vaccines have poor efficacy due to the production of viral mutants (Luo et al., 2019).

The blood-brain barrier (BBB) is a unique structure of capillaries in the brain, which composed of the end pods of vascular endothelial cells, pericytes, extracellular matrix, and astrocytes, acting as a barrier to prevent the entry of microorganisms, toxins, bioactive substances, and various solutes including drugs (Sweeney et al., 2019, Zhao et al., 2015). Recent studies have shown that the dysfunction or disruption of the BBB may be associated with various diseases, including cerebral infarction, bleeding, trauma, epilepsy, and neurodegenerative diseases (Ahmad et al., 2020). In addition, the disruption of the BBB has been linked to inflammation in the brain. Therefore, as an interface between inflammation and immune cells and brain parenchymal cells, the BBB plays a crucial role in regulating and maintaining the physiological structure and function of the brain. Recent studies showed that EV71 infection led to inflammation in the brain (Kadry et al., 2020). Therefore, it is important to explore the key role and regulatory mechanism of the BBB in the pathological progression of neuroinflammation in severe HFMD.

Astrocytes, coupled with blood vessels, regulated brain blood flow and BBB stability to support neural transmission and maintain neuronal physiological function, playing a crucial role in supporting neural structure and immune regulation (Huang et al., 2020, Schaeffer and Iadecola, 2021). Under normal physiological conditions, astrocytes alter the transport of endothelial cells across the BBB by regulating the expression of tight junction proteins through cell-cell interactions. Compared with endothelial cells cultured alone, endothelial cells co-cultured with astrocytes showed increased expression of tight junction proteins and transporters in the nucleus (Michinaga and Koyama, 2019). In addition, stress conditions can cause astrocytes to undergo reversible changes to form glial scars, and alter astrocyte morphology, physiological characteristics, function, and the response to injury and disease (Batiuk et al., 2020). Recent studies showed that the astrocyte dysfunction was associated with most neurological and psychiatric disorders (Brandebura et al., 2023). However, there is little research providing evidence on the correlation between EV71 infection and astrocyte dysfunction, currently.

High mobility group protein B1 (HMGB1) is widely present in the nucleus and plays multiple roles in transcription, replication and cell differentiation (Qu et al., 2018). As a DNA-binding protein, HMGB1 is involved in maintaining nuclear homeostasis, regulating mitochondrial function and inducing inflammation alone or in association with endogenous or exogenous pathogen molecular patterns (Nishibori et al., 2020). Emerging evidence suggests that HMGB1 is actively released by immunocompetent cells or necrotic cells to respond to stressors (Ding et al., 2021). In cells that die of necrosis or injury, HMGB1 is passively released from the nucleus into the extracellular environment (Matsuoka et al., 2010). In addition, HMGB1 activation can regulate immune response by binding to Toll like receptor 4, thereby upregulating inflammatory cytokine (Lei et al., 2022). Based on the above mechanism of action, it has been reported that HMGB1 is involved in various pathological processes, including the formation of encephalitis and intestinal inflammation caused by viral infections (Hu et al., 2023). Importantly, HMGB1 was found to be upregulated in patients with hand, foot and mouth disease and increased with increasing clinical severity (Zheng et al., 2017). However, it is currently unclear whether HMGB1 is associated with the malignant characterization of HFMD and whether it plays a key regulatory role in the process of brain lesions caused by EV71 infection.

The purpose of this study is to investigate the regulatory role of HMGB1 in the pathological process of neuroinflammation in HFMD patients caused by EV71 infection, to analyze the role of HMGB1 in regulating the activation of EV71-induced astrocytes and to further explore the regulatory mechanism of HMGB1 in BBB dysregulation.