RfeA from Streptococcus suis serotype 2 triggers NLRP3/Caspase-1-dependent pyroptosis leading to blood-brain barrier disruption.

Streptococcus suis serotype 2 (SS2) is a prominent pathogen that impacts swine and presents a zoonotic threat to humans; it is a cause of bacterial meningitis, a severe condition linked to neurological impairment and elevated mortality rates. For SS2 to access the central nervous system, it must traverse the blood-brain barrier (BBB); however, the precise mechanisms underlying this process remain incompletely elucidated. In this study, we demonstrate that the RTX family exoprotein A (RfeA), which is secreted by SS2, can be internalized by human brain microvascular endothelial cells (hBMECs) via a caveolae/lipid raft-dependent pathway. RfeA subsequently induces pyroptosis through the NLRP3/Caspase-1 pathway, a process attributed to the increase in mitochondrial reactive oxygen species (mtROS). The interaction between the N-terminus of RfeA and voltage-dependent anion channel 1 (VDAC1) leads to mtROS production, which can be suppressed by a VDAC1 oligomerization inhibitor. RfeA-induced pyroptosis results in disruption of the BBB in both the hBMEC monolayer model and the mouse infection model, thereby promoting bacterial infection of the brain. These findings elucidate a novel mechanism by which SS2 induces pyroptosis to breach the BBB, suggesting a potential target for the prevention and treatment of SS2 infection.