Streptococcus suis-induced mitophagy via Eno-HSP90AA1 interaction disrupts the blood–brain barrier

Streptococcus suis serotype 2 (SS2), a zoonotic pathogen associated with meningitis in humans and pigs, disrupts the blood-brain barrier (BBB) during infection, but underlying mechanisms remain inadequately elucidated. This study demonstrated that SS2 infection induced mitophagy in human brain microvascular endothelial cells (hBMECs), with Eno (Enolase) identified as the key bacterial protein responsible for the activation of PINK1-Parkin pathway. Using Co-immunoprecipitation, mass spectrometry, and confocal microscopy, we identified that Eno interacted with the host molecular chaperone HSP90AA1 via its N-terminal domain, necessitating the integrity of the second α-helix (residues 87-98). The interaction between Eno and HSP90AA1 may promote mitochondrial proteotoxic stress and misfolded protein accumulation, thereby contributing to mitophagy induction, while the loss of mitochondrial membrane potential (MMP) alone is insufficient to initiate this process. Importantly, Eno-induced mitophagy did not result in cell death but instead led to the degradation of the tight junction protein claudin-5 (CLDN5), thus compromising BBB integrity. Both in vitro BBB models and in vivo mouse infection studies substantiated the involvement of Eno-induced mitophagy in BBB disruption. These findings reveal a novel mechanism whereby SS2 Eno exploits host HSP90AA1 to activate mitophagy, triggering the degradation of CLDN5 to breach the BBB. This study provides new insights into SS2 pathogenesis and identifies the Eno-HSP90AA1-mitophagy axis as a potential therapeutic target for preventing bacterial meningitis.