The T6SS Effector Hcp of Hypervirulent Klebsiella pneumoniae Exacerbates Liver Abscess by Inducing Macrophage-HMGB1/RAGE-Dependent Endothelial Pyroptosis.

Objectives

Hypervirulent Klebsiella pneumoniae (hvKP) causes pyogenic liver abscess and fulminant sepsis via vascular endothelial dysfunction and injury. This study aimed to elucidate how its type VI secretion system (T6SS) effector hemolysin-coregulated protein (Hcp) compromises vascular integrity by inducing endothelial pyroptosis.

Methods

We stimulated macrophages with Hcp or hvKP strains (wild-type/ hcp-knockout/ complemented), then applied supernatants to human umbilical vein endothelial cells (HUVECs) to evaluate pyroptosis, cytokine release, and endothelial activation. Mechanistic validation studies employed high-mobility group box 1 (HMGB1)⁻/⁻ macrophages, caspase-1-knockdown (KD) HUVECs, and pharmacological inhibitors, including a receptor for advanced glycation end products (RAGE) inhibitor (FPS-ZM1) and an HMGB1-neutralizing antibody. A murine hvKP liver abscess model assessed survival, HMGB1 dynamics, and vascular pathology.

Results

Hcp stimulated macrophage HMGB1 secretion. The resulting Hcp-HMGB1 complexes were internalized by HUVECs via RAGE, thereby inducing pyroptosis and the release of interleukin (IL)-1β and IL-18 consistent with the canonical pyroptotic pathway. These effects were abolished by HMGB1 knockout, caspase-1 KD, or RAGE inhibition. Additionally, Hcp upregulated endothelial activation markers in an HMGB1-dependent manner. Mice infected with hcp-knockout hvKP showed improved survival rates, lower serum HMGB1 levels, and reduced endothelial injury.

Conclusions

Thus, the T6SS effector Hcp drives endothelial pyroptosis through macrophage-derived HMGB1- and RAGE-mediated signaling, establishing the Hcp-HMGB1-RAGE-caspase-1 axis as a promising therapeutic target for hvKP-associated endothelial dysfunction.