C5a induces caspase‐dependent apoptosis in brain vascular endothelial cells in experimental lupus

Supriya D Mahajan, Vincent M Tutino, Yonas Redae, Hui Meng, Adnan Siddiqui, Trent M Woodruff, James N Jarvis, Teresa Hennon, Stanley Schwartz, Richard J Quigg, Jessy J Alexander

Blood-brain barrier (BBB) dysfunction complicates CNS lupus, an important aspect of systemic lupus erythematosus. To gain insight into the underlying mechanism, vascular corrosion casts of brain were generated from the lupus mouse model, MRL/lpr mice and the MRL/MPJ congenic controls. Scanning electron microscopy of the casts showed loss of vascular endothelial cells in lupus mice compared to controls. Immunostaining revealed significant increase in caspase-3 expression in the brain vascular endothelial cells, which suggest that apoptosis could be an important mechanism causing cell loss, and thereby loss of BBB integrity. Complement activation occurs in lupus resulting in increased generation of circulating C5a, which caused the endothelial layer to become 'leaky'. In this study, we show that C5a and lupus serum induced apoptosis in cultured human brain microvascular endothelial cells (HBMVEC), while selective C5a receptor 1 (C5aR1) antagonist reduced apoptosis in these cells, demonstrating C5a/C5aR1-dependence. Gene expression of initiator caspases, caspase 1 and caspase 8, and proapoptotic proteins DAPK1, FADD, Cell death-inducing DFFA-like effector B (CIDEB) and BAX were increased in HBMVEC cells treated with lupus serum or C5a, indicating that both the intrinsic and extrinsic apoptotic pathways could be critical mediators of brain endothelial cell apoptosis in this setting. Overall, our findings suggest that C5a/C5aR1 signaling induces apoptosis via activation of FADD, caspase 8/3 and CIDEB in brain endothelial cells in lupus. Further elucidation of the underlying apoptotic mechanisms mediating the reduced endothelial cell number is important in establishing potential therapeutic effectiveness of C5aR1 inhibition that could prevent and/or reduce BBB alterations and preserve its physiological function in CNS lupus. This article is protected by copyright. All rights reserved.