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

Abstract

SummaryBlood-brain barrier (BBB) dysfunction complicates central nervous system 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 with controls. Immunostaining revealed a significant increase in caspase 3 expression in the brain vascular endothelial cells, which suggests 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 (HBMVECs), whereas 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 death-associated protein kinase 1, Fas-associated protein (FADD), cell death-inducing DNA fragmentation factor 45 000 MW subunit A-like effector B (CIDEB) and BCL2-associated X protein were increased in HBMVECs 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 signalling induces apoptosis through 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 the potential therapeutic effectiveness of C5aR1 inhibition that could prevent and/or reduce BBB alterations and preserve the physiological function of BBB in central nervous system lupus.

The blood brain barrier and neuropsychiatric lupus: new perspectives in light of advances in understanding the neuroimmune interface

“…One such product, C5a, not only induced disruption of an in-vitro model of an SLE BBB, but also induced caspase-mediated endothelial cell apoptosis in MRL/lpr mice [58, 59]. Additionally, antibody-antigen immune complexes may activate endothelial cells directly via NF-κB signaling, resulting in elevated cytokine and adhesion molecule expression [60], though their role in NPSLE has not been evaluated.…”

MicroRNA‐182 exacerbates blood‐brain barrier (BBB) disruption by downregulating the mTOR/FOXO1 pathway in cerebral ischemia

“…23 Inhibition of endothelial cell apoptosis and a reduction in TJ protein loss are considered important measures that protect BBB integrity in cerebral ischemic injury. 23,27 However, the relationship between miR-182, mTOR, and FOXO1, as well as the mechanism by which apoptosis and TJ protein expression are regulated, is unknown in the context of BBB permeability.…”

C5a anaphylatoxin and its role in critical illness‐induced organ dysfunction

“…84,90,109 In systemic lupus erythematosus models, C5a has been shown to induce apoptosis and reduce endothelial integrity. 110,111 Collectively, these data indicate C5a worsens cardiovascular dysfunction both through vascular leakage and pump failure, exacerbating refractory shock and tissue hypoperfusion. The effects of C5a on these key organ systems affected during critical illness are summarised in Figure 3.…”

“…With respect to the endothelium, C5a stimulates tissue factor and adhesion molecule expression with resulting disruption of the endothelial glycocalyx, leading to further DAMP release into the circulation . In systemic lupus erythematosus models, C5a has been shown to induce apoptosis and reduce endothelial integrity . Collectively, these data indicate C5a worsens cardiovascular dysfunction both through vascular leakage and pump failure, exacerbating refractory shock and tissue hypoperfusion.…”