Format

Send to:

Choose Destination
See comment in PubMed Commons below
Blood. 2014 Jan 16;123(3):377-90. doi: 10.1182/blood-2013-04-495887. Epub 2013 Nov 25.

Heme triggers TLR4 signaling leading to endothelial cell activation and vaso-occlusion in murine sickle cell disease.

Author information

  • 1Division of Hematology, Oncology and Transplantation, Vascular Biology Center, University of Minnesota, Minneapolis, MN;

Abstract

Treatment of sickle cell disease (SCD) is hampered by incomplete understanding of pathways linking hemolysis to vaso-occlusion. We investigated these pathways in transgenic sickle mice. Infusion of hemoglobin or heme triggered vaso-occlusion in sickle, but not normal, mice. Methemoglobin, but not heme-stabilized cyanomethemoglobin, induced vaso-occlusion, indicating heme liberation is necessary. In corroboration, hemoglobin-induced vaso-occlusion was blocked by the methemoglobin reducing agent methylene blue, haptoglobin, or the heme-binding protein hemopexin. Untreated HbSS mice, but not HbAA mice, exhibited ∼10% vaso-occlusion in steady state that was inhibited by haptoglobin or hemopexin infusion. Antibody blockade of adhesion molecules P-selectin, von Willebrand factor (VWF), E-selectin, vascular cell adhesion molecule 1, intercellular adhesion molecule 1, platelet endothelial cell (EC) adhesion molecule 1, α4β1, or αVβ3 integrin prevented vaso-occlusion. Heme rapidly (5 minutes) mobilized Weibel-Palade body (WPB) P-selectin and VWF onto EC and vessel wall surfaces and activated EC nuclear factor κB (NF-κB). This was mediated by TLR4 as TAK-242 blocked WPB degranulation, NF-κB activation, vaso-occlusion, leukocyte rolling/adhesion, and heme lethality. TLR4(-/-) mice transplanted with TLR4(+/+) sickle bone marrow exhibited no heme-induced vaso-occlusion. The TLR4 agonist lipopolysaccharide (LPS) activated ECs and triggered vaso-occlusion that was inhibited by TAK-242, linking hemolysis- and infection-induced vaso-occlusive crises to TLR4 signaling. Heme and LPS failed to activate VWF and NF-κB in TLR4(-/-) ECs. Anti-LPS immunoglobulin G blocked LPS-induced, but not heme-induced, vaso-occlusion, illustrating LPS-independent TLR4 signaling by heme. Inhibition of protein kinase C, NADPH oxidase, or antioxidant treatment blocked heme-mediated stasis, WPB degranulation, and oxidant production. We conclude that intravascular hemolysis in SCD releases heme that activates endothelial TLR4 signaling leading to WPB degranulation, NF-κB activation, and vaso-occlusion.

PMID:
24277079
[PubMed - indexed for MEDLINE]
PMCID:
PMC3894494
Free PMC Article
PubMed Commons home

PubMed Commons

0 comments
How to join PubMed Commons

    Supplemental Content

    Full text links

    Icon for HighWire Icon for PubMed Central
    Loading ...
    Write to the Help Desk