Abstract
Heme, released from red blood cells in sickle cell disease (SCD), interacts with toll-like receptor 4 (TLR4) to activate NF-κB leading to the production of cytokines and adhesion molecules which promote inflammation, pain, and vaso-occlusion. In SCD, TLR4 inhibition has been shown to modulate heme-induced microvascular stasis and lung injury. We sought to delineate the role of endothelial verses hematopoietic TLR4 in SCD by developing a TLR4 null transgenic sickle mouse. We bred a global Tlr4-/- deficiency state into Townes-AA mice expressing normal human adult hemoglobin A and Townes-SS mice expressing sickle hemoglobin S. SS-Tlr4-/- had similar complete blood counts and serum chemistries as SS-Tlr4+/+ mice. However, SS-Tlr4-/- mice developed significantly less microvascular stasis in dorsal skin fold chambers than SS-Tlr4+/+ mice in response to challenges with heme, lipopolysaccharide (LPS), and hypoxia/reoxygenation (H/R). To define a potential mechanism for decreased microvascular stasis in SS-Tlr4-/- mice, we measured pro-inflammatory NF-κB and adhesion molecules in livers post-heme challenge. Compared to heme-challenged SS-Tlr4+/+ livers, SS-Tlr4-/- livers had lower adhesion molecule and cytokine mRNAs, NF-κB phospho-p65, and adhesion molecule protein expression. Furthermore, lung P-selectin and von Willebrand factor immunostaining was reduced. Next, to establish if endothelial or hematopoietic cell TLR4 signaling is critical to vaso-occlusive physiology, we created chimeric mice by transplanting SS-Tlr4-/- or SS-Tlr4+/+ bone marrow into AA-Tlr4-/- or AA-Tlr4+/+ recipients. Hemin-stimulated microvascular stasis was significantly decreased when the recipient was AA-Tlr4-/-. These data demonstrate that endothelial, but not hematopoietic, TLR4 expression is necessary to initiate vaso-occlusive physiology in SS mice.
Original language | English (US) |
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Article number | 613278 |
Journal | Frontiers in immunology |
Volume | 11 |
DOIs | |
State | Published - Jan 19 2021 |
Bibliographical note
Funding Information:Conflict of Interest: JBec receives funding from Bayer not related to work herein. JBel and GV receive research funding from CSL Behring and Mitobridge (Astellas).
Funding Information:
The authors would like to thank Elena Aronovich, Jacob Lloyd, and Kristine Nachbor for assistance with laboratory work.
Funding Information:
Research funding from NIH 5R01HL114567. ZK was supported by the Hematology Research Training Grant T32 L007062/HL/ NHLBI. RK and DR-R received funding from University of Minnesota Life Sciences Undergraduate Research Program (LSSURP) 5R25HL088728-14.
Publisher Copyright:
© Copyright © 2021 Beckman, Abdullah, Chen, Kirchner, Rivera-Rodriguez, Kiser, Nguyen, Zhang, Nguyen, Hebbel, Belcher and Vercellotti.
Keywords
- Toll-like receptor 4
- endothelium
- heme
- sickle cell disease
- vaso-occlusive events