Platelet-derived LTB4 mediates neutrophil recruitment

Introduction Leukotriene B4 (LTB4) is a pro-inflammatory lipid mediator derived from arachidonic acid. It is synthesized via the 5-lipoxygenase pathway by the leukotriene A4 hydrolase (Lta4h) [1]. It is primarily secreted by neutrophils and acts as a chemoattractant, drawing more neutrophils to the area by inducing and arresting neutrophil swarming. Additionally, LTB4 triggers accompanying inflammatory responses such as reactive oxygen species production and the formation of neutrophil extracellular traps [1] [2]. Recently, lipidome analyses identified platelets as a potential source of LTB4, suggesting that this might be a mechanism by which activated platelets directly recruit immune cells to sites of injury and drive inflammation [3]

The aim of this study is to investigate the relevance of LTB4 for platelet activation, hemostasis and neutrophil recruitment.

Method Lta4h-deficient mice (Lta4h ^-/-), which are unable to form LTB4, were generated and changes in the platelet lipidome were measured by liquid chromatography tandem mass spectrometry (LC-MS/MS). Lta4h ^-/- platelet function was assessed by standard in-vitro assays, and an in vivo tail bleeding time assay. The in-vivo effects of platelet-derived LTB4 on neutrophil recruitment to sites of endothelial damage were studied in different models of sterile inflammation in the liver and the cremaster muscle using intravital microscopy.

Fig. 1 Platelet-derived LTB4 mediates neutrophil recruitment; Endothelial damage leads to the adhesion and activation of platelets. Activated platelets secrete LTB4 and attract nearby neutrophils, which in turn release LTB4, leading to the further recruitment of neutrophils. Created with BioRender.com.

Results Lta4h ^-/-mice show unaltered blood parameters. LC-MS/MS confirms the lack of LTB4 in the supernatant of activated Lta4h ^-/- platelets. Injection of the supernatant of stimulated wildtype platelets but not of Lta4h ^-/- platelets leads to strong recruitment and extravasation of neutrophils in the cremaster muscle. Intravital microscopy shows that neutrophil infiltration in the liver following ischemia reperfusion injury or hot needle injury is significantly reduced, both in the full knockout and after Lta4h ^-/-platelet transfer into previously platelet-depleted animals. Notably, platelet function in classical platelet function tests and the tail bleeding time are not affected by the absence of platelet-derived LTB4 ([Fig. 1]).

Conclusion Our study demonstrates for the first time that platelets secrete LTB4 to directly recruit neutrophils to sites of endothelial damage, making it a potent and previously unknown driver of thrombo-inflammation.

Publikationsverlauf

Artikel online veröffentlicht:
26. Februar 2024

• References

• 1 Nakamura M, Shimizu T. ‘Therapeutic target of leukotriene B4 receptors, BLT1 and BLT2: Insights from basic research’. Biochimie. Epub ahead of print 2023
• 2 Lämmermann T. et al ‘Neutrophil swarms require LTB4 and integrins at sites of cell death. in vivo’ , Nature 2013; 498: 371-375
• 3 Peng B. et al ‘Identification of key lipids critical for platelet activation by comprehensive analysis of the platelet lipidome’. Blood 2018; 132 (05) e1-e12