Receptor-Independent, Direct Membrane Binding Leads to Cell-Surface Lipid Sorting and Syk Kinase Activation in Dendritic Cells

Abstract

Summary Binding of particulate antigens by antigen presenting cells (APC) is a critical step in immune activation. Previously, we demonstrated that uric acid crystals are potent adjuvants, initiating a robust adaptive immune response. However, the mechanisms of activation are unknown. Using atomic force microscopy as a tool for real time single cell activation analysis, we report that uric acid crystals can directly engage cellular membranes, particularly the cholesterol components, with a force substantially stronger than protein based cellular contacts. Binding of particulate substances activates Syk kinase-dependent signaling in dendritic cells (DCs). These observations suggest a mechanism whereby immune cell activation can be triggered by solid structures via membrane lipid alteration without the requirement for specific cell surface receptors, and a testable hypothesis for crystal-associated arthropathies, inflammation and adjuvanticity.

Impact of obesity and hypertriglyceridemia on gout development with or without hyperuricemia: A prospective study

“…An enhanced triglyceride lipolysis in adipose tissue is speculated to potentiate a gout event because engagement of fatty acids has been demonstrated in MSU crystal-induced gouty arthritis (9). Lipid sorting and engagement along with MSU crystals on the cell surface of dendritic cells or macrophages may trigger inflammation (23). Extracellular ATP, one of the danger signals released from adipose tissue, can also trigger inflammasome in gouty arthritis (20).…”

NLRP3 inflammasome–mediated neutrophil recruitment and hypernociception depend on leukotriene B4 in a murine model of gout

“…The amount of endotoxin present in the MSU crystals injected was Ͻ5 pg (at the higher dose), as assessed using a Chromogenic Limulus amebocyte lysate assay (Endosafe). Inflammation parameters were evaluated at different time points after injection of the MSU crystals (1,3,6,15, and 24 hours after injection), and mechanical hypernociception was also evaluated at various time points after injection.…”

Inflammasome components Asc and caspase-1 mediate biomaterial-induced inflammation and foreign body response

“…After 60 min, media were removed and replaced with warm fresh media and incubated overnight at 37°C. AFM was performed as described previously except for increasing hold time to 10 s in relative intermittent contact mode in a temperature (37°C)-and CO 2 (5%)-controlled humidified chamber (17). Force curves were obtained over 300 s and analyzed using JPK image processing software.…”

“…2A). Inflammasome activation can also occur by membrane affinity triggered signaling (MATS), which involves clustering of lipid rafts at the site of contact, resulting in nonspecific cytosolic aggregation of immunoreceptor tyrosine-based activation motif (ITAM) signaling domains and activation of a Syk kinase pathway (17). The involvement of this mechanism can be examined by depleting plasma cholesterol with methyl-β-cyclodextrin (MβCD) or by inhibiting Syk activation with piceatannol.…”

“…This mechanism depends on reorganization of cholesterol rafts by interaction of the particulate matter with the plasma membrane, resulting in Syk activation. The presence of an inflammasome-activating pathway independent of phagocytosis prompted us to test the ability of biomaterials to activate the inflammasome (17). In addition, we investigated the dependence of the FBR on individual components of the inflammasome.…”