CD36 coordinates NLRP3 inflammasome activation by facilitating intracellular nucleation of soluble ligands into particulate ligands in sterile inflammation

Abstract

Particulate ligands including cholesterol crystals and amyloid fibrils induce NLRP3-dependent production of interleukin-1β (IL-1β) in atherosclerosis, Alzheimer's disease and diabetes. Soluble endogenous ligands including oxidized-LDL, amyloid-β and amylin peptides accumulate in these diseases. Here we identify a CD36-mediated endocytic pathway that coordinates the intracellular conversion of these soluble ligands to crystals or fibrils, resulting in lysosomal disruption and NLRP3-inflammasome activation. Consequently, macrophages lacking CD36 failed to elicit IL-1β production in response to these ligands and targeting CD36 in atherosclerotic mice reduced serum IL-1β and plaque cholesterol crystal accumulation. Collectively, these findings highlight the importance of CD36 in the accrual and nucleation of NLRP3 ligands from within the macrophage and position CD36 as a central regulator of inflammasome activation in sterile inflammation.

IAPP and type 1 diabetes: implications for immunity, metabolism and islet transplants

“…After 6 h of incubation, IAPP immunoreactivity can be found loosely packed in phagosome-like organelles, and from 24 to 72 h, IAPP-reactive fibrils accumulate in dense lysosome-like organelles. This timeline is consistent with that of IL1B release in hIAPP-treated cells: secretion of IL1B in unprimed or LPS-primed macrophages appears after approximately 6 h of incubation and continues thereafter (Masters et al 2010, Sheedy et al 2013, Westwell-Roper et al 2016. The requirement for longer incubation for maximal IL1B secretion indicates that the process of NLRP3 activation by hIAPP aggregates is different from that of ligands like ATP, which activate the inflammasome more rapidly.…”

“…The lack of any inflammatory action of rIAPP in these studies clearly shows that macrophage recruitment and activation is a property of IAPP aggregates rather than a biological activity of IAPP monomers. Consistent with this, application of the amyloid-binding dye Congo Red prevents hIAPP-induced inflammasome activation in BMDMs (Sheedy et al 2013), likely by either inhibiting hIAPP aggregation or possibly binding to and rendering aggregates non-toxic. Likewise, Congo Red reduced IL1B levels in cultured human islets .…”

“…Deletion of either Nlrp3 or Casp1 abrogates hIAPP-induced IL1B secretion in cells, regardless of whether they are first primed with LPS or hIAPP aggregates (Masters et al 2010, Sheedy et al 2013, Westwell-Roper et al 2016. Furthermore, pharmacological inhibition of NLRP3 with glyburide inhibited hIAPP-induced IL1B secretion (Masters et al 2010, Westwell-Roper et al 2011.…”

“…Though the mechanism of NLRP3 activation by hIAPP has not been fully elucidated, phagocytosis of hIAPP aggregates and accumulation of hIAPP fibrils within the phagolysosome system appear to play a critical role. Accumulation of IAPP immunoreactivity in macrophages occurs through a phagocytosis-dependent pathway (Badman et al 1998), and IL1B release is attenuated by inhibition of phagocytosis with cytochalasin D (Masters et al 2010, Westwell-Roper et al 2011, Sheedy et al 2013). Extracellularly applied hIAPP appears intracellularly in cultured macrophages as early as 1 h following incubation and continues to increase up to 6 h, with IAPP co-localizing with macrosialin, a late endosome/lysosome marker (Badman et al 1998).…”

“…IAPP has been reported to be an autoantigen in both T1D and the non-obese diabetic (NOD) mouse model of spontaneous autoimmune diabetes (Panagiotopoulos et al 2003, Delong et al 2011, Baker et al 2013, Wiles et al 2017. In addition, recent evidence has established IAPP aggregates as strong proinflammatory stimuli that elicit interleukin-1B (IL1B) secretion from innate immune cells (Masters et al 2010, Westwell-Roper et al 2011, Sheedy et al 2013. Intriguingly, islet amyloid forms rapidly in islets transplanted into T1D recipients and likely plays a role in islet graft inflammation and dysfunction (Andersson et al 2008, Udayasankar et al 2009, Potter et al 2010, Westwell-Roper et al 2011.…”