Interleukin-1β suppression dampens inflammatory leukocyte production and uptake in atherosclerosis.

Abstract

Aims
Targeting vascular inflammation represents a novel therapeutic approach to reduce complications of atherosclerosis. Neutralizing the pro-inflammatory cytokine interleukin-1β (IL-1β) using canakinumab, a monoclonal antibody, reduces the incidence of cardiovascular events in patients after myocardial infarction (MI). The biological basis for these beneficial effects remains incompletely understood. We sought to explore the mechanisms of IL-1β-targeted therapies.

Methods and Results
In mice with early atherosclerosis (ApoE-/- mice on a high-cholesterol diet for six weeks), we found that three weeks of NLRP3-inflammasome inhibition or anti-IL-1β treatment (using either MCC950, an NLRP3 inflammasome inhibitor which blocks production and release of active IL-1β; or a murine analog of canakinumab) dampened accumulation of leukocytes in atherosclerotic aortas, which consequently resulted in slower progression of atherosclerosis. Causally, we found that endothelial cells from atherosclerotic aortas lowered expression of leukocyte chemoattractants and adhesion molecules upon NLRP3-inflammasome inhibition, indicating that NLRP3-inflammasome- and IL-1β-targeted therapies reduced blood leukocyte recruitment to atherosclerotic aortas. In accord, adoptive transfer experiments revealed that anti-IL-1β treatment mitigated blood myeloid cell uptake to atherosclerotic aortas. We further report that anti-IL-1β treatment and NLRP3-inflammasome inhibition reduced inflammatory leukocyte supply by decreasing proliferation of bone marrow hematopoietic stem and progenitor cells, demonstrating that suppression of IL-1β and the NLRP3-inflammasome lowered production of disease-propagating leukocytes. Using bone marrow reconstitution experiments, we observed that hematopoietic cell-specific NLRP3-inflammasome activity contributed to both enhanced recruitment and increased supply of blood inflammatory leukocytes. Further experiments that queried whether anti-IL-1β treatment reduced vascular inflammation also in post-MI accelerated atherosclerosis documented the operation of convergent mechanisms (reduced supply and uptake of inflammatory leukocytes). In line with our pre-clinical findings, post-MI patients on canakinumab treatment showed reduced blood monocyte numbers.

Conclusions
Our murine and human data reveal that anti-IL-1β treatment and NLRP3-inflammasome inhibition dampened vascular inflammation and progression of atherosclerosis through reduced blood inflammatory leukocyte 1) supply and 2) uptake into atherosclerotic aortas providing additional mechanistic insights into links between hematopoiesis and atherogenesis, and into the beneficial effects of NLRP3-inflammasome- and IL-1β-targeted therapies.

Translational perspective
Therapeutic targeting of vascular inflammation represents a promising avenue to reduce complications of atherosclerosis. Neutralizing the pro-inflammatory cytokine interleukin-1β (IL-1β) reduces the incidence of cardiovascular events in patients with prior myocardial infarction. However, the mechanisms underlying these beneficial effects remain incompletely understood. This study explored how IL-1β and NLRP3-inflammasome suppression mitigated plaque progression. Our murine and human data reveal that pharmacological anti-IL-1β treatment and NLRP3-inflammasome inhibition dampened inflammatory leukocyte accumulation in atherosclerotic aortas through 1) decreased blood inflammatory leukocyte supply and 2) reduced blood inflammatory leukocyte uptake into in atherosclerotic aortas. These data provide additional mechanistic insights into links between hematopoiesis and atherogenesis, and inform future anti-inflammatory interventions in patients with atherosclerosis.