Alternate high fat diet aggravates atherosclerosis through an IL1b-dependent reprogramming of neutrophil progenitors
Systemic immune responses induced by chronic hypercholesterolemia contribute to the initiation, progression and complications of atherosclerosis. However, the consequences of an alternate high fat diet and the associated variations in plasma cholesterol levels on atherosclerosis are unknown. To address this relevant issue concerning common situations where dietary habits change over time, we developed a novel protocol in athero-prone mice that allowed us to compare the effects of alternate versus continuous high fat diet (HFD) on atherosclerosis, the overall period of time of exposure to HFD being similar between groups. We showed that alternate HFD lead to accelerated atherosclerosis in Ldlr-/-  and Apoe-/- mice compared to continuous HFD. The pro-atherogenic effect of alternate HFD was also found in Apoe-/-Rag2-/- mice lacking T, B, and NKT cells, ruling out a role for the adaptive immune system in the observed phenotype. Using different complementary in vivo approaches, we found that lipid-rich diet discontinuation in alternate group downregulated Runx1, a negative regulator downstream of TLR-4 pathways. As a result, after re-exposure to HFD, myeloid progenitors were more sensitive to hypercholesterolemia leading to acute differentiation into IL-1b- producing immature neutrophils, which caused a state of emergency myelopoiesis. Consecutively, neutrophils markedly increased in the peripheral blood, infiltrated atherosclerotic lesions and locally released neutrophil extracellular traps. Anti-Ly6G neutrophil depletion abolished the pro-atherogenic effects of alternate HFD. Specific deletion of Il1b and Il1b receptor confirmed that the IL-1b signaling pathway was a major driver of the pro-inflammatory and pro-atherogenic neutrophil signature. Finally, treatment with anti-IL-1b neutralizing antibody or inflammasome inhibitor during re-exposure to HFD reversed the pro-atherogenic effects of alternate HFD. In summary, we showed that alternate HFD accelerates atherosclerosis through IL-1b-dependent neutrophil progenitor reprogramming. Overall design: Lin- cells from femur bones of HFD exposed and non-exposed Ldlr-/- mice were dissected and single cell RNA Seq libraries were prepared with ParseBio Evercode WT Mega v2 kit.