IL-18 inhibition enlarges lesions, necrotic cores and thickens fibrous caps in clonal hematopoiesis-driven atherosclerosis.

BACKGROUND

Inflammasome activation promotes atherosclerosis in clonal hematopoiesis (CH). Active inflammasomes secrete both IL-1β and IL-18. Plasma IL-18 levels are elevated in CH. Genetic deficiency of IL-18 has been shown to reduce atherosclerosis in non-CH murine models. However, whether IL-18 inhibition promotes atherosclerosis in control or CH is unknown.

METHODS AND RESULTS

mice were transplanted with bone marrow (BM) from (20%) and wild-type (80%) mice or with control BM, fed a Western-type diet (WTD) for 8, 10 or 16 weeks and administered control or IL-18 IgG from 4 weeks onwards. IL-18 antibody treatment increased plaque collagen content and cap thickness. Unexpectedly, IL-18 antibody treatment increased the size of early lesions and promoted formation of advanced lesions with large necrotic cores in CH mice. IL-18 antibody treatment was associated with diminished interferon (IFN)-γ and AIM2 levels and reduced macrophage pyroptosis especially in CH mice. However, IL-18 antibodies increased cleaved Caspase-3 and TUNEL macrophages (indicating increased apoptosis) and reduced efferocytosis. Sc-RNA-seq analysis showed that IL-18 antibody treatment reduced expression of genes, a marker of IFN-γ signaling, and of genes mediating efferocytosis ( , in resident-like macrophage subpopulations in CH mice. Consistently, IFN-γ injection increased and expression in resident peritoneal macrophages.

CONCLUSIONS

Despite improvements in collagen and fibrous cap thickness in CH mice, IL-18 antibody treatment increased advanced necrotic lesions, reflecting a shift from pyroptotic to apoptotic cell death coupled with defective efferocytosis, events which were coordinated by reduced IFN-γ signaling. These findings indicate a mixed atherosclerosis phenotype resulting from IL-18 inhibition, advocating for alternative therapeutic strategies. Inhibition of IL-18 has been considered as a novel therapeutic approach to reduce atherosclerosis and stabilize atherosclerotic plaques. We show that IL-18 antibodies have adverse effects on atherosclerotic lesional necrosis, calling this approach into question.

HIGHLIGHTS

Inflammasome activation produces active IL-1 and IL-18 and worsens atherosclerosis in clonal hematopoiesis (CH) however the contribution of IL-18 is unknown. Antibody inhibition of IL-18 increased plaque collagen but also increased early lesion area and late lesions with large necrotic cores in CH mice. There was a reversal of AIM2 inflammasome activation but a switch to apoptosis which along with reduced efferocytosis increased necrosisThese events appeared to be coordinated by reduced IFN-γ which increased collagen but also decreased expression of efferocytotic genes. Our studies call into question whether inhibition of IL-18 would stabilize plaques in CH.