LDL delivery of microbial small RNAs drives atherosclerosis through macrophage TLR8

Abstract

Macrophages present a spectrum of phenotypes that mediate both the pathogenesis and resolution of atherosclerotic lesions. Inflammatory macrophage phenotypes are pro-atherogenic, but the natural factors that instigate this polarization are largely unknown. Here, we demonstrate that microbial small RNAs (msRNA) are enriched on LDL and drive pro-inflammatory macrophage polarization and cytokine secretion via activation of the ribonucleic acid sensor toll-like receptor 8 (TLR8). Removal of msRNA cargo during LDL re-constitution yields particles that readily promote sterol loading but fail to stimulate inflammatory activation. Competitive antagonism of TLR8 with non-targeting locked nucleic acids (nt-LNA) was found to prevent nLDL-induced macrophage polarization in vitro, and re-organize lesion macrophage phenotypes in vivo, as determined by single-cell RNA sequencing. Critically, this was associated with reduced disease burden in distinct mouse models of atherosclerosis. These results identify LDL-msRNA as instigators of atherosclerosis-associated inflammation and support alternative functions of LDL beyond cholesterol transport.

High-density lipoproteins mediate small RNA intercellular communication between dendritic cells and macrophages

“…The approaches outlined in this study would enable future studies to characterize the pathway of HDL or LDL-delivered sRNAs through the endo-lysosomal system, characterize the modulators of this process, and colocalize these RNA cargos with TLRs that drive inflammatory pathways. As indicated by previous reports of proinflammatory TLR signaling derived from LDL-associated RNA, it may be possible that HDL’s anti-inflammatory role is mediated, in part, by inducing the efflux of LDL deposited proinflammatory sRNAs within the endo-lysosomal system ( 33 ). Historically, it has been shown that HDL plays anti-inflammatory roles in macrophages by its capacity to mediate the efflux lipids from burdened cells; however, HDL can become proinflammatory in disease and HDL’s ability to transfer extracellular sRNAs to recipient macrophage endosomes may contribute to HDL functionality in disease.…”