Impact of Interleukin-6 on Plaque Development and Morphology in Experimental Atherosclerosis

TLDR

Atherosclerosis is driven by lipid accumulation and inflammation, with interleukin‑6 levels elevated in acute coronary syndrome patients and thought to worsen plaque development. The study aimed to determine how IL‑6 deficiency affects atherosclerosis in mice. The authors used ApoE‑/‑ IL‑6‑/‑ double‑knockout mice maintained on standard chow for approximately 53 weeks to evaluate IL‑6’s role. IL‑6 deficiency increased cholesterol, enlarged lesions, and produced plaques with reduced matrix‑remodeling enzymes, collagen, and inflammatory cell infiltration, showing that baseline IL‑6 is essential for lipid balance, vascular remodeling, and plaque inflammation.

Abstract

Vascular lipid accumulation and inflammation are hallmarks of atherosclerosis and perpetuate atherosclerotic plaque development. Mediators of inflammation, ie, interleukin (IL)-6, are elevated in patients with acute coronary syndromes and may contribute to the exacerbation of atherosclerosis.To assess the role of IL-6 in atherosclerosis, ApoE-/--IL-6-/- double-knockout mice were generated, fed a normal chow diet, and housed for 53+/-4 weeks. Mortality and blood pressure were unaltered. However, serum cholesterol levels and subsequent atherosclerotic lesion formation (oil red O stain) were significantly increased in ApoE-/--IL-6-/- mice compared with ApoE-/-, wild-type (WT), and IL-6-/- mice. Plaques of ApoE-/--IL-6-/- mice showed significantly reduced transcript and protein levels of matrix metalloproteinase-9, tissue inhibitor of metalloproteinase-1, collagen I and V, and lysyl oxidase (by reverse transcriptase-polymerase chain reaction and immunohistochemistry). Recruitment of macrophages and leukocytes (Mac3- and CD45-positive staining) into the atherosclerotic lesion was significantly reduced in ApoE-/--IL-6-/- mice. The transcript and serum protein (ELISA) levels of IL-10 were significantly reduced.Thus, a lifetime IL-6 deficiency enhances atherosclerotic plaque formation in ApoEK-/--IL-6-/- mice and leads to maladaptive vascular developmental processes. These observations are consistent with the notion that baseline levels of IL-6 are required to modulate lipid homeostasis, vascular remodeling, and plaque inflammation in atherosclerosis.