Endothelial let-7b knockout decreased endothelial-derived macrophage-like foam cell proliferation, attenuated intercellular lipid droplets, and reduced atherosclerotic plaque in Apoe-/- mice.
Does endothelial-specific let-7b knockout reduce atherosclerotic plaque formation and endothelial-to-macrophage-like foam cell transition in Apoe-/- mice?
Endothelial let-7b promotes atherosclerosis by upregulating hemoglobin-alpha and inducing endothelial-to-macrophage-like foam cell transition, identifying a potential novel therapeutic target.
Abstract Background Atherosclerosis is a chronic inflammatory vascular disease characterized by macrophages derived from recruited circulating monocytes that take up lipids and induce plaque formation. Evidence shows that arterial endothelial cells (ECs) also accumulate lipid droplets (LDs) and express hemoglobin under inflammatory conditions, which regulate oxidative stress in the vascular wall. Endothelial microRNA biogenesis by Dicer impair endothelial regeneration and promote atherosclerosis, partly due to the effect of miR-103. Dicer also produces let-7b in ECs, but its role in atherosclerosis remains unclear. Therefore, we hypothesize that endothelial let-7b plays a detrimental role in atherosclerosis. Methods We generated Apoe–/– mice expressing mEGFP in ECs and tdTomato in all other cells, with or without endothelial-specific let-7b knockout (Apoe–/–/BMX-CreERT2/let-7bflox/flox/ROSAmTmG) to study the effect of endothelial let-7b in atherosclerosis. Apoe–/–/BMX-CreERT2/let-7bflox/flox mice were crossed with GFP-myc-tagged Argonaute-2 (Ago2) reporter mice to study the endothelial let-7b targets in vivo after a Western diet for 4 or 12 weeks. Endothelial RISC-associated transcripts were identified through GFP-tAgo2 immunoprecipitation coupled to prime-seq RNA sequencing. Predicted let-7b binding sites were functionally validated using luciferase reporter assays. Results At predilection sites in the mice aortic arch, we identified a population of ECs within the plaque that exhibited intercellular LDs and CCs accumulation, resided beneath the flat endothelial monolayer and protruded toward the vessel lumen. Meanwhile, they contained few mitochondria sparsely distributed throughout the cytoplasm. This displayed morphological similarities to macrophage-derived foam cells. Some of these cells also expressed Mac2, yet their EGFP+ confirmed the endothelial origin, suggesting an endothelial-to-foam-cell-like transformation. We identify this phenotype as EC-derived macrophage-like foam cells (EndoFCs). Endothelial let-7b knockout decreased EndoFCs’ proliferation, attenuated intercellular LDs and crystal formation, and reduced atherosclerotic plaque. Transcriptomic profiling revealed Hba-a1/a2 as a noncanonical let-7b target. Let-7b binds Hba-a1/a2 to enhance HbA expression in ECs, and HbA was highly enriched in EndoFCs but expressed at very low levels in polygonal ECs. Deletion of let-7b lowered HbA expression in ECs, suggesting a mechanistic link between let-7b–dependent HbA upregulation and EndoFC formation. Conclusion We confirmed that endothelial let-7b worsens atherosclerosis, likely by increasing HbA expression in ECs. This rise in HbA may contribute to metabolic stress and promote the transformation of ECs into EndoFCs. Notably, this harmful effect seems specific to endothelial let-7b rather than other let-7 family members. This let-7b–Hba regulatory axis in ECs could be further investigated as a potential therapeutic target.
Zhou et al. (Fri,) conducted a other in Atherosclerosis. Endothelial-specific let-7b knockout vs. Without endothelial-specific let-7b knockout was evaluated on EndoFCs' proliferation, intercellular LDs and crystal formation, and atherosclerotic plaque. Endothelial let-7b knockout decreased endothelial-derived macrophage-like foam cell proliferation, attenuated intercellular lipid droplets, and reduced atherosclerotic plaque in Apoe-/- mice.