Macrophage-targeted Sod2 mRNA nanotherapy reduces mitochondrial oxidative stress and stabilizes vulnerable atherosclerotic plaques

Background Mitochondrial oxidative stress contributes to atherosclerotic plaque progression and instability, yet no therapies directly target mitochondrial redox imbalance. Superoxide dismutase 2 (SOD2), the primary mitochondrial antioxidant enzyme, has been linked to increased plaque vulnerability when its expression is reduced. Methods and Results We evaluated whether targeted restoration of SOD2 in plaque macrophages using p5RHH-based mRNA nanoparticles modulates mitochondrial oxidative stress and plaque phenotype. In primary monocytes from Sod2 +/- mice, p5: Sod2 nanoparticles restored SOD2 expression, reduced mitochondrial superoxide, and improved mitochondrial respiratory capacity. Transcriptomic profiling identified changes in inflammatory and metabolic pathways consistent with altered myeloid activation states. In Apoe -/- mice with advanced carotid atherosclerosis, systemically delivered p5: Sod2 nanoparticles preferentially accumulated in plaque macrophages and increased their SOD2 protein expression by approximately 1.6-fold, as quantified by flow cytometry. Treatment reduced mitochondrial, but not total cellular, reactive oxygen species without affecting plasma lipids or plaque size. However, p5: Sod2 treatment reduced plaque lipid content, decreased macrophage-rich core regions, increased collagen and ACTA2 + fibrous cap cells, reduced intraplaque hemorrhage markers, and lowered plaque vulnerability index by 30%. These changes were accompanied by reduced lesional expression of IL1β, IL6, MMP2, and MMP9 and decreased circulating inflammatory cytokines. Flow cytometry showed shifts in plaque macrophages, with fewer inflammatory/stress-associated clusters and more remodeling/repair-associated subsets. Conclusions Targeted SOD2 overexpression in plaque macrophages reduces mitochondrial oxidative stress and promotes transcriptional and matrix remodeling-associated changes consistent with plaque stabilization without affecting overall lesion burden. These findings support mitochondrial redox modulation as an immunometabolic strategy to reduce plaque vulnerability.