Background: Spermine (SPM) is known to play a role in regulating cholesterol efflux of macrophages, which is a critical anti-atherosclerotic pathway, but the underlying mechanism remains elusive. The deficiency of caspase 2 (CASP2), a target of SPM, can induce autophagy, which promotes cholesterol efflux in atherosclerosis. Herein, we aimed to explore whether SPM could regulate CASP2-mediated autophagy in the cholesterol efflux of macrophages.

Methods: Human THP-1 monocytes were induced into macrophages. After transfection and treatment with SPM or autophagy inhibitor 3-methyladenine (3-MA), the cholesterol uptake of THP-1 cell-derived macrophages and the lipid accumulation were examined using Dil-oxidized low-density lipoprotein (Dil-oxLDL) uptake assay and Oil Red O staining, respectively. The cholesterol efflux was measured by means of [³H]-cholesterol detection. Quantification of CASP2 and factors related to autophagy and apoptosis was completed using Western blotting and quantitative reverse transcription polymerase chain reaction (qRT-PCR).

Results: SPM treatment boosted cholesterol efflux and prevented lipid accumulation of THP-1 cell-derived macrophages (p < 0.001), without inducing cholesterol uptake of THP-1 cell-derived macrophages (p > 0.05). SPM upregulated the expression of autophagy-related 5 (ATG5), light chain 3 (LC3) II/LC3 I, and B-cell lymphoma-2 (Bcl-2) while downregulating Sequestosome 1 (P62) and CASP2 levels (p < 0.01). Treatment with 3-MA reversed the effects of SPM on cholesterol efflux, lipid accumulation, and autophagy-related protein expression (p < 0.01). Separately, CASP2 overexpression offset the impacts of SPM on cholesterol efflux, lipid accumulation, and expressions of proteins related to autophagy and apoptosis (p < 0.05).

Conclusion: SPM promotes autophagy to enhance the cholesterol efflux of THP-1 cell-derived macrophages by downregulating CASP2 expression.