Low-Density Lipoproteins Induce a Pro-Inflammatory, Chemotactic Mox-like Phenotype in THP-1-Derived Human Macrophages

Murine macrophages exposed to oxidized low-density lipoprotein (oxLDL) polarize into a distinct Mox phenotype characterized by impaired phagocytic and chemotactic function. Although implicated in atherosclerosis, this phenotype has not been confirmed in human macrophages. Drawing parallels to human tumor-associated macrophages, and in contrast to the murine cell response, we hypothesize that LDL/oxLDL induces a hybrid Mox-like state in human macrophages, marked by the simultaneous secretion of pro-inflammatory cytokines and anti-inflammatory factors, potentially exacerbating vascular inflammation and atherogenesis. To test this, THP-1 human monocytes were differentiated into resting macrophages, then polarized into M1-like and M2-like phenotypes, followed by treatment with native LDL, oxLDL, IL-6, or their combinations. ELISA results showed that oxLDL or LDL with IL-6 polarized resting and M1-like macrophages into a Mox-like phenotype that secreted TNF-α and TGF-β1 at levels comparable to M1- and M2-like cells, respectively. The pro-inflammatory nature of Mox-like macrophages was supported by increased THP-1 adhesion to vascular endothelial cells exposed to the macrophage-conditioned media. In microfluidic assays, LUVA human mast cells migrated toward media from Mox-like macrophages, indicating enhanced chemotaxis. In summary, the pro-inflammatory Mox-like state is triggered in human macrophages by oxLDL or LDL combined with IL-6, a key regulator of the inflammatory acute-phase response. Unlike in murine cells, this state is marked by high chemotactic activity driven by TGF-β1 secretion, which promotes mast cell recruitment and contributes to atherosclerotic plaque development and Alzheimer's disease.