Macrophage PIM1 Drives Atherosclerosis by Enhancing Foam Cell Formation Via CD36
BackgroundAtherosclerosis is characterized by the buildup of fatty plaques that thicken and stiffen arterial walls. Macrophages (M{varphi}s) significantly contribute to this process through their scavenger receptor CD36. PIM1 is a serine/threonine kinase known to modulate immune responses and cell metabolism. However, its role in M{varphi} lipid handling and atherogenesis is not well defined. This study examines the role of PIM1 in regulating CD36 expression and function in M{varphi}s during foam cell formation and atherosclerosis progression. MethodsWe performed in vitro studies by treating murine peritoneal M{varphi}s from Pim1-/- and wild-type (WT) mice with oxidized low-density lipoprotein (oxLDL). We measured CD36, PIM1, and plaque-associated proteins and mRNA levels, oxLDL binding and uptake rates, as well as foam cell formation. For in vivo studies, we fed M{varphi}-specific PIM1-deficient (Apoe-/- Lyz2Cre/+Pim1fl/fl) and their littermate control (Apoe-/-Pim1fl/fl) mice a high-fat diet for 12 weeks. We then evaluated the plaque formation in their aortic sinuses and arches. ResultsDeletion of Pim1 in M{varphi}s reduced CD36 protein expression by up to 96.7% compared to WT controls. This led to a 49.6% decrease in foam cell formation and a 25.5% reduction in cellular cholesterol after oxLDL treatment. Pharmacological inhibition of PIM kinase activity in WT M{varphi}s also impaired oxLDL handling, with a 64.5% reduction in binding and a 57.9% in uptake. Bulk RNA-seq revealed that Pim1 deficiency downregulated PPAR{gamma} signaling. Treatment with a PPAR{gamma} agonist restored CD36 levels in the PIM1 knockdown M{varphi}s, suggesting that PIM1 regulates CD36 through PPAR{gamma}. Moreover, PIM1 M{varphi}-specific deficiency caused a 69.4% reduction in atherosclerotic plaque formation. ConclusionPIM1 acts as a key upstream regulator of CD36 by enhancing PPAR{gamma} activity in M{varphi}s. The PIM1-CD36 axis promotes oxLDL binding, uptake, and foam cell formation. Targeting the PIM1/PPAR{gamma}/CD36 pathway could offer new ways to modulate M{varphi} lipid metabolism and reduce atherosclerotic plaque progression. Non-standard Abbreviations and AcronymsELISA: enzyme-linked immunosorbent assay; HFD: high-fat diet; M{varphi}s: macrophages; MCP-1: monocyte chemoattractant protein-1; ORO: oil red O; oxLDL: oxidized low-density lipoprotein; PBS: phosphate-buffered saline; PPAR{gamma}: peroxisome proliferator-activated receptor gamma; WT: wild type.