Suppression of PAPP-A mitigates atherosclerosis by mediating macrophage polarization via STAT3 signaling

Pregnancy-associated plasma protein-A (PAPP-A), a type of metalloproteinase in the insulin-like growth factor (IGF) system, has been implicated in atherosclerosis progression, but its function and mechanism in atherosclerosis is not fully understood. The study was performed to further explore the effects of PAPP-A on inflammation, macrophage polarization and atherosclerosis. In mouse macrophages stimulated by oxidized low-density lipoprotein (ox-LDL), PAPP-A expression was significantly increased. Its knockdown markedly mitigated inflammatory response and polarized macrophages to an M2-like phenotype in RAW264.7 cells upon ox-LDL treatment. Additionally, ox-LDL-induced activation of nuclear factor-κB (NF-κB) signaling pathway was dramatically restricted by PAPP-A knockdown in macrophages. However, JAK2/STAT3 activation was significantly up-regulated in RAW264.7 cells with PAPP-A inhibition after ox-LDL treatment. Importantly, we found that PAPP-A knockdown-induced polarization of M2-like phenotype in macrophages was mainly dependent on STAT3 activation. Clinical studies showed that serum PAPP-A levels were higher in patients with coronary artery disease (CAD) than that of healthy individuals. Apolipoprotein E-knockout (ApoE^-/-) mice with high fat diet (HFD)-induced atherosclerosis exhibited higher expression of PAPP-A in aortas, which was mainly colocalized with F4/80. Subsequently, we found that PAPP-A deficiency greatly alleviated plaque formation, lesion burden and collagen accumulation in HFD-fed ApoE^-/- mice. Consistent with in vitro macrophage phenotype, PAPP-A^-/- reduced F4/80 expression, NF-κB activation and inflammatory response, while improved janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) signaling and polarized macrophages to an M2-like phenotype in aortas of ApoE^-/- mice after HFD feeding. In conclusion, these findings identified PAPP-A as a positive regulator of atherosclerosis by regulating macrophage polarization via STAT3 signal, and thus could be considered as a potential therapeutic target for atherosclerosis treatment.