Serum amyloid A2–induced phenotypic switching of vascular smooth muscle cells in moyamoya disease

OBJECTIVE This study was conducted to explore the role of serum amyloid A2 (SAA2) protein in the phenotype changes of vascular smooth muscle cells (VSMCs) in moyamoya disease (MMD). METHODS Between January 2020 and August 2022, individuals with diagnosed MMD were identified through a combination of their neuroradiological assessments and medical history. Control participants consisted of healthy adult volunteers who did not have MMD or any preexisting diseases. Data-independent acquisition (DIA) mass spectrometry was used to identify differentially expressed proteins in the serum of 40 MMD patients and 20 healthy controls (HCs), a discovery cohort of 60 patients. These proteins were validated with an enzyme-linked immunosorbent assay using the serum of another 15 MMD patients and 15 HCs plus 5 randomly selected samples each from the MMD patients and the HCs in the discovery cohort, bringing the validation cohort to 20 MMD patients and 20 HCs. In vitro experiments, including western blotting, flow cytometry, scratch tests, and cell proliferation assays, were performed to explore the effects and mechanisms of these proteins on smooth muscle cells. RESULTS Proteomic analysis showed significant upregulation of SAA2 protein in the MMD serum compared to that in the HC serum (log 2 FC [MMD/HC] = 2.797, p < 0.05). SAA2 increased the proportion of VSMCs in the S phase and promoted their proliferation, migration, and contractile-to-synthetic phenotypic switching. Aspirin reversed SAA2-induced changes in VSMCs. Mechanistic studies revealed that the ERK1/2 and AKT signaling pathways play a major role in SAA2-induced changes in VSMCs. CONCLUSIONS This study revealed that SAA2 is upregulated in the serum of MMD patients. The overexpression of SAA2 in MMD patients and in subsequent in vitro experiments suggests that the SAA2 protein promotes phenotypic changes in VSMCs and is related to cerebrovascular intimal thickening in MMD, with diagnostic and therapeutic ramifications.