Objective:To analyze the differential expressions of proteins in aqueous humor in patients with exfoliation syndrome (XFS).Methods:A total of 20 patients were enrolled in the Department of Ophthalmology, People's Hospital of Hotan District from June 2020 to January 2021, including 10 patients with age-related cataract and 10 XFS patients combined with cataract, which were classified as cataract group and XFS group, respectively.A total of 50 to 100 μl aqueous humor was obtained in the middle of the anterior chamber through the intraoperative phacoemulsification channel.The proteins extracted from aqueous humor were analyzed by label-free quantitative proteomics technology.The cataract group was set as the control group, and the differentially expressed proteins (DEPs) in XFS group were screened according to P<0.05 and fold change >1.5.Gene ontology (GO) function analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) signaling pathway analysis were used to explore the function and regulatory signaling pathways of DEPs in the XFS group.This study adhered to the Declaration of Helsinki.The study protocol was approved by the Ethics Committee of Tianjin Medical University Eye Hospital (No.2020KY[L]-21).Written informed consent was obtained from each subject. Results:In comparison with the cataract group, 25 DEPs were identified in the XFS group, primarily involved in cell adhesion, receptor, hydrolase, and molecular transport.Specifically, there were 14 down-regulated proteins including complement factor H-related protein 1 (CFHR1), endoplasmic reticulum chaperone BiP (HSPA5), biglycan (BGN), FRAS1-related extracellular matrix protein 2 (FREM2), hemoglobin subunit delta (HBD), hemoglobin subunit gamma-1 (HBG1), lysosomal thioesterase PPT2 (PPT2) etc., and 11 up-regulated proteins including latent-transforming growth factor beta-binding protein 2 (LTBP2), very low-density lipoprotein receptor (VLDLR), laminin subunit alpha-2 (LAMA2), coagulation factor Ⅸ (F9).Among them, FREM2 was the most significantly differentially expressed protein in XFS group with consistent expression levels across individual samples.GO analysis revealed that these DEPs mainly localized to the extracellular matrix of collagen, bound globin-hemoglobin complex, plasma lipoprotein particles and lysosomes.Molecular functions and biological processes showed that HBD and HBG1 were involved in cellular detoxification, PPT2 in hydrolase activity, and BGN and LTBP2 in glycosaminoglycan binding.KEGG signaling pathway analysis indicated that CFHR1 and F9 were associated with complement and coagulation cascade pathways, and FREM2 and LAMA2 were linked to the extracellular matrix interaction pathway.Conclusions:Disease progression of XFS may be associated with changes in extracellular matrix proteins, disruption of the blood-aqueous humor barrier, and potential inflammatory responses.The significant down-regulation of FREM2 protein may be a potential biomarker for XFS.