Alterations of urinary proteomic profiles are correlated with return to sport after anterior cruciate ligament reconstruction

BACKGROUND: Return to sport (RTS) after anterior cruciate ligament reconstruction (ACLR) remains a critical issue in sports medicine. Despite improvements in rehabilitation, many patients fail to return to their preinjury level of activity. Previous studies have primarily focused on clinical and biomechanical factors that influence RTS; however, the impact of intrinsic physiological changes, particularly urinary proteomic profiles, has not yet been fully explored. This study aimed to identify potential urinary protein biomarkers associated with RTS in ACLR patients. METHODS: A total of 30 ACLR patients, at least 9 months post-surgery, were recruited. Patients were divided into RTS and non-RTS groups based on their ability to RTS, recovery to preinjury Tegner levels, and a leg symmetry index (LSI) of ≥ 85% on the single-leg hop (SLH) test. Furthermore, urine samples were analyzed using liquid chromatography-mass spectrometry to identify differentially expressed proteins associated with RTS. Potential biomarkers and mechanism associated with RTS were identified by series of bioinformatics and machine learning methods such as pathway enrichment methods, protein-protein interaction (PPI) network, the least absolute shrinkage and selection operator (LASSO), receiver operating characteristic curve and correlation analysis. RESULTS: Significant differences in knee muscle characteristics, including limb circumferences and isokinetic strength, were observed between the RTS and Non-RTS groups. A total of 3433 proteins were identified, with 20 upregulated and 58 downregulated in the RTS group. Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) analyses revealed key pathways including regulation of actin cytoskeleton, calcium ion binding, and Pathways related to inflammation such as IL-17 signaling pathway and neutrophil extracellular trap formation. Five proteins, including Glypican-3 (GPC3), Phosphatidylinositol transfer protein alpha isoform (PIPNA), Rap guanine nucleotide exchange factor 3 (RPGF3), Histone H1.5 (H15), and Small proline-rich protein 3 (SPRR3), were identified as potential biomarkers for evaluating RTS. CONCLUSIONS: Muscle function was the primary factor influencing RTS after ACLR. The study revealed proteomic differences between those who RTS and those who do not. The identified potential biomarkers, such as GPC3, PIPNA, RPGF3, H15, and SPRR3, may serve as candidate targets to guide interventions designed to improve RTS outcomes following ACLR. TRIAL REGISTRATION: This study was registered in the Chinese Clinical Trial Registry (ChiCTR2200061779) on 02/07/2022.