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Purpose: This study aimed to determine how different strain intensities-including normal, moderately increased, and high strain-influence protein expression profiles and related biological processes in human corneal stromal keratocytes.

Methods: A well-established in vitro model using the Flexcell FX-5000 Tension System, which replicates the natural corneal curvature and enables precise strain application to keratocytes, was used. Keratocytes were exposed to three strain levels: 3% (normal), 6% (moderately increased), and 12% (high). Following strain application, cells were collected for liquid chromatography-tandem mass spectrometry-based proteomic analysis to generate protein expression profiles. Differentially expressed proteins (DEPs) among the three groups were identified and subjected to biological pathway enrichment to reveal strain-dependent biological processes. Western blot analysis was performed to validate the expression of selected DEPs.

Results: Keratocytes exhibited strain intensity-dependent responses. Three percent strain maintained keratocytes in a quiescent phenotype, consistent with our previous findings. Six percent strain activated protective and adaptive programs to preserve tissue homeostasis under stress. In contrast, 12% strain suppressed immune-related processes and induced extracellular matrix (ECM) remodeling. Notably, procollagen-lysine, 2-oxoglutarate 5-dioxygenase 2 (PLOD2) and cathepsin L (CTSL)-two ECM remodeling-related proteins implicated in fibrotic responses-were significantly upregulated under 12% strain, highlighting a potential link between excessive mechanical stress and stromal fibrosis.

Conclusions: These findings demonstrate that corneal strain regulates keratocyte behavior in an intensity-dependent manner and suggest that high mechanical stress may drive pathologic stromal remodeling and fibrotic responses, offering mechanistic insights that may inspire future therapeutic strategies.