Cathepsin H as a causal risk factor and therapeutic target in proliferative diabetic retinopathy

BACKGROUND: Cathepsins, key lysosomal proteases, have been linked to diabetic retinopathy (DR) pathogenesis, but their causal role and therapeutic potential remain unclear. METHODS: We used bidirectional Mendelian randomization (MR) to explore causal relationships between cathepsins and DR stages, with validation by multivariable MR, Bayesian weighted MR, and colocalization analysis. Single-cell RNA Sequencing (scRNA-seq) characterized cellular expression of relevant cathepsins in DR patients and mice. Candidate inhibitors were screened via the Proteomics Drug Atlas, followed by molecular docking and dynamics simulating their binding stability. Cellular experiments (CCK-8, scratch assay, LysoTracker staining) were performed to evaluate drug efficacy. RESULTS: Cathepsin H (CtsH) showed a causal association with proliferative DR (PDR) (IVW: p = 0.01, OR = 1.059), which was confirmed by multivariable and Bayesian MR. Colocalization identified shared genetic variants between CtsH and PDR (PP.H4 = 99.99%). ScRNA-seq revealed CtsH upregulation in monocytes of DR patients’ peripheral blood mononuclear cells and in retinal macroglia/endothelial cells of DR mice. Molecular docking demonstrated stable binding of SSR 69071 and PF429242 to CtsH (binding energies: −7.7 and −6.6 kcal/mol), with 100-ns dynamics confirming complex stability. In vitro, both compounds inhibited endothelial migration and wound healing in a time- and dose-dependent manner at safe concentrations (SSR 69071 ≤ 1 μM; PF429242 ≤ 10 μM), while PF429242 additionally increased lysosomal area. CONCLUSIONS: Elevated CtsH is an independent causal risk factor for PDR. The SSR 69071 and PF429242 exhibit promising inhibitory effects, supporting CtsH as both a biomarker and therapeutic target for PDR.