Lactate-induced H3K9 lactylation disrupts the inner blood–retinal barrier by activating the PTK2–FMNL2 axis in diabetic retinopathy

Disruption of the inner blood–retinal barrier (iBRB) is a major cause of vascular leakage and vision impairment in diabetic retinopathy (DR), yet the metabolic mechanisms driving endothelial barrier failure remain incompletely understood. Here, we investigated whether lactate-induced histone lactylation contributes to iBRB dysfunction in DR. Using human epiretinal membranes and proliferative diabetic retinopathy fibrovascular membranes, diabetic rat retinas, and retinal endothelial cells, we found that lactate accumulation was associated with increased protein lactylation, with H3K9 lactylation (H3K9la) showing prominent elevation under diabetic conditions. Mechanistically, lactate enhanced H3K9la enrichment at the PTK2 promoter and promoted PTK2 transcriptional activation and phosphorylation. Activated PTK2 was associated with the cytoskeletal regulator FMNL2 and was linked to increased FMNL2 tyrosine phosphorylation, leading to cytoskeletal remodeling, VE-cadherin disruption, endothelial hyperpermeability, and iBRB impairment. Pharmacological reduction of lactate production, inhibition of CBP/p300 catalytic activity, blockade of PTK2 activity, or FMNL2 knockdown attenuated endothelial barrier defects and retinal vascular leakage. These findings identify a lactate–H3K9la–PTK2–FMNL2 signaling axis that links metabolic stress to endothelial junction disruption and iBRB dysfunction in DR, highlighting a potential metabolic–epigenetic pathway for therapeutic intervention. Lactate accumulation induces prominent H3K9 lactylation in diabetic retinopathy. H3K9 lactylation epigenetically activates PTK2 transcription in retinal endothelial cells. PTK2 activity is associated with increased FMNL2 tyrosine phosphorylation. The PTK2–FMNL2 axis destabilizes VE-cadherin junctions and impairs iBRB integrity. The lactate–H3K9la–PTK2–FMNL2 pathway links metabolic stress to retinal vascular dysfunction.