Ursolic Acid Reduces Herpes Stromal Keratitis by Downregulating SPP1 and PI3K/Akt Pathway

Herpes Stromal Keratitis (HSK), a leading cause of infectious blindness, is characterized by chronic inflammation, neovascularization, and fibrosis in the cornea following Herpes Simplex Virus type 1 (HSV-1) infection. Current treatments, primarily corticosteroids, carry significant side effects and do not fully address the underlying pathology or prevent recurrence. There's a critical need for novel therapeutic strategies targeting specific inflammatory pathways. Exosomes and their associated gene networks, particularly secreted phosphoprotein 1 (SPP1), are emerging as key mediators in inflammatory diseases, making them compelling targets for HSK intervention.

Researchers performed transcriptomic RNA sequencing on corneal tissues from HSV-1-infected mice to identify differentially expressed genes (DEGs) and construct an exosome-related gene network. Immune cell infiltration was assessed using single-cell RNA sequencing and flow cytometry. Key findings were validated in a mouse HSK model via qRT-PCR, western blot, and immunohistochemistry. The therapeutic potential of Ursolic Acid (UA) was investigated through subconjunctival administration in HSK mice, with subsequent evaluation of corneal lesions, angiogenesis, fibrosis, and key signaling pathways.

Analysis revealed 222 DEGs associated with exosomes in HSK, forming a network primarily centered on the positive regulation of cell adhesion. Within this network, SPP1 was identified as a hub gene, showing significant upregulation that correlated with clinical disease progression. SPP1 expression shifted from corneal epithelial cells in healthy corneas to infiltrating immune cells, specifically neutrophils and monocytes, during HSK. In the mouse model, treatment with Ursolic Acid significantly reduced corneal opacity, vessel in-growth, and inflammatory cell infiltration. Mechanistically, UA downregulated SPP1 expression.

This downregulation subsequently inhibited the activation of the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway, a crucial mediator of inflammation and cell survival.