Exosomal Proteins in the Aqueous Humor as Novel Biomarkers in Patients with Neovascular Age-related Macular Degeneration

Age-related macular degeneration
(AMD) describes the progressive
degeneration of the retinal pigment epithelium (RPE), retina, and
choriocapillaris and is the leading cause of blindness in people over
50. The molecular mechanisms underlying this multifactorial disease
remain largely unknown. To uncover novel secretory biomarkers related
to the pathogenesis of AMD, we adopted an integrated approach to compare
the proteins identified in the conditioned medium (CM) of cultured
RPE cells and the exosomes derived from CM and from the aqueous humor
(AH) of AMD patients by LC–ESI–MS/MS. Finally, LC–MRM
was performed on the AH from patients and controls, which revealed
that cathepsin D, cytokeratin 8, and four other proteins increased
in the AH of AMD patients. The present study has identified potential
biomarkers and therapeutic targets for AMD treatment, such as proteins
related to the autophagy–lysosomal pathway and epithelial–mesenchymal
transition, and demonstrated a novel and effective approach to identifying
AMD-associated proteins that might be secreted by RPE in vivo in the
form of exosomes. The proteomics-based characterization of this multifactorial
disease could help to match a particular marker to particular target-based
therapy in AMD patients with various phenotypes.