LAMP2A regulates endosomal protein composition and membrane identity in exosome biogenesis.

The endolysosomal system maintains cellular homeostasis through protein degradation and the release of exosomes that mediate intercellular communication. LAMP2A, a transmembrane protein, has been implicated in selective cargo loading into exosomes, or eLLoC. Here, we investigated how LAMP2A influences endosomal protein composition and function using mass spectrometry of endosomal and exosomal fractions from human retinal pigment epithelial cells. Loss of LAMP2A changed Rab GTPase distribution, reduced cortical actin association, and shifted phosphoinositide dynamics, leading to enhanced endosomal acidification and maturation. These changes extended beyond the loss of proteins containing ExoSignals, the canonical targeting motifs, suggesting that LAMP2A contributes broadly to endosomal identity. Experimental validation confirmed that LAMP2A deficiency reprograms endosomal fate toward degradation while influencing exosome composition. These findings highlight a role for LAMP2A in coordinating membrane identity, endosomal maturation, and intercellular communication through exosomes, providing insights into mechanisms that couple endosomal remodeling with cellular signaling and clearance pathways.