Lamp2 Deficiency Enhances Susceptibility to Oxidative Stress-Induced RPE Degeneration.

Purpose: Autophagy and lysosomal degradation are vital processes that protect cells from oxidative stress. This study investigated the role of lysosome-associated membrane protein 2 (Lamp2), a lysosomal protein essential for autophagosome maturation and lysosome biogenesis, in maintaining retinal health under oxidative stress. Methods: To induce oxidative stress, young Lamp2 knockout (KO) and wild-type mice received an intravenous injection of a low dose (10 mg/kg) of sodium iodate (NaIO3). We examined retinal histopathology and morphological changes in the RPE. The involvement of resident microglia or infiltrating macrophages was assessed using immunostaining, flow cytometry, and real-time PCR for chemokines and cytokines. Results: After administering a low-dose NaIO3, Lamp2 KO mice showed significant RPE degeneration, whereas wild-type mice had minimal damage. Histological analysis and electron microscopy revealed significant thinning of the outer nuclear layer and loss of RPE epithelial polarity in Lamp2 KO mice. Additionally, there was a significant increase in ionized calcium-binding adaptor molecule 1-positive microglia and macrophages in the outer retina. Early proliferation of CD45lowMHC-IIlow resident microglia was followed by the infiltration of CD45highLy6Chigh monocytes and the engraftment of CD11b+CD45high monocyte-derived macrophages. Transcript levels of monocyte chemoattractant protein 1, macrophage inflammatory protein 1β, Il- 1β, and Il-6 also increased in the retinas of Lamp2 KO mice. Furthermore, pretreatment with the macrophage-depleting agent clodronate prevented NaIO3-induced RPE degeneration and macrophage infiltration in Lamp2 KO mice. Conclusions: Lamp2 deficiency, when combined with oxidative stress, leads to RPE degeneration in vivo. Lysosomal dysfunction also promotes macrophage engraftment and triggers neurotoxic inflammation.