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Jennifer Brancato, Alvina Bragin, Frank Stefano, Kathleen Boesze-Battaglia; Role of Melanoregulin in Phagocytosis Dependent Synchronicity of Lysosomal Proteins. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6555.
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Critical in the retinal pigment epithelia’s role in phagocytosis of OS debris is the regulated biogenesis of lysosomes required for both phagolysosome and autolysosome formation. Clearance of shed photoreceptor outer segments (POS) by the lysosomal system of the RPE is essential for function and viability of photoreceptors; impairment of POS clearance contributes to retinal diseases, including age-related retinopathies. The purpose of these studies is to determine if light dependent phagocyotic uptake of POS is correlated with lysosomogenesis. Furthermore knowing that melanoregulin (MREG), a 28 kDa sorting protein is critical for lysosome maturation we asked if loss of this protein alters POS dependent lysosomogenesis
Lysosome formation and autophagy were followed in Mreg +/+ and Mreg -/- mice in response to light stimulated disk shedding. Mice were sacrificed at various times relative to light onset: -60 min, 0 min, 30 min, 1h, 2h and 6h. Lysosome dependent processes were evaluated by following endo-lysosomal and autophagy markers in purified RPE cells. mRNA was determined by qPCR and protein by western blots of cleared RPE lysates.
Lysosomogenesis appears to follow a biphasic pattern with a peak in phagolysosome related proteins at (15-30 min) and autophagy related proteins at later time points. Interestingly, the endo-lysosomal marker Cathepsin S did not follow a biphasic pattern, although its proteolytic substrate pro-Cathepsin D exhibited two distinct peaks of activity. This biphasic distribution profile was abolished in the absence of MREG.
Lysosome dependent degradation of OS debris is likely a biphasic event, requiring two pools of lysosomes. Loss of MREG diminishes the lysosomal pool at later time points; 4 hrs after lights on.
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