APOLIPOPROTEIN-E IS SYNTHESIZED IN THE RETINA BY MULLER GLIAL-CELLS, SECRETED INTO THE VITREOUS, AND RAPIDLY TRANSPORTED INTO THE OPTIC-NERVE BY RETINAL GANGLION-CELLS

We have investigated the synthesis and transport of apoE, the major ap olipoprotein of the central nervous system, in the retina of the livin g rabbit. Four hours after the injection of [S-35]methionine/cysteine into the vitreous, 44% of [S-35]Met/Cys-labeled apoE is in soluble and membrane-enclosed retinal fractions, while 50% is in the vitreous. A significant amount of intact [S-35]Met/Cys-labeled apoE is rapidly tra nsported into the optic nerve and its terminals in the lateral genicul ate and superior colliculus within 3-6 h in two distinguishable vesicu lar compartments. Muller glia in cell culture also synthesize and secr ete apoE. Taken together, these results suggest that apoE is synthesiz ed by Muller glia and secreted into the vitreous. ApoE is also interna lized by retinal ganglion cells and/or synthesized by these cells and rapidly transported into the optic nerve and brain as an intact molecu le. We discuss the possible roles of retinal apoE in neuronal dynamics .