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J. Ding, C. Bowes Rickman; Synaptic Expression of APOER2 in the Plexiform Layers of Mouse Retina. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1292. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Apolipoprotein E receptor 2 (APOER2), a member of LDL receptor family, is highly expressed in the brain and plays an important role in synaptic plasticity and neurodegeneration. However, its involvement in retinal synaptic transmission is not clear. In this study, we tested whether APOER2 is also involved in retinal synaptic transmission by first examining whether it is expressed in retinal synapses.
We performed immunohistochemistry to study the distribution of APOER2 in mouse retina. We also used double labeling of APOER2 with a presynaptic marker, SV2, and confocal microscopy to investigate its expression in retinal synapses. Calbindin and PKCα were used to identify postsynaptic processes of horizontal cells and rod bipolar cells, respectively.
Anti-APOER2 antibody (NOVUS) exhibited a punctate staining pattern in mouse retina, prominent in both the outer plexiform layer (OPL) and inner plexiform layer (IPL). In the OPL, APOER2-positive puncta were not colocalized with SV2-positive photoreceptor terminals, but enclosed within them. These puncta were not colocalized with calbindin, but some of them colocalized with PKCα, suggesting they are expressed by postsynaptic rod bipolar dendrites. In the IPL, APOER2-positive puncta were also closely apposed to SV2-positive puncta, suggesting postsynaptic expression.
In mouse retina APOER2 expression is closely associated with synapses. We will further clarify if APOER2 is expressed in pre- or postsynaptic compartment using immunoelectron microscopy. We will also identify the retinal cells that express APOER2 by multiple-labeling with different cellular markers.
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