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Teresa Puthussery, Todd Stincic, Gayet Jacqueline, William Rowland Taylor; TARPγ2 is required for normal AMPA receptor expression and function in the inner retina. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2975.
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© ARVO (1962-2015); The Authors (2016-present)
Transmembrane AMPA receptor regulatory proteins (TARPs) are auxiliary proteins that influence the synaptic targeting and functional properties of AMPA receptors. The identity and roles of TARPs in retina remain unclear. Here we provide an initial analysis of the localization, interactions and function of the TARP subunit, TARPγ2, in mammalian retina.
We used validated TARPγ2 antibodies (Neuromab) for immunohistochemistry in wild-type (wt) and stargazer mutant mice (stg), rabbit, macaque and human retinas. Levels of TARPg2 and AMPA receptor subunit (GluA) expression were compared in stg and wt mice (n = 6 each) by quantifying relative fluorescence intensity as a function of inner plexiform layer (IPL) depth using choline acetyltransferase (ChAT) staining for depth calibration. Patch-clamp recordings were made from On-starburst amacrine cells in wholemount retina from adult stg mutant mice (n=19) and stg heterozygote (het) littermates (n=14).
We observed punctate TARPγ2 immunostaining in the outer and inner plexiform layer of all species. This staining was absent in the stg mouse, which lacks TARPγ2 protein. In the IPL, the highest levels of TARPγ2 expression were at ~30% and ~70% depth, coincident with the stratification of the Off and On ChAT amacrine cells, respectively. Expression of GluA2, GluA3 and GluA4 was significantly reduced at the level of the Off- and On-ChAT dendrites in stg vs wt mice (GluA2 at Off-ChAT p=0.003, GluA2 at On-ChAT, p=0.006, GluA3 at Off-ChAT p<0.0001, GluA3 at On-ChAT, p=0.001, GluA4 at Off-ChAT p=0.003, GluA4 at On-ChAT, p=0.001). By comparison, GluA1 (GluA1 at Off-ChAT p=0.89, GluA1 at On-ChAT, p=0.58) and PSD95 (PSD95 at Off-ChAT p=0.73, PSD95 at On-ChAT, p=0.83) expression was unchanged. In On-SBACs from stg mice, the peak light-evoked excitatory conductance was reduced by 28% (het, 1.560.74±nS, stg 1.13±0.22nS, p=0.025) and the sustained component of the excitatory conductance was reduced by 50% (het, 0.61±0.37nS, stg 0.30+0.18nS, p=0.005).
TARPγ2 is required for normal inner retinal synaptic expression of GluA2, GluA3 and GluA4 but not GluA1. The pattern of expression of TARPγ2 suggests a conserved role in the circuits involved in direction selectivity. The absence of TARPγ2 reduces excitatory input to On-SBACs, consistent with the observed reduction in AMPA receptor expression.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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