Selective Knockout Of Glutamic Acid-Rich Protein 2 (GARP2) Significantly alters Cellular Dark Noise in Rod Photoreceptors

Authors

• U Broccher√≤ DA Stacks
• MN
• Nguyen
• SJ Pittler
• J Pahlberg

Abstract

GARP2, a glutamic-acid-rich protein found exclusively in rod photoreceptors, was suggested to function as a structural protein, a calcium-binding protein, a modulator of the cGMP phosphodiesterase enzyme (PDE6), and a gating inhibitor of the rod cGMP-gated cation channel, regulating visual phototransduction. GARP2 is a splice variant of the Cngb1 gene, which in the rods photoreceptor encodes the β-subunit of the cyclic nucleotide-gated cation channel and another glutamic acid-rich protein, GARP1. Mutations in Cngb1 cause retinitis pigmentosa (RP45), and β-subunit knockout mice are being studied as models of this disease. We previously showed that overexpression of GARP2 in rods accelerates phototransduction gain and slows the recovery of the light response. In this study, using ZFN-mediated gene editing, we have selectively eliminated GARP2 expression (GARP2 KO) to determine its essential functions in mouse rods. The absence of GARP2 caused perturbations of retinal structure in old KO mice. Indeed, the electroretinogram in these mice revealed functional deficits, namely a reduction in a- and b-wave amplitudes. Interestingly, single-cell patch-clamp recordings showed a significant reduction in rod photoreceptor dark noise in 3 and 6 months old KO mice, consistent with a previously proposed role for GARP2 in binding to PDE6 and stabilizing its basal activity. We suggest a role for the GARP 2-PDE6 interaction in stabilizing the PDE6 enzyme and controlling the turnover rate of cGMP in darkness, influencing the level of dark noise and the signal and noise properties of rod photoreceptors.

Scientific Focus Area: Neuroscience

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