The PDE6 mutation in the rd10 retinal degeneration mouse model causes protein mislocalization and instability and promotes cell death through increased ion influx

Abstract

The retinal degeneration model rd10 contains a missense mutation of the catalytic PDE6 β subunit, which hydrolyzes cGMP in response to light. This model produces cell death more slowly than others caused by PDE6 loss of function, making it of particular interest for studying potential therapeutics. We used morphology, biochemistry, and single-cell physiology to examine the mechanism of rd10 degeneration. Our results show that the mutation produces no alteration of RNA but does dramatically decrease maximal and basal PDE6 activity, apparently caused by a decrease in protein stability and transport. The enzymatic properties of the remaining mutant PDE6 appear to be nearly normal. We demonstrate that an increase in free cGMP, which would result from decreased PDE6 activity and serve to increase opening of the cGMP-gated channels and calcium influx, is an underlying cause of cell death: degeneration of rd10/ double mutants is slower than the parent rd10 line. Paradoxically, degeneration in rd10/ is also slower than in This rescue is correlated with a lowering of cGMP content in retinas and suggests that it may be caused by mislocalization of active PDE6. Single-cell recordings from rd10 rods show that the rates of rise and decay of the response are significantly slower; simulations indicate that these changes are primarily the result of the decrease in PDE6 concentration and rod collecting area. Together, these results provide insights into the complex mechanisms that underlie rd10-mediated retinal degeneration and a cautionary note for analysis of therapeutic interventions.

Patient-Specific Retinal Organoids Recapitulate Disease Features of Late-Onset Retinitis Pigmentosa

“…Here, we used a patient-derived RO model to demonstrate how the PDE6B mutation causes retinal degeneration in RP. Akin to the rd1 and rd10 mouse models (Bowes et al, 1990;Barhoum et al, 2008;Wang et al, 2018), this defect in PDE6B leads to an accumulation of cGMP in ROs at D193, and the accumulation increases to 10 times higher than that of control ROs as the ROs grow to D230 (Figure 6D).…”

A kinetic analysis of mouse rod and cone photoreceptor responses

“…We have used a simplified, spatially homogeneous model for photoreceptors (see, for example, Hamer et al 2005;Reingruber & Holcman, 2008;Chen et al 2010c;Korenbrot, 2012;Reingruber et al 2013;Wang et al 2018). The photoreceptor current, I, is taken to be a function of the cyclic guanosine nucleotide (cGMP) concentration c cg according to:…”

“…As we describe in the Methods section, we used a parsimonious, spatially homogeneous model of vertebrate phototransduction. Our model was derived from earlier models (see, for example, Hamer et al 2005;Reingruber & Holcman, 2008;Chen et al 2010c;Korenbrot, 2012;Reingruber et al 2013;Wang et al 2018), which were based on the known transduction reactions (see eqn 10in the Methods). In brief (see Fig.…”

KIT ligand protects against both light-induced and genetic photoreceptor degeneration

“…We finally evaluated whether KITL might provide neuroprotection in mouse models of human retinitis pigmentosa (RP). Mice homozygous for a mutation in the gene encoding the photoreceptor cGMP phosphodiesterase, Pde6b rd10 (hereafter called rd10/rd10) share many characteristics of human retinal degeneration resulting from a mutation in the homologous gene (Wang et al, 2018). Due to the fact that retinas of rd10/rd10 mice degenerate soon after birth, we performed subretinal injection of AAV8-KITL virus into the eyes of such mice (n=5) at postnatal day 3 and examined their retinal functions at postnatal day 24.…”