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

• Published in: The Journal of biological chemistry Vol. 293; no. 40; pp. 15332 - 15346
• Main Authors: Wang, Tian, Reingruber, Jürgen, Woodruff, Michael L., Majumder, Anurima, Camarena, Andres, Artemyev, Nikolai O., Fain, Gordon L., Chen, Jeannie
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 05.10.2018; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; Calcium - metabolism; Cell Death; cGMP-gated channels; cyclic GMP (cGMP); Cyclic GMP - metabolism; Cyclic Nucleotide Phosphodiesterases, Type 6 - deficiency; Cyclic Nucleotide Phosphodiesterases, Type 6 - genetics; Cyclic Nucleotide-Gated Cation Channels - deficiency; Cyclic Nucleotide-Gated Cation Channels - genetics; Disease Models, Animal; Gene Expression Regulation; Ion Transport; Membrane Potentials - physiology; Mice; Mice, Knockout; missense mutation; Molecular Bases of Disease; Mutation, Missense; Nerve Tissue Proteins - deficiency; Nerve Tissue Proteins - genetics; PDE6; phosphodiesterases; photoreceptor; phototransduction; protein mislocalization; Protein Stability; protein translocation; Protein Transport; retinal degeneration; Retinal Degeneration - genetics; Retinal Degeneration - metabolism; Retinal Degeneration - pathology; Retinal Rod Photoreceptor Cells - metabolism; Retinal Rod Photoreceptor Cells - pathology; Signal Transduction; Single-Cell Analysis; Time Factors; PDE6; protein transport; retinal degeneration; cell death; photoreceptor; cGMP-gated channels; protein stability; phototransduction; missense mutation; protein translocation; cyclic GMP (cGMP); phosphodiesterases; protein mislocalization
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.RA118.004459

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 Pde6b 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/Cngb1−/− double mutants is slower than the parent rd10 line. Paradoxically, degeneration in rd10/Cngb1−/− is also slower than in Cngb1−/−. This rescue is correlated with a lowering of cGMP content in Cngb1−/− 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.