CGMP/Protein Kinase G Signaling Suppresses Inositol 1,4,5-Trisphosphate Receptor Phosphorylation and Promotes Endoplasmic Reticulum Stress in Photoreceptors of Cyclic Nucleotide-gated Channel-deficient Mice

Hongwei Ma,Michael R Butler,Arjun Thapa,Josh Belcher,Fan Yang,Wolfgang Baehr,Martin Biel,Stylianos Michalakis,Xi-Qin Ding

doi:10.1074/jbc.m115.641159

Abstract

Photoreceptor cyclic nucleotide-gated (CNG) channels play a pivotal role in phototransduction. Mutations in the cone CNG channel subunits CNGA3 and CNGB3 are associated with achromatopsia and cone dystrophies. We have shown endoplasmic reticulum (ER) stress-associated apoptotic cone death and increased phosphorylation of the ER Ca(2+) channel inositol 1,4,5-trisphosphate receptor 1 (IP3R1) in CNG channel-deficient mice. We also presented a remarkable elevation of cGMP and an increased activity of the cGMP-dependent protein kinase (protein kinase G, PKG) in CNG channel deficiency. This work investigated whether cGMP/PKG signaling regulates ER stress and IP3R1 phosphorylation in CNG channel-deficient cones. Treatment with PKG inhibitor and deletion of guanylate cyclase-1 (GC1), the enzyme producing cGMP in cones, were used to suppress cGMP/PKG signaling in cone-dominant Cnga3(-/-)/Nrl(-/-) mice. We found that treatment with PKG inhibitor or deletion of GC1 effectively reduced apoptotic cone death, increased expression levels of cone proteins, and decreased activation of Müller glial cells. Furthermore, we observed significantly increased phosphorylation of IP3R1 and reduced ER stress. Our findings demonstrate a role of cGMP/PKG signaling in ER stress and ER Ca(2+) channel regulation and provide insights into the mechanism of cone degeneration in CNG channel deficiency.

Highlights

Cone photoreceptors undergo endoplasmic reticulum stress-associated apoptosis in cyclic nucleotide-gated (CNG) channel deficiency
Reduced Photoreceptor Apoptosis in Cnga3Ϫ/Ϫ/NrlϪ/Ϫ Mice Treated with PKG Inhibitor—We previously showed that cones of Cnga3Ϫ/Ϫ and Cnga3Ϫ/Ϫ/NrlϪ/Ϫ mice undergo early
To determine whether the beneficial effects of cGMP reduction are associated with PKG signaling, we examined the effects of PKG

Summary

Background

Cone photoreceptors undergo endoplasmic reticulum stress-associated apoptosis in CNG channel deficiency. Results: Suppressing cGMP/PKG signaling enhances inositol 1,4,5-trisphosphate receptor 1 (IP3R1) phosphorylation and inhibits endoplasmic reticulum stress and cone death. Conclusion: cGMP/PKG signaling regulates IP3R1 activity and promotes endoplasmic reticulum stress in CNG channel deficiency. We have shown endoplasmic reticulum (ER) stress-associated apoptotic cone death and increased phosphorylation of the ER Ca2؉ channel inositol 1,4,5-trisphosphate receptor 1 (IP3R1) in CNG channel-deficient mice. This work investigated whether cGMP/ PKG signaling regulates ER stress and IP3R1 phosphorylation in CNG channel-deficient cones. We investigated whether cGMP/PKG signaling contributes to ER stress and regulates IP3R1 phosphorylation in CNG channel-deficient cones. Treatment with PKG inhibitors and deletion of retGC1 effectively reduced apoptotic cone death and Müller glial cell activation and increased expression levels of cone proteins in CNG channel-deficient mice. Findings from this work support a cGMP/PKG-regulated, IP3R1-associated ER stress/apoptosis in CNG channel-deficient cones

Experimental Procedures

Results

Discussion