The cone cyclic nucleotide-gated (CNG) channel is essential for central and color vision and for visual acuity. Mutations in the two channel subunits, CNGA3 and CNGB3, are associated with achromatopsia and progressive cone dystrophy. Cones degenerate in mouse models of CNGA3 and CNGB3 deficiency and in patients with achromatopsia or cone dystrophy. There are currently no curative treatments for these diseases, in part due to a lack of understanding of the mechanisms underlying the disease pathobiology. The overarching objective of this study is to understand the mechanism(s) of cone degeneration resulting from loss of CNG channel function. Specifically, we will determine whether the accumulation of cGMP in models of CNG channel deficiency causes cone degeneration. We will perform the proposed studies using the CNGA3-/-/Nrl-/- and CNGB3-/-/Nrl-/- mouse lines. Using these mouse models provides a unique opportunity to study cone degeneration in a retina that contains only cones.
Three specific aims are proposed. The first specific aim is to determine whether the accumulation of cGMP is responsible for cone degeneration in CNGA3 deficiency. We will test the ability of guanylate cyclase (GC) inhibitors to reduce cone degeneration in the channel-deficient mice. In a corroborating experiment, we will also test this hypothesis by abolishing expression of retGC-1 (retinal guanlyate cyclase) in channel deficient cones by utilizing RNAi and/or genetic methods (generation of CNGA3-/-/Nrl-/-/retGC-1-/-). The second specific aim is to determine how cones die in CNGA3 deficiency. If cGMP is responsible for cone cell death, we will examine how the accumulation of cGMP leads to cone cell death. We will investigate the role of cGMP- dependent protein kinase (PKG) in cone degeneration. We will determine whether PKG activity is higher in the CNGA3-/-/Nrl-/- retina compared to the Nrl-/- retina, and will test whether the use of PKG inhibitors/knockdown of PKG expression can ameliorate cone degeneration. Alternate mechanisms for cone degeneration will also be investigated by studying altered gene expression in channel deficient mice (compared to WT) by using microarray analysis. The third specific aim is to determine whether CNGB3 deficiency leads to an accumulation of cGMP in cones by using CNGB3-/-/Nrl-/- mice. Upon completion of the proposed study we will have a better understanding of the mechanism(s) underlying cone degeneration resulting from CNG channel deficiency. Improving the lifespan of degenerating cones is necessary for successful treatment of inherited cone diseases. The knowledge gained in this study is crucial for the development of therapeutic strategies to prevent or retard this degeneration, both in cases in which the causative gene is one of the channel proteins and in more general cases of cone dystrophy.
Congenital achromatopsia and progressive cone dystrophy are debilitating hereditary vision disorders for which there are currently no curative treatments. Mutations in genes encoding the cone cyclic nucleotide- gated (CNG) channel subunits account for 70% of all known cases of achromatopsia. The proposed study will probe the mechanisms underlying the cone degeneration that leads to loss of vision in CNG channel- associated achromatopsia. The results will provide significant insights into both the normal cell biology of cones and the pathobiology of cone dominant inherited disease. This knowledge is essential for developing therapeutic interventions to treat cone diseases and retard or rescue vision loss.
|Ding, Xi-Qin; Matveev, Alexander; Singh, Anil et al. (2014) Exploration of cone cyclic nucleotide-gated channel-interacting proteins using affinity purification and mass spectrometry. Adv Exp Med Biol 801:57-65|
|Ma, Hongwei; Thapa, Arjun; Morris, Lynsie et al. (2014) Suppressing thyroid hormone signaling preserves cone photoreceptors in mouse models of retinal degeneration. Proc Natl Acad Sci U S A 111:3602-7|
|Michalakis, Stylianos; Xu, Jianhua; Biel, Martin et al. (2013) Detection of cGMP in the degenerating retina. Methods Mol Biol 1020:235-45|
|Xu, Jianhua; Morris, Lynsie; Thapa, Arjun et al. (2013) cGMP accumulation causes photoreceptor degeneration in CNG channel deficiency: evidence of cGMP cytotoxicity independently of enhanced CNG channel function. J Neurosci 33:14939-48|
|Ma, Hongwei; Thapa, Arjun; Morris, Lynsie M et al. (2013) Loss of cone cyclic nucleotide-gated channel leads to alterations in light response modulating system and cellular stress response pathways: a gene expression profiling study. Hum Mol Genet 22:3906-19|
|Ding, Xi-Qin; Matveev, Alexander; Singh, Anil et al. (2012) Biochemical characterization of cone cyclic nucleotide-gated (CNG) channel using the infrared fluorescence detection system. Adv Exp Med Biol 723:769-75|
|Xu, Jianhua; Morris, Lynsie M; Michalakis, Stylianos et al. (2012) CNGA3 deficiency affects cone synaptic terminal structure and function and leads to secondary rod dysfunction and degeneration. Invest Ophthalmol Vis Sci 53:1117-29|
|Thapa, Arjun; Morris, Lynsie; Xu, Jianhua et al. (2012) Endoplasmic reticulum stress-associated cone photoreceptor degeneration in cyclic nucleotide-gated channel deficiency. J Biol Chem 287:18018-29|
|Carvalho, Livia S; Xu, Jianhua; Pearson, Rachael A et al. (2011) Long-term and age-dependent restoration of visual function in a mouse model of CNGB3-associated achromatopsia following gene therapy. Hum Mol Genet 20:3161-75|
|Xu, Jianhua; Morris, Lynsie; Fliesler, Steven J et al. (2011) Early-onset, slow progression of cone photoreceptor dysfunction and degeneration in CNG channel subunit CNGB3 deficiency. Invest Ophthalmol Vis Sci 52:3557-66|