Impaired cone function and cone degeneration resulting from CNGB3 deficiency: down-regulation of CNGA3 biosynthesis as a potential mechanism.
The cone cyclic nucleotide-gated (CNG) channel is essential for central and color vision and visual acuity. This channel is composed of two structurally related subunits, CNGA3 and CNGB3; CNGA3 is the ion-conducting subunit, whereas CNGB3 is a modulatory subunit. Mutations in both subunits are associated with achromatopsia and progressive cone dystrophy, with mutations in CNGB3 alone accounting for 50% of all known cases of achromatopsia. However, the molecular mechanisms underlying cone diseases that result from CNGB3 deficiency are unknown. This study investigated the role of CNGB3 in cones, using CNGB3(-/-) mice. Cone dysfunction was apparent at the earliest time point examined (post-natal day 30) in CNGB3(-/-) mice. When compared with wild-type (WT) controls: photopic electroretingraphic (ERG) responses were decreased by approximately 75%, whereas scotopic ERG responses were unchanged; visual acuity was decreased by approximately 20%, whereas contrast sensitivity was unchanged; cone density was reduced by approximately 40%; photoreceptor apoptosis was detected; and outer segment disorganization was observed in some cones. Notably, CNGA3 protein and mRNA levels were significantly decreased in CNGB3(-/-) mice; in contrast, mRNA levels of S-opsin, Gnat2 and Pde6c were unchanged, relative to WT mice. Hence, we show that loss of CNGB3 reduces biosynthesis of CNGA3 and impairs cone CNG channel function. We suggest that down-regulation of CNGA3 contributes to the pathogenic mechanism by which CNGB3 mutations lead to human cone disease.
Ding
Xi-Qin
XQ
Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA. xi-qin-ding@ouhsc.edu
Harry
Cynthia S
CS
Umino
Yumiko
Y
Matveev
Alexander V
AV
Fliesler
Steven J
SJ
Barlow
Robert B
RB
D000818:Animals; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000172:deficiency* / Q000235:genetics; D015536:Down-Regulation; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation; D009410:Nerve Degeneration / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D014176:Protein Biosynthesis / Q000235:genetics; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism* / Q000473:pathology; D015354:Vision, Low / Q000235:genetics* / Q000378:metabolism / Q000473:pathology
C532622:CNGB3 protein, mouse; D054815:Cyclic Nucleotide-Gated Cation Channels