HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: iovs.07-1422v1 49/11/5067    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Davis, R. J. Articles by Tsang, S. H. Search for Related Content PubMed PubMed Citation Articles by Davis, R. J. Articles by Tsang, S. H.

Functional Rescue of Degenerating Photoreceptors in Mice Homozygous for a Hypomorphic cGMP Phosphodiesterase 6 b Allele (Pde6b^H620Q)

¹From Brown Glaucoma Laboratory, the ²Department of Pathology and Cell Biology, College of Physicians and Surgeons, and the ⁴Edward S. Harkness Eye Institute, Columbia University, New York, New York; ⁵Wellesley College, Wellesley, Massachusetts; the ⁶Department of Physiological Science, UCLA, Los Angeles, California; and the ⁷Jules Stein Eye Institute, UCLA School of Medicine, Los Angeles, California.

PURPOSE. Approximately 8% of autosomal recessive retinitis pigmentosa (RP) cases worldwide are due to defects in rod-specific phosphodiesterase PDE6, a tetramer consisting of catalytic (PDE6 and PDE6β) and two regulatory (PDE6) subunits. In mice homozygous for a nonsense Pde6b^rd1 allele, absence of PDE6 activity is associated with retinal disease similar to humans. Although studied for 80 years, the rapid degeneration Pde6b^rd1 phenotype has limited analyses and therapeutic modeling. Moreover, this model does not represent human RP involving PDE6B missense mutations. In the current study the mouse missense allele, Pde6b^H620Q was characterized further.

METHODS. Photoreceptor degeneration in Pde6b^H620Q homozygotes was documented by histochemistry, whereas PDE6β expression and activity were monitored by immunoblotting and cGMP assays. To measure changes in rod physiology, electroretinograms and intracellular Ca²⁺ recording were performed. To test the effectiveness of gene therapy, Opsin::Pde6b lentivirus was subretinally injected into Pde6b^H620Q homozygotes.

RESULTS. Within 3 weeks of birth, the Pde6b^H620Q homozygotes displayed relatively normal photoreceptors, but by 7 weeks degeneration was largely complete. Before degeneration, PDE6β expression and PDE6 activity were reduced. Although light-/dark-adapted total cGMP levels appeared normal, Pde6b^H620Q homozygotes exhibited depressed rod function and elevated outer segment Ca²⁺. Transduction with Opsin::Pde6b lentivirus resulted in histologic and functional rescue of photoreceptors.

CONCLUSIONS. Pde6b^H620Q homozygous mice exhibit a hypomorphic phenotype with partial PDE6 activity that may result in an increased Ca²⁺ to promote photoreceptor death. As degeneration in Pde6b^H620Q mutants is slower than in Pde6b^rd1 mice and can be suppressed by Pde6b transduction, this Pde6b^H620Q model may provide an alternate means to explore new treatments of RP.