Bax-Induced Apoptosis in Leber's Congenital Amaurosis: A Dual Role in Rod and Cone Degeneration

Pathogenesis in the Rpe65−/− mouse model of Leber's congenital amaurosis (LCA) is characterized by a slow and progressive degeneration of the rod photoreceptors. On the opposite, cones degenerate rapidly at early ages. Retinal degeneration in Rpe65 −/− mice, showing a null mutation in the gene encoding the retinal pigment epithelium 65-kDa protein (Rpe65), was previously reported to depend on continuous activation of a residual transduction cascade by unliganded opsin. However, the mechanisms of apoptotic signals triggered by abnormal phototransduction remain elusive. We previously reported that activation of a Bcl-2-dependent pathway was associated with apoptosis of rod photoreceptors in Rpe65−/− mice during the course of the disease. In this study we first assessed whether activation of Bcl-2-mediated apoptotic pathway was dependent on constitutive activation of the visual cascade through opsin apoprotein. We then challenged the direct role of pro-apoptotic Bax protein in triggering apoptosis of rod and cone photoreceptors. Quantitative PCR analysis showed that increased expression of pro-apoptotic Bax and decreased level of anti-apoptotic Bcl-2 were restored in Rpe65−/−/Gnat1−/− mice lacking the Gnat1 gene encoding rod transducin. Moreover, photoreceptor apoptosis was prevented as assessed by TUNEL assay. These data indicate that abnormal activity of opsin apoprotein induces retinal cell apoptosis through the Bcl-2-mediated pathway. Following immunohistological and real-time PCR analyses, we further observed that decreased expression of rod genes in Rpe65-deficient mice was rescued in Rpe65−/−/Bax−/− mice. Histological and TUNEL studies confirmed that rod cell demise and apoptosis in diseased Rpe65−/− mice were dependent on Bax-induced pathway. Surprisingly, early loss of cones was not prevented in Rpe65−/−/Bax−/− mice, indicating that pro-apoptotic Bax was not involved in the pathogenesis of cone cell death in Rpe65-deficient mice. This is the first report, to our knowledge, that a single genetic mutation can trigger two independent apoptotic pathways in rod and cone photoreceptors in Rpe65-dependent LCA disease. These results highlight the necessity to investigate and understand the specific death signaling pathways committed in rods and cones to develop effective therapeutic approaches to treat RP diseases.

[1]  D. Schorderet,et al.  Mechanisms of apoptosis in retinitis pigmentosa. , 2009, Current molecular medicine.

[2]  D. Bok,et al.  The Role of Interphotoreceptor Retinoid-Binding Protein on the Translocation of Visual Retinoids and Function of Cone Photoreceptors , 2009, The Journal of Neuroscience.

[3]  T. Aleman,et al.  Photoreceptor layer topography in children with leber congenital amaurosis caused by RPE65 mutations. , 2008, Investigative ophthalmology & visual science.

[4]  W. Baehr,et al.  Rpe65-/- and Lrat-/- mice: comparable models of leber congenital amaurosis. , 2008, Investigative ophthalmology & visual science.

[5]  K. Palczewski,et al.  Trafficking of Membrane-Associated Proteins to Cone Photoreceptor Outer Segments Requires the Chromophore 11-cis-Retinal , 2008, The Journal of Neuroscience.

[6]  D. Schorderet,et al.  Triggering of Bcl-2-related pathway is associated with apoptosis of photoreceptors in Rpe65−/− mouse model of Leber’s Congenital Amaurosis , 2008, Apoptosis.

[7]  W. Baehr,et al.  A model for transport of membrane-associated phototransduction polypeptides in rod and cone photoreceptor inner segments , 2008, Vision Research.

[8]  A. J. Roman,et al.  Human cone photoreceptor dependence on RPE65 isomerase , 2007, Proceedings of the National Academy of Sciences.

[9]  J. D. Bronson,et al.  The Function of Guanylate Cyclase 1 and Guanylate Cyclase 2 in Rod and Cone Photoreceptors* , 2007, Journal of Biological Chemistry.

[10]  U. Schlecht,et al.  Biological characterization of gene response in Rpe65‐/‐ mouse model of Leber's congenital amaurosis during progression of the disease , 2006, FASEB journal : official publication of the Federation of American Societies for Experimental Biology.

[11]  A. Wenzel,et al.  Phenotype of three consanguineous Tunisian families with early-onset retinal degeneration caused by an R91W homozygous mutation in the RPE65 gene , 2006, Graefe's Archive for Clinical and Experimental Ophthalmology.

[12]  M. Seeliger,et al.  Cone opsin mislocalization in Rpe65-/- mice: a defect that can be corrected by 11-cis retinal. , 2005, Investigative ophthalmology & visual science.

[13]  G. Travis,et al.  Rpe65 Is the Retinoid Isomerase in Bovine Retinal Pigment Epithelium , 2005, Cell.

[14]  Yan Li,et al.  Susceptibility to Neurodegeneration in a Glaucoma Is Modified by Bax Gene Dosage , 2005, PLoS genetics.

[15]  L. Atchaneeyasakul,et al.  Activation of the mitochondrial apoptotic pathway in a rat model of central retinal artery occlusion. , 2005, Investigative ophthalmology & visual science.

[16]  M. Cheetham,et al.  Mechanisms of cell death in rhodopsin retinitis pigmentosa: implications for therapy. , 2005, Trends in molecular medicine.

[17]  S. Haverkamp,et al.  Impaired opsin targeting and cone photoreceptor migration in the retina of mice lacking the cyclic nucleotide-gated channel CNGA3. , 2005, Investigative ophthalmology & visual science.

[18]  Jian-xing Ma,et al.  Downregulation of cone-specific gene expression and degeneration of cone photoreceptors in the Rpe65-/- mouse at early ages. , 2005, Investigative ophthalmology & visual science.

[19]  G. Fishman,et al.  Clinical phenotypes in carriers of Leber congenital amaurosis mutations. , 2005, Ophthalmology.

[20]  S. Wu,et al.  Effects of elevated intraocular pressure on mouse retinal ganglion cells , 2005, Vision Research.

[21]  E. Pugh,et al.  Deficiency of Bax and Bak protects photoreceptors from light damage in vivo , 2004, Cell Death and Differentiation.

[22]  L. Xue,et al.  A Palmitoylation Switch Mechanism in the Regulation of the Visual Cycle , 2004, Cell.

[23]  Francesco Scaravilli,et al.  Inhibition of mTOR induces autophagy and reduces toxicity of polyglutamine expansions in fly and mouse models of Huntington disease , 2004, Nature Genetics.

[24]  P. Rakoczy,et al.  Recombinant adeno-associated virus type 2-mediated gene delivery into the Rpe65-/- knockout mouse eye results in limited rescue , 2004, Genetic vaccines and therapy.

[25]  D. Chen,et al.  Preventing retinal detachment-associated photoreceptor cell loss in Bax-deficient mice. , 2004, Investigative ophthalmology & visual science.

[26]  J. Horwitz,et al.  Rpe65 Is a Retinyl Ester Binding Protein That Presents Insoluble Substrate to the Isomerase in Retinal Pigment Epithelial Cells* , 2004, Journal of Biological Chemistry.

[27]  Jian-xing Ma,et al.  Isorhodopsin rather than rhodopsin mediates rod function in RPE65 knock-out mice , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[28]  R. Rando,et al.  RPE65 operates in the vertebrate visual cycle by stereospecifically binding all-trans-retinyl esters. , 2003, Biochemistry.

[29]  J. Jais,et al.  Major role of BAX in apoptosis during retinal development and in establishment of a functional postnatal retina , 2003, Developmental dynamics : an official publication of the American Association of Anatomists.

[30]  G. Fain,et al.  Spontaneous activity of opsin apoprotein is a cause of Leber congenital amaurosis , 2003, Nature Genetics.

[31]  A. Milam,et al.  Proapoptotic bcl-2 family members, Bax and Bak, are essential for developmental photoreceptor apoptosis. , 2003, Investigative ophthalmology & visual science.

[32]  D. Oprian,et al.  Opsin activation as a cause of congenital night blindness , 2003, Nature Neuroscience.

[33]  C. Grimm,et al.  Evidence for two apoptotic pathways in light-induced retinal degeneration , 2002, Nature Genetics.

[34]  Rahul S. Rajan,et al.  A Rhodopsin Mutant Linked to Autosomal Dominant Retinitis Pigmentosa Is Prone to Aggregate and Interacts with the Ubiquitin Proteasome System* , 2002, The Journal of Biological Chemistry.

[35]  C. Zhang,et al.  Ischemic Preconditioning Attenuates Apoptotic Cell Death in the Rat Retina Materials and Methods Ischemia Methodology , 2022 .

[36]  Peter M. G. Munro,et al.  The cellular fate of mutant rhodopsin: quality control, degradation and aggresome formation. , 2002, Journal of cell science.

[37]  C. Grimm,et al.  New views on RPE65 deficiency: the rod system is the source of vision in a mouse model of Leber congenital amaurosis , 2001, Nature Genetics.

[38]  D. G. Green,et al.  Constitutive “Light” Adaptation in Rods from G90D Rhodopsin: A Mechanism for Human Congenital Nightblindness without Rod Cell Loss , 2001, The Journal of Neuroscience.

[39]  P. Sieving,et al.  Mutations in the gene encoding lecithin retinol acyltransferase are associated with early-onset severe retinal dystrophy , 2001, Nature Genetics.

[40]  S. Korsmeyer,et al.  Proapoptotic BAX and BAK: A Requisite Gateway to Mitochondrial Dysfunction and Death , 2001, Science.

[41]  R. Sidman,et al.  Phototransduction in transgenic mice after targeted deletion of the rod transducin α-subunit , 2000 .

[42]  J B Hurley,et al.  Abnormal photoresponses and light-induced apoptosis in rods lacking rhodopsin kinase. , 1999, Proceedings of the National Academy of Sciences of the United States of America.

[43]  K. Kaneda,et al.  Apoptotic DNA fragmentation and upregulation of Bax induced by transient ischemia of the rat retina , 1999, Brain Research.

[44]  D. Bok,et al.  Rpe65 is necessary for production of 11-cis-vitamin A in the retinal visual cycle , 1998, Nature Genetics.

[45]  S. Korsmeyer,et al.  Suppression of developmental retinal cell death but not of photoreceptor degeneration in Bax-deficient mice. , 1998, Investigative ophthalmology & visual science.

[46]  D. Hunt,et al.  Mutations in the retinal guanylate cyclase (RETGC-1) gene in dominant cone-rod dystrophy. , 1998, Human molecular genetics.

[47]  A. Fulton,et al.  Mutations in the RPE65 gene in patients with autosomal recessive retinitis pigmentosa or leber congenital amaurosis. , 1998, Proceedings of the National Academy of Sciences of the United States of America.

[48]  K. Palczewski,et al.  A null mutation in the photoreceptor guanylate cyclase gene causes the retinal degeneration chicken phenotype. , 1998, Proceedings of the National Academy of Sciences of the United States of America.

[49]  Denis A. Baylor,et al.  Prolonged photoresponses in transgenic mouse rods lacking arrestin , 1997, Nature.

[50]  Birgit Lorenz,et al.  Mutations in RPE65 cause autosomal recessive childhood–onset severe retinal dystrophy , 1997, Nature Genetics.

[51]  T. L. McGee,et al.  Mutations in the gene encoding the alpha subunit of the rod cGMP-gated channel in autosomal recessive retinitis pigmentosa. , 1995, Proceedings of the National Academy of Sciences of the United States of America.

[52]  D. Oprian,et al.  Rhodopsin mutation G90D and a molecular mechanism for congenital night blindness , 1994, Nature.

[53]  J. Dowling,et al.  THE BIOLOGICAL FUNCTION OF VITAMIN A ACID. , 1960, Proceedings of the National Academy of Sciences of the United States of America.

[54]  J. Dowling,et al.  VITAMIN A DEFICIENCY AND NIGHT BLINDNESS. , 1958, Proceedings of the National Academy of Sciences of the United States of America.

[55]  R. Sidman,et al.  Phototransduction in transgenic mice after targeted deletion of the rod transducin alpha -subunit. , 2000, Proceedings of the National Academy of Sciences of the United States of America.