On the molecular pathology of neurodegeneration in IMPDH1-based retinitis pigmentosa.
Retinitis pigmentosa (RP), the hereditary degenerative disease of the photoreceptor neurons of the retina, probably represents the most prevalent cause of registered blindness amongst those of working age in developed countries. Mutations within the gene encoding inosine monophosphate dehydrogenase 1 (IMPDH1), the widely expressed rate-limiting enzyme of the de novo pathway of guanine nucleotide biosynthesis, have recently been shown to cause the RP10 form of autosomal dominant RP. We examined the expression of IMPDH1, IMPDH2 and HPRT transcripts, encoding enzymes of the de novo and salvage pathways of guanine nucleotide biosynthesis, respectively, in retinal sections of mice, the data indicating that the bulk of GTP within photoreceptors is generated by IMPDH1. Impdh1(-/-) null mice are shown here to display a slowly progressive form of retinal degeneration in which visual transduction, analysed by electroretinographic wave functions, becomes gradually compromised, although at 12 months of age most photoreceptors remain structurally intact. In contrast, the human form of RP caused by mutations within the IMPDH1 gene is a severe autosomal dominant degenerative retinopathy in those families that have been examined to date. Expression of mutant IMPDH1 proteins in bacterial and mammalian cells, together with computational simulations, indicate that protein misfolding and aggregation, rather than reduced IMPDH1 enzyme activity, is the likely cause of the severe phenotype experienced by human subjects. Taken together, these findings suggest that RP10 may represent an attractive target for therapeutic intervention, based upon a strategy combining simultaneous suppression of transcripts from normal and mutant IMPDH1 alleles with supplementation of GTP within retinal tissues.
The Ocular Genetics Unit, Department of Genetics, Trinity College Dublin, Ireland. aaherne@tcd.ie
Aileen
A
Aherne
Avril
A
Kennan
Paul F
PF
Kenna
Niamh
N
McNally
David G
DG
Lloyd
Ian L
IL
Alberts
Anna-Sophia
AS
Kiang
Marian M
MM
Humphries
Carmen
C
Ayuso
Paul C
PC
Engel
Jing Jin
JJ
Gu
Beverly S
BS
Mitchell
G Jane
GJ
Farrar
Pete
P
Humphries
D000818:Animals; D002478:Cells, Cultured; D003198:Computer Simulation; D004195:Disease Models, Animal; D004591:Electrophoresis, Polyacrylamide Gel; D004596:Electroretinography; D004926:Escherichia coli; D006150:Guanine Nucleotides / Q000096:biosynthesis*; D006160:Guanosine Triphosphate / Q000378:metabolism; D006652:Histological Techniques; D007041:Hypoxanthine Phosphoribosyltransferase / Q000378:metabolism; D007168:IMP Dehydrogenase / Q000235:genetics* / Q000378:metabolism; D017403:In Situ Hybridization; D051379:Mice; D008817:Mice, Mutant Strains; D008958:Models, Molecular; D017510:Protein Folding; D012160:Retina / Q000378:metabolism* / Q000473:pathology; D012174:Retinitis Pigmentosa / Q000235:genetics / Q000503:physiopathology*
D006150:Guanine Nucleotides; D006160:Guanosine Triphosphate; D007168:IMP Dehydrogenase; C463299:IMPDH1, mouse; C488212:IMPDH2, mouse; D007041:Hypoxanthine Phosphoribosyltransferase