Restoration of visual function in P23H rhodopsin transgenic rats by gene delivery of BiP/Grp78.
The P23H mutation within the rhodopsin gene (RHO) causes rhodopsin misfolding, endoplasmic reticulum (ER) stress, and activates the unfolded protein response (UPR), leading to rod photoreceptor degeneration and autosomal dominant retinitis pigmentosa (ADRP). Grp78/BiP is an ER-localized chaperone that is induced by UPR signaling in response to ER stress. We have previously demonstrated that BiP mRNA levels are selectively reduced in animal models of ADRP arising from P23H rhodopsin expression at ages that precede photoreceptor degeneration. We have now overexpressed BiP to test the hypothesis that this chaperone promotes the trafficking of P23H rhodopsin to the cell membrane, reprograms the UPR favoring the survival of photoreceptors, blocks apoptosis, and, ultimately, preserves vision in ADRP rats. In cell culture, increasing levels of BiP had no impact on the localization of P23H rhodopsin. However, BiP overexpression alleviated ER stress by reducing levels of cleaved pATF6 protein, phosphorylated eIF2alpha and the proapoptotic protein CHOP. In P23H rats, photoreceptor levels of cleaved ATF6, pEIF2alpha, CHOP, and caspase-7 were much higher than those of wild-type rats. Subretinal delivery of AAV5 expressing BiP to transgenic rats led to reduction in CHOP and photoreceptor apoptosis and to a sustained increase in electroretinogram amplitudes. We detected complexes between BiP, caspase-12, and the BH3-only protein BiK that may contribute to the antiapoptotic activity of BiP. Thus, the preservation of photoreceptor function resulting from elevated levels of BiP is due to suppression of apoptosis rather than to a promotion of rhodopsin folding.
Gorbatyuk
Marina S
MS
Department of Molecular Genetics, University of Florida, Gainesville, FL 32610, USA. mari653@ufl.edu
Knox
Tessa
T
LaVail
Matthew M
MM
Gorbatyuk
Oleg S
OS
Noorwez
Syed M
SM
Hauswirth
William W
WW
Lin
Jonathan H
JH
Muzyczka
Nicholas
N
Lewin
Alfred S
AS
D019943:Amino Acid Substitution; D000818:Animals; D017209:Apoptosis; D001483:Base Sequence; D000229:Dependovirus / Q000235:genetics; D004195:Disease Models, Animal; D004596:Electroretinography; D004721:Endoplasmic Reticulum / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D006367:HeLa Cells; D006360:Heat-Shock Proteins / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008954:Models, Biological; D046912:Multiprotein Complexes; D020125:Mutation, Missense; D020419:Photoreceptor Cells, Vertebrate / Q000473:pathology / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D055647:Rats, Transgenic; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012160:Retina / Q000473:pathology / Q000503:physiopathology; D012174:Retinitis Pigmentosa / Q000235:genetics / Q000473:pathology / Q000503:physiopathology / Q000628:therapy; D012243:Rhodopsin / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D013312:Stress, Physiological; D051742:Transcription Factor CHOP / Q000378:metabolism; D014162:Transfection; D056811:Unfolded Protein Response / Q000235:genetics / Q000502:physiology; D014785:Vision, Ocular / Q000235:genetics* / Q000502:physiology*
C497250:Ddit3 protein, mouse; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D046912:Multiprotein Complexes; D012333:RNA, Messenger; D011994:Recombinant Proteins; D051742:Transcription Factor CHOP; D012243:Rhodopsin