Rab Escort Protein Research Articles

REP1 Modulates Autophagy and Macropinocytosis to Enhance Cancer Cell Survival.

Rab escort protein 1 (REP1), a component of the Rab geranyl-geranyltransferase 2 complex, plays a role in Rab protein recruitment in proper vesicles during vesicle trafficking. In addition to having well-known tissue degenerative phenotypes in the REP1 mutant, REP1 is tightly associated with cancer development and contributes to cell growth and survival. However, the functional mechanism of REP1 in cancer progression is largely uninvestigated. Here, we show that REP1 plays a crucial role in regulating mammalian target of rapamycin (mTOR) signaling and its downstream pathways, as well as autophagy and macropinocytosis, which are essential for cancer cell survival during metabolic stresses including starvation. REP1 small interfering RNA (siRNA) treatment downregulates mTORC1 activity in growing media, but blocks autophagosome formation under nutrient-depleted conditions. In contrast to the mild decrease of lysosomal enzyme activity seen in REP1 depletion, in REP1 knockdown the subcellular localization of lysosomes is altered, and localization of REP1 itself is modulated by intracellular nutrient levels and mTOR activity. Furthermore, REP1 depletion increases macro pinocytosis which may be a feedback mechanism to compensate autophagy inhibition. Concomitant treatment with macropinocytosis inhibitor and REP1siRNAresults in more significant cell death than autophagy blockade with REP1 knockdown. Therefore, REP1-mediated autophagy and lysosomal degradation processes act as novel regulatory mechanisms to support cancer cell survival, which can be further investigated as a potential cancer-targeting pathway.

Rep1 copy number variation is an important genetic cause of choroideremia in Chinese patients

Choroidermia (CHM) is an X-linked chorioretinal disorder caused by mutations in the Rab Escort Protein 1 (Rep-1) gene. Its diagnosis depends on clinical findings and genetic confirmation; however, mutations in Rep-1 gene are not always detected by standard Sanger sequencing. We therefore conducted multiplex ligation-dependent probe amplification (MLPA) and real-time quantitative PCR (QPCR) in cases of Chinese CHM families in which sequencing all the exons and flanking intronic regions of the CHM gene had not identified a mutation or exons could not be amplified. We hypothesized that copy number variation (CNV) within the Rep-1 gene would explain the etiology of choroideremia in these patients. In the eight unrelated families, exon deletions or duplications were detected by MLPA and QPCR in five. Our results showed CNV within the Rep-1 gene could be an important contributor in Chinese CHM patients. Sequencing of the Rep-1 gene supplemented with MLPA is therefore an important diagnostic strategy in choroideremia patients.

Novel non‐contiguous exon duplication in choroideremia

The importance of establishing a genetic diagnosis in patients with a choroideremia phenotype has been underscored by the advent of gene replacement therapy for this condition. Here, we describe a complex imbalance at the CHM locus in a male patient with classical disease. At the DNA level, this imbalance consists of 2 non-contiguous duplications (exons 1-2 and 9-12). Further characterization suggests the generation of 2 independent CHM transcriptional units, one of which may produce a deleted form of the Rab escort protein 1 protein. Expression of such a type of aberrant protein in photoreceptors may have important implications when considering gene therapy for this disorder.

Single-base substitutions in the CHM promoter as a cause of choroideremia.

Although over 150 unique mutations affecting the coding sequence of CHM have been identified in patients with the X-linked chorioretinal disease choroideremia (CHM), no regulatory mutations have been reported, and indeed the promoter has not been defined. Here, we describe two independent families affected by CHM bearing a mutation outside the gene's coding region at position c.-98: C>A and C>T, which segregated with the disease. The male proband of family 1 was found to lack CHM mRNA and its gene product Rab escort protein 1, whereas whole-genome sequencing of an affected male in family 2 excluded the involvement of any other known retinal genes. Both mutations abrogated luciferase activity when inserted into a reporter construct, and by further employing the luciferase reporter system to assay sequences 5' to the gene, we identified the CHM promoter as the region encompassing nucleotides c.-119 to c.-76. These findings suggest that the CHM promoter region should be examined in patients with CHM who lack coding sequence mutations, and reveals, for the first time, features of the gene's regulation.

Structural and Functional Recovery Following Limited Iatrogenic Macular Detachment for Retinal Gene Therapy

The early decline and recovery of retinal structure and function following iatrogenic macular detachment for retinal gene therapy is not well characterized in those with relatively preserved central visual function. Here, the recovery of retinal structure and function over the first month following iatrogenic retinal detachment for the delivery of adeno-associated viral vector encoding Rab Escort Protein 1 is described as a part of gene therapy for choroideremia. To study changes in both retinal structure and function during the first month following iatrogenic macular detachment surgery. This prospective interocularly controlled study was conducted between February 1 and December 31, 2015. Treatment consisted of a subretinal injection of 0.1 mL of a gene therapy solution containing 1 × 1011 viral particles performed unilaterally. The participants were 5 males, aged 23 to 71 years, with a clinical and genetic diagnosis of choroideremia. Retinal structure and function were assessed at baseline, 1 week, and 1 month using optical coherence tomography, logMAR visual acuity, microperimetry, the Farnsworth-Munsell (FM) 100-hue test, and the Rayleigh match. Five white male patients aged 23 to 71 years underwent unilateral subretinal gene therapy for genetically confirmed choroidermeia. Optical coherence tomographic images demonstrated a complete resolution of the resulting iatrogenic retinal detachment by 1 week in all 5 patients. At 1 month, the mean (SE) change in central foveal thickness was +9.6 (7.2) μm in treated eyes and +8.8 (12.6) μm in control eyes. The mean (SE) change in visual acuity was +5.4 (3.3) letters in treated eyes and +0.8 (3.1) letters in control eyes. At 1 month, the mean (SE) threshold sensitivity changes were -1.2 (2.1) dB in treated eyes and -1.0 (1.2) dB in control eyes. Color discrimination at the FM 100-hue changed little at 1 month (mean [SE] change in C-index, -0.2 [0.4] in treated eyes and 0.1 [0.2] in control eyes). Rayleigh matches in 1 patient were consistent with a diagnosis of pseudoprotanomaly, suggesting decreased effective optical density of the cone photopigments. Retinal structural recovery-as assessed by optical coherence tomography-occurs soon after iatrogenic detachment. Similarly, visual acuity recovers or improves within 1 month of the procedure and may not be accompanied by improvements in threshold sensitivity or color discrimination. Changes in color matching in 1 patient suggest decreased optical density of the cone photopigments in the early postoperative period.

Oncogenic role of rab escort protein 1 through EGFR and STAT3 pathway

Rab escort protein-1 (REP1) is linked to choroideremia (CHM), an X-linked degenerative disorder caused by mutations of the gene encoding REP1 (CHM). REP1 mutant zebrafish showed excessive cell death throughout the body, including the eyes, indicating that REP1 is critical for cell survival, a hallmark of cancer. In the present study, we found that REP1 is overexpressed in human tumor tissues from cervical, lung, and colorectal cancer patients, whereas it is expressed at relatively low levels in the normal tissue counterparts. REP1 expression was also elevated in A549 lung cancer cells and HT-29 colon cancer cells compared with BEAS-2B normal lung and CCD-18Co normal colon epithelial cells, respectively. Interestingly, short interfering RNA (siRNA)-mediated REP1 knockdown-induced growth inhibition of cancer cell lines via downregulation of EGFR and inactivation of STAT3, but had a negligible effect on normal cell lines. Moreover, overexpression of REP1 in BEAS-2B cells enhanced cell growth and anchorage-independent colony formation with little increase in EGFR level and STAT3 activation. Furthermore, REP1 knockdown effectively reduced tumor growth in a mouse xenograft model via EGFR downregulation and STAT3 inactivation in vivo. These data suggest that REP1 plays an oncogenic role, driving tumorigenicity via EGFR and STAT3 signaling, and is a potential therapeutic target to control cancers.

REP1 inhibits FOXO3-mediated apoptosis to promote cancer cell survival

Rab escort protein 1 (REP1) is a component of Rab geranyl-geranyl transferase 2 complex. Mutations in REP1 cause a disease called choroideremia (CHM), which is an X-linked eye disease. Although it is postulated that REP1 has functions in cell survival or death of various tissues in addition to the eye, how REP1 functions in normal and cancer cells remains to be elucidated. Here, we demonstrated that REP1 is required for the survival of intestinal cells in addition to eyes or a variety of cells in zebrafish, and also has important roles in tumorigenesis. Notably, REP1 is highly expressed in colon cancer tissues and cell lines, and silencing of REP1 sensitizes colon cancer cells to serum starvation- and 5-FU-induced apoptosis. In an effort to elucidate the molecular mechanisms underlying REP1-mediated cell survival under those stress conditions, we identified FOXO3 as a binding partner of REP1 using a yeast two-hybrid (Y2H) assay system, and we demonstrated that REP1 blocked the nuclear trans-localization of FOXO3 through physically interacting with FOXO3, thereby suppressing FOXO3-mediated apoptosis. Importantly, the inhibition of REP1 combined with 5-FU treatment could lead to significant retarded tumor growth in a xenograft tumor model of human cancer cells. Thus, our results suggest that REP1 could be a new therapeutic target in combination treatment for colon cancer patients.

Novel CHM mutations identified in Chinese families with Choroideremia

Choroideremia is a bilateral and progressive X-linked inherited disease characterized by widespread chorioretinal atrophy with relative sparing of the macular region. It is caused by mutations in the ubiquitously expressed CHM gene, which lead to the absence of the Rab escort protein 1 (REP-1), resulting in prenylation deficiency. Typical fundus appearances for choroideremia were found in 3 probands from three unrelated Chinese families in our study. We firstly used the targeted exome sequencing (TES) technology to detect mutations in CHM gene. Based on an established filtering strategy of data analyses, along with confirmation by co-segregation, a previously reported mutation (c.1584_1587del TGTT, p.V529Hfs*7) was identified in one family, while two novel mutations (c.227_232delinsTGTCATTTCA, p.Q76Lfs*7; c.710dupA, p.Y237_S238delinsX) were identified in the other two families. These findings not only expands the currently limited spectrum of Chinese disease-causing variants in CHM gene, but also increases our understanding of the phenotypic and genotypic correlations of choroideremia, and may potentially lead to improved genetic counseling and specific treatment for families with choroideremia as well.

31. AAV Gene Therapy for Choroideremia: Dose Determination Analyses

Choroideremia (CHM) is a degenerative, X-linked retinal disease characterized by deletions or mutations in the choroideremia (CHM) gene, resulting in defective or absent Rab escort protein-1 (REP-1). In normal retinas, the CHM gene is expressed in multiple cell types, including retinal pigment epithelium, photoreceptors, and choroidal cells, though there is evidence that the RPE cell is the primary disease-causing cell type. Absence or deficiency of REP-1 leads to cellular apoptosis and degeneration of the retinal pigment epithelium (RPE), choroid, and retinal photoreceptors. Choroideremia is an excellent disease candidate for gene transfer as it shares several key features with other inherited retinal degenerative diseases that are also candidates for AAV-mediated vector delivery. These features include: a) the small and localized nature of the target area, namely the retina; b) the tissue boundaries surrounding the area to be injected, which minimizes exposure of other cells to the vector and facilitates treatment with a relatively small vector dose; and c) the favorable immune status of the eye with respect to viral vector-mediated gene transfer. We are conducting a Phase 1 clinical trial to treat CHM subjects using either 5×1010 or 1×1011 vg/eye of an AAV2-hRep1 vector, and delivering the vector via a subretinal injection. Due to the lack of suitable animal models that mimic CHM disease in humans, we took a different approach to assess the potential therapeutic dose. A molecular analysis of non-human primate retinas was performed following subretinal injection of AAV2-hCHM to determine the relative amount of human Rep1 compared to endogenous monkey Rep1. Cynomolgus monkey eyes were injected subretinally with either 5×1011, 7.5×1011 or 2×1012 vg of AAV2-hRep1. Fundus images were taken following the injection of 300 ul of vector, and these images were used at the time of sacrifice to dissect the tissue associated with the injection bleb. The remaining retina was also collected and analyzed separately. RNA was isolated and absolute quantitative RT-PCR was performed using both cynomolgus monkey-specific Rep1 primers/probe and human Rep1-specific primers/probe. No human Rep1 mRNA was observed in non-injected eyes, and the amount of human Rep1 mRNA in the bleb area was determined to be at least 50 fold higher than cynomolgus Rep1 mRNA following a dose of 5×1011 vg/eye. At the two higher doses, similar levels of hRep1 mRNA, ranging from 270-380 times more than cynomolgus Rep1 mRNA, were observed. These data suggest that in the Phase 1 clinical trial, the low dose subjects (5×1010 vg/eye) will express hRep1 at a level approximately five fold higher than normal and the high dose subjects will express at least 10 fold higher levels of hRep1 than normal. Ongoing studies are evaluating the level of hRep1 in normal human retinas to confirm these ratios. Thus, the results from this non-conventional pharmacology model provide an estimate of the potential therapeutic dose of AAV2-hCHM for use in clinical studies.

Analysis of a large choroideremia dataset does not suggest a preference for inclusion of certain genotypes in future trials of gene therapy

BackgroundChoroideremia (CHM) is an X‐linked degeneration of the retinal pigment epithelium, photoreceptors, and choroid, which causes nyctalopia and progressive constriction of visual fields leading to blindness. The CHM gene encodes Rab escort protein 1 (REP‐1). In this work, we reviewed the phenotypes and genotypes of affected males with the purpose of understanding the functional effects of CHM mutations and their relationship with the phenotypes.MethodsA retrospective review of 128 affected males was performed analyzing the onset of symptoms, visual acuity, and visual fields with respect to their mutations in the CHM gene.ResultsIn rank order, reflecting data from this report, the most common mutations found in the CHM gene were nonsense mutations (41%), exon deletions (37%), and splice sites (14%) associated with a loss of functional protein. In the pool of 106 CHM mutations, we discovered four novel missense mutations (c.238C>T; p.L80F, c.819G>T; p.Q273H, c.1327A>G; p.M443V, and c.1370C>T; p.L457P) predicted to be severe changes affecting protein stability and folding with the effect similar to that of other types of mutations. No significant genotype–phenotype correlation was found with respect to the onset of nyctalopia, the onset of other visual symptoms, visual acuity, or width of visual fields.ConclusionThere is no evidence to support exclusion of CHM patients from clinical trials based on their genotypes or any potential genotype–phenotype correlations.

Genetic analysis and clinical phenotype of two Indian families with X-linked choroideremia.

Purpose:This study aims to describe the phenotype and genotype of two Indian families affected with X-linked choroideremia (CHM).Materials and Methods:In these two families, the affected individuals and unaffected family members underwent a comprehensive ophthalmic examination including an optical coherence tomography (OCT) and electroretinogram. Blood samples were collected from the families for genetic analysis. Next generation sequencing (NGS) was done using a panel of 184 genes, which covered previously associated genes with retinal dystrophies. Sequencing data were analyzed for the CHM, RPGR, and RP2 genes that have been implicated in CHM and X-linked retinitis pigmentosa (XLRP), respectively. The identified variants were confirmed by Sanger sequencing in available individuals and unrelated controls.Results:In two unrelated male patients, NGS analysis revealed a previously reported 3’-splice site change c.820-1G>C in the CHM gene in the first family and hemizygous mutation c.653G>C (p.Ser218X) in the second family. The asymptomatic family members were carriers for these mutations. Spectral domain-OCT showed loss of outer retina, preservation of the inner retina, and choroidal thinning in the affected males and retinal pigment epithelial changes in the asymptomatic carriers. The identified mutations were not present in 100 controls of Indian origin. There were no potential mutations found in XLRP-associated (RPGR and RP2) genes.Conclusion:This report describes the genotype and phenotype findings in patients with CHM from India. The identified genetic mutation leads to lack of Rab escort protein-1 (REP-1) or affects the production of a REP-1 protein that is likely to cause retinal abnormalities in patients.

Arabidopsis Rab Geranylgeranyltransferases Demonstrate Redundancy and Broad Substrate Specificity in Vitro

Posttranslational lipid modifications mediate the membrane attachment of Rab GTPases, facilitating their function in regulating intracellular vesicular trafficking. In Arabidopsis, most Rab GTPases have two C-terminal cysteines and potentially can be double-geranylgeranylated by heterodimeric Rab geranylgeranyltransferases (Rab-GGTs). Genes encoding two putative α subunits and two putative β subunits of Rab-GGTs have been annotated in the Arabidopsis thaliana genome, but little is known about Rab-GGT activity in Arabidopsis. In this study, we demonstrate that four different heterodimers can be formed between putative Arabidopsis Rab-GGT α subunits RGTA1/RGTA2 and β subunits RGTB1/RGTB2, but only RGTA1·RGTB1 and RGTA1·RGTB2 exhibit bona fide Rab-GGT activity, and they are biochemically redundant in vitro. We hypothesize that RGTA2 function might be disrupted by a 12-amino acid insertion in a conserved motif. We present evidence that Arabidopsis Rab-GGTs may have preference for prenylation of C-terminal cysteines in particular positions. We also demonstrate that Arabidopsis Rab-GGTs can not only prenylate a great variety of Rab GTPases in the presence of Rab escort protein but, unlike Rab-GGT in yeast and mammals, can also prenylate certain non-Rab GTPases independently of Rab escort protein. Our findings may help to explain some of the phenotypes of Arabidopsis protein prenyltransferase mutants.

Whole-exome sequencing reveals a novel CHM gene mutation in a family with choroideremia initially diagnosed as retinitis pigmentosa.

BackgroundGenomic mutations in about 200 genes are associated with hereditary retinal diseases. In this study, we screened for the disease-causing gene mutation in a family with X-linked retinal degenerative disease.MethodsPedigree data were collected and genomic DNA was isolated from peripheral blood of family members, who also underwent comprehensive ophthalmic examination including visual acuity, slit-lamp examination, fundus examination and visual field testing at Qilu Hospital of Shandong University. Whole-exome genomic sequencing was used to screen for gene mutations in the male proband. Sanger sequencing was used to confirm the mutation revealed in this family.ResultsTwo affected males underwent ophthalmic examination; retinitis pigmentosa (RP) was diagnosed on the basis of night blindness beginning at an early age, decreasing visual acuity, progressive loss of peripheral vision, attenuation of retinal vessels and pigment disturbance on fundus examination. However, whole-exome sequencing revealed no mutation in RP-associated genes. Instead, we identified a novel hemizygous c.1475_1476insCA mutation in the choroideremia-associated gene (CHM). The mutation was confirmed by Sanger sequencing and further excluded from the possibility as a rare polymorphism. From the genetic data and clinical findings, the diagnosis was corrected to choroideremia (CHM). Further molecular genetic analysis suggested that this novel CHM mutation caused a frame shift (p.Leu492PhefsX7) and encoded a truncated nonfunctional Rab escort protein 1 (REP-1), which caused CHM in this family. Finally, sequencing data for a pregnant female member confirmed that she did not carry the mutation and thus was carrying a healthy infant.ConclusionWe report a novel CHM mutation, c.1475_1476insCA, identified by whole-exome sequencing in a family with X-linked CHM initially diagnosed as RP. Our findings emphasize the value of a diagnostic approach that associates genetic and ophthalmologic data to facilitate the proper clinical diagnosis of rare hereditary retinal diseases such as CHM.

Molecular characterization and identification of target protein of an important vesicle trafficking gene AlRab7 from a salt excreting halophyte Aeluropus lagopoides.

The endomembrane system plays an important role during cellular adaptation of the plants with the extracellular environment. The small GTP-binding protein Rab7 located at the vacuolar membrane regulates the vesicle fusion with the vacuole and thereby helps in recycling of the molecules. This is the first report on isolation and characterization of AlRab7 gene from the halophyte plant, Aeluropus that extrudes NaCl through salt glands and grows luxuriantly throughout the year at the Gujarat coast, India. The AlRab7 encodes a protein with 206 amino acids, and a highly conserved effector-binding domain and four nucleotide-binding domains. The in silico analysis predicts the presence of the prenylation site for Rab geranylgeranyltransferase 2 and the Rab escort protein site. The C-terminal two cysteine residues in -XCC sequence are present for membrane attachment. Transcript expression of the AlRab7 gene was differentially regulated by different environmental stimuli such as dehydration, salinity, and hormone abscisic acid (ABA). The recombinant Escherichia coli cells showed improved growth in Luria Bertani medium supplemented with NaCl, KCl, mannitol, ABA, and indole-3-acetic acid. A novel Rab7 interacting partner AlRabring7 was identified by yeast two-hybrid screening.

Gene therapy for choroideremia using an adeno-associated viral (AAV) vector.

Choroideremia is an outer retinal degeneration with a characteristic clinical appearance that was first described in the nineteenth century. The disorder begins with reduction of night vision and gradually progresses to blindness by middle age. The appearance of the fundus in sufferers is recognizable by the characteristic pale color caused by the loss of the outer retina, retinal-pigmented epithelium, and choroidal vessels, leading to exposure of the underlying sclera. Choroideremia shows X-linked recessive inheritance and the choroideremia gene (CHM) was one of the first to be identified by positional cloning in 1990. Subsequent identification and characterization of the CHM gene, which encodes Rab escort protein 1 (REP1), has led to better comprehension of the disease and enabled advances in genetic diagnosis. Despite several decades of work to understand the exact pathogenesis, no established treatments currently exist to stop or even slow the progression of retinal degeneration in choroideremia. Encouragingly, several specific molecular and clinical features make choroideremia an ideal candidate for treatment with gene therapy. This work describes the considerations and challenges in the development of a new clinical trial using adeno-associated virus (AAV) encoding the CHM gene.

Gene therapy for choroideremia

AbstractPurpose This talk will cover the development and instigation of a clinical gene therapy trial for choroideremia. It will also outline some early results of the trial, which is currently still ongoing. Methods Development of the gene therapy vector involved a range of in vitro and in vivo studies, from cell‐based protein assays to ERGs in laboratory mice. The trial is an open label dose escalation study, involving two groups treated with different doses of adeno‐associated viral vector (AAV2) encoding Rab‐escort Protein 1 (REP1). A range of clinical tests are used to assess the safety and efficacy of treatment. Results Preclinical results show AAV can successfully produce functional REP1 protein in patient fibroblasts. The vector shows targeting of retinal cells and has good safety and efficacy in animal models. So far in the clinical trial, 6 patients have been treated with the low dose AAV.REP1 vector. Early results show good safety and some encouraging functional effects. Conclusions A gene therapy trial for choroideremia is ongoing, with some promising early results. This is the first time gene therapy has been tested in people with normal visual acuity and may have implications for other inherited retinal diseases.

Intramitochondrial recruitment of endolysosomes mediates Smac degradation and constitutes a novel intrinsic apoptosis antagonizing function of XIAP E3 ligase.

Intrinsic apoptosis involves BH3-only protein activation of Bax/Bak-mediated mitochondrial outer membrane permeabilization (MOMP). Consequently, cytochrome c is released from the mitochondria to activate caspases, and Smac (second mitochondria-derived activator of caspases) to inhibit XIAP-mediated caspase suppression. Dysfunctional mitochondria can be targeted for lysosomal degradation via autophagy (mitophagy), or directly through mitochondria-derived vesicle transport. However, the extent of autophagy and lysosomal interactions with apoptotic mitochondria remains largely unknown. We describe here a novel pathway of endolysosomal processing of mitochondria, activated in response to canonical BH3-only proteins and mitochondrial depolarization. We report that expression of canonical BH3-only proteins, tBid, BimEL, Bik, Bad, and mitophagy receptor mutants of atypical BH3-only proteins, Bnip3 and Bnip3L/Nix, leads to prominent relocalization of endolysosomes into inner mitochondrial compartments, in a manner independent of mitophagy. As an upstream regulator, we identified the XIAP E3 ligase. In response to mitochondrial depolarization, XIAP actuates Bax-mediated MOMP, even in the absence of BH3-only protein signaling. Subsequently, in an E3 ligase-dependent manner, XIAP rapidly localizes inside all the mitochondria, and XIAP-mediated mitochondrial ubiquitylation catalyses interactions of Rab membrane targeting components Rabex-5 and Rep-1 (RFP-tagged Rab escort protein-1), and Rab5- and Rab7-positive endolysosomes, at and within mitochondrial membrane compartments. While XIAP-mediated MOMP permits delayed cytochrome c release, within the mitochondria XIAP selectively signals lysosome- and proteasome-associated degradation of its inhibitor Smac. These findings suggest a general mechanism to lower the mitochondrial apoptotic potential via intramitochondrial degradation of Smac.

Adeno-associated virus 8-mediated gene therapy for choroideremia: preclinical studies in in vitro and in vivo models.

Choroideremia (CHM) is a slowly progressive X-linked retinal degeneration that results in a loss of photoreceptors, retinal pigment epithelium and choroid. CHM, the gene implicated in choroideremia, encodes Rab escort protein-1 (REP-1), which is involved in the post-translational activation via prenylation of Rab proteins. We evaluated AAV8.CBA.hCHM, a recombinant adeno-associated virus serotype 8 (rAAV8) vector, which targets retinal cells efficiently, for both therapeutic effect and safety in vitro and in vivo in a murine model. In vitro studies included western blot analyses and prenylation assays. In vivo studies included ophthalmoscopy, pupillometry, histology and immunofluorescence analysis. Infection with AAV8.CBA.hCHM induced the expression of REP-1 protein in a dose-responsive fashion. Transduction with AAV8.CBA.hCHM reverses the biochemical and pathogenetic defects in CHM both in vitro and in vivo and showed no safety concerns in the in vivo investigations performed in the present study. AAV8 is a promising vector for human clinical gene therapy trials for choroideremia.

Retinal gene therapy in patients with choroideremia: initial findings from a phase 1/2 clinical trial

SummaryBackgroundChoroideremia is an X-linked recessive disease that leads to blindness due to mutations in the CHM gene, which encodes the Rab escort protein 1 (REP1). We assessed the effects of retinal gene therapy with an adeno-associated viral (AAV) vector encoding REP1 (AAV.REP1) in patients with this disease.MethodsIn a multicentre clinical trial, six male patients (aged 35–63 years) with choroideremia were administered AAV.REP1 (0·6–1·0×1010 genome particles, subfoveal injection). Visual function tests included best corrected visual acuity, microperimetry, and retinal sensitivity tests for comparison of baseline values with 6 months after surgery. This study is registered with ClinicalTrials.gov, number NCT01461213.FindingsDespite undergoing retinal detachment, which normally reduces vision, two patients with advanced choroideremia who had low baseline best corrected visual acuity gained 21 letters and 11 letters (more than two and four lines of vision). Four other patients with near normal best corrected visual acuity at baseline recovered to within one to three letters. Mean gain in visual acuity overall was 3·8 letters (SE 4·1). Maximal sensitivity measured with dark-adapted microperimetry increased in the treated eyes from 23·0 dB (SE 1·1) at baseline to 25·3 dB (1·3) after treatment (increase 2·3 dB [95% CI 0·8–3·8]). In all patients, over the 6 months, the increase in retinal sensitivity in the treated eyes (mean 1·7 [SE 1·0]) was correlated with the vector dose administered per mm2 of surviving retina (r=0·82, p=0·04). By contrast, small non-significant reductions (p>0·05) were noted in the control eyes in both maximal sensitivity (–0·8 dB [1·5]) and mean sensitivity (–1·6 dB [0·9]). One patient in whom the vector was not administered to the fovea re-established variable eccentric fixation that included the ectopic island of surviving retinal pigment epithelium that had been exposed to vector.InterpretationThe initial results of this retinal gene therapy trial are consistent with improved rod and cone function that overcome any negative effects of retinal detachment. These findings lend support to further assessment of gene therapy in the treatment of choroideremia and other diseases, such as age-related macular degeneration, for which intervention should ideally be applied before the onset of retinal thinning.FundingUK Department of Health and Wellcome Trust.

Proof of concept for AAV2/5-mediated gene therapy in iPSC-derived retinal pigment epithelium of a choroideremia patient

Inherited retinal dystrophies (IRDs) comprise a large group of genetically and clinically heterogeneous diseases that lead to progressive vision loss, for which a paucity of disease-mimicking animal models renders preclinical studies difficult. We sought to develop pertinent human cellular IRD models, beginning with choroideremia, caused by mutations in the CHM gene encoding Rab escort protein 1 (REP1). We reprogrammed REP1-deficient fibroblasts from a CHM-/y patient into induced pluripotent stem cells (iPSCs), which we differentiated into retinal pigment epithelium (RPE). This iPSC-derived RPE is a polarized monolayer with a classic morphology, expresses characteristic markers, is functional for fluid transport and phagocytosis, and mimics the biochemical phenotype of patients. We assayed a panel of adeno-associated virus (AAV) vector serotypes and showed that AAV2/5 is the most efficient at transducing the iPSC-derived RPE and that CHM gene transfer normalizes the biochemical phenotype. The high, and unmatched, in vitro transduction efficiency is likely aided by phagocytosis and mimics the scenario that an AAV vector encounters in vivo in the subretinal space. We demonstrate the superiority of AAV2/5 in the human RPE and address the potential of patient iPSC–derived RPE to provide a proof-of-concept model for gene replacement in the absence of an appropriate animal model.