Dual CRALBP isoforms unveiled: iPSC-derived retinal modelling and AAV2/5-RLBP1 gene transfer raise considerations for effective therapy.

Inherited retinal diseases (IRDs) are characterised by progressive vision loss. There are over 270 causative IRD genes and variants within the same gene can cause clinically distinct disorders. One example is RLBP1 that encodes CRALBP. CRALBP is an essential protein in the rod and cone visual cycles that take place primarily in the retinal pigment epithelium (RPE) but also in Müller cells of the neuroretina. RLBP1 variants lead to three clinical subtypes: Bothnia dystrophy, retinitis punctata albescens and Newfoundland rod-cone dystrophy. We modelled RLBP1-IRD subtypes using patient-specific iPSC-derived RPE and identified pathophysiological markers that served as pertinent therapeutic read-outs. We developed an AAV2/5-mediated gene supplementation strategy and performed a proof-of-concept study in the human models, which was validated in vivo in an Rlbp1-/- murine model. Most importantly, we identified a previously unsuspected smaller CRALBP isoform that is naturally and differentially expressed both in the human and murine retina. This previously unidentified isoform is produced from an alternative methionine initiation site. This work provides further insights into CRALBP expression and RLBP1-associated pathophysiology and raises important considerations for successful gene supplementation therapy.

A dominant mutation in MAPKAPK3, an actor of p38 signaling pathway, causes a new retinal dystrophy involving Bruch's membrane and retinal pigment epithelium.

Inherited retinal dystrophies are clinically and genetically heterogeneous with significant number of cases remaining genetically unresolved. We studied a large family from the West Indies islands with a peculiar retinal disease, the Martinique crinkled retinal pigment epitheliopathy that begins around the age of 30 with retinal pigment epithelium (RPE) and Bruch's membrane changes resembling a dry desert land and ends with a retinitis pigmentosa. Whole-exome sequencing identified a heterozygous c.518T>C (p.Leu173Pro) mutation in MAPKAPK3 that segregates with the disease in 14 affected and 28 unaffected siblings from three generations. This unknown variant is predicted to be damaging by bioinformatic predictive tools and the mutated protein to be non-functional by crystal structure analysis. MAPKAPK3 is a serine/threonine protein kinase of the p38 signaling pathway that is activated by a variety of stress stimuli and is implicated in cellular responses and gene regulation. In contrast to other tissues, MAPKAPK3 is highly expressed in the RPE, suggesting a crucial role for retinal physiology. Expression of the mutated allele in HEK cells revealed a mislocalization of the protein in the cytoplasm, leading to cytoskeleton alteration and cytodieresis inhibition. In Mapkapk3-/- mice, Bruch's membrane is irregular with both abnormal thickened and thinned portions. In conclusion, we identified the first pathogenic mutation in MAPKAPK3 associated with a retinal disease. These findings shed new lights on Bruch's membrane/RPE pathophysiology and will open studies of this signaling pathway in diseases with RPE and Bruch's membrane alterations, such as age-related macular degeneration.

A novel dendritic cell subset involved in tumor immunosurveillance.

The interferon (IFN)-gamma-induced TRAIL effector mechanism is a vital component of cancer immunosurveillance by natural killer (NK) cells in mice. Here we show that the main source of IFN-gamma is not the conventional NK cell but a subset of B220(+)Ly6C(-) dendritic cells, which are atypical insofar as they express NK cell-surface molecules. Upon contact with a variety of tumor cells that are poorly recognized by NK cells, B220(+)NK1.1(+) dendritic cells secrete high levels of IFN-gamma and mediate TRAIL-dependent lysis of tumor cells. Adoptive transfer of these IFN-producing killer dendritic cells (IKDCs) into tumor-bearing Rag2(-/-)Il2rg(-/-) mice prevented tumor outgrowth, whereas transfer of conventional NK cells did not. In conclusion, we identified IKDCs as pivotal sensors and effectors of the innate antitumor immune response.

Hypolacrimia and Alacrimia as Diagnostic Features for Genetic or Congenital Conditions.

As part of the lacrimal apparatus, the lacrimal gland participates in the maintenance of a healthy eye surface by producing the aqueous part of the tear film. Alacrimia and hypolacrimia, which are relatively rare during childhood or young adulthood, have their origin in a number of mechanisms which include agenesia, aplasia, hypoplasia, or incorrect maturation of the gland. Moreover, impaired innervation of the gland and/or the cornea and alterations of protein secretion pathways can lead to a defective tear film. In most conditions leading to alacrimia or hypolacrimia, however, the altered tear film is only one of numerous defects that arise and therefore is commonly disregarded. Here, we have systematically reviewed all of those genetic conditions or congenital disorders that have alacrimia or hypolacrimia as a feature. Where it is known, we describe the mechanism of the defect in question. It has been possible to clearly establish the physiopathology of only a minority of these conditions. As hypolacrimia and alacrimia are rare features, this review could be used as a tool in clinical genetics to perform a quick diagnosis, necessary for appropriate care and counseling.

SPACR Encoded by IMPG1 Is Essential for Photoreceptor Survival by Interplaying between the Interphotoreceptor Matrix and the Retinal Pigment Epithelium.

Several pathogenic variants have been reported in the IMPG1 gene associated with the inherited retinal disorders vitelliform macular dystrophy (VMD) and retinitis pigmentosa (RP). IMPG1 and its paralog IMPG2 encode for two proteoglycans, SPACR and SPACRCAN, respectively, which are the main components of the interphotoreceptor matrix (IPM), the extracellular matrix surrounding the photoreceptor cells. To determine the role of SPACR in the pathological mechanisms leading to RP and VMD, we generated a knockout mouse model lacking Impg1, the mouse ortholog. Impg1-deficient mice show abnormal accumulation of autofluorescent deposits visible by fundus imaging and spectral-domain optical coherence tomography (SD-OCT) and attenuated electroretinogram responses from 9 months of age. Furthermore, SD-OCT of Impg1-/- mice shows a degeneration of the photoreceptor layer, and transmission electron microscopy shows a disruption of the IPM and the retinal pigment epithelial cells. The decrease in the concentration of the chromophore 11-cis-retinal supports this loss of photoreceptors. In conclusion, our results demonstrate the essential role of SPACR in maintaining photoreceptors. Impg1-/- mice provide a novel model for mechanistic investigations and the development of therapies for VMD and RP caused by IMPG1 pathogenic variants.

FATP1 inhibits 11-cis retinol formation via interaction with the visual cycle retinoid isomerase RPE65 and lecithin:retinol acyltransferase.

The isomerization of all-trans retinol (vitamin A) to 11-cis retinol in the retinal pigment epithelium (RPE) is a key step in the visual process for the regeneration of the visual pigment chromophore, 11-cis retinal. LRAT and RPE65 are recognized as the minimal isomerase catalytic components. However, regulators of this rate-limiting step are not fully identified and could account for the phenotypic variability associated with inherited retinal degeneration (RD) caused by mutations in the RPE65 gene. To identify new RPE65 partners, we screened a porcine RPE mRNA library using a yeast two-hybrid assay with full-length human RPE65. One identified clone (here named FATP1c), containing the cytosolic C-terminal sequence from the fatty acid transport protein 1 (FATP1 or SLC27A1, solute carrier family 27 member 1), was demonstrated to interact dose-dependently with the native RPE65 and with LRAT. Furthermore, these interacting proteins colocalize in the RPE. Cellular reconstitution of human interacting proteins shows that FATP1 markedly inhibits 11-cis retinol production by acting on the production of all-trans retinyl esters and the isomerase activity of RPE65. The identification of this new visual cycle inhibitory component in RPE may contribute to further understanding of retinal pathogenesis.

Caspase-dependent immunogenicity of doxorubicin-induced tumor cell death.

Systemic anticancer chemotherapy is immunosuppressive and mostly induces nonimmunogenic tumor cell death. Here, we show that even in the absence of any adjuvant, tumor cells dying in response to anthracyclins can elicit an effective antitumor immune response that suppresses the growth of inoculated tumors or leads to the regression of established neoplasia. Although both antracyclins and mitomycin C induced apoptosis with caspase activation, only anthracyclin-induced immunogenic cell death was immunogenic. Caspase inhibition by Z-VAD-fmk or transfection with the baculovirus inhibitor p35 did not inhibit doxorubicin (DX)-induced cell death, yet suppressed the immunogenicity of dying tumor cells in several rodent models of neoplasia. Depletion of dendritic cells (DCs) or CD8+T cells abolished the immune response against DX-treated apoptotic tumor cells in vivo. Caspase inhibition suppressed the capacity of DX-killed cells to be phagocytosed by DCs, yet had no effect on their capacity to elicit DC maturation. Freshly excised tumors became immunogenic upon DX treatment in vitro, and intratumoral inoculation of DX could trigger the regression of established tumors in immunocompetent mice. These results delineate a procedure for the generation of cancer vaccines and the stimulation of anti-neoplastic immune responses in vivo.

Simple and efficient: validation of a cotton wick electrode for animal electroretinography.

PURPOSE: Electroretinography (ERG) is a widely used technique to test retinal function in humans and animals. Recordings are particularly dependent on the type of electrodes used, with the best electrodes often being expensive and not always easy to use. The need of a simple and effective electrode type has led us to search the efficacy of different types of electrodes used in practice and compare them with the modified cotton wick electrode. MATERIAL AND METHODS: A modified type of electrode made of a cotton wick and impregnated with NaCl is described, and the ERG results were compared with other types of electrodes. RESULTS: Compared with standard metal wire loop electrodes, the cotton wick electrode results in obtaining higher amplitudes, a better inter-eye correlation in the same animal and a better reproducibility of the recordings over time. CONCLUSION: This cotton electrode is simple to make and easy to place. It provides reliable recordings during the entire life span of the animal and reliable comparisons between contralateral eyes, thus providing a powerful tool for ERG studies.

Best1 is a gene regulated by nerve injury and required for Ca2+-activated Cl- current expression in axotomized sensory neurons.

We investigated the molecular determinants of Ca(2+)-activated chloride current (CaCC) expressed in adult sensory neurons after a nerve injury. Dorsal root ganglia express the transcripts of three gene families known to induce CaCCs in heterologous systems: bestrophin, tweety, and TMEM16. We found with quantitative transcriptional analysis and in situ hybridization that nerve injury induced upregulation of solely bestrophin-1 transcripts in sensory neurons. Gene screening with RNA interference in single neurons demonstrated that mouse Best1 is required for the expression of CaCC in injured sensory neurons. Transfecting injured sensory neurons with bestrophin-1 mutants inhibited endogenous CaCC. Exogenous expression of the fusion protein green fluorescent protein-Bestrophin-1 in naive neurons demonstrated a plasma membrane localization of the protein that generates a CaCC with biophysical and pharmacological properties similar to endogenous CaCC. Our data suggest that Best1 belongs to a group of genes upregulated by nerve injury and supports functional CaCC expression in injured sensory neurons.

Dominant mutations in mtDNA maintenance gene SSBP1 cause optic atrophy and foveopathy.

Mutations in genes encoding components of the mitochondrial DNA (mtDNA) replication machinery cause mtDNA depletion syndromes (MDSs), which associate ocular features with severe neurological syndromes. Here, we identified heterozygous missense mutations in single-strand binding protein 1 (SSBP1) in 5 unrelated families, leading to the R38Q and R107Q amino acid changes in the mitochondrial single-stranded DNA-binding protein, a crucial protein involved in mtDNA replication. All affected individuals presented optic atrophy, associated with foveopathy in half of the cases. To uncover the structural features underlying SSBP1 mutations, we determined a revised SSBP1 crystal structure. Structural analysis suggested that both mutations affect dimer interactions and presumably distort the DNA-binding region. Using patient fibroblasts, we validated that the R38Q variant destabilizes SSBP1 dimer/tetramer formation, affects mtDNA replication, and induces mtDNA depletion. Our study showing that mutations in SSBP1 cause a form of dominant optic atrophy frequently accompanied with foveopathy brings insights into mtDNA maintenance disorders.

OPA1 gene therapy prevents retinal ganglion cell loss in a Dominant Optic Atrophy mouse model.

Dominant optic atrophy (DOA) is a rare progressive and irreversible blinding disease which is one of the most frequent forms of hereditary optic neuropathy. DOA is mainly caused by dominant mutation in the OPA1 gene encoding a large mitochondrial GTPase with crucial roles in membrane dynamics and cell survival. Hereditary optic neuropathies are commonly characterized by the degeneration of retinal ganglion cells, leading to the optic nerve atrophy and the progressive loss of visual acuity. Up to now, despite increasing advances in the understanding of the pathological mechanisms, DOA remains intractable. Here, we tested the efficiency of gene therapy on a genetically-modified mouse model reproducing DOA vision loss. We performed intravitreal injections of an Adeno-Associated Virus carrying the human OPA1 cDNA under the control of the cytomegalovirus promotor. Our results provide the first evidence that gene therapy is efficient on a mouse model of DOA as the wild-type OPA1 expression is able to alleviate the OPA1-induced retinal ganglion cell degeneration, the hallmark of the disease. These results displayed encouraging effects of gene therapy for Dominant Optic Atrophy, fostering future investigations aiming at clinical trials in patients.

Intralysosomal cystine accumulation in mice lacking cystinosin, the protein defective in cystinosis.

Cystinosis is an autosomal recessive disorder characterized by an accumulation of intralysosomal cystine. The causative gene, CTNS, encodes cystinosin, a seven-transmembrane-domain protein, which we recently showed to be a lysosomal cystine transporter. The most severe and frequent form of cystinosis, the infantile form, appears around 6 to 12 months, with a proximal tubulopathy (de Toni-Debré-Fanconi syndrome) and ocular damage. End-stage renal failure is reached by 10 years of age. Accumulation of cystine in all tissues eventually leads to multisystemic disease. Treatment with cysteamine, which reduces the concentration of intracellular cystine, delays disease progression but has undesirable side effects. We report the first Ctns knockout mouse model generated using a promoter trap approach. We replaced the last four Ctns exons by an internal ribosome entry site-betagal-neo cassette and showed that the truncated protein was mislocalized and nonfunctional. Ctns(-/-) mice accumulated cystine in all organs tested, and cystine crystals, pathognomonic of cystinosis, were observed. Ctns(-/-) mice developed ocular changes similar to those observed in affected individuals, bone defects and behavioral anomalies. Interestingly, Ctns(-/-) mice did not develop signs of a proximal tubulopathy, or renal failure. A preliminary therapeutic trial using an oral administration of cysteamine was carried out and demonstrated the efficiency of this treatment for cystine clearance in Ctns(-/-) mice. This animal model will prove an invaluable and unique tool for testing emerging therapeutics for cystinosis.

Optical Coherence Tomography: Imaging Mouse Retinal Ganglion Cells In Vivo.

Structural changes in the retina are common manifestations of ophthalmic diseases. Optical coherence tomography (OCT) enables their identification in vivo-rapidly, repetitively, and at a high resolution. This protocol describes OCT imaging in the mouse retina as a powerful tool to study optic neuropathies (OPN). The OCT system is an interferometry-based, non-invasive alternative to common post mortem histological assays. It provides a fast and accurate assessment of retinal thickness, allowing the possibility to track changes, such as retinal thinning or thickening. We present the imaging process and analysis with the example of the Opa1delTTAG mouse line. Three types of scans are proposed, with two quantification methods: standard and homemade calipers. The latter is best for use on the peripapillary retina during radial scans; being more precise, is preferable for analyzing thinner structures. All approaches described here are designed for retinal ganglion cells (RGC) but are easily adaptable to other cell populations. In conclusion, OCT is efficient in mouse model phenotyping and has the potential to be used for the reliable evaluation of therapeutic interventions.

Enrichment of non-synchronized cells in the G1, S and G2 phases of the cell cycle for the study of apoptosis.

The susceptibility of cells to apoptosis induction is deeply influenced by their position in the cell cycle. Unfortunately, however, current methods for the enrichment of cells in defined phases of the cell cycle are mostly based on the synchronization of cells by agents or conditions that are intrinsically toxic and induce apoptosis on their own. We developed a novel procedure for the purification of cells in distinct phases of the cell cycle. This method is based on the stable transfection of cells with a chimeric protein made up by histone H2B and green fluorescent protein (GFP). Cytofluorometric purification of cells defined by their size and their H2B-GFP-dependent fluorescence (which reflects chromatin and hence DNA content) allowed for the efficient separation of diploid and tetraploid cells in the fluorescence-activated cell sorter (FACS). Moreover, when applied to diploid cells, this method allowed for the enrichment of live, functional cells in the G1, S and G2 phases of the cell cycle. FACS-purified cells were viable and readily resumed the cell cycle upon reculture. While staurosporine was equally toxic for cells in any phase of the cell cycle, camptothecin was particularly toxic for cells in the S phase. Moreover, BAY11-7082, a specific inhibitor of the IKK complex required for NF-kappaB activation, exhibited a particular cell cycle-specific profile of toxicity (G2>S>G1). These results delineate a novel procedure for studying the intersection between cell cycle regulation and cell death mechanisms.

Increased immunogenicity of colon cancer cells by selective depletion of cytochrome C.

We and others have previously reported in an in vivo rat colon cancer cell model that cell death precedes and is necessary for the development of a specific antitumoral immune response. To sensitize colon cancer cells to death, we depleted cytochrome c by stable transfection with an antisense construct. Cytochrome c depletion sensitizes human and rat colon cancer cells to a nonapoptotic, nonautophagic death induced by various stimuli. This increased sensitization to a necrosis-like cell death may be related to a decrease in cellular ATP levels and an increase in reactive oxygen species production caused by cytochrome c depletion. In vivo, depletion of cytochrome c decreases the tumorigenicity of colon cancer cells in syngeneic rats without influencing their growth in immune-deficient animals. Furthermore, decreased expression of cytochrome c in tumor cells facilitates in vivo "necrotic" cell death and the induction of a specific immune response. These results delineate a novel strategy to sensitize colon cancer cells to chemotherapy and to increase their immunogenicity in immuno-competent hosts.

Cultured Cells from the Human Oocyte Cumulus Niche Are Efficient Feeders to Propagate Pluripotent Stem Cells.

Pluripotency is at the crossroads of stem cell research and biology of reproduction. The mature metaphase II oocyte contains the key factors for pluripotency induction and maintenance as assessed by its capacity to reprogram somatic nuclei. The cumulus cells (CCs) niche that surrounds the oocyte is crucial for its maturation and presumably for the oocyte to acquire its competence to confer pluripotency. In this study, we examined whether cells cultured from the human mature metaphase II oocyte CC niche (hCC) could be used as feeders for the propagation of human induced pluripotent stem cells. The induced pluripotent (iPS) cells cultured on hCC (hCC-iPS) were assessed for their pluripotency potential by their expression of pluripotency-associated genes such as Oct4, Nanog, and TRA1-60 and their competence to differentiate into the three germ layers in vitro (embryoid bodies) as well as in vivo (teratoma formation). We show that not only the hCC-iPS cells maintained their pluripotency potential, but they also exhibited much better self-renewal performance in terms of proliferation rate compared to the same cells cultured on human foreskin fibroblast (hFF) feeders (hFF-iPS). A comparative gene expression profile study of hCC and hFF revealed significant differences (P < 0.05) in expression of cellular matrix components and an upregulation in hCC of genes known to be important players in cell proliferation such as interleukin 6 gene (IL6).

Expression of SR-BI receptor and StAR protein in rat ocular tissues.

The class-B type-I scavenger receptor (SR-BI) plays a key role in cholesterol homeostasis; it mediates the selective uptake of lipoprotein cholesterol to steroidogenic tissues. We show by RT-PCR, western blot, in situ hybridization and immunohistochemistry analysis that SR-BI is highly expressed in different neuro-retinal and non-neuronal cells types on rat eye. Immunohistochemistry of the steroidogenic acute regulatory protein (StAR) involved in neurosteroid production showed the same expression pattern than SR-BI in rat eye. Our results may suggest a key role of these genes in the ocular cholesterol metabolism for membranes biosynthesis and neurosteroidogenesis.

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.

Side scatter intensity is highly heterogeneous in undifferentiated pluripotent stem cells and predicts clonogenic self-renewal.

In culture, human pluripotent stem cells (PSCs) are phenotypically (for instance, the SSEA3 expression level) and functionally (capacity to survive after single-cell dissociation) heterogeneous. We report here that the side scatter (SSC) signal measured by flow cytometry, a variable correlated with membrane irregularity and cell granularity, is very high in PSCs, even higher than in blood polymorphonuclear cells, and markedly heterogeneous. Moreover, SSC intensity rapidly and strongly decreases upon PSC differentiation into any of the three germ layers. PSCs with high SSC (HSSC cells) or low SSC (LSSC cells) values both express pluripotency markers, but HSSC cells are characterized by more frequent simultaneous expression of the membrane pluripotency factors SSEA3, SSEA4, TRA-1-81, TRA-1-60, and CD24 and by a higher mitochondrial content. Functionally, HSSC cells are more likely to generate colonies upon single-cell passage than LSSC cells. SSC monitoring might provide a simple, but robust and rapid method to estimate pluripotency variations in culture and unveils a new phenotypic and functional heterogeneity in PSCs.

Fatp1 deficiency affects retinal light response and dark adaptation, and induces age-related alterations.

FATP1 is involved in lipid transport into cells and in intracellular lipid metabolism. We showed previously that this protein interacts with and inhibits the limiting-step isomerase of the visual cycle RPE65. Here, we aimed to analyze the effect of Fatp1-deficiency in vivo on the visual cycle, structure and function, and on retinal aging. Among the Fatp family members, we observed that only Fatp1 and 4 are expressed in the control retina, in both the neuroretina and the retinal pigment epithelium. In the neuroretina, Fatp1 is mostly expressed in photoreceptors. In young adult Fatp1(-/-) mice, Fatp4 expression was unchanged in retinal pigment epithelium and reduced two-fold in the neuroretina as compared to Fatp1(+/+) mice. The Fatp1(-/-) mice had a preserved retinal structure but a decreased electroretinogram response to light. These mice also displayed a delayed recovery of the b-wave amplitude after bleaching, however, visual cycle speed was unchanged, and both retinal pigment epithelium and photoreceptors presented the same fatty acid pattern compared to controls. In 2 year-old Fatp1(-/-) mice, transmission electron microscopy studies showed specific abnormalities in the retinas comprising choroid vascularization anomalies and thickening of the Bruch membrane with material deposits, and sometimes local disorganization of the photoreceptor outer segments. These anomalies lead us to speculate that the absence of FATP1 accelerates the aging process.