Chromophore supply modulates cone function and survival in retinitis pigmentosa mouse models.

Retinitis pigmentosa (RP) is an ocular disease characterized by the loss of night vision, followed by the loss of daylight vision. Daylight vision is initiated in the retina by cone photoreceptors, which are gradually lost in RP, often as bystanders in a disease process that initiates in their neighboring rod photoreceptors. Using physiological assays, we investigated the timing of cone electroretinogram (ERG) decline in RP mouse models. A correlation between the time of loss of the cone ERG and the loss of rods was found. To investigate a potential role of the visual chromophore supply in this loss, mouse mutants with alterations in the regeneration of the retinal chromophore, 11-cis retinal, were examined. Reducing chromophore supply via mutations in Rlbp1 or Rpe65 resulted in greater cone function and survival in a RP mouse model. Conversely, overexpression of Rpe65 and Lrat, genes that can drive the regeneration of the chromophore, led to greater cone degeneration. These data suggest that abnormally high chromophore supply to cones upon the loss of rods is toxic to cones, and that a potential therapy in at least some forms of RP is to slow the turnover and/or reduce the level of visual chromophore in the retina.

Organ- and Cell-Selective Delivery of mRNA In Vivo Using Guanidinylated Serinol Charge-Altering Releasable Transporters.

Selective RNA delivery is required for the broad implementation of RNA clinical applications, including prophylactic and therapeutic vaccinations, immunotherapies for cancer, and genome editing. Current polyanion delivery relies heavily on cationic amines, while cationic guanidinium systems have received limited attention due in part to their strong polyanion association, which impedes intracellular polyanion release. Here, we disclose a general solution to this problem in which cationic guanidinium groups are used to form stable RNA complexes upon formulation but at physiological pH undergo a novel charge-neutralization process, resulting in RNA release. This new delivery system consists of guanidinylated serinol moieties incorporated into a charge-altering releasable transporter (GSer-CARTs). Significantly, systematic variations in structure and formulation resulted in GSer-CARTs that exhibit highly selective mRNA delivery to the lung (∼97%) and spleen (∼98%) without targeting ligands. Illustrative of their breadth and translational potential, GSer-CARTs deliver circRNA, providing the basis for a cancer vaccination strategy, which in a murine model resulted in antigen-specific immune responses and effective suppression of established tumors.

VISUAL OUTCOMES AFTER INTERNAL LIMITING MEMBRANE PEELING VERSUS FLAP IN THE CLOSURE OF FULL-THICKNESS MACULAR HOLES.

PURPOSE: To examine postoperative outcomes of internal limiting membrane peeling (ILMP) versus flap (ILMF) in the closure of full-thickness macular holes. METHODS: Retrospective chart review of patients who underwent pars plana vitrectomy and gas tamponade with ILMP or ILMF to close full-thickness macular hole at the Atrium Health Wake Forest Baptist from January 2012 to October 2022 with at least 3 months follow-up. Main outcome measures were type 1 primary full-thickness macular hole closure and postoperative best-corrected visual acuity in mean logMAR. RESULTS: One hundred thirty and 30 eyes underwent ILMP and ILMF, respectively. There were no significant differences in baseline characteristics between the groups. Ninety-six percent of ILMP eyes and 90% of ILMF eyes achieved primary hole closure ( P = 0.29). Among all eyes with primary hole closure, best-corrected visual acuity at 1 year was not different between the groups, but when stratified by lens status, it was superior in the ILMP versus ILMF group in pseudophakic eyes: the estimated least-squares mean best-corrected visual acuity (Snellen equivalent) (95% confidence interval) was 0.42 (20/50) (0.34, 0.49) in the ILMP group and 0.71 (20/100) (0.50, 0.92) in the ILMF group. CONCLUSION: Internal limiting membrane peeling and ILMF techniques yielded similarly high full-thickness macular hole closure rates. In pseudophakic eyes with primary hole closure, ILMF eyes had worse best-corrected visual acuity at 1 year.

Hoxb5 marks long-term haematopoietic stem cells and reveals a homogenous perivascular niche.

Haematopoietic stem cells (HSCs) are arguably the most extensively characterized tissue stem cells. Since the identification of HSCs by prospective isolation, complex multi-parameter flow cytometric isolation of phenotypic subsets has facilitated studies on many aspects of HSC biology, including self-renewal, differentiation, ageing, niche, and diversity. Here we demonstrate by unbiased multi-step screening, identification of a single gene, homeobox B5 (Hoxb5, also known as Hox-2.1), with expression in the bone marrow that is limited to long-term (LT)-HSCs in mice. Using a mouse single-colour tri-mCherry reporter driven by endogenous Hoxb5 regulation, we show that only the Hoxb5(+) HSCs exhibit long-term reconstitution capacity after transplantation in primary transplant recipients and, notably, in secondary recipients. Only 7-35% of various previously defined immunophenotypic HSCs are LT-HSCs. Finally, by in situ imaging of mouse bone marrow, we show that >94% of LT-HSCs (Hoxb5(+)) are directly attached to VE-cadherin(+) cells, implicating the perivascular space as a near-homogenous location of LT-HSCs.

Soluble CX3CL1 gene therapy improves cone survival and function in mouse models of retinitis pigmentosa.

Retinitis pigmentosa (RP) is a disease that initially presents as night blindness due to genetic deficits in the rod photoreceptors of the retina. Rods then die, causing dysfunction and death of cone photoreceptors, the cell type that mediates high acuity and color vision, ultimately leading to blindness. We investigated immune responses in mouse models of RP and found evidence of microglia activation throughout the period of cone degeneration. Using adeno-associated vectors (AAVs), delivery of genes encoding microglial regulatory signals led to the identification of AAV serotype 8 (AAV8) soluble CX3CL1 (sCX3CL1) as a promising therapy for degenerating cones. Subretinal injection of AAV8-sCX3CL1 significantly prolonged cone survival in three strains of RP mice. Rescue of cones was accompanied by improvements in visual function. AAV8-sCX3CL1 did not affect rod survival, microglia localization, or inflammatory cytokine levels in the retina. Furthermore, although RNA sequencing of microglia demonstrated marked transcriptional changes with AAV8-sCX3CL1, pharmacological depletion of up to ∼99% of microglia failed to abrogate the effect of AAV8-sCX3CL1 on cone survival. These findings indicate that AAV8-sCX3CL1 can rescue cones in multiple mouse models of RP via a pathway that does not require normal numbers of microglia. Gene therapy with sCX3CL1 is a promising mutation-independent approach to preserve vision in RP and potentially other forms of retinal degeneration.

AAV cis-regulatory sequences are correlated with ocular toxicity.

Adeno-associated viral vectors (AAVs) have become popular for gene therapy, given their many advantages, including their reduced inflammatory profile compared with that of other viruses. However, even in areas of immune privilege such as the eye, AAV vectors are capable of eliciting host-cell responses. To investigate the effects of such responses on several ocular cell types, we tested multiple AAV genome structures and capsid types using subretinal injections in mice. Assays of morphology, inflammation, and physiology were performed. Pathological effects on photoreceptors and the retinal pigment epithelium (RPE) were observed. Müller glia and microglia were activated, and the proinflammatory cytokines TNF-α and IL-1ß were up-regulated. There was a strong correlation between cis-regulatory sequences and toxicity. AAVs with any one of three broadly active promoters, or an RPE-specific promoter, were toxic, while AAVs with four different photoreceptor-specific promoters were not toxic at the highest doses tested. There was little correlation between toxicity and transgene, capsid type, preparation method, or cellular contaminants within a preparation. The toxic effect was dose-dependent, with the RPE being more sensitive than photoreceptors. Our results suggest that ocular AAV toxicity is associated with certain AAV cis-regulatory sequences and/or their activity and that retinal damage occurs due to responses by the RPE and/or microglia. By applying multiple, sensitive assays of toxicity, AAV vectors can be designed so that they can be used safely at high dose, potentially providing greater therapeutic efficacy.

Expression of glypican 3 enriches hepatocellular carcinoma development-related genes and associates with carcinogenesis in cirrhotic livers.

Glypican-3 (GPC3) protein expression was determined by immunohistochemical analysis from 29 normal livers, 80 cirrhotic livers sample taken near hepatocellular carcinoma (HCC), and 87 cirrhotic livers without HCC. The levels for miR-657 and HCC-related gene mRNAs were determined by quantitative real-time polymerase chain reaction (qRT-PCR). Also, a published microarray dataset was used for gene set enrichment analysis (GSEA) to investigate the relationship between GPC3- and HCC-related gene signatures. Kaplan-Meier analysis was used to evaluate the relationship between GPC3 and HCC recurrence. GPC3 protein expression was not detected in any of the 29 (0%) normal livers, but was detected in 32 of 87 (37%) cirrhotic livers without HCC, and 51 of 80 (64%) cirrhotic liver samples taken near HCC sites (P < 0.001). The GPC3-positive rate in cirrhotic livers of viral origin was 68% (27/40), which was significantly higher than for non-viral cirrhotic livers (11%, 5/47) (P < 0.001). Also, GPC3 expression positively correlated with mRNA expression of HCC-related genes in the qRT-PCR and GSEA evaluations. Furthermore, HCC recurrence in cirrhotic liver samples taken near HCC sites was significantly higher in the GPC3-positive group than the GPC3-negative group (Log-rank P = 0.02, HR = 3.26; 95% CI = 1.20-10.29). This study demonstrated that highly expression of GPC3 could enrich HCC-related genes' mRNA expression and positive associate with dysplasia in cirrhotic livers. Therefore, GPC3 may serve as a precancerous biomarker in cirrhotic livers.

Discovery and diagnostic value of a novel oncofetal protein: glypican 3.

Glypican 3 is a membrane-bound heparan sulfate proteoglycan, which has recently been identified as a marker for liver cancer and germ cell malignancies. Individuals with loss-of-function mutations for the glypican 3 gene exhibit Simpson-Golabi-Behmel syndrome, a rare X-linked overgrowth disorder. Expression of glypican 3 mRNA and protein is normally silenced in most adult organs and may reappear during malignant transformation. In the past few years, immunohistochemical and molecular characteristics of glypican 3 in hepatocellular carcinoma have been elucidated. More recently, glypican 3 has been emerging as a new diagnostic marker for germ cell tumors and especially testicular and ovarian yolk sac tumors. However, in other tumors such as renal cell carcinomas, squamous cell carcinomas, and melanomas, studies disagree on the level of glypican 3 expression. Finally, there is the controversial notion of glypican 3 as a tumor suppressor gene. In this review article, we update current knowledge on glypican 3 expression in normal and neoplastic tissues, evaluate its utility as a tumor marker in clinical practice, and explore its role as a novel oncofetal protein with clinical implications. Our focus is on the diagnostic value of glypican 3 in germ cell tumors and other neoplasms in addition to hepatocellular carcinoma. In conclusion, glypican 3 has been proven to be a useful immunohistochemical marker in distinguishing yolk sac tumors, choriocarcinomas, and Wilms tumors from other malignancies histologically mimicking these primitive tumors. Clinically, we recommend that glypican 3 be used as part of a panel of markers in subtyping testicular germ cell tumors.

Comparing a Head-Mounted Smartphone Visual Field Analyzer to Standard Automated Perimetry in Glaucoma: A Prospective Study.

PRECIS: Wang et al compare an FDA-registered head-mounted smartphone device (PalmScan VF2000) with standard automated perimetry (SAP) in glaucoma patients and find that the head-mounted device may not fully recapitulate SAP testing. PURPOSE: This study prospectively compared visual field testing using the PalmScan VF2000 Visual Field Analyzer, a head-mounted smartphone device, with standard automated perimetry (SAP). METHODS: Patients with glaucoma undergoing Humphrey Field Analyzer SAP testing were asked to complete in-office PalmScan testing using a Samsung S5 smartphone in a virtual reality-style headset. Glaucoma severity was defined as SAP mean deviation (MD) >-6 dB for mild, between -6 and -12 dB for moderate, and <-12 dB for severe. Global parameters MD and pattern standard deviation (PSD) from PalmScan and SAP were compared using t-tests and Bland-Altman analyses. Bland-Altmann analyses of PalmScan and SAP MD were conducted for the superonasal, superotemporal, inferonasal, and inferotemporal visual field quadrants. The repeatability of PalmScan was assessed using Spearman's correlations and intraclass correlation coefficients (ICCs). RESULTS: Fifty-one patients (51 eyes) completed both SAP and PalmScan testing and met criteria for analysis. Compared to SAP, global MD and PSD measurements from PalmScan differed by an average of +0.62±0.26 dB (range: -3.25 to +4.60 dB) and -1.00±0.24 dB (range: -6.03 to +2.77 dB), respectively, while MD scores from individual visual field quadrants differed by as much as -6.58 to +11.43 dB. Agreement of PalmScan and SAP in classifying glaucoma severity was 86.3% across all eyes. PalmScan and SAP identified the same quadrant as having the worst visual field defect in 66.7% of eyes. CONCLUSIONS: Despite advantages in cost and accessibility, the PalmScan head-mounted perimetry device may not be able to fully recapitulate SAP testing.

High-Yield, Case-Based, Interactive Workshop on Telehealth and Teleneurology With Pediatric Resident Physicians.

Introduction: Increasing prevalence of neurologic disorders with an aging global population and limited availability of neurologists may lead to worse patient outcomes. As a result of the COVID-19 pandemic, telehealth services surged, and despite easing public health measures, the demand has remained. Telehealth technology has the potential to close the physical gaps in expanding the reach of care. This academic half-day workshop sought to provide a learning opportunity in response to these concerns. Methods: The workshop consisted of small- and large-group case discussions among pediatric resident physicians (PGY 1-PGY 3) moderated by two child neurology faculty physicians over Zoom. Participants received a learner document with prereading articles and questions for each case. PowerPoint presentations with video demonstrations were used to introduce the cases and guide discussions. Results: Of the 25 attendees, 14 (56% response rate) answered a nonmandatory postsession survey. Eighty-six percent of the respondents were very or extremely satisfied with the content covered and were similarly satisfied with the effectiveness of content delivery. Seventy-nine percent of the respondents found the content helpful or very helpful in preparation for the board, and 93% anticipated applying the content covered occasionally or frequently in their clinical practice. Discussion: Small-group discussions with video demonstrations are helpful in increasing proficiency with telehealth technology and in examining board-relevant cases on pediatric patients. There is strong interest in subsequent telehealth half-day workshops that incorporate teaching through group discussions on relevant patient case scenarios.

High temporal frequency light response in mouse retina is mediated by ON and OFF bipolar cells and requires FAT3 signaling.

Vision is initiated by the reception of light by photoreceptors and subsequent processing via parallel retinal circuits. Proper circuit organization depends on the multi-functional tissue polarity protein FAT3, which is required for amacrine cell connectivity and retinal lamination. Here we investigated the retinal function of Fat3 mutant mice and found decreases in physiological and perceptual responses to high frequency flashes. These defects did not correlate with abnormal amacrine cell wiring, pointing instead to a role in bipolar cell subtypes that also express FAT3. Indeed, similar deficits were observed in mice lacking the bipolar cell glutamate receptors GRIK1 (OFF-bipolar cells) and GRM6 (ON-bipolar cells). Mechanistically, FAT3 binds to the synaptic protein PTPσ and is required to localize GRIK1 to OFF-cone bipolar cell synapses with cone photoreceptors. How FAT3 impacts ON-cone bipolar cell function at high temporal frequency remains to be uncovered. These findings expand the repertoire of FAT3's functions and reveal the importance of both ON- and OFF-bipolar cells for high frequency light response.

Charge-altering releasable transporters enhance mRNA delivery in vitro and exhibit in vivo tropism.

The introduction of more effective and selective mRNA delivery systems is required for the advancement of many emerging biomedical technologies including the development of prophylactic and therapeutic vaccines, immunotherapies for cancer and strategies for genome editing. While polymers and oligomers have served as promising mRNA delivery systems, their efficacy in hard-to-transfect cells such as primary T lymphocytes is often limited as is their cell and organ tropism. To address these problems, considerable attention has been placed on structural screening of various lipid and cation components of mRNA delivery systems. Here, we disclose a class of charge-altering releasable transporters (CARTs) that differ from previous CARTs based on their beta-amido carbonate backbone (bAC) and side chain spacing. These bAC-CARTs exhibit enhanced mRNA transfection in primary T lymphocytes in vitro and enhanced protein expression in vivo with highly selective spleen tropism, supporting their broader therapeutic use as effective polyanionic delivery systems.

Engineering circular RNA for enhanced protein production.

Circular RNAs (circRNAs) are stable and prevalent RNAs in eukaryotic cells that arise from back-splicing. Synthetic circRNAs and some endogenous circRNAs can encode proteins, raising the promise of circRNA as a platform for gene expression. In this study, we developed a systematic approach for rapid assembly and testing of features that affect protein production from synthetic circRNAs. To maximize circRNA translation, we optimized five elements: vector topology, 5' and 3' untranslated regions, internal ribosome entry sites and synthetic aptamers recruiting translation initiation machinery. Together, these design principles improve circRNA protein yields by several hundred-fold, provide increased translation over messenger RNA in vitro, provide more durable translation in vivo and are generalizable across multiple transgenes.

Telemedicine retinopathy of prematurity severity score (TeleROP-SS) versus modified activity score (mROP-ActS) retrospective comparison in SUNDROP cohort.

Identifying and planning treatment for retinopathy of prematurity (ROP) using telemedicine is becoming increasingly ubiquitous, necessitating a grading system to help caretakers of at-risk infants gauge disease severity. The modified ROP Activity Scale (mROP-ActS) factors zone, stage, and plus disease into its scoring system, addressing the need for assessing ROP's totality of binocular burden via indirect ophthalmoscopy. However, there is an unmet need for an alternative score which could facilitate ROP identification and gauge disease improvement or deterioration specifically on photographic telemedicine exams. Here, we propose such a system (Telemedicine ROP Severity Score [TeleROP-SS]), which we have compared against the mROP-ActS. In our statistical analysis of 1568 exams, we saw that TeleROP-SS was able to return a score in all instances based on the gradings available from the retrospective SUNDROP cohort, while mROP-ActS obtained a score of 80.8% in right eyes and 81.1% in left eyes. For treatment-warranted ROP (TW-ROP), TeleROP-SS obtained a score of 100% and 95% in the right and left eyes respectively, while mROP-ActS obtained a score of 70% and 63% respectively. The TeleROP-SS score can identify disease improvement or deterioration on telemedicine exams, distinguish timepoints at which treatments can be given, and it has the adaptability to be modified as needed.

Targeting Microglia to Treat Degenerative Eye Diseases.

Microglia have been implicated in many degenerative eye disorders, including retinitis pigmentosa, age-related macular degeneration, glaucoma, diabetic retinopathy, uveitis, and retinal detachment. While the exact roles of microglia in these conditions are still being discovered, evidence from animal models suggests that they can modulate the course of disease. In this review, we highlight current strategies to target microglia in the eye and their potential as treatments for both rare and common ocular disorders. These approaches include depleting microglia with chemicals or radiation, reprogramming microglia using homeostatic signals or other small molecules, and inhibiting the downstream effects of microglia such as by blocking cytokine activity or phagocytosis. Finally, we describe areas of future research needed to fully exploit the therapeutic value of microglia in eye diseases.

Effective field of view of wide-field fundus photography in the Stanford University Network for Diagnosis of Retinopathy of Prematurity (SUNDROP).

Five-field 130° wide-angle imaging is the standard of care for retinopathy of prematurity (ROP) screening with an ideal hypothetical composite field-of-view (FOV) of 180°. We hypothesized that in many real-world scenarios the effective composite FOV is considerably less than ideal. This observational retrospective study analyzed the effective FOV of fundus photos of patients screened for ROP as part of the Stanford University Network for Diagnosis of Retinopathy of Prematurity (SUNDROP) initiative. Five fundus photos were selected from each eye per image session. Effective FOV was defined as the largest circular area centered on the optic disc that encompassed retina in each of the four cardinal views. Seventy-three subjects were analyzed, 35 without ROP and 34 with ROP. Mean effective FOV was 144.55 ± 6.62° ranging from 130.00 to 153.71°. Effective FOV was not correlated with the presence or absence of ROP, gestational age, birth weight, or postmenstrual age. Mean effective FOV was wider in males compared to females. Standard five-field 130° fundus photos yielded an average effective FOV of 144.54° in the SUNDROP cohort. This implies that an imaging FOV during ROP screening considerably less than the hypothetical ideal of 180° is sufficient for detecting treatment warranted ROP.

Modeling absolute zone size in retinopathy of prematurity in relation to axial length.

Treatment outcomes in retinopathy of prematurity (ROP) are closely correlated with the location (i.e. zone) of disease, with more posterior zones having poorer outcomes. The most posterior zone, Zone I, is defined as a circle centered on the optic nerve with radius twice the distance from nerve to fovea, or subtending an angle of 30 degrees. Because the eye enlarges and undergoes refractive changes during the period of ROP screening, the absolute area of Zone I according to these definitions may likewise change. It is possible that these differences may confound accurate assessment of risk in patients with ROP. In this study, we estimated the area of Zone I in relation to different ocular parameters to determine how variability in the size and refractive power of the eye may affect zoning. Using Gaussian optics, a model was constructed to calculate the absolute area of Zone I as a function of corneal power, anterior chamber depth, lens power, lens thickness, and axial length (AL), with Zone I defined as a circle with radius set by a 30-degree visual angle. Our model predicted Zone I area to be most sensitive to changes in AL; for example, an increase of AL from 14.20 to 16.58 mm at postmenstrual age 32 weeks was calculated to expand the area of Zone I by up to 72%. These findings motivate several hypotheses which upon future testing may help optimize treatment decisions for ROP.

Single-cell multiome of the human retina and deep learning nominate causal variants in complex eye diseases.

Genome-wide association studies (GWASs) of eye disorders have identified hundreds of genetic variants associated with ocular disease. However, the vast majority of these variants are noncoding, making it challenging to interpret their function. Here we present a joint single-cell atlas of gene expression and chromatin accessibility of the adult human retina with more than 50,000 cells, which we used to analyze single-nucleotide polymorphisms (SNPs) implicated by GWASs of age-related macular degeneration, glaucoma, diabetic retinopathy, myopia, and type 2 macular telangiectasia. We integrate this atlas with a HiChIP enhancer connectome, expression quantitative trait loci (eQTL) data, and base-resolution deep learning models to predict noncoding SNPs with causal roles in eye disease, assess SNP impact on transcription factor binding, and define their known and novel target genes. Our efforts nominate pathogenic SNP-target gene interactions for multiple vision disorders and provide a potentially powerful resource for interpreting noncoding variation in the eye.

Augmentation of CD47/SIRPα signaling protects cones in genetic models of retinal degeneration.

Inherited retinal diseases, such as retinitis pigmentosa (RP), can be caused by thousands of different mutations, a small number of which have been successfully treated with gene replacement. However, this approach has yet to scale and may not be feasible in many cases, highlighting the need for interventions that could benefit more patients. Here, we found that microglial phagocytosis is upregulated during cone degeneration in RP, suggesting that expression of "don't-eat-me" signals such as CD47 might confer protection to cones. To test this, we delivered an adeno-associated viral (AAV) vector expressing CD47 on cones, which promoted cone survival in 3 mouse models of RP and preserved visual function. Cone rescue with CD47 required a known interacting protein, signal regulatory protein α (SIRPα), but not an alternative interacting protein, thrombospondin-1 (TSP1). Despite the correlation between increased microglial phagocytosis and cone death, microglia were dispensable for the prosurvival activity of CD47, suggesting that CD47 interacts with SIRPα on nonmicroglial cells to alleviate degeneration. These findings establish augmentation of CD47/SIRPα signaling as a potential treatment strategy for RP and possibly other forms of neurodegeneration.

AAV-Txnip prolongs cone survival and vision in mouse models of retinitis pigmentosa.

Retinitis pigmentosa (RP) is an inherited retinal disease affecting >20 million people worldwide. Loss of daylight vision typically occurs due to the dysfunction/loss of cone photoreceptors, the cell type that initiates our color and high-acuity vision. Currently, there is no effective treatment for RP, other than gene therapy for a limited number of specific disease genes. To develop a disease gene-agnostic therapy, we screened 20 genes for their ability to prolong cone photoreceptor survival in vivo. Here, we report an adeno-associated virus vector expressing Txnip, which prolongs the survival of cone photoreceptors and improves visual acuity in RP mouse models. A Txnip allele, C247S, which blocks the association of Txnip with thioredoxin, provides an even greater benefit. Additionally, the rescue effect of Txnip depends on lactate dehydrogenase b (Ldhb) and correlates with the presence of healthier mitochondria, suggesting that Txnip saves RP cones by enhancing their lactate catabolism.

Retinitis pigmentosa is an inherited eye disease affecting around one in every 4,000 people. It results from genetic defects in light sensitive cells of the retina, called photoreceptor cells, which line the back of the eye. Though vision loss can occur from birth, retinitis pigmentosa usually involves a gradual loss of vision, sometimes leading to blindness. Rod photoreceptors, which are responsible for vision in low light, are impacted first. The disease then affects cone photoreceptors, the cells that detect light during the day, providing both color and sharp vision. Around 100 mutated genes associated with retinitis pigmentosa have been identified, but only a handful of families with one of these mutant genes have been treated with a gene therapy specific for their mutated gene. There are currently no therapies available to treat the vast number of people with this disease. The mutations that cause retinitis pigmentosa directly affect the rod cells that detect dim light, leading to loss of night vision. There is also an indirect effect that causes cone photoreceptors to stop working and die. One theory to explain this two-step disease process relates to the fact that cone photoreceptors are very active cells, requiring a high level of energy, nutrients and oxygen. If surrounding rod cells die, cone photoreceptors may be deprived of some essential supplies, leading to cone cell death and daylight vision loss. To examine this theory, Xue et al. tested a new gene therapy designed to alleviate the potential shortfall in nutrients. The experiments used three different strains of mice that had the same genetic mutations as humans with retinitis pigmentosa. The gene therapy used a virus, called adeno-associated virus (AAV), to deliver 20 different genes to cone cells. Each of the 20 genes tested plays a different role in cells' processing of nutrients to provide energy. After administering the treatment, Xue et al. monitored the mice to see whether or not their vision was affected, and how cone cells responded. Only one of the 20 genes, Txnip, delivered using gene therapy, had a beneficial effect, prolonging cone cell survival in all three mouse strains. The mice that received Txnip also retained their ability to discern moving stripes on vision tests. Further investigations demonstrated that activating Txnip forced the cones to start using a molecule called lactate as an energy source, which could be more available to them than glucose, their usual fuel. These cells also had healthier mitochondria ­ the compartments inside cells that produce and manage energy supplies. This dual effect on fuel use and mitochondrial health is thought to be the basis for the extended cone survival and function. These experiments by Xue et al. have identified a good gene therapy candidate for treating retinitis pigmentosa independently of which genes are causing the disease. Further research will be required to test the safety of the gene therapy, and whether its beneficial effects translate to humans with retinitis pigmentosa, and potentially other diseases with unhealthy photoreceptors.