Intrinsic innate immune barriers have evolved to suppress viral infection and can reduce effective gene delivery in gene therapy. We have developed BG147, a novel cyclosporine A (CsA) analog optimized via structure-guided design to specifically inhibit interferon-induced transmembrane proteins (IFITM1-3), but not inhibit CsA target and HIV cofactor cyclophilin A. BG147 enhances VSV-G pseudotyped lentiviral vector transduction ex vivo in hematopoietic stem and progenitor cells (HSPCs) and in in vivo ocular gene therapy of photoreceptor cells in mice. Upon BG147 treatment, IFITM3 protein is mislocalized and degraded through lysosomal acidification-dependent pathways but returns 96 h after BG147 washout. Critically, HSPC transduced in the presence of BG147 showed successful engraftment in NGS mice. BG147 promises to transform ex vivo and in vivo gene therapies by transiently inhibiting intrinsic immune barriers mediated by IFITM3 to enhance a wide range of protocols.

Diabetic retinopathy (DR) is a common complication of diabetes mellitus and a leading cause of visual impairment and blindness in the working-age population. The early stage of the disease is characterized by retinal capillary dysfunction, but the mechanisms whereby hyperglycemia disturbs capillary homeostasis at this initiating stage are poorly understood, posing a barrier to the development of effective early treatments. We used two mouse models of type I diabetes that replicate early features of human retinal vascular pathology. In both the streptozotocin (STZ) model, where hypoinsulinemia is chemically induced, and in the Ins2Akita model, which develops it spontaneously because of a mutation in the insulin gene, we observed early induction of the secreted glycoprotein gene leucine-rich α-2-glycoprotein 1 (Lrg1). Using the Ins2Akita mice, we showed that Lrg1 induction preceded that of vascular endothelial growth factor A (Vegfa). LRG1 initiated retinal microvascular dysfunction by modifying transforming growth factor-β (TGFβ) signaling in pericytes, driving transdifferentiation to a more contractile fibrotic phenotype, resulting in narrower capillaries and thickened basement membrane. Using computational modeling, we showed that these early vascular changes impaired retinal blood flow and oxygen delivery, consistent with a defect in visual transduction observed in both models. This early retinal phenotype could be rescued by Lrg1 knockout or by treatment with an LRG1 function-blocking antibody in both the STZ and Ins2Akita mice. These results demonstrate that LRG1 is a driver of vascular dysfunction that contributes to the onset of DR and presents itself as a potential preemptive therapeutic target.

According to the standard view, most species including humans possess a “duplex retina”, with a rod system dedicated to low light (night) vision and a cone system dedicated to daylight vision. This separation of photon detection into a rod and cone regime is attributed to the low sensitivity of cones in dim light and saturation of rods in brighter light. However, mounting evidence gained from in vitro and in vivo studies in several species have demonstrated that specific mechanisms enable rod photoreceptors to significantly contribute to vision in bright and even very bright light. In this review we aim to elaborate on this revised framework for the duplex retina, and we propose rods should be considered to be tuned to “low contrast” rather than to “low ambient luminance”. Importantly, saturation of rod photoreceptors at higher light levels has been an assumption in research studies as well as clinical tests, and consideration of an updated role of rod photoreceptors may warrant reinterpretation of past and future results.

BACKGROUND AND PURPOSE:Angiogenesis is a pathological component of neovascular age-related macular degeneration. Current therapies, although successful, are prone to high levels of patient non-response and a loss of efficacy over time, indicating the need to explore other therapeutic avenues. We have shown that an interaction between syndecan-2 and the tyrosine phosphatase receptor CD148 (RTP Type J) results in the ablation of angiogenesis. Here we exploit this pathway to develop a peptide activator of CD148 as a therapy for neovascular age-related macular degeneration. EXPERIMENTAL APPROACH:We tested a peptide (QM107) derived from syndecan-2 in a variety of angiogenesis models and a pre-clinical model of neovascular age-related macular degeneration. We assessed the toxicological and inflammatory profiles of QM107 and its stability in vitreous humour. KEY RESULTS:QM107 inhibits angiogenesis in ex vivo sprouting assays and disrupts endothelial microcapillary formation via inhibition of cell migration. QM107 acts through CD148, leading to changes in GSK3A phosphorylation and β1 integrin activation. QM107 elicits a negligible inflammatory response and exhibits limited toxicity in cultured cells, and is stable in vitreous humour. Finally, we show proof of concept that QM107 blocks angiogenesis in vivo using a model of neovascular age-related macular degeneration. CONCLUSION AND IMPLICATIONS:We have developed a CD148 activating peptide which shows promise in inhibiting angiogenesis in models of neovascular age-related macular degeneration. This treatment could either represent an alternative or augment existing therapies, and owing to its distinct mode of action be used in patients who do not respond to existing treatments.

Microglia have recently been associated with complex functionalities both in the brain and the retina, including in synaptic function and plasticity. While investigating the morphology, protein expression profile and connectivity of microglia in the mouse outer retina, we have found that they closely resemble interneurons in the outer retina of other species. We argue that functional studies are needed to reveal whether they also perform an interneuron-like role in vision.### Competing Interest StatementThe authors have declared no competing interest.

Macular degeneration is a leading cause of blindness. Treatments to rescue vision are currently limited. Here, we study how loss of central vision affects lateral feedback to spared areas of the human retina. We identify a cone-driven gain control mechanism that reduces visual function beyond the atrophic area in macular degeneration. This finding provides an insight into the negative effects of geographic atrophy on vision. Therefore, we develop a strategy to restore this feedback mechanism, through activation of laterally projecting cells. This results in improved vision in Cnga3 −/− mice, which lack cone function, as well as a mouse model of geographic atrophy. Our work shows that a loss of lateral gain control contributes to the vision deficit in macular degeneration. Furthermore, in mouse models we show that lateral feedback can be harnessed to improve vision following retinal degeneration.

Age-related macular degeneration and other macular diseases result in the loss of light-sensing cone photoreceptors, causing irreversible sight impairment. Photoreceptor replacement may restore vision by transplanting healthy cells, which must form new synaptic connections with the recipient retina. Despite recent advances, convincing evidence of functional connectivity arising from transplanted human cone photoreceptors in advanced retinal degeneration is lacking. Here, we show restoration of visual function after transplantation of purified human pluripotent stem cell-derived cones into a mouse model of advanced degeneration. Transplanted human cones elaborate nascent outer segments and make putative synapses with recipient murine bipolar cells (BCs), which themselves undergo significant remodeling. Electrophysiological and behavioral assessments demonstrate restoration of surprisingly complex light-evoked retinal ganglion cell responses and improved light-evoked behaviors in treated animals. Stringent controls exclude alternative explanations, including material transfer and neuroprotection. These data provide crucial validation for photoreceptor replacement therapy and for the potential to rescue cone-mediated vision.

Macular degeneration is the leading cause of blindness in the developed world. Whilst most patients lose sight owing to atrophic changes, no treatments currently exist that improve the vision deficit due to atrophy. Here, we identify loss of lateral inhibition as a specific mechanism by which photoreceptor degeneration reduces visual function beyond the atrophic area. We find that this inhibition is adaptive, and that if modulated can improve visual function, making inhibitory circuits an unexpected therapeutic target for age related macular degeneration and related disorders.

At various stages of the visual system, visual responses are modulated by arousal. Here, we find that in mice this modulation operates as early as in the first synapse from the retina and even in retinal axons. To measure retinal activity in the awake, intact brain, we imaged the synaptic boutons of retinal axons in the superior colliculus. Their activity depended not only on vision but also on running speed and pupil size, regardless of retinal illumination. Arousal typically reduced their visual responses and selectivity for direction and orientation. Recordings from retinal axons in the optic tract revealed that arousal modulates the firing of some retinal ganglion cells. Arousal had similar effects postsynaptically in colliculus neurons, independent of activity in the other main source of visual inputs to the colliculus, the primary visual cortex. These results indicate that arousal modulates activity at every stage of the mouse visual system.

The operating mode of the visual system depends on behavioural states such as arousal[1][1],[2][2]. This dependence is seen both in primary visual cortex[3][3]–[7][4] (V1) and in subcortical brain structures receiving direct retinal input[4][5],[8][6]. Here we show that this effect arises as early as in the output of the retina. We first measured activity in a region that receives retinal projections[9][7], the superficial superior colliculus (sSC), and found that this activity strongly depended on behavioural state. This modulation was not mediated by feedback inputs from V1 as it was immune to V1 inactivation. We then used Neuropixels probes[10][8] to record activity in the optic tract, and we found some retinal axons whose activity significantly varied with arousal, even in darkness. To characterize these effects on a larger sample of retinal outputs, we imaged the activity of retinal boutons[11][9],[12][10] in sSC during behaviour using a calcium indicator. The activity of these boutons correlated with arousal as strongly as that of sSC neurons, and this correlation persisted also during darkness. These results reveal a novel property of retinal function in mice, which could be observed only during behaviour: retinal outputs are modulated by behavioural state before they reach the rest of the brain. [1]: #ref-1 [2]: #ref-2 [3]: #ref-3 [4]: #ref-7 [5]: #ref-4 [6]: #ref-8 [7]: #ref-9 [8]: #ref-10 [9]: #ref-11 [10]: #ref-12

The neuronal ceroid lipofuscinoses (NCLs) are inherited lysosomal storage disorders characterized by general neurodegeneration and premature death. Sight loss is also a major symptom in NCLs, severely affecting the quality of life of patients, but it is not targeted effectively by brain-directed therapies. Here we set out to explore the therapeutic potential of an ocular gene therapy to treat sight loss in NCL due to a deficiency in the transmembrane protein CLN6. We found that, although Cln6nclf mice presented mainly with photoreceptor degeneration, supplementation of CLN6 in photoreceptors was not beneficial. Because the level of CLN6 is low in photoreceptors but high in bipolar cells (retinal interneurons that are only lost in Cln6-deficient mice at late disease stages), we explored the therapeutic effects of delivering CLN6 to bipolar cells using adeno-associated virus (AAV) serotype 7m8. Bipolar cell-specific expression of CLN6 slowed significantly the loss of photoreceptor function and photoreceptor cells. This study shows that the deficiency of a gene normally expressed in bipolar cells can cause the loss of photoreceptors and that this can be prevented by bipolar cell-directed treatment.

Background The use of human pluripotent stem cell-derived retinal cells for cell therapy strategies and disease modelling relies on the ability to obtain healthy and organised retinal tissue in sufficient quantities. Generating such tissue is a lengthy process, often taking over 6 months of cell culture, and current approaches do not always generate large quantities of the major retinal cell types required. Methods We adapted our previously described differentiation protocol to investigate the use of stirred-tank bioreactors. We used immunohistochemistry, flow cytometry and electron microscopy to characterise retinal organoids grown in standard and bioreactor culture conditions. Results Our analysis revealed that the use of bioreactors results in improved laminar stratification as well as an increase in the yield of photoreceptor cells bearing cilia and nascent outer-segment-like structures. Conclusions Bioreactors represent a promising platform for scaling up the manufacture of retinal cells for use in disease modelling, drug screening and cell transplantation studies.

In the adult central nervous system, endothelial and neuronal cells engage in tight cross-talk as key components of the so-called neurovascular unit. Impairment of this important relationship adversely affects tissue homeostasis, as observed in neurodegenerative conditions including Alzheimer's and Parkinson's disease. In development, the influence of neuroprogenitor cells on angiogenesis is poorly understood. Here, we show in mouse that these cells interact intimately with the growing retinal vascular network, and we identify a novel regulatory mechanism of vasculature development mediated by hypoxia-inducible factor 2a (Hif2a). By Cre-lox gene excision, we show that Hif2a in retinal neuroprogenitor cells upregulates the expression of the pro-angiogenic mediators vascular endothelial growth factor and erythropoietin, whereas it locally downregulates the angiogenesis inhibitor endostatin. Importantly, absence of Hif2a in retinal neuroprogenitor cells causes a marked reduction of proliferating endothelial cells at the angiogenic front. This results in delayed retinal vascular development, fewer major retinal vessels and reduced density of the peripheral deep retinal vascular plexus. Our findings demonstrate that retinal neuroprogenitor cells are a crucial component of the developing neurovascular unit.

The rd1 mouse with a mutation in the Pde6b gene was the first strain of mice identified with a retinal degeneration. However, AAV-mediated gene supplementation of rd1 mice only results in structural preservation of photoreceptors, and restoration of the photoreceptor-mediated a-wave, but not in restoration of the bipolar cell-mediated b-wave. Here we show that a mutation in Gpr179 prevents the full restoration of vision in rd1 mice. Backcrossing rd1 with C57BL6 mice reveals the complete lack of b-wave in a subset of mice, consistent with an autosomal recessive Mendelian inheritance pattern. We identify a mutation in the Gpr179 gene, which encodes for a G-protein coupled receptor localized to the dendrites of ON-bipolar cells. Gene replacement in rd1 mice that are devoid of the mutation in Gpr179 successfully restores the function of both photoreceptors and bipolar cells, which is maintained for up to 13 months. Our discovery may explain the failure of previous gene therapy attempts in rd1 mice, and we propose that Grp179 mutation status should be taken into account in future studies involving rd1 mice.