Targeting the photosensitive ion channel channelrhodopsin‐2 (ChR2) to the retinal circuitry downstream of photoreceptors holds promise in treating vision loss caused by retinal degeneration. However, ...the high intensity of blue light necessary to activate channelrhodopsin‐2 exceeds the safety threshold of retinal illumination because of its strong potential to induce photochemical damage. In contrast, the damage potential of red‐shifted light is vastly lower than that of blue light. Here, we show that a red‐shifted channelrhodopsin (ReaChR), delivered by AAV injections in blind rd1 mice, enables restoration of light responses at the retinal, cortical, and behavioral levels, using orange light at intensities below the safety threshold for the human retina. We further show that postmortem macaque retinae infected with AAV‐ReaChR can respond with spike trains to orange light at safe intensities. Finally, to directly address the question of translatability to human subjects, we demonstrate for the first time, AAV‐ and lentivirus‐mediated optogenetic spike responses in ganglion cells of the postmortem human retina.
Synopsis
A red‐shifted channelrhodopsin (ReaChR) was targeted to retinal ganglion cells using three models in parallel: mouse, macaque, and human. Safe orange illumination was able to trigger light responses in all three systems.
The red‐shifted channelrhodopsin ReaChR restored light responses at the retinal, cortical, and behavioral levels in blind rd1 mice, using light intensities below the safety limit for the human retina.
Optogenetic light responses were demonstrated in explanted postmortem macaque and human retina, infected ex vivo with viral vectors encoding ReaChR.
The study presents the first electrophysiological recordings of optogenetic light responses in ganglion cells obtained directly from the human fovea as well as the far peripheral human retina.
A red‐shifted channelrhodopsin (ReaChR) was targeted to retinal ganglion cells using three models in parallel: mouse, macaque, and human. Safe orange illumination was able to trigger light responses in all three systems.
Lifting the iron curtain of vision Rosin, Boris; Sahel, Jose‐Alain
EMBO molecular medicine,
08 February 2023, Letnik:
15, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Ocular and specifically retinal toxicities of systemic medications are prevalent and encompass many disease modalities. For many of these pharmaceuticals, established follow‐up protocols are in place ...to ensure timely detection and cessation of therapy. However, while for some disorders, cessation of therapy is a viable option due to existing treatment alternatives, for some others cessation of treatment can be life threatening and/or shorten the patient's life expectancy. Such is the case for iron chelating agents used in transfusion‐dependent patients of Thalassemia, of which deferoxamine (DFO) is the most widely used. In their recent article in EMBO Molecular Medicine, Kong et al (2023) addressed the issue of DFO‐induced retinal toxicity used both in vivo and in vitro techniques. Their study suggests a potentially protective role for α‐ketoglutarate (AKG) supplementation against DFO toxicity.
J.A. Sahel and B. Rosin discuss the study by Kong et al, in this issue of EMBO Mol. Med., that shows that inhibiting HIF2α and protecting mitochondrial function via α‐ketoglutarate supplementation may effectively delay the progression of retinal degeneration in the clinic.
Orienting in space requires the processing of visual spatial cues. The dominant hypothesis about the brain structures mediating the coding of spatial cues stipulates the existence of a ...hippocampal‐dependent system for the representation of geometry and a striatal‐dependent system for the representation of landmarks. However, this dual‐system hypothesis is based on paradigms that presented spatial cues conveying either conflicting or ambiguous spatial information and that used the term landmark to refer to both discrete three‐dimensional objects and wall features. Here, we test the hypothesis of complex activation patterns in the hippocampus and the striatum during visual coding. We also postulate that object‐based and feature‐based navigation are not equivalent instances of landmark‐based navigation. We examined how the neural networks associated with geometry‐, object‐, and feature‐based spatial navigation compared with a control condition in a two‐choice behavioral paradigm using fMRI. We showed that the hippocampus was involved in all three types of cue‐based navigation, whereas the striatum was more strongly recruited in the presence of geometric cues than object or feature cues. We also found that unique, specific neural signatures were associated with each spatial cue. Object‐based navigation elicited a widespread pattern of activity in temporal and occipital regions relative to feature‐based navigation. These findings extend the current view of a dual, juxtaposed hippocampal–striatal system for visual spatial coding in humans. They also provide novel insights into the neural networks mediating object versus feature spatial coding, suggesting a need to distinguish these two types of landmarks in the context of human navigation.
Our article provides novel insights into the neural networks mediating spatial cue processing during navigation including:
Complex hippocampal–striatal involvement during visual spatial coding for flexible human navigation behavior.
Distinct neural signatures associated with object‐, feature‐, and geometry‐based navigation.
Object‐ and feature‐based navigation are not equivalent instances of landmark‐based navigation.
Coupling behavioral measures and brain imaging in naturalistic, ecological conditions is key to comprehend the neural bases of spatial navigation. This highly integrative function encompasses ...sensorimotor, cognitive, and executive processes that jointly mediate active exploration and spatial learning. However, most neuroimaging approaches in humans are based on static, motion‐constrained paradigms and they do not account for all these processes, in particular multisensory integration. Following the Mobile Brain/Body Imaging approach, we aimed to explore the cortical correlates of landmark‐based navigation in actively behaving young adults, solving a Y‐maze task in immersive virtual reality. EEG analysis identified a set of brain areas matching state‐of‐the‐art brain imaging literature of landmark‐based navigation. Spatial behavior in mobile conditions additionally involved sensorimotor areas related to motor execution and proprioception usually overlooked in static fMRI paradigms. Expectedly, we located a cortical source in or near the posterior cingulate, in line with the engagement of the retrosplenial complex in spatial reorientation. Consistent with its role in visuo‐spatial processing and coding, we observed an alpha‐power desynchronization while participants gathered visual information. We also hypothesized behavior‐dependent modulations of the cortical signal during navigation. Despite finding few differences between the encoding and retrieval phases of the task, we identified transient time–frequency patterns attributed, for instance, to attentional demand, as reflected in the alpha/gamma range, or memory workload in the delta/theta range. We confirmed that combining mobile high‐density EEG and biometric measures can help unravel the brain structures and the neural modulations subtending ecological landmark‐based navigation.
Despite the inherent mobility of natural navigation, there is only a handful of recordings of human brain activity during active exploration in space. Using Mobile Brain/Body Imaging on subjects performing landmark‐based reorientation, we retrieved exploitable neural signals in deep cortical regions and a set of visual, somatosensory, and motor areas. We discuss their neurobehavioral dynamics with respect to similar static experimental paradigms and mobile EEG correlates of locomotion control.
Inherited retinal degenerative diseases, a genetically and phenotypically heterogeneous group of disorders, affect the function of photoreceptor cells and are among the leading causes of blindness. ...Recent advances in molecular genetics and cell biology are elucidating the pathophysiological mechanisms underlying these disorders and are helping to identify new therapeutic approaches, such as gene therapy, stem cell therapy, and optogenetics. Several of these approaches have entered the clinical phase of development. Artificial replacement of dying photoreceptor cells using retinal prostheses has received regulatory approval. Precise retinal imaging and testing of visual function are facilitating more efficient clinical trial design. In individual patients, disease stage will determine whether the therapeutic strategy should comprise photoreceptor cell rescue to delay or arrest vision loss or retinal replacement for vision restoration.
MER tyrosine kinase (MERTK) encodes a surface receptor localized at the apical membrane of the retinal pigment epithelium. It plays a critical role in photoreceptor outer segment internalization ...prior to phagocytosis. Mutations in MERTK have been associated with severe autosomal recessive retinal dystrophies in the RCS rat and in humans. We present here a comprehensive review of all reported MERTK disease causing variants with the associated phenotype. In addition, we provide further data and insights of a large cohort of 1,195 inherited retinal dystrophies (IRD) index cases applying state‐of‐the‐art genotyping techniques and summarize current knowledge. A total of 79 variants have now been identified underlying rod‐cone dystrophy and cone‐rod dystrophy including 11 novel variants reported here. The mutation spectrum in MERTK includes 33 missense, 12 nonsense, 12 splice defects, 12 small deletions, 2 small insertion–deletions, 3 small duplications, and 2 exonic and 3 gross deletions. Altogether, mutations in MERTK account for ∼2% of IRD cases with a severe retinal phenotype. These data are important for current and future therapeutic trials including gene replacement therapy or cell‐based therapy.
We provide a mutation update for MER tyrosine kinase (MERTK) which encodes a surface receptor localized at the apical membrane of the retinal pigment epithelium critical for photoreceptor outer segment phagocytosis. A total of 79 variants have been identified underlying inherited retinal diseases of which 11 are reported for the first time. Altogether, mutations in MERTK account for ∼2% of IRD cases with a severe retinal phenotype. These data are important for current and future therapeutic trials including gene replacement therapy or cell based therapy.
Vascular endothelial growth factor-A (VEGF) is the angiogenic factor promoting the pathological neovascularization in age-related macular degeneration (AMD) or diabetic macular edema (DME). Evidences ...have suggested a neurotrophic and neuroprotective role of VEGF, albeit in retina, cellular mechanisms underlying the VEGF neuroprotection remain elusive. Using purified adult retinal ganglion cells (RGCs) in culture, we demonstrated here that VEGF is released by RGCs themselves to promote their own survival, while VEGF neutralization by specific antibodies or traps drastically reduced the RGC survival. These results indicate an autocrine VEGF neuroprotection on RGCs. In parallel, VEGF produced by mixed retinal cells or by mesenchymal stem cells exerted a paracrine neuroprotection on RGCs. Such neuroprotective effect was obtained using the recombinant VEGF-B, suggesting the involvement of VEGF-R1 pathway in VEGF-elicited RGC survival. Finally, glaucomatous patients injected with VEGF traps (ranibizumab or aflibercept) due to either AMD or DME comorbidity, showed a significant reduction of RGC axon fiber layer thickness, consistent with the plausible reduction of the VEGF autocrine stimulation of RGCs. Our results provide evidence of the autocrine neuroprotective function of VEGF on RGCs is crucially involved to preserve injured RGCs such as in glaucomatous patients.
Variants of the CFH gene, encoding complement factor H (CFH), show strong association with age-related macular degeneration (AMD), a major cause of blindness. Here, we used murine models of AMD to ...examine the contribution of CFH to disease etiology. Cfh deletion protected the mice from the pathogenic subretinal accumulation of mononuclear phagocytes (MP) that characterize AMD and showed accelerated resolution of inflammation. MP persistence arose secondary to binding of CFH to CD11b, which obstructed the homeostatic elimination of MPs from the subretinal space mediated by thrombospsondin-1 (TSP-1) activation of CD47. The AMD-associated CFH(H402) variant markedly increased this inhibitory effect on microglial cells, supporting a causal link to disease etiology. This mechanism is not restricted to the eye, as similar results were observed in a model of acute sterile peritonitis. Pharmacological activation of CD47 accelerated resolution of both subretinal and peritoneal inflammation, with implications for the treatment of chronic inflammatory disease.
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•CFH deficiency restricts chronic subretinal mononuclear phagocyte accumulation•In inflammation resolution, MPs are eliminated via a CD47-dependent mechanism•CFH binding to integrin CD11b curbs TSP-1 activation of integrin-associated CD47•The AMD-associated CFH variant CFH(H402) potently inhibits microglial cell elimination
Variants in complement factor H (CFH) show strong association to age-related macular degeneration. Calippe et al. find that CFH binding to mononuclear phagocytes (MP) curbs the CD47-mediated elimination of MPs that maintains homeostasis in the subretinal space. The AMD-associated CFH variant CFH(H402) increases subretinal MP accumulation, providing insight into disease etiology.
Muller glial cells (MGCs) are responsible for the homeostatic and metabolic support of the retina. Despite the importance of MGCs in retinal disorders, reliable and accessible human cell sources to ...be used to model MGC‐associated diseases are lacking. Although primary human MGCs (pMGCs) can be purified from post‐mortem retinal tissues, the donor scarcity limits their use. To overcome this problem, we developed a protocol to generate and bank human induced pluripotent stem cell‐derived MGCs (hiMGCs). Using a transcriptome analysis, we showed that the three genetically independent hiMGCs generated were homogeneous and showed phenotypic characteristics and transcriptomic profile of pMGCs. These cells expressed key MGC markers, including Vimentin, CLU, DKK3, SOX9, SOX2, S100A16, ITGB1, and CD44 and could be cultured up to passage 8. Under our culture conditions, hiMGCs and pMGCs expressed low transcript levels of RLPB1, AQP4, KCNJ1, KCJN10, and SLC1A3. Using a disease modeling approach, we showed that hiMGCs could be used to model the features of diabetic retinopathy (DR)‐associated dyslipidemia. Indeed, palmitate, a major free fatty acid with elevated plasma levels in diabetic patients, induced the expression of inflammatory cytokines found in the ocular fluid of DR patients such as CXCL8 (IL‐8) and ANGPTL4. Moreover, the analysis of palmitate‐treated hiMGC secretome showed an upregulation of proangiogenic factors strongly related to DR, including ANG2, Endoglin, IL‐1β, CXCL8, MMP‐9, PDGF‐AA, and VEGF. Thus, hiMGCs could be an alternative to pMGCs and an extremely valuable tool to help to understand and model glial cell involvement in retinal disorders, including DR.
Main Points
We developed a protocol to generate and bank human iPSC‐derived Müller Glial cells (hiMGCs).
hiMGCs showed phenotypic characteristics and transcriptomic profile of primary MGCs.
hiMGCs can be used to model the features of diabetic retinopathy.
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