Retinal ganglion cell repopulation for vision restoration in optic neuropathy: a roadmap from the RReSTORe Consortium

Retinal ganglion cell (RGC) death in glaucoma and other optic neuropathies results in irreversible vision loss due to the mammalian central nervous system's limited regenerative capacity. RGC repopulation is a promising therapeutic approach to reverse vision loss from optic neuropathies if the newly introduced neurons can reestablish functional retinal and thalamic circuits. In theory, RGCs might be repopulated through the transplantation of stem cell-derived neurons or via the induction of endogenous transdifferentiation. The RGC Repopulation, Stem Cell Transplantation, and Optic Nerve Regeneration (RReSTORe) Consortium was established to address the challenges associated with the therapeutic repair of the visual pathway in optic neuropathy. In 2022, the RReSTORe Consortium initiated ongoing international collaborative discussions to advance the RGC repopulation field and has identified five critical areas of focus: (1) RGC development and differentiation, (2) Transplantation methods and models, (3) RGC survival, maturation, and host interactions, (4) Inner retinal wiring, and (5) Eye-to-brain connectivity. Here, we discuss the most pertinent questions and challenges that exist on the path to clinical translation and suggest experimental directions to propel this work going forward. Using these five subtopic discussion groups (SDGs) as a framework, we suggest multidisciplinary approaches to restore the diseased visual pathway by leveraging groundbreaking insights from developmental neuroscience, stem cell biology, molecular biology, optical imaging, animal models of optic neuropathy, immunology & immunotolerance, neuropathology & neuroprotection, materials science & biomedical engineering, and regenerative neuroscience. While significant hurdles remain, the RReSTORe Consortium's efforts provide a comprehensive roadmap for advancing the RGC repopulation field and hold potential for transformative progress in restoring vision in patients suffering from optic neuropathies

Pericyte heterogeneity identified by 3D ultrastructural analysis of the microvessel wall

Confident identification of pericytes (PCs) remains an obstacle in the field, as a single molecular marker for these unique perivascular cells remains elusive. Adding to this challenge is the recent appreciation that PC populations may be heterogeneous, displaying a range of morphologies within capillary networks. We found additional support on the ultrastructural level for the classification of these PC subtypes—“thin-strand” (TSP), mesh (MP), and ensheathing (EP)—based on distinct morphological characteristics. Interestingly, we also found several examples of another cell type, likely a vascular smooth muscle cell, in a medial layer between endothelial cells (ECs) and pericytes (PCs) harboring characteristics of the ensheathing type. A conserved feature across the different PC subtypes was the presence of extracellular matrix (ECM) surrounding the vascular unit and distributed in between neighboring cells. The thickness of this vascular basement membrane was remarkably consistent depending on its location, but never strayed beyond a range of 150–300 nm unless thinned to facilitate closer proximity of neighboring cells (suggesting direct contact). The density of PC-EC contact points (“peg-and-socket” structures) was another distinguishing feature across the different PC subtypes, as were the apparent contact locations between vascular cells and brain parenchymal cells. In addition to this thinning, the extracellular matrix (ECM) surrounding EPs displayed another unique configuration in the form of extensions that emitted out radially into the surrounding parenchyma. Knowledge of the origin and function of these structures is still emerging, but their appearance suggests the potential for being mechanical elements and/or perhaps signaling nodes via embedded molecular cues. Overall, this unique ultrastructural perspective provides new insights into PC heterogeneity and the presence of medial cells within the microvessel wall, the consideration of extracellular matrix (ECM) coverage as another PC identification criteria, and unique extracellular matrix (ECM) configurations (i.e., radial extensions) that may reveal additional aspects of PC heterogeneity

F-spondin Is Essential for Maintaining Circadian Rhythms

The suprachiasmatic nucleus (SCN) is the master pacemaker that drives circadian behaviors. SCN neurons have intrinsic, self-sustained rhythmicity that is governed by transcription-translation feedback loops. Intrinsic rhythms within the SCN do not match the day-night cycle and are therefore entrained by light-derived cues. Such cues are transmitted to the SCN by a class of intrinsically photosensitive retinal ganglion cells (ipRGCs). In the present study, we sought to identify how axons from ipRGCs target the SCN. While none of the potential targeting cues identified appeared necessary for retinohypothalamic innervation, we unexpectedly identified a novel role for the extracellular matrix protein F-spondin in circadian behavior. In the absence of F-spondin, mice lost their ability to maintain typical intrinsic rhythmicity. Moreover, F-spondin loss results in the displacement of vasoactive intestinal peptide (VIP)-expressing neurons, a class of neurons that are essential for maintaining rhythmicity among SCN neurons. Thus, this study highlights a novel role for F-spondin in maintaining circadian rhythms

Retinal-input-induced epigenetic dynamics in the developing mouse dorsal lateral geniculate nucleus

Abstract DNA methylation plays important roles in the regulation of nervous system development and in cellular responses to environmental stimuli such as light-derived signals. Despite great efforts in understanding the maturation and refinement of visual circuits, we lack a clear understanding of how changes in DNA methylation correlate with visual activity in the developing subcortical visual system, such as in the dorsal lateral geniculate nucleus (dLGN), the main retino-recipient region in the dorsal thalamus. Here, we explored epigenetic dynamics underlying dLGN development at ages before and after eye opening in wild-type mice and mutant mice in which retinal ganglion cells fail to form. We observed that development-related epigenetic changes tend to co-localize together on functional genomic regions critical for regulating gene expression, while retinal-input-induced epigenetic changes are enriched on repetitive elements. Enhancers identified in neurons are prone to methylation dynamics during development, and activity-induced enhancers are associated with retinal-input-induced epigenetic changes. Intriguingly, the binding motifs of activity-dependent transcription factors, including EGR1 and members of MEF2 family, are enriched in the genomic regions with epigenetic aberrations in dLGN tissues of mutant mice lacking retinal inputs. Overall, our study sheds new light on the epigenetic regulatory mechanisms underlying the role of retinal inputs on the development of mouse dLGN

Shotgun proteomic analysis of the Mexican lime tree infected with "Candidatus Phytoplasma aurantifolia"

Infection of Mexican lime trees (Citrus aurantifolia L.) with the specialized bacterium "CandidatusPhytoplasma aurantifolia" causes witches' broom disease. Witches' broom disease has the potential to cause significant economic losses throughout western Asia and North Africa. We used label-free quantitative shotgun proteomics to study changes in the proteome of Mexican lime trees in response to infection by "Ca. Phytoplasma aurantifolia". Of 990 proteins present in five replicates of healthy and infected plants, the abundances of 448 proteins changed significantly in response to phytoplasma infection. Of these, 274 proteins were less abundant in infected plants than in healthy plants, and 174 proteins were more abundant in infected plants than in healthy plants. These 448 proteins were involved in stress response, metabolism, growth and development, signal transduction, photosynthesis, cell cycle, and cell wall organization. Our results suggest that proteomic changes in response to infection by phytoplasmas might support phytoplasma nutrition by promoting alterations in the host's sugar metabolism, cell wall biosynthesis, and expression of defense-related proteins. Regulation of defense-related pathways suggests that defense compounds are induced in interactions with susceptible as well as resistant hosts, with the main differences between the two interactions being the speed and intensity of the response.11 page(s

Shotgun Proteomic Analysis of the Mexican Lime Tree Infected with “<i>Candidatus</i> <i>Phytoplasma aurantifolia</i>”

Infection of Mexican lime trees (<i>Citrus aurantifolia</i> L.) with the specialized bacterium “<i>Candidatus</i> <i>Phytoplasma aurantifolia</i>” causes witches’ broom disease. Witches’ broom disease has the potential to cause significant economic losses throughout western Asia and North Africa. We used label-free quantitative shotgun proteomics to study changes in the proteome of Mexican lime trees in response to infection by “<i>Ca</i>. <i>Phytoplasma aurantifolia</i>”. Of 990 proteins present in five replicates of healthy and infected plants, the abundances of 448 proteins changed significantly in response to phytoplasma infection. Of these, 274 proteins were less abundant in infected plants than in healthy plants, and 174 proteins were more abundant in infected plants than in healthy plants. These 448 proteins were involved in stress response, metabolism, growth and development, signal transduction, photosynthesis, cell cycle, and cell wall organization. Our results suggest that proteomic changes in response to infection by phytoplasmas might support phytoplasma nutrition by promoting alterations in the host’s sugar metabolism, cell wall biosynthesis, and expression of defense-related proteins. Regulation of defense-related pathways suggests that defense compounds are induced in interactions with susceptible as well as resistant hosts, with the main differences between the two interactions being the speed and intensity of the response

Shotgun Proteomic Analysis of the Mexican Lime Tree Infected with “<i>Candidatus</i> <i>Phytoplasma aurantifolia</i>”

Infection of Mexican lime trees (<i>Citrus aurantifolia</i> L.) with the specialized bacterium “<i>Candidatus</i> <i>Phytoplasma aurantifolia</i>” causes witches’ broom disease. Witches’ broom disease has the potential to cause significant economic losses throughout western Asia and North Africa. We used label-free quantitative shotgun proteomics to study changes in the proteome of Mexican lime trees in response to infection by “<i>Ca</i>. <i>Phytoplasma aurantifolia</i>”. Of 990 proteins present in five replicates of healthy and infected plants, the abundances of 448 proteins changed significantly in response to phytoplasma infection. Of these, 274 proteins were less abundant in infected plants than in healthy plants, and 174 proteins were more abundant in infected plants than in healthy plants. These 448 proteins were involved in stress response, metabolism, growth and development, signal transduction, photosynthesis, cell cycle, and cell wall organization. Our results suggest that proteomic changes in response to infection by phytoplasmas might support phytoplasma nutrition by promoting alterations in the host’s sugar metabolism, cell wall biosynthesis, and expression of defense-related proteins. Regulation of defense-related pathways suggests that defense compounds are induced in interactions with susceptible as well as resistant hosts, with the main differences between the two interactions being the speed and intensity of the response