Physiologic Electrical Fields Direct Retinal Ganglion Cell Axon Growth In Vitro.

PurposeThe purpose of this study was to characterize the ability of applied electrical fields (EFs) to direct retinal ganglion cell (RGC) axon growth as well as to assess whether Rho GTPases play a role in translating electrical cues to directional cues.MethodsFull-thickness, early postnatal mouse retina was cultured in electrotaxis chambers and exposed to EFs of varying strengths (50-200 mV/mm). The direction of RGC axon growth was quantified from time-lapsed videos. The rate of axon growth and responsiveness to changes in EF polarity were also assessed. The effect of toxin B, a broad-spectrum inhibitor of Rho GTPase signaling, and Z62954982, a selective inhibitor of Rac1, on EF-directed growth was determined.ResultsIn the absence of an EF, RGC axons demonstrated indiscriminate directional growth from the explant edge. Retinal cultures exposed to an EF of 100 and 200 mV/mm showed markedly asymmetric growth, with 74.2% and 81.2% of axons oriented toward the cathode, respectively (P < 0.001). RGC axons responded to acute changes in EF polarity by redirecting their growth toward the "new" cathode. This galvanotropic effect was partially neutralized by toxin B and Rac1 inhibitor Z62954982.ConclusionsRGC axons exhibit cathode-directed growth in the presence of an EF. This effect is mediated in part by the Rho GTPase signaling cascade

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

Cell Lineages and the Logic of Proliferative Control

It is widely accepted that the growth and regeneration of tissues and organs is tightly controlled. Although experimental studies are beginning to reveal molecular mechanisms underlying such control, there is still very little known about the control strategies themselves. Here, we consider how secreted negative feedback factors (“chalones”) may be used to control the output of multistage cell lineages, as exemplified by the actions of GDF11 and activin in a self-renewing neural tissue, the mammalian olfactory epithelium (OE). We begin by specifying performance objectives—what, precisely, is being controlled, and to what degree—and go on to calculate how well different types of feedback configurations, feedback sensitivities, and tissue architectures achieve control. Ultimately, we show that many features of the OE—the number of feedback loops, the cellular processes targeted by feedback, even the location of progenitor cells within the tissue—fit with expectations for the best possible control. In so doing, we also show that certain distinctions that are commonly drawn among cells and molecules—such as whether a cell is a stem cell or transit-amplifying cell, or whether a molecule is a growth inhibitor or stimulator—may be the consequences of control, and not a reflection of intrinsic differences in cellular or molecular character

TGF-βs mediate feedback regulation of neurogenesis and gliogenesis in the mammalian olfactory epithelium

Proper tissue growth faces many obstacles: Considering genetic variability and environmental instability, how do developing tissues know when to stop growing or how many different cell types to produce? One strategy is to employ endogenous feedback signaling. A signal produced, by the differentiated cell types of a tissue, which feeds back to control the activity of proliferating stem and progenitor cells allows organs to tether their growth with the number of differentiated cell types in the system. This dissertation explains these ideas and discusses tissue culture, genetic and computational experiments used to understand the strategies that control developmental and regenerative neurogenesis in a model system, the olfactory epithelium (OE) of the mouse. Experiments presented here, in conjunction with previous work, show that neurogenesis and gliogenesis during OE development is regulated by multiple, stage-specific feedback loops. In the OE, neurons develop from a lineage consisting of two distinct precursor stages: a Sox2+/MASH1+ stem cell stage that gives rise to a Ngn1+ immediate neuronal precursor (INP) cell stage. Sox2+/MASH1+ stem cell proliferation is inhibited by ActivinβB, a TGF-β produced endogenously by cells of the neuronal lineage; INP proliferation is inhibited by GDF11, an activin-like TGF-β also produced endogenously within the OE. Mathematical modeling studies of unbranched cell lineages, in which Hill kinetics regulate proliferation, reveal that a feedback circuit consisting of ActivinβB and GDF11 can, in principle, simultaneously control cell number, cell-type ratios, and regenerative speed in this system. Phenotypic studies of Gdf11-/- mice, ActivinβB -/- mice, and mice null for both genes unexpectedly revealed that the stem cell of ORNs is also the progenitor of sustentacular cells, the intrinsic glial cells of the OE. These studies also show that ActivinβB and GDF11 exert opposite effects in regulating the fate choice of the OE stem cell (neuronal versus glial). These experiments support the hypothesis that tissue homeostasis is established, in part, by feedback signals that coordinate the rate at which stem and neuronal precursor cells divide with the number of end stage cells in the system

Strabismus Case #2 - Thyroid Eye Disease s/p Multiple Prior Surgeries

This symposium has been created to highlight the surgical aspects of our field and to educate neuroophthalmologists and trainees through the presentation and discussion of complex surgical neuroophthalmic case scenarios