Prospective purification and characterization of Müller glia in the mouse retina regeneration assay

Cell cycle-dependent activation of proneural transcription factor expression and reactive gliosis in rat Müller glia

Retinal Müller glia have a capacity to regenerate neurons in lower vertebrates like zebrafish, but such ability is extremely limited in mammals. In zebrafish, Müller glia proliferate after injury, which promotes their neurogenic reprogramming while inhibiting reactive gliosis. In mammals, however, how the cell cycle affects the fate of Müller glia after injury remains unclear. Here, we focused on the expression of proneural transcription factors, Ngn2 and Ascl1, and a gliosis marker glial fibrillary acidic protein (GFAP) in rat Müller glia after N-methyl-N-nitrosourea (MNU)-induced photoreceptor injury and analyzed the role of Müller glia proliferation in the regulation of their expression using retinal explant cultures. Thymidine-induced G1/S arrest of Müller glia proliferation significantly hampered the expression of Ascl1, Ngn2, and GFAP, and release from the arrest induced their upregulation. The migration of Müller glia nuclei into the outer nuclear layer was also shown to be cell cycle-dependent. These data suggest that, unlike the situation in zebrafish, cell cycle progression of Müller glia in mammals promotes both neurogenic reprogramming and reactive gliosis, which may be one of the mechanisms underlying the limited regenerative capacity of the mammalian retina.

HBEGF-TNF induce a complex outer retinal pathology with photoreceptor cell extrusion in human organoids

Human organoids could facilitate research of complex and currently incurable neuropathologies, such as age-related macular degeneration (AMD) which causes blindness. Here, we establish a human retinal organoid system reproducing several parameters of the human retina, including some within the macula, to model a complex combination of photoreceptor and glial pathologies. We show that combined application of TNF and HBEGF, factors associated with neuropathologies, is sufficient to induce photoreceptor degeneration, glial pathologies, dyslamination, and scar formation: These develop simultaneously and progressively as one complex phenotype. Histologic, transcriptome, live-imaging, and mechanistic studies reveal a previously unknown pathomechanism: Photoreceptor neurodegeneration via cell extrusion. This could be relevant for aging, AMD, and some inherited diseases. Pharmacological inhibitors of the mechanosensor PIEZO1, MAPK, and actomyosin each avert pathogenesis; a PIEZO1 activator induces photoreceptor extrusion. Our model offers mechanistic insights, hypotheses for neuropathologies, and it could be used to develop therapies to prevent vision loss or to regenerate the retina in patients suffering from AMD and other diseases.

Gene regulatory networks controlling vertebrate retinal regeneration

Injury induces retinal Müller glia of certain cold-blooded vertebrates, but not those of mammals, to regenerate neurons. To identify gene regulatory networks that reprogram Müller glia into progenitor cells, we profiled changes in gene expression and chromatin accessibility in Müller glia from zebrafish, chick, and mice in response to different stimuli. We identified evolutionarily conserved and species-specific gene networks controlling glial quiescence, reactivity, and neurogenesis. In zebrafish and chick, the transition from quiescence to reactivity is essential for retinal regeneration, whereas in mice, a dedicated network suppresses neurogenic competence and restores quiescence. Disruption of nuclear factor I transcription factors, which maintain and restore quiescence, induces Müller glia to proliferate and generate neurons in adult mice after injury. These findings may aid in designing therapies to restore retinal neurons lost to degenerative diseases.

Photobiomodulation Mediates Neuroprotection against Blue Light Induced Retinal Photoreceptor Degeneration

Potent neuroprotective effects of photobiomodulation with 670 nm red light (RL) have been demonstrated in several models of retinal disease. RL improves mitochondrial metabolism, reduces retinal inflammation and oxidative cell stress, showing its ability to enhance visual function. However, the current knowledge is limited to the main hypothesis that the respiratory chain complex IV, cytochrome c oxidase, serves as the primary target of RL. Here, we demonstrate a comprehensive cellular, molecular, and functional characterization of neuroprotective effects of 670 nm RL and 810 nm near-infrared light (NIRL) on blue light damaged murine primary photoreceptors. We show that respiratory chain complexes I and II are additional PBM targets, besides complex IV, leading to enhanced mitochondrial energy metabolism. Accordingly, our study identified mitochondria related RL- and NIRL-triggered defense mechanisms promoting photoreceptor neuroprotection. The observed improvement of mitochondrial and extramitochondrial respiration in both inner and outer segments is linked with reduced oxidative stress including its cellular consequences and reduced mitochondria-induced apoptosis. Analysis of regulatory mechanisms using gene expression analysis identified upregulation α-crystallins that indicate enhanced production of proteins with protective functions that point to the rescued mitochondrial function. The results support the hypothesis that energy metabolism is a major target for retinal light therapy.

Optimization of a Method to Isolate and Culture Adult Porcine, Rats and Mice Müller Glia in Order to Study Retinal Diseases

Müller cells are the predominant glial elements in the retina, extending vertically across this structure, and they fulfill a wealth support roles that are critical for neurons. Alterations to the behavior and phenotype of Müller glia are often seen in animal models of retinal degeneration and in retinal tissue from patients with a variety of retinal disorders. Thus, elucidating the mechanisms underlying the development of retinal diseases would help better understand the cellular processes involved in such pathological changes. Studies into Müller cell activity in vitro have been hindered by the difficulty in obtaining pure cell populations and the tendency of these cells to rapidly differentiate in culture. Most protocols currently used to isolate Müller glia use neonatal or embryonic tissue but here, we report an optimized protocol that facilitates the reliable and straightforward isolation and culture of Müller cells from adult pigs, rats and mice. The protocol described here provides an efficient method for the rapid isolation of adult mammalian Müller cells, which represents a reliable platform to study therapeutic targets and to test the effects of drugs that might combat retinal diseases.

Retinal cell death dependent reactive proliferative gliosis in the mouse retina

Neurodegeneration is a common starting point of reactive gliosis, which may have beneficial and detrimental consequences. It remains incompletely understood how distinctive pathologies and cell death processes differentially regulate glial responses. Müller glia (MG) in the retina are a prime model: Neurons are regenerated in some species, but in mammals there may be proliferative disorders and scarring. Here, we investigated the relationship between retinal damage and MG proliferation, which are both induced in a reproducible and temporal order in organotypic culture of EGF-treated mouse retina: Hypothermia pretreatment during eye dissection reduced neuronal cell death and MG proliferation; stab wounds increased both. Combined (but not separate) application of defined cell death signaling pathway inhibitors diminished neuronal cell death and maintained MG mitotically quiescent. The level of neuronal cell death determined MG activity, indicated by extracellular signal-regulated kinase (ERK) phosphorylation, and proliferation, both of which were abolished by EGFR inhibition. Our data suggest that retinal cell death, possibly either by programmed apoptosis or necrosis, primes MG to be able to transduce the EGFR–ERK activity required for cell proliferation. These results imply that cell death signaling pathways are potential targets for future therapies to prevent the proliferative gliosis frequently associated with certain neurodegenerative conditions.