Characterization of early retinal progenitor microenvironment: Presence of activities selective for the differentiation of retinal ganglion cells and maintenance of progenitors

Generation of Functional Human Retinal Ganglion Cells with Target Specificity from Pluripotent Stem Cells by Chemically Defined Recapitulation of Developmental Mechanism

Glaucoma is a complex group of diseases wherein a selective degeneration of retinal ganglion cells (RGCs) lead to irreversible loss of vision. A comprehensive approach to glaucomatous RGC degeneration may include stem cells to functionally replace dead neurons through transplantation and understand RGCs vulnerability using a disease in a dish stem cell model. Both approaches require the directed generation of stable, functional, and target-specific RGCs from renewable sources of cells, that is, the embryonic stem cells and induced pluripotent stem cells. Here, we demonstrate a rapid and safe, stage-specific, chemically defined protocol that selectively generates RGCs across species, including human, by recapitulating the developmental mechanism. The de novo generated RGCs from pluripotent cells are similar to native RGCs at the molecular, biochemical, functional levels. They also express axon guidance molecules, and discriminate between specific and nonspecific targets, and are nontumorigenic. Stem Cells 2017;35:572-585.

Stem cell therapy for glaucoma: possibilities and practicalities

Glaucoma is a progressive, neurodegenerative, optic neuropathy in which currently available therapies cannot always prevent, and do not reverse, vision loss. Stem cell transplantation may provide a promising new avenue for treating many presently incurable degenerative conditions, including glaucoma. This article will explore the various ways in which transplantation of stem or progenitor cells may be applied for the treatment of glaucoma. We will critically discuss the translational prospects of two cell transplantation-based treatment modalities: neuroprotection and retinal ganglion cell replacement. In addition, we will identify specific questions that need to be addressed and obstacles to overcome on the path to clinical translation, and offer insight into potential strategies for approaching this goal.

Adult ciliary epithelial stem cells generate functional neurons and differentiate into both early and late born retinal neurons under non-cell autonomous influences

Background

The neural stem cells discovered in the adult ciliary epithelium (CE) in higher vertebrates have emerged as an accessible source of retinal progenitors; these cells can self-renew and possess retinal potential. However, recent studies have cast doubt as to whether these cells could generate functional neurons and differentiate along the retinal lineage. Here, we have systematically examined the pan neural and retinal potential of CE stem cells.

Results

Molecular and cellular analysis was carried out to examine the plasticity of CE stem cells, obtained from mice expressing green fluorescent protein (GFP) under the influence of the promoter of the rod photoreceptor-specific gene, Nrl, using the neurospheres assay. Differentiation was induced by specific culture conditions and evaluated by both transcripts and protein levels of lineage-specific regulators and markers. Temporal pattern of their levels were examined to determine the expression of genes and proteins underlying the regulatory hierarchy of cells specific differentiation in vitro. Functional attributes of differentiation were examined by the presence of current profiles and pharmacological mobilization of intracellular calcium using whole cell recordings and Fura-based calcium imaging, respectively. We demonstrate that stem cells in adult CE not only have the capacity to generate functional neurons, acquiring the expression of sodium and potassium channels, but also respond to specific cues in culture and preferentially differentiate along the lineages of retinal ganglion cells (RGCs) and rod photoreceptors, the early and late born retinal neurons, respectively. The retinal differentiation of CE stem cells was characterized by the temporal acquisition of the expression of the regulators of RGCs and rod photoreceptors, followed by the display of cell type-specific mature markers and mobilization of intracellular calcium.

Conclusions

Our study demonstrates the bonafide retinal potential of adult CE stem cells and suggests that their plasticity could be harnessed for clinical purposes once barriers associated with any lineage conversion, i.e., low efficiency and fidelity is overcome through the identification of conducive culture conditions.

Differentiation of neuronal cells from NIH/3T3 fibroblasts under defined conditions

We attempted to test whether the differentiated NIH/3T3 fibroblasts could be differentiated into neuronal cells without any epigenetic modification. First, a neurosphere assay was carried out, and we successfully generated neurosphere-like cells by floating cultures of NIH/3T3 fibroblasts in neural stem cell medium. These spheres have the ability to form sub-spheres after three passages, and express the neural progenitor markers Nestin, Sox2, Pax6, and Musashi-1. Second, after shifting to a differentiating medium and culturing for an additional 8 days, cells in these spheres expressed the neuronal markers β-tubulin and neurofilament 200 and the astrocytic marker glial fibrillary acidic protein (GFAP). Finally, after treating the spheres with all-trans retinoic acid and taurine, the expression of β-tubulin was increased and the staining of photoreceptor markers rhodopsin and recoverin was observed. The present study shows that NIH/3T3 fibroblasts can generate neurosphere-like, neuron-like, and even photoreceptor-like cells under defined conditions, suggesting that the differentiated non-neuronal cells NIH/3T3 fibroblasts, but not pluripotent cells such as embryonic stem cells or induced pluripotent stem cells, may have the potential to be transdifferentiated into neuronal cells without adding any epigenetic modifier. This transdifferentiation may be due to the possible neural progenitor potential of NIH/3T3 fibroblasts that remains dormant under normal conditions.

Induced pluripotent stem cells generate both retinal ganglion cells and photoreceptors: therapeutic implications in degenerative changes in glaucoma and age-related macular degeneration

The direct reprogramming of somatic cells to a pluripotent state holds significant implications for treating intractable degenerative diseases by ex vivo cell therapy. In addition, the reprogrammed cells can serve as a model for diseases and the discovery of drugs and genes. Here, we demonstrate that mouse fibroblast induced pluripotent stem cells (iPSCs) represent a renewable and robust source of retinal progenitors, capable of generating a wide range of retinal cell types that includes retinal ganglion cells (RGCs), cone, and rod photoreceptors. They respond to simulated microenvironment of early and late retinal histogenesis by differentiating into stage-specific retinal cell types through the recruitment of normal mechanisms. The depth of the retinal potential of iPSCs suggests that they may be used to formulate stem cell approaches to understand and treat a wide range of retinal degenerative diseases from glaucoma to age-related macular degeneration (AMD).

SWI/SNF Chromatin Remodeling ATPase Brm Regulates the Differentiation of Early Retinal Stem Cells/Progenitors by Influencing Brn3b Expression and Notch Signaling

Based on a variety of approaches, evidence suggests that different cell types in the vertebrate retina are generated by multipotential progenitors in response to interactions between cell intrinsic and cell extrinsic factors. The identity of some of the cellular determinants that mediate such interactions has emerged, shedding light on mechanisms underlying cell differentiation. For example, we know now that Notch signaling mediates the influence of the microenvironment on states of commitment of the progenitors by activating transcriptional repressors. Cell intrinsic factors such as the proneural basic helix-loop-helix and homeodomain transcription factors regulate a network of genes necessary for cell differentiation and maturation. What is missing from this picture is the role of developmental chromatin remodeling in coordinating the expression of disparate classes of genes for the differentiation of retinal progenitors. Here we describe the role of Brm, an ATPase in the SWI/SNF chromatin remodeling complex, in the differentiation of retinal progenitors into retinal ganglion cells. Using the perturbation of expression and function analyses, we demonstrate that Brm promotes retinal ganglion cell differentiation by facilitating the expression and function of a key regulator of retinal ganglion cells, Brn3b, and the inhibition of Notch signaling. In addition, we demonstrate that Brm promotes cell cycle exit during retinal ganglion cell differentiation. Together, our results suggest that Brm represents one of the nexus where diverse information of cell differentiation is integrated during cell differentiation.