| Abstract |
Stem cell based therapies offer hope for the treatment of retinal disease.
In the mammalian retina, Muller glia possess some stem cell-like
characteristics. However, their capacity for neurogenesis remains limited.
To identify factors influencing the neurogenic potential of Muller glia in
vitro, a conditionally immortalized mouse Muller cell line (ImM10) was
generated and characterized. In addition to Muller glial genes, ImM10
cells express some genes characteristic of retinal progenitor cells.
Following treatment with specific growth factors and media supplements, a
subset of Muller glia acquired a more neuronal morphology and expressed
neuronal genes. To determine the role of environment on Muller glia
derived neurogenesis, Muller glia were cultured in three dimensional (3D)
peptide hydrogels. Cells encapsulated within 3D hydrogels expressed
different neuronal genes, compared to cells cultured on 2D flat plastic
substrates. The roles of RE-1 silencing transcription factor (REST) and
Notch signaling in Muller glia derived neurogenesis were also investigated.
REST represses neuronal genes in nonneuronal tissues, whereas Notch can
promote gliogenesis during retinal development. Inhibition of Rest
expression by RNA interference combined with pharmacological inhibition of
Notch signaling with DAPT led to the upregulation of some additional
neuronal genes in ImM10 Muller glia. Together, these results demonstrated
a modest neurogenic capacity for Muller glia. A potential barrier for
transplantation of these or any stem-like cells for therapeutic purposes
is retinal remodeling of surviving cells following retinal disease or
injury. Neuronal and synaptic remodeling was analyzed in the rd10 mouse
model of retinitis pigmentosa. Following photoreceptor degeneration,
second order neurons (horizontal, and bipolar cells) showed dendrite
retraction, cellular migration, and a loss of post-synaptic elements that
increased with disease progression. Surprisingly, the inner retina
remained relatively intact even at advanced stages of degeneration.
Furthermore, survival of small numbers of cone photoreceptors preserved
second-order neuronal circuitry locally. This study suggests that the
inner retina may remain receptive to interventions even at late stages of
disease, and that early cellular transplantation may help prevent or slow
retinal remodeling.
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