Abstract
Gliosis is a complex process comprising upregulation of intermediate filament (IF) proteins, particularly glial fibrillary acidic protein (GFAP) and vimentin, changes in glial cell morphology (hypertrophy) and increased deposition of inhibitory extracellular matrix molecules. Gliosis is common to numerous pathologies and can have deleterious effects on tissue function and regeneration. The role of IFs in gliosis is controversial, but a key hypothesized function is the stabilization of glial cell hypertrophy. Here, we developed RNAi approaches to examine the role of GFAP and vimentin in vivo in a murine model of inherited retinal degeneration, the Rhodopsin knockout (Rho-/- ) mouse. Specifically, we sought to examine the role of these IFs in the establishment of Müller glial hypertrophy during progressive degeneration, as opposed to (more commonly assessed) acute injury. Prevention of Gfap upregulation had a significant effect on the morphology of reactive Müller glia cells in vivo and, more strikingly, the reduction of Vimentin expression almost completely prevented these cells from undergoing degeneration-associated hypertrophy. Moreover, and in contrast to studies in knockout mice, simultaneous suppression of both GFAP and vimentin expression led to severe changes in the cytoarchitecture of the retina, in both diseased and wild-type eyes. These data demonstrate a crucial role for Vimentin, as well as GFAP, in the establishment of glial hypertrophy and support the further exploration of RNAi-mediated knockdown of vimentin as a potential therapeutic approach for modulating scar formation in the degenerating retina.
Highlights
Reactive gliosis is regarded as a cellular attempt to protect the surrounding tissue from further damage, in order to promote repair and limit neuronal re-modeling
We chose the RhoÀ/À model of inherited retinal degeneration because it exhibits a moderate rate of photoreceptors loss (compared to very fast models like PDEβ and much slower models like Prph2(rd2/rd2)) and we have previously found it to exhibit a strong upregulation of Gfap and vimentin and clear evidence of Müller glia hypertrophy (Hippert et al, 2015; Pearson et al, 2010)
No significant differences were observed, either in overall morphology or in apical spread, between AAVshControl treated eyes and those receiving associated viral (AAV)-shVim or AAVshGfap at either administration time point (Figure S4a). These results demonstrate that knockdown of either Vimentin or Gfap prevents one of the most striking changes in Müller glial morphology associated with retinal degeneration, the establishment of hypertrophy, without adversely affecting Müller glial morphology in the normal retina
Summary
Reactive gliosis is regarded as a cellular attempt to protect the surrounding tissue from further damage, in order to promote repair and limit neuronal re-modeling. It includes morphological, biochemical, and physiological changes, each of which can vary with the type and severity of the initiating insult (Silver & Miller, 2004). We report a crucial role for vimentin, as well as GFAP, in the establishment of retinal glial hypertrophy This raises the potential utility of RNAi-mediated knockdown of vimentin as a therapeutic approach for modulating glial hypertrophy as part of scar formation in the damaged retina
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