Nestin expression in the retina of rats with inherited retinal degeneration.

Nestin is found in radial glia and neuronal/glial progenitor cells during retinal development, and is re-expressed after acute damage in the retina of adult mammals. We have investigated nestin expression in the retina of the Royal College of Surgeons (RCS) rat model of human inherited blindness, Retinitis pigmentosa (RP). During the first postnatal week, nestin immunoreactivity was located in elongated processes resembling radial glia in both control and dystrophic animals. During the second postnatal week, the density of nestin immunoreactive radial processes decreased progressively starting in the outer retina. At postnatal day 20 (PNd20), Nestin immunoreactive radial processes were no longer visible, with immunoreactivity restricted to structures resembling Müller end-feet and/or astrocytes located in the ganglion cell layer (GCL) in both control and dystrophic rats. These morphological results were confirmed by Western blotting and qPCR analysis. The level of nestin remained low in control animals at different time points up to 1 year, but we observed a re-expression of this protein from PNd30 in the dystrophic animals. The morphology of cells re-expressing nestin resembled that of radial glia and/or Muller cells, but co-localization of nestin and glutamine synthetase (GS: a marker of mature Müller cells) was only partial. Interestingly, whereas Western blot analysis confirmed the increase in protein levels from PNd30 onwards, mRNA levels remained low in dystrophic rats. Additional studies demonstrated that the discrepancy between protein and mRNA contents could be due to a dysfunction in proteasome activity as often observed in neurodegenerative pathologies. In conclusion, because of its localization in astrocytes and in radial processes resembling radial glia in the pathologic adult retina, nestin may be involved in mechanisms such as cell migration, generation of new neurons or glial cells and/or in retinal (re)modeling in dystrophic adult animals. The lack of concomitant up-regulation of mRNAs in adult dystrophic animals suggests that the pathology could lead to transcriptional and/or metabolic changes involving the stabilization of the half-life and/or dysregulation of degradation processes of nestin protein.