Inherited Photoreceptor Degeneration Causes the Death of Melanopsin-Positive Retinal Ganglion Cells and Increases Their Coexpression of Brn3a.

Diego García-Ayuso,María P Villegas-Pérez,Manuel Vidal-Sanz,Nicolás Cuenca,Marta Agudo-Barriuso,Gema Esquiva,Isabel Pinilla,Johnny Di Pierdomenico,Francisco Manuel Nadal-Nicolás

doi:10.1167/iovs.15-16808

Abstract

To study the population of intrinsically photosensitive retinal ganglion cells (melanopsin-expressing RGCs, m+RGCs) in P23H-1 rats, a rat model of inherited photoreceptor degeneration. At postnatal (P) times P30, P365, and P540, retinas from P23H dystrophic rats (line 1, rapid degeneration; and line 3, slow degeneration) and Sprague Dawley (SD) rats (control) were dissected as whole-mounts and immunodetected for melanopsin and/or Brn3a. The dendritic arborization of m+RGCs and the numbers of Brn3a+RGCs and m+RGCs were quantified and their retinal distribution and coexpression analyzed. In SD rats, aging did not affect the population of Brn3a+RGCs or m+RGCs or the percentage that showed coexpression (0.27%). Young P23H-1 rats had a significantly lower number of Brn3a+RGCs and showed a further decline with age. The population of m+RGCs in young P23H-1 rats was similar to that found in SD rats and decreased by 22.6% and 28.2% at P365 and P540, respectively, similarly to the decrease of the Brn3a+RGCs. At these ages the m+RGCs showed a decrease of their dendritic arborization parameters, which was similar in both the P23H-1 and P23H-3 lines. The percentage of coexpression of Brn3a was, however, already significantly higher at P30 (3.31%) and increased significantly with age (10.65% at P540). Inherited photoreceptor degeneration was followed by secondary loss of Brn3a+RGCs and m+RGCs. Surviving m+RGCs showed decreased dendritic arborization parameters and increased coexpression of Brn3a and melanopsin, phenotypic and molecular changes that may represent an effort to resist degeneration and/or preferential survival of m+RGCs capable of synthesizing Brn3a.

Highlights

To study the population of intrinsically photosensitive retinal ganglion cells in P23H-1 rats, a rat model of inherited photoreceptor degeneration
There is a subtype of specialized retinal ganglion cells (RGCs) that expresses the photopigment melanopsin and responds to light
At P30, the total number of Brn3aþRGCs was significantly lower in the P23H-1 strain than in Sprague Dawley (SD) rats (P < 0.001; MannWhitney test; Table 1) and represented 93.7% of the total numbers found in SD rats (Fig. 1A), in accordance with previously published data.[51]

Summary

Methods

At postnatal (P) times P30, P365, and P540, retinas from P23H dystrophic rats (line 1, rapid degeneration; and line 3, slow degeneration) and Sprague Dawley (SD) rats (control) were dissected as whole-mounts and immunodetected for melanopsin and/or Brn3a. The different rates of retinal degeneration in the three P23H rat lines are presumably due to a position effect from different transgene insertion sites in the rat genome[76] (Steinberg RH, et al IOVS 1996;37:ARVO Abstract 3190). In this context, at approximately postnatal (P) age P120, only one photoreceptor row remains in line 1,51,77 whereas one to two rows of photoreceptor cell bodies are found in line 3 of P23H rats at this age.[78] The wildtype control for these transgenic animals is the albino SD rats

Results

Discussion

Conclusion