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X.F. Wang, A. Iannaccone, M.M. Jablonski; Contribution of Müller Cells toward the Regulation of Photoreceptor Outer Segment Assembly . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3978.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: We have previously demonstrated that both PEDF and IPTG (a permissive glycan) support photoreceptor outer segment assembly in RPE–deprived Xenopus laevis retinas. We have also demonstrated that Müller cells are likely involved in this photoreceptor–specific process; however, the mechanism(s) via which PEDF and IPTG support outer segment assembly and the role played by Müller cells within this process has not been fully explored. The purpose of the present study was to evaluate the response of photoreceptors to PEDF and IPTG in Xenopus laevis embryonic retinas when Müller cell integrity has been compromised. Methods: PEDF and IPTG were applied at 50 ng/ml and 5x10–5 M respectively, concentrations that were shown to be the most effective in supporting photoreceptor outer segment assembly in previous studies. RPE was removed from isolated Xenopus laevis embryonic retinas and RPE–deprived retinas were then put in culture media containing either PEDF or IPTG. In parallel Müller cell inhibition experiments, alpha–aminoadipic acid (α–AAA, an inhibitor of Müller cell metabolism) was added to culture at 1x10–5 M, the concentration at which the metabolism of Müller cells was disrupted, yet that of photoreceptors was not. Control retinas (with or without RPE) were matured in culture media only. Photoreceptor outer segment assembly under these experimental conditions was then graded. Results: Based on our grading scale with 4 representing the highest level (100%) of organization, the grades of photoreceptor outer segments in retinas that matured with an adherent RPE, and RPE–deprived retinas exposed to culture media only, PEDF, PEDF+α–AAA, IPTG, IPTG+α–AAA are 3.60±0.08, 0.98±0.27, 2.69±0.17, 2.44±0.23, 2.25±0.23, and 1.23±0.24, respectively. The grades of PEDF and IPTG exposed RPE–deprived retinas are significantly greater than that of RPE–deprived retinas exposed to culture media only (p<0.0001), indicating that both agents support outer segment assembly. Adding α–AAA does not significantly diminish the ability of PEDF to promote photoreceptor outer segment assembly (p=0.354). In contrast, α–AAA prevents the ability of IPTG to promote proper photoreceptor outer segment folding (p<0.0001). Conclusions: Our findings demonstrate that the regulation of photoreceptor outer segment assembly can be modulated by various external stimuli and that Müller cells can play an important role in promoting the proper folding of outer segment membranes. Given this, it appears that there are redundant mechanisms, both intrinsic and extrinsic, that collectively support photoreceptors and promote the ability to assemble outer segment membranes.
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