Molecular and cellular mechanisms of levodopa-mediated visual function rescue in albinism

Macdonald, Sarah, Keeling, Eloise, Scott, Jennifer A, Griffiths, Helen, Lotery, Andrew, Ratnayaka, J. Arjuna, Self, James Edward and Lee, Helena (2024) Molecular and cellular mechanisms of levodopa-mediated visual function rescue in albinism. Investigative Ophthalmology & Visual Science, 65 (7), [821].

Abstract

Purpose : albinism is a condition characterised by impaired melanin biosynthesis, abnormalities of retinal and optic nerve development as well as visual impairment. We have demonstrated that oral levodopa (L-DOPA) supplementation during the critical postnatal developmental period can rescue retinal development and visual function in a murine model of oculocutaneous albinism. The mechanisms through which L-DOPA rescues retinal development and visual function in albinism need to be clarified. We tested the hypothesis that administration of L-DOPA, a key component of the melanin biosynthesis pathway, alters synaptogenesis in the developing albino retina and modulates downstream factors, such as pigment epithelium derived factor (PEDF), resulting in improved eyesight.

Methods : eyes from albino (C57BL/6J-c2J) and wild type (C57BL/6J) mice given 0.5, 0.76 or, 1mg/kg total dissolved solids (TDS) doses of L-DOPA were collected at 6, 12 and 16 weeks postnatal age (PNA). Samples were snap frozen, paraffin embedded and immunostained with the pre-synaptic label synaptophysin. Frozen samples of the retina and retinal pigment epithelium (RPE) were also analysed via western blot to assess levels of PEDF in response to L-DOPA dosing. Fluorescence intensity (FI) and densitometry measurements were analysed via ImageJ.

Results : immunostaining showed that in pigmented and albino mice, different dosages of L-DOPA caused a significant difference to the FI of the retinal plexiform layers. A dose of 1mg/kg TDS in albino mice resulted in a significantly higher FI (P<0.005) at both 12 and 16 weeks PNA suggesting a reduction in synaptic pruning. Western blot analysis demonstrated that PEDF appears to act early in development, before 6 weeks PNA in mice, which overlaps with the period when synaptogenesis occurs. Additionally, our data suggests that in later stages of development, at 16 weeks PNA, there is a difference in spatial expression of PEDF in albino mice. This is because we found that in pigmented mice PEDF is present in both the whole eye and the retina/RPE whilst in albino mice PEDF was only found in the retina/RPE.

Conclusions : our work demonstrates that L-DOPA modulates presynaptic compartments, potentially influencing synaptogenesis and causing alterations in PEDF levels in the developing retina. Further work is needed to investigate the potential of PEDF as a therapeutic target for improving visual function in albinism.

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Contributors

Author: Eloise Keeling

Author: Andrew Lotery

Author: J. Arjuna Ratnayaka

Author: James Edward Self

Author: Helena Lee

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