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.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.