Author ORCID Identifier

https://orcid.org/0000-0001-6250-7489

Semester

Spring

Date of Graduation

2024

Document Type

Dissertation

Degree Type

PhD

College

School of Medicine

Department

Not Listed

Committee Chair

Visvanathan Ramamurthy, Ph.D.

Committee Member

Saravanan Kolandaivelu, Ph.D.

Committee Member

Maxim Sokolov, Ph.D.

Committee Member

Roberta Leonardi, Ph.D.

Committee Member

Justin Legleiter, Ph.D.

Abstract

Phosphodiesterase-6 (PDE6) serves as a pivotal component in the phototransduction pathways of both cone and rod photoreceptors. In cones, PDE6 consists of tetrameric subunits: inhibitory (γ') and catalytic (α'). The catalytic subunit, PDE6α', contains a C-terminal prenylation motif. Deletion of this motif is associated with achromatopsia (ACHM), a form of color blindness. The mechanisms underlying the disease and the roles of PDE6 lipidation in vision remain elusive. Meanwhile, rod PDE6 is composed of α and β catalytic subunits and γ inhibitory subunits, with alterations in the C-terminal "prenylation motif" of PDE6β linked to retinitis pigmentosa (RP) pathology. In this comprehensive investigation, we explored the functional and structural implications of PDE6β prenylation in rods and PDE6α' prenylation in cones. Using genetically modified mouse models, the prenylation motif in both cases is disrupted. In cone PDE6, the absence of the prenylation motif in PDE6α' led to altered membrane association, impacting cone sensitivity to light and response kinetics. Intriguingly, despite normal expression and assembly, unprenylated PDE6α' accumulated in the inner segment and synaptic terminal, influencing outer segment morphology and length. The preservation of cones in the ACHM model indicates potential for gene therapy to restore vision in patients with analogous PDE6C mutations. Turning to rod PDE6, the PDE6βC853S mutation disrupts PDE6β prenylation. This resulted in persistent rod function reduction, with partial mislocalization of PDE6 subunits in mutant rods, highlighting the role of PDE6β prenylation in retaining assembled protein in the outer segment. Interestingly, outer segment level of rod PDE6 protein decreased in the absence of prenylation, although reduced levels alone could not account for the observed functional impairment, as seen in rd1/+ heterozygous mice. Collectively, our study underscores the critical roles of PDE6 prenylation in both cone and rod photoreceptors. The findings provide deeper insights into the interplay between protein structure, localization, and function in the context of retinal disorders. These insights hold promise for advancing targeted therapeutic strategies aimed at mitigating vision loss associated with ACHM and RP pathologies.

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