Biology subjects

Lobo, G. P.

Publications and source records attributed to Lobo, G. P..

4 recordsLinked to original sources

bioRxiv2026

Mechanistic Insights into MYO1C-Mediated Rhodopsin Trafficking and Rod Photoreceptor Homeostasis.

Rhodopsin trafficking from the photoreceptor inner segment to the outer segment is essential for photoreceptor function, yet the molecular mechanism(s) regulating this process remain incompletely understood. MYO1C is an actin-based motor protein implicated in intracellular cargo trafficking. Here, we investigated its role in rhodopsin trafficking and photoreceptor cell homeostasis. In-silico docking identified a putative interaction between the MYO1C C-terminal region and the C-terminal region of rhodopsin containing the conserved VxPx ciliary trafficking motif. Biochemical studies confirmed that full-length MYO1C interacts with rhodopsin, whereas deletion of the MYO1C C-terminal domain abolished this interaction. Live-cell imaging, ciliary localization, and fluorescence recovery after photobleaching in hTERT-RPE1 cells demonstrated that the MYO1C C-terminal region is required for efficient rhodopsin trafficking, membrane localization, and ciliary targeting. In native murine rod photoreceptors MYO1C localized to both inner and outer segments. Global Myo1c deficiency in mice caused age-dependent rhodopsin mislocalization, apo-opsin accumulation and progressive retinal dysfunction, characterized primarily by reduced scotopic ERG responses and delayed a-wave recovery, beginning at 6-months, while photopic responses were relatively preserved. Rod-specific Myo1c deletion similarly caused progressive scotopic dysfunction and reduced a-wave recovery following light stimulation. In contrast, cone-specific Myo1c deletion preserved photopic function and a-wave recovery. Together, these findings identify MYO1C as an important regulator of rhodopsin trafficking and demonstrate a preferential, cell-autonomous requirement for MYO1C in maintaining rod photoreceptor homeostasis and phototransduction recovery. These findings establish a mechanistic link between MYO1C-dependent rhodopsin trafficking and age-dependent rod photoreceptor cell dysfunction.

cell biology↗

bioRxiv2025

Rescue of the Stargardt Disease phenotype in Abca4 knockout mice through dietary modulation of the vitamin A receptor RBPR2

Mutations in the ABCA4 gene in Stargardt disease (STGD1) causes accumulation of cytotoxic lipofuscin, resulting in RPE atrophy and photoreceptor dysfunction. One component of lipofuscin is the all-trans-retinal derivative, bisretinoid N-retinylidene-N-retinylethanolamine (A2E). Since ocular A2E biosynthesis relies on circulating all-trans-retinol bound to retinol binding protein 4 (RBP4-ROL), we hypothesized that modulating vitamin A receptors, such as the retinol binding protein receptor 2, RBPR2, which regulate serum RBP4-ROL concentration, should attenuate A2E production. In-silico analysis revealed multiple retinoic acid response element (RARE) binding sites on the murine Rbpr2 gene promotor, which was confirmed in vitro by EMSA and ChIP assays. In vitro luciferase assays showed that Rbpr2 promotor activity was induced by exogenous {beta}-carotene (BC) metabolites. Dietary BC supplementation of Abca4-/- mice, a mouse model for STGD1, increased hepatic all-trans-retinoic acid and 9-cis-retinoic acid production, which induced Rbpr2 mRNA expression. This mechanism decreased serum RBP4 protein levels, fundus autofluorescence (AF) and ocular A2E accumulation, altogether improving photoreceptor and RPE function. Conversely, such a rescue was not observed in either Abca4-/- mice fed a diet devoid of BC or in double knockout Rbpr2-/-;Abca4-/- mice. Thus, there was a significant inverse correlation between dietary BC supplementation and Rbpr2 gene presence in Abca4-/- mice, to that of lipofuscin accumulation in Abca4-/- mice on diets devoid of BC or in Rbpr2-/-;Abca4-/- mice. Our results provide impetus to pursue BC supplemented diets as therapeutic interventions for STGD1 patients with ABCA4 gene mutations and identifies a novel role for the vitamin A receptor RBPR2 in this process.

cell biology↗

bioRxiv2024

Loss of the systemic vitamin A transporter RBPR2 affects the quantitative balance between chromophore and opsins in visual pigment synthesis

The distribution of dietary vitamin A/all-trans retinol (ROL) throughout the body is critical for maintaining retinoid function in peripheral tissues and for generating visual pigments for photoreceptor cell function. ROL circulates in the blood bound to the retinol binding protein 4 (RBP4) as RBP4-ROL. Two membrane receptors, RBPR2 in the liver and STRA6 in the eye are proposed to bind circulatory RBP4 and this mechanism is critical for internalizing ROL into cells. Here, we present a longitudinal investigation towards the importance of RBPR2 and influence of the diet on systemic retinoid homeostasis for visual function. Age matched Rbpr2-KO (Rbpr2-/-) and wild-type (WT) mice were fed either a vitamin A sufficient (VAS) or a vitamin A deficient (VAD) diet. At 3- and 6-months, we performed retinoid quantification of ocular and non-ocular tissues using HPLC analysis and complemented the data with visual physiology, rhodopsin quantification by spectrophotometry, and biochemical analysis. At 3-months and compared to WT mice, Rbpr2-/- mice fed either vitamin A diets displayed lower scotopic and photopic electroretinogram (ERG) responses, which correlated with HPLC analysis that revealed Rbpr2-/- mice had significantly lower hepatic and ocular retinoid content. Interestingly, with the exception of the liver, long-term feeding of Rbpr2-/- mice with a VAS diet promoted all- trans retinol accumulation in most peripheral tissues. However, even under VAS dietary conditions significant amounts of unliganded opsins in rods, together with decreased visual responses were evident in aged mice lacking RBPR2, when compared to WT mice. Together, our analyses characterize the molecular events underlying nutritional blindness in a novel mouse model and indicate that loss of the liver specific RBP4-ROL receptor, RBPR2, influences systemic retinoid homeostasis and rhodopsin synthesis, which causes profound visual function defects under severe vitamin A deficiency conditions.

cell biology↗

bioRxiv2020

Motor Protein MYO1C is Critical for Photoreceptor Opsin Trafficking and Vision

Unconventional myosins linked to deafness are also proposed to play a role in retinal cell physiology. However, their direct role in photoreceptor function remains unclear. We demonstrate that systemic loss of the unconventional myosin MYO1C in mice specifically affected opsin trafficking, leading to loss of visual function. Electroretinogram analysis of Myo1c knockout (Myo1c-KO) mice showed a progressive loss of photoreceptor function. Immunohistochemistry and binding assays demonstrated MYO1C localization to photoreceptor inner and outer segments (OS) and identified a direct interaction of rhodopsin with the MYO1C cargo domain. In Myo1c-KO retinas, rhodopsin mislocalized to rod inner segments (IS) and cell bodies, while cone opsins in OS showed punctate staining. In aged mice, the histological and ultrastructural examination of the phenotype of Myo1c-KO retinas showed progressively shorter photoreceptor OS. These results demonstrate that MYO1C is critical for opsin trafficking to the photoreceptor OS and for normal visual function.

cell biology↗