analyzing-photoreceptor-degeneration-preservation-retinitis

Analyzing Photoreceptor Degeneration and Preservation in a Retinitis Pigmentosa Murine Model

Retinopathies affect hundreds of millions of people worldwide and are significant causes of visual impairment and blindness. Among these diseases, ...

Fluminense Federal University

PI3K/Akt is an important pathway implicated in the proliferation and survival of cells in the CNS. Here we investigated the participation of the PI3K/Akt signal pathway in cell cycle of developing retinal progenitors. Immunofluorescence assays performed in cultures of chick embryo retinal cells and intact tissues revealed the presence of phosphorylated Akt and 4E-BP1 in cells with typical mitotic profiles. Blockade of PI3K activity with the chemical inhibitor LY 294002 (LY) in retinal explants blocked the progression of proliferating cells through G2/M transition, indicated by an expressive increase in the number of cells labeled for phosphorylated histone H3 in the ventricular margin of the retina. No significant level of cell death could be detected at this region. Retinal explants treated with LY for 24 h also showed a significant decrease in the expression of phospho-Akt, phospho-GSK-3 and the hyperphosphorylated form of 4E-BP1. Although no change in the expression of cyclin B1 was detected, a significant decrease in CDK1 expression was noticed after 24 h of LY treatment both in retinal explants and monolayer cultures. Our results suggest that PI3K/Akt is an active pathway during proliferation of retinal progenitors and its activity appears to be required for proper CDK1 expression levels and mitosis progression of these cells.

Inhibition of PI3K/Akt pathway impairs G2/M transition of cell cycle in late developing progenitors of the avian embryo retina.

Previous studies demonstrated that exogenous ATP is able to regulate proliferation of retinal progenitor cells (RPCs) in vitro possibly via P2Y receptor, a G protein-coupled receptor. Here, we evaluated the function of adenine nucleotides in vivo during retinal development of newborn rats. Intravitreal injection of apyrase, an enzyme that hydrolyzes nucleotides, reduced cell proliferation in retinas at postnatal day 2 (P2). This decrease was reversed when retinas were treated together with ATPγ-S or ADPβ-S, two hydrolysis-resistant analogs of ATP and ADP, respectively. During early postnatal days (P0 to P5), an increase in ectonucleotidase (E-NTPDase) activity was observed in the retina, suggesting a decrease in the availability of adenine nucleotides, coinciding with the end of proliferation. Interestingly, intravitreal injection of the E-NTPDase inhibitor ARL67156 increased proliferation by around 60 % at P5 rats. Furthermore, immunolabeling against P2Y receptor was observed overall in retina layers from P2 rats, including proliferating Ki-67-positive cells in the neuroblastic layer (NBL), suggesting that this receptor could be responsible for the action of adenine nucleotides upon proliferation of RPCs. Accordingly, intravitreal injection of MRS2179, a selective antagonist of P2Y receptors, reduced cell proliferation by approximately 20 % in P2 rats. Moreover, treatment with MRS 2179 caused an increase in p57 and cyclin D1 expression, a reduction in cyclin E and Rb phosphorylated expression and in BrdU-positive cell number. These data suggest that the adenine nucleotides modulate the proliferation of rat RPCs via activation of P2Y receptors regulating transition from G1 to S phase of the cell cycle.

Adenine Nucleotides Control Proliferation In Vivo of Rat Retinal Progenitors by P2Y Receptor.

Adenine nucleotides through P2Y receptor stimulation are known to control retinal progenitor cell (RPC) proliferation by modulating expression of the p57, a cell cycle regulator. However, the role of Gi protein-coupled P2Y and P2Y receptors also activated by adenine nucleotides in RPC proliferation is still unknown. Gene expression of the purinergic P2Y subtype was detected in rat retina during early postnatal days (P0 to P5), while expression levels of P2Y were low. Immunohistochemistry assays performed with rat retina on P3 revealed P2Y receptor expression in both Ki-67-positive cells in the neuroblastic layer and Ki-67-negative cells in the ganglion cell layer and inner nuclear layer. Nonetheless, P2Y receptor expression could not be detected in any stratum of rat retina. Intravitreal injection of PSB 0739 or clopidogrel, both selective P2Y receptor antagonists, increased by 20 and 15%, respectively, the number of Ki-67-positive cells following 24 h of exposure. Moreover, the P2Y receptor inhibition increased cyclin D1 and decreased p57 expression. However, there were no changes in the S phase of the cell cycle (BrdU-positive cells) or in mitosis (phospho-histone-H3-positive cells). Interestingly, an increase in the number of cyclin D1/TUNEL-positive cells after treatment with PSB 0739 was observed. These data suggest that activation of P2Y receptors is required for the successful exit of RPCs from cell cycle in the postnatal rat retina.

P2Y but not P2Y Purinergic Receptor Controls Postnatal Rat Retinogenesis In Vivo.

Platelet Activating Factor (PAF) is a known phospholipid mediator of inflammation. Since its first description in 1972, it has emerged as a key regulator of vital cellular signaling functions, as proliferation, cell adhesion, and apoptosis. Evidence suggests that interactions between PAF and its receptor (PAFR) play a critical role in nervous system tissues, including the retina. The retina is a very important constituent of the visual system, along with the cornea, sclera, choroid, iris, and ciliary body, that acts synergistically to provide vision and to maintain optical homeostasis. There is evidence that PAF may regulate a wide range of physiological functions in the visual system tissues, such as eye development, inflammation, epithelial wound healing, and synapsis. Due to their multiple functions, PAF and PAFR also have important pathological and clinical implications in ocular disorders such as Choroidal Neovascularization (CNV), Age Macular Degeneration, (AMD), Diabetic Retinopathy (DR), transplant responses, and pharmacological interactions. Studies with PAFR antagonists have shown promising results such as inhibition of neovascularization and chloroquine-induced retinopathies, as well as reducing inflammation and retinal cell death. Due to the importance of PAFR signaling in the visual system and ophthalmology research, this review aims to provide a general overview of current and future perspectives about PAF in eye biology.

Article	Year
Inhibition of PI3K/Akt pathway impairs G2/M transition of cell cycle in late developing progenitors of the avian embryo retina. PloS one\| PubMed ID: 23301080	2013
Adenine Nucleotides Control Proliferation In Vivo of Rat Retinal Progenitors by P2Y Receptor. Molecular neurobiology\| PubMed ID: 27558237	2017
P2Y but not P2Y Purinergic Receptor Controls Postnatal Rat Retinogenesis In Vivo. Molecular neurobiology\| PubMed ID: 29574630	2018
Platelet activating factor in the eye: Physiological roles, diseases and future perspectives. Prostaglandins & other lipid mediators\| PubMed ID: 33358892	2021

Lucianne Fragel-Madeira

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