Correlation between photoreceptor injury-regeneration and behavior in a zebrafish model

Rapid Assessment of Ocular Toxicity from Environmental Contaminants Based on Visually Mediated Zebrafish Behavior Studies

The presence of contaminants in the environment has increased in recent years, and studies have demonstrated that these contaminants have the ability to penetrate the blood-retinal barrier and directly affect the visual systems of organisms. Zebrafish are recognized as an ideal model for human eye diseases due to their anatomical and functional similarities to the human eye, making them an efficient and versatile organism for studying ocular toxicity caused by environmental contaminants in the field of environmental toxicology. Meanwhile, zebrafish exhibit a diverse repertoire of visually mediated behaviors, and their visual system undergoes complex changes in behavioral responses when exposed to environmental contaminants, enabling rapid assessment of the ocular toxicity induced by such pollutants. Therefore, this review aimed to highlight the effectiveness of zebrafish as a model for examining the effects of environmental contaminants on ocular development. Special attention is given to the visually mediated behavior of zebrafish, which allows for a rapid assessment of ocular toxicity resulting from exposure to environmental contaminants. Additionally, the potential mechanisms by which environmental contaminants may induce ocular toxicity are briefly outlined.

Intraocular delivery of ZIF-90-RhB-GW2580 nanoparticles prevents the progression of photoreceptor degeneration

Photoreceptor degeneration is one of the major causes of progressive blindness which lacks of curative treatment. GW2580, a highly selective inhibitor of colony-stimulating factor 1 receptor, has the protective potential on neurons; however, little was known about the application of GW2580 on photoreceptor degeneration. In this study, BV-2 and 661W cells coculture system was constructed to investigate the interaction between microglia and photoreceptors. GW2580 was loaded into zeolitic imidazolate framework-90-rhodamine B (ZIF-90-RhB) to synthesize a novel kind of nanoparticles, namely, ZIF-90-RhB-GW2580, through a one-step self-assembly approach. A photoreceptor degeneration model was generated by intense light exposure in zebrafish and ZIF-90-RhB-GW2580 nanoparticles were delivered by the intraocular injection. The results showed that in vitro GW2580 treatment promoted phenotypic transformation in microglia and led to the blockade of photoreceptor apoptosis. Following the intraocular delivery of ZIF-90-RhB-GW2580 nanoparticles, the microglial proliferation and inflammatory response were significantly inhibited; moreover, the photoreceptors underwent alleviated injury with a recovery of retinal structure and visual function. In conclusion, the intraocular injection of ZIF-90-RhB-GW2580 at the early stage enables the precise delivery and sustained release of the GW2580, thus preventing the progression of photoreceptor degeneration.

The adenosine A (2A) receptor antagonist SCH58261 protects photoreceptors by inhibiting microglial activation and the inflammatory response

Photoreceptor degeneration is a principal event in a variety of human retinal diseases. Progressive apoptosis of photoreceptors leads to impaired vision and blindness, for which there is no curative treatment. Adenosine 2A receptors (A_2AR) are expressed in microglia. Blockade of A_2AR has been shown to protect neurons via suppression of inflammation. However, the therapeutic effects of A_2AR antagonists on photoreceptor degeneration have not been characterized. In this study, adult zebrafish were exposed to short term high-intensity light to induce photoreceptor death. SCH58261, a selective A_2AR antagonist, was immediately injected into the vitreous body. Photoreceptor degeneration and microglia-induced inflammation were evaluated using immunohistochemistry, quantitative real-time polymerase chain reaction, polarization sensitive optical coherence tomography, and optomotor response. Co-culture of BV2 and 661W cells was used to investigate the interaction between microglia and photoreceptors. The results showed that A_2AR was over-expressed during photoreceptor degeneration. Following intraocular SCH58261 injection, microglial activation and release of inflammatory factors were inhibited, and photoreceptor survival increased. Inactivation of microglia prevented apoptosis and autophagy in photoreceptors. Our results showed that SCH58261 intervention at the early stage of photoreceptor degeneration protected photoreceptors through inhibition of the inflammatory response, apoptosis, and autophagy.

Incomplete Recovery of Zebrafish Retina Following Cryoinjury

Zebrafish show an extraordinary potential for regeneration in several organs from fins to central nervous system. Most impressively, the outcome of an injury results in a near perfect regeneration and a full functional recovery. Indeed, among the various injury paradigms previously tested in the field of zebrafish retina regeneration, a perfect layered structure is observed after one month of recovery in most of the reported cases. In this study, we applied cryoinjury to the zebrafish eye. We show that retina exposed to this treatment for one second undergoes an acute damage affecting all retinal cell types, followed by a phase of limited tissue remodeling and regrowth. Surprisingly, zebrafish developed a persistent retinal dysplasia observable through 300 days post-injury. There is no indication of fibrosis during the regeneration period, contrary to the regeneration process after cryoinjury to the zebrafish cardiac ventricle. RNA sequencing analysis of injured retinas at different time points has uncovered enriched processes and a number of potential candidate genes. By means of this simple, time and cost-effective technique, we propose a zebrafish injury model that displays a unique inability to completely recover following focal retinal damage; an outcome that is unreported to our knowledge. Furthermore, RNA sequencing proved to be useful in identifying pathways, which may play a crucial role not only in the regeneration of the retina, but in the first initial step of regeneration, degeneration. We propose that this model may prove useful in comparative and translational studies to examine critical pathways for successful regeneration.

Visual Function is Gradually Restored During Retina Regeneration in Adult Zebrafish

In comparison to mammals, zebrafish are able to regenerate many organs and tissues, including the central nervous system (CNS). Within the CNS-derived neural retina, light lesions result in a loss of photoreceptors and the subsequent activation of Müller glia, the retinal stem cells. Müller glia-derived progenitors differentiate and eventually restore the anatomical tissue architecture within 4 weeks. However, little is known about how light lesions impair vision functionally, as well as how and to what extent visual function is restored during the course of regeneration, in particular in adult animals. Here, we applied quantitative behavioral assays to assess restoration of visual function during homeostasis and regeneration in adult zebrafish. We developed a novel vision-dependent social preference test, and show that vision is massively impaired early after lesion, but is restored to pre-lesion levels within 7 days after lesion. Furthermore, we employed a quantitative optokinetic response assay with different degrees of difficulty, similar to vision tests in humans. We found that vision for easy conditions with high contrast and low level of detail, as well as color vision, was restored around 7–10 days post lesion. Vision under more demanding conditions, with low contrast and high level of detail, was regained only later from 14 days post lesion onwards. Taken together, we conclude that vision based on contrast sensitivity, spatial resolution and the perception of colors is restored after light lesion in adult zebrafish in a gradual manner.

Subtype-dependent regulation of Gβγ signalling

G protein-coupled receptors (GPCRs) transmit information to the cell interior by transducing external signals to heterotrimeric G protein subunits, Gα and Gβγ subunits, localized on the inner leaflet of the plasma membrane. Though the initial focus was mainly on Gα-mediated events, Gβγ subunits were later identified as major contributors to GPCR-G protein signalling. A broad functional array of Gβγ signalling has recently been attributed to Gβ and Gγ subtype diversity, comprising 5 Gβ and 12 Gγ subtypes, respectively. In addition to displaying selectivity towards each other to form the Gβγ dimer, numerous studies have identified preferences of distinct Gβγ combinations for specific GPCRs, Gα subtypes and effector molecules. Importantly, Gβ and Gγ subtype-dependent regulation of downstream effectors, representing a diverse range of signalling pathways and physiological functions have been found. Here, we review the literature on the repercussions of Gβ and Gγ subtype diversity on direct and indirect regulation of GPCR/G protein signalling events and their physiological outcomes. Our discussion additionally provides perspective in understanding the intricacies underlying molecular regulation of subtype-specific roles of Gβγ signalling and associated diseases.

The Application of Methylprednisolone Nanoscale Zirconium-Porphyrin Metal-Organic Framework (MPS-NPMOF) in the Treatment of Photoreceptor Degeneration

Background

Photoreceptor degeneration is one of the most refractory oculopathy in the world, leading to vision loss in severe cases. Methyprednisolone is one of the most commonly prescribed medications for the treatment of retinal degenerative diseases, either by oral administration or repeated intraocular injections. However, the efficacy was unsatisfactory due to its systemic or local side effects and short retention time within the retina.

Methods

Nanoscale zirconium-porphyrin metal-organic framework (NPMOF) was synthesized and characterized. The biotoxicity and imaging capability of NPMOF were evaluated using zebrafish embryos and larvae. NPMOF was then used as a skeleton and loaded with methylprednisolone (MPS) to prepare a novel kind of nanoparticle, MPS-NPMOF. Photoreceptor degeneration was induced by high-intensity light exposure in adult zebrafish. MPS-NPMOF was delivered to the injured retina by intraocular injection. The photoreceptor regeneration and its underlying mechanism were explored by immunohistochemistry, quantitative real-time polymerase chain reaction and behavioral test.

Results

NPMOF not only had low biotoxicity but also emitted bright fluorescence. Following a single MPS-NPMOF intraocular injection, the injured retina exhibited the faster photoreceptor regeneration with better visual function by promoting the cell proliferation.

Conclusion

NPMOF is an ideal carrier and could be applied in tracking and delivering medications. By intraocular injection, the novel drug delivery system, MPS-NPMOF, accomplishes the sustained release of drug and plays a therapeutic role in photoreceptor degeneration.

Trimethyltin chloride induces reactive oxygen species-mediated apoptosis in retinal cells during zebrafish eye development

Trimethyltin chloride (TMT), one of the most widely used organotin compounds in industrial and agricultural fields, is widespread in soil, aquatic systems, foodstuffs and household items. TMT reportedly has toxic effects on the nervous system; however, there is limited information about its effects on eye development and no clear associated mechanisms have been identified. Therefore, in the present study, we investigated eye morphology, vison-related behavior, reactive oxygen species (ROS) production, apoptosis, histopathology, and gene expression to evaluate the toxicity of TMT during ocular development in zebrafish embryos. Exposure to TMT decreased the axial length and surface area of the eye and impaired the ability of zebrafish to recognize light. 2',7'-dichlorofluorescein diacetate and acridine orange assays revealed dose-dependent increases in ROS formation and apoptosis in the eye. Furthermore, pyknosis of retinal cells was confirmed through histopathological analysis. Antioxidative enzyme-related genes were downregulated and apoptosis-inducing genes were upregulated in TMT-treated zebrafish compared to expression in controls. Retinal cell-specific gene expression was suppressed mainly in retinal ganglion cells, bipolar cells, and photoreceptor cells, whereas amacrine cell-, horizontal cell-, and Müller cell-specific gene expression was enhanced. Our results demonstrate for the first time the toxicity of TMT during eye development, which occurs through the induction of ROS-mediated apoptosis in retinal cells during ocular formation.