The observation of the Zebrafish’s (Danio rerio) innate capacity to regenerate retinal cells has resulted in its identification as an ideal New Alternative Model (NAM) for ocular disease research. As a result of the negative impact on the person’s quality of life that visual impairment causes and the high amount of people suffering from this condition, an estimated 295 million people are believed to suffer from moderate to severe visual impairment worldwide, the study of eye diseases is of high priority within the scientific research community. Thus, Zebrafish has been used in the development of new treatments and the Early Drug Discovery for different eye-related pathologies such as cataracts, glaucoma, diabetic retinopathy, age-related macular degeneration, and photoreceptor degeneration, and in the research of retinal regeneration. Within this context, it is important to highlight the advantages that Zebrafish can bring to the field of ophthalmology and the capabilities of this aquatic model to replicate human eye disease.
Characteristics of the Zebrafish
Zebrafish offers a number of characteristics that makes it the ideal preclinical NAM for ophthalmological research:
- High fertility and fecundity rate, with capacity of producing hundreds of offspring at a time, with a single mating pair.
- Highly conserved genetic homology with humans as it has 82% orthologues of human disease-associated genes.
- External embryonic development and transparency during the larval stage, allowing in vivo organ monitoring without the need for the use of invasive methods.
- Ability of retinal regeneration by the capacity of reversion of Müller glia cells to stem cells that can create neuronal precursor cells.
- Zebrafish eye development is very similar to that of humans. Recapitulating with high fidelity the physiological events of the process.
- Relative big size of the eyes facilitating their manipulation during early embryogenesis.
- Development of visual response at 72 hours post-fertilization (hpf), by which time eye anatomy and physiology are functionally similar to humans. This enables the use of zebrafish embryos under 6 hpf when they are in the embryonic stage and are not under animal care policies. The 2010 European Commission Directive 2010/63/EU currently considers research conducted with Zebrafish 5-6 dpf (days post- fertilization) to be an alternative to animal testing and, thus, is a replacement for animal research based on their dependency on vitellus feeding, revealing their embryonic condition.
- Easy genetic manipulation capacity for disease modeling.
- Fast, cost-effective, and highly reliable NAM.
Eye Diseases Models in Zebrafish
As a result of these similarities, it has been possible to replicate a number of common eye diseases in Zebrafish. These include:
- Ocular Coloboma, a congenital disease whereby part of the tissue comprising the eye is missing.
- Anophthalmia/Microphthalmia, an eye condition whereby a person is born without one or both eyes or whereby one or both eyes are unusually small.
- Glaucoma, a common eye condition involving damage to the optic nerve.
- Corneal dystrophies, eye diseases involving changes in the cornea. Corneal dystrophies are generally hereditary and degenerative.
- Cataract, the development of a cloudy area in the lens of the eye that is very common with aging.
Existing research and potential applications
The laboratory of Daniel Goldman, PhD, a professor at the University of Michigan’s Molecular and Behavioral Neuroscience Institute has uncovered strategies that Zebrafish use to regenerate a damaged retina. Goldman and his team believe that this information may one day help doctors repair and treat damaged retinas in humans. It has recently been discovered that Wnt and heparin-binding epidermal-like growth factor (HB-EGF) signaling play a critical role during retina regeneration. In addition, a number of innovative techniques have been developed with a view to harnessing the regenerative capacity of Zebrafish retinal cells. A study conducted by Watanabe, K., Nishimura, Y., Oka, T. et al. identified coumarin derivatives capable of staining Zebrafish retinal cells within a relatively short time and at low concentrations, making them suitable for in -vivo imaging of the Zebrafish retina. Continued research will seek to explore whether these findings can be applied to mammals, and ultimately humans.
Zebrafish have also been widely used in ocular Drug Discovery, such as the screening of new anti-angiogenic compounds or neuroprotective Drugs, as well as in ocular toxicity testing. Through its “Target Validation and Disease Models” service, Biobide specializes in the development of Zebrafish disease models for use in preclinical stages of Drug Discovery and/or target identification. The CRO’s (Corporate Research Organization) wide-ranging expertise allows it to generate transgenic or mutant Zebrafish models of diseases through different techniques such as genetic mutations, transgenically-induced gene alterations, or Drug-induced metabolic alterations. Advanced services include the development of Zebrafish xenografts, which have proven useful in the study of tumor development, while toxicity assays represent a further avenue of research in which Zebrafish could be put to effective use. This process enables the characterization of the role of a protein or pathway of interest and provides selection arguments with a view to defining the required properties of the compounds to be screened.
Conclusion
Visual impairment represents an important loss of life quality for millions of people worldwide so it is an important medical and scientific challenge. A vast amount of existing research has shown that Zebrafish is an ideal NAM in the quest to discover and provide treatments and cures for a wide range of ocular diseases. To address this, the Zebrafish model has contributed to basic research, Early Drug Discovery, and toxicity testing of ocular diseases.
Among the numerous laboratories conducting comparative studies on Zebrafish with a view to carrying out disease modeling, Drug Screening and toxicity testing, Biobide is optimally positioned to provide a tailored service that will add value to clients’ R&D&I. Specializing in Zebrafish and operating under Good Laboratory Practice (GLP), the company has developed and validated time-saving and cost-effective toxicity and efficacy assays, as well as disease models for use in preclinical stages.
Sources
- Could a tiny fish hold the key to curing blindness? (2020 – NIH National Eye Institute, (https://www.nei.nih.gov/about/news-and-events/news/could-tiny-fish-hold-key-curing-blindness#:~:text=When%2520a%2520zebrafish%2520loses%2520its,projects%252C%2520nearly%252080%2520incorporate%2520zebrafish)
- R. Richardson, D. Tracey-White, A. Webster & M. Moosajee, The zebrafish eye—a paradigm for investigating human ocular genetics (2016) – Nature Journal, (https://www.nature.com/articles/eye2016198)
- Yiwen Hong & Yan Luo, Zebrafish Model in Ophthalmology to Study Disease Mechanism and Drug Discovery (2021), NIH – National Library of Medicine, (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8400593/)
- Animal Care and Use Program - University of Michigan, (https://animalcare.umich.edu/regenerative-properties-zebrafish-used-treating-blinding-eye-diseases#:~:text=The%2520tiny%2520zebrafish%2520may%2520hold,an%2520injured%2520or%2520diseased%2520retina)
- Koehi Watanabe et al., In vivo imaging of zebrafish retinal cells using fluorescent coumarin derivatives (2010) – BMC Neuroscience, (https://bmcneurosci.biomedcentral.com/articles/10.1186/1471-2202-11-116)
- Steven Cassar, Christina Dunn & Meg Ferrell Ramos, Zebrafish as an Animal Model for Ocular Toxicity Testing: A Review of Ocular Anatomy and Functional Assays (2020) – Sage Journals, (https://journals.sagepub.com/doi/full/10.1177/0192623320964748)
