Characterization of proliferative, glial and angiogenic responses after a CoCl₂‐induced injury of photoreceptor cells in the adult zebrafish retina

Abstract

The adult zebrafish is considered a useful model for studying mechanisms involved in tissue growth and regeneration. We have characterized cytotoxic damage to the retina of adult zebrafish caused by the injection of cobalt chloride (CoCl ) into the vitreous cavity. The CoCl concentration we used primarily caused injury to photoreceptors. We observed the complete disappearance of cones, followed by rods, across the retina surface from 28 to 96 hr after CoCl injury. The loss of 30% of bipolar cells was also observed by 50 hr after lesion (hpl). CoCl injury provoked a strong induction of the proliferative activity of multipotent Müller glia and derived progenitors. The effect of CoCl on retina cells was significantly reduced by treatment with glutamate ionotropic receptor antagonists. Cone photoreceptor regeneration occurred 25 days after injury. Moreover, a single dose of CoCl induced vascular damage and regeneration, whereas three injections of CoCl administered weekly provoked neovascular-like changes 20 days after injury. CoCl injury also caused microglial reactivity in the optic disc, retina periphery and fibre layer. CoCl -induced damage enhanced pluripotency and proneural transcription factor gene expression in the mature retina 72 hpl. Tumour necrosis factor alpha, vascular endothelial growth factor (VEGF) and VEGF receptor mRNA levels were also significantly enhanced by 72 hpl. The injury paradigm we have described in this work may be useful for the discovery of signalling molecules and pathways that participate in the regenerative response and it may serve as a model to screen for compounds that could potentially treat aberrant angiogenesis.

An insight on established retinal injury mechanisms and prevalent retinal stem cell activation pathways in vertebrate models

“…The injury mechanism of the retina has shown a wide range of variations ranging from whole‐cell retinal injury to exploiting each layer individually viz. photoreceptor, 9 , 10 , 11 ganglionic layer, 12 etc, using light, chemicals, transgenic lines, and genetic ablations. Various injury methods were applied with the following aims: To determine where the regeneration capacity lies within the retina.…”

“…Introduced by Maier and Wolberg in 1979, 42 it can destroy the whole retina 43 when used in high doses, and intravitreal injection of lower doses is efficient in targeting different individual layers such as the inner nuclear layers, 44 amacrine layers, 12 and photoreceptors. 11 , 42 The injury mechanism usually follows a microknife for incision followed by injection of ouabain in the intravitreal cavity.…”

“… 48 HIF, in turn, stimulates the production of vascular endothelial growth factors that causes neovascularization and aberrant angiogenesis. 49 CoCl 2 ‐mediated hypoxic injury involves intravitreal administration and has been used to target different retinal layers such as the photoreceptors 11 and ganglionic layers. 50 …”

Zebrafish as an Animal Model for Ocular Toxicity Testing: A Review of Ocular Anatomy and Functional Assays

“…The literature has many examples, detailed below; however, 70% of those studies have been reported only during the past 5 years, indicating that the use of the model in this field is still in its larval stage. Outside of chemical toxicology, zebrafish studies focused on eyes are also adding to our understanding of radiation toxicity, 150,151 ocular diseases, [152][153][154] retinal genetics and regeneration, [155][156][157][158] as well as aiding therapeutic discovery. [159][160][161] An exception among areas of ocular toxicology studied using zebrafish is how ethanol effects the developing embryo; this has been studied for more than 40 years.…”

P2X7 and A2A receptor endogenous activation protects against neuronal death caused by CoCl2‐induced photoreceptor toxicity in the zebrafish retina

“…We have previously described a model of retinal degeneration that primarily involves photoreceptor death across the surface of the retina of zebrafish (Medrano et al, 2018). The injury model consisted in injecting a single dose of CoCl2 within the vitreous cavity.…”