Methylnitrosourea (MNU)-induced Retinal Degeneration and Regeneration in the Zebrafish: Histological and Functional Characteristics

Abstract

Retinal degenerative diseases, e.g. retinitis pigmentosa, with resulting photoreceptor damage account for the majority of vision loss in the industrial world. Animal models are of pivotal importance to study such diseases. In this regard the photoreceptor-specific toxin N-methyl-N-nitrosourea (MNU) has been widely used in rodents to pharmacologically induce retinal degeneration. Previously, we have established a MNU-induced retinal degeneration model in the zebrafish, another popular model system in visual research. A fascinating difference to mammals is the persistent neurogenesis in the adult zebrafish retina and its regeneration after damage. To quantify this observation we have employed visual acuity measurements in the adult zebrafish. Thereby, the optokinetic reflex was used to follow functional changes in non-anesthetized fish. This was supplemented with histology as well as immunohistochemical staining for apoptosis (TUNEL) and proliferation (PCNA) to correlate the developing morphological changes. In summary, apoptosis of photoreceptors occurs three days after MNU treatment, which is followed by a marked reduction of cells in the outer nuclear layer (ONL). Thereafter, proliferation of cells in the inner nuclear layer (INL) and ONL is observed. Herein, we reveal that not only a complete histological but also a functional regeneration occurs over a time course of 30 days. Now we illustrate the methods to quantify and follow up zebrafish retinal de- and regeneration using MNU in a video-format.

Cellular Signaling in Müller Glia: Progenitor Cells for Regenerative and Neuroprotective Responses in Pharmacological Models of Retinal Degeneration

“…In recent studies, visual acuity measurements have shown decreasing visual function until day 3, followed by complete restoration of visual acuity on day 30. This is consistent with the histological degenerative and regenerative changes observed after MNU administration, with maximum apoptosis occurring on day 3 [137]. Notably, significant advancement has been achieved in elucidating the cell signal transmission mechanism that promotes the transition of Müller glia into MGPCs.…”

Subretinal delivery of erythropoietin alleviates the N-methyl-N-nitrosourea-induced photoreceptor degeneration and visual functional impairments: an in vivo and ex vivo study

“…Moreover, the observation that cones are also killed by MNU toxicity does not correspond to cone degeneration in RP patients, since the demise of this population occurs in a secondary wave after rod death. A higher susceptibility of the rod photoreceptors to MNU has been reported in arvicanthis and zebrafish which are both conedominant species (Boudard et al, 2010;Tappeiner et al, 2013;Maurer et al, 2014). Therefore, it is highly possible that the cone photoreceptors might be rather protected from the MNU effects than saved by the EPO.…”

Centella asiaticaextract prevents visual impairment by promoting the production of rhodopsin in the retina

“…Alkylating agents targeting photoreceptor cells such as MNU rapidly induce retinal damage through apoptosis in many animal species, including mice [29,30]. Such damage usually develops into benign and malignant tumors several months after exposure to MNU and rapidly causes specific photoreceptor cell death [14,31]. This resulted in a loss of retinal layer structure and marked retinal thinning, which was observed in a concentration-dependent manner after exposure to MNU [32].…”

“…MNU is as a pharmacological substance used to induce retinal degeneration in animal models [14]. Therefore, in animal experiments, we induced retinal damage with MNU to determine whether CA-HE50 has a protective effect against retinal damage.…”