Preliminary characterization of a novel form of progressive retinal atrophy in the German Spitz dog associated with a frameshift mutation in GUCY2D

Animal models for the evaluation of retinal stem cell therapies

Retinal degeneration (RD) diseases leading to severe vision loss can affect photoreceptors (PRs) that are responsible for phototransduction, or retinal pigmented epithelium (RPE) providing support for PRs. Human pluripotent stem cell (hPSC)-based therapies are a potential approach for restoration of retinal structure in patients with currently incurable RD diseases. Currently, there are two targeted hPSC therapeutics: PR rescue and PR replacement. PR rescue involves the transplantation of RPE or other neural progenitors into the subretinal space to slow down or prevent further RD. RPE transplantation plays a critical role in preserving photoreceptors by providing trophic support and maintaining retinal integrity, particularly in diseases like age-related macular degeneration (AMD). Advances in RPE transplantation methods, such as polarized monolayer cultures and scaffold-based approaches, have shown promise in enhancing graft survival and integration. However, limitations include inconsistent integration, variable neurotrophic factor secretion, and immune rejection risks in non-autologous transplants. In PR replacement, stem cell-derived photoreceptor-like cells or photoreceptor progenitors (PRP) obtained are transplanted into the eye. While PRPs are commonly obtained from retinal organoids (ROs), alternative sources, such as early differentiation stages or direct differentiation protocols, are also utilized to enhance the efficiency and scalability of PRP generation. Challenges include achieving proper integration, forming outer segments, rosette formation, and avoiding immune rejection or tumorigenicity. Various animal models that simulate human RD diseases are being used for establishing surgical feasibility, graft survival and visual functional recovery but fail to replicate clinical immune challenges. Rodent models lack macula-like structures and have limited reliability in detecting subtle functional changes, while larger animal models pose ethical, logistical, and financial challenges. Immunocompromised models have been developed for minimizing xenograft issues. Visual functional testing for efficacy includes optokinetic testing (OKN), electroretinography (ERG), and electrophysiological recordings from the retina and brain. These tests often fail to capture the complexity of human visual recovery, highlighting the need for advanced models and improved functional testing techniques. This review aims to aggregate current knowledge about approaches to stem cell transplantation, requirements of animal models chosen for validating vision benefits of transplantation studies, advantages of using specific disease models and their limitations. While promising strides have been made, addressing these limitations remains essential for translating stem cell-based therapies into clinical success.

Supplemental vibrissal extensions as an alternative to improve the tactile sensitivity of blind dogs - a preliminary approach investigation

OBJECTIVE

This preliminary study suggests a way to artificially extend vibrissae of blind dogs to assist ambulation and avoiding facial contact with obstacles.

PROCEDURES

Fourteen irreversibly blind dogs had 5-6 mystacial vibrissae on each side of the face supplementally extended by attaching carefully chosen adult pig hairs to them and were subjected to a maze test before and after the procedure. In three of these dogs the test was repeated one more time after all the extensions had fallen off. Collision counts and course times with and without extensions were analyzed and compared. A p-value > 0.05 was considered significant.

RESULTS

Median number of collisions was significantly higher post-extensions (5 IQR 2.25) and after extensions had fallen off (4 IQR 7.50) compared to pre-extensions (1 IQR 1), p = 0.021. Median times were significantly higher pre-extension (25.6 IQR 8.98) and after the extensions had fallen off, compared to the post-extension performance (22.8 IQR 8.55), p = 0.04.

CONCLUSION

Vibrissae play an important role in the tactile perception of blind dogs, and our preliminary results suggest that extending this sensory organ possibly improves obstacle location and their quality of life.