An in vivo model of focal light emitting diode-induced cone photoreceptor phototoxicity in adult pigmented mice: Protection with bFGF

An overview of retinal light damage models for preclinical studies on age-related macular degeneration: identifying molecular hallmarks and therapeutic targets

Age-related macular degeneration (AMD) is a complex, multifactorial disease leading to progressive and irreversible retinal degeneration, whose pathogenesis has not been fully elucidated yet. Due to the complexity and to the multiple features of the disease, many efforts have been made to develop animal models which faithfully reproduce the overall AMD hallmarks or that are able to mimic the different AMD stages. In this context, light damage (LD) rodent models of AMD represent a suitable and reliable approach to mimic the different AMD forms (dry, wet and geographic atrophy) while maintaining the time-dependent progression of the disease. In this review, we comprehensively reported how the LD paradigms reproduce the main features of human AMD. We discuss the capability of these models to broaden the knowledge in AMD research, with a focus on the mechanisms and the molecular hallmarks underlying the pathogenesis of the disease. We also critically revise the remaining challenges and future directions for the use of LD models.

Inherited Retinal Dystrophies: Role of Oxidative Stress and Inflammation in Their Physiopathology and Therapeutic Implications

Inherited retinal dystrophies (IRDs) are a large group of genetically and clinically heterogeneous diseases characterized by the progressive degeneration of the retina, ultimately leading to loss of visual function. Oxidative stress and inflammation play fundamental roles in the physiopathology of these diseases. Photoreceptor cell death induces an inflammatory state in the retina. The activation of several molecular pathways triggers different cellular responses to injury, including the activation of microglia to eliminate debris and recruit inflammatory cells from circulation. Therapeutical options for IRDs are currently limited, although a small number of patients have been successfully treated by gene therapy. Many other therapeutic strategies are being pursued to mitigate the deleterious effects of IRDs associated with oxidative metabolism and/or inflammation, including inhibiting reactive oxygen species’ accumulation and inflammatory responses, and blocking autophagy. Several compounds are being tested in clinical trials, generating great expectations for their implementation. The present review discusses the main death mechanisms that occur in IRDs and the latest therapies that are under investigation.

Intravitreal and subretinal syngeneic bone marrow mononuclear stem cell transplantation improves photoreceptor survival but does not ameliorate retinal function in two rat models of retinal degeneration

PURPOSE

To study and compare effects of syngeneic bone marrow mononuclear stem cells (BM-MNCs) transplants on inherited retinal degeneration in two animal models with different etiologies: the RCS and the P23H-1 rats. To compare the safety and efficacy of two methods of intraocular delivery: subretinal and/or intravitreal.

METHODS

A suspension of BM-MNCs was injected subretinally or intravitreally in the left eyes of P23H-1 and RCS rats at post-natal day (P) 21. At different survival intervals after the injection: 7, 15, 30 or 60 days, the retinas were cross-sectioned, and photoreceptor survival and glial cell responses were investigated using immunodetection of cones (anti-cone arrestin), synaptic connections (anti-bassoon), microglia (anti-Iba-1), astrocytes and Müller cells (anti-GFAP). Electroretinographic function was also assessed longitudinally.

RESULTS

Intravitreal injections (IVIs) or subretinal injections (SRIs) of BM-MNCs did not produce adverse effects. The transplanted cells survived for up to 15 days but did not penetrate the retina. Both IVIs and SRIs increased photoreceptor survival, decreased synaptic degeneration and glial fibrillary acidic protein (GFAP) expression in Müller cells but did not modify microglial cell activation and migration or the electroretinographic responses.

CONCLUSIONS

Intravitreal and subretinal syngeneic BM-MNCs transplantation decreases photoreceptor degeneration and shows anti-gliotic effects on Müller cells but does not ameliorate retinal function. Moreover, syngeneic BM-MNCs transplants are more effective than the xenotransplants of these cells. BM-MNC transplantation has potential therapeutic effects that merit further investigation.

7,8-Dihydroxiflavone Maintains Retinal Functionality and Protects Various Types of RGCs in Adult Rats with Optic Nerve Transection

To analyze the neuroprotective effects of 7,8-Dihydroxyflavone (DHF) in vivo and ex vivo, adult albino Sprague-Dawley rats were given a left intraorbital optic nerve transection (IONT) and were divided in two groups: One was treated daily with intraperitoneal (ip) DHF (5 mg/kg) (n = 24) and the other (n = 18) received ip vehicle (1% DMSO in 0.9% NaCl) from one day before IONT until processing. At 5, 7, 10, 12, 14, and 21 days (d) after IONT, full field electroretinograms (ERG) were recorded from both experimental and one additional naïve-control group (n = 6). Treated rats were analyzed 7 (n = 14), 14 (n = 14) or 21 d (n = 14) after IONT, and the retinas immune stained against Brn3a, Osteopontin (OPN) and the T-box transcription factor T-brain 2 (Tbr2) to identify surviving retinal ganglion cells (RGCs) (Brn3a⁺), α-like (OPN⁺), α-OFF like (OPN⁺Brn3a⁺) or M4-like/α-ON sustained RGCs (OPN⁺Tbr⁺). Naïve and right treated retinas showed normal ERG recordings. Left vehicle-treated retinas showed decreased amplitudes of the scotopic threshold response (pSTR) (as early as 5 d), the rod b-wave, the mixed response and the cone response (as early as 10 d), which did not recover with time. In these retinas, by day 7 the total numbers of Brn3a⁺RGCs, OPN⁺RGCs and OPN⁺Tbr2⁺RGCs decreased to less than one half and OPN⁺Brn3a⁺RGCs decreased to approximately 0.5%, and Brn3a⁺RGCs showed a progressive loss with time, while OPN⁺RGCs and OPN⁺Tbr2⁺RGCs did not diminish after seven days. Compared to vehicle-treated, the left DHF-treated retinas showed significantly greater amplitudes of the pSTR, normal b-wave values and significantly greater numbers of OPN⁺RGCs and OPN⁺Tbr2⁺RGCs for up to 14 d and of Brn3a⁺RGCs for up to 21 days. DHF affords significant rescue of Brn3a⁺RGCs, OPN⁺RGCs and OPN⁺Tbr2⁺RGCs, but not OPN⁺Brn3a⁺RGCs, and preserves functional ERG responses after IONT.

Animal Models of LED-Induced Phototoxicity. Short- and Long-Term In Vivo and Ex Vivo Retinal Alterations

Phototoxicity animal models have been largely studied due to their degenerative communalities with human pathologies, e.g., age-related macular degeneration (AMD). Studies have documented not only the effects of white light exposure, but also other wavelengths using LEDs, such as blue or green light. Recently, a blue LED-induced phototoxicity (LIP) model has been developed that causes focal damage in the outer layers of the superior-temporal region of the retina in rodents. In vivo studies described a progressive reduction in retinal thickness that affected the most extensively the photoreceptor layer. Functionally, a transient reduction in a- and b-wave amplitude of the ERG response was observed. Ex vivo studies showed a progressive reduction of cones and an involvement of retinal pigment epithelium cells in the area of the lesion and, in parallel, an activation of microglial cells that perfectly circumscribe the damage in the outer retinal layer. The use of neuroprotective strategies such as intravitreal administration of trophic factors, e.g., basic fibroblast growth factor (bFGF), brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF) or pigment epithelium-derived factor (PEDF) and topical administration of the selective alpha-2 agonist (Brimonidine) have demonstrated to increase the survival of the cone population after LIP.

Short- and Long-Term Study of the Impact of Focal Blue Light-Emitting Diode-Induced Phototoxicity in Adult Albino Rats

Background: In adult rats we study the short- and long-term effects of focal blue light-emitting diode (LED)-induced phototoxicity (LIP) on retinal thickness and Iba-1⁺ activation. Methods: The left eyes of previously dark-adapted Sprague Dawley (SD) rats were photoexposed to a blue LED (20 s, 200 lux). In vivo longitudinal monitoring of retinal thickness, fundus images, and optical retinal sections was performed from 1 to 30 days (d) after LIP with SD-OCT. Ex vivo, we analysed the population of S-cone and Iba-1⁺ cells within a predetermined fixed-size circular area (PCA) centred on the lesion. Results: LIP resulted in a circular focal lesion readily identifiable in vivo by fundus examination, which showed within the PCAs a progressive thinning of the outer retinal layer, and a diminution of the S-cone population to 19% by 30 d. In parallel to S-cone loss, activated Iba-1⁺ cells delineated the lesioned area and acquired an ameboid morphology with peak expression at 3 d after LIP. Iba-1⁺ cells adopted a more relaxed-branched morphology at 7 d and by 14–30 d their morphology was fully branched. Conclusion: LIP caused a progressive reduction of the outer retina with loss of S cones and a parallel dynamic activation of microglial cells in the lesioned area.