COMPARISON BETWEEN HUMAN NERVE GROWTH FACTOR PAINLESS (HNGFP) AND DEXAMETHASONE INTRAVITREAL IMPLANTS AS ANTI-INFLAMMATORY STRATEGIES TO SAVE CONES FROM DEGENERATION IN RETINITIS PIGMENTOSA

In the present thesis, I investigate potential therapeutic agents for Retinitis Pigmentosa (RP), a retinal degenerative condition that primarily affects photoreceptors. Rod-specific mutations are mainly responsible for the onset of the degenerative process, causing as first symptoms night blindness and peripheral visual impairment. The major problems for patients manifest when cones, deputed to color vision, visual acuity, and spatial discrimination, degenerate too. The biological reason for this degeneration is one of the major research topics of RP investigations worldwide as saving these photoreceptors could rescue the relevant properties of vision and permit the patients a normal life. Currently, different biological mechanisms are the candidates for this so-called bystander effect, including oxidative and metabolic stress, and inflammation responses triggered by rod death. Considering the relevance that inflammatory responses have recently acquired as contributors to the progression of this and CNS diseases, we dedicated the present thesis research to test the cone-rescue potential of one potent anti-inflammatory drug (Dexamethasone), and a new potential one, hNGFp (human Nerve Growth factor painless). Dexamethasone systemic administration was found to have a positive impact on mouse models of RP by significantly lowering inflammatory responses in terms of gene expression and activated microglia and maintenance of cone photoreceptors number. However, long-term treatment with corticosteroids could have different systemic side effects such as hyperglycemia, hypercholesterolemia, and muscle loss. To avoid these effects, we decided to test Dexamethasone ocular implants which are used in humans to treat eye diseases such as uveitis and cystoid macular edema. Their peculiarity is a constant but low and slow release of the chemical principle guaranteeing daily supply of the drug to retinal cells. Glucocorticoid receptors are known to be expressed in Müller glia and microglia thus inflammation lowering should be the main effect of this treatment. On the other hand, we decided to test another potential therapeutic molecule, hNGFp, a well-known neurotrophic factor that recently showed anti-inflammatory properties by switching the microglia phenotype from an activated to a resting state in the CNS. For both Dexamethasone and hNGFp we used the rd10 mutant mouse as a model, because it bears a phosphodiesterase mutation similar to humans and shows a typical rod-cone degeneration pattern analogous to the human one. Retinal degeneration follows a characteristic center-to-periphery gradient, and photoreceptors start to die when retinal development is already complete as is the case for human RP. The mutation responsible for the rd10 phenotype is spontaneous, selected by crossing, and affects the beta subunit of Phosphodiesterase 6 of rods, impairing the phototransduction. To analyze the effect of the treatments with the drugs mentioned above, we used ocular surgery accompanied by molecular and histological analyses. We implanted the animals with fractions of original Dexamethasone implants (Ozurdex) and administered them with intranasal or intravitreal hNGFp. Then, we collected and analyzed retinal sections or retinal whole mounts stained with cell-type specific antibodies. In parallel, we quantified the expression of genes connected to inflammatory responses and photoreceptors' survival. The final goal was to assess the effects on global biological processes to identify mutation-independent therapeutic strategies, favoring their translation to clinics. In this thesis, I will summarize the current knowledge regarding RP and the therapeutic strategies under investigation to target cone degeneration, also giving an overview of retinal organization. Then, I will illustrate and discuss the results obtained with my research.