Anatomy and Neuroscience - Theses

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    Nanosecond Laser Therapy for the Management of Age-related Macular Degeneration
    Findlay, Quan ( 2021)
    Age-related macular degeneration (AMD) is a chronic, progressive disease affecting the central retina and remains the leading cause of irreversible vision loss in developed nations. AMD is a multifactorial disease encompassing a complex interplay between ageing, environmental and genetic risk factors which ultimately lead to chronic inflammation and death of photoreceptors. While the pathophysiology of AMD is still not fully understood, recent advances have highlighted the involvement of the innate immune system and RPE dysfunction to be fundamental to the development and progression of this debilitating condition. As such, therapies that can influence these two systems have the potential to slow progression of disease. Despite advances in the treatment of neovascular AMD, there remains no effective treatment for non-neovascular AMD and importantly, interventions that address the progression from early to sight-threatening late AMD remain limited. The progression to late stages is usually slow, providing a large window of opportunity to intervene. Novel laser treatments, specifically short-duration pulsed lasers such as the subthreshold nanosecond laser (SNL), offer a potential therapeutic option. The fundamental aims of this study were to investigate SNL-induced cellular response in the RPE that may have potential benefits for addressing pathologic changes that occur in the RPE/BM interface in AMD, and to determine whether changes to the RPE are associated alterations to systemic innate immunity. SNL treatment, delivered in a single session, to the posterior eye in wildtype mice was confirmed using immunohistochemistry to selectively target the RPE without causing damage to the overlying retina. The laser-ablated RPE monolayer was healed within 3 days post-treatment with evidence indicative of newly proliferated daughter cells. Importantly, this proliferative response was also observed in the non-laser treated fellow eye. RNA sequencing and pathway analysis of laser-treated RPE identified biologically-relevant pathways including the promotion of cell survival and cell proliferation, and the inhibition of inflammation and apoptosis. Together, the fellow eye effect and RNA sequencing results suggest that a SNL-induced systemic change involving innate immunity may likely be involved. Systemic change in leukocyte phagocytosis function following SNL treatment was examined for 12-month old wildtype and in the mouse model of AMD (P2X7-null mice). Real-time flow cytometry showed a laser-induced reduction in total phagocytosis capacity of yellow-green fluorescent beads 3 months following SNL treatment. Subsequent ultrastructural studies in the P2X7-null mice showed a significant thinning of the pathologically thickened Bruch’s Membrane (a hallmark feature in AMD). The role of SNL in altering the systemic response, including phagocytosis and cytokine changes, was investigated in a cohort of patients with intermediate AMD. Similar to the rodent results, a substantial reduction in peripheral monocyte phagocytosis was also observed for all subsets of monocyte populations occurring from 3 months following SNL treatment. This reduction was sustained for at least 12 months post-treatment without any significant recovery to pre-laser levels. Cytometric bead array demonstrated significant changes to cytokine-profile with an acute elevation of 9 to 13 cytokines involved in inflammation (of a total of 13 cytokines) at the 2 weeks to 3 month post-treatment time points using 200 SNL spots. At the 6 month time point, a significant increase in interleukin-6 remains in the laser-treated participants compared to pre-laser levels. In summary, these findings indicate that SNL can induce a rejuvenating response by promoting RPE proliferation in both the treated eye and the non-treated eye while also reducing the thickness of BM in the eye that received SNL treatment. This study also provides evidence that SNL therapy has the potential to modify systemic immune responses, including phagocytosis function and cytokine-profile. Taken together, our results indicate a potential role for SNL treatment of AMD to slow progression of disease.