AbstractAge related Macular Degeneration (AMD) is the leading cause of blindness in the elderly population of developed countries. Advanced AMD is categorised into two subtypes, “dry” AMD and “wet” or neovascular AMD (nAMD). nAMD is characterised by choroidal neovascularisation (CNV), which is the growth of newly formed blood vessels into the retina. A neovascular lesion is formed, and the end stage of nAMD is macular fibrosis in which the neovascular lesion transitions into a fibrovascular lesion. This fibrosis in the retina causes irreparable vision loss. Macular fibrosis affects around one third of nAMD patients. At present, it is not understood how the neovascular lesion in nAMD transitions into a fibrovascular lesion.
The laser-induced CNV model is a well-recognised murine model of CNV, however, it does not display key features of sub-retinal fibrosis. The third chapter of this thesis describes an in vivo murine model of sub-retinal fibrosis secondary to nAMD. The two-stage laser model of sub-retinal fibrosis was developed by causing a second laser burn to the neovascular lesion formed in the laser-induced CNV model 7 days after initial laser burn. The model resulted in fibrovascular sub-retinal lesions, with neovascularisation that did not regress after 40 days. This is a more accurate representation of macular fibrosis in patients. Using tissues from this model, this thesis aimed to identify the myofibroblast precursors which contribute to macular fibrosis secondary to nAMD.
Macrophages have been identified as a key cell in macular fibrosis development. We saw an influx of infiltrating F4/80+ cells in the two-stage laser model discussed in chapter 3. Until recently, it was assumed that macrophages only had indirect roles in fibrosis development, however recent research has shown that macrophages can transition directly into myofibroblasts to contribute directly to fibrosis in organs such as the liver. Stimulating macrophages with TGF-β2 can mediate this transition. In chapter 4 we show that macrophages play a role in an in vivo model of sub-retinal fibrosis, and in human samples through Macrophage-to-Myofibroblast Transition (MMT).
The complement system has been widely recognised to play a role in AMD and retinal dysfunction. Our group has previously shown that complement component C3a is increased in the serum of patients with sub-retinal fibrosis. Chapter 5 presents the findings that complement component C3a can mediate MMT in bone marrow derived macrophages in vitro. We found that blocking C3a during the two-stage laser model resulted in reduced leakage and neovascularisation in the lesion. Together, the data presented in this thesis suggests that the interaction between macrophages and the complement system may play a role in sub-retinal fibrosis development following neovascular AMD.
|Date of Award||Jul 2020|
|Supervisor||Mei Chen (Supervisor) & Heping Xu (Supervisor)|