Investigating the role of perivascular mesenchymal stem cells in macular fibrosis secondary to neovascular age-related macular degeneration

老年性黄斑变性（AMD）是一种影响黄斑的疾病，黄斑是眼睛后部视网膜的中心部分，导致老年人逐渐丧失中央视力。全球有2亿人受到AMD的影响，预计到2040年这一数字将增加到3亿。在发达国家，老年性黄斑变性是老年人失明的最常见原因。AMD有两种高级形式：湿性（也称为新生血管性AMD）和干性（也称为地理萎缩）；前者约占amd相关视力障碍的80%。湿性黄斑变性发生时，病变血管生长到黄斑，造成液体渗漏和出血，损害视力。目前的治疗方法是将VEGF抑制剂（如Lucentis或Avastin）注射到眼睛中，这可以减少血管的生长。虽然这种治疗可以稳定甚至改善视觉功能，但50%的治疗眼睛最终会在黄斑发生纤维化（瘢痕）。不像皮肤上的疤痕可以治愈伤口，黄斑上的疤痕反而会降低VEGF抑制剂的功效。病变血管中出现的纤维血管膜最终会破坏整个黄斑。目前，由于对疾病机制的了解不足，没有药物可以预防或治疗这种疾病。当称为肌成纤维细胞的细胞浸润并积聚在黄斑时，湿性AMD的新血管发展成纤维血管疤痕。肌成纤维细胞产生过量的瘢痕形成细胞外基质，如胶原和纤维连接素。包括黄斑在内的健康视网膜中没有肌成纤维细胞，我们还不知道它们来自哪里以及它们如何在湿性AMD中被激活。这一知识对于开发湿性黄斑变性和黄斑纤维化的治疗干预至关重要。最近，血管周围间充质干细胞（pMSC），一种存在于血管周围的独特类型的细胞被确定为多种器官（包括肺、肾、心脏和皮肤）损伤性瘢痕中肌成纤维细胞的主要来源。已知这些pMSCs可以保护血管并保持其完整性。在受伤期间，它们从血管壁上脱离，前往受损部位，参与组织修复和再生。当损伤持续存在或损伤介导的炎症不能迅速消退时，这些pMSCs会扩张并成为肌成纤维细胞，导致器官纤维化。我们发现，在眼睛内，视网膜和脉络膜也包含一个pMSCs网络。在湿性amd介导的视网膜纤维化实验模型中，超过60%的肌成纤维细胞来源于pMSCs， pMSCs的基因缺失减少了视网膜纤维化。我们的目的是了解为什么pMSCs在湿性AMD中成为肌成纤维细胞，以及我们如何预防或逆转这一过程。我们将使用先进的基因组技术来揭示视网膜纤维化不同阶段病变组织中单个pMSCs的基因表达谱。这将告诉我们哪些pMSC亚型会产生肌成纤维细胞以及控制这一过程的途径。我们将在来自视网膜、脉络膜和视网膜瘢痕组织的pMSC培养物中验证这些途径。然后，我们将利用体外和体内视网膜纤维化模型，用药理学方法来阻止或逆转pMSCs向肌成纤维细胞的分化。我们的研究结果将为进一步的研究提供信息，并增强我们对湿性AMD和其他由异常组织修复引起的视力威胁疾病（如增殖性糖尿病视网膜病变[PDR]和增殖性玻璃体视网膜病变[PVR]）的视网膜修复和纤维化的理解。最终，我们的研究将致力于开发视网膜纤维化的有效治疗方法。

Age-related macular degeneration (AMD) is a disease that affects the macula, the central part of the retina at the back of the eye, causing progressive loss of central vision in the elderly. Globally, 200 million people are affected by AMD and this number is expected to increase to 300 million by 2040. In the developed world, AMD is the most common cause of blindness in the elderly. AMD has two advanced forms: wet (also known as neovascular AMD) and dry (also known as geographic atrophy); the former accounts for ~80% of AMD-related visual impairment. Wet AMD occurs when diseased blood vessels grow into the macula, causing fluid leakage and bleeding that impairs vision. It is currently treated with injections of VEGF inhibitor (e.g. Lucentis or Avastin) into the eye, which reduces the growth of blood vessels. Although such treatment can stabilise or even improve visual function, 50% of treated eyes eventually develop fibrosis (scarring) in the macula. Unlike scarring of the skin, which heals the wound, scarring in the macula, instead reduces the efficacy of VEGF inhibitors. The fibrovascular membranes that emerge from diseased blood vessels eventually destroy the entire macula. Currently, there are no medications to prevent or treat this condition due to a poor understanding of the disease mechanism. New blood vessels in wet AMD develop into fibrovascular scar when cells, called myofibroblasts, infiltrate and accumulate in the macula. Myofibroblasts produce excessive amounts of scar-forming extracellular matrix such as collagens and fibronectins. Myofibroblasts are absent from the healthy retina, including the macula, and we do not yet know where they come from and how they are activated in wet AMD. This knowledge is crucial for developing therapeutic interventions to wet AMD and macular fibrosis. Recently, perivascular mesenchymal stem cells (pMSC), a unique type of cell residing around blood vessels were identified as a major source of myofibroblasts in injury-induced scars in multiple organs, including the lung, kidney, heart, and skin. These pMSCs are known to safeguard blood vessels and maintain their integrity. During injury, they detach from blood vessel walls and travel to the site of damage, where they participate in tissue repair and regeneration. When the injury persists or when injury-mediated inflammation does not resolve promptly, these pMSCs expand and become myofibroblasts leading to organ fibrosis. We have found that within the eye, the retina and choroid also contain a network of pMSCs. In an experimental model of wet AMD-mediated retinal fibrosis, over 60% of myofibroblast originated from pMSCs, and genetic deletion of pMSCs reduced retinal fibrosis. Our aim is to understand why pMSCs become myofibroblasts in wet AMD and how we might prevent or reverse this process. We will use advanced genomic techniques to uncover the gene expression profile of individual pMSCs within the diseased tissue at different stages of retinal fibrosis. This will inform us of which pMSC subtypes give rise to myofibroblasts and the pathways that control this process. We will verify these pathways in pMSC cultures derived from the retina, choroid, and retinal scar tissue. We will then target these pathways with pharmacological approaches to prevent or reverse the differentiation of pMSCs into myofibroblasts using in vitro and in vivo models of retinal fibrosis. Our results will inform further research and enhance our understanding of retinal repair and fibrosis in wet AMD and other sight-threatening diseases caused by abnormal tissue repair (e.g. proliferative diabetic retinopathy [PDR] and proliferative vitreoretinopathy [PVR]). Ultimately, our research will aim in developing effective treatments for retinal fibrosis.