The Stem Cell Niche and Lens Fibrotic Disease

描述(由申请者提供)：干细胞生态位通过尚未被很好理解的机制来调节干细胞功能。我们开发了一种“体外”培养模型系统，它使我们能够研究干细胞/祖细胞在其自然微环境中对损伤的行为反应。该系统被建立为纤维性晶状体疾病、后囊混浊的模型，涉及晶状体上皮细胞向后囊的集体迁移和间充质细胞的出现。这种疾病的病因尚不清楚。最近，在晶状体中发现了一小部分MyoD/G8抗原阳性的上皮细胞-骨骼肌干细胞。在我们的“体外”模型中，我们已经在赤道区(EQ)晶状体上皮细胞之间的缝隙中发现了这些G8阳性(G8pos)的上胚层-骨骼肌干细胞，在我们的模拟白内障手术后，它们仍然紧密地附着在晶状体囊上。在我们的“体外”模型中，我们检测到G8抗原阳性的上皮细胞-骨骼肌干/祖细胞从EQ区内的自然微环境移动到集体迁移的晶状体上皮细胞的前沿。G8pos骨骼肌干/祖细胞可能为晶状体纤维性疾病中检测到的1-平滑肌肌动蛋白阳性肌成纤维细胞提供来源。我们假设，在晶状体损伤和白内障手术中可能发生的G8pos上皮细胞-骨骼肌干细胞生态位的破坏，导致间充质细胞前体的异常调节和出现，1)驱动晶状体上皮细胞的集体迁移以闭合伤口，2)转分化为肌成纤维细胞，导致纤维化。我们的“体外”培养模型提供了一个独特的机会，可以提出一些基本的问题，比如干细胞和干细胞周围的晶状体细胞之间，以及细胞和基质微环境之间的相互作用是如何在干细胞内被调节的，所有这些都是对创伤的反应。阐明这些机制不仅可以拓宽我们对干细胞/祖细胞亚群在损伤诱导的生态位改变时的行为的理解，而且还可以导致抗纤维化疗法的发展，以保护视力。这一建议的主要目的是：1)验证一种假设，即晶状体损伤后在龛外发现的G8pos细胞来自于G8pos上皮细胞-骨骼肌干细胞群体的扩增和/或晶状体上皮细胞向G8谱系的募集。2)验证一种假设，即钙粘附素介导的细胞-细胞和整合素介导的细胞-基质相互作用是维持正常的G8干细胞生态位所必需的关键决定因素，并在损伤后改变以产生G8pos间充质前体细胞。3)验证假设，即G8pos上皮细胞骨骼肌干细胞生态位的改变导致间充质前体的异常调节和出现，从而驱动晶状体上皮细胞的集体迁移，并最终转分化为肌成纤维细胞。与公共卫生相关：晶状体纤维性疾病导致晶状体混浊，导致白内障的形成，从而阻碍视力。晶状体纤维性疾病的确切病因尚不清楚，该项目的长期目标是了解位于晶状体中的G8pos骨骼肌干细胞亚群在诱导晶状体纤维性疾病中的作用。G8pos骨骼肌干细胞位于晶状体中，损伤后从干细胞巢中涌出。阐明这些机制不仅可以拓宽我们对干细胞在损伤后其生态位改变时的行为的理解，还可以促进抗纤维化疗法的发展，以保护视力。

DESCRIPTION (provided by applicant): The stem cell niche regulates stem cell function through mechanisms not well understood. We have developed an "ex vivo" culture model system, which allows us the unique ability to study stem/progenitor cell behavior response to injury within their native microenvironment. This system was established as a model for the fibrotic lens disease, Posterior Capsule Opacification, which involves collective migration of lens epithelial cells onto the posterior capsule and the emergence of mesenchymal cells. The etiology of this disease is unknown. Recently, a small subpopulation of myo D/G8 antigen positive epiblast-skeletal muscle stem cells has been identified in the lens. In our "ex vivo" model we have identified a these G8 positive (G8pos) epiblast- skeletal muscle stem cells within a niche nestled among the lens epithelial cells of the equatorial zone (EQ), that remain tightly adherent to the lens capsule after our mock cataract surgery. Upon injury in our "ex vivo" model we detect G8 antigen positive epiblast-skeletal muscle stem/progenitor cells moving from their native microenvironment within the EQ zone to the leading edge of the collectively migrating lens epithelial cells. G8pos skeletal muscle stem/progenitor cells may provide the source of 1-smooth muscle actin positive myofibroblasts detected in lens fibrotic diseases. We hypothesize that disruption of the G8pos epiblast- skeletal muscle stem cell niche, such that could occur during lens injury and cataract surgery, causes the aberrant regulation and emergence of mesenchymal cell precursors that 1) drive the collective migration of the lens epithelial cells for wound closure and 2) transdifferentiate into myofibroblasts causing fibrosis. Our "ex vivo" culture model provides the unique opportunity to ask fundamental questions regarding how reciprocal interactions are regulated within the stem cell niche, such as between niche stem/progenitor cells and their surrounding lens cells, and between the cells in the niche and their matrix microenvironment, all in response to wounding. Elucidation of such mechanisms could not only broaden our understanding of the behavior of a subset of stem/progenitor cells in response to injury-induced changes to their niche but also lead to the development of anti-fibrotic therapeutics to preserve vision. The major goals of this proposal are to 1) Examine the hypothesis that G8pos cells found outside the niche following injury to the lens are derived from amplification of the G8pos epiblast-skeletal muscle stem cell population and/or by recruitment of lens epithelial cells to the G8 lineage. 2) Examine the hypothesis that cadherin-mediated cell-cell and integrin-mediated cell- matrix interactions are critical determinants essential to maintain the normal G8 stem cell niche and are altered upon injury for emergence of G8pos mesenchymal precursor cells. 3) Examine the hypothesis that alterations in the G8pos epiblast skeletal muscle stem cell niche causes the aberrant regulation and emergence of mesenchymal precursors that drive collective migration of lens epithelial cells and ultimately transdifferentiate into myofibroblast. PUBLIC HEALTH RELEVANCE: Lens fibrotic disease causes lens opacities leading to the formation of cataracts which block vision. The exact etiology of lens fibrotic disease is unknown and the long term goals of this project are to understand the role of a subpopulation of G8pos skeletal muscle stem cells, which are located in the lens and emerge from their stem cell niche upon injury, in the induction of lens fibrotic disease. Elucidation of such mechanisms could not only broaden our understanding of stem cell behavior in response to injury-induced changes to their niche but also lead to the development of anti-fibrotic therapeutics to preserve vision.