Jobling Andrew I, Gentle Alex, Metlapally Ravikanth, McGowan Bryan J, McBrien Neville A
Department of Optometry and Vision Sciences, The University of Melbourne, Victoria 3010, Australia.
J Biol Chem. 2009 Jan 23;284(4):2072-9. doi: 10.1074/jbc.M807521200. Epub 2008 Nov 14.
Reduced extracellular matrix accumulation in the sclera of myopic eyes leads to increased ocular extensibility and is related to reduced levels of scleral transforming growth factor-beta (TGF-beta). The current study investigated the impact of this extracellular environment on scleral cell phenotype and cellular biomechanical characteristics. Scleral cell phenotype was investigated in vivo in a mammalian model of myopia using the myofibroblast marker, alpha-smooth muscle actin (alpha-SMA). In eyes developing myopia alpha-SMA levels were increased, suggesting increased numbers of contractile myofibroblasts, and decreased in eyes recovering from myopia. To understand the factors regulating this change in scleral phenotype, the competing roles of TGF-beta and mechanical stress were investigated in scleral cells cultured in three-dimensional collagen gels. All three mammalian isoforms of TGF-beta altered scleral cell phenotype to produce highly contractile, alpha-SMA-expressing myofibroblasts (TGF-beta3>TGF-beta2>TGF-beta1). Exposure of cells to the reduced levels of TGF-beta found in the sclera in myopia produced decreased cell-mediated contraction and reduced alpha-SMA expression. These findings are contrary to the in vivo gene expression data. However, when cells were exposed to both the increased stress and the reduced levels of TGF-beta found in myopia, increased alpha-SMA expression was observed, replicating in vivo findings. These results show that although reduced scleral TGF-beta is a major contributor to the extracellular matrix remodeling in the myopic eye, it is the resulting increase in scleral stress that dominates the competing TGF-beta effect, inducing increased alpha-SMA expression and, hence, producing a larger population of contractile cells in the myopic eye.
近视眼中巩膜细胞外基质积累减少导致眼球伸展性增加，这与巩膜转化生长因子-β（TGF-β）水平降低有关。本研究调查了这种细胞外环境对巩膜细胞表型和细胞生物力学特性的影响。在近视的哺乳动物模型中，使用肌成纤维细胞标志物α-平滑肌肌动蛋白（α-SMA）在体内研究巩膜细胞表型。在发生近视的眼睛中，α-SMA水平升高，提示收缩性肌成纤维细胞数量增加，而在从近视恢复的眼睛中α-SMA水平降低。为了解调节巩膜表型这种变化的因素，在三维胶原凝胶中培养的巩膜细胞中研究了TGF-β和机械应力的竞争作用。TGF-β的所有三种哺乳动物同工型均改变巩膜细胞表型，产生高收缩性、表达α-SMA的肌成纤维细胞（TGF-β3>TGF-β2>TGF-β1）。将细胞暴露于近视巩膜中发现的降低水平的TGF-β，会导致细胞介导的收缩减少和α-SMA表达降低。这些发现与体内基因表达数据相反。然而，当细胞暴露于近视中发现的增加的应力和降低水平的TGF-β时，观察到α-SMA表达增加，这与体内研究结果一致。这些结果表明，虽然巩膜TGF-β降低是近视眼细胞外基质重塑的主要因素，但导致的巩膜应力增加在与TGF-β的竞争效应中占主导地位，诱导α-SMA表达增加，从而在近视眼中产生更多收缩性细胞。
