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William J. Foster, Joshua T. Davis, Peter K. Lam, Deborah C. Otteson, Paul A. Janmey; Substrate Elastic Modulus Regulates Müller Cell Expression of Extracellular Matrix Genes Known To Play a Role in Proliferative Vitreoretinopathy. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5341.
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The mechanical properties of tissue have been increasingly recognized to be a significant factor in the regulation of cell behavior. Matrix stiffness, in particular, has a marked influence on numerous cell types, including hepatocytes, glia, neurons, and mesenchymal stem cells. To understand the mechanosensitivity of Müller cells and the association of matrix stiffness with the development of proliferative vitreoretinopathy (PVR) and related pathologic retinal conditions, we examined the expression of extracellular matrix-related genes in Müller cells using quantitative, real-time PCR, when cells are cultured on substrates of varying elastic modulus.
A conditionally immortalized mouse Müller cell line (ImM10) was cultured on polyacrylamide substrates with a calibrated Young’s modulus of 500 Pa, 1000 Pa, and 5000 Pa with glass as a control. A uniform coating of laminin was cross-linked to the substrates. Müller cells were cultured for 21 days and then harvested, mRNA was extracted, and real-time PCR was performed for four replicates. We then examined changes in genes that demonstrated at least a 4-fold increase or decrease in expression of mRNA between different substrates and that continuously increased or decreased with substrate elastic modulus.
Of the 85 ECM genes tested, four genes met our criteria. Ctgf (connective tissue growth factor, 103-fold change, p=0.04), Tnc (tenascin C, 41-fold change, p=0.035), Col1a1 (collagen, type I, alpha 1, 23-fold change, p=0.001), Col4a3 (collagen, type IV, alpha 3, 19-fold change, p=0.05) were upregulated on softer substrates.
The expression of some genes that are known to play a role in PVR is strongly influenced by substrate stiffness in Müller cells. Substantial Ctgf expression has been previously found in PVR membranes. Tnc, an extracellular matrix glycoprotein, is known to contribute to angiogenesis, retinal axon outgrowth, and response to retinal and optic nerve injury, and collagen is known to play a role in the structure of PVR membranes. Tissue elastic modulus may play a critical role in the development and progression of retinal disorders.
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