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Peter K. Lam, Josh T. Davis, Joseph C. Manarang, Deborah C. Otteson, Alison M. McDermott, William J. Foster; Substrate Elastic Modulus Influences Phagocytosis By Retinal Müller Cells. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1862.
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The stiffness of the environment in which a cell exists has recently been shown to influence cell processes such as proliferation, motility, and gene expression. In addition, pathologic conditions, such as macular degeneration and diabetic retinopathy, result in changes in the mechanical properties of ocular tissues. To better understand the mechanosensitivity of Müller cells and its possible role in the retinal response to pathologic conditions, we studied the phagocytosis of fluorescent latex beads by Müller cells when cultured on substrates of varying elastic modulus.
A conditionally immortalized mouse Müller cell line (ImM10) was cultured on polyacrylamide substrates with calibrated Young’s moduli of 500 Pa, 1000 Pa, and 5000 Pa, with laminin-coated glass as a control. A uniform coating of laminin was cross-linked to the substrates. After 21 days in culture, a defined number of fluorescent beads suspended in PBS were placed in each well. After an incubation time of 2 hours, flow cytometry was performed to determine the distribution in the number of beads per cell.
The number of both uncoated and Bovine Serum Albumin coated beads phagocytosed by Müller cells decreased continuously as a function of increasing substrate elastic modulus. When compared to control, cells cultured on the 500 Pa control gel had a 5-fold higher rate of phagocytosis of uncoated beads (p<0.0001) and a 2.2-fold higher rate of phagocytosis of BSA-coated beads (p<0.0001).
To the best of our knowledge, this is the first demonstration that the local mechanical environment can influence the rate of phagocytosis by Müller cells. Phagocytosis is known to be important in tissue remodeling, and the phagocytic activity of Müller cells may be influenced by changes in tissue elastic modulus induced by pathologic conditions such as age-related macular degeneration and diabetes.
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