Investigative Ophthalmology & Visual Science, Vol 38, 456-468, Copyright © 1997 by Association for Research in Vision and Ophthalmology

ARTICLES AND REPORTS

Tractional force generation by porcine Muller cells. Development and differential stimulation by growth factors

C Guidry
Department of Ophthalmology, Eye Foundation Hospital, University of Alabama at Birmingham 35294, USA.

PURPOSE: To assess the ability of retinal Muller cells to generate tractional forces during dedifferentiation in culture and to assess their responsiveness to contraction-stimulating growth factors. METHODS: Muller cells were isolated from papain-DNase-digested porcine retina. The identity of the isolated cells was confirmed by immunodetection of carbonic anhydrase II (CA-II), cellular retinaldehyde-binding protein (CRALBP), glial fibrillary acidic protein (GFAP), vimentin, and alpha smooth muscle actin (alpha SMA). Tractional force generation was assessed as a function of Muller cell contraction of collagenous extracellular matrices in vitro. The effects of potential promoters were assessed by addition directly to culture medium. The contributions of specific promoting to the contraction- promoting activity in serum were assessed by adding neutralizing antibodies and measuring loss of stimulatory activity. RESULTS: Freshly isolated Muller cells did not generate substantial matrix contraction. However, this activity increased 150-fold within 12 days in culture and continued to increase during the next 21 days. Development of the capacity for extracellular matrix contraction coincided with the acquisition of immunodetectable alpha SMA and loss of GFAP. Matrix contraction by Muller cells was stimulated in a dose-dependent fashion by human serum, platelet-derived growth factor (PDGF), and insulin-like growth factor-I (IGF-I). Muller cells were not stimulated by transforming growth factor beta 1 (TGF beta 1), transforming growth factor beta 2 (TGF beta 2), or endothelin-1 (E1). Neutralizing antibodies against PDGF and IGF-I reduced the activity in human serum by 37% and 58%, respectively, and 87% when added together. CONCLUSIONS: Porcine Muller cells in culture acquire the ability to contract extracellular matrices and thus generate tractional forces. Acquisition of this activity coincides with alpha SMA expression and loss of GFAP. Further, this activity is dependent on the presence of exogenous promoters, including PDGF or IGF-I.

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