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SM Ghazi-Nouri, DG Charteris, SE Moss, GA Limb; Expression of NT-4 and TrkB by Human Müller Cells . Invest. Ophthalmol. Vis. Sci. 2002;43(13):666.
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Purpose: Neurotrophins (NTs) regulate the proliferation and differentiation of neurons in the central nervous system via a family of specialized receptors, including TrkA, TrkB, and TrkC. As little is known about their expression or potential role in human retinal Müller cells, we investigated the expression of NT4 and its receptor TrkB in an immortalized human Müller cell line, as well as the expression of NT4 in normal human retina. Methods: Müller cell lysates and supernatants obtained from the Müller cell line (MIO-M1) after various times in culture were examined for the presence of NT4 and TrkB by standard western blotting assays. Immunohistochemical staining for NT4 was also performed in cultured cells and in 7µm sections of normal retina. Results: Western blots for NT4 revealed the presence of an approximately 75 kD band in all cell lysates examined. However, immunoblotting of recombinant human NT4 resulted in the detection of two bands of 14 and 28 kD. Unlike that observed in the cell lysates, NT4 was not detected in cell supernatants after various times of incubation. Immunohistochemical staining for this factor was also observed in cultured cells and in the inner nuclear cell layer of normal human retina. In addition, western blots for TrkB revealed two bands corresponding to approximately 75 and 85 kD in the cell lysates. Conclusion: Our findings indicate that human Müller cells express NT4 and a truncated form of TrkB, which to our knowledge has not been previously reported in the literature. Our observations suggest that NT-4 may be present in complex forms within these cells, either on its own or with the truncated form of TrkB. Production of NT4 by Müller cells may have important implications for photoreceptor cell survival, which has been ascribed to this factor.
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