Vitronectin is present in epithelial cells of the intact lens and promotes epithelial mesenchymal transition in lens epithelial explants.
OBJECTIVE
Extracellular matrix (ECM) accumulates during the development of posterior capsule opacification (PCO). Vitronectin, an ECM component that is generally prominent in wound healing, has been detected in PCO specimens. Here we set out to investigate the distribution of vitronectin in the lens and determine how it, and other ECM components, influence the lens epithelial phenotype.


METHODS
Rat lens epithelial explants were cultured on vitronectin, fibronectin, and laminin substrata. Explants were monitored for cell migration and the appearance of markers for epithelial mesenchymal transition (EMT), using phase contrast microscopy and immunohistochemistry, respectively. Explants were also monitored for evidence of Smad signaling. Vitronectin expression was analyzed in embryonic and postnatal rodent lens development by immunohistochemistry, western blotting, and in situ hybridization.


RESULTS
Vitronectin, like fibronectin and laminin, provided a good substratum for cellular attachment and migration. However, in the case of vitronectin and fibronectin, this was accompanied by a major phenotypic change. On either vitronectin or fibronectin, but not laminin, most of the cells became elongated, spindle-shaped and were strongly reactive for filamentous alpha-smooth muscle actin. In these respects this transition was typical of the well known TGFbeta-induced EMT. In explants cultured on vitronectin and fibronectin, but not laminin, cell nuclei showed prominent reactivity for Smad 2/3. Vitronectin was also shown to be expressed during embryonic and postnatal development. Initially mRNA and protein were detected in all lens cells, however as development progressed, expression became restricted to cells of the epithelium and transition zone.


CONCLUSIONS
The results clearly show that lens cell engagement with a vitronectin or a fibronectin, but not laminin, substratum has a potent EMT promoting effect and that Smad 2/3 signaling is involved. Thus when considering strategies to slow or prevent PCO, these results highlight the need to take into account ECM molecules such as vitronectin that have the capacity to promote EMT.
Taliana
Lavinia
L
Save Sight Institute and Department of Anatomy and Histology, University of Sydney, Sydney, NSW, Australia.
Evans
Margaret D M
MD
Ang
Sharyn
S
McAvoy
John W
JW
D000818:Animals; D000831:Animals, Newborn; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology* / Q000378:metabolism*; D005353:Fibronectins / Q000502:physiology; D066298:In Vitro Techniques; D007797:Laminin / Q000502:physiology; D007903:Lens Capsule, Crystalline / Q000166:cytology* / Q000196:embryology* / Q000254:growth & development / Q000378:metabolism; D008648:Mesoderm / Q000166:cytology*; D051379:Mice; D051381:Rats; D015398:Signal Transduction; D051899:Smad2 Protein / Q000378:metabolism; D051900:Smad3 Protein / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism; D019096:Vitronectin / Q000378:metabolism / Q000502:physiology*
D005353:Fibronectins; D007797:Laminin; D051899:Smad2 Protein; C497784:Smad2 protein, rat; D051900:Smad3 Protein; C497787:Smad3 protein, rat; D016212:Transforming Growth Factor beta; D019096:Vitronectin