David J. Collison

A focus on the human lens in vitro.

The lens is a unique organ in that it is avascular and non-innervated, obtaining all nutrients from the aqueous and vitreous humours that bathe the lens. All lenses attempt to achieve the same goal, namely to maintain transparency and focus light on to the retina. However, the mechanisms by which these processes are maintained, or disrupted leading to a loss of transparency, are likely to differ in some cases between animals and humans. To allow comparison to take place, human in vitro models have been developed, ranging from whole organ culture to the generation of human lens cell lines. All have their merits and limitations, but as a whole, they permit extensive studies of lens cell behaviour and function to be carried out. Together, these in vitro methods allow the biological events of the lens to be further understood. Moreover, they could help identify the mechanisms that give rise to cataract and posterior capsule opacification, a problem that occurs following surgery, providing therapeutic targets for their prevention.

Molecular and functional mapping of regional differences in P2Y receptor expression in the rat lens

Extracellular ATP has been shown to mobilize intracellular Ca(2+) in cultured ovine lens epithelial cells and in human lens epithelium, suggesting a role for purines in the modulation of lens transparency. In this study, we characterized the expression profiles of P2Y receptor isoforms throughout the rat lens at both the molecular and the functional levels. RT-PCR indicated that P2Y(1), P2Y(2), P2Y(4) and P2Y(6) are expressed in the lens, while P2Y(12), P2Y(13) and P2Y(14) are not. Immunohistochemistry, using isoform specific antibodies, indicated that the epithelium does not express P2Y(1) and P2Y(2), but that the underlying fiber cells, which differentiate from the epithelial cells, exhibit strong membranous labeling. Although co-expressed in fiber cells, differences in P2Y(1) and P2Y(2) expression were apparent. P2Y(1) expression extended deeper into the lens than P2Y(2), and its expression co-localized with Cx50 gap junction plaques, while P2Y(2) did not. Labeling for P2Y(4) and P2Y(6) receptors were observed in both epithelial cells and fiber cells, but the labeling was predominantly cytoplasmic in nature. While purine agonist (ATP, ADP, UTP and UDP) application to the lens induced mobilization of intracellular Ca(2+) in cortical fiber cells, little to no effect was observed in the anterior and equatorial epithelium. Thus the inability of UTP and UDP to mobilize intracellular Ca(2+) in the epithelium and the predominately cytoplasmic location of P2Y(4) and P2Y(6) suggests that these receptors may represent an inactive pool of receptors that may be activated under non-physiological conditions. In contrast, our results indicated that P2Y(1) and P2Y(2) are functionally active in fiber cells and their differential subcellular expression patterns suggest they may regulate distinct processes in the lens under steady state conditions.