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D.R. Whikehart, K. Mishler; Wounding Transfers Telomerase Activity to the Central Human Corneal Endothelium . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4385.
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It has been recently shown (Whikehart et al.: Mol Vis. 2005;11: 816–24) that telomerase activity normally exists in the peripheral, but not central, human corneal endothelium. Such activity is indicative of the presence of transient amplifying cells. We endeavored to demonstrate transfer of that activity to the central endothelium following the administration of a mechanical wound.
Pairs of human corneal–limbal sections (with no demonstrable pathology) were tested. One cornea was subjected to the gentle surface infliction of a mechanical wound while the fellow cornea (unwounded) served as a control. All corneas were kept in Optisol and incubated at 37 deg C in an incubator for up to 48 hr. Corneas were divided into central and peripheral areas with a 4 mm trephine and carefully scraped from each surface. Each tissue set was assayed for telomerase (human telomerase reverse transcriptase) activity using a commercial variation of the TRAP method. Briefly, positive results are seen as a series of DNA telomere repeat products (visualized by SYBR green after amplification by PCR).
As previously reported (op cit) no activity appeared in the central cornea while activity was seen in the periphery when assaying the control (unwounded) corneas. After 48 hr of wounding, both the peripheral and central areas of the corneal endothelium showed marked activity. After 24 hr of wounding, peripheral activity was seen as usual, but only a minimal amount of activity was seen centrally to indicate a lag in the synthesis of telomeric DNA.
This study shows that telomerase activity is transferred centrapitally into the central human corneal endothelium within 48 hr of mechanical wounding. The results suggest that transient amplifying cells are dividing and moving into the central endothelium as a result of the wound and confirms BrdU results reported by Whikehart et al (op cit) and others. The source of the transient amplifying cells has been suggested to be stem cells residing beyond the periphery of the cornea. This is indicated by data from our lab showing the existence of nestin markers in the trabecular meshwork and, possibly, at Schwalbe's line. Normally, central human corneal endothelial cells themselves would not be expected to divide due to the relatively higher levels of p53 and TAp63 found centrally (Paull, Whikehart: Mol Vis 2005; 11: 328–34). Both the putative stem cells and the transient amplifying cells may be stimulated by cytokines generated by damaged cells in the wounded area.
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