In our studies of normal growth-limited human keratocytes, the induction of myofibroblast differentiation by TGFβ appeared to be age dependent, in that keratocytes isolated from older individuals required a longer exposure time. Although it was not possible to characterize this age dependence more fully, it should be noted that donor age was also associated with the appearance of chromosomal abnormalities, as previously described by Pattenati et al.,
26 in whose original work keratocytes from donors older than 18 years showed a much greater likelihood (17/24 donors) of having chromosomally abnormal cells, most commonly involving aneuploidy with gains or losses of sex chromosomes, along with various deletions and translocations in 10% to 91% of cells. Our finding that corneal fibroblasts from a 62-year-old donor showed an abnormal karyotype is consistent with their finding, although the appearance of polyploidy was not reported. Karyotype analysis of normal, untelomerized cultured corneal fibroblasts from an older donor identified a 46, X, +10 karyotype, more characteristic of the abnormalities identified by Pattenati et al.
26 The karyotype obtained from 10-year-old donor cells that had been transfected with hTERT was shown to be normal (46, XY) indicating the hTERT infection was not directly associated with the development of polyploidy in the cell lines from the older donor. It is interesting to speculate on whether these chromosomal aberrations may influence the TGFβ response of human keratocytes and, in part, explain the apparent age-dependent differences in TGFβ noted in culture. In this regard, Pattenati et al.
26 have noted that the most frequent chromosomes exhibiting aneuploidy, deletions, and translocation are those important in the regulation of collagen synthesis, adhesion, and turnover, suggesting that the adult cornea may be deficient in essential keratocyte responses during corneal repair. Furthermore, corneal wound repair in the adult human has been shown to be highly variable, with healing of partial incisional wounds ranging from a typical fibrotic response and complete healing to retention of an epithelial plug with no wound fibrosis.
41 This variation in the wound-healing responses explains, in part, the highly variable refractive results noted after radial keratotomy—an early form of refractive surgery for which older patients show a slightly more pronounced effect (0.7 D per decade of life)
42 that can be linked to the poorer wound-healing response.
41 Of interest, chromosomal aberrations in the keratocytes are also highly variable and weakly correlated with age.
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