Sexual differences in branched chain amino acid metabolism into fatty acids and cholesterol in Harderian gland of golden hamster

PURPOSE: To investigate the telomere hypothesis of cellular aging as the mechanism for cell cycle arrest in normal human corneal endothelium. METHODS: The corneal endothelium and epithelium from 21 human corneas from 13 donors 5 weeks to 84 years of age were dissected and frozen at -70 degrees C. Purified DNA, digested with the restriction enzyme, HinfI, was run on 0.7% agarose gels, probed with radiolabeled (AATCCC)4, and exposed to a phosphor screen. The length of the terminal restriction fragment (TRF) was determined by densitometry. RESULTS: The cells of the corneal endothelium had TRF lengths ranging from 11.0 to 14.0 kbp (mean, 12.2 +/- 0.9). Corneal epithelial specimens showed TRF lengths that were always less than (mean, 10.4 +/- 1.0; range 9.0-12.0) the corresponding endothelial TRF lengths. Human corneal endothelial cells, transformed with human papillomavirus type 16 oncogenes E6 and E7, showed decreasing TRF lengths from 11 kbp at population doubling level (PDL) 15 to 9.5 kbp at PDL 73. Neither the endothelial and epithelial cells from human donors nor the transformed pre-immortalized human endothelial cells showed evidence of telomerase activity. CONCLUSIONS: Human corneal endothelial cells have long telomeres throughout life. Their limited replicative ability does not appear to result from critically short telomere lengths.