EFFECT OF 1,25-DIHYDROXYVITAMIN D-3 ON PROLIFERATION IN SENESCENT IMR-90 HUMAN FIBROBLASTS

The response of IMR-90 human fetal lung fibroblasts at high population doubling level (PDL > 42) to 1,25-dihydroxyvitamin D-3[1,25(OH)(2)D-3 ] was investigated to clarify whether some metabolic and molecular par ameters of senescent cells are affected by the hormone treatment. Pyru vate kinase, lactate dehydrogenase and glucose-6-phosphate dehydrogena se activity significantly increased after treatment of confluent-phase cells with 10 nM 1,25(OH)(2)D-3 for 24 h. Steroid specificity was est ablished by the failure of 10 nM levels of 25-hydroxyvitamin D-3 to af fect the enzyme activities, while estradiol-17 beta and progesterone p roduced a slight increase in glucose-6-phosphate dehydrogenase and lac tate dehydrogenase levels, respectively. 1,25(OH)(2)D-3 also affected fibroblast proliferation, protein content/cell and DNA synthesis. The cell number significantly decreased after a 48 h incubation with 1,25( OH)(2)D-3 at various concentrations (0.01-1 nM) when compared with con trol fibroblasts, while an increase in the protein content/cell was de monstrated. The same experiment, carried out by protracting the incuba tion with the hormone for 72 h, showed a similar trend, but 10 nM 1,25 (OH)(2)D-3 was also able to inhibit cell proliferation and to stimulat e protein synthesis. The incorporation of [H-3]thymidine into DNA incr eased after the treatment of high PDL fibroblasts with 0.01-1 nM of ho rmone for 48 h in comparison with controls. In conclusion, these data demonstrate that 1,25(OH)(2)D-3 stimulates some enzymatic activities i n confluent-phase senescent IMR-90 human fibroblasts and also affects cell proliferation, protein content and DNA synthesis in sub-confluent -phase cells.