Characterization of the tissue regression process in the uteru...

Whether old uteri that have undergone involution do so by an apoptotic mechanism was examined by the presence of known biochemical and morphological markers for programmed cell death. Terminin, a protein identified by an unique monoclonal antibody, has three forms, Tp-90, Tp-60, and Tp-30: Tp-90 (the 90 kDa form) is only present in growing and quiescent non-growing cells; Tp-60 (the 60 kDa form) is found in senescent cells; and finally, Tp-30 (the 30 kDa form) is found in cells committed to apoptotic death. Biochemical analysis of a protein, Tp30, previously identified as a marker for the commitment to programmed cell death, was performed with both young (5-month-old) and old (24-month-old) C57BL/6J mouse uteri. In addition to biochemical analysis of Tp30 presence in uterine tissue, propidium iodide (PI) staining and DNA framentation by nick-end labelling with fluorescence-conjugated UTP were used to characterize apoptosis-related changes in the chromatin organization of the nucleus. Results indicate that within the old uterus Tp-30 is indeed detected in the tissue extracts and was the major terminin band, while Tp-90 and Tp-60 were the major bands observed in extracts of the younger mouse uterus. The presence of Tp30 in the older uterine tissue suggests that the tissue regression which has occurred in the uterus of older mice may be apoptotic in nature. This suggestion is further supported by the demonstration of increases in the number of cells showing apoptotic morphology, i.e. positive staining with UTP reflecting the presence of nuclei with nicked DNA, localized exclusively in the uterine stroma of older females. The presence of DNA fragmentation, as reflected by UTP staining, was virtually absent from the young uteri. These data suggest that apoptosis may be a part of the cellular mechanism contributing to the regression of uterine tissue in the older female during involution, appearing as an age-dependent event.