An Autoradiographic Study of <sup>3</sup>H-Proline Utilization by Aging Mouse Skeletal Tissues

Abstract

Autoradiographic data of <sup>3</sup>H-proline turnover by mouse skeletal cell compartments of different age were subjected to graphical analysis for the further characterization of the effects of age on skeletal cell metabolic behavior. Periosteal osteoblasts showed early significant age changes by 26 weeks of age, paralleling the previously reported histocytomorphological changes. Age changes appeared to be nonsignificant in metaphyseal osteoblasts at 52 weeks of age, however, the total turnover of <sup>3</sup>H-proline was adjusted to the reduced functional demands associated with trabecular remodeling and closure of the epiphyseal plate. The dramatic changes observed in <sup>3</sup>H-proline uptake and turnover of the epiphyseal plate cartilage cells coincided with the closure of the plate and termination of matrix formation. In addition, highly significant age changes occurred in response to the cessation of functional demands. Residual articular cartilage cells appeared to be capable of retaining their viability, staving off early age changes, thus insuring a reasonably healthy joint function in older animals. The effects of age on the skeletal cell utilization of <sup>3</sup>H-proline were best expressed as a series of steady-state events of diminishing activity. The time table for significant age changes varied in different cell compartments and also in similar cell types located at different anatomical sites. Modulation of the time table for skeletal cell aging appeared to be dictated by functional demands.