Cell proliferation of human fibroblasts and osteoblasts in osteogenesis imperfecta: influence of age

Clinical studies indicate that as a group, osteogenesis imperfecta (OI) subjects are shorter than age- and sex-matched controls. Not only somatic growth, but also cellular growth appears to be impaired, and these may be related to defects in extracellular matrix common to this disorder. We have investigated the growth characteristics of dermal fibroblasts and trabecular osteoblasts isolated from patients with OI and control subjects of various ages. Cell growth curves and cell doubling times were determined by measuring cell number using crystal violet dye binding. Growth curves were modeled by a modified logistic function, the three parameters of which are markers for biologically relevant growth parameters: the plateau value or upper asymptote, which reflects the maximum cell density upon confluence; the maximal growth rate (microM); and the lag time. Both normal human fibroblasts and osteoblasts showed an age-dependent decrease in microM. Normal fibroblasts exhibited no age-dependence to their upper asymptote or lag time. Fibroblasts derived from patients with OI did not have significantly different upper asymptote values microM, or lag times when compared with normal fibroblasts. Normal osteoblasts had a decrease in upper asymptote, decrease in microM, but a relatively constant lag time with increasing age. In contrast, OI osteoblast microM was decreased relative to that of normal subjects. For osteoblasts from OI patients, decreased microM appeared unrelated to the age of the subject, whereas OI fibroblasts did exhibit an age-dependent decrease in microM. The percentage of collagenase-digestible protein (a measure of collagen synthesis) produced by normal human fibroblasts correlated well with microM. Treating normal human osteoblasts with the proline analogue 3,4-dehydroproline, which destabilizes collagen triple helix formation and alters collagen synthesis, secretion, and turnover, also decreased microM. A dose response to varying concentrations of 3,4-dehydroproline was observed for normal human bone cell microM. These data suggest a link between type I collagen synthesis and cellular proliferation.