Terminal differentiation of nuchal ligament fibroblasts: Characterization of synthetic properties and responsiveness to external stimuli

The temporal expression of elastogenesis is unique among connective tissues in that elastin production occurs primarily during late fetal and early neonatal periods and is essentially fully repressed once fiber assembly is completed. To test whether elastin synthesis in adult nuchal ligament fibroblasts is permanently repressed or whether the cells retain the ability to reinitiate production upon proper stimulation, we examined in adult ligament cells various parameters known to be involved in the regulation of elastin production. Elastin synthetic capacity, as determined by the levels of steady-state tropoelastin mRNA, of adult tissue was significantly decreased relative to fetal tissue. Likewise, fibroblasts grown from explants of adult ligament had about a fourfold decrease in elastin production and elastin-specific mRNA levels. On the other hand, adult cells were similar to fetal ligament cells in that they were sensitive to gluococorticoid stimulation and demonstrated chemotactic responsiveness to elastin peptides. Since our previous studies have shown that the extracellular matrix (ECM) plays an important role in influencing elastin phenotypic expression, fetal and adult fibroblasts were grown on slices of nonviable adult ligament to test if repression of elastin production was directed by factors in ECM of adult tissues. No change in elastin synthesis was detected with either cell type grown on adult ligament, whereas both fetal and adult cells demonstrated increased elastin production in response to contact with fetal ligament. These results suggest that adult ligament ECM does not provide a metabolic signal to shut off the elastin gene and that adult cells remain responsive to external stimuli that may reinitiate high levels of elastin synthesis.