Incresead DNA content and nuclear phenotypic alterations associated with mechanical load in wrap-around joint chiken tendons*

ABSTRACT

Tendons are highly superstructures with a capacity to respond to variation in load. Fibroblasts in tendon cartilage respond to mechanical stimuli through metaplasia and the expression of new synthetic activities fallowing gene activation. In study we examined the changes in the nuclear phenotypes of calcaneus communis and flexor digitorum superficiales tendons in 21-and 41-day-old chickens. Video image analysis was used to examine fibroblasts in Feugen-stained tendon sections. The parameters studient included integrated optical desnsity, optical density, nuclear area, feret-ratio, gray average. standard deviation of the gray average per nucleus, and entropy. Compared to diploid chicken erythocytes, fibroblasts had larger amounts of DNA in the G2 phase and showed polyploidy. The DNA content of the fibroblasts incresead with age. In both tendons, the nuclei of 41-day-old chickens had a higher DNA content and optical density, i.e. more packed chromatin, than in 21-day-old chickens. The linear correlation of nuclear area vs integrated optical density (R2 por cento) was greater in flexor digitorum superficialis than in calcaneus communis nuclei. The latter showed a marked dispersion around the fitted line, with R2=0,44 por cento for 41-day-old chickens. The high feret-ratios of calcaneus communis nuclei indicated more spherical nuclei. These results show that fibroblast nuclei in both types of tendon respond to a compressive load around the articulation type involved. Molecular order and collagen fiber crystallinity apparently contribute to signaling by the extracellular matrix to the cells analized here.