Nuclear image changes in cells originating from tenocytes that migrated from tendon explants

Tenocytes migrating from cultured rat tendon explants have been shown to aggregate and gradually align in parallel rows with the tendon's long axis as the explant culture period extends to 12 days, leading to structure remodeling of collagen bundles. It is well established that tendon architecture and mechanical load influence fibroblast phenotypes. In this study, we examined cells derived from tenocytes that migrated from tendon explants cultured for 8 and 12 days to determine whether their chromatin supraorganization differed based on their varying organization. Image analysis and immunofluorescence were used to assess features indicative of chromatin transcriptional expression or repression activities. While no differences occurred in Feulgen-DNA amounts, DNA methylation markers, or distribution of acetylated H3K9 when comparing cells derived from 8- and 12-day tendon cultures, we observed differences in light absorbance, fractal dimension, and concentration of stained chromatin at the image periphery (margination). Increased levels of the trimethylated H3K27 and decreased levels of 5-hydroxymethylcytosine (both repressive markers) in cells derived from the 12-day tendon explants provide evidence of chromatin condensation at that time. Elevated levels of the translational activating markers H3K4me2 and H3K4me3 in cells derived from tenocytes that extensively aligned in parallel rows in the explants during the extended tendon culture period, may suggest acquired or enhanced expression of specific gene sets, despite the concurrent indication of greater overall chromatin compaction. Further assays are needed to explore whether these findings correlate with a differential potential of tenocyte-derived cells for extracellular matrix synthesis and their implication in practical bioengineering applications.