Nuclear phenotypes and DNA fragmentation in tendon fibrob- lasts of NOD mice

Changes in DNA/chromatin structure, ploidy degrees and cell death possibly caused by oxidative stress during the insulin-dependent diabetes have been reported for different cell types. However, all these studies have been carried in streptozotocin-induced diabetic rats or mice and showed contradictory results. In this work, nuclear phenotypes and DNA fragmentation were investigated in fibroblasts from mice spontaneously developing insulindependent diabetes (NOD) and compared with healthy (BALB/C) mice. Geometric, densitometric and textural parameters obtained for Feulgen-stained nuclei by image analysis were used to define nuclear phenotypes. Significant differences were observed for nuclear sizes and for densitometric and textural parameters of the tendon nuclei. Optical density, Feulgen-DNA values, transmittance variability per nucleus and nuclear entropy values were significantly higher in the NOD mice. The Feulgen-DNA amounts for the NOD and BALB/C mice were found to be distributed into several doubling Feulgen-DNA classes. The frequency of nuclei with the smallest Feulgen-DNA amounts, which may represent DNA fragmentation and loss, was lower in fibroblasts of the NOD mice (2.3%) in comparison to the BALB/C mice (38%). In contrast, the frequency of polyploid nuclei in NOD mice was higher (24.5%) than that in BALB/C mice (1.9%). Based on optical density, transmittance variability per nucleus, and nuclear entropy data, a larger contrast between highly and less densely packed states, was demonstrated for the fibroblasts of the NOD mice. Maybe the deeper condensation of the highly packed chromatin evident in NOD fibroblasts is related to silencing of some genes involved with changes in tendon supraorganization with the diabetes.