Detection and Quantification of Nuclear Morphology Changes in Apoptotic Cells by Fluorescence Microscopy and Subsequent Analysis of Visualized Fluorescent Signals

Background: Apoptosis results in specific and stage-dependent morphological alterations of the cell nucleus, including pyknosis and cell shrinking. The experimental investigation of apoptotic processes is still challenging and routinely based on the assessment of molecular events like chromatin fragmentation and caspase enzyme activity. Alternatively, the establishment of a fluorescence microscopy nuclear morphology assay would provide a simple and robust low-cost method for detection and quantification of apoptotic cascades. Materials and Methods: Model cell lines LNCaP and MDA-MB-231 were incubated in the presence of the apoptosis-inducer cycloheximide (CHX). After evaluation of apoptotic cascades by terminal deoxynucleotidyl transferase-dUTP nick-end labeling (TUNEL) assay, stained cell nuclei were analyzed regarding area, perimeter, major and minor axis, as well as brightness of nuclear fluorescence signal. Results: When compared to vehicle-treated control cells, administration of CHX led to significantly reduced cell growth and elevated rates of chromatin fragmentation of both cell lines as shown by cell counting and TUNEL assay, respectively. These apoptotic effects were accompanied by apoptosis-specific modulations of the nuclei demonstrated by diminished nuclear morphology parameters, such as area, perimeter, major and minor axis, as well as elevated levels of nuclear staining intensity. Conclusion: We present a computerized method for apoptosis detection and quantification using images of fluorescent dye-stained cell nuclei. The advantages of this nuclear morphology assay include the (i) ability to routinely assess apoptosis by a fast, highly reproducible low-cost technique, (ii) applicability of an experimental approach analyzing high numbers of single nuclei and (iii) detection of apoptosis in early, as well as late, stages of the apoptotic cascade.