Proliferating Cell Nuclear Antigen (PCNA) Detection of Cellular Proliferation in Hypothyroid and Hyperthyroid Rat Hearts

Immunocytochemical techniques examining the expression of cell proliferation-related markers such as proliferating cell nuclear antigen (PCNA), may be employed to provide visual and quantitative evidence of cell proliferation. The efficacy of this method in frozen samples was tested on sections of 2-day-old rat heart. Mouse monoclonal anti-PCNA and goat anti-mouse IgG2aperoxidase-conjugated antibodies were applied to tissue cross-sections. PCNA positive (PCNA+) cells were evident in these sections as intensely stained, dark brown nuclei. This method was then applied to the hearts of four groups of adult rats (1) 1 month hyperthyroid, (2) 1 month hypothyroid, (3) 6 days hyperthyroid following 1 month hypothyroidism, or (4) euthyroid, in order to assess the ability of identifying and quantifying PCNA+ cell types (myocyte, endothelial, or remaining, “other” cells). Serial cross-sections were prepared, half of the sections processed using the PCNA technique, while corresponding sections were stained with hematoxylin and eosin. Identification of PCNA+ cell types was made by comparison of PCNA with H&E sections. PCNA labeling indices for a given cell type were expressed as the proportion of PCNA+ nuclei per 1000 nuclei. No PCNA+ myocyte nuclei were observed in any of the adult hearts. Only hypothyroid/hyperthyroid demonstrated significantly higher PCNA labeling of endothelial and “other” nuclei compared to euthyroid. This finding agrees with previous morphometric data which suggested capillary growth in these hearts. Results demonstrate that quantitation of PCNA expression on frozen heart tissue is possible, and can be used to provide direct, discernible evidence for cell proliferation.