Pro-apoptotic effects of parathyroid hormone in intestinal cells

Apoptosis, a form of programmed cell death, is a process fundamental to normal growth and development, immune response, tissue remodeling after injury or insult, and homeostasis of the intestinal epithelium. Recently, it has become apparent that apoptosis is a crucial process in skeletal development and homeostasis, and that signaling by the parathyroid hormone (PTH) receptor can either promote or suppress apoptosis depending on the cellular context. In this study, we evaluated the role of PTH in intestinal apoptosis using human colonic Caco-2 cells. To that end, Caco-2 cells were exposed to PTH (10-8 mol/L) for 1-5 days. Evaluation of cell survival by use of resazurin staining, 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) staining, and crystal violet staining revealed that PTH treatment diminishes the number of viable cells. Assessment of cells after PTH treatment by use of propidium iodide showed that the hormone increased the number of red-stained (dead) cells (178%, 5 days). Moreover, we found that the hormone induced disruption of actin filaments with changes to cellular shape, alteration of cell-to-cell junctions, externalization of membrane phosphatidylserine, chromatin condensation, and DNA fragmentation of the nucleus, which are morphological features consistent with apoptosis. In addition, PTH treatment revealed a cytosolic staining pattern of 14-3-3. However, the significance of such differential localization for 14-3-3 function remains unknown. Taken together, the present study suggests that PTH promotes apoptosis in Caco-2 intestinal cells.