Pro-apoptotic effects of parathyroid hormone in intestinal cells

Abstract

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 evaluate the role of PTH in the intestinal apoptosis using the 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 the 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 used of propidium iodide shows that the hormone increases the number of red-stained (dead) cells (+ 178%, 5 days). Moreover, we found that the hormone induces 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 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.