Expression of PTHrP and the PTH PTHrP receptor in purified alveolar epithelial cells, myoepithelial cells, and stromal fibroblasts derived from the lactating rat mammary gland

Parathyroid hormone-related protein (PTHrP) is produced by the lactating ma mmary gland and secreted into the milk; however, the function of PTHrP duri ng lactation is unknown. Since messenger RNA for both PTHrP and the PTH/PTH rP receptor have been demonstrated within mammary tissue, a paracrine or au tocrine function for PTHrP has been proposed. To investigate this hypothesi s in lactating tissue, the expression of PTHrP and the PTH/PTHrP receptor w as examined in purified subpopulations of cells derived from lactating rat mammary glands. Subpopulations of stromal, myoepithelial, and alveolar epit helial cells were isolated from mammary tissue using enzymatic digestion an d immunomagnetic purification. Isolated cells were phenotypically character ized by immunohistochemistry and ultrastructural morphology. The purity of the separated alveolar and myoepithelial cells was assessed ultrastructural ly and ranged from 91 to 96%. Messenger RNA and protein expression of PTHrP and the PTH/PTHrP receptor were examined using reverse transcription polym erase chain reaction, immunohistochemistry, and Western blot analysis, resp ectively. PTHrP mRNA and protein were expressed in alveolar epithelial cell s and stromal fibroblasts, whereas PTH/PTHrP receptor mRNA and protein were expressed in all three cell types. The expression patterns for PTHrP and t he PTH/PTHrP receptor support an autocrine or paracrine function for PTHrP in alveolar epithelial cells and stromal fibroblasts and a paracrine functi on for PTHrP in myoepithelial cells in the rat mammary gland during lactati on. (C) 1999 Academic Press.