Apoptosis or programmed cell death is a physiological form of cell death that occurs in embryonic development and during involution of organs. It is characterized by distinct biochemical and morphological changes such as DNA fragmentation, plasma membrane blebbing and cell volume shrinkage. Many hormones, cytokines and growth factors are known to act as general and/or tissue-specific survival factors preventing the onset of apoptosis. In addition, many hormones and growth factors are also capable of inducing or facilitating programmed cell death under physiological or pathological conditions, or both. Steroid hormones are potent regulators of apoptosis in steroid-dependent cell types and tissues such as the mammary gland, the prostate, the ovary and the testis. Growth factors such as epidermal growth factor, nerve growth factor, platelet-derived growth factor (PDGF) and insulin-like growth factor-I act as survival factors and inhibit apoptosis in a number of cell types such as haematopoietic cells, preovulatory follicles, the mammary gland, phaeochromocytoma cells and neurones. Conversely, apoptosis modulates the functioning and the functional integrity of many endocrine glands and of many cells that are capable of synthesizing and secreting hormones. In addition, exaggeration of the primarily natural process of apoptosis has a key role in the pathogenesis of diseases involving endocrine tissues. Most importantly, in autoimmune diseases such as autoimmune thyroid disease and type 1 diabetes mellitus, new data suggest that the immune system itself may not carry the final act of organ injury: rather, the target cells (i.e. thyrocytes and beta cells of the islets) commit suicide through apoptosis. The understanding of how hormones influence programmed cell death and, conversely, of how apoptosis affects endocrine glands, is central to further design strategies to prevent and treat diseases that affect endocrine tissues. This short review summarizes the available evidence showing where and how hormones control apoptosis and where and how programmed cell death exerts modulating effects upon hormonally active tissues.
Growth factors in mammary gland function
