Endocrine Abstracts

Objectives: Glucocorticoids (GCs) intervene in different physiological activities in almost all systems of the human organism. However, GCs are also potent inducers of apoptosis in many cell types and tissues. It is known, that glucocorticoid-induced apoptosis affects the musculoskeletal system, circulatory system, nervous system, endocrine system, reproductive system, and the immune system. Nevertheless, the exact mechanisms of GCs action in human normal hematopoiesis are still not clear. Besides, direct effects of GCs on hematopoietic stem and progenitor cells (HSPCs) may be obscured in the intact human organism. For this reason, the effects of GCs on hematopoietic system were analyzed in studies performed in vitro, and we used primary human CD34+ HSPCs as a model system.

Materials and methods: Human cord blood-derived CD34+-enriched hematopoietic progenitor cells were examined for expression of different glucocorticoid receptors (GR-α and GR-β) at the protein level by immunocytofluorescence. In addition, the GR activity status was analyzed by detection of phosphorylated form of GR-α, the most biologically active form of GRs. Furthermore, quantitative studies of GC-dependent biological stimulation of CD34+ HSPCs were performed, and the apoptosis activity was estimated by qRT-PCR analysis of selected apoptotic genes expression, including BAX, BCL-2 and BCL-xL.

Results: It was found that GRs expression, in the total and phosphorylated forms, were detected at the protein level in the population of human early HSPCs. Moreover, exposure of human CD34+ HSPCs to non-physiological concentrations of GCs (0, 10−5, 10−4 M/l of hydrocortisone) significantly induced apoptosis in those cells, and resulted in the increased expression of mRNA for apoptosis-related BAX gene and anti-apoptotic BCL-2 and BCL-xL, when compared to established physiological dose of GC (10−6 M/l). Importantly, we observed that higher GCs doses considerably increased BAX: BCL-2 ratio.

Conclusions: This study importantly augments the current knowledge about the role of glucocorticoids in normal human hematopoiesis. Our data may provide basis for creating novel therapeutic strategies for hematologic complications in endocrine diseases.