The Role of Adenosine Receptor Agonists in Regulation of Hematopoiesis
The review summarizes data evaluating the role of adenosine receptor signaling in murine hematopoietic functions. The studies carried out utilized either non-selective activation of adenosine receptors induced by elevation of extracellular adenosine or by administration of synthetic adenosine analogs having various proportions of selectivity for a particular receptor. Numerous studies have described stimulatory effects of non-selective activation of adenosine receptors, manifested as enhancement of proliferation of cells at various levels of the hematopoietic hierarchy. Subsequent experimental approaches, considering the hematopoiesis-modulating action of adenosine receptor agonists with a high level of selectivity to individual adenosine receptor subtypes, have revealed differential effects of various adenosine analogs. Whereas selective activation of A(1) receptors has resulted in suppression of proliferation of hematopoietic progenitor and precursor cells, that of A(3) receptors has led to stimulated cell proliferation in these cell compartments. Thus, A(1) and A(3) receptors have been found to play a homeostatic role in suppressed and regenerating hematopoiesis. Selective activation of adenosine A(3) receptors has been found to act curatively under conditions of drug- and radiation-induced myelosuppression. The findings in these and further research areas will be summarized and mechanisms of hematopoiesis-modulating action of adenosine receptor agonists will be discussed.