ANANDAMIDE, A NATURAL LIGAND FOR THE PERIPHERAL CANNABINOID RECEPTOR IS A NOVEL SYNERGISTIC GROWTH-FACTOR FOR HEMATOPOIETIC-CELLS

We recently demonstrated that the gene encoding the peripheral. cannab inoid receptor (Cb2) may be a proto-oncogene involved in murine myeloi d leukemias. We show here that Cb2 may have a role in hematopoietic de velopment, RNAse protection analysis showed that Cb2 is normally expre ssed in spleen and thymus. Cb2 mRNA is also expressed in 45 of 51 cell lines of distinct hematopoietic lineages, ie, myeloid, macrophage, ma st, B-lymphoid, T-lymphoid, and erythroid cells, The effect of the fat ty acid anandamide, an endogenous ligand for cannabinoid receptors, on primary murine marrow cells and hematopoietic growth factor (HGF)-dep endent cell lines was then investigated. in vitro colony cultures of n ormal mouse bone marrow cells showed anandamide to potentiate interleu kin-3 (IL-3)-induced colony growth markedly, Whereas HGFs alone stimul ate proliferation of ?he various cell lines in serum-free culture only weakly, anandamide enhances the proliferative response of the cell li nes to HGFs profoundly. This was apparent for responses induced by IL- 3, granulocyte-macrophage colony-stimulating factor, granulocyte colon y-stimulating factor, and erythropoietin. Anandamide was already effec tive at concentrations as low as 0.1 to 0.3 mu mol/L and plateau effec ts were reached at 0.3 to 3 mu mol/L. The addition of anandamide as si ngle growth factor had no effect, The costimulatory effect of anandami de was nor evident when cells were cultured with fetal calf serum (FCS ), suggesting that FCS contains anandamide or another ligand capable o f activating the peripheral cannabinoid receptor. Other cannabinoid li gands did not enhance the proliferative responsiveness of hematopoieti c cells to HGFs. Transfection experiments of Cb2 in myeloid 32D cells showed that anandamide specifically activates proliferation through ac tivation of the peripheral cannabinoid receptor, Anandamide appears to he a novel and synergistic growth stimulator for hematopoietic cells. (C) 1997 by The American Society of Hematology.