Objective: The cellular and molecular mechanisms of hematopoietic stimulation have been studied. However, an understanding of negative effects in the hematopoietic system remains elusive. To this end, we studied the effects of vasoactive intestinal peptide (VIP) on bone marrow (BM) progenitors.
Materials and methods: Different BM cell subsets were used to perform clonogenic assay for granulocytic (CFU-GM) or erythroid (BFU-E and CFU-E) progenitors with 10(-7)-10(-13) M VIP. The relevant receptor was verified with specific antagonists, or agonists, semi-quantitative RT-PCR, and chemical cross-linking studies with stromal membranes.
Results: Assays performed with unfractionated mononuclear cells and enriched CD34(+) cells showed dose-dependent inhibition on BM progenitors with significant inhibition up to 10(-10) M. Nylon wool separated cells, which depleted stroma, reversed the inhibitory effects of VIP between 10 and 20%. Combined experimental evaluation indicated that the effects of VIP on BM functions are mediated through the type 1 receptor (VPAC1). VIP induced the production of TGF-beta and TNF-alpha in BM mononuclear cells and stroma. These cytokines are partly involved in reversing the suppressive effects of VIP on CFU-GM.
Conclusions: The effect of VIP on BM progenitors could be mediated through direct and indirect mechanism. Direct effects were evident by the suppressive effects of VIP on clonogenic assays with highly purified CD34(+) cells. Indirect effects were mediated through putative functions of the stromal cells and the production of TGF-beta and TNF-alpha.