Abstract
To characterize the transcriptional program that governs terminal granulocytic differentiation in vivo, we performed comprehensive microarray analyses of human bone marrow (BM) populations highly enriched in promyelocytes (PMs), myelocytes/metamyelocytes (MYs), and neutrophils (bm-PMNs). These analyses identified 11,310 genes involved in differentiation, of which 6,700 were differentially regulated including granule proteins and surface receptors previously not identified in neutrophils. Functional clustering demonstrated that differentially expressed genes were assigened to all of the major gene categories including apoptosis, cell cycle, chaperones, enzymes, immunity proteins, kinases, motor proteins, signal transducers, structural proteins, and transcription factors. In an attempt to define the developmental distance between PM, MY, and bm-PMN populations, we assessed the Pearsons correlation coefficient (γ) by correlating the transcriptomes (=all 44.760 probe sets, Affymetrix) of BM populations. The correlation coefficients among replicates of BM populations were in the range of 0.97–0.99. On the other hand the correlation coefficients between BM populations were 0.81 (γPM - MY), 0.79 (γMY - bm-PMN), and 0.52 (γPM - bm-PMN), and thus, provided a useful quantitative measure reflecting the hierarchical relationship between the three BM populations. Additional correlation of bm-PMN and peripheral blood-PMN transcriptomes revealed a high similarity of both populations (γbm-PMN - pb-PMN=0.95) indicating a termination of granulocytic differentiation in the BM microenvironment during steady state hematopoesis. Differentiation of PMs towards MYs was accompanied by a marked decline of proliferative and general cellular activity as defined by downregulation of E2F target genes, cyclin dependent kinases 2/4/6, and various metabolic, proteasomal, and mitochondrial genes. Expression patterns of apoptosis genes indicated death control by the p53-pathway in PMs and by death receptor pathways in bm-PMNs. Effector proteins critical for host defense were expressed successively throughout granulocytic differentiation, whereas receptors and receptor ligands essential for the activation of the host defense program were terminally upregulated in bm-PMNs. The upregulation of ligand-receptor pairs, which are defined inducers as well as target genes of NF-kB, suggests a constitutive activation of NF-kB in bm-PMNs by autocrine loops. Overall, these results define a granulocytic differentiation model governed by a highly coordinated fail-safe program, which promotes completion of differentiation before cells gain responsiveness towards activating stimuli that accompany infections.
Author notes
Corresponding author
