Myelomatous plasma cells display an aberrant gene expression pattern similar to that observed in normal memory B cells.

Memory B cells (MBCs) remain in a quiescent state for years, expressing pro-survival and anti-apoptotic factors while repressing cell proliferation and activation genes. During their differentiation into plasma cells (PCs), their expression pattern is reversed, with a higher expression of genes related to cell proliferation and activation, and a lower expression of pro-survival genes. To determine whether myelomatous PCs (mPCs) share characteristics with normal PCs and MBCs and to identify genes involved in the pathophysiology of multiple myeloma (MM), we compared gene expression patterns in these three cell sub-types. We observed that mPCs had features intermediate between those of MBCs and normal PCs, and identified 3455 genes differentially expressed in mPCs relative to normal PCs but with a similar expression pattern to that in MBCs. Most of these genes are involved in cell death and survival, cell growth and proliferation and protein synthesis. According to our findings, mPCs have a gene expression pattern closer to a MBC than a PC with a high expression of genes involved in cell survival. These genes should be physiologically inactivated in the transit from MBC to PC, but remain overexpressed in mPCs and thus may play a role in the pathophysiology of the disease.

The CD27+ memory B cells display changes in the gene expression pattern in elderly individuals.

Memory B cells (MBCs) have a very long life-span as compared to naïve B cells (NBCs), remaining viable for years. It could predispose them to suffer misbalances in the gene expression pattern at the long term, which might be involved in the development of age-related B-cell disorders. In order to identify genes whose expression might change during life, we analyzed the gene expression patterns of CD27- NBCs versus CD27+ MBCs in young and old subjects. Using microarray assays we observed that the expression pattern of CD27- NBCs versus CD27+ MBCs is significantly different. Furthermore, in order to evaluate the age effect, we compared the gene expression pattern of young versus aged subjects in both cell populations. Interestingly, we did not find significant differences in the CD27- NBC population between young and aged individuals, whereas we found 925 genes differentially expressed in CD27+ MBCs. Among these genes, 193 were also differentially expressed in CD27+ MBCs as compared to CD27- NBCs, most of them involved in cell survival, cell growth and proliferation, cellular development and gene expression. We conclude that gene expression profiles of CD27- NBCs and CD27+ MBCs are different. Moreover, whereas the gene expression pattern of CD27+ MBCs varies with age, the same does not happen in CD27- NBCs. This suggests that MBCs undergo time-dependent changes which could underlie a higher susceptibility to dysfunction with age. This article is protected by copyright. All rights reserved.

A conditional mouse mutant in the tumor suppressor SdhD gene unveils a link between p21(WAF1/Cip1) induction and mitochondrial dysfunction.

Mutations in mitochondrial complex II (MCII; succinate dehydrogenase, Sdh) genes cause familiar pheochromocytoma/paraganglioma tumors. Several mechanisms have been proposed to account for Sdh-mutation-induced tumorigenesis, the most accepted of which is based on the constitutive expression of the hypoxia-inducible factor 1α (Hif1α) at normal oxygen tension, a theory referred to as "pseudo-hypoxic drive". Other molecular processes, such as oxidative stress, apoptosis, or chromatin remodeling have been also proposed to play a causative role. Nevertheless, the actual contribution of each of these mechanisms has not been definitively established. Moreover, the biological factors that determine the tissue-specificity of these tumors have not been identified. In this work, we made use of the inducible SDHD-ESR mouse, a conditional mutant in the SdhD gene, which encodes the small subunit of MCII, and that acts as a tumor suppressor gene in humans. The analysis of the Hif1α pathway in SDHD-ESR tissues and in two newly derived cell lines after complete SdhD loss -a requirement for hereditary paraganglioma type-1 tumor formation in humans- partially recapitulated the "pseudo-hypoxic" response and rendered inconsistent results. Therefore, we performed microarray analysis of adrenal medulla and kidney in order to identify other early gene expression changes elicited by SdhD deletion. Our results revealed that each mutant tissue displayed different variations in their gene expression profiles affecting to different biological processes. However, we found that the Cdkn1a gene was up-regulated in both tissues. This gene encodes the cyclin-dependent kinase inhibitor p21(WAF1/Cip1), a factor implicated in cell cycle, senescence, and cancer. The two SDHD-ESR cell lines also showed accumulation of this protein. This new and unprecedented evidence for a link between SdhD dysfunction and p21(WAF1/Cip1) will open new avenues for the study of the mechanisms that cause tumors in Sdh mutants. Finally, we discuss the actual role of Hif1α in tumorigenesis.

Gene and miRNA expression profiles of hematopoietic progenitor cells vary depending on their origin.

Hematopoietic progenitor cells (HPCs) from granulocyte colony-stimulating factor (G-CSF)-mobilized peripheral blood (G-PB), bone marrow (BM), or umbilical cord blood (CB) have differing biological properties and differing kinetics of engraftment post-transplantation, which might be explained, at least in part, by differing gene and miRNA expression patterns. To assess the differences in gene and miRNA expression, we analyzed whole genome expression profiles as well as the expression of 384 miRNAs in CD34(+) cells isolated from 18 healthy individuals (6 individuals per subtype of HPC source). We identified 43 genes and 36 miRNAs differentially expressed in the various CD34(+) cell sources. We observed that CD34(+) cells from CB and BM showed similar gene and miRNA expression profiles, whereas CD34(+) cells from G-PB had a very different expression pattern. Remarkably, 20 of the differentially expressed genes are targets of the differentially expressed miRNAs. Of note, the majority of genes differentially expressed in CD34(+) cells from G-PB are involved in cell cycle regulation, promoting the process of proliferation, survival, hematopoiesis, and cell signaling, and are targets of overexpressed and underexpressed miRNAs in CD34(+) cells from the same source. These data suggest significant differences in gene and miRNA expression among the various HPC sources used in transplantation. We hypothesize that the differentially expressed genes and miRNAs involved in cell cycle and proliferation might explain the differing kinetics of engraftment observed after transplantation of hematopoietic stem cells obtained from these different sources.

Granulocyte colony-stimulating factor produces long-term changes in gene and microRNA expression profiles in CD34+ cells from healthy donors.

Granulocyte colony-stimulating factor is the most commonly used cytokine for the mobilization of hematopoietic progenitor cells from healthy donors for allogeneic stem cell transplantation. Although the administration of this cytokine is considered safe, knowledge about its long-term effects, especially in hematopoietic progenitor cells, is limited. On this background, the aim of our study was to analyze whether or not granulocyte colony-stimulating factor induces changes in gene and microRNA expression profiles in hematopoietic progenitor cells from healthy donors, and to determine whether or not these changes persist in the long-term. For this purpose, we analyzed the whole genome expression profile and the expression of 384 microRNA in CD34(+) cells isolated from peripheral blood of six healthy donors, before mobilization and at 5, 30 and 365 days after mobilization with granulocyte colony-stimulating factor. Six microRNA were differentially expressed at all time points analyzed after mobilization treatment as compared to the expression in samples obtained before exposure to the drug. In addition, 2424 genes were also differentially expressed for at least 1 year after mobilization. Of interest, 109 of these genes are targets of the differentially expressed microRNA also identified in this study. These data strongly suggest that granulocyte colony-stimulating factor modifies gene and microRNA expression profiles in hematopoietic progenitor cells from healthy donors. Remarkably, some changes are present from early time-points and persist for at least 1 year after exposure to the drug. This effect on hematopoietic progenitor cells has not been previously reported.

Impact of constitutional polymorphisms in VCAM1 and CD44 on CD34+ cell collection yield after administration of granulocyte colony-stimulating factor to healthy donors.

UNLABELLED: Background The number of CD34(+) cells mobilized from bone marrow to peripheral blood after administration of granulocyte colony-stimulating factor varies greatly among healthy donors. This fact might be explained, at least in part, by constitutional differences in genes involved in the interactions tethering CD34(+) cells to the bone marrow. DESIGN AND METHODS: We analyzed genetic characteristics associated with CD34(+) cell mobilization in 112 healthy individuals receiving granulocyte colony-stimulating factor (filgrastim; 10 µg/kg; 5 days). RESULTS: Genetic variants in VCAM1 and in CD44 were associated with the number of CD34(+) cells in peripheral blood after granulocyte colony-stimulating factor administration (P = 0.02 and P = 0.04, respectively), with the quantity of CD34(+) cells ×106/kg of donor (4.6 versus 6.3; P < 0.001 and 7 versus 5.6; P = 0.025, respectively), and with total CD34(+) cells ×106 (355 versus 495; P = 0.002 and 522 versus 422; P = 0.012, respectively) in the first apheresis. Of note, granulocyte colony-stimulating factor administration was associated with complete disappearance of VCAM1 mRNA expression in peripheral blood. Moreover, genetic variants in granulocyte colony-stimulating factor receptor (CSF3R) and in CXCL12 were associated with a lower and higher number of granulocyte colony-stimulating factor-mobilized CD34(+) cells/µL in peripheral blood (81 versus 106; P = 0.002 and 165 versus 98; P=0.02, respectively) and a genetic variant in CXCR4 was associated with a lower quantity of CD34(+) cells ×106/kg of donor and total CD34(+) cells ×106 (5.3 versus 6.7; P = 0.02 and 399 versus 533; P = 0.01, respectively). Conclusions In conclusion, genetic variability in molecules involved in migration and homing of CD34(+) cells influences the degree of mobilization of these cells.