Bone marrow microenvironmental changes in aged mice compromise V(D)J recombinase activity and B cell generation

Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655, USA.
Seminars in Immunology (Impact Factor: 5.17). 11/2005; 17(5):347-55. DOI: 10.1016/j.smim.2005.05.012
Source: PubMed


B cell generation and immunoglobulin (Ig) diversity in mice is compromised with aging. Our recent work sought to understand mechanism(s) that contribute to reduced B cell production in aged mice. Using in vivo labeling, we found that reduction in marrow pre-B cells reflects increased attrition during passage from the pro-B to pre-B cell pool. Analyses of reciprocal bone marrow (BM) chimeras reveal that the production rates of pre-B cells are controlled primarily by microenvironmental factors, rather than intrinsic events. To understand changes in pro-B cells that could diminish production of pre-B cells, we evaluated rag2 expression and V(D)J recombinase activity in pro-B cells at the single cell level. The percentage of pro-B cells that express rag2 is reduced in aged mice and is correlated with both a loss of V(D)J recombinase activity in pro-B cells and reduced numbers of pre-B cells. Reciprocal BM chimeras revealed that the aged microenvironment also determines rag2 expression and recombinase activity in pro-B cells. These observations suggest that extrinsic factors in the BM that decline with age are largely responsible for less efficient V(D)J recombination in pro-B cells and diminished progression to the pre-B cell stage. These extrinsic factors may include cytokines and chemokines derived from BM stromal cells that are essential to the development of B cell precursors. The changes during aging within the BM hematopoietic microenvironment most likely are linked to the physiology of aging bone. Bone degrades with age (osteoporosis) due to decreased formation of new bone by osteoblasts. Marrow stem cells (MSC) are considered the progenitor of both adipocytes, osteoblasts and hematopoietic stromal cells and a controlled reciprocal regulation exists of osteoblast versus adipocyte differentiation; with age adipocytes increase, and osteoblast decrease. It is possible that stromal cell generation from MSC is compromised during aging. Currently, understanding of BM microenvironmental factors that regulate rag gene expression is very limited. However, as early progenitors differentiate, it is increasing clear that a limited set of transcription factors (e.g. ikaros, PU.1, E2A, EBF, pax5) regulate B-lineage specific genes, and that expression and stability of these factors is responsive to the microenvironment. Current and future work by several groups will strive to understand mechanisms that regulate these factors and how aging impacts these regulatory circuits.

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Available from: Rachel M Gerstein
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    • "In contrast to red blood cells, platelets and the myeloid lineage cells, production of the lymphoid lineage is considerably diminished with age both in humans and mice [1], but answers to why and how this happens are still lacking. Almost all present knowledge of age-related transcriptional changes in precursor B cells has been derived from mice, and points to alterations both in key proteins driving the differentiation [2]–[7], and to modification in the supporting microenvironment [8], [9]. So far, only two studies in humans have analyzed global gene expression employing developing precursor B cells from children [10] and adults [11], respectively; neither of the publications includes both age groups. "
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    ABSTRACT: Molecular mechanisms explaining age-related changes in the bone marrow with reduced precursor B cell output are poorly understood. We studied the transcriptome of five precursor B cell subsets in individual bone marrow samples from 4 healthy children and 4 adults employing GeneChip® Human Exon 1.0 ST Arrays (Affymetrix®) and TaqMan® Array MicroRNA Cards (Life Technologies™). A total of 1796 mRNAs (11%) were at least once differentially expressed between the various precursor B cell subsets in either age group (FDR 0.1%, p≤1.13×10(-4)) with more marked cell stage specific differences than those related to age. In contrast, microRNA profiles of the various precursor B cell subsets showed less hierarchical clustering as compared to the corresponding mRNA profiles. However, 17 of the 667 microRNA assays (2.5%) were at least once differentially expressed between the subsets (FDR 10%, p≤0.004). From target analysis (Ingenuity® Systems), functional assignment between postulated interacting mRNAs and microRNAs showed especially association to cellular growth, proliferation and cell cycle regulation. One functional network connected up-regulation of the differentiation inhibitor ID2 mRNA to down-regulation of the hematopoiesis- or cell cycle regulating miR-125b-5p, miR-181a-5p, miR-196a-5p, miR-24-3p and miR-320d in adult PreBII large cells. Noteworthy was also the stage-dependent expression of the growth promoting miR-17-92 cluster, showing a partly inverse trend with age, reaching statistical significance at the PreBII small stage (up 3.1-12.9 fold in children, p = 0.0084-0.0270). The global mRNA profile is characteristic for each precursor B cell developmental stage and largely similar in children and adults. The microRNA profile is much cell stage specific and not changing much with age. Importantly, however, specific age-dependent differences involving key networks like differentiation and cellular growth may indicate biological divergence and possibly also altered production potential with age.
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    • "This is most readily observed as a decline in the number of pre-B cells within the bone marrow, but more recent studies also indicate that early B cell precursors, including common lymphoid progenitors and pro-B cells, are also adversely affected by the aging process (Riley et al., 1991; Stephan et al., 1996; Sherwood et al., 1998; Miller et al., 2003; Van der Put et al., 2003; Labrie et al., 2005). The consequences of diminished B cell development in old mice are not well characterized, but may contribute to alterations in B cell longevity (Johnson et al., 2002; Kline et al., 1999; Labrie et al., 2005) and composition of the B cell receptor repertoire (Klinman et al., 1997; Wilson et al., 2005) during senescence. Whether similar alterations in B cell development are observed in humans is speculative; however, naïve B cells are reduced in number in the periphery in old age (Nunez et al., 1996; Huppert et al., 1999; Ogawa et al., 2000; Rossi et al., 2003) Previously, it has been shown that old murine bone marrow cells deficient in surface IgM, when used as a source of pre-B cells, generated new B cells with substantial changes in the antibody repertoire to the phosphorylcholine (PC) epitope (Klinman et al., 1997). "
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