Inflammatory Changes in Bone Marrow Microenvironment Associated with Declining B Lymphopoiesis

Abstract

B lymphopoiesis arrests precipitously in rabbits such that by 2 to 4 months of age, prior to sexual maturity, little to no B lymphopoiesis occurs in the bone marrow (BM). Previously, we showed that in mice, adipocytes inhibit B lymphopoiesis in vitro by inducing inflammatory myeloid cells which produce IL-1β. Here, we characterized rabbit BM after the arrest of B lymphopoiesis and found a dramatic increase in fat, increased CD11b+ myeloid cells, and upregulated expression of the inflammatory molecules, IL-1β and S100A9 by the myeloid cells. We added BM fat, CD11b+ myeloid cells, and recombinant S100A9 to B lymphopoiesis cultures and found that they inhibited B lymphopoiesis and enhanced myelopoiesis. Unlike IL-1β which inhibits B lymphopoiesis by acting on early lymphoid progenitors, S100A9 inhibits B lymphopoiesis by acting on myeloid cells and promoting the release of inflammatory molecules, including IL-1β. Many molecules produced by adipocytes activate the NLRP3 inflammasome, and the NLRP3 inhibitor, glybenclamide restored B lymphopoiesis and minimized induction of myeloid cells induced by adipocyte-conditioned medium in vitro. We suggest that fat provides an inflammatory microenvironment in the BM, and promotes/activates myeloid cells to produce inflammatory molecules such as IL-1β and S100A9, which negatively regulate B lymphopoiesis.

CellFishing.jl: an ultrafast and scalable cell search method for single-cell RNA-sequencing

“…Similarly, H2-Ab1, H2-Eb1, and H2-Aa, which encode components of the major histocompatibility complex present on the surface of antigen-presenting cells, are negatively regulated, suggesting that immature B cells do not actively express these genes as much as mature B cells. We also found that S100a8, Betas, S100a9, Fos, and Camp are positively regulated in immature B cells; although these genes appear to be upregulated in a tissue-specific manner rather than in a cell type-specific manner, cytokines encoded by S100a8 and S100a9 were recently reported to regulate B lymphopoiesis in rabbit bone marrow [33]. Overall, our method detected reasonable DEGs in many cases; however, we could not find evidence implying the relationship between Malat1 (a long intergenic noncoding RNA) and B-cell development, and therefore, we hypothesize that this is a false positive due to its high variability regardless of cell type.…”

CellFishing.jl: an ultrafast and scalable cell search method for single-cell RNA sequencing

“…Similarly, H2-Ab1, H2-Eb1, and H2-Aa, which encode components of the major histocompatibility complex present on the surface of antigen-presenting cells, are negatively regulated, suggesting that immature B cells do not actively express these genes as much as mature B cells. We also found that S100a8, Beta-s, S100a9, Fos, and Camp are positively regulated in immature B cells; although these genes appear to be upregulated in a tissue-specific manner rather than in a cell type-specific manner, cytokines encoded by S100a8 and S100a9 were recently reported to regulate B lymphopoiesis in rabbit bone marrow [32]. Overall, our method detected reasonable DEGs in many cases; however, we could not find evidence implying the relationship between Malat1 (a long intergenic noncoding RNA) and B-cell development, and therefore, we hypothesize that this is a false positive due to its high variability regardless of cell type.…”

Obesity Accelerates Age Defects in Mouse and Human B Cells

“…In mice fed a high-fat diet (HFD), early B cell development is characterized by decreased frequencies of B cell subsets in the bone marrow (BM) and reduced expression of early lymphoid commitment markers such as the B cell transcription factor PAX5 ( 44 ). Mechanistic experiments using co-cultures of BM cells with the OP9 stromal cell line have shown that BM adipocytes secrete soluble factors that drive the development of myeloid-derived suppressor cells (MDSCs) ( 45 , 46 ). MDSC inhibition of B lymphopoiesis is mediated by MDSC-derived IL-1β and the inflammatory molecule complex called calprotectin, suggesting that these may be therapeutic targets for the restoration of B lymphoiesis in obesity and aging.…”