Interleukin-6 deficiency affects bone marrow stromal precursors, resulting in defective hematopoietic support

Abstract

Interleukin-6 (IL-6) is a critical factor in the regulation of stromal function and hematopoiesis. In vivo bromodeoxyuridine incorporation analysis indicates that the percentage of Lin ؊ Sca-1 ؉ hematopoietic progenitors undergoing DNA synthesis is diminished in IL-6-deficient (IL-6 ؊/؊ ) bone marrow (BM) compared with wild-type BM. Reduced proliferation of IL-6 ؊/؊ BM progenitors is also observed in IL-6 ؊/؊ long-term BM cultures, which show defective hematopoietic support as measured by production of total cells, granulocyte macrophage-colony-forming units (CFU-GMs), and erythroid burstforming units (BFU-Es). Seeding experiments of wild-type and IL-6 ؊/؊ BM cells on irradiated wild-type or IL-6-deficient stroma indicate that the hematopoietic defect can be attributed to the stromal and not to the hematopoietic component. In IL-6 ؊/؊ BM, stromal mesenchymal precursors, fibroblast CFUs (CFU-Fs), and stroma-initiating cells (SICs) are reduced to almost 50% of the wild-type BM value. Moreover, IL-6 ؊/؊ stromata show increased CD34 and CD49e expression and reduced expression of the membrane antigens vascular cell adhesion molecule-1 (VCAM-1), Sca-1, CD49f, and Thy1. These data strongly suggest that IL-6 is an in vivo growth factor for mesenchymal precursors, which are in part implicated in the reduced longevity of the long-term repopulating stem cell compartment of IL-6 ؊/؊ mice. IntroductionInterleukin-6 (IL-6) is a multifunctional cytokine with a major role in inflammatory responses and is the primary inducer of acutephase proteins. 1 IL-6 also regulates the proliferation and differentiation of hematopoietic cells from several lineages at different maturation stages. 1 In synergy with IL-3, IL-6 stimulates proliferation of granulocyte-macrophage, megakaryocyte, and erythroid progenitors. [2][3][4][5] This cooperation has also been shown in several in vivo model systems designed to evaluate the effect of IL-6 on the stem cell compartment. 3,4,6 The specific contribution of IL-6 to homeostasis in the lymphohematopoietic system has been evaluated in the IL-6 Ϫ/Ϫ mouse model, which showed a clear reduction in the number of the earliest clonogenic precursors and in the function of long-term repopulating stem cells (LTRSCs). 7 IL-6 Ϫ/Ϫ mice show a decrease in absolute numbers of spleen colonyforming units (CFU-Ss) at day 12 and of pre-CFU-S hematopoietic progenitors, as well as a deficit in the LTRSC compartment. 7 In addition to the effects in early hematopoiesis, IL-6 Ϫ/Ϫ mice show defects in T-and B-cell function 8 and in acute-phase responses. 9 These results strongly suggest an important in vivo role for IL-6 in the survival and self-renewal of hematopoietic stem cells (HSCs) and early progenitors.IL-6 is produced by a variety of cells including T and B cells, macrophages, fibroblasts, bone marrow stromal cells, and mesenchymal cells. [10][11][12] The adherent stromal cell layer in long-term bone marrow cultures (LTBMCs) is necessary for balanced proliferation and differentiation of hematopoietic progenitors. 13 ...

Melphalan exposure induces an interleukin-6 deficit in bone marrow stromal cells and osteoblasts

“…In the bone marrow microenvironment, IL-6 regulates B-cell differentiation and stimulation of T-cells, both necessary to maintain the immune system[10]. An IL-6 deficiency in the microenvironment decreases DNA synthesis in normal hematopoietic progenitor cells[11]. Long-term bone marrow cultures established from IL-6 knockout mice had delayed stromal cell layer development[11].…”

“…An IL-6 deficiency in the microenvironment decreases DNA synthesis in normal hematopoietic progenitor cells[11]. Long-term bone marrow cultures established from IL-6 knockout mice had delayed stromal cell layer development[11]. Additionally, reduced hematopoietic support activity, measured by CFU-GM, BFU-E, and cobblestone areas, which are characteristic of active hematopoietic proliferation was noted in the absence of IL-6 as well [11].…”

“…Long-term bone marrow cultures established from IL-6 knockout mice had delayed stromal cell layer development[11]. Additionally, reduced hematopoietic support activity, measured by CFU-GM, BFU-E, and cobblestone areas, which are characteristic of active hematopoietic proliferation was noted in the absence of IL-6 as well [11]. Moreover, IL-6 deficient mice have impaired immune and acute-phase responses[12].…”

Enhancing the efficacy of mesenchymal stem cell therapy

“…Of note, a lack of bone marrow support for cardiac repair in aged animals has been documented [110] , indicating that the MSC-initiated healing process may be compromised by the impaired tissue cross-talk mechanism, leading to a greater susceptibility of the old heart to ischemic injury and an inefficient response to protective interventions. IL-6 deficiency, for instance, affects bone marrow stromal precursor cells, resulting in defective hematopoietic support [54] . This host tissue impairment represents a significant hurdle to regenerative medicine because most preclinical therapeutic studies are based on the use of young animals, but stem cell therapy typically targets the elderly.…”

“…This finding prompted us to adopt an MSC-boosting protocol based on 4 g/mL poly(I:C) for 24 h, which induced IL-6, IL-10, IL-11, LIF, VEGF, SDF1 and HGF without IL-6 and a host of other cytokines similar to the antiviral response mediated by dsRNA-sensing PRRs [46] . Given the prominent roles of IL-6 in stem cell maintenance and cardiac regeneration [6,[54][55][56] , transient low-dose priming of MSC TLR2/4 may also represent a physiologically significant mechanism for tissue repair. It has indeed been shown recently that TLR2/6-dependent stimulation of MSCs promotes angiogenesis in vitro and in vivo in bone tissue engineering [57] .…”