Bone marrow-specific knock-in of a non-activatable Ikkα kinase mutant influences haematopoiesis but not atherosclerosis in Apoe-deficient mice

PLoS One. 2014 Feb 3;9(2):e87452. doi: 10.1371/journal.pone.0087452. eCollection 2014.

Abstract

Background: The Ikkα kinase, a subunit of the NF-κB-activating IKK complex, has emerged as an important regulator of inflammatory gene expression. However, the role of Ikkα-mediated phosphorylation in haematopoiesis and atherogenesis remains unexplored. In this study, we investigated the effect of a bone marrow (BM)-specific activation-resistant Ikkα mutant knock-in on haematopoiesis and atherosclerosis in mice.

Methods and results: Apolipoprotein E (Apoe)-deficient mice were transplanted with BM carrying an activation-resistant Ikkα gene (Ikkα(AA/AA)Apoe(-/-) ) or with Ikkα(+/+)Apoe(-/-) BM as control and were fed a high-cholesterol diet for 8 or 13 weeks. Interestingly, haematopoietic profiling by flow cytometry revealed a significant decrease in B-cells, regulatory T-cells and effector memory T-cells in Ikkα(AA/AA)Apoe(-/-) BM-chimeras, whereas the naive T-cell population was increased. Surprisingly, no differences were observed in the size, stage or cellular composition of atherosclerotic lesions in the aorta and aortic root of Ikkα(AA/AA)Apoe(-/-) vs Ikkα(+/+)Apoe(-/-) BM-transplanted mice, as shown by histological and immunofluorescent stainings. Necrotic core sizes, apoptosis, and intracellular lipid deposits in aortic root lesions were unaltered. In vitro, BM-derived macrophages from Ikkα(AA/AA)Apoe(-/-) vs Ikkα(+/+)Apoe(-/-) mice did not show significant differences in the uptake of oxidized low-density lipoproteins (oxLDL), and, with the exception of Il-12, the secretion of inflammatory proteins in conditions of Tnf-α or oxLDL stimulation was not significantly altered. Furthermore, serum levels of inflammatory proteins as measured with a cytokine bead array were comparable.

Conclusion: Our data reveal an important and previously unrecognized role of haematopoietic Ikkα kinase activation in the homeostasis of B-cells and regulatory T-cells. However, transplantation of Ikkα(AA) mutant BM did not affect atherosclerosis in Apoe(-/-) mice. This suggests that the diverse functions of Ikkα in haematopoietic cells may counterbalance each other or may not be strong enough to influence atherogenesis, and reveals that targeting haematopoietic Ikkα kinase activity alone does not represent a therapeutic approach.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apolipoproteins E / deficiency*
  • Apolipoproteins E / genetics
  • Atherosclerosis / genetics*
  • Atherosclerosis / metabolism
  • Atherosclerosis / pathology
  • B-Lymphocytes / metabolism
  • Bone Marrow / metabolism*
  • Bone Marrow Cells / metabolism
  • Bone Marrow Transplantation / methods
  • Cells, Cultured
  • Flow Cytometry
  • Hematopoiesis / genetics*
  • I-kappa B Kinase / genetics*
  • I-kappa B Kinase / metabolism
  • Interleukin-12 / metabolism
  • Lipoproteins, LDL / metabolism
  • Macrophages / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Mice, Transgenic
  • Mutation*
  • T-Lymphocytes / metabolism
  • Tumor Necrosis Factor-alpha / metabolism

Substances

  • Apolipoproteins E
  • Lipoproteins, LDL
  • Tumor Necrosis Factor-alpha
  • oxidized low density lipoprotein
  • Interleukin-12
  • I-kappa B Kinase

Grant support

This work was supported by the Deutsche Forschungsgemeinschaft (DFG, www.dfg.de) (WE1913/11-2 to CW, KO2948/1-2 to RRK and CW), by the DFG International graduate school grant IRTG1508/1-TP6 (to CW, PVT, JB, MPJdW), by the Alexander von Humboldt Foundation (http://www.humboldt-foundation.de/web/home.html) (3.3 BEL/1129548, to HN), by the START Program of the Faculty of Medicine of RWTH Aachen (http://www.medizin.rwth-aachen.de/go/id/tfy) (to HN and AZ), and by the Netherlands Organization for Health Research and Development (http://www.zonmw.nl/en/) (to MPJdW). MPJdW is an established investigator of the Netherlands Heart Foundation (2007T067) (www.hartstichting.nl). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.