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


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.


CONCLUSIONS
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.
Institute of Molecular Cardiovascular Research, RWTH Aachen University, Aachen, Germany.
Pathricia V
PV
Tilstam
Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, The Netherlands ; Department of Medical Biochemistry, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Marion J
MJ
Gijbels
Centre d'Immunologie de Marseille-Luminy, Aix-Marseille Université, Marseille, France.
Mohamed
M
Habbeddine
Centre d'Immunologie de Marseille-Luminy, Aix-Marseille Université, Marseille, France.
Céline
C
Cudejko
Institute of Molecular Cardiovascular Research, RWTH Aachen University, Aachen, Germany ; Institute of Biochemistry and Molecular Cell Biology, RWTH Aachen University, Aachen, Germany.
Yaw
Y
Asare
Institute of Molecular Cardiovascular Research, RWTH Aachen University, Aachen, Germany.
Wendy
W
Theelen
Institute of Molecular Cardiovascular Research, RWTH Aachen University, Aachen, Germany.
Baixue
B
Zhou
Institute for Cardiovascular Prevention, Ludwig-Maximilians-University Munich, Munich, Germany.
Yvonne
Y
Döring
Institute for Cardiovascular Prevention, Ludwig-Maximilians-University Munich, Munich, Germany.
Maik
M
Drechsler
Institute of Molecular Cardiovascular Research, RWTH Aachen University, Aachen, Germany.
Lukas
L
Pawig
Institute of Molecular Cardiovascular Research, RWTH Aachen University, Aachen, Germany.
Sakine
S
Simsekyilmaz
Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, The Netherlands.
Rory R
RR
Koenen
Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, The Netherlands ; Department of Medical Biochemistry, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Menno P J
MP
de Winther
Centre d'Immunologie de Marseille-Luminy, Aix-Marseille Université, Marseille, France.
Toby
T
Lawrence
Institute of Biochemistry and Molecular Cell Biology, RWTH Aachen University, Aachen, Germany ; August-Lenz-Stiftung, Institute for Cardiovascular Research, Ludwig-Maximilians-University Munich, Munich, Germany.
Jürgen
J
Bernhagen
Rudolf Virchow Center and Institute of Clinical Biochemistry and Pathobiochemistry, University of Würzburg, Würzburg, Germany ; Department of Vascular Surgery, Klinikum rechts der Isar Technical University Munich, Munich, Germany ; German Centre for Cardiovascular Research, partner site Munich Heart Alliance, Munich, Germany.
Alma
A
Zernecke
Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, The Netherlands ; Institute for Cardiovascular Prevention, Ludwig-Maximilians-University Munich, Munich, Germany ; German Centre for Cardiovascular Research, partner site Munich Heart Alliance, Munich, Germany.
Christian
C
Weber
Institute of Molecular Cardiovascular Research, RWTH Aachen University, Aachen, Germany.
Heidi
H
Noels
D000818:Animals; D001057:Apolipoproteins E / Q000172:deficiency* / Q000235:genetics; D050197:Atherosclerosis / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D001402:B-Lymphocytes / Q000378:metabolism; D001853:Bone Marrow / Q000378:metabolism*; D001854:Bone Marrow Cells / Q000378:metabolism; D016026:Bone Marrow Transplantation / Q000379:methods; D002478:Cells, Cultured; D005434:Flow Cytometry; D006410:Hematopoiesis / Q000235:genetics*; D051550:I-kappa B Kinase / Q000235:genetics* / Q000378:metabolism; D018664:Interleukin-12 / Q000378:metabolism; D008077:Lipoproteins, LDL / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009154:Mutation; D013601:T-Lymphocytes / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D001057:Apolipoproteins E; D008077:Lipoproteins, LDL; D014409:Tumor Necrosis Factor-alpha; C099252:oxidized low density lipoprotein; D018664:Interleukin-12; D051550:I-kappa B Kinase