Receptor activator of nuclear factor-κB ligand is a novel inducer of myocardial inflammation.
OBJECTIVE
Although increased levels of myocardial receptor activator of nuclear factor (NF)-κB ligand (RANKL) have been reported in heart failure, the role of this pathway in mediating activation of inflammatory pathways during myocardial remodelling is less well understood. This study sought to determine the role of myocardial RANKL in regulating cytokine expression.


RESULTS
A marked increase in RANKL expression occurred as early as 6h following transverse aortic constriction (TAC) in mouse hearts and persisted at 3 and 17 days. An increase in tumour necrosis factor-α (TNF-α), interleukin (IL)-1α, and IL-1β was observed in the hypertrophied hearts only at 3 or 17 days after TAC. Treatment with losartan significantly attenuated TAC-induced cardiac hypertrophy, in parallel with decreased expression of RANKL, TNF-α, IL-1α, and IL-1β. Furthermore, injection of a RANKL-neutralizing monoclonal antibody attenuated RANKL-induced cytokine expression. RANKL stimulated expression of TNF-α, IL-1α, and IL-1β in neonatal rat cardiomyocytes via activation of NF-κB. RANKL-induced NF-κB activation and expression of these cytokines were both attenuated when RANK, receptor for RANKL, or TRAF2 or TRAF6, adaptors for RANK, was silenced by siRNA. Furthermore, inhibitors of phospholipase C (PLC), protein kinase C (PKC), and inhibitor of κB kinase also significantly inhibited RANKL-induced cellular activities, but inhibitors of phosphatidylinositol 3-kinase, extracellular signal-regulated kinase, or p38 mitogen-activated protein kinase were without effect.


CONCLUSIONS
Our data demonstrate for the first time that the pressure-overloaded myocardium generates RANKL, which induces TNF-α, IL-1α, and IL-1β production via a RANK-TRAF2/TRAF6-PLC-PKC-NF-κB-mediated autocrine mechanism.
Division of Endocrinology and Metabolism, Department of Internal Medicine,  College of Medicine, Chung-Ang University, Seoul 156-755,  Republic of Korea.
Sangmi
S
Ock
Jihyun
J
Ahn
Seok Hong
SH
Lee
Hongryeol
H
Park
Jang Won
JW
Son
Jae Gyun
JG
Oh
Dong Kwon
DK
Yang
Wang Soo
WS
Lee
Ho-Shik
HS
Kim
Jaerang
J
Rho
Goo Taeg
GT
Oh
Evan Dale
ED
Abel
Woo Jin
WJ
Park
Jeong-Ki
JK
Min
Jaetaek
J
Kim
D047228:Angiotensin II Type 1 Receptor Blockers / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D057134:Antibodies, Neutralizing / Q000494:pharmacology; D019898:Autocrine Communication; D006332:Cardiomegaly / Q000235:genetics / Q000276:immunology* / Q000517:prevention & control; D002478:Cells, Cultured; D016207:Cytokines / Q000235:genetics / Q000378:metabolism*; D004195:Disease Models, Animal; D018836:Inflammation Mediators / Q000378:metabolism*; D053582:Interleukin-1alpha / Q000235:genetics / Q000378:metabolism; D053583:Interleukin-1beta / Q000235:genetics / Q000378:metabolism; D019808:Losartan / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009205:Myocarditis / Q000235:genetics / Q000276:immunology* / Q000517:prevention & control; D032383:Myocytes, Cardiac / Q000276:immunology*; D053245:RANK Ligand / Q000037:antagonists & inhibitors / Q000378:metabolism*; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D053246:Receptor Activator of Nuclear Factor-kappa B / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D047992:TNF Receptor-Associated Factor 2 / Q000235:genetics / Q000378:metabolism; D048029:TNF Receptor-Associated Factor 6 / Q000235:genetics / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation
D047228:Angiotensin II Type 1 Receptor Blockers; D000911:Antibodies, Monoclonal; D057134:Antibodies, Neutralizing; D016207:Cytokines; D018836:Inflammation Mediators; D053582:Interleukin-1alpha; D053583:Interleukin-1beta; D053245:RANK Ligand; D012333:RNA, Messenger; D053246:Receptor Activator of Nuclear Factor-kappa B; D047992:TNF Receptor-Associated Factor 2; D048029:TNF Receptor-Associated Factor 6; C505689:Tnfsf11 protein, mouse; D014409:Tumor Necrosis Factor-alpha; D019808:Losartan