Classical NF-κB activation impairs skeletal muscle oxidative phenotype by reducing IKK-α expression.
BACKGROUND
Loss of quadriceps muscle oxidative phenotype (OXPHEN) is an evident and debilitating feature of chronic obstructive pulmonary disease (COPD). We recently demonstrated involvement of the inflammatory classical NF-κB pathway in inflammation-induced impairments in muscle OXPHEN. The exact underlying mechanisms however are unclear. Interestingly, IκB kinase α (IKK-α: a key kinase in the alternative NF-κB pathway) was recently identified as a novel positive regulator of skeletal muscle OXPHEN. We hypothesised that inflammation-induced classical NF-κB activation contributes to loss of muscle OXPHEN in COPD by reducing IKK-α expression.


METHODS
Classical NF-κB signalling was activated (molecularly or by tumour necrosis factor α: TNF-α) in cultured myotubes and the impact on muscle OXPHEN and IKK-α levels was investigated. Moreover, the alternative NF-κB pathway was modulated to investigate the impact on muscle OXPHEN in absence or presence of an inflammatory stimulus. As a proof of concept, quadriceps muscle biopsies of COPD patients and healthy controls were analysed for expression levels of IKK-α, OXPHEN markers and TNF-α.


RESULTS
IKK-α knock-down in cultured myotubes decreased expression of OXPHEN markers and key OXPHEN regulators. Moreover, classical NF-κB activation (both by TNF-α and IKK-β over-expression) reduced IKK-α levels and IKK-α over-expression prevented TNF-α-induced impairments in muscle OXPHEN. Importantly, muscle IKK-α protein abundance and OXPHEN was reduced in COPD patients compared to controls, which was more pronounced in patients with increased muscle TNF-α mRNA levels.


CONCLUSIONS
Classical NF-κB activation impairs skeletal muscle OXPHEN by reducing IKK-α expression. TNF-α-induced reductions in muscle IKK-α may accelerate muscle OXPHEN deterioration in COPD.
NUTRIM School for Nutrition, Toxicology & Metabolism, Department of Respiratory Medicine, Maastricht University Medical Centre +, Maastricht, the Netherlands. Electronic address: a.remels@maastrichtuniversity.nl.
A H V
AH
Remels
NUTRIM School for Nutrition, Toxicology & Metabolism, Department of Respiratory Medicine, Maastricht University Medical Centre +, Maastricht, the Netherlands. Electronic address: h.gosker@maastrichtuniversity.nl.
H R
HR
Gosker
NUTRIM School for Nutrition, Toxicology & Metabolism, Department of Respiratory Medicine, Maastricht University Medical Centre +, Maastricht, the Netherlands. Electronic address: r.langen@maastrichtuniversity.nl.
R C
RC
Langen
NIHR Respiratory Biomedical Research unit, Royal Brompton and Harefield NHS Foundation Trust and Imperial College, London SW3 6NP, UK. Electronic address: M.Polkey@rbht.nhs.uk.
M
M
Polkey
Department of Respiratory Medicine, Institute of Tuberculosis and Lung Diseases, Warsaw, Poland. Electronic address: p.sliwinski@wp.pl.
P
P
Sliwinski
Pneumology Department and Research Unit, Cruces Hospital, Basque Country University, Barakaldo, Spain. Electronic address: med001901@hotmail.com.
J
J
Galdiz
NUTRIM School for Nutrition, Toxicology & Metabolism, Department of Respiratory Medicine, Maastricht University Medical Centre +, Maastricht, the Netherlands. Electronic address: b.vdborst@maastrichtuniversity.nl.
B
B
van den Borst
NUTRIM School for Nutrition, Toxicology & Metabolism, Department of Respiratory Medicine, Maastricht University Medical Centre +, Maastricht, the Netherlands.
N A
NA
Pansters
NUTRIM School for Nutrition, Toxicology & Metabolism, Department of Respiratory Medicine, Maastricht University Medical Centre +, Maastricht, the Netherlands. Electronic address: a.schols@maastrichtuniversity.nl.
A M W J
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Schols
D000368:Aged; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D051550:I-kappa B Kinase / Q000235:genetics / Q000378:metabolism*; D008297:Male; D051379:Mice; D008875:Middle Aged; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism*; D010084:Oxidation-Reduction / Q000187:drug effects; D010641:Phenotype; D029424:Pulmonary Disease, Chronic Obstructive / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology; D052097:Quadriceps Muscle / Q000378:metabolism / Q000503:physiopathology; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology
D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D051550:I-kappa B Kinase
3-monooxygenase/tryptophan 5-monooxygenase activation protein, zeta polypeptide; 50S ribosomal subunit protein L15; 60S ribosomal protein L13a; ACTB; ALAS1; ATP; Ad; Adenosine triphosphate; Adenoviral; B2M; BMI; Beta Cytoskeletal Actin; Body mass index; CA; COPD; COXIV; CS; Chronic obstructive pulmonary disease; Citrate synthase; Classical NF-κB; Constitutively active; Cytochrome c oxidase 4; DMEM; Delta-aminolevulinate synthase 1; Dulbecco's Modified Eagle Medium; FEV1; FVC; Forced expiratory volume in one second; Forced vital capacity; GAPDH; GUSB; Gapdh, Glyceraldehyde-3-phosphate dehydrogenase; Gfp; Glucuronidase, bèta; Green fluorescent protein; HAD; HBSS; HCBP; HMBS; HPRT; Hank's Balanced Salt solution; Hprt, Hypoxanthine phosphoribosyltransferase 1; Human carnitine-palmitoyl transferase B; Hydroxymethylbilane Synthase; IKK-α; Icam-1; Ikk-α, IκB kinase alpha; Ikk-β; Il-1β; Intra-cellular adhesion molecule 1; IκB kinase beta; IκBα; Mlc; Myhc; Myosin heavy chain; Myosin light chain; NF-κB; NS; Not significant; Nrf; Nuclear factor kappa B; Nuclear respiratory factor; OXPHEN; Oxidative metabolism; Oxidative phenotype; Oxidative phosphorylation; Oxphos; PBS; PGC-1; PPAR; PPIA; Pgc-1, Peroxisome proliferator-activated receptor gamma co-activator 1; Phosphate-buffered saline; Ppar, Peroxisome proliferator-activated receptor; RPL13A; RPLO; SD; SEM; SR; Skeletal muscle; Standard deviation; Standard equality of the mean; Super repressor; TFAM; TNF-α; Tfam, Mitochondrial transcription factor A; Tnf-α, Tumour necrosis factor alpha; UBC; Ubiquitin C; WT; Wild-type; YWHAZ; interleukin 1β; nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor alpha; peptidylprolyl isomerase A (cyclophilin A); β-hydroxyacyl-CoA dehydrogenase; β2m, Beta 2 microglobulin