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Extended report
TLR4 as receptor for HMGB1 induced muscle dysfunction in myositis
  1. Mei Zong1,
  2. Joseph D Bruton2,
  3. Cecilia Grundtman1,3,
  4. Huan Yang4,
  5. Jian Hua Li4,
  6. Helene Alexanderson1,5,
  7. Karin Palmblad6,
  8. Ulf Andersson6,
  9. Helena E Harris1,
  10. Ingrid E Lundberg1,
  11. Håkan Westerblad2
  1. 1Rheumatology Unit, Department of Medicine, Karolinska University Hospital, Solna, Karolinska Institutet, Stockholm, Sweden
  2. 2Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden
  3. 3Department of Experimental Pathophysiology and Immunology, Innsbruck Medical University, Innsbruck, Austria
  4. 4Laboratory of Biomedical Science, Feinstein Institute for Medical Research, Manhasset, New York, USA
  5. 5Department of Physical Therapy, Orthopedic/Rheumatology Unit, Karolinska University Hospital, Solna, Karolinska Institutet, Stockholm, Sweden
  6. 6Department of Women's and Children's Health, Karolinska University Hospital, Solna, Karolinska Institutet, Stockholm, Sweden
  1. Correspondence to Dr Mei Zong, Rheumatology Unit, CMM L8:04, Karolinska University Hospital, Stockholm, Solna SE-171 76, Sweden; mei.zong{at}


Objectives Polymyositis and dermatomyositis are characterised by muscle weakness and fatigue even in patients with normal muscle histology via unresolved pathogenic mechanisms. In this study, we investigated the mechanisms by which high mobility group box protein 1 (HMGB1) acts to accelerate muscle fatigue development.

Methods Intact single fibres were dissociated from flexor digitorum brevis (FDB) of wild type, receptor for advanced glycation endproduct (RAGE) knockout and toll like receptor 4 (TLR4) knockout mice and cultured in the absence or presence of recombinant HMGB1. A decrease in sarcoplasmic reticulum Ca2+ release during a series of 300 tetanic contractions, which reflects the development of muscle fatigue, was determined by measuring myoplasmic free tetanic Ca2+. TLR4 and major histocompatibility complex (MHC)-class I expression in mouse FDB fibres were investigated by immunofluorescence and confocal microscopy. Immunohistochemistry was used to investigate TLR4, MHC-class I and myosin heavy chain expression in muscle fibres of patients.

Results Our results demonstrate that TLR4 is expressed in human and mouse skeletal muscle fibres, and coexpressed with MHC-class I in muscle fibres of patients with myositis. Furthermore, we show that HMGB1 acts via TLR4 but not RAGE to accelerate muscle fatigue and to induce MHC-class I expression in vitro. In order to bind and signal via TLR4, HMGB1 must have a reduced cysteine 106 and a disulphide linkage between cysteine 23 and 45.

Conclusions The HMGB1-TLR4 pathway may play an important role in causing muscle fatigue in patients with polymyositis or dermatomyositis and thus is a potential novel target for future therapy.

  • Inflammation
  • Polymyositis
  • Dermatomyositis
  • Autoimmune Diseases
  • Cytokines

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