title: Differences in glutamate receptors and inflammatory cell numbers are associated with the resolution of pain in human rotator cuff tendinopathy.
abstract: BACKGROUND
  The relationship between peripheral tissue characteristics and pain symptoms in soft tissue inflammation is poorly understood. The primary aim of this study was to determine immunohistochemical differences in tissue obtained from patients with persistent pain and patients who had become pain-free after surgical treatment for rotator cuff tendinopathy. The secondary aim was to investigate whether there would be differences in glutaminergic and inflammatory gene expression between disease-derived and healthy control cells in vitro.
  
  
  METHODS
  Supraspinatus tendon biopsies were obtained from nine patients with tendon pain before shoulder surgery and from nine further patients whose pain had resolved completely following shoulder surgery. Histological markers relating to the basic tendon characteristics, inflammation and glutaminergic signalling were quantified by immunohistochemical analysis. Gene expression of glutaminergic and inflammatory markers was determined in tenocyte explants derived from painful rotator cuff tendon tears in a separate cohort of patients and compared to that of explants from healthy control tendons. Dual labelling was performed to identify cell types expressing nociceptive neuromodulators.
  
  
  RESULTS
  Tendon samples from patients with persistent pain demonstrated increased levels of metabotropic glutamate receptor 2 (mGluR2), kainate receptor 1 (KA1), protein gene product 9.5 (PGP9.5), CD206 (macrophage marker) and CD45 (pan-leucocyte marker) versus pain-free controls (p <0.05). NMDAR1 co-localised with CD206-positive cells, whereas PGP9.5 and glutamate were predominantly expressed by resident tendon cells. These results were validated by in vitro increases in the expression of mGluR2, N-methyl-D-aspartate receptor (NMDAR1), KA1, CD45, CD206 and tumour necrosis factor alpha (TNF-α) genes (p <0.05) in disease-derived versus control cells.
  
  
  CONCLUSIONS
  We conclude that differences in glutamate receptors and inflammatory cell numbers are associated with the resolution of shoulder pain in rotator cuff tendinopathy, and that disease-derived cells exhibit a distinctly different neuro-inflammatory gene expression profile to healthy control cells.
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Botnar Research Centre, Windmill Road, Oxford, OX3 7LD, UK. bendean1979@gmail.com.
authors.forename: Benjamin John Floyd
authors.initials: BJ
authors.lastname: Dean
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Botnar Research Centre, Windmill Road, Oxford, OX3 7LD, UK. sarah.snelling@ndorms.ox.ac.uk.
authors.forename: Sarah J B
authors.initials: SJ
authors.lastname: Snelling
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Botnar Research Centre, Windmill Road, Oxford, OX3 7LD, UK. Stephanie.dakin@ndorms.ox.ac.uk.
authors.forename: Stephanie G
authors.initials: SG
authors.lastname: Dakin
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Botnar Research Centre, Windmill Road, Oxford, OX3 7LD, UK. Richard.murphy@ndorms.ox.ac.uk.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Murphy
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Botnar Research Centre, Windmill Road, Oxford, OX3 7LD, UK. Kassim.javaid@ndorms.ox.ac.uk.
authors.forename: Muhammad Kassim
authors.initials: MK
authors.lastname: Javaid
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Botnar Research Centre, Windmill Road, Oxford, OX3 7LD, UK. Andrew.carr@ndorms.ox.ac.uk.
authors.forename: Andrew Jonathan
authors.initials: AJ
authors.lastname: Carr
mesh_terms: D000293:Adolescent; D000328:Adult; D002452:Cell Count / Q000379:methods; D002478:Cells, Cultured; D005260:Female; D006801:Humans; D018836:Inflammation Mediators / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D010146:Pain / Q000175:diagnosis / Q000378:metabolism*; D010147:Pain Measurement / Q000379:methods; D017470:Receptors, Glutamate / Q000378:metabolism*; D017006:Rotator Cuff / Q000378:metabolism* / Q000473:pathology; D052256:Tendinopathy / Q000175:diagnosis / Q000378:metabolism*; D055815:Young Adult
chemical_list: D018836:Inflammation Mediators; D017470:Receptors, Glutamate