title: Environmental cold exposure increases blood flow and affects pain sensitivity in the knee joints of CFA-induced arthritic mice in a TRPA1-dependent manner.
abstract: BACKGROUND
  The effect of cold temperature on arthritis symptoms is unclear. The aim of this study was to investigate how environmental cold affects pain and blood flow in mono-arthritic mice, and examine a role for transient receptor potential ankyrin 1 (TRPA1), a ligand-gated cation channel that can act as a cold sensor.
  
  
  METHODS
  Mono-arthritis was induced by unilateral intra-articular injection of complete Freund's adjuvant (CFA) in CD1 mice, and in mice either lacking TRPA1 (TRPA1 KO) or respective wildtypes (WT). Two weeks later, nociception and joint blood flow were measured following exposure to 10 °C (1 h) or room temperature (RT). Primary mechanical hyperalgesia in the knee was measured by pressure application apparatus; secondary mechanical hyperalgesia by automated von Frey system; thermal hyperalgesia by Hargreaves technique, and weight bearing by the incapacitance test. Joint blood flow was recorded by full-field laser perfusion imager (FLPI) and using clearance of (99m)Technetium. Blood flow was assessed after pretreatment with antagonists of either TRPA1 (HC-030031), substance P neurokinin 1 (NK1) receptors (SR140333) or calcitonin gene-related peptide (CGRP) (CGRP8-37). TRPA1, TAC-1 and CGRP mRNA levels were examined in dorsal root ganglia, synovial membrane and patellar cartilage samples.
  
  
  RESULTS
  Cold exposure caused bilateral primary mechanical hyperalgesia 2 weeks after CFA injection, in a TRPA1-dependent manner. In animals maintained at RT, clearance techniques and FLPI showed that CFA-treated joints exhibited lower blood flow than saline-treated joints. In cold-exposed animals, this reduction in blood flow disappears, and increased blood flow in the CFA-treated joint is observed using FLPI. Cold-induced increased blood flow in CFA-treated joints was blocked by HC-030031 and not observed in TRPA1 KOs. Cold exposure increased TRPA1 mRNA levels in patellar cartilage, whilst reducing it in synovial membranes from CFA-treated joints.
  
  
  CONCLUSIONS
  We provide evidence that environmental cold exposure enhances pain and increases blood flow in a mono-arthritis model. These changes are dependent on TRPA1. Thus, TRPA1 may act locally within the joint to influence blood flow via sensory nerves, in addition to its established nociceptive actions.
authors.affiliation: Centre for Cardiovascular Excellence, Waterloo Campus, King's College London, Franklin-Wilkins Building, 150 Stamford St, London, SE1 9NH, UK. elizabeth.fernandes@kcl.ac.uk.|Programa de Pós-Graduação, Universidade Ceuma, São Luís, MA, 65075-120, Brazil. elizabeth.fernandes@kcl.ac.uk.
authors.forename: Elizabeth S
authors.initials: ES
authors.lastname: Fernandes
authors.affiliation: Centre for Cardiovascular Excellence, Waterloo Campus, King's College London, Franklin-Wilkins Building, 150 Stamford St, London, SE1 9NH, UK. fiona.a.russell@kcl.ac.uk.
authors.forename: Fiona A
authors.initials: FA
authors.lastname: Russell
authors.affiliation: Centre for Cardiovascular Excellence, Waterloo Campus, King's College London, Franklin-Wilkins Building, 150 Stamford St, London, SE1 9NH, UK. khadija.k.alawi@kcl.ac.uk.
authors.forename: Khadija M
authors.initials: KM
authors.lastname: Alawi
authors.affiliation: Centre for Cardiovascular Excellence, Waterloo Campus, King's College London, Franklin-Wilkins Building, 150 Stamford St, London, SE1 9NH, UK. claire.sand@hotmail.com.
authors.forename: Claire
authors.initials: C
authors.lastname: Sand
authors.affiliation: Centre for Cardiovascular Excellence, Waterloo Campus, King's College London, Franklin-Wilkins Building, 150 Stamford St, London, SE1 9NH, UK. liangli@medimmune.com.
authors.forename: Lihuan
authors.initials: L
authors.lastname: Liang
authors.affiliation: Centre for Cardiovascular Excellence, Waterloo Campus, King's College London, Franklin-Wilkins Building, 150 Stamford St, London, SE1 9NH, UK. rsalamon@ulb.ac.be.
authors.forename: Robin
authors.initials: R
authors.lastname: Salamon
authors.affiliation: Centre for Cardiovascular Excellence, Waterloo Campus, King's College London, Franklin-Wilkins Building, 150 Stamford St, London, SE1 9NH, UK. jenniferbodkin@hotmail.co.uk.
authors.forename: Jennifer V
authors.initials: JV
authors.lastname: Bodkin
authors.affiliation: Centre for Cardiovascular Excellence, Waterloo Campus, King's College London, Franklin-Wilkins Building, 150 Stamford St, London, SE1 9NH, UK. aisah.aubdool@kcl.ac.uk.
authors.forename: Aisah A
authors.initials: AA
authors.lastname: Aubdool
authors.affiliation: Genomics Centre, Waterloo Campus, King's College London, Franklin-Wilkins Building, 150 Stamford St, London, SE1 9NH, UK. matthew.arno@kcl.ac.uk.
authors.forename: Matthew
authors.initials: M
authors.lastname: Arno
authors.affiliation: Wolfson Centre for Age-Related Diseases, Guy's Campus, King's College London, London, SE1 1UL, UK. clive.gentry@kcl.ac.uk.
authors.forename: Clive
authors.initials: C
authors.lastname: Gentry
authors.affiliation: Centre for Cardiovascular Excellence, Waterloo Campus, King's College London, Franklin-Wilkins Building, 150 Stamford St, London, SE1 9NH, UK. smilliesj@hotmail.com.
authors.forename: Sarah-Jane
authors.initials: SJ
authors.lastname: Smillie
authors.affiliation: Wolfson Centre for Age-Related Diseases, Guy's Campus, King's College London, London, SE1 1UL, UK. stuart.bevan@kcl.ac.uk.
authors.forename: Stuart
authors.initials: S
authors.lastname: Bevan
authors.affiliation: Institute of Pharmaceutical Science, Waterloo Campus, King's College London, Franklin-Wilkins Building, 150 Stamford St, London, SE1 9NH, UK. julie.keeble@kcl.ac.uk.
authors.forename: Julie E
authors.initials: JE
authors.lastname: Keeble
authors.affiliation: Wolfson Centre for Age-Related Diseases, Guy's Campus, King's College London, London, SE1 1UL, UK. marzia.malcangio@kcl.ac.uk.
authors.forename: Marzia
authors.initials: M
authors.lastname: Malcangio
authors.affiliation: Centre for Cardiovascular Excellence, Waterloo Campus, King's College London, Franklin-Wilkins Building, 150 Stamford St, London, SE1 9NH, UK. sue.brain@kcl.ac.uk.
authors.forename: Susan D
authors.initials: SD
authors.lastname: Brain
mesh_terms: D000818:Animals; D001169:Arthritis, Experimental / Q000139:chemically induced / Q000378:metabolism* / Q000473:pathology; D001783:Blood Flow Velocity / Q000187:drug effects / Q000502:physiology*; D003080:Cold Temperature / Q000009:adverse effects*; D005620:Freund's Adjuvant / Q000008:administration & dosage / Q000633:toxicity*; D006614:Hindlimb / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D007270:Injections, Intra-Articular; D007596:Joints / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D008297:Male; D051379:Mice; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010147:Pain Measurement / Q000187:drug effects / Q000379:methods; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology; D000074025:TRPA1 Cation Channel; D050051:Transient Receptor Potential Channels / Q000096:biosynthesis* / Q000172:deficiency
chemical_list: D000074025:TRPA1 Cation Channel; D050051:Transient Receptor Potential Channels; C475685:Trpa1 protein, mouse; D005620:Freund's Adjuvant