title: Reduced tissue osmolarity increases TRPV4 expression and pro-inflammatory cytokines in intervertebral disc cells.
abstract: The mechanical behaviour and cellular metabolism of intervertebral discs (IVDs) and articular cartilage are strongly influenced by their proteoglycan content and associated osmotic properties. This osmotic environment is a biophysical signal that changes with disease and may contribute to the elevated matrix breakdown and altered biologic response to loading observed in IVD degeneration and osteoarthritis. This study tested the hypothesis that changes in osmo-sensation by the transient receptor potential vallinoid-4 (TRPV4) ion channel occur with disease and contribute to the inflammatory environment found during degeneration. Immunohistochemistry on bovine IVDs from an inflammatory organ culture model were used to investigate if TRPV4 is expressed in the IVD and how expression changes with degeneration. Western blot, live-cell calcium imaging, and qRT-PCR were used to investigate whether osmolarity changes or tumour necrosis factor α (TNFα) regulate TRPV4 expression, and how altered TRPV4 expression influences calcium signalling and pro-inflammatory cytokine expression. TRPV4 expression correlated with TNFα expression, and was increased when cultured in reduced medium osmolarity and unaltered with TNFα-stimulation. Increased TRPV4 expression increased the calcium flux following TRPV4 activation and increased interleukin-1β (IL-1β) and IL-6 gene expression in IVD cells. TRPV4 expression was qualitatively elevated in regions of aggrecan depletion in degenerated human IVDs. Collectively, results suggest that reduced tissue osmolarity, likely following proteoglycan degradation, can increase TRPV4 signalling and enhance pro-inflammatory cytokine production, suggesting changes in TRPV4 mediated osmo-sensation may contribute to the progressive matrix breakdown in disease.
authors.affiliation: Leni & Peter W. May Department of Orthopaedics, Box 1188, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA.james.iatridis@mssm.edu.
authors.forename: B A
authors.initials: BA
authors.lastname: Walter
authors.forename: D
authors.initials: D
authors.lastname: Purmessur
authors.forename: A
authors.initials: A
authors.lastname: Moon
authors.forename: J
authors.initials: J
authors.lastname: Occhiogrosso
authors.forename: D M
authors.initials: DM
authors.lastname: Laudier
authors.forename: A C
authors.initials: AC
authors.lastname: Hecht
authors.forename: J C
authors.initials: JC
authors.lastname: Iatridis
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002417:Cattle; D016207:Cytokines / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D007249:Inflammation / Q000473:pathology; D018836:Inflammation Mediators / Q000378:metabolism*; D007403:Intervertebral Disc / Q000378:metabolism* / Q000473:pathology; D008954:Models, Biological; D000070614:Nucleus Pulposus / Q000378:metabolism; D009924:Organ Culture Techniques; D009994:Osmolar Concentration; D009995:Osmosis; D015398:Signal Transduction; D050916:TRPV Cation Channels / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D016207:Cytokines; D018836:Inflammation Mediators; D050916:TRPV Cation Channels; D014409:Tumor Necrosis Factor-alpha; D002118:Calcium