Kappa opioid receptor signaling protects cartilage tissue against posttraumatic degeneration
Ling Wu, … , Yunfeng Lin, Denis Evseenko
Ling Wu, … , Yunfeng Lin, Denis Evseenko
Published January 12, 2017
Citation Information: JCI Insight. 2017;2(1):e88553. https://doi.org/10.1172/jci.insight.88553.
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Research Article Bone biology

Kappa opioid receptor signaling protects cartilage tissue against posttraumatic degeneration

Abstract

Osteoarthritis is the most common form of arthritis, and pain relief with opioid-like drugs is a commonly used therapeutic for osteoarthritic patients. Recent studies published by our group showed that the kappa opioid receptor (KOR) is highly expressed during human development in joint-forming cells. However, the precise role of this receptor in the skeletal system remains elusive. The main aim of the current study was to investigate the role of KOR signaling in synovial and cartilaginous tissues in pathological conditions. Our data demonstrate that KOR null mice exhibit accelerated cartilage degeneration after injury when compared with WT mice. Activation of KOR signaling increased the expression of anabolic enzymes and inhibited cartilage catabolism and degeneration in response to proinflammatory cytokines such as TNF-α. In addition, selective KOR agonists increased joint lubrication via the activation of cAMP/CREB signaling in chondrocytes and synovial cells. Taken together, these results demonstrate direct effects of KOR agonists on cartilage and synovial cells and reveals a protective effect of KOR signaling against cartilage degeneration after injury. In addition to pain control, local administration of dynorphin or other KOR agonist represents an attractive therapeutic approach in patients with early stages of osteoarthritis.

Authors

Ling Wu, Shu Zhang, Ruzanna Shkhyan, Siyoung Lee, Francesca Gullo, Claire D. Eliasberg, Frank A. Petrigliano, Kai Ba, Jing Wang, Yunfeng Lin, Denis Evseenko

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Figure 5

Dynorphin A increases the expression of lubricin/PRG4 in chondrocytes.

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Dynorphin A increases the expression of lubricin/PRG4 in chondrocytes. (...
(A) Immunohistochemistry for lubricin was performed on sagittal sections of medial femoral condyles from WT or kappa opioid receptor (KOR) 1 knockout (Oprk1–/–) mice. Scale bars: 20 μm. Images are representative samples from a total of 6. (B) Lubricin-positive chondrocytes were counted on sagittal sections of femoral condyle. Mean ± SD (n = 6). Each data point represents the average of 3 counts for 1 mouse. (C) Murine chondrocytes were isolated from rib cartilage of WT or Oprk1–/– mice. Western blot was performed to detect the expression of lubricin. (D) Chondrocytes were isolated from femoral heads of hip joints of 17-week-old human fetus. Dynorphin A stimulates a dose-dependent increase in lubricin expression. (E) Real-time PCR revealed expression of the proteoglycan 4 (PRG4) gene in fetal chondrocytes at the mRNA level. Mean ± SD (n = 3). Each data point represents the average of 3 repeats from 3 tissue donors. (F) Pig articular chondrocytes were treated with KOR-selective agonist U50,488H (1 μM) for up to 48 hours. Western blot was performed to detect phosphorylation of cAMP responsive element binding protein (CREB) at serine 133. (G) Dynorphin (1 μM) treatment increases intracellular concentration of cAMP in chondrocytes. Each data point represents the average of 2 repeats from 3 tissue donors. (H) Fetal chondrocytes were treated with 10 μM forskolin (Fsk) for 24 hours. Expression of lubricin was determined by Western blot. (I) PKA inhibitor (KT 5720, 1 μM) reduced lubricin expression and CREB phosphorylation upon dynorphin treatment. (J) Knockdown of PKA catalytic subunit α by siRNA (PRKACA-siRNA) reduced lubricin expression and CREB phosphorylation upon dynorphin treatment. P values in B and E were calculated using Student’s t test. P values in G were calculated with 1-way ANOVA followed by Tukey honest significant difference post-hoc test. Blots in panel C, D, F, H, I, and J are representative of 1 of 3 independent experiments.