Background: Potassium ion channels are implicated in aged-associated osteoarthritis and joint pain. The two-pore-domain potassium ion channel, TRESK, regulates neuronal excitability and governs resting cellular membrane potential. However, little is known about the role of TRESK in maintaining knee joint homeostasis. In a rat model of cancer-induced bone pain, over expression of TRESK, attenuated the bone pain [1]. Osteoarthritis affects all joint tissues, including the cartilage and subchondral bone, leading to joint pain. Bone sclerosis and cartilage calcification are key histopathological features of osteoarthritis. Chondrocytes, the main cell type in the cartilage, undergo a phenotypic shift, increasing calcification of the cartilage. Peripheral nerves can regulate bone remodelling, accelerating subchondral bone sclerosis.
Purpose: The aim of this pilot study was to determine whether TRESK influences joint homeostasis in aged-mice through regulating cartilage and bone health.
Methods: Paraffin-embedded, knee joint sections of aged (2 years and 6 months approximately) TRESK knockout (n=4) and wild-type control (n=3) C57BL/6 male mice were sectioned at 5µm thickness and at least 4 sections per knee joint were analysed for histopathological changes, by observers blinded to the groups. Thickness of the subchondral bone was analysed on haematoxylin and eosin stained sections. Osterix is a transcriptional factor which is expressed by osteoblasts (bone forming cells). Osterix-immunohistochemistry was performed to assess whether chondrocytes were adopting osteoblast-like phenotype. Trabecular bone area within the subchondral bone region and osterix-positive chondrocytes in the cartilage were quantified using Image-J (Fiji) software. Univariate comparisons were made using student’s T-test. A two- tailed P < 0.05 was taken to indicate statistical significance. Data is shown as mean ± standard deviation.
Ethical Considerations: All procedures complied with the UK Animals (Scientific Procedures) Act of 1986 and were performed under a UK Home Office Project Licence in accordance with the University of Kent Policy on the use of Animals in Scientific Research and the ARRIVE guidelines.
Results: Knee-joints of aged wildtype control mice showed osteoarthritis-like changes, these included cartilage damage and subchondral bone remodelling. Aged TRESK-knockout mice had thicker trabecular bone measured as percentage of trabecular bone within the subchondral bone region compared to wildtype control mice (knockout: 45% ± 4.5, wildtype: 37% ± 2.5, p=0.04). Increased percentage of osterix-positive chondrocytes were observed in the cartilage of TRESK-knockout (62% ± 2.5) compared to wildtype control (46% ± 8.9) mice, although this difference did not reach significance (p=0.08).
Conclusion: This proof-of-concept study highlights that TRESK is indeed an important ion channel that regulates joint homeostasis through maintaining cartilage and bone health. Loss of TRESK can exacerbate age-associated osteoarthritis-like changes observed in mice knee joints. Further studies are needed to elucidate its role in osteoarthritis and joint pain.