Abstract
BackgroundChondrocyte apoptosis is a central feature in the progression of osteoarthritis (OA), and would be triggered by sustained elevation of intracellular calcium ion (Ca2+), also known as a cellular second messenger. Transient receptor potential ankyrin 1 (TRPA1) is a membrane-associated cation channel, and the activation of which causes an influx of cation ions, in particularly Ca2+, into the activated cells. Therefore, we investigate the potential role of TRPA1 in mediating Ca2+ influx to promote chondrocyte apoptosis in OA.MethodsThe expression of TRPA1 in interleukin (IL)-1β-treated rat chondrocytes was assessed by Polymerase chain reaction (PCR) and Western blot (WB), and the functionality of TRPA1 channel by Ca2+ influx measurements. Meanwhile, the chondrocyte apoptosis in IL-1β-treated cells was measured by TUNEL assay and flow cytometry. The measurement of mitochondrial membrane potential and apoptosis-associated proteins after inhibition of TRPA1 were also performed in IL-1β-treated rat chondrocytes.ResultsAfter being induced by IL-1β, the gene and protein expression of TRPA1 was increased in the dose-dependent manner. Meanwhile, Ca2+ influx mediated by TRPA1 in rat chondrocytes was also enhanced. Pharmacological inhibition of TRPA1 downregulated the apoptotic rate in IL-1β-treated rat chondrocytes. In addition, the membrane potential depolarization was improved and significantly increased expression of apoptosis-associated proteins also reduced by the TRPA1 antagonist.ConclusionsWe found the IL-1β caused the increased functional expression of TRPA1, the activation of which involved IL-1β-induced apoptosis in rat chondrocytes. The potential mechanism may be linked to the intracellular calcium overload mediated by TRPA1 and attendant mitochondrial dysfunction.
Highlights
Knee Osteoarthritis (OA), the most common form of arthritis, is a major cause of joint pain, activity limitation, and physical disability in the elderly [1]
IL-1β increased gene and Protein expression of Transient receptor potential ankyrin 1 (TRPA1) in rat chondrocytes In the present study, the IL-1β was found to increase gene TRPA1 expression gradually in a dose-dependent manner: the expression of TRPA1 increased up to the 10 ng/ml at 12 h or 24 h (Fig. 1a)
IL-1β enhanced Ca2+ influx mediated by TRPA1 in rat chondrocytes To confirm the calcium load mediated by TRPA1 channel in rat chondrocytes, Ca2+ influx measurement was introduced in the study
Summary
Knee Osteoarthritis (OA), the most common form of arthritis, is a major cause of joint pain, activity limitation, and physical disability in the elderly [1]. Transient receptor potential (TRP) ion channels are a large family of membrane-associated cation channels, which most permeable to Ca2+ [11]. Emerging evidences suggested the vital role of overload Ca2+ influx through TRP ion channels in cell deaths [13], such as hypoxia-induced apoptosis in H9C2 Cells [14], acidic solution-triggered apoptosis in synovial fibroblasts [15], and even monoiodoacetic acid (MIA) -mediated apoptosis in chondrocytes [16]. Chondrocyte apoptosis is a central feature in the progression of osteoarthritis (OA), and would be triggered by sustained elevation of intracellular calcium ion (Ca2+), known as a cellular second messenger. Transient receptor potential ankyrin 1 (TRPA1) is a membrane-associated cation channel, and the activation of which causes an influx of cation ions, in Ca2+, into the activated cells. We investigate the potential role of TRPA1 in mediating Ca2+ influx to promote chondrocyte apoptosis in OA
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