Abnormal expression of key genes and proteins in the canonical Wnt/β-catenin pathway of articular cartilage in a rat model of exercise-induced osteoarthritis

Abstract

To investigate the molecular pathogenesis of the canonical Wnt/β-catenin pathway in exercise-induced osteoarthritis (OA), 30 male healthy Sprague Dawley rats were divided into three groups (control, normal exercise‑induced OA and injured exercise‑induced OA groups) in order to establish the exercise‑induced OA rat model. The mRNA and protein expression levels of Runx‑2, BMP‑2, Ctnnb1, Sox‑9, collagen Ⅱ, Mmp‑13, Wnt‑3a and β‑catenin in chondrocytes were detected by reverse transcription‑quantitative polymerase chain reaction, western blotting and immunohistochemical staining. The mRNA levels of Runx‑2, BMP‑2 and Ctnnb1 were upregulated in the normal exercise‑induced OA and injured exercise‑induced OA groups; while Runx‑2 and BMP‑2 were upregulated in the injured exercise‑induced OA group when compared with the normal exercise‑induced OA group. The protein levels of Mmp‑13, Wnt‑3a and β‑catenin were increased and collagen Ⅱ was reduced in the normal exercise‑induced OA and injured exercise‑induced OA groups. Ctnnb1, Wnt‑3a and β‑catenin, which are key genes and proteins in the canonical Wnt/β‑catenin pathway, were abnormally expressed in chondrocytes of the exercise‑induced OA rat model. Ctnnb1, β‑catenin and Wnt‑3a were suggested to participate in the pathogenesis of exercise‑induced OA by abnormally activating the Wnt/β‑catenin pathway during physical exercise due to excessive pressure. The results of the present study may provide an improved understanding of the pathogenesis of exercise-induced OA.

Figure 1

mRNA expression levels of Runx-2, BMP-2, Ctnnb1 and Sox-9 in groups A, B and C. ^*P<0.05 and ^&P<0.01 between groups. Runx-2, runt-related transcription factor 2; BMP-2, bone morphogenetic protein 2; Ctnnb1, catenin (cadherin-associated protein) β1, Sox-9, sex determining region Y-box 9; group A, injured exercise-induced osteoarthritis group; group B, normal exercise-induced osteoarthritis group; group C, control group.

Figure 2

Immunoblotting of β-catenin, Mmp-13, Wnt-3a and collagen II. The representative immunoblotting images of β-catenin, Mmp-13, Wnt-3a and collagen II and the densitometric analysis are presented (n=10/group). ^*P<0.05 and ^&P<0.01 between groups. Mmp-13, matrix metalloproteinase 13; Wnt-3a, wingless-type MMTV integration site family member 3A; group A, injured exercise-induced osteoarthritis group; group B, normal exercise-induced osteoarthritis group; group C, control group.

Figure 3

Immunohistochemical localization of Wnt-3a in the chondrocytes (n=10/group). Data are presented as the mean ± standard deviation. ^*P<0.05 and ^&P<0.01 between groups. Magnification of superficial zone, ×200; magnification of middle zone, ×400; and magnification of deep zone, ×400. Wnt-3a, wingless-type MMTV integration site family member 3A; group A, injured exercise-induced osteoarthritis group; group B, normal exercise-induced osteoarthritis group; group C, control group.

Figure 4

Immunohistochemical localization of β-catenin in chondrocytes (n=10/group). Data are presented as the mean ± standard deviation. ^*P<0.05 and ^&P<0.01 between groups. Magnification of superficial zone, ×200; magnification of middle zone, ×400; and magnification of deep zone, ×400. Group A, injured exercise-induced osteoarthritis group; group B, normal exercise-induced osteoarthritis group; group C, control group.