Correlation between Gene Expression and Osteoarthritis Progression in Human

Abstract

Osteoarthritis (OA) is a multifactorial disease characterized by gradual degradation of joint cartilage. This study aimed to quantify major pathogenetic factors during OA progression in human cartilage. Cartilage specimens were isolated from OA patients and scored 0-5 according to the Osteoarthritis Research Society International (OARSI) guidelines. Protein and gene expressions were measured by immunohistochemistry and qPCR, respectively. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays were used to detect apoptotic cells. Cartilage degeneration in OA is a gradual progress accompanied with gradual loss of collagen type II and a gradual decrease in mRNA expression of SOX9, ACAN and COL2A1. Expression of WNT antagonists DKK1 and FRZB was lost, while hypertrophic markers (RUNX2, COL10A1 and IHH) increased during OA progression. Moreover, DKK1 and FRZB negatively correlated with OA grading, while RUNX2 and IHH showed a significantly positive correlation with OA grading. The number of apoptotic cells was increased with the severity of OA. Taken together, our results suggested that genetic profiling of the gene expression could be used as markers for staging OA at the molecular level. This helps to understand the molecular pathology of OA and may lead to the development of therapies based on OA stage.

Keywords: OARSI grading; cartilage degeneration; gene expression; hypertrophy; osteoarthritis.

Figure 1

Histological changes of OA cartilage. Five micrometer paraffin sections of cartilage stained by Alcian blue and Safranin O (scale bar 250 µm). The severity of the OA lesion was graded on a scale of 0–5.

Figure 2

The protein expression of collagen type II, collagen type X and GREM1 was visualized by IHC (scale bar 250 μm). (A) Representative pictures are shown. Images were taken using the Nanozoomer. G0, G1, G2, G3, G4, G5 = Grade 0, Grade 1, Grade 2, Grade 3, Grade 4, Grade 5; (B) Quantification of positive staining was performed by ImageJ software (Wayne Rasband, Bethesda, MD, USA).

Figure 3

Correlation between histopathological grade and chondrocyte apoptosis. (A) The TUNEL assay was performed to identify chondrocyte apoptosis at different stages of OA (scale bar: 100 μm). Arrows indicate apoptotic cells; (B) Apoptotic cells were counted in the superficial layer (SL) and middle layer (ML) in cartilage sections for quantification. Apoptosis is quantified as the percentage apoptotic cells with respect to the total cells counted.