The G/T polymorphism of the COL1A1 gene exhibits a clinically significant influence on bone remodelling, leading to a predisposition to degenerative diseases. The enhancement of bone turnover and further loss of bone mass are thought to be the primary pathological changes in the early degenerative course of temporomandibular joint osteoarthritis (TMJ OA), with the appearance of low-density lesions. Thus, it was hypothesized that this polymorphism may also affect this type of bone lesion in TMJ OA. A total of 130 TMJ OA patients with low-density lesions (cortical bone erosion, condylar head resorption, cyst-like lesion) and 186 healthy individuals were recruited. DNA samples were extracted from buccal mucosa swabs; genotyping was performed by high-resolution melting assay. The distribution of genotypes in these groups was compared using a multivariate logistic regression model. No significant differences in the distributions of TT and TG genotypes were observed between the groups ( P > 0.05). Significance was detected for GG homozygous carriers ( P = 0.043); this genotype might be a risk factor for this type of low-density lesion (odds ratio 1.643, 95% confidence interval 1.016–2.658). This study indicates that the GG genotype might be a risk factor for low-density lesions in the TMJ.
Temporomandibular joint osteoarthritis (TMJ OA) is one of the most serious subtypes of temporomandibular joint disorder (TMD). TMJ OA affects the individual’s daily life because it causes orofacial pain, mandible movement dysfunction, and facial asymmetry. Furthermore, it is a complex disease affected by several factors, including ageing, sex, trauma, sustained overload, malocclusion, oestrogen level, and genetic factors. TMJ OA is a degenerative disease characterized by a progressive loss of articular cartilage, changes in the subchondral bone, and inflammation of the synovial membrane and associated peri-articular structures.
OA is traditionally considered to be caused by articular cartilage degeneration. Changes in the subchondral bone may also play a pivotal role in TMJ damage during the induction and progression of OA. In cone beam tomography (CBCT) images, subchondral osseous changes in the condyles are usually manifested as low-density lesions (erosion, resorption, or cyst-like lesions) or high-density lesions (sclerosis). The enhancement of bone turnover and further loss of bone mass, seen as cortical bone erosion, condylar head resorption, or cyst-like lesions, are thought to be the primary pathological changes in OA and the decrease in bone turnover and subsequent densification of bone shown as osteophyte formation and subchondral sclerosis.
The extracellular matrix (ECM) collagen of subchondral bone is mainly composed of type I, with very small amounts of other collagen types, such as III, V, and VI. Type I collagen is a heterotrimer consisting of two α1(I) and one α2(I) chains. However, certain genetic and environmental factors may lead to the synthesis of homotrimers comprising three α1(I) chains. One such genetic factor is the G/T polymorphism in the COL1A1 gene, which results in the synthesis of about 15% homotrimers. Compared to the heterotrimer, the homotrimer shows less efficient fibrillogenesis and different stability. Furthermore, the homotrimer fibrils have lower tensile strength. Type I collagen homotrimers have been identified in the subchondral bone of osteoarthritic joints, with collagen type I heterotrimers being predominant in normal joints, indicating a change in phenotype. The presence of these homotrimers accounts for narrowed disorganized collagen type I fibres and reduced mineralization, and a decrease in the mechanical stability of the osteoarthritic joint.
COL1A1 , encoding the alpha-1 chain of type I collagen, is located on chromosome 17 at position 17q21.33. It undergoes several complex post-translational modifications or regulation, which may be affected by a transversion of the guanine base (G) to thymine (T) in the upstream regulatory region. This single nucleotide polymorphism (SNP) affects the binding site of the transcription factor specificity protein 1 (Sp1), in the upstream regulatory region of the COL1A1 gene. Studies have reported that this polymorphism is associated with bone metabolism, causing a decrease in bone mineral density (BMD). Furthermore, the G/T polymorphism of the COL1A1 gene exhibits a clinically significant influence on bone remodelling, leading to a predisposition to degenerative diseases such as osteoporosis, degenerative lumbar disc disease, and rheumatoid arthritis. These are characterized by low bone mass and micro-architectural deterioration of the bone tissue.
Thus, it was hypothesized that the G/T polymorphism within the regulatory region of the COL1A1 gene may also be involved in bone lesions in the aetiopathogenesis of TMJ OA. The aim of this study was to investigate the association of the G/T polymorphism with susceptibility to low-density lesions in the subchondral bone of the TMJ.
Materials and methods
Collection of samples
Patients with primary TMJ OA according to the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) were included. The data of 130 patients were collected from 3 March 2010 to 10 June 2014 at a hospital of stomatology in Wuhan, China. A total of 186 healthy control subjects were recruited among orthodontic and implant patients at the same hospital. These two groups of patients underwent clinical and radiological examinations, including cone beam computed tomography (CBCT) or magnetic resonance imaging (MRI). The sex ratio of the healthy control group was matched to that of the case group. All of the subjects voluntarily signed an informed consent form. Buccal mucosal cells were collected using sterile swabs. This study was approved by the ethics committee of the hospital of stomatology.
DNA samples and genotyping
Genomic DNA samples were extracted from the buccal mucosa sterile swabs using a DNA extraction kit (Omega Bio-Tek, Norcross, GA, USA) following the manufacturer’s protocol. The region of the G/T polymorphism of COL1A1 was then amplified by semi-nested PCR. Primers were designed using Primer Premier 5.0 (Premier Biosoft international, Palo Alto, CA, USA ) PCR-1 was conducted using the external primers 5′-GGGCTGAGGTGCTGAGAT-3′ (F primer) and 5′-GACCCCTGTCGCCTATTA-3′ (R1 primer) in a reaction volume of 15 μl containing 1.5 μl of 10× buffer, 0.25 μl of dNTP mixture (10 mM), 2.0 μl of template DNA (20 ng/μl), 10.7 μl of ddH 2 O, and 0.2 μl of each external primer (10 μM) added to the specific reaction with 2.5 U of Bio Taq DNA polymerase (Bioline, Ecogen, Barcelona, Spain). The PCR was performed with a temperature cycle of denaturation at 94 °C for 5 min and annealing at 50 °C for 30 s and then 30 cycles of 94 °C for 30 s, 58 °C for 30 s, 72 °C for 30 s (primer extension), and 72 °C for 5 min (product extension). Next, 2 μl of PCR-1 product was re-amplified using specific internal primers 5′-GAAAACCCAAGAAGCAAGGA-3′ (F and R2) under the same conditions, except 1× LC Green Plus (Idaho Technology, Salt Lake City, UT, USA) was added in this reaction.
The high-resolution melting (HRM) analysis method was used to detect the G/T polymorphism; positive samples underwent repeat genotyping. Direct sequencing was conducted to check the accuracy of the HRM genotyping.
Hardy–Weinberg equilibrium was evaluated with Arlequin 3.0 software. The distribution of alleles and genotypes in these groups was compared. The relationship between the SNP and low-density lesions of the TMJ OA was also analyzed. Association analysis was performed using a multivariate logistic regression model adjusted for possible covariates in TMJ OA using SPSS version 13 (SPSS Inc., Chicago, IL, USA). The difference was considered statistically significant when P < 0.05.
A total of 130 TMJ OA patients with low-density lesions (77 males and 53 females, mean age 33.7 ± 12.4, range 16–79 years) and 186 healthy individuals (98 males and 88 females, mean age 36.3 ± 17.2, range 16–63 years) were recruited. The general characteristics of these subjects, particularly the radiological changes seen, including anterior disc displacement with or without reduction, joint space narrowing, joint surface flattening, cortical bone erosion, condylar head resorption, and subchondral cyst-like lesions, are given in Table 1 and shown in Fig. 1 . The mean age of subjects included in the two groups differed significantly ( P < 0.05); by contrast, no significant difference was observed between the two groups in regard to sex. Thus, the association studies were adjusted for the effect of age using the logistic regression model.
|Variables||TMJ OA group
( n = 130) (%)
( n = 186) (%)
|Mean ± SD||33.7 ± 12.4||36.3 ± 17.2|
|Sex, n (%)||0.118|
|Male||77 (59.2)||98 (52.7)|
|Female||53 (40.8)||88 (47.3)|
|Clinical characteristics, n (%)|
|Limitation of mouth opening||48 (36.9)|
|Pain on mouth opening||43 (33.1)|
|Deviation of mouth opening||39 (30.0)|
|Friction sounds in the joint||52 (40.0)|
|Tenderness of the joint||79 (60.8)|
|Tenderness of the masticatory muscles||30 (23.1)|
|Radiological examination, n (%)|
|Perforation of the disc||53 (40.8)|
|Flattening of the joint surface||80 (61.5)|
|Condylar head erosion or resorption||96 (73.8)|
|Subchondral cyst||24 (18.5)|
|Joint space narrowing||81 (62.3)|