MATN3 Gene Polymorphism Is Associated with Osteoarthritis in Chinese Han Population: A Community-Based Case-Control Study

Background. The matrilin, especially matrilin-3 (MATN3), are reported to play important roles in the pathophysiology of osteoarthritis (OA). To explore the relationship between MATN3 SNP6 (rs8176070) and primary OA, we conducted a community-based case-control study. Methods. A total of 732 community residents aged 40–84 years participated in the community-based study in Northeast China. After taking physical and radiographic examinations, 420 of the residents were diagnosed OA (216 women and 204 men). The other 312 individuals without any symptoms of osteoarthritis or signs in the radiographs (156 women and 156 men) were considered as healthy controls. After obtaining the DNA of case and control groups, genotypes of the MATN3 SNP6 were determined by polymerase chain reaction followed by restriction enzyme digestion. The numbers of patients with different OA subtypes were also calculated. Results. The distribution of genotypes and alleles of the MATN3 SNP6 between OA patients and controls was different significantly. The BB carrier tends to be associated with the increased osteoarthritis (P = 0.025, OR = 1.724, 95% CI = 1.071–2.77), especially the knee osteoarthritis (P = 0.021, OR = 2.402, 95% CI = 1.141–5.060) and lumber osteoarthritis (P = 0.020, OR = 1.880, 95% CI = 1.103–3.204). Bb carrier increased hand osteoarthritis risk (P = 0.002, OR = 5.380, 95% CI = 1.828–15.835). The B allele might have an effect on the increased knee osteoarthritis (P = 0.000, OR = 3.143, 95% CI = 2.283–4.328). Conclusion. These findings suggest that the MATN3 gene polymorphism might be associated with osteoarthritis in the Chinese Han population.

The matrilin (MATNs) are a family of oligomeric extracellular matrix (ECM) proteins consisting at least of four 2 The Scientific World Journal related proteins, termed matrilin-1 through -4 containing. The MATNs contain common structural motifs including von Willebrand factors A (vWFA) domains, epidermal growth factor (EGF)-like domains, and coiled-coil domains [15]. Matrilin-3 (MATN3) is the least complex member of the matrilin family, consisting of only one vWFA domain, four EGF-like domains, and a C-terminal coiled-coil domain. In humans, nine missense mutations in the matrilin-3 gene (MATN3) that affect the vWFA domain (typically the βsheets) have been found in patients with multiple epiphyseal dysplasia (MED), characterized by delayed and irregular ossification of the epiphyses and early-onset osteoarthritis [16][17][18][19]. Mutations in MATN3 have also been reported in other osteochondrodysplasias, including bilateral hereditary microepiphyseal dysplasia, a MED-like disorder characterized by small epiphyses in the hip and knee joints, spondyloepimetaphyseal dysplasia, which includes a number of conditions associated with vertebral, epiphyseal, and metaphyseal anomalies [20], and idiopathic hand osteoarthritis [21]. It has been found that enhanced matrilin-3 gene and protein expression was correlated with the extent of tissue damage in osteoarthritis patients [22]. These findings suggest that tight regulation of matrilin-3 expression is essential for maintenance of the cartilage ECM microenvironment.
Recently, few studies aimed to investigate the relationship between a functional single-nucleotide polymorphism (SNP) in the MATN3 (rs8176070) and OA, while the results were inconsistent. Two studies found the mutation of SNP6 was associated with susceptibility to hand osteoarthritis in the Caucasian population sample [21,23]. One found the variation of MATN3 was not associated with OA in the European population [24]. Our objective was to assess the relationship between MATN3 rs8176070 (SNP6) and primary OA (including cervical, lumber, and knee and hand osteoarthritis) in Chinese Han population.

Study Subjects.
The study was performed in Heilongjiang province, a northeast region, from 2005 to September 2009. The study population was drawn from the population aged 40 years and over living in communities using stage-stratified sampling methods. First, Xiangfang district representing the middle economic level for urban areas of Heilongjiang province was selected from 7 districts of Harbin, then 4 of 19 communities were randomly selected, and all the residents of sampled communities were investigated. Finally, a total of 800 people were selected and invited to participate in the study; 732 people completed the survey and donated their blood samples. All these people were examined at the 2nd Affiliated Hospital of Harbin Medical University, Heilongjiang, Harbin, China. All these people took radiographs of cervical, lumber, knees, and hands. Radiographs, including anterior-posterior hand and lateral and anterior-posterior cervical, lumber, and knee radiographs, were read by two radiologists blindly and independently who were unaware of the clinical findings until a consensus was reached. People with no sign or symptom of osteoarthritis, other arthritis or joint diseases at any site according to their medical history (such as pain, swelling, tenderness, or restriction of movement), and with no sign in the 7 radiographs, were considered as control group. At the same time, people were recruited into OA group with symptoms or signs of OA and radiographic signs of OA according to the Kellgren-Lawrence grading. Patients with inflammatory arthritis (rheumatoid or autoimmune disease), posttraumatic, or postseptic arthritis were excluded. Demographic and other information including stage, type, onset age, and family history were obtained by using questionnaires. Both patients and controls in this study were Han ethnicity and were all free from systemic, chronic, autoimmune, allergic, and anti-inflammatory diseases. Finally, a total of 420 patients with OA (216 women and 204 men) and 312 healthy controls (156 women and 156 men) were enrolled in the study. This study was conducted in compliance with the guidelines of the Declaration of Helsinki. All participates were given written informed consent before their participation in this study.
The Kellgren-Lawrence grade represents disease severity reflecting on radiographs. Radiographic findings of OA were classified into mild (Kellgren-Lawrence grade 1 or 2) and severe (Kellgren-Lawrence grade 3 or 4). The functional or symptomatic statuses of OA patients were classified as functionally or symptomatically good (Lequesne's functional index = 10) and poor (Lequesne's functional index > 10) (showed in Table 1) [25].

Statistical Analysis.
In this case-control study, we used Pearson's chi-square test to determine the significance of differences in allelic and genotypic frequencies between osteoarthritis patients and control groups. P < 0.05 was considered statistically significant. Odds ratios (ORs) with 95% confidence intervals (CIs) were also calculated. Hardy-Weinberg equilibrium test was performed by using a χ 2 test. All statistical analyses were performed with SPSS version 15.0 software (SPSS Inc., Chicago, IL, USA). We analyzed the frequency of the MATN3 SNP6 in 420 patients and 312 controls. The genotype distribution exhibited a significant difference between OA patients and control groups. The genotype of BB increased the risk of OA (odds ratio [OR] = 1.724, 95% confidence interval [CI] = 1.071-2.770; P = 0.025), especially the knee OA (OR = 2.402, 95% CI = 1.141-5.060; P = 0.021) and the lumber OA (OR = 1.880, 95% CI = 1.103-3.204; P = 0.020). The genotype of Bb was a risk factor for hand OA (OR = 5.380, 95% CI = 1.828-15.835; P = 0.002), but not for cervical OA.

Discussion
Osteoarthritis is the most common form of arthritis. It is the foremost cause of disability in the elderly population, affecting approximately 10% of population over the age of 60 years [26]. In OA, the earliest histological changes involve edema in the articular cartilage, suggesting an alteration in 4 The Scientific World Journal   the balance between the proteoglycan and collagen networks. Articular cartilage is mostly made of extracellular-specialized collagens and proteoglycans. The physical properties of articular cartilage support frictionless movements and the load-bearing capacity of the joints [27]. The role of MATN3 in cartilage homeostasis was demonstrated. Some researchers found that functional knockout of MATN3 in mice could induce premature hypertrophy of articular chondrocytes which could contribute to the development of osteoarthritis in adult mice [28]. To our knowledge, the previous studies only investigated the relationship between MATN3 polymorphism and hand OA or knee OA [21,23,24]. Two articles claimed that the SNP6 variation is associated with hand OA, but not knee [21,23], while another article claimed that the mutation of SNP6 is not associated with OA [24]. Our study is the first to analyze the distribution of polymorphisms of MATN3 gene in a group of Chinese osteoarthritis patients and unrelated healthy controls. In this study, we replicated that the mutation of SNP6 is associated with hand OA, as well as lumber OA and knee OA. Contrary to the anterior researches, we found the distribution of SNP6 genotypes had some relationship with knee OA, which might contribute to the ethnicity variation.
We investigate the MATN3 SNP6 in the patients with OA, and we divided the patients suffering from different sites into different subgroups: knee OA, lumber OA, cervical OA, and hand OA as well. So our results better evaluate the relationship between the MATN3 polymorphism and osteoarthritis, especially the subtype of OA.
Present study has some limitations that should be considered. Firstly, our sample size was relatively small, which may limit statistical power to detect any existing association, especially the number of patients with hand OA. The limited sample size might lead to the distribution of genotype and allele might departure from the real condition.
The Scientific World Journal 5 Secondly, the control of MATN3 expression and activity in vivo is complex and not well understood, and could be subjected to modulation by polymorphisms in other genes. Thirdly, lack of original data for each patient with his or her Kellgren-Lawrence grade limited our further analysis of the relationship between the MATN3 gene polymorphism and the severity of osteoarthritis. Moreover, the patients were all from the northeast region of China, so our results might not represent the whole condition of China.
In conclusion, our results suggest that the investigated polymorphism in the MATN3 gene might play a role in osteoarthritis in the Han population. Further study with a larger population size remains to be conducted for a definitive affirmation of correlates of MATN3 gene polymorphism in osteoarthritis patients.