Background/Purpose

 Osteoarthritis (OA), characterized by gradual loss of articular cartilage in the joint, is a leading cause of disability among the elderly people. Though the etiology and pathogenesis of OA is obscure. Several studies have suggested that OA is not only related with aging, calcium and vitamin D deficiency; OA risk is also associated with several genetic susceptibility loci. The aim of this study to elucidate the genetic background of osteoarthritis.

Methods

In a case-control study; 500 cases with knee osteoarthritis (KOA) and an equal number of age matched healthy controls were included. Cases were diagnosed using the ACR guidelines for KOA. Blood were drawn for DNA, RNA and lymphocyte isolation. PCR-RFLP method, TaqMan assay were carried out to identify the SNPs. Total RNA isolated from whole blood of healthy controls and patients suffering from KOA were analyzed for ESR- α, CALM-1 and GDF-5 mRNA by quantitative reverse transcriptase-PCR. ESR- α, CALM-1 and GDF-5 protein level were detected by western blot analysis in control and cases from peripheral blood lymphocytes. The haplotype analyses were carried out using Haploview software . All statistical analysis was performed with the SPSS software.

Results

The variant genotype of ESR- α, CALM-1 and GDF-5 genes were found to be present at relatively higher frequency in cases than the controls. Risk increased in cases that carried combination of variant genotypes of ESR α (Btg-AA) and GDF-5 (TT); CALM-1 (ApeKI-TG) and GDF-5 (TT); CALM-1(ApeKI-TG) and ESR α (Btg-AA) resulting in 4-6 fold elevated risk to KOA. The haplotype C-G-G and T-G-G of ESR- α gene reduced the risk to OA. In contrast the haplotype T-G-C containing variant of all three polymorphism of CALM-1 gene was over represented in the cases, increasing the risk to 3 fold .A significant association of this variant genotype was also found with clinical scores of KOA (VAS, WOMAC). RT-PCR data revealed that mRNA expression of GDF-5, ESR-α and CALM-1 in OA patients downregulate significantly 0.3, 0.64 and 0.48 -fold in blood when compared with the controls respectively. Protein Expression of GDF-5 was significantly decreased 0.24-fold in cases. Similar to that observed in GDF-5, westernblot analysis revealed that expression of ESR-α and CALM-1 proteins were also found to be decreased in lymphocyte. 

Conclusion

This study demonstrate that polymorphism in genes involved in the development, maintenance and repair of bone and cartilage such as  GDF-5, CALM-1and ESR- α modify the susceptibility to knee OA. Several fold higher risk was found in cases carrying haplotype of variant alleles of CALM-1 gene. Likewise, several folds increase in risk in individuals with variant genotype of GDF-5 with ESR- α (BtgI) or CALM-1 and ESR- α (BtgI) or CALM-1 and GDF-5  have further demonstrated that the importance of gene-gene interection in the development of knee OA. In addition, our data of gene expression by q-PCR and protein expression by western blotting of GDF-5, CALM-1 and ESR-α also suggest the relevance of these genes in pathophysiology of OA patients.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/genes-involved-in-cartilage-synthesis-and-risk-to-knee-osteoarthritis/