**7. Interleukin 1 beta (IL1B) gene**

Loughlin *et al.* [93] said that IL-1 is the primary catabolic cytokine of the OA joint and can stimulate the synthesis of several proteinases, which can result in the breakdown of cartilage extracellular matrix proteins. The 2 IL-1 genes (*IL1A* and *IL1B*) and the gene encoding IL-1Ra (*IL1RN*) are located on chromosome 2q13 within a 430-kb genomic fragment [94]. Loughlin *et al.* 2002 reported that IL-1R antagonist (IL-1Ra) competes with IL-1 for binding to the IL-1 receptors and can act as an inhibitor of cartilage loss. When the catabolic and anabolic activities of the cytokines are balanced, cartilage integrity is maintained. If there is an imbalance favoring catabolism, however, cartilage destruction can proceed, resulting in OA. It is, therefore, reasonable to propose that a proportion of the genetic susceptibility to OA may be encoded for by variation in the activity of interleukins and that for chromosome 2q this susceptibility could reside within the IL-1 gene clusters. Stern *et al.* [95] reported that IL1B 5810 G > A SNP genotypes marker were not in Hardy-Weinberg equilibrium (p < 0.05 in both non-erosive and erosive hand OA subgroups). Statistically significant association with the IL1B 5810 AA genotype was found in the erosive hand OA subgroup (relative risk 3.8, p = 0.007). This IL1B 5810 AA genotype association was also significant between erosive and non-erosive hand OA subjects (relative risk 4.01, p = 0.008). As expected, significant linkage disequilibrium was present between IL1B 5810 SNP and IL1A (−)889 SNP, other IL1B SNPs, and the nearest IL1RN SNP examined. The IL1B 5810A allele occurs most frequently on haplotypes with the SNP alleles IL1B 1423C, IL1B 1903 T, IL1B 5887C, and IL1A (−)889C. Genotypes at null loci failed to show evidence suggesting population stratification that might account for the spurious association. Sezgin *et al.* [95] said that some researchers had suggested an association between the IL-1 gene cluster and the occurrence of OA.

Previously, Moos *et al.* [96] investigated the distribution of polymorphic alleles of four different genes encoding TNF-alpha, IL1RN, IL1B and IL-6 in the knee or hip OA patients with controls. The analysis of genotype frequencies for the IL1B gene, more OA patients than controls was homozygous for allele 2, although any significant differences for the TNF-alpha, IL1RN and IL-6 polymorphisms were found.

## **8. SMAD3 (SMAD family member 3) gene**

Smad3 was found on human chromosome 15q22.33.The classic TGF-β mediated signaling pathway involves Smad activation. Smads are a family of intracellular proteins that comprise three classes of signaling molecules: - receptor-associated Smads (2 and 3 for TGF- β, 1, 5, and 8 for BMP signaling), the co-factor Smad4, and the inhibitory Smads (6and7) [97]. The receptor-activated SMADs include SMADs 1, 2, 3, 5, and 8. SMADs 2 and 3 respond to TGF- β and activins [97, 98], whereas SMAD1, 5, and 8 function in BMP signaling pathways [99–101]. The receptor-associated Smads bind to the type I receptor, and on ligand binding and activation, are phosphorylated and released into the cytoplasm. The activated receptor-associated Smads form a trimeric heterodimer with the co-factor Smad4, translocate to the nucleus, and influence gene transcription [102].

Yao *et al.* [103] reported that Smad3 gene mutation is a possible predisposing factor for human OA and found gene mutation in OA, providing insight into the function of SMAD3 mediated TGF-b signals in the development of OA and also suggested that Smad3 gene mutation may be a risk factor for genetic susceptibilities to OA.

Ferguson *et al.* [104] has established that the TGF- β Smads inhibit chondrocyte maturation, whereas the BMP-related Smads accelerate maturation. Many studies have shown that transforming growth factor- β (TGF- β) signals function as crucial regulators in bone formation, remodeling and maintenance. [105]. Micheal *et al.* [106] have shown that loss of Smad3 results in impaired immune responses, accelerated wound healing decreased bone density, OA and access to colon cancer.

Yang *et al*. [107] showed that Smad3-mediated TGF- β signals are essential for maintaining articular cartilage in the quiescent state by repressing chondrocyte differentiation and controlling matrix molecule synthesis. Consequently, impairment of TGF-b signals due to Smad3 disruption results in phenotypes resembling human Osteoarthritis.

Wu *et al.* [108] suggested that Loss of Smad3 appears to enhance bone morphogenetic protein signaling in the articular chondrocytes, leading to hypertrophy and OA-like changes. The observation further supports the crucial role of Smad3 that Smurf2 overexpression leads to dephosphorylation of Smad3 and is associated with a spontaneous OA phenotype in transgenic mice.

Also, Cherlet *et al.* [109] reported that Smad3 levels are lower in women than in men, which is consistent with other data showing that estrogens inhibit *SMAD3* transcriptional activity Nevertheless, Valdes *et al.* found that the genetic association of the *SMAD3* intronic SNP with OA was significant in both men and women and that effect sizes were remarkably similar between sexes, confirming the robustness of the result. Valdes *et al.* [109] reported that four SNPs (rs266335, rs12901499, rs6494629, and rs2289263) were found to be nominally significantly associated with

**235**

in the Japanese population.

A4, or C.

*Genetics in Osteoarthritis Knee*

*DOI: http://dx.doi.org/10.5772/intechopen.93890*

**9. Growth differentiation factor-5 (***GDF-5***)**

**10. Estrogen receptor alpha (***ESR- α***) gene**

knee OA (*P* < 0.05), but only 1 of them, rs12901499, was nominally associated also with hip OA (*P* < 0.021) and also observed that the major allele G was found at a

Hotten *et al*. [9] determined that the *GDF5* gene contains two exons. Miyamoto

*et al*. [113] reported that the gene encoding growth differentiation factor-5 (*GDF-5*) is associated with Osteoarthritis in Asian populations. An SNP in the 5′ untranslated region (UTR) of *GDF-5* showed significant association with hip osteoarthritis in 2 independent Japanese populations. This association was replicated for knee osteoarthritis in Japanese and Han Chinese populations. This SNP, located in the *GDF-5* core promoter, exert allelic differences on transcriptional activity in chondrogenic cells, with the susceptibility allele showing reduced activity. The findings implicated *GDF-5* as a susceptibility gene for Osteoarthritis and suggested that decreased *GDF-5* expression is involved in the pathogenesis of Osteoarthritis. [2] also isolated and characterized human *GDF5,* which they designated *CDMP1*, as well as human *GDF6 (CDMP2*). *GDF6* is predominantly expressed at sites of skeletal morphogenesis. Al-Yahyaee *et al*. [114–117] identified two mutations in the *GDF5* gene: a silent 1137A-G transition encoding lysine and a 1-bp deletion, 1144delG, predicting a frame shift resulting in loss of the biologically active C terminus of the protein. Thomas *et al*. [118] found that heterozygotes for the C400Y mutation had phenotypes resembling brachydactyly types A1,

The estrogen receptor (*ESR-α*) is a ligand-activated transcription factor composed of several domains essential for hormone binding, DNA binding, and activation of transcription. Alternative splicing results in several *ESR-α* mRNA transcripts, which differ primarily in their 5′ untranslated regions. The translated receptors show less variability [4, 119]. Ponglikitmongkol *et al*. [120, 121] showed that the human *ESR-α* gene is more than 140 kb long. It contains eight exons, and the position of its introns has been highly conserved, being, for example, remarkably similar to those of one of the chicken thyroid hormone receptor genes. Sputnik *et al*. [122] reported that *ESRα* isoform is a ligand-activated transcription factor composed of several essential domains for hormone binding and activation of transcription. *ESRα* is an essential mediator in the signal transduction pathway. Jin *et al.* [123] reported that Estrogen receptors (*ESR-α*) are known to play an essential role in the pathophysiology of Osteoarthritis. To investigate *ESRα* gene polymorphisms for its association with primary knee osteoarthritis, they conducted a casecontrol association study in patients with primary knee osteoarthritis and healthy individual in the Korean population. Jin *et al.* (2004) investigated the association between haplotypes of three polymorphism in *PVU II* in intron 1(IVS1-397 T/C), Xba I in intron 1(IVS1-351A/G) and Big I in exon 8 (exon8 229G/A) of *ESR-α* gene and primary knee OA in the Korean population, first two SNP in intron one also investigated by Bergink et al. [124] in Rotterdam population. Ushiyama *et al*. [125] found on *ESR-α* gene association between a genotype of *PVU II* and Xba I polymorphisms in Intron 1 and generalized Osteoarthritis with a severe radiographic change

higher frequency among OA patients than among controls [109–112].

#### *Genetics in Osteoarthritis Knee DOI: http://dx.doi.org/10.5772/intechopen.93890*

knee OA (*P* < 0.05), but only 1 of them, rs12901499, was nominally associated also with hip OA (*P* < 0.021) and also observed that the major allele G was found at a higher frequency among OA patients than among controls [109–112].
