The non-MHC quantitative trait locus Cia5 contains three major arthritis genes that differentially regulate disease severity, pannus formation, and joint damage in collagen- and pristane-induced arthritis.

Cia5 is a locus on rat chromosome 10 which regulates the severity of collagen- and pristane-induced arthritis (CIA and PIA). To refine the region toward positional identification, Cia5 subcongenic strains were generated and studied in PIA and CIA. The protective effect of the telomeric locus Cia5a was confirmed in both models. A second arthritis severity locus (Cia5d) was identified within the most centromeric portion of Cia5. DA.F344(Cia5d) rats had a significantly lower median arthritis severity index in PIA, but not in CIA, compared with DA. On histologic analyses DA.F344(Cia5a) and DA.F344(Cia5d) congenics with PIA preserved a nearly normal joint architecture compared with DA, including significant reduction in synovial hyperplasia, pannus, angiogenesis, inflammatory infiltration, bone and cartilage erosions. Cia5 and Cia5a synovial levels of IL-1beta mRNA were reduced. Although both DA.F344(Cia5) and DA.F344(Cia5a) rats were protected in CIA, the arthritis scores of DA.F344(Cia5) were significantly higher than those of DA.F344(Cia5a), suggesting the existence of a third locus where F344-derived alleles centromeric from Cia5a contribute to increased arthritis severity. The existence of the third locus was further supported by higher levels of autoantibodies against rat type II collagen in DA.F344(Cia5) congenics compared with DA.F344(Cia5a). Our results determined that Cia5 contains three major arthritis severity regulatory loci regulating central events in the pathogenesis of arthritis, and differentially influencing CIA and PIA. These loci are syntenic to regions on human chromosomes 17q and 5q implicated in the susceptibility to rheumatoid arthritis, suggesting that the identification of these genes will be relevant to human disease.

The non-major histocompatibility complex quantitative trait locus Cia10 contains a major arthritis gene and regulates disease severity, pannus formation, and joint damage.

OBJECTIVE: To construct rats congenic for the chromosome 2 arthritis-regulatory quantitative trait locus Cia10, originally identified in a (DA x ACI)F(2) intercross rat strain that had been assessed for collagen-induced arthritis (CIA), and to determine the effect of this congenic interval on arthritis severity, joint histologic structure, and cytokine transcription in rats with pristane-induced arthritis (PIA). METHODS: A 52.6-MB interval derived from the ACI (CIA- and PIA-resistant) strain and containing the Cia10 interval was introgressed into the DA (arthritis-susceptible) background through genotype-guided congenic breeding. Homozygous male and female DA.ACI(Cia10) congenic rats were studied for their susceptibility to and severity of PIA, and were compared with same-sex DA rats. Histologic analyses were done on hind paws collected on day 32 following the pristane injection. Levels of interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNFalpha) messenger RNA (mRNA) were measured with real-time polymerase chain reaction on synovial tissues from day-32 ankles. RESULTS: Both male and female DA.ACI(Cia10) congenic rats developed a significantly milder form of arthritis, with a 95% and 92% reduction in the arthritis severity index compared with DA male and female controls, respectively (males P < or = 0.001 and females P = 0.003). DA.ACI(Cia10) congenic rat synovial tissue was more likely to preserve its normal histologic architecture, including minimal to no cartilage and bone erosions, synovial hyperplasia, and pannus formation, and reduced numbers of vessels (angiogenesis), when compared with DA synovial tissue. There was a 2.7- and 2.4-fold reduction in the amount of IL-1beta and TNFalpha mRNA, respectively, in the synovial tissue of DA.ACI(Cia10) congenic rats compared with DA rats. Sequencing analyses of complementary DNA for the Cia10-predicted candidate gene Ptpn8, the rat homolog of the rheumatoid arthritis (RA)-susceptibility gene PTPN22, revealed no polymorphisms between the DA and ACI strains. CONCLUSION: This study determined that Cia10 harbors a major autoimmune arthritis-regulatory gene. This gene regulates clinical disease severity, histologic damage, and the levels of at least two central proinflammatory cytokines. We are in the process of narrowing down the critical region for positional cloning of the Cia10 gene. The identification of this gene will provide novel targets or pathways for focused candidate-gene studies in RA.

Identification of two novel female-specific non-major histocompatibility complex loci regulating collagen-induced arthritis severity and chronicity, and evidence of epistasis.

OBJECTIVE: To identify additional sex-specific and epistatic quantitative trait loci (QTL) regulating collagen-induced arthritis (CIA) severity overall, as well as within different stages during the disease course, in an intercross between major histocompatibility complex-identical inbred rat strains DA/Bkl (susceptible) and ACI/Hsd (resistant). METHODS: Arthritic male (DA x ACI)F2 intercross offspring (n = 143) were analyzed separately from the females (n = 184). Phenotypic extremes (maximum arthritis scores [MAS]) were genotyped and used for QTL analysis. All 327 rats were genotyped with the simple sequence-length polymorphism (SSLP) markers closest to the peak of Cia7 and Cia10, the major loci previously identified in this intercross, and with SSLPs covering chromosomes 12 and 18. Phenotypes studied were disease onset, arthritis severity scores on days 14-39, MAS, mean and cumulative arthritis scores, delayed-type hypersensitivity, and antibody responses to rat type II collagen. RESULTS: A new female-specific arthritis-severity recessive locus was identified on rat chromosome 12 (Cia25), with a maximum effect observed on day 28 (logarithm of odds [LOD] 4.7). The homozygous DA genotype at Cia25 was associated with a 45% higher median arthritis score in females. Sequencing analyses of the Cia25 candidate gene Ncf1 revealed polymorphisms between DA and ACI. The previously identified locus, Cia10, was found to be male-specific. A 2-locus interaction model analysis identified a novel recessive chromosome 18 QTL, Cia26, which was dependent on Cia7, with its maximum effect observed at later stages during the disease course (peak LOD score of 3.6 for arthritis scores on day 39). CONCLUSION: This study identified 2 novel female-specific loci, and 1 male-specific locus. Cia25 regulates MAS and disease severity during the mid-to-late stages of the disease course and may be accounted for by Ncf1 polymorphisms. Cia26 is in epistasis with Cia7 and regulates later stages of disease, suggesting an involvement in disease perpetuation and/or chronicity.