Genetic dissection of experimental arthritis in the DA rat

Sammanfattning: Rheumatoid arthritis (RA) is a chronic inflammatory disease affecting peripheral joints. Persistent inflammation causes cartilage deterioration with severe joint deformations as a consequence. The etiology is largely unknown but complex interactions between genetic and environmental factors contribute to the disease. The disease is also clinically heterogeneous which further hampers etiological investigations. Analogs of certain disease pathways can be studied in experimental models mimicking RA. A more thorough characterization of such disease pathways may tell us of discrete disease subsets of RA. Numerous experimental models for RA exists, both spontaneous and induced. The DA rat is remarkably arthritis prone, an intradermal injection of a mineral oil is sufficient to induce arthritis. The difference in arthritogenicity between the arthritis inducers depends on the genetic susceptibility threshold of each rat strain. The general aim of this thesis was to by a genome - inducer approach identify a suitable experimental system to use for mapping arthritis susceptibility genes in the rat, and through this approach identify genes of equal importance in humans, ultimately to provide new insights for pathway characterization of RA. I characterized the arthritis susceptibility in a set of recombinant congenic strains overlapping several arthritis regulating regions on rat chromosome 4, in five arthritis models; collagen type H-induced arthritis, pristane-induced arthritis, mycobacteria-induced arthritis, squalene-induced arthritis and oil-induced arthritis. All five induced arthritis-models were regulated by chromosome 4 genes. A 10 cM fragment that harbor the Oia2 locus mediated arthritis down-regulation in collagen type H induced arthritis and squalene-induced arthritis. Oil-induced arthritis was completely prevented. Further fine mapping was continued in oilinduced arthritis. By using 18 Oia2 intra-recombinant congenic strains the arthritis regulating interval was fine-mapped to 1.2Mb. The arthritis regulating interval was further mapped to 600 kb that only harbor a Ctype lectin gene complex denoted Aplec. Comparison of gene sequences identified a nonsense mutation in Dcar1 in the DA strain as the most possible arthritis-regulating rat gene. The human homolog to rat Dcir, one of the other genes in the complex, was tested in a patient 1 control material. One SNP showed significant association to RA. Association was pronounced in RF-negative patients The genome - inducer approach was also applied in mapping of the arthritis regulating region, Oia3, on rat chromosome 10 in the F7 generation of an advanced intercross (AIL) between the arthritis susceptible rat strain DA, and the arthritis resistant PM I AV I. To chose the most appropriate arthritis model for linkage mapping in the AIL pristane-induced arthritis, squaleneinduced arthritis and oil-induced arthritis was induced. Pristane-induced arthritis was the most appropriate for the population. Aplec and the newly identified arthritis regulating gene Ncf1 was also mapped to determine the mapping resolution. Linkage mapping of Oia3 identified two distinct quantitative trait loci (QTL), one at D10Rat13 at 97.2Mb, and an other at D10Got158 at 105.2Mb. The placement for the Ncf1 gene, and the Aplec were both less than 100kb, 200kb surrounding the Oia3 peak marker was considered as the confidence interval. The proximal Oia3 QTL contains the Protein kinase C alpha gene together with a set of calcium channel voltage-dependent gamma subunit genes. The distal Oia3 QTL contain a cluster of dendritic cell derived Ig-like receptors, among them the homolog to the human CMRF35 gene previously associated to psoriasis. In conclusion the search for appropriate experimental systems to map arthritis susceptibility regions, subsequent congenic mapping in oil induced arthritis, lead to the identification of Aplec, a C-type lectin complex, that codes for genes important in a number of immunological processes. The human homolog to rat showed association to RA in a patient/control material.