Congenic mice provide evidence for a genetic locus that modulates spontaneous arthritis caused by deficiency of IL-1RA

A New Understanding of the Role of IL-1 in Age-Related Intervertebral Disc Degeneration in a Murine Model

Increased cytokine expression, in particular interleukin-1β (IL-1β), is considered a hallmark of intervertebral disc degeneration. However, the causative relationship between IL-1 and age-dependent degeneration has not been established. To investigate the role of IL-1 in driving age-related disc degeneration, we studied the spine phenotype of global IL-1α/β double knockout (IL-1KO) mice at 12 and 20 months. Multiplex ELISA analysis of blood revealed significant reductions in the concentrations of IFN-γ, IL-5, IL-15, TNF-α, IP-10, and a trend of reduced concentrations of IL-10, macrophage inflammatory protein 1α (MIP-1α), keratinocyte chemoattractant/human growth-regulated oncogene (KC/GRO), and IL-6. However, the circulating level of MIP-2, a neutrophil chemoattractant, was increased in the IL-1KO. The alterations in systemic cytokine levels coincided with altered bone morphology-IL-1KO mice exhibited significantly thicker caudal cortical bone at 12 and 20 months. Despite these systemic inflammatory and bony changes, IL-1 deletion only minimally affected disc health. Both wild-type (WT) and IL-1KO mice showed age-dependent disc degeneration. Unexpectedly, rather than protecting the animals from degeneration, the aging phenotype was more pronounced in IL-1KO animals: knockout mice evidenced significantly more degenerative changes in the annulus fibrosis (AF) together with alterations in collagen type and maturity. At 20 months, there were no changes in nucleus pulposus (NP) extracellular matrix composition or cellular marker expression; however, the IL-1KO NP cells occupied a smaller proportion of the NP compartment that those of WT controls. Taken together, these results show that IL-1 deletion altered the systemic inflammatory environment and vertebral bone morphology. However, instead of protecting discs from age-related disc degeneration, global IL-1 deletion amplified the degenerative phenotype. © 2019 American Society for Bone and Mineral Research.

Decreased expression levels of Ifi genes is associated to the increased resistance to spontaneous arthritis disease in mice deficiency of IL-1RA

Background

The mouse strain BALB/c deficient in IL-1 receptor antagonist protein (Il-1ra) develops spontaneous arthritis disease (SAD) while the strain DBA/1 IL1rn^-/- with the same deficiency does not. Previously, we mapped a QTL on chromosome 1 for SAD and then developed a congenic mouse strain BALB.D1-1^-/- that contains the QTL genomic fragment associated with resistance from DBA/1^-/- on a BALB/c^-/- background. The congenic strain was relatively resistant to spontaneous arthritis and had delayed onset and reduced severity of disease. We obtained whole genome expression profiles from the spleen of the congenic strain BALB.D1-1^-/- and four other strains, the wild type BALB/c, DBA/1 and the deficient DBA/1 IL1rn^-/- and the BALB/c IL1rn^-/-. We then compared the similarities and differences between the congenic strain and the four parental strains. Here we report the selected potential causal genes based on differential expression levels as well as function of genes.

Results

There is a considerable number of genes that are differentially expressed between the congenic strain and the three parental strains, BALB/c, DBA/1, and DBA/1^-/-. However there only a few differentially expressed genes were identified by comparing the congenic strain and the BALB/c^-/-strain. These differentially expressed genes are mainly from T-cell receptor beta chain (Tcrb) and interferon-activatable protein (Ifi) genes. These genes are also differentially expressed between congenic strain and BALB/c strains. However, their expression levels in the congenic strain are similar to that in DBA/1 and DBA/1^-/-. The expression level of Tcrb-j gene is positively associated with two genes of Ifi gene 200 cluster.

Conclusions

Decreased expression levels of Ifi genes is associated to the increased resistance to spontaneous arthritis disease and with down regulation of expressions of Tcrb genes in the mouse congenic strain. Ifi genes may play an important role in the susceptibility to SAD in mice.

Electronic supplementary material

The online version of this article (doi:10.1186/s12865-016-0163-y) contains supplementary material, which is available to authorized users.

Validation of simple sequence length polymorphism regions of commonly used mouse strains for marker assisted speed congenics screening

Marker assisted speed congenics technique is commonly used to facilitate backcrossing of mouse strains in nearly half the time it normally takes otherwise. Traditionally, the technique is performed by analyzing PCR amplified regions of simple sequence length polymorphism (SSLP) markers between the recipient and donor strains: offspring with the highest number of markers showing the recipient genome across all chromosomes is chosen for the next generation. Although there are well-defined panels of SSLP makers established between certain pairs of mice strains, they are incomplete for most strains. The availability of well-established marker sets for speed congenic screens would enable the scientific community to transfer mutations across strain backgrounds. In this study, we tested the suitability of over 400 SSLP marker sets among 10 mouse strains commonly used for generating genetically engineered models. The panel of markers presented here can readily identify the specified strains and will be quite useful in marker assisted speed congenic screens. Moreover, unlike newer single nucleotide polymorphism (SNP) array methods which require sophisticated equipment, the SSLP markers panel described here only uses PCR and agarose gel electrophoresis of amplified products; therefore it can be performed in most research laboratories.

Genomic locus on chromosome 1 regulates susceptibility to spontaneous arthritis in mice deficiency of IL-1RA

BACKGROUND

To understand the role of genetic factors on chromosome 1 in the regulation of spontaneous arthritis in mice deficient in IL-1 receptor antagonist protein (IL_1RA), we previously used speed congenic breeding to transfer the QTL region from DBA/1(-/-) mice that are resistant to spontaneous arthritis into BALB/c(-/-) mice which are susceptible. We were able to establish two congenic strains which exhibited a delayed onset and reduced severity of disease. In this study, we asked a different set of questions. How will the QTL region from BALB/c(-/-) interact with the rest of the genome in the DBA/1(-/-) background? Will the DBA/1(-/-) mice become susceptible to spontaneous arthritis if the QTL genomic region on chromosome 1 was replaced with the genomic fragment of the same region from BALB/c(-/-)? We conducted the congenic breeding with the similar procedure as that of congenic strains with BALB/c(-/-) background.

RESULT

Instead of BALB/c(-/-), DBA/1(-/-) was used as the recurrent parent while BALB/c(-/-) was used as the donor parent. By the 6(th) generation we determined that all of the chromosomes in the progeny were of DBA/1(-/-) origin with the exception of the QTL portion of chromosome 1 which is heterozygous of BALB/c(-/-) and DBA/1(-/-) origin. We then intercrossed selected mice to produce homozygous strains containing the homozygous genomic region of BALB/c(-/-) on chromosome 1, while the rest of genome are homozygous DBA/1(-/-). This strain was observed for the development of spontaneous arthritis. Up to 9 weeks of age, both congenic strain and DBA/1(-/-) did not develop arthritis. However, after 9 weeks, the congenic strain started to exhibit signs of arthritis, while the DBA/1(-/-) remained free from disease.

CONCLUSION

The result indicates a strong influence of genetic factor(s) on the QTL of chromosome 1 on the susceptibility to spontaneous arthritis. Identification of genetic factors within this QTL region in the future will significantly enhance our understanding of molecular mechanism of spontaneous arthritis.