The Cdkn2a gene product ARF is a critical regulator of IFNb mediated Lyme arthritis

Lyme disease is caused by infection with Borrelia burgdorferi, with a spectrum of clinical disorders. Murine studies with B6 and C3H mice have demonstrated that genetic differences in the host response play an essential role in regulating the severity of Lyme arthritis. C3H mice generate a robust induction of type I IFN response in joint tissue at one week of infection which leads to severe Lyme arthritis at 4 weeks post-infection, while B6 mice develop mild disease without a type I IFN profile. We used a forward genetic approach and identified B. burgdorferi arthritis- associated locus 1 (Bbaa1) on Chr4, which includes type I IFN cluster. B6.C3-Bbaa1 congenic mice display more severe Lyme arthritis than B6 mice. The blocking of type I IFN receptor and the IFNb subtype in Bbaa1 mice suppressed arthritis back to B6 level, so we concluded the Bbaa1 locus intrinsically controls IFNb production, and the differential expression of IFNb controls the severity of Lyme arthritis. However, the IFNb genes of C3H and B6 mice are identical, prompting focus on other genetic factors within the Bbaa1 locus as regulators of IFNb. Reciprocal radiation chimeras between B6.C3-Bbaa1 and B6 mice revealed myeloid cells in the joint tissue as IFNb initiators. Advanced congenic lines were generated to reduce the genetic contribution from C3H Bbaa1 region. RNA-seq of bone marrow-derived macrophages (BMDMs) from B6 and advanced interval specific recombinant congenic lines, ISRCL3 and ISRCL4, revealed novel candidates that may regulate Ifnb. In this study, we identify the Cdkn2a gene encoded ARF as a critical regulator of IFNb mediated Lyme arthritis, and investigate mechanistic interactions that modulate IFNb expression in Lyme arthritis development. Overall design: BMDM's from B6, ISRCL4 and ISRCL3 mice were treated with B. burgdorferi for 0hr, 3hr or 6hr in order to identify genes (protein coding and non-coding RNAs) that are expressed in the Bbaa1 locus from 87.968-94.68Mbps. Genes expressed in this region will be candidates for further identification of the gene that regulates IFNb. Gene expression were compared between control group, B6, and ISRCL4/ISRCL3 congenic mice.