IFNβ is a critical regulator of Lyme arthritis severity in mice and is regulated by the tumor suppressor gene Cdkn2a on murine Chr4

Abstract

Abstract Lyme disease is caused by infection with the tick-borne spirochete Borrelia burgdorferi, and results in a spectrum of clinical disorders. Infected C3H mice develop severe Lyme arthritis while B6 mice display mild disease, allowing analysis of host genetic contribution to disease. We used forward genetics to identify a region on Chr4, Bbaa1, that includes the Type I IFN cluster and regulates arthritis severity. The development of congenic mice, B6.C3-Bbaa1, isolating the C3H allele of Bbaa1 onto the background of B6 mice demonstrated that Bbaa1 regulates arthritis severity by modulating Type I IFN expression. IFNβ was identified as the key effector for Lyme arthritis severity, however, paradoxically there are no polymorphisms between C3H and B6 in this gene. To identify regulators of IFNβ in the Bbaa1 locus, candidate genes were subjected to siRNA silencing. A single gene, Cdkn2a, was identified as the modulator of IFNβ expression, and its encoded protein ARF was found to regulate the magnitude of IFNβ expression. Reconstitution of Arf−/− mice with hematopoietic cells expressing the C3H allele of Arf developed severe arthritis, whereas mice reconstituted with cells expressing the B6 Arf allele developed mild arthritis. ARF was found to regulate B. burgdorferi induced IFNβ through p53 and BCL6 in myeloid cells. Indeed, targeted blocking of BCL6 enhanced IFNβ activation in the joint tissue of B6 mice and resulted in increased severity of Lyme arthritis. Results were similar in Rag-1-deficient mice, indicating dependence on myeloid cells expression of BCL6. Thus, we have identified novel pathways modulating IFNβ expression in Lyme arthritis development which could lead to therapeutic discovery.