Autophagy reduces the accumulation of misfolded HLA-B27 in a rat model of spondyloarthritis (THER2P.951)

Abstract

Abstract The MHC class I allele HLA-B27 is strongly associated with the development of spondyloarthritis (SpA) in humans, and when expressed in rats causes a SpA-like inflammatory disease. HLA-B27 has the tendency to misfold, and when up regulated by IFNγ and TNFα can cause ER stress leading to an unfolded protein response (UPR), which promotes pro-inflammatory cytokine production and may be critical for disease development. We examined whether alteration of autophagy affects HLA-B27 misfolding and UPR activation. Bone marrow-derived macrophages were obtained from HLA-B27-transgenic (TG), HLA-B7-TG and Lewis control (WT) rats and autophagy was induced with rapamycin. Western blot (WB) and immunofluorescence analysis of LC3B-II expression revealed a normal autophagic response in HLA-B27 expressing cells. Activation of autophagy with rapamycin reduced the accumulation of misfolded HLA-B27 induced by TNFα and IFNγ by 50%, while properly folded HLA-B27 heavy chains were minimally affected. Inhibition of autophagic flux with bafilomycin resulted in an exacerbation of the UPR upon HLA-B27 upregulation as measured by XBP1 splicing and expression of UPR target genes. These results demonstrate for the first time that induction of autophagy can reduce the accumulation of misfolded HLA-B27, and blocking autophagic flux exacerbates the UPR in HLA-B27 expressing cells. Alteration of the autophagic pathway may be a promising therapeutic tool in the treatement of SpA.