背景:已知HLA-B27与脊柱关节炎(SpA)的关联已有50年,但仍然无法解释。我们最近表明,HLA-B27/人β2微球蛋白(hβ2m)转基因果蝇在翼形视盘中表达,通过与I型BMP受体(BMPR1)萨克斯管(Sax)物理相互作用来下调骨形态发生蛋白(BMP)途径,导致无交叉静脉表型。
方法:研究了转基因果蝇翅膀中激活素/转化生长因子β(TGFβ)途径与HLA-B27/hβ2m之间的遗传相互作用。HLA-B27结合的肽组在翼形视盘中表征。在来自HLA-B27/hβ2m大鼠(B27大鼠)的肠系膜淋巴结(mLN)T细胞中,HLA-B27与激活素受体样激酶2(ALK2)之间的物理相互作用,ALK3和ALK5BMPR1,小母亲的磷酸化针对十食截瘫(SMADs)和由其配体诱导的非规范BMP/TGFβ途径的蛋白质,和TGFβ途径的靶基因的转录水平,进行了评估。
结果:在HLA-B27/hβ2m转基因果蝇中,通过活化素/TGFβ途径的不适当信号,涉及狒狒(Babo),I型激活素/TGFβ受体,导致了无交叉静脉表型,除了去调节BMP途径。我们在HLA-B27/hβ2m转基因果蝇翼形视盘中鉴定了与HLA-B27结合的肽,该肽具有经典结合基序。我们展示了特定的物理相互作用,HLA-B27/hβ2m与哺乳动物Sax和Babo的直系同源物之间,即ALK2和ALK5(即TGFβ受体I),在B27大鼠的mLN细胞中。在来自B27大鼠的T细胞中,响应TGFβ1的SMAD2/3的磷酸化幅度增加,显示TGFβ途径失调的证据。因此,该通路的几个靶基因在B27大鼠T细胞中的表达增加,在基础条件下和/或TGFβ暴露后,包括Foxp3Rorc,Runx1和Maf。有趣的是,Tgfb1在来自B27大鼠的幼稚T细胞中表达降低,甚至在病前,与促炎模式一致的观察结果。
结论:本研究表明HLA-B27改变了果蝇和B27大鼠的TGFβ途径。鉴于该途径在CD4+T细胞分化和调节中的重要性,其紊乱可能导致在B27大鼠中观察到的促炎辅助性T细胞17的异常扩增和调节性T细胞表型的改变。
BACKGROUND: Association of HLA-B27 with spondyloarthritis (SpA) has been known for 50 years, but still remains unexplained. We recently showed that HLA-B27 expressed in wing imaginal disc from HLA-B27/human-β2 microglobulin (hβ2m) transgenic Drosophila deregulated bone morphogenetic protein (BMP) pathway by interacting physically with type I BMP receptor (BMPR1) Saxophone (Sax), leading to crossveinless phenotype.
METHODS: Genetic interaction was studied between activin/transforming growth factor β (TGFβ) pathway and HLA-B27/hβ2m in transgenic Drosophila wings. The HLA-B27-bound peptidome was characterized in wing imaginal discs. In mesenteric lymph node (mLN) T cells from HLA-B27/hβ2m rat (B27 rat), physical interaction between HLA-B27 and activin receptor-like kinase-2 (ALK2), ALK3 and ALK5 BMPR1s, phosphorylation of small mothers against decapentaplegic (SMADs) and proteins of the non-canonical BMP/TGFβ pathways induced by its ligands, and the transcript level of target genes of the TGFβ pathway, were evaluated.
RESULTS: In HLA-B27/hβ2m transgenic Drosophila, inappropriate signalling through the activin/TGFβ pathway, involving Baboon (Babo), the type I activin/TGFβ receptor, contributed to the crossveinless phenotype, in addition to deregulated BMP pathway. We identified peptides bound to HLA-B27 with the canonical binding motif in HLA-B27/hβ2m transgenic Drosophila wing imaginal disc. We demonstrated specific physical interaction, between HLA-B27/hβ2m and mammalian orthologs of Sax and Babo, i.e. ALK2 and ALK5 (i.e. TGFβ receptor I), in the mLN cells from B27 rat. The magnitude of phosphorylation of SMAD2/3 in response to TGFβ1 was increased in T cells from B27 rats, showing evidence for deregulated TGFβ pathway. Accordingly, expression of several target genes of the pathway was increased in T cells from B27 rats, in basal conditions and/or after TGFβ exposure, including Foxp3, Rorc, Runx1 and Maf. Interestingly, Tgfb1 expression was reduced in naive T cells from B27 rats, even premorbid, an observation consistent with a pro-inflammatory pattern.
CONCLUSIONS: This study shows that HLA-B27 alters the TGFβ pathways in Drosophila and B27 rat. Given the importance of this pathway in CD4 + T cells differentiation and regulation, its disturbance could contribute to the abnormal expansion of pro-inflammatory T helper 17 cells and altered regulatory T cell phenotype observed in B27 rats.