Involvement of B cells, immunoglobulins, and Syk in the pathogenesis of abdominal aortic aneurysm I. Involvement of B cells, immunoglobulins, and Syk in the pathogenesis of abdominal aortic aneurysm I

Background—Abdominal aortic aneurysm (AAA) is a potentially life-threatening disease that is common in older individuals. Currently, therapeutic options are limited to surgical interventions. Although it has long been known that AAA tissue is enriched in B cells and immunoglobulins, their involvement in AAA pathogenesis remains controversial. Methods and Results— We investigated the role of B cells and immunoglobulins in a murine model of AAA, induced with a periaortic application of CaCl2, and in human AAA. Both human and mouse AAA tissue showed B cell infiltration. Mouse AAA tissue showed deposition of IgG and activation of Syk, a key molecule in B cell activation and immunoglobulin function, which were localized to infiltrating cells including B cells and macrophages. B cell-deficient muMT mice showed suppression of AAA development that was associated with reduced activation of Syk and less expression of Mmp9. Administration of exogenous immunoglobulins restored the blunted Syk activation and AAA development in muMT mice. Additionally, exogenous immunoglobulins induced IL-6 and MMP9 secretions in human AAA tissue cultures. Furthermore, administration of R788, a specific Syk inhibitor, suppressed AAA expansion, reduced inflammatory response, and reduced immunoglobulin deposition in AAA tissue. Conclusions—From these results, we concluded that B cells and immunoglobulins participated in AAA pathogenesis by promoting inflammatory and tissue destructive activities. Finally, we identified Syk as a potential therapeutic target. Overall design: We used B cell-deficient (uMT) mice to obtain this data set of mouse aortic transcriptome in the absence of B cells. Mice were treated with periaortic application of 0.5 M CaCl2 (uMT_Ca) to induce abdominal aortic aneurysm. Periaortic application of physiological saline instead of CaCl2 was performed as a sham operation (uMT_sham). To observe the effect of immunoglobulins, a group of mice with CaCl2 treatment received intraperitoneal injection of mouse polyclonal IgG (uMT_Ca+IgG). Aortic samples were obtained 7 days after the CaCl2 challenge. Mouse gamma globulin Aortic tissues were homogenized in TRIzol (Invitrogen) and total RNA was isolated with RNeasy (Qiagen). Transcriptome analyses were performed using the SurePrint G3 Mouse Gene Expression 8x60K Microarray Kit (Agilent).

背景——腹主动脉瘤（Abdominal aortic aneurysm, AAA）是一种在老年人群中高发的潜在致死性疾病，目前临床治疗手段仅局限于外科手术干预。尽管学界早已明确AAA病灶组织中B细胞与免疫球蛋白富集，但二者在AAA发病机制中的作用仍存在争议。
方法与结果——本研究针对氯化钙（CaCl₂）动脉周围给药诱导的小鼠AAA模型与人类AAA病灶，探究了B细胞与免疫球蛋白的致病作用。结果显示，人类与小鼠的AAA病灶组织均存在B细胞浸润。小鼠AAA病灶组织可见IgG沉积与B细胞活化关键分子Syk的激活，且该现象定位于浸润的B细胞与巨噬细胞等细胞群体中。B细胞缺陷型muMT小鼠的AAA发生受到抑制，伴随Syk激活水平降低与Mmp9表达下调。向muMT小鼠外源性补充免疫球蛋白，可恢复其受损的Syk激活与AAA发生进程。此外，外源性免疫球蛋白可诱导人类AAA组织培养物分泌IL-6与MMP9。进一步研究发现，给予特异性Syk抑制剂R788可抑制AAA扩张、减轻炎症反应并减少AAA病灶内的免疫球蛋白沉积。
结论——综上，本研究证实B细胞与免疫球蛋白通过促进炎症反应与组织破坏参与AAA的发病机制，并确定Syk可作为潜在的治疗靶点。
总体设计：本研究使用B细胞缺陷型muMT小鼠构建了无B细胞状态下的小鼠主动脉转录组数据集。对小鼠实施动脉周围0.5 M氯化钙给药（uMT_Ca组）以诱导腹主动脉瘤，以动脉周围给予生理盐水作为假手术对照（uMT_sham组）。为观察免疫球蛋白的作用，另一组氯化钙处理的小鼠经腹腔注射小鼠多克隆IgG（uMT_Ca+IgG组）。于氯化钙给药7天后采集主动脉样本。将小鼠主动脉γ球蛋白组织在TRIzol（Invitrogen）中匀浆，采用RNeasy（Qiagen）试剂盒提取总RNA，使用SurePrint G3小鼠基因表达8x60K微阵列芯片试剂盒（Agilent）进行转录组分析。