Single-cell transcriptomic heterogeneity of bone marrow plasma cells in light-chain amyloidosis and monoclonal gammopathy of undetermined significance

Light chain amyloidosis (AL) is a life-threatening plasma cell dyscrasia manifested by irreversible damage of multiple organs caused by monoclonal immunoglobulin light chain, production of pathogenic bone marrow plasma cells (BMPCs). Although AL is featured by both misfolding of monoclonal protein and plasma cell proliferation, the functional subclones and molecular mechanism of BMPCs in AL remain elusive. Also, inter-individual heterogeneities of AL determine the chemotherapy response and organ tropism of light chains, which require well-defined molecular subtypes. To address these, we conducted single-cell RNA sequencing (scRNA-seq) of BMPCs donated by patients with AL, patients with monoclonal gammopathy of undetermined significance (MGUS), and healthy controls. Single-cell transcriptome revealed a continuity of bone marrow plasma cell (BMPC) functional subclones, delineating DNA repair, cell proliferation, immunoglobulin production, etc., with the gradient of signaling entropy and immunoglobulin production. The amyloidosis-associated genes, such as the amyloid-beta binding Apolipoprotein E (APOE), Cystatin 3 (CST3), and Complement C1q A Chain (C1QA), were up-regulated in a subclone enriched in AL. The speculated light chain-producing subclones in AL up-regulated neutrophil degranulation pathways, transport to and modifications in Golgi apparatus, and asparagine N-linked protein glycosylation. Cyclin D1 (CCND1)hi AL, consisted of larger main subclones which highly expressed Bcl-2 complex and B-cell differentiation genes, was sensitive to venetoclax that targets Bcl-2. A major subset of CCND1low AL harbored larger carbohydrate-synthesizing subclone and up-regulated CCND2 and the amyloidosis-associated genes. Collectively, our results provided frontier insights into the functional subclones and molecular mechanism of BMPCs in AL, associated with amyloidosis, light chain production and venetoclax sensitivity, as knowledge for the future research on AL pathogenesis, AL subtypes and AL-specific therapies.

轻链淀粉样变性（Light chain amyloidosis, AL）是一种危及生命的浆细胞病，由致病性骨髓浆细胞（bone marrow plasma cells, BMPCs）产生的单克隆免疫球蛋白轻链引发多器官不可逆损伤。尽管AL以单克隆蛋白错误折叠与浆细胞增殖为共同特征，但AL中BMPCs的功能性亚克隆与分子机制仍不明晰。此外，AL的个体间异质性决定了化疗应答与轻链的器官嗜性，因此亟需明确的分子亚型。为解决上述问题，我们对AL患者、意义未明单克隆丙种球蛋白病（monoclonal gammopathy of undetermined significance, MGUS）患者及健康对照者的BMPCs开展了单细胞RNA测序（single-cell RNA sequencing, scRNA-seq）。单细胞转录组分析揭示了骨髓浆细胞功能性亚克隆的连续性，以信号熵与免疫球蛋白产生的梯度为依据，描绘了DNA修复、细胞增殖、免疫球蛋白产生等功能模块。淀粉样变性相关基因，如淀粉样β结合蛋白载脂蛋白E（Apolipoprotein E, APOE）、胱抑素3（Cystatin 3, CST3）及补体C1q A链（Complement C1q A Chain, C1QA），在AL富集的亚克隆中呈上调表达。我们推测的AL中轻链产生亚克隆上调了中性粒细胞脱颗粒通路、高尔基体转运与修饰及天冬酰胺N连接糖基化通路。Cyclin D1（CCND1）高表达型AL包含更大的主要亚克隆，该亚克隆高表达Bcl-2复合物与B细胞分化基因，对靶向Bcl-2的维奈克拉（venetoclax）敏感。另一主要的CCND1低表达型AL亚群拥有更大的碳水化合物合成亚克隆，并上调了CCND2及淀粉样变性相关基因。综上，本研究结果为AL中BMPCs的功能性亚克隆与分子机制提供了前沿见解，关联了淀粉样变性、轻链产生与维奈克拉敏感性，可为未来AL发病机制、AL亚型及AL特异性治疗的相关研究提供理论依据。