ABSTRACT: 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.
