Gene Expression Profiles of Bone Marrow Stromal Cells and Their Correlation with Clinical Characteristics of Patients with Multiple Myeloma

Abstract

Introduction: Multiple myeloma (MM) is a hematologic malignancy characterized by the clonal proliferation of plasma cells. Recently, increasing evidence supports the hypothesis that bone marrow (BM) microenvironmental cells play important roles in the proliferation, survival, and drug resistance of clonal plasma cells. The aim of this study is to investigate expression profiles of BM stromal cells cultured from MM patients and to explore their relationship with clinical characteristics of patients. Methods: BM stromal cells were cultured from BM aspirates of 12 patients newly diagnosed with MM. As the control groups, BM stromal cells were cultured from 8 B-cell lymphoma patients without BM involvement, and 5 patients with cytopenia with no apparent evidence of hematologic malignancies were also analyzed. Fluorescence in situ hybridization (FISH) studies for IGH, RB1, 1q, p16, IGH/FGFR3, IGH/MAF, TP53 were performed. RNA from BM stromal cells was extracted and gene expression profiles were analyzed using HumanHT-12 Expression v4 BeadChips (Illumina, Inc., San Diego, CA, USA). Results: The growth rates of BM stromal cells from MM patients were variable between patients, and showed no apparent differences compared with control groups. Flow cytometric analysis of cultured BM stromal cells showed no expression of hematopoietic lineage antigens such as CD45 and positive expression of CD90, CD105, and CD44, which was consistent with a mesenchymal stem cell phenotype. The stromal cells were devoid any contamination by CD138-positive plasma cells. FISH study using probes for abnormalities frequently found in MM did not show any abnormalities in BM stromal cells from MM patients. In unsupervised clustering using the results of gene expression profiles, MM and control groups did not form clearly separated clusters. Although the gene expression profiles of BM stromal cells of MM patients were heterogeneous, they showed preferential grouping into clusters reflecting characteristic clinical presentation. Many of differentially expressed genes of BM stromal cells from MM patients with multiple lytic bone lesions were associated with cell to cell interactions and formation of extracellular matrix. Differentially expressed genes of BM stromal cells from MM patients with renal failure were associated with cell proliferation. BM stromal cells from an MM patient with amyloidosis demonstrated significant higher expression levels of the lambda light chain gene. Conclusions: Because BM stromal cells from MM patients did not show clonal markers identified in myeloma cells, it is unclear whether BM microenvironmental cells in MM patients are primarily tumoral. The gene expression profiles of BM stromal cells in MM patients were different between patients with different clinical presentations, and we could suggest that these genes may play important roles in MM pathogenesis and manifestation of clinical symptoms. Further study is needed to investigate the expression levels of these genes in a larger number of MM patients and to define their pathogenetic roles and prognostic significance in MM.