m6A reader hnRNPA2B1 drives multiple myeloma osteolytic bone disease.

Rationale: Bone destruction is a hallmark of multiple myeloma (MM) and affects more than 80% of patients. Although previous works revealed the roles of N6-methyladenosine (m6A) reader hnRNPA2B1 in the development of tumors, whether hnRNPA2B1 regulates bone destruction in MM is still unknown. Methods: Alizarin red S staining, TRAP staining, ELISA and quantitative real-time PCR assays were used to evaluate osteogenesis and osteoclastogenesis in vitro. X ray and bone histomorphometric analysis were preformed to identify bone resorption and bone formation in vivo. Exosome isolation and characterization were demonstrated by transmission electron microscopy, dynamic light scattering, immunofluorescence and flow cytometry assays. The interactions between hnRNPA2B1 and primary microRNAs were examined using RNA pull-down and RIP assays. Coimmunoprecipitation assay was used to test the interaction between hnRNPA2B1 and DGCR8 proteins. Luciferase assay was established to assess miRNAs target genes. Results: Here we show that myeloma cells hnRNPA2B1 mediates microRNAs processing and upregulates miR-92a-2-5p and miR-373-3p expression. These two microRNAs are transported to recipient monocytes or mesenchymal stem cells (MSCs) through exosomes, leading to activation of osteoclastogenesis and suppression of osteoblastogenesis by inhibiting IRF8 or RUNX2. Furthermore, clinical studies revealed a highly positive correlation between the level of myeloma cells hnRNPA2B1 and the number of osteolytic bone lesions in myeloma patients. Conclusions: This study elucidates an important mechanism by which myeloma-induced bone lesions, suggesting that hnRNPA2B1 may be targeted to prevent myeloma-associated bone disease.

Bacterial infections exacerbate myeloma bone disease.

Multiple myeloma is characterized by osteolytic lesions caused by reduced bone formation and activated bone resorption. An important feature of myeloma is a failure of bone healing after successful treatment. In this work, clinical studies indicated a highly positive correlation between bone marrow bacteria abundance and bone lesion numbers of myeloma patients in complete remission. Coculture experiments demonstrated that marrow Escherichia coli (E. coli) promotes osteoclast differentiation and inhibits osteoblast differentiation. Mechanism studies showed that E. coli lipopolysaccharides (LPS) activated NF-κB p65 signaling and reduced phosphorylated smad1/5/9 binding ability with RUNX2 promoter, leading to decreased RUNX2 expression in osteoblast progenitors. Additionally, LPS enhanced phosphorylated NF-κB p65 binding ability with NFATc1 promoter, leading to increased NFATc1 expression in osteoclast progenitors. In vivo studies revealed E. coli contributes to osteolytic bone lesion, and elimination of E. coli infection assists healing of bone lesion in mouse model of myeloma in complete remission. These findings establish a heretofore unrecognized effect for E. coli in the genesis of myeloma bone disease and suggest a new treatment strategy.