Targeting Enterobacter cloacae attenuates osteolysis by reducing ammonium in multiple myeloma

• E. cloacae promotes osteolysis by producing ammonium, which increases the protein level of CCL3 and accelerates osteoclastogenesis in MM.

• Targeting E. cloacae to reduce ammonium attenuates osteolysis in MM.

Multiple myeloma (MM)-induced bone disease affects not only patients' quality of life but also their overall survival. Our previous work demonstrated that the gut microbiome plays a crucial role in MM progression and drug resistance. However, the role of altered gut microbiota in MM bone disease remains unclear. In this study, we show that intestinal E. cloacae is significantly enriched in MM patients with osteolysis. Through fecal microbial transplantation and single bacterial colonization experiments in a 5TGM1 MM mouse model, we found that intestinal colonization of E. cloacae promotes osteolysis by increasing circulating ammonium levels. Elevated ammonium promotes osteoclastogenesis by increasing Trap protein levels in osteoclast precursors and by acetylating and stabilizing CCL3 protein in MM cells. Inhibition of ammonium synthesis, using E. cloacae with a deleted dcd gene, along with probiotic supplementation, alleviated osteolysis in MM. Overall, our work suggests that E. cloacae promotes osteolysis in MM by synthesizing ammonium. This establishes a novel mechanism and potential intervention strategy for managing MM with osteolysis.