Osteoporosis and other manifestations of bone disease are frequent in patients with systemic mastocytosis (SM) in association with the presence of mast cell infiltrates in bone marrow, although the mechanisms behind bone disease remain poorly understood. We find that extracellular vesicles (EVs) released by neoplastic mast cells and present in the serum of patients with SM (SM-EVs) block osteoblast differentiation and mineralization in culture, and when injected into mice diminish the expression of osteoblast markers, and trabecular bone volume and microarchitecture. We demonstrate that miRNA-30a and miRNA-23a, increased in SM-EVs and neoplastic mast cell-derived EVs, attenuate osteoblast maturation by suppressing expression of RUNX2 and SMAD1/5, essential drivers of osteogenesis. Thus, SM-EVs carry and deliver miRNAs that epigenetically interfere with bone formation and can contribute to bone mass reduction in SM. These findings also suggest possibilities for novel approaches to the management of bone disease in mast cell proliferative disorders.

Significance: Pathological findings in systemic mastocytosis (SM) are generally attributed to an increase in the mast cell burden and associated production of mast cell mediators. We now describe that serum from patients with SM contains extracellular vesicles (EVs) with a mast cell signature and that their concentrations correlate with surrogate markers of disease. These SM-EVs have the ability to alter hepatic stellate cell function including promoting a fibrotic phenotype, partly through the introduction of activated KIT. Tyrosine kinase inhibitors used to treat SM reversed these effects. These observations provide additional insight into how mast cells influence other organ systems in mastocytosis and suggest that targeting the release and/or effects of EVs might be of value in conjunction with existing therapeutic approaches.