Fig. 2: Extracellular Glu stimulates OCLs formation in pre-malignant samples.

Primary CD14⁺ monocytes, isolated from MGUS and SMM (A) and MM patients (B), were cultured in differentiating medium in the presence or absence of Glu (0.5 mM) followed by TRAP staining. OCLs were scored as multinucleated TRAP-positive cells (≥3 nuclei) and counted by light microscopy. Graph represents the absolute number of OCL of each individual patient (MGUS + SMM n = 23, P = 0.0007 assessed by paired t-test; MM n = 16, P = 0.26 assessed by paired t-test) Right panel, Representative TRAP staining, for the identification of differentiated OCLs, performed at day 14 of incubation in the absence or in the presence of Glu, as indicated. Scale bar, 500 µm. C Number of OCLs obtained after 15 days of culture in standard medium in the absence of Glu. Graph represents the median number counted by light microscopy of each individual patient. P = 0.0059 as assessed two-sided Student’s t-test for unpaired data. Glu glutamate, OCLs osteoclasts, MGUS monoclonal gammopathy of undetermined significance, SMM smoldering multiple myeloma, MM multiple myeloma, TRAP Tartrate-Resistant Acid Phosphatase.