Fig. 2: Deficiency of CIITA expression in osteocytes impairs myeloma-induced bone lesions.

a Western blots show the expression of CIITA in osteocytes, MSCs, and osteoblasts isolated from wild-type (WT) or osteocyte-specific Ciita-knockout (Ciita KO) mice. The expression of GAPDH served as protein loading controls. Images shown are representative of two independent experiments. b–k WT and osteocyte-specific Ciita KO mice were intrafemorally injected with the murine myeloma cell line Vk12598 (1 × 10⁶ cells/mouse). The mice not receiving myeloma cells (No MM) served as controls. Shown are the concentrations of M-proteins in mouse sera (b), representative μ-CT images of mouse femurs (c), and percentages of BV/TV (d), Tb.Th (e), Tb.N (f), Tb.Sp (g), OS/BS (h), Ob.S/BS (i), ES/BS (j), and Oc.S/BS (k). l BFR/BS was measured by calcein injection, and the bone sections were imaged and analyzed. Shown are representative images and summarized data of bone formation in mouse femurs. Scale bar: 20 µm. m-p Osteocytes isolated from WT or Ciita-KO mice injected with or without myeloma cells, were cultured for generating the osteocyte CM. The osteoblast precursor MC3T3-E1 and the osteoclast precursor Raw264.7 were cultured with the osteocyte CM. After culturing, the cells were stained with Alizarin red-S for osteoblast differentiation or TRAP staining for osteoclast differentiation. Shown are the summarized data from Alizarin red-S staining (m) and the numbers of multinuclear (≥3) TRAP⁺ cells (n, left). Real-time PCR and ELISA assays show the relative expression of Tnfsf11 and Sost mRNA in osteocytes (o) and the serum levels of RANKL or sclerostin in mice (p). (n, right) Primary osteocytes isolated from mouse femurs were knocked down by Ciita siRNA (siCiita). The CM of WT or siCiita was cultured with myeloma cells for 48 hours. Data are mean ± SD (n = 5 mice/group). P values were determined using one-way ANOVA with Tukey’s multiple comparisons test.