Fig. 4

Trabecular bone area is reduced and osteoclastogenesis is enhanced in prolactin (PRL)-receptor-null mice subjected to monoarticular adjuvant-induced arthritis (MAIA). Mice null (Prlr-/-) or not (Prlr+/+) for the PRL receptor were injected with complete Freund’s adjuvant (CFA) into the right knee joint once every 7 days to induce MAIA. The experiments ended on day 18 after the initial CFA injection, when all evaluations were performed. a Representative images of hematoxylin-eosin-stained tibiofemoral joint sections. Scale bar 500 μm. Ep epiphyseal plate, Bm bone marrow, Ct cortical bone, Tb trabecular bone, c cartilage, sm synovial membrane. Graph indicates the values of trabecular bone area (trabecular surface area divided by the total bone area). b Representative images of tartrate-resistance alkaline phosphatase (TRAP)-stained tibiofemoral joint sections where TRAP-positive purple spots (multinucleated cells (osteoclasts)) below the growth plate are indicated (arrows). Scale bar 200 μm. Graph shows the number of osteoclast per bone surface (N.Oc./BS). c Quantification by quantitative real-time PCR (qRT-PCR) of the mRNA levels of the osteoclast gene markers: Trap, Mmp9, Ctsk, and Tnfrsf11a in the knee joints. d qRT-PCR-based quantification of the mRNA levels of Tnfrsf11 and Tnfrsf11b and of the Tnfrsf11/Tnfrsf11b mRNA ratio in the knee joints. Values are means ± SEM (n = 5–12). *P < 0.05, **P < 0.01, ***P < 0.001, n.s. non-significant